Drought sensitivity of an N 2 ‐fixing tree may slow temperate deciduous forest recovery from disturbance

Increased drought intensity and frequency due to climate change may reduce the abundance and activity of nitrogen (N2 )-fixing plants, which supply new N to terrestrial ecosystems. As a result, drought may indirectly reduce ecosystem productivity through its effect on the N cycle. Here, we manipulated growing season net rainfall across a series of plots in an early successional mesic deciduous forest to understand how drought affects the aboveground productivity of the N2 -fixing tree Robinia pseudoacacia and three co-occurring nonfixing tree species. We found that lower soil moisture was associated with reduced productivity of R. pseudoacacia but not of nonfixing trees. As a result, the relative biomass and density of R. pseudoacacia declined in drier soils over time. Greater aboveground biomass of R. pseudoacacia was also associated with greater total soil N, extractable inorganic N, N mineralization rates, and productivity of nonfixing trees. These soil N effects may reflect current N2 fixation by R. pseudoacacia saplings, or the legacy effect of former trees in the same location. Our results suggest that R. pseudoacacia promotes the growth of nonfixing trees in early succession through its effect on the N cycle. However, the sensitivity of R. pseudoacacia to dry soils may reduce N2 fixation under scenarios of increasing drought intensity and frequency, demonstrating a mechanism by which drought may indirectly diminish potential forest productivity and recovery rate from disturbance.