Data from: Carboxylate release as a nutrient-acquisition strategy in mycorrhizal plant species in phosphorus-impoverished environments

Plants acquire phosphorus (P) in different ways, including using specialised root structures such as cluster roots and mycorrhizal symbioses. However, mycorrhizal fungi are less effective at acquiring P from severely P-impoverished soils; yet many mycorrhizal plants thrive in such environments. Hence, we studied what nutrient-acquisition and -utilisation strategies allow these species to persist in these habitats. We chose 19 species (from mycorrhizal and non-mycorrhizal families) from P-impoverished environments in south-western Australia. Leaf element concentrations, including P, nitrogen (N), and manganese (Mn), as well as N and carbon (C) stable isotopes, were measured to explore the likely nutrient-acquisition and -utilisation strategies. Leaf Mn concentrations ([Mn]) were used as a proxy for carboxylates released by roots. Subsequently, glasshouse experiments were conducted to measure the root carboxylate release of seedlings of the selected species grown in nutrient solutions. Most mycorrhizal plant species with high leaf [Mn] showed a considerable release of root carboxylates, which mobilise both P and Mn in soil, just like most non-mycorrhizal Proteaceae with their specialised cluster roots do. The leaf [N] and [P] of arbuscular mycorrhizal species were higher than those of species with cluster roots and ectomycorrhizal species. Arbuscular mycorrhizal plant species exhibited a significantly more negative δ15N than other mycorrhizal species, indicating they accessed more inorganic N, while cluster-rooted non-mycorrhizal species had a positive δ15N, indicating they accessed more organic N. Myrtaceae exhibited a less negative δ13C value and higher leaf [Mn] at a drier location, indicating a higher water-use efficiency. Their higher leaf [Mn] suggests that photosynthesis was reduced less than leaf growth, providing a greater surplus of carbon, which was released as carboxylates from the roots. Synthesis. Many mycorrhizal plant species very likely depended on root carboxylate release to acquire P at the P-impoverished study sites. Arbuscular mycorrhizal species exhibited a less conservative nutrient-utilisation strategy with higher leaf [P] than cluster-rooted non-mycorrhizal species and accessed more inorganic N. This supports the contention that the non-mycorrhizal species were not only more efficient at acquiring P but also at using it; their δ15N values indicated that they accessed less organic N.

植物获取磷（P）的途径多样，可通过特化根系结构（如簇根（cluster roots））以及构建菌根共生（mycorrhizal symbioses）关系实现。然而，菌根真菌从严重缺磷土壤中获取P的能力相对有限，但诸多菌根植物仍可在这类生境中茁壮成长。为此，本研究旨在揭示支撑这些物种在这类生境中存续的养分获取与利用策略。我们从澳大利亚西南部的缺磷生境中选取了19个物种，涵盖菌根与非菌根植物类群。本研究测定了供试物种的叶片元素浓度（包括P、氮（N）、锰（Mn））以及N、碳（C）的稳定同位素比值，以探究其潜在的养分获取与利用策略。其中，叶片锰浓度（[Mn]）被用作根系羧酸盐释放量的替代表征指标。后续我们开展了温室实验，测定了在营养液中培养的供试物种幼苗的根系羧酸盐释放量。多数叶片[Mn]较高的菌根植物可释放大量根系羧酸盐，能够活化土壤中的P与Mn，这与多数依靠特化簇根的非菌根山龙眼科（Proteaceae）植物的功能一致。丛枝菌根（arbuscular mycorrhizal）植物的叶片[N]与[P]浓度均高于簇根植物与外生菌根（ectomycorrhizal）植物。丛枝菌根植物的δ15N显著低于其他菌根植物，表明其获取的无机氮占比更高；而具簇根的非菌根植物δ15N为正值，说明其获取的有机氮占比更高。桃金娘科（Myrtaceae）植物在较干燥生境中，其δ13C负值更小且叶片[Mn]更高，表明其具备更高的水分利用效率。其较高的叶片[Mn]意味着光合作用受抑制程度低于叶片生长，从而产生更多富余碳，并以羧酸盐形式通过根系释放到土壤中。综上，在本次研究的缺磷样地中，多数菌根植物很可能依赖根系释放羧酸盐来获取P。丛枝菌根植物的养分利用策略相对不保守，其叶片[P]高于簇根非菌根植物，且获取更多无机氮。这一结果支持下述观点：非菌根植物不仅在P获取上效率更高，养分利用效率也更优；其δ15N值表明它们获取的有机氮占比更低。