Seasonal community stability increased with water addition and shrub removal but reduced with nitrogen addition in semi-arid grassland

Stability is a useful indicator of the functioning and sustainability of an ecosystem, and much studies have explored the effects of anthropogenic disturbance on the inter-annual stability of plant community. However, the effects of multiple anthropogenic stressors on seasonal community stability have not been clearly elucidated, especially for vulnerable semi-arid grasslands. During the growing season in the 5th year of the experiment, we determined how nitrogen (N) addition, water addition and shrub removal altered seasonal community stability in a semi-arid grassland dominated by the shrub Caragana microphylla on the Mongolian Plateau. We found that shrub removal, N addition and water addition had different effects on the stability of community and plant functional groups (PFGs). Shrub removal increased seasonal community stability mostly via increases in the stability of perennial forbs and C-4 plants, and shrub removal did not alter the effects of N addition or water addition on seasonal community stability or PFG stability. N addition decreased seasonal community stability mostly via decreases in the stability of perennial rhizome grasses and C-4 plants. Water addition increased seasonal community stability mostly via increases in the stability of annuals and biennials, perennial forbs, perennial rhizome grasses, dominant species and C-4 plants. Species asynchrony and PFG stability but not species richness or soil abiotic or biotic variables helped to maintain seasonal community stability under N addition or water addition. Our findings indicate that future scenarios of increases in N deposition and shrub encroachment will strongly reduce community stability in drylands, and that future scenarios of increases in precipitation together with shrub removal might help to maintain the stability of this and other dryland ecosystems. Read the free Plain Language Summary for this article on the Journal blog.