Leaf phenotypic plasticity and integration balance plant adaptation to water table decline: a mesocosm experiment

Abstract

Functional trait-based approaches have been widely used to explore the relationship between plants and their surroundings. Yet, whether phenotypic plasticity and phenotypic integration are differently functional coordination to enhance plant adaptation to declining water levels is still lacking in empirical knowledge. We conducted a mesocosm experiment in an alpine wetland with two dominant plants, Carex muliensis (hygrophytes) and Pedicularis longiflora var. tubiformis (mesophytes), exposed to four water table gradients (WT10, WT0, WT-20 and WT-50, representing the water table at 10 cm, 0 cm, -20 cm and -50 cm from the surface). We measured leaf traits related to resource use strategies, and the relationship between leaf phenotypic plasticity and integration. We found that hygrophytes shifted their leaf traits towards resource-conserving strategies, such as increasing leaf thickness and decreasing leaf area and specific leaf area, under water table decline. In contrast, mesophytes shifted their leaf traits towards resource-acquisition strategies, enhancing their competitiveness and fitness at low water levels. We also found a negative correlation between leaf phenotypic plasticity and integration in both plant species, suggesting a trade-off between them. which was attributed to the fact that wetland plants may prioritize traits that reduce water loss (e.g. larger leaf thickness), resulting in lower integration with other traits (photosynthetic and nutrient use related traits). We conclude that, water table decline alters plant leaf resource use strategies and that the balance between leaf phenotypic plasticity and integration contributes to plant adaptation to water table decline. This study improves our understanding of the role of leaf phenotypic plasticity and integration in plant adaptation in the context of declining water levels in wetlands will help predict the future structure and composition of alpine wetland ecosystems.