Soil phosphorus (P) availability in lowland tropical rainforests influences the distribution and growth of tropical tree species. Determining the P-acquisition strategies of tropical tree species could therefore yield insight into patterns of tree β-diversity across edaphic gradients. In particular, the synthesis of root phosphatases is likely to be of significance given that organic P represents a large pool of potentially available P in tropical forest soils. It has also been suggested that a high root phosphatase activity in putative nitrogen (N)-fixing legumes might explain their high abundance in lowland neotropical forests under low P supply. Here, we measured phosphomonoesterase (PME) activity on the first three root orders of co-occurring tropical tree species differing in their N fixation capacity, growing on soils of contrasting P availability in Panama. Our results show that root PME activity was higher on average in P-poor than in P-rich soils, but that local variation in PME activity among co-occurring species within a site was larger than that explained by differences in soil P across sites. Legumes expressed higher PME activity than non-legumes, but nodulated legumes (i.e., actively fixing nitrogen) did not differ from legumes without nodules, indicating that PME activity is unrelated to N fixation. Finally, PME activity declined with increasing root order, but the magnitude of the decline varied markedly among species, highlighting the importance of classifying fine roots into functional groups prior to measuring root traits. Our results support the hypothesis that low-P promotes a high root PME activity, although the high local variation in this trait among co-occurring species points toward a high functional diversity in P-acquisition strategies within an individual community.

中文翻译：

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尽管物种间差异很大，但低磷时热带树木的根磷酸酶活性更高

低地热带雨林中土壤磷 (P) 的有效性影响热带树种的分布和生长。因此，确定热带树种的 P 获取策略可以深入了解跨土壤梯度的树木 β 多样性模式。特别是，根磷酸酶的合成可能很重要，因为有机磷代表了热带森林土壤中大量潜在的可用磷。也有人提出，假定固氮 (N) 豆科植物的高根磷酸酶活性可能解释了它们在低磷供应下的低地新热带森林中的高丰度。在这里，我们测量了共生热带树种的前三个根级的磷酸单酯酶 (PME) 活性，这些树种的固氮能力不同，生长在巴拿马磷含量对比鲜明的土壤上。我们的结果表明，贫磷土壤中根系 PME 活性平均高于富磷土壤，但一个地点内共生物种 PME 活性的局部变化大于不同地点土壤磷差异所解释的差异。豆科植物比非豆科植物表达更高的 PME 活性，但有瘤的豆科植物（即积极固氮）与没有瘤的豆科植物没有区别，表明 PME 活性与固氮无关。最后，PME 活性随着根序的增加而下降，但下降的幅度因物种而异，这突出了在测量根性状之前将细根分类为功能组的重要性。我们的结果支持低磷促进高根 PME 活性的假设，