Root-released carboxylates enhance the availability of manganese (Mn), which enters roots through transporters with low substrate specificity. Leaf Mn concentration ([Mn]) has been proposed as a signature for phosphorus (P)-mobilising carboxylates in the rhizosphere. Here we test whether leaf [Mn] provides a signature for root functional types related to P acquisition. Across 727 species at 66 sites in Australia and New Zealand, we measured leaf [Mn] as related to root functional type, while also considering soil and climate variables. To further assess the specific situations under which leaf [Mn] is a suitable proxy for rhizosphere carboxylate concentration, we studied leaf [Mn] along a strong gradient in water availability on one representative site. In addition, we focused on two systems where a species produced unexpected results. Controlling for background site-specific variation in leaf [Mn] with soil pH and mean annual precipitation, we established that mycorrhizal species have significantly lower leaf [Mn] than non-mycorrhizal species with carboxylate-releasing root structures, e.g., cluster roots. In exception to the general tendency, leaf [Mn] did not provide information about root functional types under seasonally waterlogged conditions, which increase iron availability and thereby interfere with Mn-uptake capacity. Two further exceptions were scrutinised, leading to the conclusion that they were ‘anomalous’ in not functioning like typical species in their families, as expected according to the literature. Leaf [Mn] variation provides considerable insights on differences in belowground functioning among co-occurring species. Using this approach, we concluded that, within typical mycorrhizal families, some species actually depend on a carboxylate-releasing P-mobilising strategy. Likewise, within families that are known to produce carboxylate-releasing cluster roots, some do not produce functional cluster roots when mature. An analysis of leaf [Mn] can alert us to such ‘anomalous’ species.

中文翻译：

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叶锰浓度作为评估缺磷环境中地下植物功能的工具

根部释放的羧酸盐提高了锰 (Mn) 的可用性，锰通过底物特异性低的转运蛋白进入根部。叶锰浓度 ([Mn]) 已被提议作为根际中磷 (P) 动员羧酸盐的特征。在这里，我们测试叶子 [Mn] 是否为与 P 获取相关的根功能类型提供签名。在澳大利亚和新西兰 66 个地点的 727 个物种中，我们测量了与根功能类型相关的叶 [Mn]，同时还考虑了土壤和气候变量。为了进一步评估叶子 [Mn] 是根际羧酸盐浓度的合适代表的具体情况，我们在一个代表性地点研究了叶子 [Mn] 沿水可用性的强梯度。此外，我们专注于两个系统，其中一个物种产生了意想不到的结果。控制叶 [Mn] 与土壤 pH 值和年平均降水量的背景站点特定变化，我们确定菌根物种的叶 [Mn] 显着低于具有释放羧酸根结构的非菌根物种，例如簇根。除了一般趋势外，在季节性淹水条件下，叶子 [Mn] 没有提供有关根功能类型的信息，这会增加铁的可用性，从而干扰 Mn 吸收能力。对另外两个例外情况进行了仔细审查，得出的结论是，正如文献中所预期的那样，它们在功能上不像其家族中的典型物种那样“异常”。叶 [Mn] 变异提供了对共生物种地下功能差异的重要见解。使用这种方法，我们得出结论，在典型的菌根科中，有些物种实际上依赖于释放羧酸盐的磷动员策略。同样，在已知会产生释放羧酸根的簇根的家族中，有些在成熟时不会产生功能性簇根。对叶子 [Mn] 的分析可以提醒我们注意此类“异常”物种。