与温带地区相比,人们对在热带山脉中,尤其是热带针叶林中,沿海拔梯度的个体树种生长减少的原因知之甚少.我们的研究目的是检验气候或土壤条件是否会导致在高海拔分布的卡西亚松(Pinus kesiya,一种在南亚和东南亚广泛分布的松树)的生长减少.我们对越南中南部山脉中沿海拔梯度约在900～2000米之间的卡西亚松的树干直径增量和其年轮中13C(△13C)的同位素判别进行分析.同时确定其生长与△13C、气候和土壤变量的关系.研究发现,树木的断面积生长量(BAI)与温度或降水之间没有一致的相关关系.相反,沿海拔梯度,我们发现BAI与△13C以及与上层矿质土壤的C/N比和δ15N特征呈显著负相关.BAI与土壤中有效磷(Pa)和“碱性”阳离子(钙、镁、钾)的浓度呈正相关.我们的结论是,较高海拔下的较低温度会对树木生长产生间接影响,主要通过产生较高的C/N比并降低氮(N)和P矿化率而产生作用,而这些影响因其他负面反馈而进一步受到阻碍.主要包括:降水增加的淋溶作用而导致较低浓度的“碱性”阳离子以及较高海拔土壤矿化的N和P的有效性降低.本研究结果可以进一步解释卡西亚松的最高生长极限以及该物种在其他山区出现的情况.“,”Aims In contrast to temperate regions,the reasons for growth reductions of individual tree species along elevational gradients in tropical mountain ranges are poorly known,especially for tropical conifers.We aimed at testing whether climatic or edaphic conditions are responsible for the reduced growth of Pinus kesiya,a widely distributed pine species of southern and south-eastern Asia,at higher elevations.Methods We analysed the stem diameter increment and the isotope discrimination against 13C(△13C)in tree rings of P.kesiya along an elevational gradient of～900 to～2000 m a.s.l.in the mountain ranges of South-Central Vietnam,and related growth to △13C and to climatic and edaphic variables.Important findings We found no consistent correlation patterns between the basal area increment(BAI)of the trees and temperature or precipitation.In contrast,across the elevational gradient,we obtained significantly negative correlations of BAI with △13C and with the C/N ratios and the δ15N signature of the upper mineral soil.BAI was positively correlated with the concentrations of plant-available phosphorus(Pa)and of“base”cations(calcium,magnesium,potassium)in the soil.We conclude that lower temperatures at higher elevations exert an indirect effect on tree growth by inducing higher C/N ratios and by reducing the rate of nitrogen(N)and P mineralization,which may be further hampered by lower concentrations of“base”cations(upon enhanced leaching by precipitation)and a negative feedback from low availability of mineralized N and P at higher elevations.Our results may be transferable to the uppermost growth limit of P kesiya and to other montane regions of the species\'occurrence.