Abstract: Aims Studying legacy effects (i.e. the indirect effect that persists for a period after casual factors cease) can provide novel insights into the role of ecological drivers. Leaf lifespan is among the key traits with multi-level functions. It is clear about the direct effects of water and nitrogen (N) amendment on leaf lifespan, but it remains unclear about their legacy effects on leaf lifespan and the associated mechanisms.
Methods We performed a five-year field experiment with supplemental water and N, and quantified the legacy effects of field water and N addition on the leaf lifespan, length and growth rate of four dominant species, Agropyron cristatum, Cleistogenes squarrosa, Leymus chinensis and Stipa grandis in a temperate steppe.
Important findings Across all the species, the legacies of water and N addition increased their leaf length and growth rate directly but decreased their leaf lifespan through direct and indirect pathways. Leaf lifespan was positively linked with leaf length but negatively associated to leaf growth rate. The legacy effect of water addition on leaf lifespan was greater than that of N addition. Field N addition induced soil acidification and eutrophication, as well as altered soil microbes, but only eutrophication had negative legacy effects on leaf lifespan. These findings provide substantial evidence that rainfall and N amendment have negative legacy effects on leaf lifespan, and also highlight that multiple mechanisms or pathways determine legacy effects. Additionally, our results suggest that field water and N manipulations may influence the other leaf traits and functions.

Key words: leaf traits, nitrogen deposition, rainfall increase, soil legacy effects, steppe dominants, structural equation models