Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing 100101, China.
College of Resources and Environment, University of Chinese Academy of Sciences, Yanqi Lake, Huairou District, Beijing 101408, China.
Tree Physiol. 2017 Nov 1;37(11):1515-1526. doi: 10.1093/treephys/tpx046.
Evidence shows that many tree species can take up organic nitrogen (N) in the form of free amino acids from soils, but few studies have been conducted to compare organic and inorganic N uptake patterns in temperate and tropical tree species in relation to mycorrhizal status and successional state. We labeled intact tree roots by brief 15N exposures using field hydroponic experiments in a temperate forest and a tropical forest in China. A total of 21 dominant tree species were investigated, 8 in the temperate forest and 13 in the tropical forest. All investigated tree species showed highest uptake rates for NH4+ (ammonium), followed by glycine and NO3- (nitrate). Uptake of NH4+ by temperate trees averaged 12.8 μg N g-1 dry weight (d.w.) root h-1, while those by tropical trees averaged 6.8 μg N g-1 d.w. root h-1. Glycine uptake rates averaged 3.1 μg N g-1 d.w. root h-1 for temperate trees and 2.4 μg N g-1 d.w. root h-1 for tropical trees. NO3- uptake was the lowest (averaging 0.8 μg N g-1 d.w. root h-1 for temperate trees and 1.2 μg N g-1 d.w. root h-1 for tropical trees). Uptake of NH4+ accounted for 76% of the total uptake of all three N forms in the temperate forest and 64% in the tropical forest. Temperate tree species had similar glycine uptake rates as tropical trees, with the contribution being slightly lower (20% in the temperate forest and 23% in the tropical forest). All tree species investigated in the temperate forest were ectomycorrhizal and all species but one in the tropical forest were arbuscular mycorrhizal (AM). Ectomycorrhizal trees showed significantly higher NH4+ and lower NO3- uptake rates than AM trees. Mycorrhizal colonization rates significantly affected uptake rates and contributions of NO3- or NH4+, but depended on forest types. We conclude that tree species in both temperate and tropical forests preferred to take up NH4+, with organic N as the second most important N source. These findings suggest that temperate and tropical forests demonstrate similar N uptake patterns although they differ in physiology of trees and soil biogeochemical processes.
证据表明，许多树种可以从土壤中吸收以游离氨基酸形式存在的有机氮（N），但很少有研究比较温带和热带树种在与菌根状态和演替状态有关的情况下吸收有机和无机 N 的模式。我们在中国的温带森林和热带森林中使用田间水培实验对完整的树根进行了短暂的 15N 暴露标记。共调查了 21 个主要树种，温带森林 8 个，热带森林 13 个。所有被调查的树种对 NH4+（铵）的吸收速率最高，其次是甘氨酸和 NO3-（硝酸盐）。温带树木对 NH4+的平均吸收速率为 12.8 μg N g-1干重（d.w.）根 h-1，而热带树木的平均吸收速率为 6.8 μg N g-1 d.w.根 h-1。温带树木甘氨酸的平均吸收速率为 3.1 μg N g-1 d.w.根 h-1，热带树木的平均吸收速率为 2.4 μg N g-1 d.w.根 h-1。NO3-的吸收最低（温带树木平均为 0.8 μg N g-1 d.w.根 h-1，热带树木平均为 1.2 μg N g-1 d.w.根 h-1）。NH4+的吸收占温带森林中所有三种 N 形式总吸收量的 76%，占热带森林的 64%。温带树种的甘氨酸吸收速率与热带树种相似，但其贡献略低（温带森林为 20%，热带森林为 23%）。温带森林中调查的所有树种都是外生菌根，而热带森林中除一种外都是丛枝菌根（AM）。外生菌根树木的 NH4+吸收速率和 NO3-吸收速率显著高于丛枝菌根树木。菌根定植率显著影响 NO3-或 NH4+的吸收速率和贡献，但取决于森林类型。我们得出的结论是，温带和热带森林中的树种都更喜欢吸收 NH4+，而有机 N 是第二重要的 N 来源。这些发现表明，尽管温带和热带森林在树木生理学和土壤生物地球化学过程方面存在差异，但它们表现出相似的 N 吸收模式。
