Nutrient accumulation in aboveground biomass of planted tropical trees: a meta-analysis

Efficient nutrient use is essential for biomass production by tropical trees growing in infertile soils. Accumulation of nitrogen (N) and phosphorus (P) in the aboveground biomass of four groups of tree stands [Acacia, Eucalyptus, N2-fixing trees excluding Acacia, and other non-N2-fixing broadleaved (ONNFB) trees] were investigated using meta-analyses of a range of biomass data to test the hypothesis that fast-growing Acacia and Eucalyptus trees accumulate fewer nutrients. Data for 83 tropical tree stands were selected from the literature. Standardized major axis regressions were applied between the log10-transformed biomass and N or P accumulation. Nutrient use efficiency was compared with aboveground biomass and topsoil conditions. The slope of the regression between aboveground biomass and N accumulation for Eucalyptus was significantly smaller than the slopes for the N2-fixing trees (excluding Acacia) and the ONNFB trees. N use efficiency of Eucalyptus increased with biomass more than that of N2-fixing trees (excluding Acacia) and the ONNFB trees, because their stems and twigs tended to accumulate less N than in the other groups as biomass increased. The regressions between aboveground biomass and P accumulation had a common slope, and the intercepts of Acacia and Eucalyptus were significantly lower than that of ONNFB trees. P use efficiency of Acacia was consistently higher than that of the ONNFB trees. P use efficiency is more affected by other factors like soil conditions than is N use efficiency, and the differences in the tree groups significantly affect the use efficiency of both nutrients. These results explained some aspects of the general suitability of Acacia and Eucalyptus species for tropical plantations on infertile soils.对于生长在贫瘠土壤中的热带树木而言，养分高效利用是其生物量生产的核心前提。本研究通过对多组生物量数据开展元分析（meta-analyses），探究了四类林分[金合欢（Acacia）、桉树（Eucalyptus）、非金合欢固氮树木、其他非固氮阔叶树（ONNFB）]的地上生物量中氮（Nitrogen, N）与磷（Phosphorus, P）的积累特征，以验证“速生金合欢与桉树的养分积累量更低”这一假说。研究从已发表文献中筛选得到83个热带林分的相关数据。本研究采用标准化主轴回归（standardized major axis regressions）分析法，对经以10为底对数转换的生物量与氮、磷积累量进行拟合分析，并对比了不同林分的养分利用效率与地上生物量、表层土壤条件之间的关联。结果显示，桉树地上生物量与氮积累量的回归斜率，显著低于非金合欢固氮树木及其他非固氮阔叶树的对应回归斜率。随着生物量提升，桉树的氮利用效率增长幅度高于非金合欢固氮树木与其他非固氮阔叶树，这是因为随着生物量增加，桉树的茎与细枝的氮积累量相对其他林分组更低。地上生物量与磷积累量的回归分析显示，四类林分具有共同的回归斜率，且金合欢与桉树的回归截距显著低于其他非固氮阔叶树。金合欢的磷利用效率始终高于其他非固氮阔叶树。相较于氮利用效率，磷利用效率更易受土壤条件等其他因素影响；而不同林分组间的差异，会显著影响两类养分的利用效率。本研究结果从部分层面解释了金合欢与桉树树种在贫瘠土壤热带人工林种植中的普遍适宜性。