The mycorrhizal type governs root exudation and nitrogen uptake of temperate tree species
The mycorrhizal type governs root exudation and nitrogen uptake of temperate tree species
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DOI：
10.1093/treephys/tpx131
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发表时间：
2018-01-01
期刊：
影响因子：
4
通讯作者：
Meier, Ina C.
中科院分区：
文献类型：
--
作者：
Liese, Rebecca;Luebbe, Torben;Meier, Ina C.
尽管温带森林中两种主要的菌根群落对碳(C)和氮(N)循环的耦合存在差异，但丛枝菌根（AM）和外生菌根（ECM）树种的生物地球化学循环之间的系统差异仍然缺乏描述。然而，根据菌根类型进行分类，为预测温带生态系统对环境变化的反应提供了一个全球框架概念的机会。摘要针对不同菌根类型对植物生物地球化学循环的两个关键过程（根系分泌和氮素获取）的影响，在大型中生态系统进行了四种温带落叶乔木菌根类型的干旱试验。我们假设（H1）干旱导致干旱敏感的ECM树木根系分泌物减少更多，（H2）干旱导致ECM树木根系分泌物减少更多，（H3） AM树木无机氮吸收高于ECM树木。与H2相反，我们发现在土壤水分充足时，不同菌根类型的根系分泌量没有系统差异，但在土壤干旱条件下，ECM树的根系分泌量几乎增加了两倍。此外，干旱处理的ECM树根系分泌物的光合C成本增加了近10倍，而AM树仅增加了一倍，这证实了H1。对于H3，我们证实AM树比ECM树具有更高的绝对和相对无机氮吸收速率，而有机氮吸收在菌根类型之间没有差异。我们得出的结论是，与AM树相比，ECM树在无机氮吸收方面效率较低，但ECM树增加了根碳释放，作为对干燥土壤的适应性响应，以保持水力导电性和/或养分有效性。这些关键生物地球化学过程的系统差异支持了菌根类型在温带森林碳氮耦合循环中的关键作用。
Even though the two dominant mycorrhizal associations of temperate tree species differentially couple carbon (C) and nitrogen (N) cycles in temperate forests, systematic differences between the biogeochemical cycles of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species remain poorly described. A classification according to the mycorrhizal type offers the chance, though, to develop a global frame concept for the prediction of temperate ecosystem responses to environmental change. Focusing on the influence of mycorrhizal types on two key plant processes of biogeochemical cycling (root exudation and N acquisition), we investigated four temperate deciduous tree species per mycorrhizal type in a drought experiment in large mesocosms. We hypothesized that (H1) C loss by root exudation is higher in ECM than in AM trees, (H2) drought leads to higher reductions in root exudation of drought-sensitive ECM trees and (H3) inorganic N uptake is higher in AM than in ECM trees. In contradiction to H2, we found no systematic difference in root exudation between the mycorrhizal types at ample soil moisture, but almost twofold higher exudation in ECM trees when exposed to soil drought. In addition, photosynthetic C cost of root exudation strongly increased by similar to 10-fold in drought-treated ECM trees, while it only doubled in AM trees, which confirms H1. With respect to H3, we corroborated that AM trees had higher absolute and relative inorganic N acquisition rates than ECM trees, while the organic N uptake did not differ between mycorrhizal types. We conclude that ECM trees are less efficient in inorganic N uptake than AM trees, but ECM trees increase root C release as an adaptive response to dry soil to maintain hydraulic conductivity and/or nutrient availability. These systematic differences in key biogeochemical processes support hints on the key role of the mycorrhizal types in coupling C and N cycles in temperate forests.