Arbuscular Mycorrhizal Colonization Increased Above-Belowground Feedback of Maize In a Degraded Coal Mining Area Soil By Increasing The Photosynthetic Carbon Assimilation And Allocation of Mazie

A three-compartment culture system was used to study the mechanism by which the AM fungus Funneliformis mosseae inuences host plant growth and soil organic carbon (SOC) content in a coal mining area. A 13 CO 2 pulse tracing technique traced the allocation of maize photosynthetic C in shoots, roots, AM fungus and soil to detect C accumulation and allocation in mycorrhizal (inoculated with Funneliformis mosseae) and non-mycorrhizal treatments.AM fungal inoculation signicantly increased the 13 C concentration and content in both above- and below-ground plant parts. Mycorrhizal inoculation signicantly enhanced the anti-aging ability by increasing soluble sugars and catalase activity (CAT) in maize leaves while reducing foliar malondialdehyde content (MDA) and leaf temperature to promote plant growth. AM fungi also increased P uptake to promote maize growth. Soil organic carbon (SOC), glomalin, microbial biomass carbon (MBC) and nitrogen (MBN) contents increased signicantly after inoculation. A mutually benecial system was established involving maize, the AM fungus and the microbiome, and the AM fungus became an important regulator of C ux between the above- and below-ground parts of the system. Inoculation with the AM fungus promoted plant growth, C xation and allocation belowground to enhance soil quality. The positive above-belowground feedback appeared to be established. methods which cannot give a direct indication of the allocation of primary products. Here, a greenhouse experiment was conducted and 13 CO 2 pulse labeling was used to quantify the effects of AM inoculation on the allocation of photosynthetic products above- and below-ground and the effects of AM fungal inoculation on C storage in plants and soil. The effects of hyphae on C allocation were studied using three-compartment microcosms to collect AM fungal biomass and then calculate the amount of 13 C in the biomass. The work aimed to unveil the mechanisms by which AM fungi promote C sinks in plants and soil under controlled conditions, and to provide a theoretical basis for the role of AM fungi in C storage in the soil and in photosynthate allocation above- and below-ground in a nutrient-poor soil from a coal mining area in northwest China.


Introduction
In a natural system there is positive above-belowground feedback that is essential for a healthy ecosystem (Mariotte et al. 2018).
However, some arti cial practices such as coal mining disrupt this and lead to environmental degradation (Rocha-Nicoleite et al. 2017).
It is therefore important to devise methods for the ecological restoration of mining areas (De and Mitra 2002;Shrestha and Lal 2006).
Inoculation with arbuscular mycorrhizal fungi has been demonstrated to be an effective biotic method to achieve ecological restoration  (Godbold et al. 2006; Kiers et al. 2011). Four to twenty percent of plant photosynthetic products are transferred to the AM fungi to build hyphae that extend into the soil and in uence soil C storage (Bago et al. 2000; Godbold et al. 2006). A 13 C labelling experiment has found that AMF received 4.3% plant xed C in 24h (Tomè et al. 2015). Kaiser et al. (2015) found that mycorrhizal fungi directly transported C from plant photosynthetic products to the soil and even to soil microbes (Kaiser et al. 2015). AM fungi therefore plays an important role in C cycling from above-to below-ground.
Previous studies show that AM fungi affect the association between roots and soil by increasing nutrient uptake and the resistance of These studies indicate that AM fungal inoculation in uences plant physiological traits and promotes C sequestration by host plants (Miller et al. 2002;Zhu and Miller 2003). In return, photosynthate is allocated belowground. An increase in root biomass may increase the space for colonization by AM fungi while AM inoculation decrease the root-to-shoot ratio through ameliorating plant nutrient status (Veresoglou et al. 2012). In addition, the AM fungi produce hyphae that extend into the soil and then exert important effects on the soil environment (Zhu and Miller 2003;Godbold et al. 2006). Hyphae, spores and vesicles of AM fungi are widely present in soils and the extraradical biomass can form up to 32% of the total soil microbial biomass, contributing up to 15% of SOC (Miller and Kling 2000). Some studies suggest an increased or accelerated photosynthetic down-regulation with AMF under greenhouse conditions (Goicoechea et al. 2014).
Establishment of mycorrhizal symbiosis often increases allocation of C to the roots and further to the mycorrhizal fungi (Řezáčová et al. 2017). As feedback, the roots and AM fungi exude sugars and organic acids to the soil and thus to soil microorganisms, which may be activated to metabolize accumulated soil mineral nutrients for the growth of the host plants (Zhang et al. 2016). When hyphae die, a portion of their C is rapidly decomposed by other microorganisms and converted to CO 2 which may enter the atmosphere or some recalcitrant organic compounds such as chitin and glomalin that can remain in the soil for years to decades (Gleixner et al. 2002;Wilson et al. 2009;Smith and Read 2010;Treseder 2013). In addition, the contribution of AM fungi to the C cycle also depends on both the ERH and exudates from AM fungal hyphae such as glomalin which can contribute to soil C aggregation and soil quality enhancement (Wright and Upadhyaya 1996;Tisdall et al. 1997;Zhu and Miller 2003;Zhang et al. 2016). However, several research showed that plant C allocated to hyphae was high enough to cause the depression of host plants in some experiments especially in nutrient-limited areas or the establishment stages of roots and hyphae (Jakobsen 1999;Gavito et al. 2019).
It is important to promote vegetation restoration and soil organic matter accumulation for a mining area ecological restoration, understand the mechanisms by which AM fungi promote soil C storage is helpful. However, most studies have been conducted under eld conditions and factors such as soil heterogeneity and climatic variability have had a substantial impact on the results. Recent efforts have been made to quantify how AM associations may affect the overall C balance and C uxes in different types of photosynthetic metabolism using stable 13 C isotopes, but have ignored how much C the AM fungi receive because of the paucity of available methods to quantify this directly (Lendenmann et al. 2011;Slavíková et al. 2017;Řezáčová et al. 2017 and.In previous studies, different results were got under different nutritional conditions, host plants and growth stages. Quanti cation of the contribution of AM fungi to the exchange of photosynthetic products between above-and below-ground pools have been based mainly on δ 13 C and C% value, methods which cannot give a direct indication of the allocation of primary products. Here, a greenhouse experiment was conducted and 13 CO 2 pulse labeling was used to quantify the effects of AM inoculation on the allocation of photosynthetic products above-and below-ground and the effects of AM fungal inoculation on C storage in plants and soil. The effects of hyphae on C allocation were studied using three-compartment microcosms to collect AM fungal biomass and then calculate the amount of 13 C in the biomass. The work aimed to unveil the mechanisms by which AM fungi promote C sinks in plants and soil under controlled conditions, and to provide a theoretical basis for the role of AM fungi in C storage in the soil and in photosynthate allocation above-and below-ground in a nutrient-poor soil from a coal mining area in northwest China.

Soil, plants and AM fungus
Sandy soil collected from Daliuta mining area, Yulin, Shanxi Province, China was sieved ( 2 mm), sterilized at 121℃ and 103 kPa for 2 h and air-dried for three days before use. Selected soil physicochemical properties were: available phosphorus (AP, NaHCO 3 extracted), 2.97 mg kg −1 ; available potassium (AK), 12.9 mg kg −1 ; organic matter content, 1.25 g kg −1 ; pH, 7.39; conductivity, 834 µS cm −1 ; and water holding capacity, 18.6%. The low AP, AK and conductivity indicate a nutrient-limited environment for plants. Maize (Zea mays L., cultivar Nuoyu 2) was selected as the host plant and seeds were provided by the Seeds Company of the Chinese Academy of Agricultural Sciences.

Experimental design and management
The experiment was conducted using 55 × 28 × 26 cm three-compartment microcosms (Fig. 1a). On the left was the root compartment (RC), in the middle the buffer zone (BC) and on the right the hyphal compartment (HC). We used a 1-mm nylon mesh to allow hyphae and ne roots (but not coarse roots) into the BC in order to avoid the roots extending to the HC and ensuring enough hyphae in the HC for collection. The BC and HC were separated by 30-µm pore nylon mesh to allow hyphae in and exclude all roots. The soil in the RC and BC was sterilized sandy soil sieved to 2 mm and the medium in the HC was 0.8-1.2 mm glass beads immersed in 5% HCl for 24 h and washed with distilled water several times before use to collect clean hyphae. There were 25 kg, 5 kg and 22 kg soil, respectively, in the RC, BC and HC of each pot. Two treatments were established, mycorrhizal (inoculated with F. mosseae) and non-mycorrhizal controls (CK). One hundred of inoculum was applied to the root compartment of the mycorrhizal treatment by layering and the non-mycorrhizal treatment received 100 g sterilized inoculum. the effects of AM fungi on maize growth, stress resistance and C allocation were determined compared with the control. There were three replicates of each treatment and a total of six microcosms were used. We added 100 mg N (as NH 4 NO 3 ), 30 mg P (as KH 2 PO 4 ), and 150 mg K (as K 2 SO 4 ) per kg to the RC to meet the basic nutrient demand of maize at the seedling stage, watered the soil to maximum water holding capacity and then preconditioned the soil for 24 h before transplanting. Maize seeds were sown in plastic seedling pots and then transplanted to the RC at the three-leaf stage on April 5th, 2017. There were two maize plants in each RC. An EM50 data logger (ICT International, Armidale, NSW, Australia) was used daily to maintain the soil moisture content within 75 to 80% of the water holding capacity. Deionized water (100 ml) was added to the HC every day plus 100 ml 1/10 Hoagland's nutrient solution every three days to ensure hyphal growth. Maize growth was maintained by adding 50 mg N (as NH 4 NO 3 ), 15 mg P (as KH 2 PO 4 ), and 75 mg K (as K 2 SO 4 ) to the RC soil 25 days after transplanting to alleviate plant nutrient de ciency.

CO 2 pulse labeling chamber and procedure
Previous studies indicate that 13 C from photosynthesis may be transferred to each plant part, AM fungi and soil and even to soil microbes within one day (Kuzyakov and Cheng 2004;Kaiser et al. 2015). 13 CO 2 stable isotope pulse labeling for three days starting at the tasseling stage 63 days after transplanting was used to trace the distribution of maize photosynthetic C among plant parts, AM fungus and soil. The labeling chamber was 110 × 110 × 75 cm in size (Fig. 1b). The mycorrhizal treatments and non-mycorrhizal controls were randomly placed in two labeling chambers with good light transmission and repositioned randomly each day to minimize variation due to the labeling process. LI-6400 handheld probes (LI-COR Biosciences, Lincoln, NE; to probe the real time concentration of CO 2 ), air fans, silica gel and thermometers (to determine the real-time temperature) were placed in the airtight chambers before labeling as shown in Fig. 1b. The 12 CO 2 in the labeling chamber was consumed by placing maize pots in the glasshouse chambers at 08:00 in the morning. When the CO 2 concentration in the labeling chambers was 50 ppm at 09:00 the 13 CO 2 (atom > 99.99%) gas was injected at 30-min intervals into the chambers to maintain a constant 13 CO 2 concentration of 300-450 ppm.
At 15:00 13 CO 2 gas was injected for the last time and the concentration of 13

Sampling and measurement
The photosynthetic rates of the third and fourth fully expanded leaves (from the top) were measured at 10:00 one day before labeling to test the effects of the AM fungus on plant photosynthetic ability. An LI-6400 handheld probe (Licor Biosciences, Lincoln, NE) was leaves (completely withered leaves), stems, and roots. Leaf areas and shoot and root biomass were determined. All plant parts were oven-dried to constant weight and ground to 0.15 mm. Shoot P and K concentrations were determined by digestion with H 2 SO 4 -H 2 O 2 and analysis using ICP-AES (Thomas et al. 1967). Rhizosphere soil was sampled by the quartering method and then passed through a 2-mm sieve. The soil was divided into two portions to determine the carbon allocation to the soil and the effects of the AM fungus on soil properties. One portion was stored at 4℃ to determine microbial biomass and the remainder was air-dried outdoors. Wet sieving was used to collect hyphae. The glass beads in the hyphal compartment were transferred to buckets and washed ve times with distilled water. Glass rods were used to mixed the glass beads and water. The supernatant was immediately passed through a 30-µm pore sieve to collect the hyphae. The AM fungal hyphae were dried at 80℃, ground to 0.15 mm and homogenized before analysis.
The carbon allocation, δ 13 C value and C% content of each plant part and soil and hyphal samples were fully quanti ed using a Deltaplus XP mass spectrometer (Thermo Fisher, Waltham, MA) and an elemental analyzer at the stable isotope laboratory of the Chinese Academy of Agricultural Sciences. The accuracies of measurement of C content and C isotopic composition were 0.1% and 0.2‰, respectively (Deniro and Epstein 1978).
Root segments were stained with 0.05% Trypan blue and examined under a microscope (Nikon, Tokyo, Japan) to determine the percentage of root length colonized (Phillips and Hayman 1970). The mycorrhizal colonization in every compartment was calculated as the number of mycorrhizal root segments/total number of root segments examined × 100%, which may be described as the percentage of root length colonized or the colonization frequency. The hyphal length density was determined by the method of Jakobsen et al. (1992). SOC content was determined by standard dichromate oxidation (Bremner and Jenkinson 1960). Brie y, the easily extractable soil glomalin (EEG) was extracted with alkaline citrate (20 mM

Data calculations
Total area of maize leaves (only green leaves) was calculated by the following equations.
where Si is area of a single leaf i and S is the total leaf area. 13 C distribution rate in each plant part: R, 13 The mycorrhizal contribution of each plant biomass and shoot P and K nutrition (MC%): Differences between mycorrhizal treatment and non-mycorrhizal control of mycorrhizal colonization, hyphal length density, shoot and root biomass, P and K concentration, SPAD value, total leaf area, MDA, CAT, soluble protein, soluble sugar, and starch were compared by Student's t-test at P < 0.05. The differences in photosynthetic indexes and soil physical and chemical properties between mycorrhizal and non-mycorrhizal treatments were compared by Student's t-test. Differences in δ 13 C,C%, 13 C concentration and 13 C content in plants and soil samples between mycorrhizal and non-mycorrhizal treatments were also examined using Student's t-test.

Results
Mycorrhizal colonization, hyphal length density and plant biomass and P and K concentrations As shown in Table 1 the roots in the inoculated treatment were colonized by F. mosseae in both the root and buffer compartments in which the root mycorrhizal colonization rate reached 77 and 81%, respectively. The hyphal length density was 1.56 m g −1 soil in the root compartment with no colonization or mycelium found in the non-mycorrhizal control. Both mycorrhizal colonization and hyphal length density indicate that the AM fungus colonized the maize roots and the hyphae extended into the soil. Shoot, root and total biomass values were signi cantly higher in the mycorrhizal treatment than in the non-mycorrhizal control. The mycorrhizal contributions to shoot, root and total biomass were 13.6, 25.4 and 17.3%, respectively. In addition, AM fungal inoculation signi cantly increased shoot P concentrations and contributed 45.4%, which was 3.5mg g −1 in mycorrhizal treatment but only 1.9mg g −1 in nonmycorrhizal treatment. There was no in uence observed on K concentrations (Table 1). Physiological characteristics and photosynthetic indices of maize Inoculation with F. mosseae increased plant resistance to environmental stress and the photosynthetic e ciency. As shown in Table 2, inoculation signi cantly increased CAT activity and the soluble protein, soluble sugar and starch contents of leaves (P < 0.05), by 2 U g −1 FW min −1 , 0.02 mg g −1 , 0.5% and 0.11 %, respectively. MDA, which can indicate plant senescence, also decreased signi cantly in the mycorrhizal treatment. In addition, inoculation signi cantly promoted plant photosynthetic ability. Furthermore, the Pn signi cantly increased from 31.0 to 33.5 µmol CO 2 m −2 s −1 because of AM fungal inoculation (Table 3). Inoculation also increased plant resistance to high temperatures by increasing the Tr and decreasing leaf temperature (Table 3). Inoculation decreased the Ci owing to decreased respiration and increased photosynthesis. Thus, inoculation promoted both resistance of maize to stress and photosynthetic C xation.

C assimilation and allocation
AM fungal inoculation signi cantly in uenced the δ 13 C, C%, 13 C concentration and 13 C content of intermediate leaves, roots, soil and hyphae at P < 0.05 and signi cantly increased the C% of the soil (Fig. 2). The 13 C concentration and content of maize and soil were signi cantly higher in the mycorrhizal treatment than in the non-mycorrhizal control, indicating that the AM fungus promoted C xation in both maize and soil. The 13 C concentration of maize followed the sequence: young leaves > stems > intermediate leaves > senescent leaves > roots. The 13 C concentration in the hyphae of the AM fungus was about 100 µg g −1 , equivalent to that in the intermediate and senescent leaves of maize and much higher than in the roots (Fig. 2c). The sum of 13 C xation in above-and below-ground parts in the mycorrhizal treatment was 4.00 mg while it was 3.02 mg on the non-mycorrhizal control (Fig. 2d). The MC% to the sum of 13 C content in all parts was 25% and was 24% to 13 C content only in soil (Fig. 2d). Although the 13 C content in maize shoots increased, the percentage of the 13 C in maize shoots declined by 5.89%, possibly indicating that inoculation promoted C accumulation and allocation to the belowground parts. Compared to the non-mycorrhizal control, mycorrhizal inoculation reduced the proportion of the 13 C distribution to the stems but increased the percentages of the distribution to the roots, soil and hyphae (Fig. 3). The 13 C content belowground involved soil, hyphae and roots, accounting for about 17.7% of the total 13 C content and much higher than the 11.8% in the non-mycorrhizal control (Fig. 2d). As a result, the AM fungus increased photosynthetic C xation and soil C content. Inoculation also changed the distribution of photosynthetic products among shoots, roots and soil and tended to promote the allocation of photosynthetic C belowground.

Soil properties
As shown in Table 4 the SOC, EEG and TG values in the inoculated treatment were, respectively, 0.64, 173 and 515 g kg −1 and increased by 21.2, 85.9 and 62.4% compared to the non-mycorrhizal control. Inoculation also promoted the biomass of soil microorganisms. The MBC and MBN in the mycorrhizal treatment were 100 and 46.7 mg kg −1 and were signi cantly higher than in the non-mycorrhizal control. Soil AP in the mycorrhizal treatment was signi cantly lower than in the control but there was no signi cant difference in soil AK between mycorrhizal and non-mycorrhizal treatments. This may be related to the higher shoot biomass and larger microbial biomass in the mycorrhizal treatment. Here, mycorrhizal inoculation increased soil C deposition and the biomass of soil microorganisms while reducing soil available P and K contents.

Discussion
Validation of a novel method for fully quantifying carbon allocation in the plant-AM fungus-soil system The contribution of AM fungi to C allocation and sequestration belowground has long been a matter of interest and debate because accurate quanti cation, especially in realistic conditions, is very di cult (Parihar et al. 2020). There are a number of approaches to the estimation of the amount of C allocated to mycorrhiza. Numerous recent efforts have been made to quantify how AM symbiosis would affect the overall C balance and C uxes in different type of photosynthetic metabolism using the stable 13  been reported that AM fungi increased assimilation by plants and the carbon allocation to soil. However, how much carbon AM fungi receive is unclear because it is di cult to collect hyphae from soil. In addition, NanoSIMS has demonstrated that AM fungi transferred C to soil and soil microbes (Kaiser et al. 2015). However, it is di cult to calculate the absolute amount of carbon. Here, we used a compartment culture system and mixed glass beads with soil to collect AM fungal hyphae, and combined with hyphal weight, the carbon allocation to the AM fungus was calculated. In addition, separated plant parts were studied in order to understand the carbon allocation in more details. Numerous studies report that aboveground respiration levels in mycorrhizal treatments declined coincident with increased C drain belowground (Řezáčová et al. 2017 and 2018). Here, we focus on the carbon assimilated to organic matter.
Although a large percentage of carbon assimilated by photosynthesis is used for respiration, it is related to the carbon in organic  2 and 4). These results indicate that the mycorrhizal bene ts of nutrient uptake exceeded the C cost to the plant to construct the hyphal network. Especially, the shoot P concentration in mycorrhizal treatment was much higher than it in non-mycorrhizal treatment which was lower than threshold of shoot P concentration from silking stage to mature stage of maize (Jones 1983 AM fungi may increase the potential resistance to environmental stress in coal mining areas and increase their nutrient uptake capacity, as well as contributing to plant growth and the accumulation of photosynthetic products (Xie et al. 1995;Hajiboland et al. 2010).
AM fungi regulate the allocation of photosynthetic products Symbiotic associations between AM fungi and plants affect the transportation and allocation of photosynthetic products in plants (Lendenmann et al. 2011;Slavíková et al. 2017;Řezáčová et al. 2018). Here, the 13 CO 2 pulse labeling method was used to label the maize and quantitatively determine the allocation of photosynthetic C in various plant parts and in the soil and the inoculated AM fungus and this is consistent with previous studies. Inoculation with the AM fungus increased the concentration and total amount of 13 C in the plants (Fig 2 and 3). This is supported by previous studies showing that AM fungi increase the C xation capacity of their host plants (Hoeksema et al. 2010). We also observed signi cantly higher 13 C concentrations in the intermediate leaves and roots in the mycorrhizal treatment as well as higher concentrations of 13 C in the young and senescent leaves and stems than in nonmycorrhizal controls (Fig 2c). Higher 13 C concentrations in plant parts indicate stronger photosynthesis in young leaves than the intermediate and senescent leaves. Here, inoculation with the AM fungus increased the 13 C content in the plants and soil and also signi cantly changed the allocation of 13 C between the above-and below-ground parts of the system (Fig 3). Although inoculation increased the concentration of total 13 C and each part of the 13 C, the above-ground 13  Here, the C% and 13 C concentrations in the hyphae were equivalent to those in the leaves and were higher than in the roots (Fig   2b and 2c). This is consistent with a previous study in which 14 C was xed by plants and then transferred to AM fungi within a few minutes (Clemmensen et al. 2013). In fact, AM fungi contain 5 to 20% of the photosynthetic C (Jakobsen and Rosendahl 1990; Johnson et al. 1997). Therefore, AM fungi are regulators of C ux pools from above-to below-ground (Zhu and Miller 2003).
AM fungi enhance C ux to soil microorganisms Mycorrhizal inoculation signi cantly increased SOC and glomalin in the soil (Table 4). When a symbiotic relationship has formed a portion of the photosynthetic products is allocated to the AM fungi for extension of hyphae and development of spores in the soil (Gavito et al. 2005; Godbold et al. 2006). Previous studies show that the turnover time is usually 5-6 days. When the AM fungi die, part of their C may be decomposed by other microorganisms and then released to the atmosphere or enter the soil C cycle (Staddon et al. 2003;Treseder 2013). There is also a portion of C produced by AM fungi, for example in their cell walls, in the form of chitin that can remain in the soil for decades. The soil average organic C content in the inoculated treatment increased by 21.3% compared with the uninoculated control (Table 4). Thus, although the AM fungus had a rapid turnover rate in the soil the C stored by the fungus in the soil was measurable, maintaining a stable hyphal network that is important in soil C sequestration (Friese and Allen 1991). In the mycorrhizal treatment the soil contents of EEG and TG increased signi cantly (  (Li et al. 1991). Therefore, in the mycorrhizal treatment the contents of available P in the soil declined signi cantly ( Table 4). The results support the prevalence of a positive plant-soil feedback in the AM system (Bahram et al. 2020). Interaction between the host plants and the AM fungus increased the nutritional status of the host plants and also promoted plant growth and nutrient especially P status and the distribution of photosynthetic products belowground to supply both the roots and the AM fungus ( Table 1).
The results support the promotion of the accumulation of C in the soil by the AM fungal association by promoting the distribution of photosynthetic products from the above-ground parts of the host plant to the intra-and extraradical mycelium (Leake et al. 2004). This stimulates the accumulation of microbial biomass. The hyphae release exudates and stabilize the soil structure and can also provide C sources for the soil microbial community and promote the growth of soil microorganisms (Toljander et  . Therefore, a mutually bene cial system is formed among host plants, AM fungi and soil microorganisms which affects the soil C cycle and enhances soil nutrient conditions. Here, AM inoculation promoted the growth and P nutrition of maize in the nutrient-limited soil and the photosynthetic C allocation to the soil. The enhanced microbial and environmental conditions in the nutrient-poor soil regulated a good feedback mechanism to increase plant growth.

Conclusions
Here, we established a suitable method to quantify the carbon allocation in plants, AM fungus and soil, and additionally in different plant parts. We also determined soil nutrient and SOC change caused by the AM fungus to detect above-belowground feedback regulated by the AM fungal association. Our results indicate that mycorrhizal colonization aided in the promotion of plant growth through increased stress resistance and mineral nutrient uptake. The AM fungus regulated the carbon allocation to functional leaves and increased plant photosynthetic activity. Mycorrhizal colonization also stimulated C allocation belowground to roots, hyphae and microorganisms. Soil available P and K contents decreased signi cantly because of the mycorrhizal nutrient uptake pathway to host plants. The positive feedback regulated by the AM fungus was established (Fig. 4). Mycorrhizal inoculation may therefore be a useful technique for ecological restoration and land reclamation in mining areas of northwest China, acting through above-belowground interactions and positive feedback. However, the current pot experiment was conducted in greenhouse conditions and further studies are required to verify the results under eld conditions. Figure 1 Schematic diagrams of (a) the three-compartment microcosm and (b) the pulse labeling device. RC, root compartment; BC, buffer compartment; HC, hyphal compartment. One-mm nylon mesh was used to separate the RC and BC and 30 μm nylon mesh was used to separate the BC and HC.   Distribution of 13C in different plant parts and the soil; bars are mean values + standard errors (n = 3); different lowercase letters indicate a signi cant difference between mycorrhizal and non-mycorrhizal treatments at P < 0.05.

Figure 4
Schematic representation of increased above-belowground feedback through enhanced plant carbon assimilation and allocation.