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 [<i>Acacia</i>, <i>Eucalyptus</i>, N₂-fixing trees excluding <i>Acacia</i>, 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 <i>Acacia</i> and <i>Eucalyptus</i> 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 <i>Eucalyptus</i> was significantly smaller than the slopes for the N₂-fixing trees (excluding <i>Acacia</i>) and the ONNFB trees. N use efficiency of <i>Eucalyptus</i> increased with biomass more than that of N₂-fixing trees (excluding <i>Acacia</i>) 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 <i>Acacia</i> and <i>Eucalyptus</i> were significantly lower than that of ONNFB trees. P use efficiency of <i>Acacia</i> 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 <i>Acacia</i> and <i>Eucalyptus</i> species for tropical plantations on infertile soils.

对于生长在贫瘠土壤中的热带树木而言，养分高效利用是其实现生物量生产的必要条件。本研究通过对多组生物量数据开展荟萃分析，对4类林分[金合欢属（*Acacia*）、桉树属（*Eucalyptus*）、非金合欢属固氮树木（N₂-fixing trees）以及其他非固氮阔叶树（other non-N₂-fixing broadleaved，简称ONNFB）]的地上生物量中氮（N）与磷（P）的累积特征展开调查，旨在验证“速生的金合欢属与桉树属树木养分累积量更低”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法，对经log₁₀转换的生物量与氮、磷累积量之间的关系进行拟合，并将养分利用效率与地上生物量及表层土壤条件进行关联对比。结果显示，桉树属林分的地上生物量与氮累积量之间的回归斜率，显著低于非金合欢属固氮树木与ONNFB林分的对应斜率；桉树属的氮素利用效率随生物量提升的增幅显著高于非金合欢属固氮树木与ONNFB林分，这是因为随着生物量增加，桉树属的茎与细枝的氮累积量相较于其他类群更低。地上生物量与磷累积量之间的回归具有共同斜率，且金合欢属与桉树属的回归截距显著低于ONNFB林分；金合欢属的磷素利用效率始终高于ONNFB林分。相较于氮素利用效率，磷素利用效率更易受土壤条件等其他因素影响；且树木类群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属与桉树属树种为何更适配贫瘠土壤的热带人工林种植。