Response of plant functional traits to water table gradients in the Zoige Alpine wetland, China

Abstract

Aims Functional trait-based approaches have been widely used to explore the relationship between plants and their surroundings. However, the response of plant functional traits to water table gradients in alpine wetlands has not been well understood so far. Methods Here, we conducted a mesocosm experiment in which five common plant species were collected at four water table gradients (WT10, WT0, WT-20, and WT-50, which represent the water table at 10 cm, 0 cm, -20 cm and -50 cm from the surface) and classified into two types based on clustering analysis of photosynthetic traits: hydrophytes(Carex muliensis, Equisetum ramosissimum and Caltha scaposa) and mesophytes (Pedicularis longiflora var. tubiformis and Juncus allioides). The adaptation strategies of alpine wetland plants to water level changes were revealed by analyzing differences in plant responses to water level gradients and trade-offs between traits. Results Hydrophytes had higher morphological traits, such as higher leaf dry matter content (LDMC), while mesophytes had higher photosynthetic traits, such as higher maximum electron transfer rate (ETRmax) and stoichiometric traits, such as total nitrogen (TN). The morphological, photosynthetic and stoichiometric traits of hydrophytes decreased with decreasing water level gradient, while mesophytes showed the opposite pattern. Stepwise regression analysis indicated that leaf area (LA) and TN of both hydrophytes and mesophytic were most sensitive to water level changes, and these two traits could be used indirectly to predict the response of alpine wetland plants to water level changes. In addition, the number of correlations among hydrophytes traits was higher than that of mesophytes, reflecting that the mutual regulation and trade-offs among hydrophytes traits were better than that of mesophytes. Conclusions Taken together, alpine wetland water table declines have a negative feedback effect on hydrophytes and a positive feedback effect on mesophytes growth. Such information contributes to predict and assess the effects of declining water levels on plant growth in alpine wetlands.