Microbial Indices Related to Soil Carbon as Affected by Management Practices in Arid Forest and Agricultural Ecosystems

A study was conducted to investigate how management affects soil carbon (C) pools, mineralization kinetics, and related microbiological properties. Soils were sampled from two sites in central Iran. At the Lordegan forest (LOR) site, soil under an oak forest was compared with its adjacent deforested counterpart. At the Fozveh Research Station (FRS) site, adjacent fields under alfalfa and tall fescue cropping were compared. At the LOR site, soil organic C (SOC), total nitrogen (TN), microbial biomass C (MBC), β-glucosidase activity (βG), and potentially mineralizable C (C₀) were significantly greater in the forest than in the deforested counterpart. At the FRS site, the soil cropped to alfalfa showed significantly greater values of SOC, TN, MBC, βG, and C₀ than that cropped to tall fescue. Overall, soil biodegradable C pools and related processes are largely affected by management practices in the semiarid to arid environments, confirming the role of management as a significant driver of soil C change.     

Soil microbial community composition under Eucalyptus plantations of different age in subtropical China

Eucalyptus is one of the fastest growing woody plants in the world, but few studies have reported the soil microbial community composition in Eucalyptus ecosystems. This study investigated the soil microbial communities in plantations of 3-, 7-, 10- and 13-year-old Eucalyptus in subtropical China based on phospholipid fatty acids (PLFA) analysis. The variation in soil microbial biomass and community compositions were influenced by sampling site and season and the interaction of both, which were consistent with the variation in soil total nitrogen (TN), soil organic carbon (SOC) and soil moisture. The number and abundances of PLFAs, and the amount of soil TN and SOC were higher in plantation of 13-year-old Eucalyptus than those in other younger plantations, suggesting that the soil properties and the soil microbial community composition is not negatively affected by the planting of Eucalyptus. The ratio of monounsaturated-to-branched fatty acids, the proportional abundance (mol%) of bacterial PLFA and fungal PLFA varied significantly with Eucalyptus plantations of different age, suggesting that the individual PLFA signatures might be sensitive indicators of soil properties associated with forest plantations.     

Bacterial and fungal response to nitrogen fertilization in three coniferous forest soils

Forest soil carbon (C) pools may act as sinks for, or sources of, atmospheric carbon dioxide, while nitrogen (N) fertilization may affect the net exchange of C in forest ecosystems. Since all major C and N processes in soil are driven by soil microorganisms, we evaluated the effects of N fertilization on biomass and bacterial and fungal activity in soils from three Norway spruce forests with different climatic and N availability conditions. N deposition and net N mineralization were higher at the sites in southern Sweden than at the site in northern Sweden. We also studied the extent to which N fertilization altered the nutrient(s) limiting bacterial growth in soil. We found that on average microbial biomass was reduced by ～40% and microbial activity by ～30% in fertilized plots. Bacterial growth rates were more negatively affected by fertilization than fungal growth rates, while fungal biomass (estimated using the phospholipid fatty acid (PLFA) 18:2ω6,9) decreased more than bacterial biomass as a consequence of fertilization. The microbial community structure (indicated by the PLFA pattern) was changed by fertilization, but not in the same way at the three sites. Soil bacteria were limited by a lack of carbon in all forests, with the carbon limitation becoming more evident in fertilized plots, especially in the forests that had previously been the most N-limited ones. This study thus showed that the effects of N fertilization differed depending on the conditions at the site prior to fertilization.     

Neotyphodium coenophialum‐endophyte infection affects the ability of tall fescue to use sparingly available phosphorus

Neotyphodium coenophialum, (Morgan‐Jones & Gams) Glenn, Bacon & Hanlin, infected tall fescue (Festuca arundinacea Schreb.) plants perform better than non‐infected isolines on phosphorus (P)‐deficient soils. Our objective was to characterize growth and P uptake dynamics of tall fescue in response to endophyte infection and P source at low P availability in soil. Two tall fescue genotypes (DN2 and DN4) infected with their naturally occurring N. coenophialum strains (E+), and in noninfected (E‐) forms were grown in Lily soil (fine loamy siliceous, mesic Typic Hapludult) in a greenhouse for 20 weeks. Three soil P treatments were imposed: no P supplied (control) and P supplied as commercial fertilizer (PF) or as phosphate rock (PR) at the level of 25 mg P kg^‐1 soil. Interaction of tall fescue genotype and endophyte status had a significant influence on mineral element uptake suggesting high specificity of endophyte‐tall fescue associations. Endophyte infection did not affect root dry matter (DM) when no P was supplied but shoot DM was reduced by 20%. More biomass was produced and greater P uptake rate occurred in PR than PF treatment. Root DM was greater in E+ DN4 than E‐DN4 when supplied with either PF or PR. In contrast, endophyte infection did not affect root DM of DN2, regardless of P source. Relative growth rate (RGR) of E+ plants grown with PR was 16% greater than that of E‐plants. Endophyte infection did not improve growth or P uptake in PF treatment. When PR was supplied, P uptake rate was 24% greater in E+ DN2 than E‐ DN2, but endophyte infection did not benefit DN4. Phosphorus‐use efficiency was 6% less in E+ DN2 but 16% greater in E+ DN4 compared to E‐ plants, regardless of P source. Root exudates of E+ DN2, but not E+ DN4 solubilized more P from PR than those of E‐ plants. The correlation between root RGR and P uptake rate was relatively high for E‐ plants (r=0.76), but low for E+ plants (r=0.27) grown with PR. Results suggest that P uptake by E+ tall fescue might rely on mechanisms other than an increase in root biomass (surface area). Endophyte infection modified tall fescue responses to P source. This phenomenon was associated with modes of P acquisition which included enhanced activity of root exudates in releasing P from PR in E+ plants (DN2), and increased root biomass (DN4). The dominant means of P acquisition may be determined by a specific association of endophyte and tall fescue genomes. Endophyte‐tall fescue association plasticity contributes to widespread success of symbiotic in marginal resource conditions.     

Specific response of fungal and bacterial residues to one-season tillage and repeated slurry application in a permanent grassland soil

The dynamics of fungal and bacterial residues to a one-season tillage event in combination with manure application in a grassland soil are unknown. The objectives of this study were (1) to assess the effects of one-season tillage event in two field trials on the stocks of microbial biomass, fungal biomass, microbial residues, soil organic C (SOC) and total N in comparison with permanent grassland; (2) to determine the effects of repeated manure application to restore negative tillage effects on soil microbial biomass and residues. One trial was started 2 years before sampling and the other 5 years before sampling. Mouldboard ploughing decreased the stocks of SOC, total N, microbial biomass C, and microbial residues (muramic acid and glucosamine), but increased those of the fungal biomarker ergosterol in both trials. Slurry application increased stocks of SOC and total N only in the short-term, whereas the stocks of microbial biomass C, ergosterol and microbial residues were generally increased in both trials, especially in combination with tillage. The ergosterol to microbial biomass C ratio was increased by tillage, and decreased by slurry application in both trials. The fungal C to bacterial C ratio was generally decreased by these two treatments. The metabolic quotient qCO₂ showed a significant negative linear relationship with the microbial biomass C to SOC ratio and a significant positive relationship with the soil C/N ratio. The ergosterol to microbial biomass C ratio revealed a significant positive linear relationship with the fungal C to bacterial C ratio, but a negative one with the SOC content. Our results suggest that slurry application in grassland soil may promote SOC storage without increasing the role of saprotrophic fungi in soil organic matter dynamics relative to that of bacteria.     

Microbial communities of a native perennial bunchgrass do not respond consistently across a gradient of land-use intensification

To test if native perennial bunchgrasses cultivate the same microbial community composition across a gradient in land-use intensification, soils were sampled in fall, winter and spring in areas under bunchgrasses (‘plant’) and in bare soils (‘removal’) in which plots were cleared of living plants adjacent to native perennial bunchgrasses (Nassella pulchra). The gradient in land-use intensification was represented by a relict perennial grassland, a restored perennial grassland, and a perennial grass agriculture site on the same soil type. An exotic annual grassland site was also included because perennial bunchgrasses often exist within a matrix of annual grasses in California. Differences in soil resource pools between ‘plant’ and ‘removal’ soils were observed mainly in the relict perennial grassland and perennial grass agriculture site. Seasonal responses occurred in all sites. Microbial biomass carbon (C) and dissolved organic C were greater under perennial bunchgrasses in the relict perennial grassland and perennial grass agriculture site when comparing treatment means of ‘plant’ vs. ‘removal’ soil. In general, soil moisture, microbial respiration, and nitrate decreased from fall to spring in ‘plant’ and ‘removal’ soils, while soil ammonium and net mineralizable nitrogen (N) increased only in ‘plant’ soils. A canonical correspondence analysis (CCA) of phospholipid fatty acid (PLFA) profiles from all sites showed that land-use history limits the similarity of microbial community composition as do soil C and N dynamics among sites. When PLFA profiles from individual sites were analyzed by CCA, different microbial PLFA markers were associated with N. pulchra in each site, indicating that the same plant species does not retain a unique microbial fingerprint across the gradient of land-use intensification.     

菌渣还田对设施土壤微生物量碳、氮的影响

[目的]探究设施土壤微生物量碳、氮对菌渣还田的响应,为实现设施瓜菜生产的可持续发展提供理论依据和技术支持。[方法]以草菇菌渣为材料,在山东省莘县进行了田间试验,以常规鸡粪还田为对照(CON),设置5个菌渣(FR)还田量,研究菌渣还田对设施土壤有机碳(SOC)、全氮(TN)和微生量碳(MBC)、氮(MBN)的影响。[结果] 5个菌渣还田处理的菌渣使用量分别为15,30,45,60和75 t/hm~2)相比CON增加了SOC和TN。SOC分别增加了12.0%,11.2%,21.6%,33.1%和31.7%,TN分别增加了3.1%,6.3%,19.9%,29.4%和26.4%。除FR_1以外,其他4个菌渣还田处理相比增加了MBC和MBN,MBC分别增加了16.1%,19.9%,36.8%和50.7%,MBN分别增加了3.3%,37.7%,40.4%和60.9%。相比CON,高量菌渣还田处理增加了MBC/SOC和MBN/TN。相关分析表明,MBC,MBN与SOC和TN均呈极显著正相关。[结论]菌渣还田可以提高土壤有机碳、土壤全氮和土壤微生物碳、氮。土壤微生物碳、氮含量随着菌渣还田量的增加而增加,因此菌渣还田是提高设施土壤微生物活性及土壤肥力的有效措施。     

Warming and grazing affect soil labile carbon and nitrogen pools differently in an alpine meadow of the Qinghai�CTibet Plateau in China

Purpose

Small but highly bioactive labile carbon (C) and nitrogen (N) pools are of great importance in controlling terrestrial C and N fluxes, whilst long-term C and N storage is determined by less labile but relatively large sizes of C and N pools. Little information is available about the effects of global warming and grazing on different forms of C and N pools in the Qinghai?CTibet Plateau of China. The aim of this study was to investigate the effects of warming and grazing on the sizes of different soil labile C and N pools and N transformation in this region.

Materials and methods

A free-air temperature enhancement system in a controlled warming?Cgrazing experiment had been implemented since May 2006. Infrared heaters were used to manipulate temperature, and a moderate grazing intensity was simulated by Tibetan sheep. After 3 years?? warming, soil samples were taken from the four treatment plots: no warming with no grazing; no warming with grazing; warming with no grazing; and warming with grazing. Concentrations of inorganic N in the 40?Ccm soil profiles were measured by a flow injection analyser. Microbial biomass C (MBC) and microbial biomass N (MBN) were measured by the fumigation?Cextraction method, and soluble organic C (SOC) and soluble organic N (SON) were determined by high-temperature catalytic oxidation. Total N (TN), C isotope composition (??¹³C) and N isotope composition (??¹⁵N) were determined using an isotope ratio mass spectrometer. Net N transformation under low temperature was studied in a laboratory incubation experiment.

Results and discussion

Warming and grazing treatments affected soil C and N pools differently, and these effects varied with soil depth. Warming significantly increased TN, MBC, MBN, and SON and decreased ??¹³C at the 10?C20 and 20?C30 cm soil depths, whilst grazing generally decreased SON at the 10?C20 and 20?C30 cm, and MBC at 20?C30 cm. At the 0?C10 cm depth, neither warming nor grazing alone affects these soil parameters significantly, indicating that there could be considerable perturbation on the soil surface. However, grazing alone increased NO ₃ ^? ?CN, total inorganic N, SOC and ??¹⁵N at the 0?C10 cm depth. Incubated at 4°C, warming (particularly with grazing) led to net immobilization of N, but no-warming treatments led to net N mineralization, whilst nitrification was strong across all these treatments. Correlations between MBC and SOC, and TN and MBN or SON were positive. However, SON was less well correlated with TN and MBN compared with the highly positive correlations between SOC and MBC.

Conclusions

It is clearly demonstrated that warming and grazing affected labile C and N pools significantly, but differently after 3 years?? treatments: Warming tended to enlarge labile C and N pools through increased litter inputs, whilst grazing tended to increase inorganic N pools, decrease SON and accelerate N cycling. Grazing might modify the mode that warming affected soil C and N pools through its strong impacts on microbial processes and N cycling. These results suggested that interactive effects of warming and grazing on C and N pools might have significant implications for the long-term C and N storage and productivity of alpine meadow ecosystem in the Qinghai?CTibet Plateau of China.     

Effects of flue gas desulfurization gypsum by-products on microbial biomass and community structure in alkaline–saline soils

Purpose

For an alkaline?Csaline region in Northwest China, we examined the responses of soil microbial communities to flue gas desulfurization gypsum by-products (FGDB), a new ameliorant for alkaline?Csaline soils. In 2009 and 2010, we collected soils from 0?C20?cm and 20?C40?cm depths along an experimental FGDB gradient (0, 0.74, 1.49, 2.25, and 3.00?kg FGDB m^?2).

Materials and methods

As a measure of microbial community composition and biomass, we analyzed phospholipid fatty acids (PLFAs). We used real-time quantitative polymerase chain reaction (qPCR) to measure abundance of bacterial 16?S rRNA copy numbers. Additionally, physicochemical soil parameters were measured by common laboratory methods.

Results and discussion

Microbial community composition differed along the FGDB gradient; however, the microbial parameters did not follow a linear response. We found that, in 2009, total PLFA concentrations, and concentrations of total bacterial and Gram-negative bacterial PLFAs were slightly higher at intermediate FGDB concentrations. In 2010, total PLFA concentrations, and concentrations of total bacterial, Gram-positive bacterial, Gram-negative bacterial, and fungal PLFAs as well as the fungal:bacterial PLFA ratio were highest at 1.49?kg FGDB m^?2 and 3.00?kg FGDB m^?2. PLFA concentrations often differed between 2009 and 2010; however, the patterns varied across the gradient and across microbial groups. For both years, PLFA concentrations were generally higher at 0?C20?cm depth than at 20?C40?cm depth. Similar results were obtained for the 16?S rRNA copy numbers of bacteria at 0?C20?cm depth. FGDB addition resulted in an increase in soil Ca²⁺ and NO ₃ ^? ?CN and a decrease in pH and electrical conductivity (EC). Shifts in PLFA-based microbial community composition and biomass could partly be explained by pH, soil organic carbon, total nitrogen (TN), soil moisture, EC, inorganic nitrogen, C/N, and Ca²⁺. Indirect effects via shifts in abiotic soil properties, therefore, seem to be an important pathway through which FGDB affect soil microbial communities.

Conclusions

Our results demonstrate that addition of FGDB leads to significant changes in soil physicochemical and microbial parameters. As such, addition of FGDB can have large impacts on the functioning of soil ecosystems, such as carbon and nitrogen cycling processes.     

Labile,recalcitrant, microbial carbon and nitrogen and the microbial community composition at two Abies faxoniana forest elevations under elevated temperatures

We investigated the interactions of altitude and artificial warming on the soil microbial community structure in a subalpine Abies faxoniana forest in southwestern China after four years of warming. Open top chambers (OTCs) at two elevations (3000 m and 3500 m) were established, and their soil microbial characteristics, organic carbon (C) and nitrogen (N) were measured. The microbial community structure was quantified by phospholipid fatty acid (PLFA) analysis. A two-step sulfuric acid hydrolysis was used to quantify the labile and recalcitrant C fractions in the soil organic matter. The results showed that bacterial PLFAs and gram-negative bacterial PLFAs increased and the fungal PLFAs and the fungi/bacteria ratio decreased with warming at the high altitude. By contrast, the warming effects on those parameters at low altitude were small. The higher proportion of labile easily decomposable soil C may explain the different responses of the microbial community composition at the two altitudes. An RDA analysis confirmed that the variations in the soil community structure were significantly associated with soil organic matter properties such as the sizes of the soil labile N pool (LP-N), the recalcitrant N pool (RP-N), and the labile C pool as well as dissolved organic C (DOC) and dissolved organic N concentrations (DON). Our results also showed that labile C and N pools increased with the altitude, but the microbial biomass C as measured with chloroform fumigation techniques decreased. Warming increased only the recalcitrant C pools at the high altitude. Given the longer mean residence time for recalcitrant C and the much greater size of this soil organic carbon pool, the results indicated that a rise in temperature in our case increased soil C pools at higher altitudes, at least during the early stages of experimental soil warming. Warming could also cause changes in the composition of the microbial community and enzyme activities, consequently leading to functional changes in soil ecosystem processes at the high altitude.     

陕西靖边花豹湾聚湫坝地土壤微生物群落结构 特征及其影响因子

以黄土高原天然形成的花豹湾聚湫为研究对象,系统分析了3个剖面中土壤的机械组成、有机碳(SOC)、全氮(TN)、微生物生物量碳(MBC)和微生物生物量氮(MBN),并利用磷脂脂肪酸法(PLFA)测定了土壤中细菌、真菌和放线菌的数量,重点讨论了微生物数量和群落结构与碳、氮含量及机械组成之间的相关性。结果表明:1砂粒含量沿着坝尾-坝前的方向有逐渐降低的趋势,粉砂粒和黏粒含量则有逐渐升高的趋势,在垂直方向上可划分出5个明显的沉积旋回(深度分别为0~40、50~60、70~80、100~120和240~260 cm);2聚湫坝地土壤微生物主要含有脂肪酸(15:0 iso、18:1 w9c、18:1 w7c、16:0 10-methyl),约占PLFA总量的54%,土壤微生物以细菌为主,约占65%~75%,放线菌约占15%~25%,真菌约占5%~10%;33种多样性指数的变化趋势基本一致,依次为A剖面B剖面C剖面,3个剖面的土壤微生物群落结构存在比较明显的差异,其中A剖面分化明显;4土壤微生物总量、细菌数量和真菌数量与土壤中粉粒和黏粒含量以及MBC、MBN、SOC和TN均呈显著(P0.05)或极显著(P0.01)的正相关关系;5土壤中细颗粒组分可能是影响微生物数量和群落结构的主要因子。     

Soil microbial biomass and activity in Chinese tea gardens of varying stand age and productivity

Tea (Camellia sinensis) is a globally important crop and is unusual because it both requires an acid soil and acidifies soil. Tea stands tend to be extremely heavily fertilized in order to improve yield and quality, resulting in a great potential for diffuse pollution. The microbial ecology of tea soils remains poorly understood; an improved understanding is necessary as processes affecting nutrient availability and loss pathways are microbially mediated. We therefore examined the relationships between soil characteristics (pH, organic C, total N, total P, available P, exchangeable Al), the soil microbial biomass (biomass C, biomass ninhydrin-N, ATP, phospholipid fatty acids—PLFAs) and its activities (respiration, net mineralization and nitrification). At the Tea Research Institute, Hangzhou (TRI), we compared fields of different productivity levels (low, medium and high) and at Hongjiashan village (HJS) we compared fields of different stand age (9, 50 and 90 years). At both sites tea soils were compared with adjacent forest soils. At both sites, soil pH was highest in the forest soil and decreased with increasing productivity and age of the tea stand. Soil microbial biomass C and biomass ninhydrin-N were significantly affected by tea production. At TRI, microbial biomass C declined in the order forest>low>high>middle production and at HJS in the order stand age 50>age 9>forest>age 90. Soil pH had a strong influence on the microbial biomass, demonstrated by positive linear correlations with: microbial biomass C, microbial biomass ninhydrin-N, the microbial biomass C:organic C ratio, the microbial biomass ninhydrin-N:total N ratio, the respiration rate and specific respiration rate. Above pH_(KCl) 3.5 there was net N mineralization and nitrification, and below this threshold some samples showed net immobilization of N. A principal component (PC) analysis of PLFA data showed a consistent shift in the community composition with productivity level and stand age. The ratio of fungal:bacterial PLFA biomarkers was negatively and linearly correlated with specific respiration in the soils from HJS (r²=0.93, p=0.03). Our results demonstrate that tea cultivation intensity and duration have a strong impact on the microbial community structure, biomass and its functioning, likely through soil acidification and fertilizer addition.     

Changes in soil microbial community composition in response to fertilization of paddy soils in subtropical China

Repeated fertilizer applications to cultivated soils may alter the composition and activities of microbial communities in terrestrial agro-ecosystems. In this study, we investigated the effects of different long term fertilization practices (control (CK), three levels of mineral fertilizer (N₁P₁K₁, N₂P₂K₂, and N₃P₃K₃), and organic manure (OM)) on soil environmental variables and microbial communities by using phospholipid fatty acid (PLFA) biomarkers analysis in subtropical China. Study showed that OM treatment led to increases in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents, while the mineral fertilizer treatment led to increases in dissolved organic carbon (DOC) content. Changes in soil microbial communities (eg. bacteria, actinomycetes) were more noticeable in soils subjected to organic manure applications than in the control soils or those treated with mineral fertilizer applications. Fungal PLFA biomarkers responded differently from the other PLFA groups, the numerical values of fungal PLFA biomarkers were similar for all the OM and mineral fertilizer treatments. PCA analysis showed that the relative abundance of most PLFA biomarkers increased in response to OM treatment, and that increased application rates of the mineral fertilizer changed the composition of one small fungal PLFA biomarker group (namely 18:3ω6c and 16:1ω5c). Further, from the range of soil environmental factors that we examined, SOC, TN and TP were the key determinants affecting soil microbial community. Our results suggest that organic manure should be recommended to improve soil microbial activity in subtropical agricultural ecosystems, while increasing mineral fertilizer applications alone will not increase microbial growth in paddy soils.     

Land use change and soil nutrient transformations in the Los Haitises region of the Dominican Republic

We characterized soil cation, carbon (C) and nitrogen (N) transformations within a variety of land use types in the karst region of the northeastern Dominican Republic. We examined a range of soil pools and fluxes during the wet and dry seasons in undisturbed forest, regenerating forest and active agricultural sites within and directly adjacent to Los Haitises National Park. Soil moisture, soil organic matter (SOM), soil cations, leaf litter C and pH were significantly greater in regenerating forest sites than agricultural sites, while bulk density was greater in active agricultural sites. Potential denitrification, microbial biomass C and N, and microbial respiration g⁻¹ dry soil were significantly greater in the regenerating forest sites than in the active agricultural sites. However, net mineralization, net nitrification, microbial biomass C, and microbial respiration were all significantly greater in the agricultural sites on g⁻¹ SOM basis. These results suggest that land use is indirectly affecting microbial activity and C storage through its effect on SOM quality and quantity. While agriculture can significantly decrease soil fertility, it appears that the trend can begin to rapidly reverse with the abandonment of agriculture and the subsequent regeneration of forest. The regenerating forest soils were taken out of agricultural use only 5-7 years before our study and already have soil properties and processes similar to an undisturbed old forest site. Compared to undisturbed mogote forest sites, regenerating sites had smaller amounts of SOM and microbial biomass N, as well as lower rates of microbial respiration, mineralization and nitrification g⁻¹ SOM. Initial recovery of soil pools and processes appeared to be rapid, but additional research must be done to address the long-term rate of recovery in these forest stands.     

Effects of short-term conservation management practices on soil organic carbon fractions and microbial community composition under a rice-wheat rotation system

The objective of this study was to investigate the effects of short-term (less than 2 years) conservation managements [no-tillage (NT) and crop residue returning] on top soil (0–5 cm) microbial community composition and soil organic C (SOC) fractions under a rice-wheat rotation at Junchuan town of Hubei Province, China. Treatments were established following a split-plot design of a randomized complete block with tillage practices [conventional tillage (CT) and NT] as the main plot and residue returning level [no residue returning (0) and all residues returned to fields from the preceding crop (S, 2,146 kg C ha^?1)] as the subplots. The four treatments were CT with or without residue returning (CT0 and CTS) and NT with or without residue returning (NT0 and NTS). The abundances of microbial groups [total FLFAs, fungal biomass, bacterial biomass, fungal biomass/bacterial biomass (F/B), monounsaturated fatty acids/saturated fatty acids (MUFA/STFA), and microbial stress] were determined by phospholipid fatty acid (PLFA) analysis of soil. The ratio of MUFA/STFA reflects aeration of soil and greater MUFA/STFA means better aeration condition of soil. Moreover, the microbial stress, the ratio of cy19:0 to 18:1ω7, was regarded as an indicator of physiological or nutritional stress of microbial community. PLFA profiles were dominated by the fatty acids iC15:0 (9.8 %), C16:0 (16.5 %), 10Me17:0 (9.9 %), and Cyc19:0 (8.3 %), together accounting for 44.6 % of the total PLFAs. Compared with CT, NT significantly increased microbial biomass C (MBC) by 20.0 % but did not affect concentrations of total organic C (TOC), dissolved organic C (DOC), easily oxidizable C (EOC), and SOC of aggregates. Residue returning significantly increased MBC by 18.3 % and SOC content of 2–1-mm aggregate by 9.4 %. NT significantly increased total PLFAs by 9.8 % and fungal biomass by 40.8 % but decreased MUFA/STFA by 15.5 %. Residue returning significantly enhanced total PLFAs, bacterial biomass, fungal biomass, F/B, and MUFA/STFA by 31.1, 36.0, 95.9, 42.5, and 58.8 %, respectively, but decreased microbial stress by 45.9 %. Multivariate analysis (redundancy analysis and partial correlation analysis) indicated that SOC of 2–1-mm aggregate was related to changes in the composition of soil microbial groups, suggesting that SOC of 2–1-mm aggregate was sensitive to changes in soil microbial community composition affected by short-term conservation management practices in our study.     

Soil ameliorants alter physicochemical properties and fungal communities in saline-sodic soils of Northeast China

To understand the mechanisms of soil ameliorants affecting microbial communities is important for saline-sodic soils reclamation. High-throughput sequencing was used to characterize the fungal community in soils amended with four types of ameliorants over an 8-year period. Besides a control without any additional ameliorant (CK), other four treatments including 1) amendment with sandy soil (SS), 2) amendment with desulfurization gypsum (DG), 3) amendment with farm manure (FM), and 4) amendment with a mixture of SS, DG, and FM (M) were analyzed. Soil pH and electrical conductivity significantly decreased with the addition of soil ameliorants, whereas the soil organic carbon (SOC), total nitrogen (TN), and SOC/TN ratio (C/N) significantly increased in the FM and M treatments compared with the CK treatment. Fungal richness increased significantly with the mixed ameliorants addition (M). Distinct fungal community structures were observed in the treatments with soil ameliorants. The fungal community composition was significantly associated with the SOC, C/N, aggregate content with a diameter > 0.25 mm and geometric mean diameter. The changes in these soil characteristics were highly correlated with the ameliorants additions, suggesting that the impacts of ameliorants on the soil fungal community occurred indirectly as a result of alterations to soil physiochemical properties.     

干旱热带地区土地利用变化对土壤微生物群落组成及有机碳含量的影响

Restoration of forests poses a major challenge globally,particularly in the tropics,as the forests in these regions are more vulnerable to land-use change.We studied land-use change from natural forest (NF) to degraded forest (DF),and subsequently to either Jatropha curcas plantation (JP) or agroecosystem (AG),in the dry tropics of Uttar Pradesh,India,with respect to its impacts on soil microbial community composition as indicated by phospholipid fatty acid (PLFA) biomarkers and soil organic carbon (SOC) content.The trend of bacterial PLFAs across all land-use types was in the order:NF ＞ JP ＞ DF＞ AG.In NF,there was dominance of gram-negative bacterial (G-) PLFAs over the corresponding gram-positive bacterial (G+) PLFAs.The levels of G-PLFAs in AG and JP differed significantly from those in DF,whereas those of G+ PLFAs were relatively similar in these three land-use types.Fungal PLFAs,however,followed a different trend:NF ＞ JP ＞ DF =AG.Total PLFAs,fungal/bacterial (F/B) PLFA ratio,and SOC content followed trends similar to that of bacterial PLFAs.Across all land-use types,there were strong positive relationships between SOC content and G-,bacterial,fungal,and total microbial PLFAs and F/B PLFA ratio.Compared with bacterial PLFAs,fungal PLFAs appeared to be more responsive to land-use change.The F/B PLFA ratio,fungal PLFAs,and bacterial PLFAs explained 91％,94％,and 73％ of the variability in SOC content,respectively.The higher F/B PLFA ratio in JP favored more soil C storage,leading to faster ecosystem recovery compared to either AG or DF.The F/B PLFA ratio could be used as an early indicator of ecosystem recovery in response to disturbance,particularly in relation to land-use change.     

有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮

土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。     

Drying and rewetting effects on soil microbial community composition and nutrient leaching

The effects of a dry-rewetting event (D/RW) on soil microbial properties and nutrient release by leaching from two soils taken from adjacent grasslands with different histories of management intensity were studied. These were a low-productivity grassland, with no history of fertilizer application and a high-productivity grassland with a history of high fertilizer application, referred to as unimproved and improved grassland, respectively. The use of phospholipid fatty acid analysis (PLFA) revealed that the soil of the unimproved grassland had a significantly greater microbial biomass, and a greater abundance of fungi relative to bacteria than did the improved grassland. Soils from both grasslands were maintained at 55% water holding capacity (WHC) or dried to 10% WHC and rewetted to 55% WHC, and then sampled on days 1, 3, 9, 16, 30 and 50 after rewetting. The D/RW stress significantly reduced microbial biomass carbon (C), fungal PLFA and the ratio of fungal-to-bacterial PLFA in both soils. In contrast, D/RW increased microbial activity, but had no effect on total PLFA and bacterial PLFA in either soil. Microbial biomass nitrogen (N) was reduced significantly by D/RW in both soils, but especially in those of the improved grassland. In terms of nutrient leaching, the D/RW stress significantly increased concentrations of dissolved organic C and dissolved organic N in leachates taken from the improved soil only. This treatment increased the concentration of dissolved inorganic N in leachate of both soils, but this effect was most pronounced in the improved soil. Overall, our data show that D/RW stress leads to greater nutrient leaching from improved than from unimproved grassland soils, which have a greater microbial biomass and abundance of fungi relative to bacteria. This finding supports the notion that soils with more fungal-rich communities are better able to retain nutrients under D/RW than are their intensively managed counterparts with lower fungal to bacterial ratios, and that D/RW can enhance nutrient leaching with potential implications for water quality.     

Effect of Long-Term Soil Management on the Mutual Interaction Among Soil Organic Matter, Microbial Activity and Aggregate Stability in a Vineyard

Vineyard management practices to enhance soil conservation principally focus on increasing carbon (C) input, whereas mitigating impacts of disturbance through reduced tillage has been rarely considered. Furthermore, information is lacking on the effects of soil management practices adopted in the under-vine zone on soil conservation. In this work, we evaluated the long-term effects (22 years) of alley with a sown cover crop and no-tillage (S + NT), alley with a sown cover crop and tillage (S + T), and under-vine zone with no vegetation and tillage (UV) on soil organic matter (SOM), microbial activity, aggregate stability, and their mutual interactions in a California vineyard in USA. Vegetation biomass, microbial biomass and activity, organic C and nitrogen (N) pools, and SOM size fractionation and aggregate stability were analysed. Soil characteristics only partially reflected the differences in vegetation biomass input. Organic C and N pools and microbial biomass/activity in S + NT were higher than those in S + T, while the values in UV were intermediate between the other two treatments. Furthermore, S + NT also exhibited higher particulate organic matter C in soil. No differences were found in POM C between S + T and UV, but the POM fraction in S + T was characterized by fresher material. Aggregate stability was decreased in the order: S + NT > UV > S + T. Tillage, even if shallow and performed infrequently, had a negative effect on organic C and N pools and aggregate stability. Consequently, the combination of a sown cover crop and reduced tillage still limited SOM accumulation and reduced aggregate stability in the surface soil layer of vineyards, suggesting relatively lower resistance of soils to erosion compared to no-till systems.