Nitrogen addition alleviates drought effects on water status and growth of Moso bamboo (Phllostachys edulis)

Forest ecosystems are increasingly exposed to climate-change-induced drought and nitrogen deposition. However, the role of nitrogen deposition in shaping the responses of plant water use and growth to drought remains unclear. In this study, we conducted an ecosystem-scale manipulation experiment with sixteen plots of 400 m2 to explore responses of water use and growth patterns in a Moso bamboo (Phllostachys edulis) forest to throughfall reduction treatment (TRT) (-50%) and nitrogen (N) addition (100 kg ha−1 yr−1 of nitrogen) for two years. We found that TRT significantly reduced daily total canopy transpiration (EL), leaf water potential, leaf area index (LAI) and basal area increment in a unit stand area (BAI) by decreasing hydraulic conductance (K) and photosynthetic rate. N addition pronouncedly caused lower EL and higher LAI due to increased stomatal conductance sensitivity to vapor pressure deficit, photosynthetic rate, and intrinsic water use efficiency (WUEi) as well as decreased ratio of cross-sectional area of the culm wall to total leaf area (AS/AL) and root/ leaf ratio. The interaction of TRT and N addition caused an increase in leaf water potential at midday (20.6%) and BAI (+25%) compared with the TRT, accounting for the increased stomatal conductance sensitivity, K, photosynthetic rate and WUEi. Our results suggest that N addition alleviates drought effects on foliar water state and growth of Moso bamboo through altered stomatal conductance sensitivity, hydraulic architecture, and photosynthesis. Our findings highlight the key role of coupling processes of forest carbon, nitrogen and water in shaping plant water use and growth, suggesting that interactive effect of drought and nitrogen deposition on plant hydraulic properties should be considered under a changing environment.