Invasion by Hyptis suaveolens modifies the effects of altered rainfall variability on nutrient cycling across seasons in a dry tropical grassland experiment

Abstract

Ecosystems often recover rapidly when changes in climatic conditions are moderate, but extreme changes may push the ecosystem beyond its biological threshold, resulting in rather profound changes in its functioning and species composition. We experimentally evaluated how the ecosystem functioning of tropical grassland may change under changing precipitation variability by investigating shifts in soil properties and their relation to plant invasions. We found that soil moisture, soil pH, inorganic N content (NO3 - N + NH4 - N), N mineralization rate, and soil CO2 flux increase with a rise in rainfall. Moreover, the grassland plots invaded by Hyptis suaveolens, particularly those with increased precipitation, demonstrated elevated mineralization rates, substantial nutrient accumulation, and a reduced microbial biomass in comparison to the uninvaded plots. Our study highlighted that, following soil moisture (SM) and soil temperature (ST), N mineralization emerged as the third primary driver of soil CO2 flux. Enhanced precipitation led to increased N mineralization and subsequent CO2 emissions. The results indicate that escalated CO2 flux in invaded plots could be linked to invasive H. suaveolens adverse effects on soil processes, potentially leading to short-term inefficient nutrient cycling and elevated CO2 emissions, with potential consequences for the overall stability of the ecosystem. © 2024 Université Laval.