Observational and experimental evidence for the effect of altered precipitation on desert and steppe communities

Changes in precipitation pattern are likely to affect the community structure and ecosystem function in drylands. Observational and experimental studies can provide insight into how plant community in desert and grassland ecosystems responds to precipitation changes, however, the studies combining both approaches are rare. Here, we reported the results of altered precipitation effects on desert-shrub community and steppe-grass community from both a natual precipitation gradient and an experiment manipulating precipitation in Inner Mongolia, northern China. We found that precipitation changes along the natural gradient could well explain species richness and aboveground plant biomass (AGB), inducing their positive relationships in shrub- or grass-dominated community. In the manipulative experiment, 40% and 60% increased precipitation increased species richness and Shannon's diversity in grass-dominated community, and 60% increased precipitation increased AGB in grass-dominated community, while 60% reduced precipitation decreased plant density and AGB in shrub and grass-dominated communities. Species richness, Shannon's diversity, plant density and AGB were positively related to increased precipitation in the manipulative experiment. The positive relationship between species richness and AGB in the grass-dominated community could be shaped by the manipulative precipitation gradient, but no significant relationship was found in the shrub-dominated community in the experiment. Our study highlights that species richness and AGB in desert and steppe community consistently respond to altered precipitation along the natural gradient and in experiment. Extreme drought or high precipitation-induced shifts of the composition and production of herbaceous plants in the shrub-dominated community can contribute to shape the positive associations of community structure and function with precipitation changes. The high vulnerability of grass-dominated community in response to precipitation extremes presents a great challenge to effectively manage steppe ecosystem in future repaid climate changes.