4.2 The plasticity of morphological and physiological traits
Functional traits can be divided into morphological traits and
physiological traits (Liu & Ma, 2015). Strong plasticity of variability
was observed in whole plant traits, especially in the morphological
traits, and coefficient of variation was the accepted method used to
standardize variability among traits with fundamentally different units
(Acasuso-Rivero et al., 2019). Morphological traits involve the shape
and structure of each organ, responses of individuals to environmental
changes based on internal genes, and adaptations of plants to
environmental heterogeneity (Hu et al., 2008). In our research, the leaf
area, stem pitch number, height, and shoot basal diameter were
attributed to morphological traits. All these traits had high
coefficients of variation, which were higher than 20%, indicating that
morphological traits are sensitive under the stress of environmental
factors. Higher phenotypic plasticity contributed to P. australisbeing able to adapt to a wide range of niches under salinity stress in
the Yellow River Delta.
Physiological traits are related to biochemical processes and
reproduction (Zhang & Luo, 2004). Some researchers showed that
physiological traits were more susceptible to soil properties with
regard to morphological traits (Schneider et al., 2017). Compared with
morphological traits, the coefficient of variation values of
physiological traits contained the SPAD, leaf thickness, SLA, and leaf
water content in our research and were lower than 20%. The lower
coefficients of variation indicated relatively lower plasticity and
stable intrinsic properties of P. australis under various
environmental stressors. SLA and leaf thickness, although shown as
morphological traits (Smith & Knapp, 2001), were regarded as
physiological traits in some research (Zhang & Luo, 2004; Wright et
al., 2004). They remain relatively stable under specific environments,
and were not only influenced by soil factors, but also influenced by
factors including leaf tissue characteristics (such as the epidermis
cells and mesophyll cells) and chemical composition.
In the Yellow River Delta, the mode of P. australis morphological
traits is an integrated system in growth, but physiological traits have
different mode to reflect the environmental stress. Grouping plants by
functional trait types rather than by organs could help us more
accurately understand the process of plant growth and the response to
environmental stress. It’s worth noting that while plasticity is not
equal to fitness (Acasuso-Rivero et al., 2019), the relationship between
them is still worth studying in the Yellow River Delta under
environmental stress.