氮在自然界中的循环转化过程，是生物圈内基本的物质循环之一。土壤中通过氮的获取和损失进行着反覆循环。大气中的氮经微生物等作用而进入土壤，为动植物所利用，最终又在微生物的参与下返回大气中。
纽约大学的科学家发现，在地球上普遍存在，对生态环境来说很重要的真菌在这个关键的自然循环-氮循环中亦承担了重要的角色。
几乎所有的植物都与它们根部的这种叫菌根真菌（mycorrhizas fungi）的微生物共生，而均根真菌中最常见的一种类型是丛枝菌根真菌（arbuscular mycorrhiza fungi ，AMF），其与地球上2/3的植物物种共生。与大部分的真菌不同，AM真菌从糖中获得能量给养，并在它们的共生体上生长，而不是在有机体的分解物上。不过，令人惊奇的是，研究人员发现，AM真菌能够在腐烂的有机物上茁壮成长，并从中获得大量的氮。分析结果表明，在根部真菌数量庞大，因此植物根部也存在着同样多的氮。另外，真菌寿命比根的生命短暂的多，因此这项发现表明了在生态系统中氮循环的速度。
这项研究是由约克大学生物学系的Angela Hodge博士和Alastair Fitter教授共同完成的，研究结果发布在最新一期的Proceedings of the National Academy of Sciences杂志上。
由于这些真菌不能在纯净的培养皿中生长，研究人员创造了一个微生态系统，将真菌和植物根部分离，但允许它们获得一片有机物，并用稳定的同位素追踪氮和碳的移动。结果表明，该真菌能够更好地利用被分解的有机物，相比于重新找到新的植物共生。
此外，降低真菌碳的供应并不会减少真菌在有机物中的生长。Hodge博士表示，很久以前他们就知道这种真菌在磷循环中承担了重要的作用，而现在的这项研究表明其在氮循环中同样也具有重要的作用，或能为开发农学新产品提供新的思路。(生物谷Bioon.com)
生物谷推荐原文出处：
PNAS doi: 10.1073/pnas.1005874107
Substantial nitrogen acquisition by arbuscular mycorrhizal fungi from organic material has implications for N cycling
Department of Biology, University of York, York YO10 5YW, United Kingdom
Arbuscular mycorrhizal (AM) fungi are obligate biotrophs that acquire carbon (C) solely from host plants. AM fungi can proliferate hyphae in, and acquire nitrogen (N) from, organic matter. Although they can transfer some of that N to plants, we tested the hypothesis that organic matter is an important N source for the AM fungi themselves. We grew pairs of plants with and without the AM fungus Glomus hoi in microcosms that allowed only the fungus access to a 15N/13C-labeled organic patch; in some cases, one plant was shaded to reduce C supply to the fungus. The fungal hyphae proliferated vigorously in the patch, irrespective of shading, and increased plant growth and N content; ~3% of plant N came from the patch. The extraradical mycelium of the fungus was N-rich (3–5% N) and up to 31% of fungal N came from the patch, confirming the hypothesis. The fungus acquired N as decomposition products, because hyphae were not 13C-enriched. In a second experiment, hyphae of both G. hoi and Glomus mosseae that exploited an organic material patch were also better able to colonize a new host plant, demonstrating a fungal growth response. These findings show that AM fungi can obtain substantial amounts of N from decomposing organic materials and can enhance their fitness as a result. The large biomass and high N demand of AM fungi means that they represent a global N pool equivalent in magnitude to fine roots and play a substantial and hitherto overlooked role in the nitrogen cycle.
