Data from: Contrasting effects of ectomycorrhizal and arbuscular mycorrhizal tropical tree species on soil nitrogen cycling: the potential mechanisms and corresponding adaptive strategies

While it is increasingly recognized that ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) tree species vary in their effects on soil nitrogen (N) cycling, little is known about the mechanisms causing and how ECM and AM trees adapt to this variation. Using monoculture plots of six ECM and eight AM tropical trees planted in a common garden, we examined whether the contrasting effects of ECM and AM trees on soil N cycling could be explained by their differences in plant traits. Furthermore, rhizosphere effects on soil N transformations and soil exploration by fine roots were also measured to assess whether ECM and AM trees differed in N acquisition capacities. Results showed that soil NH 4+N concentration, net N mineralization and net nitrification rates were markedly lower, but soil C:N ratio was significantly higher beneath ECM trees than beneath AM trees. This more closed N cycling caused by ECM trees was attributed to their resource-conservative traits, especially the poorer leaf litter decomposability compared with AM trees. To adapt to their induced lower soil N availability, ECM trees were found to have greater rhizosphere effects on NO 3-N concentration, net N mineralization and net nitrification rates to mine N, and higher soil exploration in terms of root length density to scavenge N from soils, indicating that these two strategies work in synergy to meet N demand of ECM trees. These findings suggest that ECM and AM trees have contrasting effects on soil N cycling owing to their differences in leaf litter decomposability and correspondingly possess different N acquisition capacities.

尽管学界日益认识到外生菌根（ectomycorrhizal, ECM）与丛枝菌根（arbuscular mycorrhizal, AM）树种对土壤氮（N）循环的调控效应存在差异，但目前对其背后的作用机制以及两类树种如何适应这种差异的认知仍较为匮乏。本研究依托同质园（common garden）中定植的6种外生菌根树种与8种丛枝菌根热带树种的单优种植样地，探究外生菌根与丛枝菌根树种对土壤氮循环的差异化效应是否可通过植物性状差异予以解释。此外，本研究还测定了根际效应对土壤氮转化过程的影响，以及细根的土壤探查能力，以此评估外生菌根与丛枝菌根树种在氮获取能力上是否存在差异。研究结果显示，相较于丛枝菌根树种，外生菌根树种根际土壤的铵态氮（NH₄⁺-N）浓度、净氮矿化速率与净硝化速率均显著更低，而土壤碳氮比则显著更高。外生菌根树种所引发的这种更趋闭合的氮循环，可归因于其资源保守型性状，尤其是相较于丛枝菌根树种更弱的叶片凋落物分解性。为适应其诱导产生的更低土壤氮有效性，外生菌根树种对硝态氮（NO₃⁻-N）浓度、净氮矿化速率与净硝化速率表现出更强的根际效应以挖掘土壤氮源，同时通过更高的根长密度提升土壤探查能力以从土壤中攫取氮素，表明这两种策略协同作用以满足外生菌根树种的氮需求。上述研究结果表明，外生菌根与丛枝菌根树种因叶片凋落物分解性的差异，对土壤氮循环产生了截然相反的调控效应，并由此具备了差异化的氮获取能力。