Effects of water exchange rate on morphological and physiological characteristics of two submerged macrophytes from Erhai Lake

Abstract

Growth patterns of aquatic macrophytes have been shown to vary in response to hydrological properties; however, such properties are typically characterized by water level fluctuation, flow velocity, flooding season, and sedimentation, but not by water exchange rate (WER). Herein, we experimentally investigated how WER (three levels: exchange 0%, 20%, and 40% of total water per day) affects water and sediment properties, and the consequences that these variations have on the individual responses of two submerged macrophytes, Hydrilla verticillata and Myriophyllum aquaticum which were planted in two different sediment types (sand and clay). In the experiment without ramets, it was found that turbidity, pH value, and dissolved carbon dioxide concentration of the system water were statistically unaffected by WER, while water dissolved oxygen (DO) concentration and sediment oxidation–reduction potential (ORP, in both sediments) consistently increased with increasing WER, regardless of experimental time. In the experiment containing ramets, biomass accumulation and relative growth rate (RGR) of both species gradually increased with increasing WER regardless of sediment type. The mechanisms were related to (a) increased oxygen availability, as indicated by gradually increased water DO concentration and sediment ORP; and (b) enhanced phosphorus (P) and nitrogen (N) absorbing abilities associated with stimulated root growth, reflected in increased mean root length, specific root length, and the root/above‐ground biomass ratio, with increasing WER. Additionally, in the experiments containing ramets, significant linear relationships were consistently detected between sediment ORP and root parameters, root parameters and plant nutrients (N and P), and plant nutrients and plant growth conditions (biomass accumulation and RGR). These results demonstrate that WER plays an important role in determining oxygen availability and thus impacts the growth of submerged macrophytes by altering the ability of roots to absorb nutrients, indicating that ecosystem functions are more sensitive to WER than previously recognized.

Effect of water exchange rate on interspecies competition between submerged macrophytes: functional trait hierarchy drives competition

“…Therefore, as WER increased, more biomass was allocated to above-ground tissues (leaves and stems) in two Myriophyllum species (Fig. 3), which is consistent with the ndings of previous studies of plant adjustment strategies to DCD and/or DO de ciency (e.g., Yuan et al, 2018).…”

“…Three water exchange rates, i.e., statistic water (0% replacement of the whole water body per day), medium WER (20%), and high WER (40%) were applied. This range of WER variation is reasonable for natural ecosystems (including Erhai Lake) according to our previous studies (e.g., Yuan et al, 2018). Two replacement series (of V. natans vs. M. aquaticum and V. natans vs. M. spicatum) were performed to increase the universality of our ndings.…”

“…These traits may have differential responses to WER variation among species that coexist in the same aquatic community owing to differences in species tolerance thresholds. For example, our previous studies have found that separately cultured submerged macrophytes Hydrilla verticillata and Myriophyllum aquaticum exhibited similar response patterns when subjected to increasing WER; however, these adjustments were greater in M. aquaticum than in H. verticillate, resulting in a more dramatic increase of plant biomass in M. aquaticum (Yuan et al, 2018). Similar links between hierarchical traits and plant tness to hydrological variation have been observed in various wetland species (Pan et al, 2012;Pan et al, 2019).…”

“…Despite accumulating evidence of interspeci c differences in functional traits in plants subjected to WER (Yuan et al, 2018;Pan et al, 2019), it remains unknown whether such differences can consequently alter the outcome of interspecies competition. Here, we examined the potential effects of WER on interactions between coexisting submerged macrophytes, and the links between relative competitive ability and functional traits in these species.…”

Dual-Source Optimization of the “Diverting Water from the Yangtze River to Tai Lake (DWYRTL)” Project Based on the Euler Method

“…It is recommended that the total water intake in the future should not exceed 20% of the total annual lake water intake, i.e., 20 × 10 8 m 3 /a. e rate at which water flows through Tai Lake is mainly affected by the wind field and the exchange rate of water; an excessive flow rate will have a certain adverse effect on the stability of the ecosystem [33][34][35].…”