The foliar C and N stable isotopic compositions(δ 13C and δ 15N) and the relationships between these compositions and environmental factors of C3 plants in the Ethiopia Rift Valley were investigated. There were three distribution patterns for foliar δ 13C with mean values of ?26.7‰±0.4‰,?29.7‰± 0.6‰,and ?26.9‰± 1.2‰ in cold-moist,temperate-moist,and arid-hot environments,respectively. The δ 15N values ranged from ?1.4‰± 1.7‰ to 14.3‰± 0.1‰,with higher values under arid-hot conditions and the lowest values in plants growing at higher altitudes under cold-moist conditions. A strong negative relationship between mean annual precipitation and δ 15N explained more than half of the observed variation in the δ 15N values(r2 = 0.54,P < 0.001);a modest positive relationship was also found between δ 15N and tem-perature(r2 = 0.32,P < 0.01). A weakly positive relationship existed between δ 13C and temperature,and changes in δ 13C values with precipitation and altitude followed quadratic curves. This suggests a shift in the effects of water and heat conditions caused by altitude on carbon isotopic discrimination.
LIU XiaoHongZHAO LiangJuGASAW MenassieGAO DengYiQIN DaHeREN JiaWen
In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known detailedly. This study presented two δ13C series in annual tree rings for Chinese hem-lock (Tsuga chinensis Pritz) and alpine pine (Pinus densata Mast),and investigated the relationships between climatic parameters and stable carbon discrimination (△13C) series,and evaluated the poten-tial of climatic reconstruction using △13C in both species,in a temperate-moist region of Chuanxi Pla-teau,China. The raw δ13C series of the two species was inconsistent,which may be a result of different responses caused by tree's inherent physiological differences. After removing the low-frequency ef-fects of CO2 concentration,the high-frequency (year-to-year) inter-series correlation of △13C was strong,indicating that △13C of the two tree species were controlled by common environmental conditions. The △13C series of the species were most significantly correlated with temperature and moisture stress,but in different periods and intensity between the species. During the physiological year,the impacts of temperature and moisture stress on △13C occur earlier for Chinese hemlock (previous December to February for moisture stress and February to April for temperature,respectively) than for alpine pine (March to May for moisture stress and April to July for temperature,respectively). In addition,in temperate-moist regions,the control on △13C of single climatic parameter was not strongly dominant and the op-timal multiple regressions functions just explained the 38.5% variance of the total. Therefore,there is limited potential for using δ13C alone to identify clear,reliable climatic signals from two species.
LIU XiaoHongSHAO XueMeiWANG LiLiZHAO LiangJuWU PuCHEN TuoQIN DaHeREN JiaWen
Abstract：The carbon isotopic composition （δ13C） of tree rings was used to assess changes in intrinsic water-use efficiency （Wi） to increasing atmospheric CO2 and climate change during the period of 1891–2003. Five Qinghai spruce （Picea crassifolia） stands were selected in the Qilian Mountains, growing along a precipitation gradient. All five δ13C were correlated to each other, but two sites （DDS and CLS）, which are far from the main body of the mountains, show relative weak connections to other sites. Although trees at all sites had improved their Wi in response to increasing atmospheric CO2 concentration, spruce growing in the regions far away from the main body of the mountains were less sensitive to improved Wi than those of other sites. Based on the correlation between carbon isotope discrimination （Δ） and Palmer Drought Severity Index （PDSI）, the drought history covering the period of 1891–2003 was reconstructed in the study region. The two most severe drought epochs of the late 1920s and the last decade were caused by reduced precipitation and climate warming, respectively. Our results will be useful in assessing any further spatial climate-related bioclimatic information.
