Physiological and morphological responses of the invasive grass, Microstegium vimineum, to varying resource availabilities

Background/Question/Methods

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 physiology and growth patterns 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 biomass, photosynthesis, and tracked survival rates of M. vimineum.

Results/Conclusions

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. Leaf mass per area (LMA) was greatest for plants within the 70% shade group, and LMA was significantly affected by shade and water availability. Although plants experiencing moderate nitrogen availability had the greatest LMA, nitrogen did not significantly affect LMA. Furthermore, there were no significant interactions between the three resources.

Shade, nitrogen and drought interactively affected photosynthesis rates and mortality. Plants exposed to full sunlight were 1.7 times more likely to experience photosynthetic shut down during drought than plants in moderate to deep shade. Plants exposed to high nitrogen levels were 1.5 times more likely to experience photosynthetic shut down, compared to plants in lower nitrogen treatment groups. However, the combination of full sunlight and high nitrogen availability made plants less likely to experience photosynthetic shut down, compared to plants with lower resource availability. Furthermore, shade plants were less likely to survive drought, and mortality was higher in moderate to deep shade. Taken together, the growth and mortality data suggest that plants with the highest resource availability produce the greatest biomass, and are the most resistant and resilient to drought stress.