Does Water Stress Affect Community Invasibility in a SubHumid Temperate Grassland?

Abstract

Aim

Under climate change scenarios, droughts are expected to become more frequent and severe in some regions, influencing the likelihood of successful biological invasion in ecosystems. We evaluate the effect of water stress on the invasibility of different Uruguayan grassland communities, focusing on the potential invasion of Eragrostis plana.

Location

Eastern Uruguay grasslands, Campos of Río de la Plata grasslands.

Methods

Monoliths from three grassland communities (sparsely, densely, and tall densely vegetated communities), which differ in soil characteristics and species diversity, were collected in the field. These monoliths were transported to a growth chamber, where they were subjected to a water stress experiment consisting of two treatments: with and without water stress. Water stress involved the suspension of irrigation for 20 days. Subsequently, each monolith was sown with seeds of E. plana. Community characteristics and seedling emergence were assessed. Seedling emergence and survival of E. plana were compared across water stress treatments and communities, and relationships with functional groups cover, standing dead biomass, bare soil, and species richness were analyzed.

Results

Differences in E. plana germination and survival were primarily associated with grassland community type rather than the effect of water stress. The sparsely vegetated community exhibited the highest levels of invasion, regardless of water stress, compared with densely and tall densely vegetated communities. The invasion of E. plana was negatively associated with the cover of erect grasses (its own functional group) and with species richness, both variables that decreased with water stress.

Conclusions

The germination of E. plana was mainly limited by biotic factors that varied among grassland communities, particularly the cover of erect grasses and species richness, both of which can decline under water stress. Management of E. plana should consider the heterogeneity of grassland communities in eastern Uruguay, especially the high invasibility of the sparsely vegetated community.