图1. 芒萁吸收铵态氮和硝态氮的速率。A：¹⁵N标记芒萁根段实验，B：野外¹⁵N标记芒萁实验

 图2.微宇宙控制实验中不同处理下铵态氮（A）和硝态氮（B）的浓度。P：仅栽种芒萁，P+E：栽种芒萁并添加蚯蚓，P+A：栽种芒萁并接种AMF，P+A+E：栽种芒萁并同时接种蚯蚓和AMF

根据“蚯蚓、植物和AMF对氮的供应和吸收在不同的氮形态上（铵态氮和硝态氮）有显著差异，从而影响蚯蚓和AMF对植物氮吸收的互作”的假设，近日，中国科学院华南植物园生态及环境科学中心博士研究生何新星，在导师傅声雷和张卫信的指导下，构建了三个独立但彼此关联的实验：室内稳定同位素15N标记芒萁根段实验、野外15N标记芒萁实验以及室内15N标记的微宇宙控制实验。通过室内芒萁根段标记和野外标记实验，发现芒萁无论是生理水平上还是野外土壤环境下皆倾向于吸收铵态氮。该研究以外来种蚯蚓南美岸蚓（Pontoscolex corethrurus）和林下蕨类植物芒萁（Dicranopteris dichotoma）为研究对象，其中南美岸蚓在是中国南亚热带和热带人工林中的支配种，芒萁是人工林林下的支配种。通过室内的微宇宙控制实验，发现接种南美岸蚓提高了土壤铵态氮的浓度，未影响硝态氮的浓度。接种菌根真菌（AMF）降低了土壤铵态氮浓度，对硝态氮无显著影响。同时接种AMF和蚯蚓芒萁氮吸收提高。单独接种蚯蚓未影响芒萁氮的吸收。单独接种AMF，芒萁的叶片和粗根中氮浓度提高，但总氮吸收量未受影响。以上研究表明，AMF帮助芒萁吸收了蚯蚓促进的铵态氮；由于蚯蚓促进的铵态氮是以“热点”的形式分布于土壤，无AMF协助时芒萁根系不能有效接触到蚯蚓促进的铵态氮“热点”，而无蚯蚓时土壤中较低浓度的铵态氮则限制了AMF向其宿主植物输送氮。在氮形态上的配合，是蚯蚓和AMF互作影响植物氮吸收的重要机制。

相关研究成果Soil Biology and Biochemistry上。该研究得到国家自然科学基金、广东省联合基金以及中科院创新团队国际合作项目等的资助。（来源：中国科学院华南植物园）

Cooperation of earthworm and arbuscular mycorrhizae enhanced plant N uptake by balancing absorption and supply of ammonia

Abstract   Earthworms and arbuscular mycorrhizal fungi (AMF) interact to regulate plant nitrogen (N) supply, but the mechanisms through which they affect plant N uptake are unclear. We hypothesized that earthworms, plants and the associated AMF exhibit different preferences for different forms of inorganic N (NH4+ and NO3−), which could regulate the effect of earthworms and AMF interaction on plant N acquisition. We outlined three independent but complementary experiments to test this hypothesis in the context of exotic earthworm, Pontoscolex corethrurus. The earthworm is dominating the plantation forests in subtropical and tropical regions of China, which have their understory dominated by the fern Dicranopteris dichotoma. By employing an excised root 15N incubation experiment and a field in situ 15N experiment, we found that the fern prefers to use NH4+ rather than NO3−. Then we did a 2 × 2 factorial microcosm experiment using AMF (Rhizophagus intraradices) and earthworms (P. corethrurus). The exotic earthworm increased soil NH4+ concentration but did not affect soil NO3− concentration, while the AMF decreased soil NH4+ concentration but had no effect on soil NO3− concentration. The increase in soil NH4+ induced by the earthworms was efficiently utilized by the AMF, and significantly increased the total N uptake by the fern. In contrast, the AMF alone increased the N concentration of leaves and coarse roots, but not the total plant N uptake, primarily due to the lower levels of available NH4+ compared with the earthworm treatments. The uninoculated fern did not benefit from the earthworm-induced increase in soil NH4+, suggesting that the root of the fern cannot access the ‘NH4+ hotspots’ created by the earthworms. Our work suggests that successful cooperation of earthworms and AMF on plant N uptake depends on the correct match in N-form.

原文链接：http://www.sciencedirect.com/science/article/pii/S0038071717306375#