六盘山主要树种叶片稳定性碳同位素组成的时空变化特征

为了认识树种叶片水分利用效率的种内和种间差异及随水分生境条件和季节的变化特征,2010年6—9月份,在宁夏六盘山香水河小流域(半湿润区)和叠叠沟小流域(半干旱区),测定了两种不同水分生境内主要树种的叶片稳定碳同位素组成(δ13C)。结果表明:同一树种叶片δ13C值存在着明显的冠层部位差异,但各树种表现各异,其中华北落叶松(Larix prin-cipris-rupprechtii)、白桦(Betula platyphylla)和油松(Pinus tablaeformis)表现为上部>中部>下部,而华山松(Pinus arman-dii)和辽东栎(Quercus liaotungensis)为下部>上部>中部。各树种叶片的δ13 C值表现出明显的季节变化特征,但其变化随水分生境条件而异。在半湿润区,各树种的δ13 C值在生长季初期较高,但随生长季的持续而降低;在半干旱区,各树种的δ13C值呈现出"高—低—高"的变化态势。在两种不同水分生境下,华北落叶松和沙棘(Hippophae rhamnoildes)叶片的δ13 C值存在着明显的种内个体差异:旱季,同一树种在半干旱区树木叶片的δ13C要大于半湿润区;但雨季两地树木叶片的δ13C差异不大,说明这种季节差异受当地降雨量的季节分配格局影响较大。

Spatial-temporal Pattern of Stable Carbon Isotope Composition of Dominant Tree Species in Liupanshan Mountain

The leaf δ13C values of dominant tree species were measured from June to September in 2010 in the south(Xiangshuihe Watershed,semi-humid area) and north(Diediegou Watershed,semi-arid area) of Liupanshan Mountain,Ningxia.The differences in leaf δ13C between species and individuals were analyzed,and its seasonal pattern was also determined.The results showed that leaf δ13C increased with increase of canopy height of Larix principris-rupprechtii,Betula platyphylla,Pinus tablaeformis,but the leaf δ13C in the low canopy of Pinus armandii and Quercus liaotungensis were higher compared with those of the mid-and upper parts in the canopy.The leaf δ13C values of species were various in different periods of growing season,being relatively higher δ13C in the early stage than that in the middle and late phases.And the characteristics of seasonal pattern in leaf δ13C were correlated with water environmental condition of habitat.In the semi-humid area,the leaf δ13C of tree species decreased over the time,but in the semi-arid area,the seasonal change in the leaf δ13C followed as a ’high-low-high’ pattern during the growing season.The leaf δ13C among individual trees of L.principris-rupprechtii and Hippophae rhamnoides in two different water environmental regions were significantly different,but it was mainly influenced by the seasonal pattern of rainfall in different stages of growing season,semi-arid area with the highest values in dry season(the early and late stage of the growing season) had similar δ13C values in rainy season(the medium stage of the growing season) in semi-humid area.It showed that the ability of water use of the same tree species could be improved through long-term adaptation to drought.