Microstegium vimineum (Japanese stilt grass) is an invasive annual grass native to Asia. Although it is a C4 species, M. vimineum is frequently found in moist, shady habitats such as the understory of mesic forests. Despite these findings, the roles of light and moisture availability on M. vimineum establishment, survival and reproduction are poorly understood. Further, although nutrients limit plant growth in many terrestrial ecosystems, few studies explore how nitrogen availability interacts with light and moisture to affect M. vimineum. To address these issues, I conducted a greenhouse experiment in which I subjected individual plants to different combinations of shade, nitrogen fertilizer and watering regimes and measured leaf, root and stem biomass, and the seed output of M. vimineum.
The effect of drought on leaf and stem dry mass varied with shade treatment, and the effect of nitrogen supply on stem and root dry mass varied with shade treatment. First, shade effect on stems increased with decreasing nitrogen and water availability. Second, the shade effect on leaves increased with decreasing water availability. Third, shade effect on roots increased with decreasing nitrogen availability. In general, plants under high light and high nitrogen treatments produced the greatest average stem and leaf biomass. Plants under high light and an intermediate nitrogen treatment produced the most root mass. In addition to the interactive effects of shade and drought treatment on growth, shade and drought interactively affected mortality. Several shaded plants succumbed to drought stress, whereas all plants under full sun survived drought treatment. Taken together, the growth and mortality data suggest that plants in the full sun treatment were more resistant and resilient to drought stress than shaded plants.