大气氮沉降影响树木水力结构,进而影响树木的生长和生存.然而,目前关于叶片水力性状对氮沉降的响应尚不明确,而且该响应可能与物种或植物功能型有关.本研究以中国东北地区水曲柳(Fraxinus mandshurica,阔叶被子植物)和兴安落叶松(Larix gmelinii,针叶裸子植物)人工林为研究对象,利用长达16年的施氮(10 g N m-2 yr-1)试验研究了氮添加对两种树种叶片水力性状的影响.用自然干燥法测定了叶片压力-容积曲线,用复水动力学法量化了叶片最大水力导度(Kleafmax)和抗栓塞阻力(P50leaf).研究结果表明,与水曲柳相比,兴安落叶松具有较高的Kleafmax和较强的干旱容忍性(即较低的质壁分离点的相对含水量(RWCtlp)和弹性模量(ε),较负的P50leaf).此外,氮添加增加了水曲柳的叶膨压损失点水势(πtlp)、叶饱和含水量时的渗透势(πo)和叶水容(Cleaf_mass),但对兴安落叶松的这些性状影响不显著,表明水曲柳对氮添加更敏感.氮添加增加了水曲柳和兴安落叶松的Keef_max和P50leaf°水曲柳的πtlp和π0均与叶密度(LD)正相关,而Cleaf_mass与LD负相关.兴安落叶松的Kleaf_max与LD正相关,JP50leaf与LD负相关.两个树种的Kleaf_max与P50leaf均呈负相关关系.我们的研究表明,长期氮添加降低了这两个重要造林树种的叶片干旱容忍性,这一发现加深了我们对氮沉降背景下树木水力表现的理解.“,”Aims Atmospheric nitrogen (N) deposition influences tree hydraulic architecture and thus the growth and survival;but the responses of leaf hydraulic traits remain uncertain,and may vary with species or plant functional types.Methods We used the 16-year N addition experiment (10 g N m-2 year-1) on Fraxinus mandshurica (ash,broadleaf angiosperm) and Larix gmelinii (larch,conifer gymnosperm) plantations in northeastern China and examined the effect of N addition on their leaf hydraulics.We measured the leaf pressure-volume traits by the bench drying method and quantified the maximum leaf hydraulic conductance (Kleaf_max) and resistance to embolism (P50leaf) by the timed rehydration method.Important Findings Larch had higher Kleaf_max and stronger drought tolerance (i.e.,lower relative water content at turgor loss point (RWCtlp) and modulus of elasticity (e),and more negative P50leaf) than ash.N addition increased the leaf osmotic potential at turgor loss (πtlp) and full turgor (πo),and leaf capacitance (Cleaf_mass) for ash but not for larch,indicating that ash is more sensitive to N addition.N addition consistently increased Kleaf_max and P50leaf values for both species.πtlp and πo were positively while Cleaf_rnass was negatively correlated with leaf density(LD) for ash.Kleaf_max was positively but P50leaf was negatively related with LD for larch.There were negative relationships between Kleaf_max and P50leaf for both species.Overall,our findings suggest that long-term N addition decreases the leaf drought tolerance for these two important tree species,which improve the understanding of the tree hydraulic performance under N deposition.