Temporal and functional pattern of secreted enzyme activities in an ectomycorrhizal community

The ectomycorrhizal community of an oak forest has been monitored monthly throughout fifteen months. Eight enzymatic activities secreted by the ectomycorrhizal root tips and involved in the mobilization of nutrients from soil organic matter have been measured using microplate assays, resulting in potential activity patterns of individual fungal species. Both the species structure of the community and the specific activity level of each individual species changed with the season and soil horizon. This versatility may be an adaptative response of the ectomycorrhizal fungal community to a highly variable environment. The results also suggest that some ectomycorrhizal fungi behave as occasional saprobes and contribute to the decomposition of soil organic matter and nutrient cycling together with true saprotrophic fungi.     

Soil niche effect on species diversity and catabolic activities in an ectomycorrhizal fungal community

The species of an ectomycorrhizal (ECM) community were investigated in a temperate oak forest by morphotyping and ITS rDNA sequencing. Thirty-six ECM morphotypes were found at the site. The niche effect (as organic soil, mineral soil or dead woody debris artificially introduced in the soil) on the ECM community structure and on the potential catabolic activities of the most abundant morphotypes was studied. The morphotypes in each niche were subjected to enzymatic tests developed for hydrolytic and oxidative enzymes involved in the decomposition of organic compounds. The ECM community structure varied widely depending on the soil horizon or habitat patch. The species richness was higher in the A1 horizon than in the other niches. Different ECM species had different activity patterns for the eight enzymatic tests while co-occurring in the same niche. Catabolic activities also changed within species between niches. Dead woody debris were extensively colonized by two saprotrophic fungi (Megacollybia platyphylla and Armillaria sp.) and, in this particular niche, ECM morphotypes predominantly belonged to the genera Lactarius and Tomentella. These morphotypes showed high chitinase activities. This study suggested also that some ECM fungi could obtain nutrients via the chitin degradation of dead or live saprobes.     

Ectomycorrhizal and Saprotrophic Fungal Communities Vary Across mm-Scale Soil Microsites Differing in Phosphatase Activity

To understand nutrient cycling in soils, soil processes and microorganisms need be better characterized. To determine whether specific trophic groups of fungi are associated with soil enzyme activity, we used soil imprinting to guide mm-scale sampling from microsites with high and low phosphatase activities in birch/Douglas-fir stands. Study 1 involved sampling one root window per site at 12 sites of different ages (stands); study 2 was conducted at one of the stem-exclusion stands, at which 5 root windows had been installed. Total fungal and ectomycorrhizal (EM) fungal terminal-restriction fragment length polymorphism (TRFLP) fingerprints differed between high-and low-phosphatase activity microsites at 8 of 12 root windows across 12 sites. Where differences were detected, fewer EM fungi were detected in high-than low-phosphatase activity microsites. Using 5 root windows at one site, next-generation sequencing detected similar fungal communities across microsites, but the ratio of saprotrophic to EM fungal reads was higher in high-phosphatase activity microsites in the two windows that had low EM fungal richness. In windows with differences in fungal communities, both studies indicated that EM fungi were less successful than saprotrophic fungi in colonizing fine-scale, organic matter-rich microsites. Fine-scale sampling linked with in situ detection of enzyme activity revealed relationships between soil fungal communities and phosphatase activity that could not be observed at the scales employed by conventional approaches, thereby contributing to the understanding of fine-scale phosphorus cycling in forest soils.     

Relationship between soil enzyme activities, nutrient cycling and soil fungal communities in a northern hardwood forest

Soil fungi are highly diverse and act as the primary agents of nutrient cycling in forests. These fungal communities are often dominated by mycorrhizal fungi that form mutually beneficial relationships with plant roots and some mycorrhizal fungi produce extracellular and cell-bound enzymes that catalyze the hydrolysis of nitrogen (N)- and phosphorus (P)- containing compounds in soil organic matter. Here we investigated whether the community structure of different types of mycorrhizal fungi (arbuscular and ectomycorrhizal fungi) is correlated with soil chemistry and enzyme activity in a northern hardwood forest and whether these correlations change over the growing season. We quantified these relationships in an experimental paired plot study where white-tailed deer (access or excluded 4.5 yrs) treatment was crossed with garlic mustard (presence or removal 1 yr). We collected soil samples early and late in the growing season and analyzed them for soil chemistry, extracellular enzyme activity and molecular analysis of both arbuscular mycorrhizal (AM) and ectomycorrhizal/saprotrophic fungal communities using terminal restriction fragment length polymorphism (TRFLP). AM fungal communities did not change seasonally but were positively correlated with the activities of urease and leucine aminopeptidase (LAP), enzymes involved in N cycling. The density of garlic mustard was correlated with the presence of specific AM fungal species, while deer exclusion or access had no effect on either fungal community after 4.5 yrs. Ectomycorrhizal/saprotrophic fungal communities changed seasonally and were positively correlated with most soil enzymes, including enzymes involved in carbon (C), N and P cycling, but only during late summer sampling. Our results suggest that fine scale temporal and spatial changes in soil fungal communities may affect soil nutrient and carbon cycling. Although AM fungi are not generally considered capable of producing extracellular enzymes, the correlation between some AM taxa and the activity of N acquisition enzymes suggests that these fungi may play a role in forest understory N cycling.     

Potential for monoterpenes to affect ectomycorrhizal and saprotrophic fungal activity in coniferous forests is revealed by novel experimental system

The fungal community in coniferous forest soils plays a pivotal role in ecosystem processes such as decomposition and carbon and nutrient cycling. Both saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter and roots of some tree species. Previous work has noted the differential effects of monoterpenes on the mycelial growth of a range of both SP and ECM fungi when grown in artificial nutrient media. This study used a novel experimental system to assess the effect of environmentally relevant concentrations of monoterpenes on the activity of ECM and SP fungi grown on more natural substrata. Exposure of the ECM fungus Paxillus involutus (Batsch) Fr. to vapours of either α-pinene or β-pinene resulted in a significantly greater proportion of root tips being colonised by the fungus when it was grown with seedlings of Picea abies (L.) Karst. Exposure to monoterpenes resulted in a significant decrease in respiration rate of two species of litter degrading SP fungi, Mycena galopus var. candida J. E. Lange and Collybia butyracea (Bull.) P. Kumm. There was no difference in response between the two SP species, despite the fact that previous tests in liquid nutrient media, with monoterpenes at higher concentrations, indicated that one species was sensitive and one was not. The high volatility and low solubility of monoterpenes in water make them challenging to work with. The experimental system developed here, although still artificial, provides a bridge between pure culture studies in defined media and all the complexities of forest soils in the field, by allowing the exposure of fungi to environmentally relevant monoterpene concentrations in more natural substrata.     

Invertebrate grazing determines enzyme production by basidiomycete fungi

Extracellular enzymes produced by heterotrophic microorganisms in the soil are responsible for the decomposition of organic compounds. Basidiomycete fungi are the primary decomposer agents in temperate wooded ecosystems and contribute extensively to extracellular enzyme activity and nutrient mineralisation within soils. Growth and development of basidiomycete mycelia is influenced by soil-dwelling invertebrate grazers with potential implications for fungal activity and ecosystem functioning. The impacts of four invertebrate taxa belonging to Isopoda, Myriapoda, Collembola and Nematoda on the production of eight hydrolytic enzymes by four saprotrophic basidiomycetes (Phanerochaete velutina, Resinicium bicolor and two strains of Hypholoma fasciculare) were compared in a factorial microcosm study. Grazing generally increased enzyme production but invertebrates had species-specific impacts on enzyme activity. The magnitude of grazing influenced enzyme activity; macrofauna (woodlice and millipedes) induced the greatest responses. Enzymatic responses varied markedly between fungi. Grazing enhanced enzyme activity in the exploitative mycelial networks of P. velutina and H. fasciculare, while the opposite effects were observed in the explorative R. bicolor networks. The impacts of soil fauna on nutrient mineralisation depend on fungal community composition. β-glucosidase, cellobiohydrolase, N-acetylglucosaminidase, acid phosphatase and phosphodiesterase activities were affected most frequently by grazing and invertebrate activity, and thus had direct consequences for carbon, nitrogen and phosphorous cycling. The results indicate that invertebrate diversity and community composition may influence the spatial distribution and activity of extracellular enzymes with direct implications for nutrient mineralisation and trunover in woodland soils.     

Soil structural responses to alterations in soil microbiota induced by the dilution method and mycorrhizal fungal inoculation

This investigation examines the effect of manipulating soil microbial community composition and species richness on the development of soil structure over a seven month period in planted (with or without mycorrhizal fungi) and in unplanted macrocosms. The dilution method effectively resulted in soil communities with consistently contrasting levels of species (TRF) richness. In particular, the 10^?6 dilution of field soil resulted in less rich communities in bare unplanted soil than did the 10^?1 soil dilution. However, this was not the case in planted soils where root activity was a powerful influence on species richness. After seven months, principal components analysis (PCA) separated bacterial community composition primarily on planting regime; planted mycorrhizal, planted non-mycorrhizal and bare soil treatments all contained different bacterial community compositions. A consistent finding in planted and unplanted soils was that aggregate stability was positively correlated with small pore sizes. Mycorrhizal colonisation decreased plant biomass and also resulted in reduced soil bacterial species richness, lower percentage organic matter and smaller pore sizes relative to planted but non-mycorrhizal soils. However, soil aggregate stability and water repellency were increased in these (mycorrhizal) soils probably due to AMF hyphal activities including enmeshment and/or glomalin production. In contrast, bacterial TRF richness was positively correlated with aggregate stability in the bare and non-mycorrhizal planted soils. Soil organic carbon was an important factor in all treatments, but in the bare soil where there was no additional input of labile C from roots, the percentage C could be directly related to fungal TRF richness. The less species rich bare soil contained more organic C than the more species rich bare soil. This suggests a degree of redundancy with regard to mineralisation of organic matter when additional, more utilisable C sources are unavailable. Understanding the effects of microbial diversity on functional parameters is important for advancing sustainable soil management techniques, but it is clear that soil is a dynamic ecosystem.     

Effects of addition of maize litter and earthworms on C mineralization and aggregate formation in single and mixed soils differing in soil organic carbon and clay content

C mineralization and aggregate stability directly depend upon organic matter and clay content, and both processes are influenced by the activity of microorganisms and soil fauna. However, quantitative data are scarce. To achieve a gradient in C and clay content, a topsoil was mixed with a subsoil. Single soils and the soil mixture were amended with 1.0 mg maize litter C g soil⁻¹ with and without endogeic earthworms (Aporrectodea caliginosa). The differently treated soils were incubated for 49 days at 15 °C and 40% water holding capacity. Cumulative C mineralization, microbial biomass, ergosterol content and aggregate fractions were investigated and litter derived C in bulk soil and aggregates were determined using isotope analyses. Results from the soil mixture were compared with the calculated mean values of the two single soils. Mixing of soil horizons differing in carbon and clay content stimulated C mineralization of added maize residues as well as of soil organic matter. Mixing also increased contents of macro-aggregate C and decreased contents of micro-aggregate C. Although A. caliginosa had a stimulating effect on C mineralization in all soils, decomposition of added litter by A. caliginosa was higher in the subsoil, whereas A. caliginosa decreased litter decomposition in the soil mixture and the topsoil. Litter derived C in macro-aggregates was higher with A. caliginosa than with litter only. In the C poor subsoil amended with litter, A. caliginosa stimulated the microbial community as indicated by the increase in microbial biomass. Furthermore, the decrease of ergosterol in the earthworm treated soils showed the influence of A. caliginosa on the microbial community, by reducing saprotrophic fungi. Overall, our data suggest both a decrease of saprotrophic fungi by selective grazing, burrowing and casting activity as well as a stimulation of the microbial community by A. caliginosa.     

Extracellular enzyme activity in the mycorrhizospheres of a boreal fire chronosequence

Saprotrophic microbes are typically credited with producing extracellular enzymes that recycle organic matter, though roots and mycorrhizal fungi also can contribute and may compete with the saprotrophs. We examined extracellular enzyme activity associated with the mycorrhizospheres of arbuscular mycorrhizal, ectomycorrhizal, dual-colonized (arbuscular and ectomycorrhizal), and ericoid mycorrhizal plants in a fire chronosequence in Alaska. Bulk soil and soil from beneath host plants were gathered in July 2004 and assayed for five enzymes that target organic C, P, and N substrates. Compared to bulk soil, activities of the C-targeting enzymes β-1,4-glucosidase and peroxidase were lower in arbuscular mycorrhizospheres and ericoid mycorrhizospheres, respectively. Moreover, extracellular enzyme activity varied among mycorrhizosphere types. Specifically, N-targeting leucine aminopeptidase was highest in arbuscular mycorrhizospheres, followed by ericoid and ectomycorrhizal/dual-colonized mycorrhizospheres; β-1,4-glucosidase had the reverse pattern. In addition, enzymatic stoichiometry suggested that extracellular enzyme producers invested more in C-acquisition than in N-acquisition in recent fire scars compared to mature forests. These data extend previous findings that roots and mycorrhizal fungi compete with saprotrophs by showing that the strength of this effect varies by mycorrhizal host. As a result the community composition of mycorrhizal host plants might mediate enzymatic activity in boreal soils.     

Phyllostachys edulis (moso bamboo) rhizosphere increasing soil microbial activity rather than biomass

Purpose

Rhizosphere and fertilization might affect soil microbial activities, biomass, and community. This study aimed to evaluate the impacts of Phyllostachys edulis (moso bamboo) rhizospheres on soil nutrient contents and microbial properties in a moso bamboo forest with different fertilizer applications and to link soil microbial activities with abiotic and biotic factors.

Materials and methods

The experiment included three treatments: (1) application of 45% slag fertilizer (45%-SF); (2) application of special compound fertilizer for bamboos (SCF); and (3) the control without any fertilizer application (CK). Simultaneously, bulk soils and 0.5, 2.5, 4.5, and 6.5-year-old (y) bamboo rhizosphere soils were selected. Soil nutrient contents were analyzed. Microbial activities were evaluated based on the activities of soil enzymes including β-glucosidase, urease, protease, phosphatase, and catalase. The total microbial biomass and community were assessed with the phospholipid fatty acids (PLFAs) method.

Results and discussion

In the CK and SCF treatments, organic matter contents of rhizosphere soils were significantly higher than those of bulk soils. Soil β-glucosidase, urease, protease, phosphatase, and catalase activities in rhizosphere soils were higher than those of bulk soils, with the sole exception of β-glucosidase of 0.5 y rhizosphere soil in the 45%-SF treatment. Compared with the CK treatment, fertilizer applications tended to increase soil total PLFAs contents and changed soil microbial community. Moso bamboo rhizospheres did not significantly increase the total microbial biomass. In the SCF treatment, the Shannon index of bulk soil was significantly lower than those of rhizosphere soils.

Conclusions

Our results suggested that both rhizospheres and fertilizer applications could change the soil microbial community structures and that moso bamboo rhizosphere could increase microbial activity rather than biomass in the forest soils with different fertilizer applications.

     

Woodland trees modulate soil resources and conserve fungal diversity in fragmented landscapes

Resource islands around woody plants are thought to define the structure and function of many semiarid and arid ecosystems, but their role in patterning of soil microbial communities remains largely unexamined in dry environments. This study examined soil resource distribution and associated fungal communities in two Allocasuarina luehmannii (buloke) remnants of semiarid north-western Victoria, Australia. These savannah-like woodlands are listed as endangered due to extensive clearing for agriculture. We used the DNA-based profiling technique T-RFLP and ordination-based statistical methods to compare fungal community compositions in surface soils from two remnants (located 1.6 km apart) and three sampling positions (beneath individual buloke canopies; grassy inter-canopy areas; and adjoining cleared paddocks). Resource island formation beneath buloke trees was clearly evident in soil physicochemical properties (e.g. threefold concentrations of total carbon and nitrogen in canopy versus non-canopy soils). This heterogeneity of resources was moderately correlated with soil fungal community compositions, which were distinct for each sampling position. We argue that fungal composition patterns reflected multiple roles of fungi in dryland ecosystems, namely: responses of saprotrophic fungi to tree organic matter inputs; specificity of ectomycorrhizal fungi to tree rooting zones; and fungal involvement in biological soil crusts that variably covered non-canopy soils. Our data did not indicate that buloke canopy areas were particular hotspots of soil fungal diversity, but that they increased landscape-level diversity by supporting a distinct suite of fungi. In addition, we provide evidence of phylogenetic differentiation of soil fungal communities between our two remnants, which adds to growing evidence of fungal genetic structure at localised scales. These findings highlight the importance of remnant trees in conserving both soil resources and microbial genetic diversity. In addition, evidence of differentiation of soil fungal phylogenetics between nearby but isolated remnants suggests that conserving soil fungal diversity requires conservation of host habitats over their entire (remaining) range, and indicates previously unseen consequences of tree loss from extensively cleared landscapes.     

Low importance for a fungal based food web in arable soils under mineral and organic fertilization indicated by Collembola grazers

We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web.     

Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species.Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed.Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.     

Fire severity shapes plant colonization effects on bacterial community structure,microbial biomass,and soil enzyme activity in secondary succession of a burned forest

The increasing frequency and severity of wildfires has led to growing attention to the effects of fire disturbance on soil microbial communities and biogeochemical cycling. While many studies have examined fire impacts on plant communities, and a growing body of research is detailing the effects of fire on soil microbial communities, little attention has been paid to the interaction between plant recolonization and shifts in soil properties and microbial community structure and function. In this study, we examined the effect of a common post-fire colonizer plant species, Corydalis aurea, on soil chemistry, microbial biomass, soil enzyme activity and bacterial community structure one year after a major forest wildfire in Colorado, USA, in severely burned and lightly burned soils. Consistent with past research, we find significant differences in soil edaphic and biotic properties between severe and light burn soils. Further, our work suggests an important interaction between fire severity and plant effects by demonstrating that the recolonization of soils by C. aurea plants only has a significant effect on soil bacterial communities and biogeochemistry in severely burned soils, resulting in increases in percent nitrogen, extractable organic carbon, microbial biomass, β-glucosidase enzyme activity and shifts in bacterial community diversity. This work propounds the important role of plant colonization in succession by demonstrating a clear connection between plant colonization and bacterial community structure as well as the cycling of carbon in a post-fire landscape. This study conveys how the strength of plant–microbe interactions in secondary succession may shift based on an abiotic context, where plant effects are accentuated in harsher abiotic conditions of severe burn soils, with implications for bacterial community structure and enzyme activity.     

Influence of long-term fertilisation and crop rotation on changes in fungal and bacterial residues in a tropical rice-field soil

Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated soil organic matter formation. However, accumulation of microbial biomass and responses of bacterial and fungal residues to the management practices are different and poorly characterized in rice soils. The objectives of this study were to evaluate the effects of mineral fertiliser (MIN), farmyard manure (FYM) and groundnut oil cake (GOC) on crop yield and co-accumulation of microbial residues and microbial biomass under rice-monoculture (RRR) and rice–legume–rice (RLR) systems. In the organic fertiliser treatments and RLR, rice grain yield and stocks of soil and microbial nutrients were significantly higher than those of the MIN treatment and RRR, respectively. The increased presence of saprotrophic fungi in the organic fertiliser treatments and RRR was indicated by significantly increased ergosterol/C_mic ratio and extractable sulphur. In both crop rotation systems, the long-term application of FYM and GOC led to increased bacterial residues as indicated by greater accumulation of muramic acid. In contrast, the higher fungal C/bacterial C ratio and lower ergosterol/C_mic ratio in the MIN treatment, is likely caused by a shift within the fungal community structure towards ergosterol-free arbuscular mycorrhizal fungi (AMF). The organic fertiliser treatments contributed 22 % more microbial residual C to soil organic C compared to the MIN treatment. Our results suggest that the negative relationship between the ratios ergosterol/C_mic and fungal C/bacterial C encourages studying responses of both saprotrophic fungi and AMF when assessing management effects on the soil microbial community.     

水分含量对秸秆还田土壤碳矿化和微生物特性的影响

An 80-d incubation experiment was conducted to investigate straw decomposition,the priming effect and microbial characteristics in a non-fertilized soil(soil 1) and a long-term organic manure-fertilized soil(soil 2) with and without13 C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect,microbial biomass C(Cmic),and β-glucosidase activity,and more abundant populations of bacteria and fungi than the soil 1. Also,soil CO2 emission,Cmic,β-glucosidase activity,and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw,the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity(WHC) were significantly higher by 31% and 17%,respectively,compared to those at 25% of WHC. In contrast,β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmicdecreased as straw availability decreased,which was mainly attributed to the reduction of straw-derived Cmic. Amended soils,except the amended soil 2 at 25% of WHC,had a more abundant fungal population as straw availability decreased,indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.     

不同有机物料与化肥配施对土壤真菌群落结构和生态功能的影响

为减少土壤土传病害,保障农田土壤健康,指导有机物料合理利用,在有机物料用量和化肥用量一致的基础上,设置单施化肥（CK）、羊粪+化肥（A）、木薯渣+化肥（P）、木本泥炭+化肥（M）、味精废浆料+化肥（I）5个处理,以玉米为供试作物进行了有机物料与化肥配施试验,观察了不同处理下土壤真菌群落结构的变化。结果表明：施用有机物料降低了土壤真菌群落多样性,但提高了真菌群落丰富度,其中味精废浆料配施化肥处理的真菌群落丰富度最高,各处理土壤中优势真菌门类均为子囊菌门、担子菌门和被孢菌门。施用有机物料后,木薯渣、木本泥炭和味精废浆料处理的子囊菌门的相对丰度均增加,担子菌门的相对丰度均降低;而羊粪处理表现出相反趋势,子囊菌门的相对丰度降低,担子菌门的相对丰度增加。冗余分析结果表明,土壤pH是影响真菌群落的主要环境因子,其次为有机质、电导率和速效钾,而碱解氮和有效磷的影响较小。另外,有机物料与化肥配施可以提高腐生营养型和共生营养型真菌的比例,减少病原菌的数量,其中以木本泥炭与化肥配施的效果更显著,这有利于维持土壤生态系统的稳定,为作物生产提供健康的土壤条件。     

Effects of yak excreta on soil organic carbon mineralization and microbial communities in alpine wetlands of southwest of China

Purpose

Improving knowledge of how soil organic carbon (SOC) mineralization responds to excreta application is essential to better understand whether wetland carbon (C) pools will react to grazing. We investigated microbial activity and community structure in the different treatments of excreta addition experiments to examine how soil C mineralization responds to the excreta input in terms of microbial activities and compositions in wetland soils.

Materials and methods

The microcosms of mineralization incubation of excreta addition were established. The structure of the microbial community was described by the fatty acid composition of the phospholipids (PLFA). The methylumbelliferyl-linked substrates (MUB) and l-dihydroxyphenylalanine (L-DOPA) substrates were used to investigate the activities of β-glucosidase (BG), N-acetyl-glucosaminidase (NAG), acid phosphatase (AP), cellobiohydrolase (CBH), and phenol oxidase (PO).

Results and discussion

Excreta addition altered the cumulative C mineralization in swamp meadow (SM) and peatland (PL) soils, but SM was lower than PL. Excreta addition increased the biomass of individual PLFA and the fungi/bacteria ratio, suggesting that microbes are stimulated by nutrients and that the soil microbial community composition is modified by excreta inputs. The hydrolytic enzyme activities were higher in the PL soils than in the SM soils, but the trend was opposite for PO activity. The changes in pH, fungi, actinomycetes (ACT), AP, and CBH after yak fecal input significantly influenced the soil CO₂ efflux. Our findings suggest that yak grazing could influence the rate of C cycling in wetland soils by influencing microbial communities, enzyme activities, and soil pH.

Conclusions

This study suggest that the yak excreta addition increased cumulative C mineralization in SM and PL soils, and the effect of dung addition was more significant than urine addition. The effect of yak excreta addition on SOC mineralization was related with the soil pH, microorganism structure, and enzyme activity which modified by the excreta addition. Soil pH, fungi, AP, and CBH were positively correlated with SOC mineralization, but ACT was negatively correlated with SOC mineralization. In addition, the changes in C and N sources with yak excreta addition play an important role in altering microbial enzyme activities. The input of yak feces into wetlands because of grazing could increase SOC mineralization and thereby promote C emission.

     

长期无机有机肥配施对红壤性水稻土微生物群落多样性及酶活性的影响

【目的】长期有机与无机肥配合施用是促进农田生产力和土壤有机碳固定的重要技术途径。本文以江西省红壤研究所长期不同施肥试验田的表土(0—15 cm)为对象,探讨不同施肥措施对土壤微生物群落多样性和酶活性的影响。【方法】在水稻收获后,采集表土壤样品,提取土壤总DNA。采用聚合酶链反应结合变性梯度凝胶电泳(PCR-DGGE)的方法研究土壤微生物的群落结构多样性,并结合克隆测序研究土壤微生物的群落组成;用实时荧光定量PCR(q PCR)的方法研究土壤微生物的丰度。土壤细菌定量和群落结构分析的分子标靶基因分别为16S rRNA基因V3区和V6区片段,土壤真菌定量和群落结构分析的标靶基因均为18S rRNA基因。DGGE分析采用8%的聚丙烯酰胺凝胶分离细菌和真菌,所用变性梯度分别为35%65%和20%40%。同时采用荧光微孔板检测技术测定土壤几丁质酶、α-葡萄糖苷酶、β-葡萄糖苷酶、纤维素酶、酸性磷酸单脂酶和木聚糖酶活性;用紫外分光光度计法测定土壤过氧化物酶活性。【结果】PCR-DGGE分析表明,与不施肥对照(CK)相比,有机无机肥配施(NPKM),土壤细菌的香农指数和丰富度指数显著增大,而土壤真菌的香农指数和丰富度指数在不同施肥处理间无显著差异。DGGE图谱聚类分析显示,NPKM处理的土壤细菌和真菌的群落结构显著区别于其他3个处理。后续的切胶测序得出,土壤细菌分属于Chloroflexi(绿弯菌门),Proteobacteria(变形菌门)和Firmicutes(厚壁菌门);NPKM处理下隶属于Clostridum(梭菌属)和Anaerolineaceae(厌氧绳菌科)的两类细菌显著增加。土壤真菌主要分属于Basidiomycota(担子菌门)和Ascomycota(子囊菌门),这些真菌条带在DGGE图谱上的分布不同处理间均无明显的规律性,因而不同处理间真菌的群落分布未出现较清晰的变化。q PCR的结果显示,土壤细菌和真菌拷贝数在不同处理间无显著差异。土壤酶的检测结果表明,与CK相比,单施氮肥(N)处理的土壤几丁质酶活性显著提高,常规氮磷钾处理(NPK)处理的几丁质酶和α-葡萄糖苷酶活性显著增强,NPKM处理提高了土壤几丁质酶、纤维素酶和过氧化物酶活性;酸性磷酸单酯酶和木聚糖酶活性在各处理间无显著差异。归一化酶活性值,NPKM处理显著高于CK和其他施肥处理。【结论】长期有机无机肥配施可显著提高土壤细菌多样性,并改变土壤细菌和真菌的群落结构,提高土壤酶活性,因而提高了农田生态系统的生产力并对生态系统健康有改善作用。     

Mineral fertilizer alters cellulolytic community structure and suppresses soil cellobiohydrolase activity in a long-term fertilization experiment

Nutrient inputs to soil can alter mineralization of organic matter and subsequently affect soil carbon levels. To understand how elemental interactions affect the biogeochemistry and storage of soil C, we examined soils receiving long-term applications of mineral fertilizer and manure-containing fertilizers. As cellulose is the dominant form of carbon entering arable soils, cellulolytic communities were monitored through enzymatic analysis, and characterization of the abundance (real-time PCR) and diversity (terminal restriction fragment length polymorphism, T-RFLP) of fungal cellobiohydrolases (cbhI) genes. The data showed that long-term mineral fertilization increased soil organic C and crop productivity, and reduced soil heterotrophic respiration and cellobiohydrolases (CBH) activity. Correspondingly, the diversity and community structure of cellulolytic fungi were substantially altered. The variation in cellulolytic fungi is mainly attributable to shifts in the proportion of Eurotiomycetes. In addition, CBH activity was significantly correlated with the diversity and community structure of cellulolytic fungi. These results suggest that enhanced C storage by mineral fertilizer addition occurs not only from extra organic carbon input, but may also be affected through the cellulose decomposing community in arable soil.