Plant traits are generally considered to be results of plant adaptation to environmental changes (Franks et al. 2014; Zuo et al. 2017). They play important roles in the ecological characteristics of plant communities, predicting the results of biodiversity changes, and reflecting global climate change scenarios (Franks et al. 2014; Van der Plas et al. 2020; Zuo et al. 2017). Previous studies have found that there may be coordinated or trade-off relationship between above- and below-ground plant traits (Asefa et al. 2022; Zhan et al. 2016). The strong coordinated relationships were found between root and leaf traits of desert plants in the arid and semi-arid regions of northern China (Liu et al. 2010). Similarly, the coordinated relationships were also found between above- and below-ground traits of herbaceous plants in response to water limitation (Perez-Ramos et al. 2012; Zhao et al. 2020). While, other studies have found the trade-off relationships between above- and below-ground traits of plants as affected by soil nutrients (e.g., nitrogen and phosphorus) or light (Freschet et al. 2018; Zhan et al. 2016; Zhao et al. 2020). Above- and below-ground plant tissues take different strategies of resource acquisition under low light and nitrogen conditions, therefore leading to a trade-off relationship (Freschet et al. 2018). In addition to abiotic factors, biotic factors (e.g., competition) can also influence the relationship between above- and below-ground traits (Asefa et al. 2022). At present, the relationships between above- and below-ground traits of terrestrial plants have been advanced (Asefa et al. 2022; Laliberté 2017); such relationship for wetland plants at the large scale is relatively limited.
Plant traits at different levels (e.g., species- or community-level) reflect different perspectives on how environmental factors drive plant traits (Fu et al. 2019; Westerband et al. 2021). Many studies have investigated responses of plant traits to environmental changes at the species level (Barwise and Kumar 2020; Rao et al. 2022). As the dominance of different species in a plant community is different, traits of single or several species cannot fully reflect the overall characteristics of the community. Research of plant traits at the community level is currently trending (Haubrock et al. 2021; Kothari et al. 2023). The metric of community-weighted mean (CWM) is an important indicator for calculating plant community traits (Huang et al. 2022). It is based on the “biomass-ratio hypothesis”, which is generally assumed that ecosystem function is determined by the trait value of dominant species (Wen and Jin 2019).
Studies on the community-level traits are mostly focusing on grassland and forest ecosystems (Moor et al. 2017; Wang et al. 2016; Zuo et al. 2017). In grasslands of northern China, seed length of plant community significantly decreased, but seed thickness significantly increased in response to precipitation reduction (Luo et al. 2022). In forests of eastern China, changes in precipitation significantly affected leaf thickness of plant communities (Wang et al. 2016). The leaf nitrogen content of plant communities increased significantly with the decreasing of precipitation from eastern to western China (Wang et al. 2022). In comparison, studies on wetland plant traits at community level and the relationship with environmental factors are at a relatively small scale (Moor et al. 2017; Pan et al. 2020b; Zhao et al. 2020). For example, the rising floodwater led to a significant increase in leaf area of plant communities along the Colorado River in the United States (McCoy-Sulentic et al. 2017). The significant correlations were also found between CWMs and productivity of plant communities in both Erhai wetland and Liangzi Lake in China (Fu et al. 2014; Ma et al. 2022).
Precipitation is one of the most important environmental factors affecting plant traits (Franks et al. 2014; Gong et al. 2021; March-Salas et al. 2022). Precipitation-induced changes in the availability of soil resources (e.g., water and nutrients) complicate plant-environment relationships (Muscarella et al. 2016; Reich et al. 2020). The variation in availability of water and nutrients may affect plant phenotypes, nutrient acquisition, and reproductive phenology, further change the intensity of interspecific competition (Freschet et al. 2018; Li et al. 2018). Plants commonly take acquisitive and conservative resource strategies in nutrient-rich and -poor habitats, respectively (Chen et al. 2023; Henneron et al. 2020; Yang et al. 2023). In the former strategy, plants have high leaf nitrogen content, high photosynthetic capacity, high respiration rate, and fast growth rate. For the latter strategy, plants have relatively low efficiency of resource utilization. Previous studies have shown that wetland plants prefer taking the acquisition strategy, exhibiting high plant height, leaf nitrogen and phosphorus content, and specific leaf area, in response to waterlogged conditions (Pan et al. 2020a; Yang et al. 2021).
Our previous study has shown that species number and coverage of clonal plants accounted for a high proportion in plant communities of typical marsh wetlands in northern China (Shao et al. 2023). The composition of plant community is significantly different between low and high soil moisture conditions, which is greatly influenced by the precipitation. In the present study, plant traits at both species- and community-level under low and high soil moisture conditions in nine typical marsh wetlands of northern China were measured. The relationships between above- and below-ground traits of clonal plants, and the influencing environmental factors of plant traits were analyzed. Specifically, the following two questions were addressed: (1) What are the differences in plant traits and the influencing environmental factors among these marsh wetlands, and between low and high soil moisture conditions? (2) What are the relationships between above- and below-ground traits of clonal plants in these wetlands?