PS 45-198 - Heterogeneity and global change drivers affect the phenology of a dominant grass in tallgrass prairie restoration

Abstract: Nutrient enrichment and drought alter plant community structure and functioning, but less is known about the interaction of these global change drivers on plant phenology. Biotic conditions such as species diversity can also affect plant phenology, hypothesized to result from differential use of resources among species in diverse communities. We leveraged a long-term experiment that has manipulated soil to increase resource heterogeneity (and plant diversity) and contained rainfall reduction shelters to test the effects of environmental heterogeneity, nutrient enrichment, and the interactive effects global change drivers (nutrient enrichment and drought) on the phenology of a dominant grass (Andropogon gerardii) commonly used to restore prairie. Every two weeks throughout the 2021 growing season, we recorded the timing of major developmental stages of A. gerardii in replicated plots representing four soil heterogeneity treatments (control, nutrient heterogeneity, depth heterogeneity, and maximum heterogeneity; n=4 per plot-level treatment) and in response to reduced precipitation in plots where only nutrients were manipulated. The heterogeneity treatments were created by manipulating soil nitrogen availability (three levels: enriched, ambient and reduced) and depth (two levels: deep and shallow). We predicted (1) increasing environmental heterogeneity would delay and increase variation in the start dates of major developmental stages of big bluestem, (2) nitrogen enrichment would delay the flowering of big bluestem, (3) drought would delay the flowering of big bluestem, and (4) drought would obscure the effect of nitrogen enrichment. We found that prairie restored with heterogeneity in nitrogen availability accelerated the average start date of the boot, first spikelet, and emerged spikelet stages, with no effect on variation. This acceleration was driven by the effect of nitrogen enrichment on the flowering of big bluestem. Average start dates of boot, first spikelet, emerged spikelet, and anthesis stages were advanced across all nitrogen enrichment subplot treatments. Drought expanded the flowering length of big bluestem, but did not otherwise affect development timing. No interactive effects between nitrogen and precipitation treatments were detected. Understanding the relationship between the plant phenology and soil resources could aid in understanding the timing and heterogeneity of resources provisioned to higher trophic levels and capacity for restorations to promote greater diversity in higher trophic levels.