生命科学学院知识库

全球氮沉降在短短的三十年时间内涨幅近一倍，对全球生物多样性及生态系统稳定性造成了严重的威胁。丛枝菌根（Arbuscular mycorrhiza, AM）真菌是一类重要的土壤微生物，能与绝大部分陆生植物物种的根系形成互惠共生体。AM真菌可为植物提供氮（N）、磷（P）等矿质元素，对植物生长、元素循环及生态系统可持续性具有重要的调控作用。已有研究表明，土壤N肥力的增加会改变AM真菌与植物之间的共生关系，但在土壤N增加的情境下，AM真菌如何影响植物生长及群落组成？这一问题目前仍所知甚少。本研究通过在高寒草甸生态系统中设立长期施N（0、5、10和15 g N m-2 yr-1；对应为N0、N5、N10及N15）及菌根抑制（添加及不添加苯菌灵）交互处理样地，结合在温室内设置施N（0、50和100 mg N kg-1土；对应为N0、N1及N2）及AM真菌接种（接种及不接种Funneliformis coronaturm）短期实验处理（供试植物：高粱，Sorghum haipense），研究了不同土壤N肥力下AM真菌对植物的影响作用。主要研究结果如下：
（1）连续6年的野外施N及苯菌灵添加均显著降低了AM真菌的总侵染率、泡囊侵染率以及根外菌丝密度。施N及苯菌灵处理均显著增加植物群落的地上生物量和植物N含量，但两种处理对植物地下生物量及植物P含量均无显著影响。植物群落的菌根生长效应（MGR）在N5处理中为显著负效应，N吸收效应（MNR）在N5和N10处理中为显著负效应，而磷吸收效应（MPR）则不受各施N处理的显著影响。施N及苯菌灵处理均显著降低了植物群落的物种丰富度，且对植物群落的物种组成有显著的影响。（2）通过4个月的温室实验处理，结果表明，施N显著降低了高粱根系中的AM真菌总侵染率和泡囊侵染率；同时，施N显著增加了高粱地上生物量，但却降低了地下生物量。在三种施N处理中，接种AM真菌均显著提高了高粱的地上生物量、植物总N和植物总P含量，且施N及AM真菌接种对高粱生物量和总N含量均存在显著交互作用。高粱的菌根生长效应（MGR）、N吸收效应（MNR）以及磷吸收效应（MPR）在各施N处理中大多表现为正效应（仅有N1条件下的MNR为无显著正效应），且均随土壤N肥力的上升呈现先降后升的趋势。
综上，本研究发现土壤N肥力的增加会显著降低AM真菌侵染率；在植物个体水平上，AM真菌的侵染促进了植物生物量的增加及N、P元素的吸收，且植物的菌根效应随土壤N肥力的上升均呈现先下降后上升的趋势；在群落水平上，虽然土壤N肥力对植物的菌根生长及N、P吸收响应无明显影响，但AM真菌的存在能缓解施N对植物物种多样性的负影响作用，表明AM真菌对N沉降情境下的植物多样性维持具有一定的作用。

Global N deposition has nearly doubled in a short period of 30 years, posing a serious threat to global biodiversity and ecosystem stability. Arbuscular mycorrhiza (AM) fungi are an important type of soil micro-organism that can form reciprocal symbiosis with the root system of most terrestrial plant species. AM fungi can provide plants with mineral elements such as nitrogen (N) and phosphorus (P), which have important regulatory effects on plant growth, element cycling, and ecosystem sustainability. Studies have shown that an increase in fertility of soil N will change the symbiotic relationship between AM fungi and plants, but how does AM fungi affect plant growth and community composition in the situation of increasing soil N? This issue is still poorly understood.This study based on a long-term N (0, 5, 10, and 15 g N m-2 yr-1; corresponding to N0, N5, N10, and N15) and mycorrhizal inhibition (with and without benomyl) interactively treats plots in the alpine meadow ecosystem, and combined a short-term experimental treatment with N (0, 50, and 100 mg N kg-1 soil; corresponding to N0, N1, and N2) and AM fungus inoculation (inoculation and non-inoculation of Funineliformis coronaturm) in the greenhouse (The plant under test: Sorghum haipense), which studied the effects of arbuscular mycorrhizal fungi on plants under different soil N fertility. The main results are as follows:
(1) The total length colonization, vesicle colonization, and extraradical hyphal length density were significantly decreased in field-applied N and benomyl addition for 6 consecutive years. Both N application and benomyl treatment significantly increased the above-ground biomass and plant N content of plant communities, but both treatments had no significant effect on plant biomass and plant P content. The mycorrhizal growth effect (MGR) of plant community was significantly negative in N5 treatment, Nitrogen uptake effect (MNR) was a significant negative effect in N5 and N10 treatments, and the phosphorus uptake effect (MPR) was not affected significantly by N treatments. Both nitrogen application and benomyl treatment significantly reduced the species richness of plant communities and had a significant impact on the species composition of plant communities.
(2) After 4 months of greenhouse treatment, the results showed that applying N significantly reduced the total length colonization and vesicle colonization of AM fungi in sorghum roots; at the same time, N application significantly increased the aboveground biomass of Sorghum, however, it reduced the underground biomass. In the three N treatments, inoculation of AM fungi significantly increased the above-ground biomass, plant total N and plant total P content of sorghum, and there was a significant interaction between N and AM inoculation on sorghum biomass and total N content. The mycorrhizae growth effect (MGR), nitrogen uptake effect (MNR), and phosphorus uptake effect (MPR) of sorghum exhibited positive effects in most N treatments (only N1 had no significant positive effect on MNR), and with the increase of soil N fertility, it showed the tendency of falling first and then rising.
In summary, the study found that the increase of soil N fertility will significantly reduce the root length colonization of AM fungi; At the individual plant level, AM fungi promoted the increase of plant biomass and the absorption of N and P elements, and the mycorrhizal effect(MR) of plants showed a tendency of falling first and then rising.with the increase of soil N fertility. At the community level, although the soil N fertility had no significant effect on the mycorrhiza growth and N, P uptake response of plants, the presence of AM fungi could alleviated the negative effect of N on plant species diversity, indicating that AM fungi have a certain effect on the maintenance of plant diversity under N deposition.