Verification of the accuracy of the recent 50 years of tree growth and long-term change in intrinsic water-use efficiency using xylem Δ14C and δ13C in trees in an aseasonal tropical rainforest

Growth analysis based on tree-ring chronology is difficult in trees in aseasonal tropical rain forests, because annual growth rings may be unclear or completely absent. Fortunately, tree growth history recorded in xylem tissue is capable of providing valuable information on the responses of trees and forests to past and present environmental changes, including global warming. We have developed a new technique for aseasonal tropical forest trees which derives their growth rates from xylem Δ14C, and verified its accuracy. We also determined, from xylem δ13C, the intrinsic water-use efficiency (iWUE) in the past 50 years. We analyzed changes in xylem Δ14C and δ13C in 23 canopy trees of 12 species in 6 families growing in Pasoh Forest Reserve, Malaysia; each stem diameter at breast height (DBH) was recorded 14 times from 1969 to 2011. We found a significant positive relationship between the growth rates determined by 14C dating and the past DBH data. On the other hand, leaf-internal CO2 (Ci...在无季节性热带雨林的树木中，基于树轮年代学（tree-ring chronology）的生长分析往往难以开展，这是因为此类树木的年轮可能模糊不清，甚至完全缺失。所幸的是，木质部（xylem）组织所记录的树木生长历史，能够为树木与森林响应包括全球变暖在内的古今环境变化提供宝贵的科学信息。 我们针对无季节性热带森林树木开发了一项新技术，可通过木质部Δ¹⁴C推导其生长速率，并验证了该技术的准确性。此外，我们还借助木质部δ¹³C测定了过去50年的内在水分利用效率（intrinsic water-use efficiency，iWUE）。我们对马来西亚巴沙森林保护区（Pasoh Forest Reserve）内6科12种共23株冠层树木的木质部Δ¹⁴C与δ¹³C变化进行了分析；1969年至2011年间，这些树木的胸径（DBH）累计被记录14次。 我们发现，通过¹⁴C测年得到的生长速率与过往胸径数据之间存在显著正相关关系。另一方面，叶片内部二氧化碳（Ci……