Partitioning of soil phosphorus among arbuscular and ectomycorrhizal trees in tropical and subtropical forests

Partitioning of soil phosphorus (P) pools has been proposed as a key mechanism maintaining plant diversity, but experimental support is lacking. Here, we provided different chemical forms of P to 15 tree species with contrasting root symbiotic relationships to investigate plant P acquisition in both tropical and subtropical forests. Both ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) trees responded positively to addition of inorganic P, but strikingly, ECM trees acquired more P from a complex organic form (phytic acid). Most ECM tree species and all AM tree species also showed some capacity to take up simple organic P (monophosphate). Mycorrhizal colonization was negatively correlated with soil extractable P concentration, suggesting that mycorrhizal fungi may regulate organic P acquisition among tree species. Our results support the hypothesis that ECM and AM plants partition soil P sources, which may play an ecologically important role in promoting species coexistence in tropical and subtropical forests.

土壤磷（P）库的分区被提出为维持植物多样性的关键机制，但目前仍缺乏相应的实验证据支持。本研究选取15种根系共生特征存在差异的树木物种，施加不同化学形态的磷素，以探究其在热带与亚热带森林中的磷素获取策略。外生菌根（ectomycorrhizal, ECM）与丛枝菌根（arbuscular mycorrhizal, AM）树木均对无机磷添加产生正向响应，但令人意外的是，外生菌根树木可从复杂有机形态磷——植酸（phytic acid）中获取更多磷素。多数外生菌根树木物种与所有丛枝菌根树木物种，均具备摄取简单有机磷——单磷酸酯（monophosphate）的能力。菌根定殖率与土壤可提取磷浓度呈负相关，这表明菌根真菌可能调控不同树木物种的有机磷获取能力。本研究结果支持‘外生菌根与丛枝菌根植物可分区利用土壤磷源’这一假说，该过程可能在热带与亚热带森林中对促进物种共存发挥重要的生态作用。