荒漠油蒿（Artemisia ordosica）根围AM真菌分布与土壤酶活性

于2007年10月在油蒿(Artemisia ordosica)集中分布区选取4个典型样地,分别从0～10cm、10～20cm、20～30cm、30～40cm和40～50cm土层采集根围土样,分离其丛枝菌根(arbuscular mycorrhiza,AM)真菌并测定了3种土壤酶活性.结果表明,在各样地0～50cm土层中油蒿根系AM真菌菌丝定殖率均很高,有典型的泡囊与丛枝结构.菌丝定殖率与泡囊定殖率呈显著正相关,但菌丝、泡囊和丛枝定殖率与AM真菌孢子密度和土壤酶活性之间都无相关性;孢子密度在不同样地及采样深度间差异明显,与土壤有机质、速效磷和速效氮含量都呈一定正相关关系.孢子密度与脲酶和酸性磷酸酶活性有显著或极显著相关关系,与碱性磷酸酶活性之间的相关性受到土壤pH的显著影响.孢子密度的峰值出现在0～10cm表层土,并随土壤剖面深度增加而降低.土壤酶活性在土壤垂直剖面显示与孢子密度同样的规律.不同样地间AM真菌分布及油蒿根系定殖率的差异表明,油蒿与AM真菌之间有良好共生性,对维护荒漠生态环境系统结构的完整性具有重要意义.     

丛枝菌根真菌N代谢与C代谢研究进展

N元素是植物需求量最大的元素,丛枝菌根（arbuscular mycorrhizal,AM）真菌可以与大部分植物形成共生关系,通过根外菌丝促进植物对N元素的吸收。C元素也是AM真菌完成其生命过程的必备元素,AM真菌依赖宿主植物提供所必需的C源。近年来对AM真菌的N代谢途径的研究有了新的进展,AM真菌中与代谢途径相关酶的发现,相关基因的克隆,更进一步验证了N元素在AM真菌中的代谢途径。对C代谢及与N代谢的关系也有所涉及。综述近几年文献,总结了AM真菌的最新研究进展。     

The arbuscular mycorrhizal symbiosis links N mineralization to plant demand

Arbuscular mycorrhizal (AM) fungi facilitate inorganic N (NH₄ ⁺ or NO₃ ⁻) uptake by plants, but their role in N mobilization from organic sources is unclear. We hypothesized that arbuscular mycorrhizae enhance the ability of a plant to use organic residues (ORs) as a source of N. This was tested under controlled glasshouse conditions by burying a patch of OR in soil separated by 20-μm nylon mesh so that only fungal hyphae can pass through it. The fate of the N contained in the OR patch, as influenced by Glomus claroideum, Glomus clarum, or Glomus intraradices over 24 weeks, was determined using ¹⁵N as a tracer. AM fungal species enhanced N mineralization from OR to different levels. N recovery and translocation to Russian wild rye by hyphae reached 25% of mineralized N in G. clarum, which was most effective despite its smaller extraradical development in soil. Mobilization of N by G. clarum relieved plant N deficiency and enhanced plant growth. We show that AM hyphae modify soil functioning by linking plant growth to N mineralization from OR. AM species enhance N mineralization differentially leading to species-specific changes in the quality of the soil environment (soil C-to-N ratio) and structure of the soil microbial community.     

Dynamics within mutualism and the maintenance of diversity: inference from a model of interguild frequency dependence

Numerical models have suggested that the dynamics within mutualisms are not important for the maintenance of diversity. In this study it is demonstrated that the dynamics within mutualism can contribute to the maintenance of diversity within its participants, using a general model of frequency dependence between two mutualistically interacting guilds. Specifically, it is demonstrated that while mutualisms may exhibit positive feedback in density, there may be a negative feedback within a mutualism as a result of the change in composition within the interacting guild. Such a negative feedback results from an asymmetry in the delivery of benefit between participants of the mutualism that generates a negative interguild frequency dependence. This dynamic contributes to the maintenance of diversity within the interacting guilds. Conditions are identified for the maintenance of diversity and the maximization of benefit from mutualism within the context of the model. The utility of these conditions for testing hypotheses using data from the mutualistic interaction between plants and mycorrhizal fungi is then demonstrated.     

Alteration of Soil Carbon Pools and Communities of Mycorrhizal Fungi in Chaparral Exposed to Elevated Carbon Dioxide

We examined the effects of atmospheric carbon dioxide (CO₂) enrichment on belowground carbon (C) pools and arbuscular mycorrhizal (AM) fungi in a chaparral community in southern California. Chambers enclosing intact mesocosms dominated by Adenostoma fasciculatum were exposed for 3.5 years to CO₂ levels ranging from 250 to 750 ppm. Pools of total C in bulk soil and in water-stable aggregates (WSA) increased 1.5- and threefold, respectively, between the 250- and 650-ppm treatments. In addition, the abundance of live AM hyphae and spores rose markedly over the same range of CO₂, and the community composition shifted toward dominance by the AM genera Scutellospora and Acaulospora. Net ecosystem exchange of C with the atmosphere declined with CO₂ treatment. It appears that under CO₂ enrichment, extra C was added to the soil via AM fungi. Moreover, AM fungi were predominant in WSA and may shunt C into these aggregates versus bulk soil. Alternatively, C may be retained longer within WSA than within bulk soil. We note that differences between the soil fractions may act as a potential feedback on C cycling between the soil and atmosphere.     

可降解和不可降解微塑料对滨海湿地土壤有机碳矿化的影响

微塑料（MPs）作为一种新型污染物已经在土壤中被广泛发现。然而;MPs对土壤有机碳（SOC）矿化的影响;尤其在不同类型（可降解和不可降解）MPs之间存在怎样的差异还不清楚;相关的作用机制也有待进一步揭示。本研究通过向滨海湿地土壤中分别添加聚乳酸（PLA）（可降解）和聚乙烯（PE）（不可降解）MPs;建立了为期100天的室内土壤培养实验。结果表明:两种MPs添加均显著降低了CO₂累积排放量;并且PE-MPs的抑制效应显著强于PLA-MPs。通过对土壤物理、化学和微生物指标分析发现:MPs添加显著提高了SOC含量和土壤团聚体稳定性;而降低了溶解性有机碳、NH₄⁺-N和NO₃^--N的含量;MPs添加降低了土壤细菌群落多样性和碳分解相关细菌和酶的活性。因此;MPs添加导致SOC矿化可利用性底物降低、土壤团聚体物理保护增强和SOC矿化相关细菌和酶活性降低;是抑制SOC矿化（CO₂排放）的主要机制。总体而言;与可降解的PLA-MPs相比;不可降解的PE-MPs对土壤物理、化学和微生物指标的影响程度更为显著。本研究结果能够为深入了解MPs在滨海湿地土壤中的环境效应提供重要的数据支撑和理论依据。     

Distribution of dominant arbuscular mycorrhizal fungi among five plant species in undisturbed vegetation of a coastal grassland

Most plant species in mixed grassland vegetation are colonized by arbuscular mycorrhizal (AM) fungi. Previous studies have reported differences in host preferences among AM fungi, although the fungi are known to lack host specificity. In the present study, the distribution of phylogenetic groups of AM fungi belonging to a clade of Glomus species was studied in five plant species from a coastal grassland in Denmark. The occurrence of the fungi was determined by PCR analyses of fungal large subunit ribosomal DNA sequences amplified from root fragments using a specific primer set. The results showed that the dominant Glomus species were able to colonize all the studied plant species, supporting the view that the AM fungi represent a large underground interconnecting mycelial network.     

Elevated CO2 may impair the beneficial effect of arbuscular mycorrhizal fungi on the mineral and phytochemical quality of lettuce

Arbuscular mycorrhizal fungi (AMF) can improve growth and nutritional quality of greenhouse‐grown lettuces cultivated at ambient CO₂. Moreover, mycorrhizal symbiosis is predicted to be important in defining plant responses to elevated atmospheric CO₂ concentrations. Our main objective was to assess the effects of elevated CO₂ on growth and nutritional quality of greenhouse‐grown lettuces inoculated or not with AMF. Results showed that the accumulation of mineral nutrients (e.g. P, Cu, Fe) and antioxidant compounds (carotenoids, phenolics, anthocyanins, ascorbate) induced by AMF in leaves of lettuces cultivated at ambient CO₂ may diminish or disappear under elevated CO₂. It is hypothesized that a relevant quantity of photoassimilates could be used for improving shoot growth and spreading mycorrhizal colonization in detriment to the secondary metabolism. However, important differences can be found among different cultivars of lettuces.     

Arbuscular mycorrhizae and terrestrial ecosystem processes

Arbuscular mycorrhizal fungi (AMF; phylum Glomeromycota) are ubiquitous in terrestrial ecosystems. Despite their acknowledged importance in ecology, most research on AMF has focused on effects on individual plant hosts, with more recent efforts aimed at the level of the plant community. Research at the ecosystem level is less prominent, but potentially very promising. Numerous human‐induced disturbances (including global change and agro‐ecosystem management) impinge on AMF functioning; hence study of this symbiosis from the ecosystem perspective seems timely and crucial. In this paper, I discuss four (interacting) routes via which AMF can influence ecosystem processes. These include indirect pathways (through changes in plant and soil microbial community composition), and direct pathways (effects on host physiology and resource capture, and direct mycelium effects). I use the case study of carbon cycling to illustrate the potentially pervasive influence of AMF on ecosystem processes. A limited amount of published research on AMF ecology is suited for direct integration into ecosystem studies (because of scale mismatch or ill‐adaptation to the ‘pools and flux’ paradigm of ecosystem ecology); I finish with an assessment of the tools (experimental designs, response variables) available for studying mycorrhizae at the ecosystem scale.     

AMF和PGPR联合修复菲和芘污染土壤的效应

丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）与根围促生细菌（plant growth-promoting rhizobacteria,PGPR）联合降解有毒有机物、修复污染土壤和促进植物生长的作用倍受关注。本试验旨在探究AMF与PGPR联合降解土壤中菲和芘的效应,以菲和芘1:1混合处理浓度各0、50mg/kg、100mg/kg和150mg/kg下对高羊茅Festuca elata接种AMF根内根孢囊霉Rhizophagus intraradices（Ri）、变形球囊霉Glomus versiforme（Gv）、PGPR荧光假单胞菌Pseudomonas fluorescens Ps2-6、芽孢杆菌Bacillus velezensis Ps3-2、Ri+Ps2-6、Ri+Ps3-2、Gv+Ps2-6、Gv+Ps3-2和不接种对照共36个处理。结果表明,供试AMF增加了PGPR的定殖数量;接种PGPR则显著提高AMF的侵染率。AMF、PGPR或AMF+PGPR处理均显著降低土壤中菲和芘含量,促进植物对土壤中菲和芘的吸收,显著提高高羊茅根系和叶片内的菲和芘含量。在土壤中菲和芘100mg/kg和150mg/kg水平下,Gv与Ps2-6及Ri与Ps2-6能相互促进对土壤中菲和芘的去除效应,其中接种Gv+Ps2-6组合处理的去除率最高,达到95%-98%,土壤中多酚氧化酶、脱氢酶和过氧化氢酶活性显著高于单接种处理和不接种对照,而酸性磷酸酶活性变化则表现为相反趋势。其中以Gv+Ps2-6组合处理的多酚氧化酶活性最高,为0.17mg/g,是不接种对照的1.9倍;脱氢酶和过氧化氢酶活性分别达到1.32µg/(g·h)和1.81mL/g;酸性磷酸酶活性则比不接种对照土壤降低27%-45%;易提取球囊霉素相关土壤蛋白含量和总球囊霉素相关土壤蛋白含量分别是不接种对照的1.6倍和1.5倍。