Abstract
In lacustrine wetlands connected to rivers, the changes in flood regimes caused by hydrological projects lead to changes in the community traits of dominant macrophytes and, consequently, influence the structure and function of wetland vegetation. However, community trait responses of macrophytes to the timing and duration of flood disturbance have been rarely quantified. In 2011–2019, we investigated plant species diversity, density, and biomass in three dominant macrophyte communities (Carex brevicuspis C.B. Clarke, Miscanthus sacchariflorus (Maxim.) Hackel, and Polygonum hydropiper L.) through monthly field surveys in Dongting Lake wetlands. Partial least squares regressions were used to analyze how the variations in hydrological regimes affected plant community traits. Apparent inter-annual fluctuations in plant community traits were detected during 2011–2019. The species richness and Shannon index of diversity of Miscanthus and Polygonum communities increased, whereas the Shannon index of diversity of Carex community decreased. Variation in flooding had a greater effect on Polygonum and Carex community traits than on Miscanthus community traits. Flooding disturbed all plant communities, especially when the duration and timing varied. Shorter inundation periods caused the biomass of Miscanthus community to decline, and that of Carex and Polygonum communities to increase. Earlier flood recession caused the species richness and Shannon index of diversity of Polygonum and Miscanthus community to increase, and those of Carex community to decrease. These findings imply that shorter inundation durations and earlier flood recession generated by the operation of the Three Gorges Dam have changed the macrophyte growth pattern.
Highlights
Wetlands have the hydrological characteristics of alternating between land and water, and dry and wet (Zhang et al, 2020a,b)
The flood rising time in all the three studied plant communities shifted to an earlier date, whereas the inundation duration exhibited a parabolic trajectory, shortening (Table 1 and Figure 4)
There was a negative correlation between flood rising time and inundation duration, and a significant positive correlation between flood recession time and inundation duration (Figure 4)
Summary
Wetlands have the hydrological characteristics of alternating between land and water, and dry and wet (Zhang et al, 2020a,b). The timing and duration of flooding affect plant species composition and productivity in wetlands by stimulating or inhibiting germination and the subsequent growth, by modifying oxygen availability and limiting the light intensity and nutrients (Coops et al, 2003; Liu et al, 2017; Yao et al, 2020). Several studies have described the effect of flood regime on plants in wetlands (Keddy, 1983; Chen et al, 2015b; Lawson et al, 2015; Gao et al, 2019). Prolonged inundation causes the species richness of intermittent wetland seed bank to decline, whereas short floods increase biomass and species richness of macrophyte communities (Casanova and Brock, 2000). Studies on the combined effects of quantified timing and duration of flooding on the traits of vegetation communities are rare
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