酯酶同工酶在食用菌菌种选育中的应用研究

采用聚丙烯酰胺凝胶电泳 ,分析了不同培养时间和不同培养基种类对平菇、杏鲍菇、白灵菇酯酶同工酶的影响 ,结果表明在不同培养时间和不同培养基条件下 ,酯酶同工酶酶谱的酶带呈现不同的多态性 ,由此提示同工酶在食用菌菌种选育的应用上应固定最佳培养时间及最适培养基种类 ,并在所有操作条件一致的情况下 ,才能得到稳定准确的分析结果     

Environmental stress response limits microbial necromass contributions to soil organic carbon

The majority of dead organic material enters the soil carbon pool following initial incorporation into microbial biomass. The decomposition of microbial necromass carbon (C) is, therefore, an important process governing the balance between terrestrial and atmospheric C pools. We tested how abiotic stress (drought), biotic interactions (invertebrate grazing) and physical disturbance influence the biochemistry (C:N ratio and calcium oxalate production) of living fungal cells, and the subsequent stabilization of fungal-derived C after senescence. We traced the fate of ¹³C-labeled necromass from ‘stressed’ and ‘unstressed’ fungi into living soil microbes, dissolved organic carbon (DOC), total soil carbon and respired CO₂. All stressors stimulated the production of calcium oxalate crystals and enhanced the C:N ratios of living fungal mycelia, leading to the formation of ‘recalcitrant’ necromass. Although we were unable to detect consistent effects of stress on the mineralization rates of fungal necromass, a greater proportion of the non-stressed (labile) fungal necromass C was stabilised in soil. Our finding is consistent with the emerging understanding that recalcitrant material is entirely decomposed within soil, but incorporated less efficiently into living microbial biomass and, ultimately, into stable SOC.     

Fungal and bacterial N2O production regulated by soil amendments of simple and complex substrates

Fungal N₂O production results from a respiratory denitrification that reduces NO₃⁻/NO₂⁻ in response to the oxidation of an electron donor, often organic C. Despite similar heterotrophic nature, fungal denitrifiers may differ from bacterial ones in exploiting diverse resources. We hypothesized that complex C compounds and substances could favor the growth of fungi over bacteria, and thereby leading to fungal dominance for soil N₂O emissions. Effects of substrate quality on fungal and bacterial N₂O production were, therefore, examined in a 44-d incubation after soils were amended with four different substrates, i.e., glucose, cellulose, winter pea, and switchgrass at 2 mg C g⁻¹ soil. During periodic measurements of soil N₂O fluxes at 80% soil water-filled pore space and with the supply of KNO₃, substrate treatments were further subjected to four antibiotic treatments, i.e., no antibiotics or soil addition of streptomycin, cycloheximide or both so that fungal and bacterial N₂O production could be separated. Up to d 8 when antibiotic inhibition on substrate-induced microbial activity and/or growth was still detectable, bacterial N₂O production was generally greater in glucose- than in cellulose-amended soils and also in winter pea- than in switchgrass-amended soils. In contrast, fungal N₂O production was more enhanced in soils amended with cellulose than with glucose. Therefore, fungal-to-bacterial contribution ratios were greater in complex than in simple C substrates. These ratios were positively correlated with fungal-to-bacterial activity ratios, i.e., CO₂ production ratios, suggesting that substrate-associated fungal or bacterial preferential activity and/or growth might be the cause. Considering substrate depletion over time and thereby becoming limited for microbial N₂O production, measurements of soil N₂O fluxes were also carried out with additional supply of glucose, irrespective of different substrate treatments. This measurement condition might lead to potentially high rates of fungal and bacterial N₂O production. As expected, bacterial N₂O production was greater with added glucose than with added cellulose on d 4 and d 8. However, this pattern was broken on d 28, with bacterial N₂O production lower with added glucose than with added cellulose. In contrast, plant residue impacts on soil N₂O fluxes were consistent over 44-d, with greater bacterial contribution, lower fungal contribution, and thus lower fungal-to-bacterial contribution ratios in winter pea- than in switchgrass-amended soils. Real-time PCR analysis also demonstrated that the ratios of 16S rDNA to ITS and the copy numbers of bacterial denitrifying genes were greater in winter pea- than in switchgrass-amended soils. Despite some inconsistency found on the impacts of cellulose versus glucose on fungal and bacterial leading roles for N₂O production, the results generally supported the working hypothesis that complex substrates promoted fungal dominance for soil N₂O emissions.     

Compartmentalization of the soil animal food web as indicated by dual analysis of stable isotope ratios (N/N and C/C)

The soil animal food web has become a focus of recent ecological research but trophic relationships still remain enigmatic for many taxa. Analysis of stable isotope ratios of N and C provides a powerful tool for disentangling food web structure. In this study, animals, roots, soil and litter material from a temperate deciduous forest were analysed. The combined measurement of δ¹⁵N and δ¹³C provided insights into the compartmentalization of the soil animal food web. Leaf litter feeders were separated from animals relying mainly on recent belowground carbon resources and from animals feeding on older carbon. The trophic pathway of leaf litter-feeding species appears to be a dead end, presumably because leaf litter feeders (mainly diplopods and oribatid mites) are unavailable to predators due to large size and/or strong sclerotization. Endogeic earthworms that rely on older carbon also appear to exist in predator-free space. The data suggest that the largest trophic compartment constitutes of ectomycorrhizal feeders and their predators. Additionally, there is a smaller trophic compartment consisting of predators likely feeding on enchytraeids and potentially nematodes.     

西北地区耕地土壤真菌DNA提取方法比较

由于西北土壤理化性质的复杂性和真菌特殊性,所以从土壤中提取真菌基因组DNA就相对细菌更困难。在2种常用的土壤微生物基因组DNA提取方法与在传统提取方法的基础上,结合了一种专门适用于真菌的提取方法进行了比较,并且利用真菌28SrDNA通用引物U1/U2进行扩增。三种提取方法比较结果表明:SDS法提取的DNA纯度最低,传统CTAB-SDS的DNA产量最低,实验室的提取方法既可以提高DNA产量又可以保证DNA的片段完整性,并且本实验室的提取方法扩增效果最好,可广泛应用于西北地区土壤真菌的分子生物学研究。     

高氮和NO2-对中亚热带森林土壤N2O和NO产生的影响

利用15N同位素标记方法,研究在两种水分条件即60％和90％ WHC下,添加硝酸盐(NH4NO3,N 300 mg kg-1)和亚硝酸盐(NaNO2,N 1 mg kg-1)对中亚热带天然森林土壤N2O和NO产生过程及途径的影响.结果表明,在含水量为60％ WHC的情况下,高氮输入显著抑制了N2O和NO的产生(p＜0.01);但当含水量增为90％ WHC后,实验9h内抑制N2O产生,之后转为促进.所有未灭菌处理在添加NO2-后高氮抑制均立即解除并大量产生N2O和NO,与对照成显著差异(p＜0.01),在60％ WHC条件下,这种情况维持时间较短(21 h),但如果含水量高(90％ WHC)这种情况会持续很长时间(2周以上),说明水分有效性的提高和外源NO2-在高氮抑制解除中起到重要作用.本实验中N2O主要来源于土壤反硝化过程,而且加入未标记NO2-后导致杂合的N2O(14N15NO)分子在实验21 h内迅速增加,表明这种森林土壤的反硝化过程可能主要是通过真菌的“共脱氮”来实现,其贡献率可多达80％以上.Spearman秩相关分析表明未灭菌土壤NO的产生速率与N2O产生速率成显著正相关性(p＜0.05),土壤含水量越低二者相关性越高.灭菌土壤添加NO2-能较未灭菌土壤产生更多的NO,但却几乎不产生N2O,表明酸性土壤的化学反硝化对NO的贡献要大于N2O.     

The influence of soil properties on the structure of bacterial and fungal communities across land-use types

Land-use change can have significant impacts on soil conditions and microbial communities are likely to respond to these changes. However, such responses are poorly characterized as few studies have examined how specific changes in edaphic characteristics do, or do not, influence the composition of soil bacterial and fungal communities across land-use types. Soil samples were collected from four replicated (n = 3) land-use types (hardwood and pine forests, cultivated and livestock pasture lands) in the southeastern US to assess the effects of land-use change on microbial community structure and distribution. We used quantitative PCR to estimate bacterial–fungal ratios and clone libraries targeting small-subunit rRNA genes to independently characterize the bacterial and fungal communities. Although some soil properties (soil texture and nutrient status) did significantly differ across land-use types, other edaphic factors (e.g., pH) did not vary consistently with land-use. Bacterial–fungal ratios were not significantly different across the land-uses and distinct land-use types did not necessarily harbor distinct soil fungal or bacterial communities. Rather, the composition of bacterial and fungal communities was most strongly correlated with specific soil properties. Soil pH was the best predictor of bacterial community composition across this landscape while fungal community composition was most closely associated with changes in soil nutrient status. Together these results suggest that specific changes in edaphic properties, not necessarily land-use type itself, may best predict shifts in microbial community composition across a given landscape. In addition, our results demonstrate the utility of using sequence-based approaches to concurrently analyze bacterial and fungal communities as such analyses provide detailed phylogenetic information on individual communities and permit the robust assessment of the biogeographical patterns exhibited by soil microbial communities.     

不同程度重金属污染对稻田土壤真菌群落结构的影响

为了研究土壤真菌群落结构在不同程度重金属污染中的变化,本文用Illumina Hi Seq高通量测序技术分析了苏南地区某金属冶炼厂和加工产业区的重金属污染水稻土的真菌群落结构,发现不同程度重金属污染对水稻季土壤真菌丰度和群落结构均有显著影响。经过真菌主成分分析发现,PC1影响因素对样品处理差异的贡献率是35.96%,PC2影响因素对样品处理差异的贡献率是21.48%;通过真菌冗余度分析发现,重金属Pb和Cu污染对土壤真菌群落结构的影响显著;通过对真菌属水平的相对丰度分析表明,重金属污染会显著降低敏感真菌的丰度,如被孢霉属相对丰度最高降低了87.50%、木霉属最高降低了99.46%、离壳菌属和菇属最高降低了100.00%,同时耐性真菌的相对丰度会提高,如类球囊霉属的相对丰度最高增加了98倍、四枝孢霉属最高增加了56倍、根囊壶菌属最高增加了2.62倍。综上所述,不同程度重金属污染对稻田土壤真菌群落结构有显著影响,且随着污染程度的增加,抗逆真菌相对数量和种类显著增加,敏感真菌的相对数量急剧减少,真菌群落结构随着重金属污染程度增加进一步分化。     

高砷硫铁矿周边农田土壤砷分布及真菌群落结构特征研究

本文主要以高砷硫铁矿区周边农田中的真菌群落为研究对象,研究利用Miseq高通量测序技术系统的分析了矿区周边不同区域土壤中真菌的群落特征,对硫铁矿区周边土壤真菌群落的适应机制进行了探究分析。结果表明,(1)砷、铁复合污染土壤可促使土壤真菌丰富度降低,而对土壤真菌多样的影响则表现为先促进后抑制;(2)砷、铁复合污染抑制土壤中Ascomycota(子囊菌门)代谢,促进Basidiomycota(担子菌门)代谢,而对Zygomycota(接合菌门)则表现为低浓度促进,高浓度抑制,对Fusarium(镰刀菌属)、Pseudallescheria(假霉样真菌属)、Cryptococcus(隐球菌属)也呈现“低浓度促进、高浓度抑制”作用;(3)砷、铁的复合物污染使土壤中真菌群落结构产生了明显差异,环境因子对土壤环境真菌群落结构差异影响大小依次为有效砷、总砷、总铁。     

Microbial populations,enzyme activities and nitrogen-phosphorus-potassium enrichment in earthworm casts and in the surrounding soil of a pineapple plantation

Summary Total populations of bacteria and fungi, dehydrogenase activity (as a measure of total potential microbial activity), and urease and phosphatase activities were determined in earthworm casts and surrounding laterite soils planted to pineapple. The casts contained higher microbial populations and enzyme activities than the soil. Except for fungal populations, statistically significant (P = 0.05) increases were found in all other parameters. Microbial populations and enzyme activities showed similar temporal trends with higher values in spring and summer and lower values in winter. The earthworm casts contained higher amounts of N, P, K and organic C than the soil (P = 0.05). Selective feeding by earthworms on organically rich substrates, which break down during passage through the gut, is likely to be responsible for the higher microbial populations and greater enzyme activity in the casts.