Environmental adaptability of the genus Carex-A case study of Carex heterostachya and Carex breviculmis in northwest China

Carex heterostachya and Carex breviculmis are easy to develop lawns in a short period while taking on high ornamental significance in northwest China where summer temperatures are high, rainfall is uneven, and soil is scarce. Several questions were raised, which are elucidated as follows: what type of plant functional characteristic has they formed for long-term survival and adaptation to this environment; which plant is more adaptable; which leaf functional characteristic are critical to photosynthetic characteristics. The following conclusions were drawn based on the exploration of the leaf functional characteristic of the two plants using gas exchange technology and field emission electron scanning technology: (a) C. breviculmis refers to a slow investment-return plant, exhibiting strong environmental adaptability and plasticity, and it is resistant to barrenness, drought, and shade. C. heterostachya refers to a type of quick investment-return plant, with high photosynthetic efficiency, well-developed transport tissue, and relatively shade-tolerant. The soil with low water content and poorer soil applies to C. breviculmis cultivation, and C. heterostachya applies to cultivation in the environment with sufficient light and rich nutrients. Moreover, C. breviculmis and C. heterostachya can be adopted to enrich the diversity of understory landscape. (b) Carex exhibits strong environmental adaptability, large variation in eco-physiological characteristics, as well as strong plasticity. Leaf anatomical characteristics are stable, whereas differences exist in the interspecific variability and plasticity. (c) when the genus Carex grew in the semi-shade and the soil environment was arid, specific leaf area (SLA) can become the main factor for the photosynthetic availability of Carex, the thickness of the stratum corneum, the thickness of the upper serve as secondary factors. The above-described findings can lay a theoretical basis for the cultivation and application of Carex and the expansion of turfgrass germplasm resources.


Introduction
The demand for turfgrass has increased on a year-to-year basis with the expansion of lawn planting area. The research on ecological adaptability of turfgrass can provide more professional assistance for the application of lawn, the expansion of turfgrass species, and management of lawn through the analysis of the correlation between turfgrass and environmental factors (Więcław 2017). The genus Carex (Cyperaceae) characterize by its wide distribution and considerable number of species (Schütz 2000). It is the largest genus of the Cyperaceae family with nearly 2000 species worldwide and Carex breviculmis R.Br and Carex heterostachya Bunge are included. They have better environmental adaptability. C. breviculmis originated in southern China (Dai et al. 2010) and New Zealand, appeared in southeast Asia, New Guinea (GROUP 2015), Australia (Majure and Bryson 2008) and was introduced in USA ( Majure and Bryson 2008). C. heterostachya occured in China (Dai et al. 2010) and Korea (Egorova 1999),and it appeared in Russia and the Far East (Bruhl et al. 2007). On the other hand, the turf-quality of Carex is being gradually explored. Shokoya et al. (2022)suggested that grey sedge (Carex amphibola), Leavenworth's sedge (Carex leavenworthii), 'Little Midge' palm sedge (Carex muskingumensis) and Texas sedge (Carex texensis) can be established and maintained as a low-input turf in dry shade using certain management measures. Furthermore, C. heterostachya is characterized by tolerance to trampling and strong resistance to weeds (Zhang et al. 1995), C. breviculmis has the characteristics of cold-resistance and salt-resistance; it also exerts better landscape effect in winter (Yang et al. 2014). The northwest of China is characterized by the semi-arid climate and scarce soil, such that most turfgrass has low adaptability, and the quality of turfgrass is low. Notably, C. heterostachya and C. breviculmisare can show different qualities from them. Existing research placing a major focus on Carex (Cyperaceae) has been primarily limited to plant phylogeny (Oda et al. 2019), classification (Group et al. 2021), seed germination (Kettenring & Galatowitsch 2007;Kettenring et al. 2006), the variability and phenotypic plasticity of Carex species (Hinzke et al. 2022;Więcław et al. 2022) as well as mycorrhizal status of the genus Carex (Miller et al. 1999). The environmental adaptability and survival adaptation strategies regarding the genus Carex has been rarely explored.
Plants interact with the environment in the long-term evolution and development to form plant leaf eco-physiological characteristics and leaf anatomical characteristics, so as to adapt to changes in the external environment (Maza-Villalobos et al. 2022). For instance, Leymus chinensis in response to extreme drought in Inner Mongolia grasslands by decreasing plant height, leaf dry matter content, specific leaf area and increasing water use efficiency (Yue et al. 2019). Photosynthesis lays a basis of plants for maintaining the physiological activities. Turfgrass has been primarily adopted in the shade environment, such that the light condition serves as the factor limiting the growth of turfgrass (Shokoya et al. 2022). Shading exerts different effects on forage growth and production in the Loess Plateau of China. To be specific, enhanced shading will reduce leaf thickness, leaf dry matter content, leaf mass per unit area and net photosynthetic rate of lucerne (Medicago sativa), as well as white clover (Trifolium compensation). Nevertheless, the leaf dark respiration rate, light compensation point and maximum assimilation rate of cocksfoot (Dactylis glomerata) are not affected by shading, such suggesting the excellent adaptability of cocksfoot (Yang et al. 2019). In a study of ecological adaptations of four typical plants in tropical rainforests in Hainan Province, China, it is found the physiological adaptations alone are not sufficient and plants need to adapt accordingly through morphological structures (Qin et al. 2022). Leaf anatomical characteristics can indicate plant stress resistance . which includes drought resistance. Through the comparison of the anatomical structure of Camellia oleifera leaves, it is found that the plant species with larger spongy tissue and larger ratio of palisade tissue thickness to spongy tissue thickness have stronger adaptability for low-hot valley area in Guizhou Province, China (Hu et al. 2022). In addition, the plasticity and variability of its structure and anatomical characteristics can also be obtained, which can well indicate the adaptation strategies of Carex in various ecological environments. Więcław (2017) analyzed that Carex morphological characteristics were mainly related to soil organic matter content, calcium and carbonate content, habitat fertility, elevation and habitat disturbance. From the perspective of generative and vegetative traits variability, research show that Carex lepidocarpa, Carex flava and Carex demissa and Carex demissa was fairly similar, while it is somewhat higher in Carex viridula. Soil potassium conditions that indicate as a factor for intra-specific variability. Sites with lower contents of bioavailable potassium hosted C. buekii individuals which are generally smaller than those at sites showing higher soil potassium contents (Więcław et al. 2022).
On the other hand, existing research has suggested that leaf functional characteristic and photosynthesis are coordinated with each other for a long period (Nam et al. 2017;Wright et al. 2004). Exploring the correlation between leaf functional characteristic and photosynthetic characteristics can provide more insights into the adaptability of plants to the environment (Maza-Villalobos et al. 2022). Li et al. (2018) investigated the factors for plant photosynthetic capacity based on the anatomical structure of leaves. They have suggested that plants with thick or dense leaves show certain advantages under strong light, and mesophyll cells output photosynthetic products more efficiently with the increase of the leaf vein density, such that photosynthetic products can be produced more efficiently. Dong et al. (2022) investigated the reference indicators for screening highlight efficiency germplasms of the genus Herperis. They highlighted that the ratio of palisade tissue to sponge tissue can serve as a vital reference indicator for screening highlight efficiency germplasm resources of this genus. Using the above-described method, Li and Tian (2022) studied the correlation between leaf morphology and photosynthetic physiological characteristics exhibited by six garden plants in Lanzhou City. It is preferred that the dry matter content of emerging leaves is the explanatory variable that most significantly affects the photosynthetic characteristics. The research on the evaluation index of light efficiency or the main driving factor of plant ecological adaptation and resource acquisition of Carex species has been relatively limited for the genus Carex.
Thus, several questions are raised about whether C. breviculmis and C. heterostachya with extensive environmental adaptability play a higher turf-quality in northwest China, what are their photosynthetic characteristics, anatomical characteristics and eco-physiological characteristics, whether leaf anatomical characteristic is correlated with photosynthetic properties in the case of Carex, since there is no distinction between the palisade tissue and the sponge tissue in mesophyll cells, as well as how to screen the germplasm resources of Carex that can use light energy efficiently. Lastly, Plants with high exhibit a higher sensitivity to the environment potential adaptability (Valladares et al. 2000). The comparison of the coefficient of variation and plasticity index about various functional characteristic suggested whether C. breviculmis or C. heterostachya is more adaptable.
To answer the above-mentioned questions, C. breviculmis and C. heterostachya growing on university campuses in Northwest China were taken as the research object, and their leaf functional characteristic was analyzed to explain the physiological and ecological responses of plants in a heterogeneous environment by combining the characteristics of the external environment. The internal relationship between photosynthetic characteristics and leaf functional characteristic was explored through correlation analysis and redundancy analysis to clarify plant growth strategies, thus laying a theoretical basis for screening grass species with the potential to be ideal turfgrass in the future. This study suggested that the further research should place a focus on high development and utilization value of C. breviculmis and C. heterostachya in landscape applications to increase the diversity of turfgrass species and the richness of landscape layers.

Plant materials and growth condition
In 2000, the plant seeds originated purchased from a seedling company in Shandong Province, China, and were sown on the campus of Northwest Agriculture and Forestry University Yangling demonstration area, Shaanxi Province (108°5′18″ E, 34°5′4″ N) in the same period. The introduction site is characterized by a temperate continental monsoon climate. The annual precipitation reaches 635.1 mm, the annual average temperature is 12.9 °C, the annual average sunshine hours are 2163.8 h. Two Carex species naturally formed a lawn with high ornamental value after the growth in the shade for years, playing a role in beautifying the campus environment (Fig. 1). As indicated by the leaf shape index listed in Table 1, the leaves of C. heterostachya are slender and long, and its lawn height reaches 26.507 cm; C. breviculmis is shorter and wider, with its lawn height after natural lawn formation reaching 15.750 cm. C. breviculmis and C. heterostachya contribute to the lawn, with high lawn density and cover degree. From the ornamental perspective, the leaves of C. heterostachya are soft, the texture is good, the uniformity is high, the flat is uniform and neat, the leaves of C. breviculmis are bright green in colour, the texture is slightly hard, and the leaves are curved and bow-shaped and naturally droop, thus making people feel like returning to nature.
The optimal growing season was selected for plants in summer (end of July) for this experiment. During the period from 08:00 to 18:00 on the day of the test, the sample environment exhibited the characteristics: The wind speed did not change much during the day. The changes of air temperature (TA) and photosynthetically active radiation (PAR) 1 3 tended to first increase and then decrease. PAR reached the maximum at 14:00 with a value of 113.043 μmol m −2 s −1 , and TA reached a maximum at 16:00 with a value of 35.5 ℃. The average of PAR was 58.526 μmol m −2 s −1 and the average of TA reached 33.5 ℃. CA of the sample environment first decreased and then increased at 16:00 slightly. RH reached its maximum with a value of 57.02% at 08:00 and then tended to decrease. When the temperature began to drop from the peak, RH tended to rise (Fig. 2). For soil conditions, the relative water content of soil was 35.57% at the soil depth of 10-20 cm. The soil organic matter content was 10.664 g kg −1 , and soil total nitrogen only reached 3.8 g kg −1 . The soil total carbon content was 6.2 g kg −1 , suggesting that the ratio of C:P was relatively low. Moreover, the total phosphorus in soil was 8.5 g kg −1 , which was relatively barren. In brief, the sample locations were in a semishaded environment with higher air temperatures and lower relative soil humidity on a single day. The content of organic matter in soil was lower (Prout et al. 2021), and the photosynthetic effective radiation was the most significant at 14:00 in the day. What's more, the nitrogen and phosphorus in soil were lower, thus hindering plant absorption.

Sampling method
Three quadrats (100 × 100 cm) were randomly selected on the plots with C. heterostachya and C. breviculmis growing over 10 m apart. Four plants were randomly selected from the respective quadrat, and leaves of the measuring part was fully expanded from the respective plant (Sheng et al. 2023).

Diurnal variation of photosynthetic parameters
Photosynthetic Diurnal variation parameters were developed based on a LI-6400XT portable photosynthesis measurement system (Li-Cor Inc, Lincoln, Nebraska, USA), with natural sunlight as the light source. The middle position of the leaves was examined, and several contents (e.g., including net photosynthetic rate (PN), transpiration rate (TR), stomatal conductance (GS), atmospheric CO 2 concentration (CA), intercellular CO 2 concentration (CI), air temperature (TA), relative humidity (RH), and photosynthetically active  radiation (PAR)) were examined every 2 h from 8:00 to 18:00. The calculation was conducted after the measurement as follows: light use efficiency (LUE) = Pn/PAR; water use efficiency (WUE) = Pn/Tr; Stomatal limitation (LS) = (CA-CI) /CA.
The light-response curves were fitted using a modified Right-Angle Hyperbolic Model (YE 2010), The fitting model formula is expressed as Eq. (1). The light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (α), maximum net photosynthetic rate (PNMAX), and dark breathing rate (RD) of the two types of plants after fitting and calculation were calculated in accordance with the method proposed by Li et al. (2018).
where I denotes the photosynthetically active radiation; β and γ represent correction factor; β expresses Light suppression term; γ is Light saturation term (YE 2010; Ye 2007).
The light-response curves were fitted using a modified Right-Angle Hyperbolic Model (YE 2010). The fitting model formula is expressed in Eq. (2). The CO 2 saturation point (CSP), the CO 2 compensation point (CCP), the initial carboxylation rate (η), the photorespiration rate (RP), and the maximum net photosynthetic rate (ANMAX) were determined using the method proposed by Ye (2007). Furthermore, the maximum carboxylation rate (VCMAX) and maximum electron conductivity (JMAX) of the two plants were determined using the fitaci function in SPSS. (1) where β and γ represent correction factor; β' denotes CO 2 suppression term; γ' expresses CO 2 saturation term (YE 2010;Ye 2007).

Leaf eco-physiological characteristics and anatomical characteristics measurements
Leaf eco-physiological characteristics: the average of leaf length and leaf area (LA) was measured using leaf area meter (Li-3000C) (Kanagaraj et al. 2023). The average thickness of a single leaf (LT) and the average width was recorded with an electronic vernier caliper following the direction of the main vein on the same side of the leaf (de Antonio et al. 2023).
The leaves were immersed in water at 5 °C to avoid light after the fresh weight of leaves (LFW) was obtained on an electronic balance. After 12 h, the water on the surface of the leaves was quickly absorbed with absorbent paper, and the saturated fresh weight of the leaves (LSFW) was examined on the electronic balance. The leaf samples were placed in an oven at 105 ℃ for 30 min. Subsequently, they were dried at 70 ℃ till their weight remained unchanged. The weight at this time was the dry weight of the leaf (LDW). Three leaves of the respective plant species were collected for three replicates. Next, the calculation was conducted after measurement as follows: the leaf shape index = the leaf length/width of plant; specific leaf area (SLA) = LA/LDW; leaf dry matter content (LDMC) = LDW/LSFW; leaf relative water content (LRWC) = (LFW − LDW)/(LSFW − LDW); leaf tissue density (LTD) = LDW/(LT × LA). Anatomical characteristics: the complete leaves of the respective plant growing in the sun were selected, and the leaf tissue close to the middle or lower position was cut. First, the cut tissue blocks were quickly placed into 4% glutaraldehyde at 4 °C overnight for over 12 h. Subsequently, the samples were rinsed and then dehydrated with PBS buffer solution and different concentration gradients of ethanol (30%, 50%, 70%, 80%, 90%, and 100%). The samples were dried with a critical point dryer (EMCPD300), sprayed with gold using a sputter coater (Q150TS), and then magnified to 300 times under a field emission scanning electron microscope (HITACHI, Japan, FESEM S-4800) for observation and photography. Lastly, the high of siliceous papillose (SP), the thickness of cuticle (CUT), the thickness of upper epidermis (UET), the thickness of lower epidermal (LET), the thickness of main vein (MVT), the vessel area (VA), main vessel area (MVA), and vessel area/vascular bundle area (MVA/VA), the number of bulliform cells (BC) were obtained. Three to five leaves of the respective plant species were collected in terms of four replicates. (2)

Characteristics of turfgrass and soil conditions
The height of the lawn was measured by randomly selecting ten points in the quadrats and using vernier calipers. The number of turfgrass branches per quadrant was calculated. Subsequently, the number of branches per unit area was calculated, and the turfgrass density reached its average value. 1m 2 wooden frame was placed in the sample area, and the images were captured. The absolute cover values of plant was examined using the "Photographic method" (Vanha-Majamaa et al. 2000). The respective square was photographed and then imported into Photoshop 2020 with a 10 × 10 intersection grid for calculation. Furthermore, each intersection of the grid with vegetation was recorded as a 'hit' and then multiplied by 100 to determine the values. The soil chemical property samples were sampled using the "Diagonal method". To be specific, two vertices and midpoints were taken on a diagonal line in the respective quadrat as the sample points, the soil samples of 0-10 cm depth were drilled vertically using a soil drill with a diameter of 5 cm, 50 g of each soil sample was mixed into a plastic bag, and then the soil samples were taken back to the laboratory to determine the index content. The soil organic carbon content and the organic matter content were determined using the potassium dichromate method, the total nitrogen content was obtained based on the Kjeldahl method, and the total phosphorus content was determined using the sulfuric acid-perchloric acid digestion-molybdenum-antimony colourimetric method (Zhang et al. 2021).

Statistical analyses
The data were analyzed through the independent sample T test in SPSS 26. The correlation between photosynthetic characteristics and leaf functional characteristics was analyzed through the Pearson and redundancy analysis. Correlation analysis (Pearson) refers to a method that is capable of investigating the linear correlation between two variables, while redundancy analysis (RDA) refers to a method to study the correlation between groups of variables, which could prioritize explanatory variables and rank the significance of their effect . The leaf functional characteristic affecting photosynthetic characteristics first fell into two matrices prior to the RDA analysis, including one for the leaf eco-physiological characteristics and the other the for anatomical characteristic. All the data would be standardized first and subjected to detrended correspondence analysis (DCA) (Grinn-Gofron et al. 2018). As indicated by the results, the maximum gradient length of eco-physiological characteristics reached 0.12, less than 3, and the maximum gradient length of anatomical characteristics was 0.12. Accordingly, the RDA model was selected for sorting. Next, the most significant explanatory variables were selected from leaf eco-physiological characteristics and anatomical characteristic and then re-analyzed. The most significant effect on the photosynthetic characteristics of the two Carex species was obtained. Lastly, the results of RDA analysis and correlation analysis were analyzed to check whether the results were accurate. If the results were consistent, the analysis results could be acceptable (Dong et al. 2022), and they were plotted in Origin 2019. The data in the graph are expressed as the mean ± SD.

Diurnal variation of photosynthetic parameters
From 08:00 to 18:00, PN, TR, GS and LS of both plants tended to increase first and then decrease. PN of C. heterostachya and C. breviculmis reached its maximum at 12:00 noon, the PN of C. heterostachya notably exceeded that of C. breviculmis (p < 0.05). The GS of the two plants reached its maximum at 10.00, whereas C. heterostachya significantly reached over C. breviculmis (p < 0.05). The peak time of TR of C. heterostachya and C. breviculmis was different. C. heterostachya reached its maximum at 10:00, whereas C. breviculmis was peaked at 12:00. With the rise of the temperature, the plant occurred stomatal closure, and the LS value was peaked at 14:00. LS of C. breviculmis reached over that of C. heterostachya. The change trend of CI in the two plants was opposite to that in PN, TR and GS, and the CI of C. heterostachya exceeded that of C. breviculmis in the respective period. LUE was peaked twice a day. The LUE peak of C. heterostachya was identified at 12:00, later than that of C. breviculmis. However, the LUE of C. heterostachya remarkably exceeded that of C. breviculmis (p < 0.05). At 12:00, the WUE of C. breviculmis exhibited a significant "midday depression", and the WUE tended to decrease at 12:00, correlated with the increase of TA and the enhancement of Tr. In general, WUE was significantly higher for C. breviculmis than that in terms of C. heterostachya (p < 0.05) (Fig. 3).

Light response curve parameters and CO 2 response curve parameters
The changes of light response curves of C. heterostachya and C. breviculmis were similar (Fig. 4). C. heterostachya and C. breviculmis grew in semi-shaded environment for a long time, such that their LCP remained at a low level, 9.163 ± 2.174 and 10.163 ± 3.453, respectively. The plants showed photoinhibition when the PAR was lower than LCP. The PN showed an approximately linear increase when the PAR was between LCP and LSP. The PN was limited when the PAR was higher than LSP. As depicted in Table 2, the PNMAX of C. breviculmis was significantly higher than that of C. heterostachya, and LCP, LSP of C. breviculmis also exceeded those of C. heterostachya (p < 0.05).
Besides, the CO 2 response curves of C. heterostachya and C. breviculmis varied similarly (Fig. 4). At the insufficient concentration of CO 2 in the air, CO 2 inhibition occurred, and photosynthesis was limited. PN reached its maximum value at the concentration of CO 2 higher than the limit of a certain concentration. As depicted in Table 2 1 3 no significant difference was reported in ANMAX between the two plants, and no significant difference was reported in η, CSP and JMAX between two plants (p > 0.05). VCMAX refers to a vital parameter to characterize the photosynthetic capacity of vegetation. The VCMAX of C. breviculmis notably exceeded that of C. heterostachya (p < 0.05). Furthermore, the CCP and RP of C. breviculmis were significantly higher than those of C. heterostachya (p < 0.05).

Leaf eco-physiological characteristics and anatomical characteristics
Six eco-physiological characteristics of leaves were observed in Table 3: the LT, LA and SLA of C. heterostachya obviously reached over those of C. breviculmis (p < 0.05). The LRWC and LDWC of C. breviculmis notably exceeded those of C. heterostachya (p < 0.05). LTD of C. breviculmis was remarkably higher than that of C. heterostachya (p < 0.05).
In general, the anatomical structure of the leaves was "V"-shaped in cross section, comprising epidermal cells, mesophyll cells, and leaf veins. Moreover, there were major vascular bundles with large area in the main vein, and many others were also distributed in the mesophyll. The vascular bundle structure distributes mechanical tissues up and down. The upper epidermal cells were large, the outer wall of the cell had smooth and continuous cuticle. The lower epidermis cell was small, and its outer side was the cuticle, which had siliceous papillose out of it (Fig. 5). As depicted in Table 3, (1) epidermal characteristics exhibited by leaves: CUT of C. breviculmis was significantly larger than C. heterostachya (p < 0.05), which was 1.8 times of C. heterostachya, and C. heterostachya had SP with a height of 18.175um, whereas C. breviculmis did not; UET of C. breviculmis was significantly larger than that of C. heterostachya (p < 0.05).
(2) Conducting tissue characteristics: The MVA of C. heterostachya was significantly larger than C. breviculmis (p < 0.05); VA of C. heterostachya notably exceeded that of C. breviculmis  Table 2 Light response curve parameters, CO 2 response curve parameters of Carex heterostachya and Carex breviculmis α apparent quantum efficiency, PNMAX maximum net photosynthetic rate in light curve, LSP light saturation point, LCP light compensation point, RD dark breathing rate, η initial carboxylation rate, ANMAX maximum net photosynthetic rate in CO 2 response curve, CSP CO 2 saturation point, CCP CO 2 compensation point, RP photorespiration rate, VCMAX maximum carboxylation rate, JMAX maximum electron conductivity. Data represent means ± SD of four independent experiments. Different letters following each value within a column indicate significant differences at p < 0.05. The same letter means no significant difference. F: square of intra-group and inter-group dispersion/degree of freedom; Sig: significance  degree of variation of leaf eco-physiological characteristic was relatively large. LRWC exhibited the highest variability (CV: 109.170% and 106.545%, respectively) and the most significant plasticity (PI: 0.229 and 0.256, respectively). SLA achieved the lowest variability (CV: 0.225 and 0.809, respectively) (PI: 0.016 and 0.019, respectively). The CV of leaf anatomical characteristic ranged from 0.603% to 17.086%, and the PI were 0.017-0.341. The all CV and PI of leaf anatomical characteristic were lower, such that they exhibited stronger stability than eco-physiological characteristics. From the perspective of interspecific differences, the interspecific differences in eco-physiological characteristics were not large, whereas there was a significant difference in leaf anatomical characteristic. The C. breviculmis's CV of VA, MVA/VA were significantly larger than those of C. heterostachya. It has greater plasticity and better adaptability to the current habitat than C. heterostachya.

Correlations among multiple leaf functional characteristic in Carex
Among eco-physiological characteristics, LT, SLA, LA, LTD, and LDWC were correlated with photosynthetic characteristics (Fig. 6).   6 Heat map of correlations between photosynthetic parameters, eco-physiological characteristics, and leaf anatomical characteristics in two Carex species. Blue is negative correlation, red is positive correlation, the darker the colour, the stronger the correlation (*p < 0.05, **p < 0.01). α apparent quantum efficiency, PNMAX maximum net photosynthetic rate in light curve, LSP light saturation point, LCP light compensation point; RD dark breathing rate, η initial carboxylation rate, ANMAX maximum net photosynthetic rate in CO 2 response curve, CSP CO 2 saturation point, CCP CO 2 compensation point, RP photorespiration rate, VCMAX maximum carboxylation rate, JMAX maximum electron conductivity. LT leaf thickness, LA leaf area, SLA specific leaf area, LTD leaf tissue density, LRWC leaf relative water content, LDWC leaf dry matter content, CUT thickness of cuticle, SP high of siliceous papillose, UET thickness of upper epidermis, LET thickness of lower epidermal, MVT thickness of main vein, MVA main vessel vascular bundle structure area, VA vessel area, MVA/VA vessel area/vascular bundle area, BC number of bulliform cells

Key factors for the light efficiency of the Carex species
To further screen the critical variables from multiple characteristic with significant correlations, it is considered that the coefficients of variation of the eco-physiological characteristics and the leaf anatomical characteristic are significantly different. The built-in algorithm of the Canoco software was adopted to screen six vital explanatory variables from the leaf morphological characteristics (Fig. 7). The explanatory variables of the first axis and the second axis reached 52.45% and 25.52%, suggesting that the first and second axes accounted for 77.97% of the variation in photosynthetic characteristics exhibited by the two Carex species (Table 4). SLA (explains 52.00%, p = 0.012) exhibited the longest arrow length and significantly affected the photosynthetic characteristics (p < 0.05) ( Table 5). A small angle was found between the arrow directions of SLA and LUE, TR, PN, and GS (acute angle), suggesting that SLA shows a strong positive correlation with LUE, TR, PN, as well as GS. A relatively large angle was reported between  1 3 the arrows of SLA and WUE, LSP, and RP (obtuse angle), suggesting the significantly negative correlation between SLA and WUE, LSP, and RP. Four vital leaf anatomical characteristics were screened using the built-in algorithm of the Canoco software (Fig. 7). The explanatory variables of the first and second axis reached 52.48% and 24.00%, suggesting that the first two axes accounted for 76.48% of the variation in photosynthetic characteristics of the two Carex species (Table 6). The arrow length of CUT (explains 51.90%, p = 0.02) was the longest, and the effect on the photosynthetic characteristics was significant (p < 0.05) ( Table 7). The included angle between CUT and WUE reached its minimum (acute angle), and they showed a strong positive correlation. The angle between CUT and GS, TR, PN, LUE was the largest (obtuse angle), and CUT had negative correlation with the above-described four indicators. UET (explained 20.10%, p = 0.02) effect on the photosynthetic characteristics was also significant (p < 0.05). The angle between UET and RP reached its minimum, suggesting a strong positive correlation, and the angle between UET and LUE reached its maximum, suggesting a negative correlation. The results of RDA and the value of r in Pearson analysis were consistent. The above three significant explanatory variables (SLA, CUT, UET) were re-analyzed, suggesting that the explanatory variables of the first axis accounted for 52.17% (more than half) of the variation of the photosynthetic characteristics (Table 8), SLA contributed 67.4% more than half and exhibited the longest arrow length and significantly affected the photosynthetic characteristics (p < 0.05) ( Table 9).

Diurnal variation characteristics of photosynthetic parameters
The diurnal variation of photosynthetic parameters is capable of indicating the adaptability of plants to the  environment, which is another essential method to investigate the effect of environmental factors on plant growth and metabolism (Morales et al. 2020). Zhou et al. (2020) increased the PN of plants by improving the light quality, such that increasing the accumulation of total organic carbon (TOC) content. CI is capable of determining the amount of carbon source providing plant photosynthesis (Tominaga et al. 2018). LUE indicates the plant efficiency in fixing solar energy and how well ecosystems convert sunlight into stored chemical energy (Baldocchi & Penuelas 2019). Under semi-shading environment, this study suggested that C. heterostachya was characterized by its stronger photosynthetic capacity, higher net photosynthetic rate (PN), and more organic matter accumulated per unit time and unit leaf area. The soil environment where the two plants grow is characterized by low humidity in summer, and the plants are capable of absorbing and using less water. Under water stress, it is reported that for two different citrus genotypes (i.e., Carrizo citrange and Cleopatra mandarin), closure of stomata along with reductions in transpiration and photosynthetic rates aims at reducing water loss (Abideen et al. 2020). With the change of seasons, the ambient temperature tends to increase, and the photosynthetic parameters of Mediterranean trees show seasonal changes. The environment was subjected to severe drought at the temperature over 29-32 ℃ such that the top value of all variables (e.g., net photosynthesis, stomatal conductance, electron-transport rate) decreased by 29-19% on average (Sperlich et al. 2019). The photosynthetic capacity of Carex breviculmis decreased at the daily average temperature of 33.5 ℃. The possible reason for this result is that plant photosynthesis and carbon assimilation were affected by heat stress, and the light energy conversion rate of plant photochemical reaction center declined (Balfagón et al. 2019). Transpiration and water loss can be effectively reduced at high temperatures and in a dry environment by reducing stomatal conductance, enhancing stomatal limit value, effectively using water in leaves, as well as maintaining its own growth through low photosynthesis. It served as an excellent ground cover that exhibited drought resistance and water saving characteristics. C. heterostachya was not affected by the environment. With the rise of the temperature, TR reached the peak in advance, while the stomata were closed to reduce the leaf temperature and plant water loss (Marchin et al. 2022). Higher TR and GS can facilitate the water vapour exchange between C. heterostachya leaves and the external environment, the photosynthetic products can accumulate, and the growth rate can be increased (Xinqiang et al. 2020).

Photoresponse parameters and CO 2 -response parameters
In general, plants exhibiting low light compensation point (LCP) and light saturation point (LSP) have been recognized as typical shade-tolerant plants (Arenas-Corraliza et al. 2019). For instance, Rubiaceae species is possible by lower mean LSP in the heavily shadowed understory of tropical forests (Torres-Leite et al. 2019). With the increase of the PAR from 0 to 600 μmol m −2 s −1 , two shade-tolerant Calathea plants also had lower LSP and PNMAX (Hoang Chinh et al. 2018). The LCP of C. breviculmis and C. heterostachya were less than 20 μmol m −2 s −1 , and their LSP were all less than 1000 μmol m −2 s −1 , suggesting that they were shade plant and suitable for turfgrass growing in shade under the tree. Yang et al. (2014) obtained higher LCP and LSP of C. breviculmis, which may be due to the fact that the grass grows in the shade for a long time. C. heterostachya exhibits a more significant ability to utilize low light than C. breviculmis. C. heterostachya more significantly applies to the cultivation of C. heterostachya in low light or shading environments, whereas C. breviculmis may be well grown in semi-shading environments.
CO 2 compensation point (CCP) and CO 2 saturation point (CSP) are crucial indicators for determining whether plants exhibit the genetic characteristics of high light efficiency. Photosynthesis is largely constrained by stomatal conductance at extremely high temperatures, such that CCP of tropical trees tends to decline (Slot et al. 2019). Both C. breviculmis and C. heterostachya may be affected by temperature, resulting in reduced CCP. However, plants with lower CCP are characterized by high photosynthetic rate, low respiration rate, as well as fast growth (Dong et al. 2016). The higher VCMAX of C. breviculmis may be due to the competition between CO 2 and Rubisco enzyme binding site increases the carboxylation rate (Marcus et al. 2005).The VCMAX of leaves represents a vital rate-limiting reaction in the process of photosynthesis, playing a critical role in the rate of photosynthesis (Schurr et al. 2006). The VCMAX of C. breviculmis notably exceeds that of C. heterostachya, such that makes C. breviculmis exhibit high light efficiency and high growth potential. Using CO 2 for photosynthesis contributes to the production of organic matter and the growth of C. heterostachya. Thus, C. heterostachya grows faster into lawns. The photorespiration rate (RP) indicates the ability of plants to use high concentrations of O 2 for respiration to consume photosynthetic products under light conditions. The high RP rate of C. heterostachya hinders the accumulation of photosynthetic products to a certain extent (Paixao et al. 2019).

Differences in leaf eco-physiological characteristics and anatomical character
Leaf is a bridge connecting plant physiology and external environment, exhibiting a significant ability to perceive 1 3 heterogeneous environments. It is a survival strategy for plants to adapt to environmental changes by regulating the functional characteristic of leaves to cope with different habitats (García-Cervigón et al. 2021).
(1) C. heterostachya: Leaf morphology is capable of affecting the photosynthetic area of leaves, and leaf area (LA) indicates the ability of plants to intercept light (Huang et al. 2021) C. heterostachya can capture different degrees of light energy and performed stronger photosynthesis through larger leaves. Moreover, as indicated by the larger vessel area (VA), vascular bundle area (MVA), and vessel area/vascular bundle area (MVA/VA) of C. heterostachya, its conducting tissue is well developed, and leaf water conduction is positively correlated with photosynthetic capacity (Hernandez and Park 2022), explaining why its conducting tissue can facilitate the photosynthetic reaction with CO 2 and H 2 O as the raw materials. Ju et al. (2022) suggested that there is a correlation between thicker leaves and the absorption rate of nitrogen and phosphorus. Accordingly, the conducting tissue of C. heterostachya can more significantly promote plants to transport photosynthetic products (e.g., nitrogen and phosphorus) under poor soil and low moisture content. Notably, the semi-shaded environment alleviated the drought stress and facilitated biomass production, such that the SLA of C. heterostachya was larger than that of C. breviculmis. Moreover, C. heterostachya exhibited a siliceous papillose structure outside the stratum corneum, leading to its excellent self-protection ability and significantly greater than C. breviculmis.
(2) C. breviculmis: For leaf anatomy, a significantly thicker palisade was also reported in drought-resistant tropical trees under soil moisture deficit, and the photosynthesis rates shows a positive correlation with the palisade mesophyll thickness (Hernandez and Park 2022). As a result, C. breviculmis's thicker cuticle (CUT) and epidermal cells take on vital significance to helping plants reduce water transpiration (Chen 2021). Larger vesicular cells are critical to maintaining cellular water potential. C. breviculmis has large vacuoles to regulate leaf extension and curling, such that the loss of water potential in plants under drought stress can be prevented, and their ability to adapt to drought can be improved, affecting leaf morphology and light and water use capacity (Xiang et al. 2012). LDMC has been commonly adopted to characterize the ability of plants to preserve nutrients (van Bodegom et al. 2014). The size of leaf tissue density (LTD) indicates the plant's water demand and the plant's resistance (Xu et al. 2023) (e.g. resistance to high temperature and drought). As revealed by the higher LRWC, LDWC and LTD values of C. breviculmis, its leaves exhibit higher osmotic regulation function and stronger drought resistance in the environment with low soil nutrient utilization and low humidity. Besides, higher temperatures can lead to the increased photochemical activity (i.e. electron-transport rate and photochemical quenching) and the decreased heat dissipation capacity (i.e. lower lutein pool, Chl a/b and β-carotene/neoxanthin ratio) (Saez et al. 2019). The leaf mass per unit area slightly decreases at higher temperatures, accounting for the reason why the PN and SLA of C. breviculmis is lower.
As indicated by the theoretical analysis of leaf economic spectrum, C. heterostachya is a fast investment-income species and tends to select survival strategies with strong photosynthetic ability, larger than leaf area but short lifespan. Besides, C. breviculmis refers to a slow investment-income species and tends to select weak photosynthetic ability, smaller SLA, and longer lifespan. The two completely different survival strategies are the result of species adapting to the environment in the long-term evolution, revealing that different plants are capable of optimizing the allocation of resources by adjusting their own plant functional traits.

Variability and plasticity of eco-physiological characteristics and leaf anatomical character
Leaf tissue structure exhibits strong variability and plasticity. Characteristics with a coefficient of variation greater than 50% are considered ecologically adaptive characteristic, and those achieving a smaller coefficient of variation are relatively stable system evolution characteristic, revealing the potential adaptive capacity of species (Zhang et al. 2021). The plasticity index indicates the ability of a species to resist environmental stress, and a higher level of plasticity suggests a stronger system regulation ability (Diethelm et al. 2022). LRWC exhibited the greatest variability and plasticity among the eco-physiological characteristics of the two plants, suggesting the results of adaptation to external drought stress. The plants increased the relative water content of leaves to improve their water retention and drought resistance, and the plant cell wall was more elastic, thus contributing to the inhibition of the decline of leaf water potential when plants lose water and adapt to the water-deficit environment (Limousin et al. 2022). The leaf functional traits of woody plants were examined under drought and shading, Wang and Wang (2022) have suggested that shade alleviates the adverse effect of drought on photosynthesis by decreasing stomatal limitation and photoinhibition and increasing leaf relative water content, such that biomass production can be facilitated. In this study, despite the characteristics of Northwest China (e.g., higher temperatures and higher evaporation in summer), the semi-shading also played a role in alleviating plant drought stress.
The leaf anatomical characteristic of C. heterostachya exhibit relatively low plasticity and variability, and all characteristic are relatively stable, all of which belong to evolutionary characteristic. The plasticity and variability of C. breviculmis are stronger than those of C. heterostachya, suggesting that C. breviculmis is capable of maintaining the relative stability and adaptability of leaves in heterogeneous ecosystems through plasticity, enhancing the resistance and resilience to biotic and abiotic factors in the system. In terms of the anatomical structure, two indicators with the greatest interspecific variation were VA and MVA/VA. The conducting tissue is a vital structure for the adaptation of desert wetlands and oasis riparian plants to the environment (Zhou et al. 2012). In this study, C. breviculmis could regulate the conducting tissue, which connected the above-ground and underground structures of the ecosystem, to adapt environment. What's more, the plasticity of conducting tissue can enhance the ability of C. breviculmis to absorb water and salt to better adapt to the environment.

Key factors for the light efficiency of the Carex species
From the leaf eco-physiological characteristics, Wright's research suggested that SLA was a characteristics correlated with light capture and photosynthetic capacity (Wright et al. 2004). The larger the SLA, the larger PN will be. The reason for the above result is that the larger the SLA, the greater the GS and TR will be, such that the plant can capture more light energy while achieving a higher metabolic rate per unit mass of plant (Wright et al. 2004) and increasing the growth rate of plants. The Cerrado tree Dalbergia miscolobium in shade environments exhibits increased height, leaf number, chlorophyll content, as well as specific leaf area (Mendonça et al. 2020), consistent with the conclusion of this study. In brief, shade-loving plants exhibits thinner leaves, larger SLA, and better photosynthetic capacity. In the relatively poor soil environment, plants facilitate SLA accumulation by increasing PN, TR and WUE of plants, such that specific growth strategies can be formulated (Sánchez-Blanco et al. 2019). However, there was a negative correlation between SLA and WUE, as indicated by the analysis of this study, which may be correlated with the arid environment. The leaf area index (LAI) and SLA of vegetation in the desert steppe ecotone in northern China were lower. Furthermore, the WUE of photosynthesis increases with the increase of nitrogen content per unit leaf area caused by drought (Wei et al. 2016).
Among the leaf anatomical characteristic, CUT most significantly affects the photosynthetic characteristics exhibited by the two Carex species. This study reveals a positive correlation between CUT and WUE since the cuticle serves as the major transpiration barrier to restrict nonstomatal water loss (Chen 2021). Moreover, CUT can enhance the reflection of solar radiation, thus contributing to the prevention of water loss, and water utilization can be improved by reducing TR and GS (Puglielli et al. 2023). Thakur et al. (2019) reported that plants gain more resources to sustain growth at high altitudes by increasing the thickness of their epidermal cells. The thickened epidermal cell may enhance the capability to light energy capture (Bernado et al. 2021). However, this study revealed that UET is significantly correlated with RP while showing a significant negative correlation with LUE, which can be interpreted by the arid environment. On the one hand, plants provide themselves with more "defensive" construction (e.g., increasing leaf thickness, reducing water transpiration and enhancing their ability to adapt to drought) to maintain high drought resistance. Photorespiration refers to a metabolic pathway formed in the long-term evolution process to adapt to environmental changes and enhance stress resistance of plants (Kambona et al. 2023). Besides, there is less water in the soil, such that less substrates play a role in photosynthesis. Plants only maintain their own growth through low photosynthesis to effectively use the water in the leaves.
In brief, when the genus Carex grew in the semi-shade and the soil environment was arid, SLA was one of the most important indicator in eco-physiological characteristics, CUT and UET were the most important indicator in anatomical characteristics to evaluate photosynthetic characteristics of plant. The explanatory variables were optimized, and the significance of their effects was ranked. The result suggested that SLA more significantly affected the photosynthetic characteristics of the two Carex species. The SLA of C. heterostachya was significantly larger than that of C. breviculmis, CUT and UET were lower than C. breviculmis, suggesting that C. heterostachya exhibited higher photosynthetic efficiency and high utilization of light energy.

Conclusion
C. heterostachya and C. breviculmis have different resource acquisition strategies after undergoing long-term environmental adaptation and evolution. C. breviculmis refers to a slow investment-return plant. The variability and plasticity of leaf functional character of C. breviculmis were stronger, and it exhibits strong environmental adaptability in longterm shaded environments. And C. breviculmis are high water utilization, high CO 2 utilization capacity, drought resistance and barren resistance. The advantage of C. heterostachya is that C. heterostachya can better adapt and maintain photosynthesis with the increase of air temperature and photosynthetically active radiation. C. heterostachya is a quick investment-return plant. C. heterostachya has a welldeveloped conducting tissue, leading to its higher efficiency in transporting nutrients and accumulating organic matter. Furthermore, C. heterostachya photosynthetic efficiency is high, which has high efficiency in capturing and fixing solar energy. Both C. heterostachya and C. breviculmis have shade tolerance, but C. heterostachya is more than C. breviculmis. Lastly, SLA can serve as the main indicators to evaluate the light efficiency of Carex. C. heterostachya and C. breviculmis have extensive applications, especially in areas with continental monsoon climates. They are benefical to increase the diversity of turfgrass species and meet people's more demand for turfgrass to a certain extent. Moreover, they can be employed in shading environments and beside buildings, adding layers to the landscape configuration. Lastly, C. breviculmis can be planted in places with poorer soil water content and poorer soil nutrients to rapidly grow lawns. C. heterostachya and C. breviculmis are potential turfgrasses.