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Soil nitrogen cycling is determined by the competition between mycorrhiza and ammonia‐oxidizing prokaryotes
Ecology ( IF 4.8 ) Pub Date : 2020-01-23 , DOI: 10.1002/ecy.2963
Chikae Tatsumi 1 , Takeshi Taniguchi 2 , Sheng Du 3 , Norikazu Yamanaka 2 , Ryunosuke Tateno 4
Affiliation  

Mycorrhizal fungi have considerable effects on soil carbon (C) storage, as they control the decomposition of soil organic matter (SOM), by modifying the amount of soil nitrogen (N) available for free-living microbes. Through their access to organic N, ectomycorrhizal (ECM) fungi compete with free-living soil microbes; this competition is thought to slow down SOM decomposition. However, arbuscular mycorrhizal (AM) fungi cannot decompose SOM, and therefore must wait for N to first be processed by free-living microbes. It is unclear what form of N the ECM fungi and free-living microbes compete for, or which microbial groups compete for N with ECM fungi. To investigate this, we focused on the N transformation steps (i.e., the degradation of high-molecular-weight organic matter, mineralization, and nitrification) and the microbes driving each step. Simple comparisons between AM forests and ECM forests are not sufficient to assert that mycorrhizal types would determine the N transformation steps in soil, because soil physiochemistry, which strongly affects N transformation steps, differs between the forests. We used an aridity gradient with large differences in soil moisture, pH, and SOM quantity and quality, to distinguish the mycorrhizal and physicochemical effects on N transformation. Soil samples (0-10 cm depth) were collected from AM-symbiotic black locust forests under three aridity levels, and from ECM-symbiotic oak forests under two aridity levels. Soil physicochemical properties, extractable N dynamics and abundance, composition, and function of soil microbial communities were measured. In ECM forests, the ammonia-oxidizing prokaryotic abundance was low, whereas that of ECM fungi was high, resulting in lower nitrate N content than in AM forests. Since ECM forests did not have lower saprotrophic fungal abundance and prokaryotic decompositional activity than the AM forests, the hypothesis that ECM fungi could reduce SOM decay and ammonification by free-living microbes, might not hold in ECM forests. However, the limitation of ECM fungi on nitrate N production would result in a feedback that will accelerate plant dependence on these fungi, thereby raising soil C storage through an increase in the ECM biomass and plant C investment in soils.

中文翻译:

土壤氮循环由菌根和氨氧化原核生物之间的竞争决定

菌根真菌对土壤碳 (C) 储存有相当大的影响,因为它们通过改变可用于自由生活微生物的土壤氮 (N) 的量来控制土壤有机质 (SOM) 的分解。通过获取有机氮,外生菌根 (ECM) 真菌与自由生活的土壤微生物竞争;这种竞争被认为会减慢 SOM 的分解速度。然而,丛枝菌根 (AM) 真菌不能分解 SOM,因此必须等待 N 首先被自由生活的微生物处理。目前尚不清楚 ECM 真菌和自由生活微生物竞争哪种形式的 N,或者哪些微生物群与 ECM 真菌竞争 N。为了对此进行研究,我们专注于 N 转化步骤(即高分子量有机物的降解、矿化和硝化)以及驱动每个步骤的微生物。AM 森林和 ECM 森林之间的简单比较不足以断言菌根类型将决定土壤中的 N 转化步骤,因为强烈影响 N 转化步骤的土壤物理化学在森林之间是不同的。我们使用土壤水分、pH 值和 SOM 数量和质量差异很大的干旱梯度来区分菌根和理化对 N 转化的影响。土壤样品(0-10 厘米深度)是从三个干旱级别下的 AM-共生黑刺槐林和两个干旱级别下的 ECM-共生橡树林中收集的。测量了土壤理化特性、可提取氮动态和土壤微生物群落的丰度、组成和功能。在 ECM 森林中,氨氧化原核生物丰度较低,而 ECM 真菌的含量较高,导致硝酸盐 N 含量低于 AM 森林。由于 ECM 森林的腐生真菌丰度和原核分解活性并不低于 AM 森林,因此 ECM 真菌可以通过自由生活的微生物减少 SOM 腐烂和氨化的假设在 ECM 森林中可能不成立。然而,ECM 真菌对硝酸盐 N 生产的限制将导致反馈,这将加速植物对这些真菌的依赖,从而通过增加 ECM 生物量和植物 C 在土壤中的投资来提高土壤 C 储存。ECM 真菌可以通过自由生活的微生物减少 SOM 腐烂和氨化的假设在 ECM 森林中可能不成立。然而,ECM 真菌对硝酸盐 N 生产的限制将导致反馈,这将加速植物对这些真菌的依赖,从而通过增加 ECM 生物量和植物 C 在土壤中的投资来提高土壤 C 储存。ECM 真菌可以通过自由生活的微生物减少 SOM 腐烂和氨化的假设在 ECM 森林中可能不成立。然而,ECM 真菌对硝酸盐 N 生产的限制将导致反馈,这将加速植物对这些真菌的依赖,从而通过增加 ECM 生物量和植物 C 在土壤中的投资来提高土壤 C 储存。
更新日期:2020-01-23
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