Effects of nitrogen addition and elevated carbon dioxide on microclimate vapour pressure deficit in a semi‐arid grassland

Abstract Microclimate vapour pressure deficit (VPD), being regulated by plant traits and canopy structure, can profoundly affect plant growth with subsequent influence on ecosystem water and energy exchanges. However, the mechanisms underlying this feedback under global change scenarios remain unclear. As part of a 3‐year (2021–2023) manipulative experiment using open‐top chambers in a semi‐arid grassland, this study was conducted to examine the effects of nitrogen (N) addition and elevated carbon dioxide (eCO 2 ) on plant growth and its feedback to ecosystem water and energy exchanges and microclimate VPD. Nitrogen addition enhanced evapotranspiration through increased stomatal conductance and plant biomass growth, resulting in decreased air temperature and increased relative humidity and subsequent reductions in daily and daytime microclimate VPD. By contrast, eCO 2 decreased community stomatal conductance and evapotranspiration, leading to suppressed relative humidity and intensified daily and daytime microclimate VPD. In addition, the combined N addition and eCO 2 treatment showed no net effect on microclimate VPD, as the stomatal conductance reduction counteracted the biomass‐mediated increase in evapotranspiration. Moreover, the interaction effect between N addition and eCO 2 on VPD was statistically non‐significant. Synthesis . Our findings suggest that plant‐mediated evapotranspiration and canopy structure regulate microclimate VPD under N addition and eCO 2 . By examining the influence of plant traits on microclimate processes, we advance our understanding of plant–environment feedback mechanisms and facilitate predictions regarding ecosystem responses to global change.