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

1. Stability is a useful indicator of the functioning and sustainability
of an ecosystem, and many studies have explored the effects of
anthropogenic disturbance on the inter-annual stability of plant
communities. However, the effects of multiple anthropogenic stressors on
seasonal community stability have not been clearly elucidated, especially
for vulnerable semi-arid grasslands. 2. 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. 3. We found that shrub removal, N addition, and water
addition had different effects on the stability of the community and plant
functional groups (PFGs). Shrub removal increased seasonal community
stability mostly via increases in the stability of perennial forbs and C4
plants, and shrub removal did not alter the effects of N addition or water
addition on seasonal community stability or PFG stability. 4. N addition
decreased seasonal community stability mostly via decreases in the
stability of perennial rhizome grasses and C4 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 C4 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. 5. 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.