Interactions between plants and soil microbes influence plant productivity, diversity, and community composition. The influence of climate change on the relationship between plants and microbes, however, has not been well studied. Plant population responses depend upon the co-evolutionary relationships of plants and their associated microbes, which may be influenced by such environmental features as changes in drought frequency. To investigate the effects of global change on the interactions between plants and soil microbes, we quantified feedbacks in response to a reduction of water availability, through a greenhouse experiment associated with drought exposure. We hypothesized that water manipulations in the field would result in different soil microbial communities and that such differences in soil microbes would alter plant traits. To test our hypothesis, Stipa pulchra, a native perennial grass, was grown in pots inoculated with soil collected from a long term (10 year) water manipulation experiment. Pots were either inoculated with soil from drought or ambient treatment plots. Each inoculation condition received two watering treatments; high (watered every other day) and low (watered when plant exhibited stress). We measured plant traits (e.g., plant height, width, growth rate, leaf count) over the course of 13 weeks.
The main effect of inoculation treatment was seen within the initial four weeks, indicating that water manipulations in the field did alter the soil microbial community. Within weeks 1-4, plants grown with drought adapted microbes in combination with a high watering treatment had a higher initial growth rate and maintained a higher leaf count through weeks 1-10. As expected, plant traits had lower performance when grown with ambient-adapted microbes in a low watering treatment exhibiting a lower growth rate relative to all other treatments. Plants grown with drought-adapted microbes in the low watering treatment maintained greater average height than all other treatments, however, leaf abundance decreased after week 10. Treatment effects diminished later in the experiment, perhaps, due to shifts in the microbial community to the experiment water manipulation. The differences in the soil microbial community altered the response of plants grown in microbe inoculated pots to water manipulations in the greenhouse. Apart from addressing our hypothesis, results will help contribute to a mechanistic understanding of the mechanisms underlying plant-soil microbe interactions, as well as, provide a predictive power in studies of anthropogenic environmental changes.