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