氮在自然界中的循環(huán)轉(zhuǎn)化過程，是生物圈內(nèi)基本的物質(zhì)循環(huán)之一,。土壤中通過氮的獲取和損失進行著反覆循環(huán),。大氣中的氮經(jīng)微生物等作用而進入土壤，為動植物所利用,，最終又在微生物的參與下返回大氣中,。
紐約大學(xué)的科學(xué)家發(fā)現(xiàn),，在地球上普遍存在，對生態(tài)環(huán)境來說很重要的真菌在這個關(guān)鍵的自然循環(huán)-氮循環(huán)中亦承擔(dān)了重要的角色,。
幾乎所有的植物都與它們根部的這種叫菌根真菌（mycorrhizas fungi）的微生物共生,，而均根真菌中最常見的一種類型是叢枝菌根真菌（arbuscular mycorrhiza fungi ，AMF）,，其與地球上2/3的植物物種共生,。與大部分的真菌不同，AM真菌從糖中獲得能量給養(yǎng),，并在它們的共生體上生長,，而不是在有機體的分解物上。不過,，令人驚奇的是,，研究人員發(fā)現(xiàn)，AM真菌能夠在腐爛的有機物上茁壯成長,，并從中獲得大量的氮,。分析結(jié)果表明，在根部真菌數(shù)量龐大,，因此植物根部也存在著同樣多的氮,。另外，真菌壽命比根的生命短暫的多,，因此這項發(fā)現(xiàn)表明了在生態(tài)系統(tǒng)中氮循環(huán)的速度,。
這項研究是由約克大學(xué)生物學(xué)系的Angela Hodge博士和Alastair Fitter教授共同完成的，研究結(jié)果發(fā)布在最新一期的Proceedings of the National Academy of Sciences雜志上,。
由于這些真菌不能在純凈的培養(yǎng)皿中生長,，研究人員創(chuàng)造了一個微生態(tài)系統(tǒng)，將真菌和植物根部分離,，但允許它們獲得一片有機物,，并用穩(wěn)定的同位素追蹤氮和碳的移動。結(jié)果表明,，該真菌能夠更好地利用被分解的有機物,，相比于重新找到新的植物共生。
此外,，降低真菌碳的供應(yīng)并不會減少真菌在有機物中的生長,。Hodge博士表示，很久以前他們就知道這種真菌在磷循環(huán)中承擔(dān)了重要的作用,，而現(xiàn)在的這項研究表明其在氮循環(huán)中同樣也具有重要的作用,，或能為開發(fā)農(nóng)學(xué)新產(chǎn)品提供新的思路。(生物谷Bioon.com)
生物谷推薦原文出處：
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.
