The Key Laboratory for Silviculture and Conservation of Ministry of Education, Beijing Forestry University, Beijing 100083, China.
Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON, Canada.
Sci Total Environ. 2022 Nov 20;848:157840. doi: 10.1016/j.scitotenv.2022.157840. Epub 2022 Aug 5.
Although the effects of nitrogen deposition on tree water relations are studied extensively, its impact on the relative sensitivities of stomatal and xylem hydraulic conductance to vapor pressure deficit and water potential is still poorly understood. This study investigated the effects of a 7-year N deposition treatment on the responses of leaf water relations and sensitivity of canopy stomatal conductance to vapor pressure deficit (VPD) and water potential, as well as the sensitivity of branch hydraulic conductance to water potential in a dominant tree species (Quercus wutaishanica) and an associated tree species (Acer mono) in a temperate forest. It was found that the N deposition increased stomatal sensitivity to VPD, decreased stomatal sensitivity to water potential, and increased the vulnerability of the hydraulic system to cavitation in both species. The standardized stomatal sensitivity to VPD, however, was not affected by the N deposition, indicating that the stomata maintained the ability to regulate the water balance under nitrogen deposition condition. Although the increased stomatal sensitivity to VPD could compensate the decreased stomatal sensitivity to water potential to some extent, the combined response would increase the percentage loss of hydraulic conductivity (PLC) when 50 % loss in stomatal conductance occurred, particularly in the dominant species Q. wutaishanica. The result indicates that N deposition would increase the risk of hydraulic failure in those species if the soil and/or air becomes drier under future climate change scenarios. The results of the study can have significant implications on the modelling of ecosystem vulnerability to drought under the scenario of atmospheric nitrogen deposition.
虽然氮沉降对树木水分关系的影响已经得到了广泛的研究，但它对气孔导度和木质部水力导度对蒸汽压差和水势的相对敏感性的影响仍知之甚少。本研究调查了 7 年氮沉降处理对叶片水分关系和冠层气孔导度对蒸汽压差（VPD）和水势的敏感性以及主导树种（白皮松）和伴生树种（槭树）分支水力导度对水势敏感性的影响在温带森林中。结果表明，氮沉降增加了气孔对 VPD 的敏感性，降低了气孔对水势的敏感性，并增加了两个物种水力系统对空化的脆弱性。然而，标准化的气孔对 VPD 的敏感性不受氮沉降的影响，表明在氮沉降条件下，气孔仍然能够调节水分平衡。尽管气孔对 VPD 的敏感性增加在一定程度上可以补偿气孔对水势的敏感性降低，但综合响应会增加水力传导率损失（PLC）的百分比当气孔导度损失 50%时，特别是在主导物种白皮松中。结果表明，如果未来气候变干燥，氮沉降会增加这些物种水力系统故障的风险。本研究的结果对大气氮沉降情景下生态系统对干旱脆弱性的建模具有重要意义。
