干旱和坡向互作对栓皮栎和侧柏生长的影响

The interaction of drought and slope aspect on growth of Quercus variabilis and Platycladus orientalis

用年轮学方法测定了不同坡向的栓皮栎和侧柏的年轮宽度及相应的年树干面积增长量,同时测定了旱季碳稳定同位素比值(δ13C)及不同坡向之间的微气象指标差异,分析了不同坡向两种树木径向生长与旱季降雨量的关系,目的是探索在华北石质山区季节性干旱条件下坡向对栓皮栎和侧柏生长的影响。结果显示阴坡栓皮栎和侧柏年轮和年增加的截面积显著大于阳坡,两个树种都表现出阳坡δ13C值显著(P<0.05)大于阴坡,阳坡栓皮栎δ13C值比阴坡高1.17,而阳坡侧柏的δ13C值比阴坡高0.56。白天,阳坡气温高于阴坡、相对湿度低于阴坡、饱和蒸汽压匮缺高于阴坡。分析显示旱季降雨量和栓皮栎的树干截面积年增长量显著(P<0.05)相关,而旱季的降雨量和侧柏的截面积年生长没有显著关系。结果表明:相对于侧柏,干旱条件更严重的影响到栓皮栎生长和叶片水分利用效率,反映出这两种树木耐旱能力的差异,以及应对干旱策略的不同。华北石质山区的土壤储水能力低,阳坡较大的蒸散加剧了干旱对树木生长的不利影响。

Quercus variabilis Blume （cork oak） and Platycladus orientalis （L.） Franco （arborvitae） are widely used as afforestation tree species in the rocky mountains of northern China, and they play important role in ecological restoration in this region where there are a fragile ecological environment with thin soil depth and remarkable precipitation seasonality due to monsoonal influence. However, in recent years, we found the two species differentially performed on the different slope aspects. In this paper, we measured tree-ring width and the corresponding area increment by dendrochronology, and leaf δ^13C of the two main afforestation tree species growing on different topographic slope aspects in the dry season. Combining with weather records and the soil moisture, we analyzed the effects of water status on tree growth to study variation in growth of the two species on the different slope aspects. The main purpose is to explore effects of seasonal drought on growth and development of Q. variabilis and P. orientalis forests, and the soil carrying capacity of the forest density. The results showed that the tree-ring width of the two species on shady slopes was significantly greater （P〈0.05） than that on sunny slopes. The corresponding basal area increment on shady slopes was also significantly （ P〈0.05 ） greater than that on sunny slopes. The δ^13C values of the two species on sunny slopes were significantly （P〈0.05） greater than that on shady slopes,with cork oak 1.17 greater and arborvitae 0.56 greater. In day time, especially at noon, there were higher air temperature, lower relative humidity, and greater vapor pressure deficit （ VPD ） on sunny slopes than those on shady slopes. The maximum differences in the air temperature, relative humidity, and vapor pressure deficit all occurred at 14：00, by which the air temperature on sunny slopes was 1.5 ℃ higher than that on shady slopes, the relative humidity was 1.6% greater than that on Shady slopes, and the VPD was 4.1 kPa greater than that on shady slopes. The air temperature on shady slopes in the early morning and evening was slightly higher than that on sunny slopes. The soil moisture on sunny slopes was significantly lower than that on shady slopes in the dry season, however there was no significant difference in the soil moisture between sunny and shady slopes in the wet season. The soil moisture in the dry season was only half of the wet season. Correlation analyses displayed that the precipitation in dry season was significantly （P〈0.05） correlated with the annual basal area increment of cork oak, especially on the sunny slope, the correlation coefficient reached 0.7. However, the precipitation in dry season was not significantly correlated to the basal area increment of arborvitae. Those results indicated that drought condition more severely inhibited growth and water use efficiency of cork oak than that of arborvitae, reflecting that there existed variations in tolerance and responsive strategy to drought stress. With shallow soil thickness and low capacity of water storage, the higher evapotranspiration on the sunny slopes exacerbated the adverse effects of drought on tree growth.