Global climate change models predict changes in both precipitation variability and temperature. Increased intra-annual variability in rainfall is predicted to result in larger, but less frequent rain events. Annual plant species may be particularly affected by changes in precipitation and temperature, as these are both important germination cues that can alter community composition. Using long-term data on species abundance in annually tilled fields at the Kellogg Biological Station Long Term Ecological Research site, we determined if variation in early season rainfall and temperature variation predicted end of season biomass for six common weed species. To test the causality of these relationships, we conducted field experiments in which we manipulated early season rainfall amount and temperature using rain shelters and infrared reflective material to elevate nighttime temperature. We then measured seedling emergence (18 days after manipulations) and final biomass.
Results/Conclusions
Analysis of the long-term data revealed that the biomass of three species was predicted by the amount of rain and temperature during the first week after tillage. Digitaria ischaemum and Setaria faberi increased under wet and cool or warm and dry initial conditions, while the biomass of Chenopodium album increased when early season conditions were cool and dry.
In the experimental study, altered initial water affected total seedling density and final community biomass while warming minimally affected either. Seedling density increased with more water and this response occurred across all species analyzed. Community biomass did not differ in response to the precipitation treatment, but the biomass of Digitaria sanguinalis and Digitaria ischaemum increased in response to more initial water while Setaria faberi and Chenopodium album biomass decreased. Though community biomass did not differ across treatments, higher initial water increased species richness.
A one week alteration of precipitation amount after tillage resulted in detectable shifts in community composition. While there was no change in overall biomass, larger rainstorms resulted in decreased abundance of the dominant species Setaria faberi and greater species richness. These results demonstrate that early season changes in rainfall distribution patterns can alter species composition in mesic annual communities.
