Determine leaf manganese concentration to estimate rhizosheath carboxylates of mycorrhizal plants in forest ecosystems

Root exudation of carboxylates is a key response to phosphorus (P) limitation for many plant species. However, sampling and quantitative and qualitative determination of root exudates under field conditions faces various challenges. Recently, multiple studies have demonstrated that manganese (Mn) concentration in mature leaves may serve as a proxy for rhizosheath carboxylate concentration. In this issue of Plant and Soil, the paper by Yan and co-authors shows that leaf Mn concentration ([Mn]) was higher in P-limited forests of southern China than in forests of northern China that exhibit higher soil [P]. This study revealed the potential relationships between rhizosheath carboxylates and leaf [Mn] in the studied Chinese flora, and indicates a potential common strategy (i.e. root carboxylate exudation) among plants, including many mycorrhizal plants, in P-limited forests. Despite the fact that there is great variation among plant species, and the molecular basis underlying the positive correlation between plant Mn uptake and root release of carboxylates remains largely unexplored, this study has paved the road for an easy and reliable way to assess rhizosheath carboxylates in forest ecosystems. In combination with the handheld X-ray fluorescence spectroscopy system that enables non-destructive analysis of [Mn] in dried mature leaves (e.g., herbarium specimens), researchers are now able to estimate the patterns of root-released carboxylates for a broad range of plant species under various environmental conditions, in an easy, rapid and low-costs way.