Abstract
Phragmites australis is the dominant species in the Yellow River Delta and plays an important role in wetland ecosystems. Ecological responses of the P. australis community to soil properties were investigated in 96 areas along the coastal-inland regions in the Yellow River Delta of China. The aim was to evaluate the relationship between phenotypic variation and environmental factors, reveal which functional traits could well respond to changes in electrical conductivity and soil water content, and the ecological strategies of P. australis . Within the range of soil water content (9.39–36.92%) and electrical conductivity (0.14–13.29 ms/cm), the results showed that the effects of soil water content and salinity were not equally important for the characterization of the morphological and physiological variability, and that plant functional traits including leaf traits and stem traits responded more strongly to soil salinity than soil water content. Our results suggested that salinity leads to reduced average height, specific leaf area, leaf area, and base stem diameter, but increased leaf water content and leaf thickness. The relationships between functional traits and electrical conductivity were generally linear and logarithmic. The coefficients of variation of morphological traits showed more phenotypic plasticity than the physiological traits. Salinity also led to the stress tolerator/competitor-stress tolerator (S/CS) strategies of P. australis ; with the decrease of environmental stress, the main strategy gradually moved to the competitor (C) strategy, making P. australis the dominant species in the Yellow River Delta.
KEYWORDS: Soil water content, Electrical conductivity, Functional traits, Plasticity, Life strategies.
INTRODUCTION
Plant functional traits could be divided as different types as traits of groups of plants that reflect similar responses to environmental factors or exert similar effects on community dynamic processes based on plant morphology and physiology (Duckworth et al., 2000; Guo et al., 2017). Morphological and physiological features that could reflect plant ecological strategies (Spasojevic et al., 2014; Chai et al., 2016). Owing to the adaptability and plasticity to environmental gradients, individual plants have highly variable traits. The variation in plant functional traits determines the feedback of plants in response to various environmental factors (Li et al., 2014; Guan et al., 2017). Functional traits can be used to quantify a wide range of natural and anthropogenic disturbances (Wang et al., 2015; Chai et al., 2016).
Numerous studies have reported the relationships among plant communities and other environmental factors such as salinity in various habitats (Wang et al., 2012; González-Alcaraz et al., 2014, McCoy-Sulentic et al., 2017). These studies have greatly contributed to our understanding of soil–plant interactions that benefit wetland ecosystem restoration. Plant growth is highly dependent on soil water content. Many researchers have reported that community structure (Pérez-Ramos et al., 2012), species composition (Li et al., 2008), and vegetation growth (Yu et al., 2014; Gong et al., 2014) could be affected by soil water content. Salinity is one of the major environmental factors limiting plant growth and productivity (Sdouga et al., 2019). Salinity also affects multiple trait strategy-dimensions, causes consequences for ecosystem functions (De Battisti et al., 2020), and leads to environmental filtering that drives plant community assembly processes (Yi et al., 2020). Plants adapt to heterogeneous habitats through plasticity in growth strategies and functional traits, as well as the optimal allocation and trade-offs of various traits (Mason et al., 2013; Donovan et al., 2014; Guan et al., 2017). Plant functional traits have been useful in answering many important ecological questions at a range of scales (Mason et al., 2013; Pérez-Harguindeguy et al., 2013), providing a tool for determining the feedback of plants under stressful conditions.
Competitor, stress tolerator, ruderal (CSR) theory is a prominent strategy scheme advanced by Grime (1977) and reviewed by Grime & Pierce (2012), in which the three principal strategies represent viable trait combinations. They have also been used to investigate and interpret community processes, such as succession and the relationship between species richness and productivity (Caccianiga et al., 2006; Cerabolini et al., 2016). Three core leaf functional traits, specific leaf area (SLA), leaf dry matter content (LDMC), and leaf area (LA), were used as criteria to determine the ecological strategies of the individual or population of the plant being studied. The plant CSR strategy taxonomy goes beyond the previous research that focused on analyzing plant ecological strategies solely by using CSR strategies or functional trait pedigree (Pierce et al., 2017; Xu et al., 2019).
Phragmites australis , a widespread species occurring in both freshwater and brackish habits, has strong environmental adaptability and phenotypic plasticity (Yang et al., 2014). The broad range of adaptions to soil water content and salinity has led to the successful growth of P. australis in high-salinity areas (Burdick et al., 2001; Achenbach et al., 2013; Guo et al., 2018). A field investigation was carried out in the Yellow River Delta in order to reveal the responses of community characteristics and functional traits of P. australis to soil water content and salinity. Here, we hypothesized that (1) the effects of soil water content and salinity were not equally important in characterizing the morphological and physiological variability; and (2) the differences in morphological traits, physiological traits, adaptive mechanisms, and ecological strategies ofP. australis in response to environmental stress were dominated by functional traits.
MATERIALS AND METHODS