Guixiang Yuan

Environmental and ontogenetic effects on intraspecific trait variation of a macrophyte species across five ecological scales.

Although functional trait variability is increasingly used in community ecology, the scale- and size-dependent aspects of trait variation are usually disregarded. Here we quantified the spatial structure of shoot height, branch length, root/shoot ratio and leaf number in a macrophyte species Potamogeton maackianus, and then disentangled the environmental and ontogenetic effects on these traits. Using a hierarchical nested design, we measured the four traits from 681 individuals across five ecological scales: lake, transect, depth stratus, quadrat and individual. A notable high trait variation (coefficient variation: 48–112%) was observed within species. These traits differed in the spatial structure, depending on environmental factors of different scales. Shoot height and branch length were most responsive to lake, transect and depth stratus scales, while root/shoot ratio and leaf number to quadrat and individual scales. The trait variations caused by environment are nearly three times higher than that caused by ontogeny, with ontogenetic variance ranging from 21% (leaf number) to 33% (branch length) of total variance. Remarkably, these traits showed non-negligible ontogenetic variation (0–60%) in each ecological scale, and significant shifts in allometric trajectories at lake and depth stratus scales. Our results highlight that environmental filtering processes can sort individuals within species with traits values adaptive to environmental changes and ontogenetic variation of functional traits was non-negligible across the five ecological scales.

Linking carbon and nitrogen metabolism to depth distribution of submersed macrophytes using high ammonium dosing tests and a lake survey.

Strategies of carbon (C) and nitrogen (N) utilisation are among the factors determining plant distribution. It has been argued that submersed macrophytes adapted to lower light environments are more efficient in maintaining C metabolic homeostasis due to their conservative C strategy and ability to balance C shortage. We studied how depth distributions of 12 submersed macrophytes in Lake Erhai, China, were linked to their C-N metabolic strategies when facing acute dosing. dosing changed C-N metabolism significantly by decreasing the soluble carbohydrate (SC) content and increasing the -N and free amino acid (FAA) content of plant tissues. The proportional changes in SC contents in the leaves and FAA contents in the stems induced by dosing were closely correlated (positive for SC and negative for FAA) with the colonising water depths of the plants in Lake Erhai, the plants adapted to lower light regimes being more efficient in maintaining SC and FAA homeostasis. These results indicate that conservative carbohydrate metabolism of submersed macrophytes allowed the plants to colonise greater water depths in eutrophic lakes, where low light availability in the water column diminishes carbohydrate production by the plants.

Functional traits composition predict macrophytes community productivity along a water depth gradient in a freshwater lake

Functional trait composition of plant communities has been proposed as a helpful key for understanding the mechanisms of biodiversity effects on ecosystem functioning. In this study, we applied a step-wise modeling procedure to test the relative effects of taxonomic diversity, functional identity, and functional diversity on macrophytes community productivity along water depth gradient. We sampled 42 plots and 1513 individual plants and measured 16 functional traits and abundance of 17 macrophyte species. Results showed that there was a significant decrease in taxonomic diversity, functional identity (i.e., stem dry mass content, leaf [C] and leaf [N]), and functional diversity (i.e., floating leaf, mean Julian flowering date and rooting depth) with increasing water depth. For the multiple-trait functional diversity (FD) indices, functional richness decreased, while functional divergence increased with water depth gradient. Macrophyte community productivity was strongly determined by functional trait composition within community, but not significantly affected by taxonomic diversity. Community-weighted means (CWM) showed a two times higher explanatory power relative to FD indices in determining variations in community productivity. For nine of sixteen traits, CWM and FD showed significant correlations with community productivity, although the strength and direction of those relations depended on selected trait. Furthermore, functional composition in a community affected productivity through either additive or opposite effects of CWM and FD, depending on the particular traits being considered. Our results suggested both mechanisms of mass ratio and niche complementarity can operate simultaneously on variations in community productivity, and considering both CWM and FD would lead to a more profound understanding of traits–productivity relationships.

Predicting Changes in Macrophyte Community Structure from Functional Traits in a Freshwater Lake: A Test of Maximum Entropy Model

Trait-based approaches have been widely applied to investigate how community dynamics respond to environmental gradients. In this study, we applied a series of maximum entropy (maxent) models incorporating functional traits to unravel the processes governing macrophyte community structure along water depth gradient in a freshwater lake. We sampled 42 plots and 1513 individual plants, and measured 16 functional traits and abundance of 17 macrophyte species. Study results showed that maxent model can be highly robust (99.8%) in predicting the species relative abundance of macrophytes with observed community-weighted mean (CWM) traits as the constraints, while relative low (about 30%) with CWM traits fitted from water depth gradient as the constraints. The measured traits showed notably distinct importance in predicting species abundances, with lowest for perennial growth form and highest for leaf dry mass content. For tuber and leaf nitrogen content, there were significant shifts in their effects on species relative abundance from positive in shallow water to negative in deep water. This result suggests that macrophyte species with tuber organ and greater leaf nitrogen content would become more abundant in shallow water, but would become less abundant in deep water. Our study highlights how functional traits distributed across gradients provide a robust path towards predictive community ecology.

A functional-trait approach reveals community diversity and assembly processes responses to flood disturbance in a subtropical wetland

Despite the strong effects of disturbance on plant community diversity and assembly, we do not fully understand how different aspects of taxonomic or functional diversity respond to disturbance or how different assembly processes change along a disturbance gradient. In this study, plant communities were sampled and the distributions of three functional traits were measured in 45 plots across a flood disturbance gradient in Poyang Lake wetland in China. We examined the within-community means, ranges, variances, kurtoses, and other parameters of trait values. Results showed that the effects of disturbance depended largely on the aspects of diversity considered. Along the flood disturbance gradient, taxonomic/functional richness did not change, while Shannon–Wiener diversity and evenness and functional evenness and dispersion showed significant unimodal patterns. Communities experiencing the highest disturbance levels tended to have significantly shorter shoot heights with lower specific leaf area (SLA). We also found a significant non-random functional trait distribution: a significant reduction in the range and variance of SLA and a more even distribution of the measured traits compared with the null model. Our results highlight that niche-based assembly processes play structuring roles in wetland plant community response to flood disturbance gradients and that both environmental filtering and limiting similarity can work on the same traits (e.g., SLA) through hierarchical effects on the distribution of functional traits within communities.

Relationships between relative growth rate and its components across 11 submersed macrophytes

The relationships between relative growth rate and its components across 11 submersed macrophytes were examined in a short-term experimental study. Plants were grown in identical conditions in pots that were submersed in tanks. The average values for relative growth rate ranged from 17.4 to 94.5 mg g−1 d−1. The net assimilation rate, based on the increase in plant dry weight per unit leaf area in a fixed time, varied fivefold among species and showed a strong, positive correlation with relative growth rate. The leaf area ratio, leaf mass ratio, and specific leaf area were not significantly correlated with the relative growth rate, although these parameters were important in the adaptive responses of macrophytes to environmental stress. These results suggest that the physiological components (net assimilation rate) would be the main determinant of relative growth rate in submersed macrophytes, which highlights the importance of net assimilation rate in explaining differences in macrophyte species performance in freshwater habitat.