Ecophysiological Differentiation of Two Mosla Species in Response to Nitrogen and Water Levels

Abstract

Terrestrial ecosystems are experiencing increased inputs of nitrogen (N) and temporal fluctuations in precipitation, causing flooding or drought, and this could strongly affect the fate of terrestrial plant species, as they might have different abilities to adapt to the changing environment. We grew Mosla dianthera (a widespread species) and M. hangchowensis (an endangered species) under three water treatments (drought, sufficient water, and waterlogging) in combination with three levels of N supply (low, intermediate, and sufficient N) to study the ecophysiological responses of the congeneric species to those simulated environmental changes. The two species showed different responses to waterlogging and drought treatments, particularly when there was abundant N supply in the system. For example, under sufficient N but drought or waterlogging conditions, M. dianthera increased root mass ratio (RMR) and decreased leaf mass ratio (LMR), total leaf area (LA), and leaf area ratio (LAR); such changes can enhance water acquisition and reduce water loss under both drought and waterlogging conditions, in contrast to the general lack of change in those parameters with M. hangchowensis. These differentiations in traits suggest that increased N availability might worsen drought and waterlogging injury to M. hangchowensis and thus accelerate the decline of this population. However, M. dianthera maybe better adapted to high N availability and both drought and waterlogging conditions. We hypothesize that the different adaptive abilities to high N availability and drought and waterlogging conditions are partly responsible for the ecological differentiation observed between these two species in the field and may determine their fate in their native habitat. Further research should test this hypothesis in field experiments.