Determinants of Soil Microbial Communities: Effects of Agricultural Management, Season, and Soil Type on Phospholipid Fatty Acid Profiles

Abstract Phospholipid fatty acid (PLFA) profiles were measured in soils from organic, low-input, and conventional farming systems that are part of the long term Sustainable Agriculture Farming Systems (SAFS) Project. The farming systems differ in whether their source of fertilizer is mineral or organic, and in whether a winter cover crop is grown. Sustained increases in microbial biomass resulting from high organic matter inputs have been observed in the organic and low-input systems. PLFA profiles were compared to ascertain whether previously observed changes in biomass were accompanied by a change in the composition of the microbial community. In addition, the relative importance of environmental variables on PLFA profiles was determined. Redundancy analysis ordination showed that PLFA profiles from organic and conventional systems were significantly different from April to July. On ordination plots, PLFA profiles from the low-input system fell between organic and conventional systems on most sample dates. A group of fatty acids (i14:0, a15:0, 16:1ω7c, 16:1ω5c, 14:0, and 18:2ω6c) was enriched in the organic plots throughout the sampling period, and another group (10Me16:0, 2OH 16:1 and 10Me17:0) was consistently lower in relative abundance in the organic system. In addition, another group (15:0, a17:0, i16:0, 17:0, and 10Me18:0) was enriched over the short term in the organic plots after compost incorporation. The relative importance of various environmental variables in governing the composition of microbial communities could be ranked in the order: soil type > time > specific farming operation (e.g., cover crop incorporation or sidedressing with mineral fertilizer) > management system > spatial variation in the field. Measures of the microbial community and soil properties (including microbial biomass carbon and nitrogen, substrate induced respiration, basal respiration, potentially mineralizable nitrogen, soil nitrate and ammonium, and soil moisture) were seldom associated with the variation in the PLFA profiles. Received: 3 February 1997; Accepted: 7 August 1997     

土壤微生物群落对枯落物输入的响应

枯落物分解在陆地生态系统物质循环能量流动中起着关键性作用,明确枯落物输入对土壤微生物群落的影响有助于理解土壤微生物生物多样性和陆地生态系统功能的相互关系。本文采用整合分析方法,以中国为研究区域,以不添加枯落物为对照组,探究土壤微生物(真菌、细菌、放线菌)及微生物生物量碳、生物量氮对枯落物输入的响应。结果表明:与不添加枯落物相比,添加枯落物后土壤微生物生物量碳、生物量氮分别显著增加3.9%和4.4%;土壤真菌PLFA、细菌PLFA及总微生物PLFA分别增加4.0%、3.1%和2.4%。枯落物输入对土壤微生物的影响受到气候条件、年降水量、植被类型及土壤酸碱度等因素的显著影响;不同气候类型下,土壤微生物对枯落物输入的响应呈现出亚热带季风气候区>温带季风气候区>温带大陆气候区的趋势,以及随着年降水量的增加呈现出先升高后降低的趋势;不同植被类型下,土壤微生物对枯落物输入的响应呈现出阔叶林>草地≈混交林>针叶林的趋势。     

Species-dependent responses of soil microbial properties to fresh leaf inputs in a subtropical forest soil in South China

Aims Forest disturbance from extreme weather events due to climate change could increase the contribution of fresh green leaves to the litter layer of soil and subsequently alter the composition and activity of the soil microbial properties and soil carbon cycling. The objective of this study was to compare the effect of naturally fallen litter and fresh leaves on the soil microbial community composition and their activities.Methods Fresh leaves and normal fallen litter were collected from four tree species (Pinus elliottii, Schima superba, Acacia mangium, A. auriculaeformis) in subtropical China and mixed with soil. Soil microbial community composition was determined using PLFAs, and its activity was quantified by soil respiration. During a 12-month period, the decomposition rate of litter was measured bimonthly using a litterbag method. Soil microbial samples were collected after 6 and 12 months. Soil respiration was measured monthly.Important findings We found that fresh leaves decomposed faster than their conspecific fallen litter. Although total microbial biomass and bacterial biomass were similar among treatments, soil fungal biomass was higher in fresh leaf than fallen litter treatments, resulting in greater values of the Fungal phospholipid fatty acids (PLFAs)/Bacterial PLFAs ratio. Fungal PLFA values were greater for Schima superba than the other species. The effect of litter type on soil respiration was species-dependent. Specifically, fallen litter released 35% more CO₂ than fresh leaves of the conifer P. elliottii. The opposite pattern was observed in the broadleaf species whose fresh leaf treatments emitted 17%–32% more CO₂ than fallen litter. Given future predictions that global climate change will cause more disturbances to forests, these results indicate that conifer and broadleaf forests in subtropical China may respond differently to increased fresh litter inputs, with net soil microbial respiration decreasing in conifer forests and increasing in broadleaf forests.     

Successional and seasonal variations in soil and litter microbial community structure and function during tropical postagricultural forest regeneration: a multiyear study

Soil microorganisms regulate fundamental biochemical processes in plant litter decomposition and soil organic matter (SOM) transformations. Understanding how microbial communities respond to changes in vegetation is critical for improving predictions of how land‐cover change affects belowground carbon storage and nutrient availability. We measured intra‐ and interannual variability in soil and forest litter microbial community composition and activity via phospholipid fatty acid analysis (PLFA) and extracellular enzyme activity across a well‐replicated, long‐term chronosequence of secondary forests growing on abandoned pastures in the wet subtropical forest life zone of Puerto Rico. Microbial community PLFA structure differed between young secondary forests and older secondary and primary forests, following successional shifts in tree species composition. These successional patterns held across seasons, but the microbial groups driving these patterns differed over time. Microbial community composition from the forest litter differed greatly from those in the soil, but did not show the same successional trends. Extracellular enzyme activity did not differ with forest succession, but varied by season with greater rates of potential activity in the dry seasons. We found few robust significant relationships among microbial community parameters and soil pH, moisture, carbon, and nitrogen concentrations. Observed inter‐ and intrannual variability in microbial community structure and activity reveal the importance of a multiple, temporal sampling strategy when investigating microbial community dynamics with land‐use change. Successional control over microbial composition with forest recovery suggests strong links between above and belowground communities.     

Inorganic nitrogen and microbial biomass dynamics before and during spring snowmelt

Recent work in seasonally snow covered ecosystems has identifiedthawed soil and high levels of heterotrophic activity throughout the winterunder consistent snow cover. We performed measurements during the winter of1994 to determine how the depth and timing of seasonal snow cover affectsoil microbial populations, surface water NO loss during snowmelt, and plant Navailability early in the growing season. Soil under early accumulating,consistent snow cover remained thawed during most of the winter and bothmicrobial biomass and soil inorganic N pools gradually increased under thesnowpack. At the initiation of snowmelt, microbial biomass N pools increasedfrom 3.0 to 5.9 g n m^-2,concurrent with a decrease in soil inorganic N pools. During the latterstages of snowmelt, microbial biomass N pools decreased sharply without aconcurrent increase in inorganic N pools or significant leaching losses. Incontrast, soil under inconsistent snow cover remained frozen during most ofthe winter. During snowmelt, microbial biomass initially increased from 1.7to 3.1 g N m^-2 and thendecreased as sites became snow-free. In contrast to smaller pool sizes,NO export during snowmeltfrom the inconsistent snow cover sites of 1.14 (±0.511) g N m^-2 was significantly greater (p< 0.001) than the 0.27 (±0.16) g N m^-2 exported from sites with consistent snowcover. These data suggest that microbial biomass in consistentlysnow-covered soil provides a significant buffer limiting the export ofinorganic N to surface water during snowmelt. However, this buffer is verysensitive to changes in snowpack regime. Therefore, interannual variabilityin the timing and depth of snowpack accumulation may explain the year toyear variability in inorganic N concentrations in surface water theseecosystems.     

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。     

Effect of soil microorganisms and labile C availability on soil respiration in response to litter inputs in forest ecosystems: A meta‐analysis

Litter inputs can influence soil respiration directly through labile C availability and, indirectly, through the activity of soil microorganisms and modifications in soil microclimate; however, their relative contributions and the magnitude of any effect remain poorly understood. We synthesized 66 recently published papers on forest ecosystems using a meta‐analysis approach to investigate the effect of litter inputs on soil respiration and the underlying mechanisms involved. Our results showed that litter inputs had a strong positive impact on soil respiration, labile C availability, and the abundance of soil microorganisms, with less of an impact related to soil moisture and temperature. Overall, soil respiration was increased by 36% and 55%, respectively, in response to natural and doubled litter inputs. The increase in soil respiration induced by litter inputs showed a tendency for coniferous forests (50.7%)> broad‐leaved forests (41.3%)> mixed forests (31.9%). This stimulation effect also depended on stand age with 30‐ to 100‐year‐old forests (53.3%) and ≥100‐year‐old forests (50.2%) both 1.5 times larger than ≤30‐year‐old forests (34.5%). Soil microbial biomass carbon and soil dissolved organic carbon increased by 21.0%‐33.6% and 60.3%‐87.7%, respectively, in response to natural and doubled litter inputs, while soil respiration increased linearly with corresponding increases in soil microbial biomass carbon and soil dissolved organic carbon. Natural and doubled litter inputs increased the total phospholipid fatty acid (PLFA) content by 6.6% and 19.7%, respectively, but decreased the fungal/bacterial PLFA ratio by 26.9% and 18.7%, respectively. Soil respiration also increased linearly with increases in total PLFA and decreased linearly with decreases in the fungal/bacterial PLFA ratio. The contribution of litter inputs to an increase in soil respiration showed a trend of total PLFA > fungal/bacterial PLFA ratio > soil dissolved organic carbon > soil microbial biomass carbon. Therefore, in addition to forest type and stand age, labile C availability and soil microorganisms are also important factors that influence soil respiration in response to litter inputs, with soil microorganisms being more important than labile C availability.     

Litterfall and litter nutrient dynamics under cocoa ecosystems in lowland humid Ghana

There have been few studies quantifying litterfall, standing litterstock and gross litter decomposition following forest conversion to plantation crops such as cocoa. Additionally, an assessment of changing processes occurring in forest floor litter systems with plantation age is lacking. We investigated litterfall production, standing litter changes and litter decomposition along a chronosequence of shaded cocoa farm fields (secondary forest, 3, 15 and 30-year-old) in the moist semi-deciduous forest belt in the Ashanti Region of Ghana in West Africa over 24 months. Mean annual litterfall production differed significantly among study sites and ranged from 5.0 to 10.4 Mg DM ha^?1. Similarly, standing litter differed significantly between land-use /plot ages. The results showed significant differences in quality between litter from forest and litter from cocoa plantations. Litterfall from forests had higher concentrations of nitrogen and lower concentration of soluble polyphenols and lignin compared to litter from cocoa systems. Monthly decomposition coefficients (k) estimated as $ k = {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} \mathord{\left/ {\vphantom {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}}} \right. } {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}} $ , where A is litterfall production during the month, L₀ is the standing litterstock at the beginning of the month and L₁ is the standing litterstock at the end of the month. Annual decomposition coefficients (k _L ) were similar in cocoa systems (0.221–0.227) but higher under secondary forests (0.354). Correlations between litter quality parameters and the decomposition coefficient showed nitrogen and lignin concentrations as well as ratios that include nitrogen are the best predictors of decomposition for the litters studied. Our results confirm the hypothesis that decomposition decreases following forest conversion to shaded cocoa systems because of litter quality changes and that decomposition rates correlate to litter quality differences between forest and cocoa ecosystems. The study also showed that standing litter pools and litterfall production in recently converted cocoa plantations are low compared to secondary forests or mature cocoa systems. Management strategies involving the introduction of upper canopy species during plantation development with corresponding replacement of tree mortality with diverse fast growing species will provide high quality and quantity litter resources.     

The Impact of Invasive Earthworms on Soil Respiration and Soil Carbon Within Temperate Hardwood Forests

Improving current understanding of the factors that control soil carbon (C) dynamics in forest ecosystems remains an important topic of research as it plays an integral role in the fertility of forest soils and the global C cycle. Invasive earthworms have the potential to alter soil C dynamics, though mechanisms and effects remain poorly understood. To investigate potential effects of invasive earthworms on forest C, the forest floor, mineral soil, fine root biomass, litterfall and microbial litter decay rates, and total soil respiration (TSR) over a full year were measured at an invaded and uninvaded deciduous forest site in southern Ontario. The uninvaded site was approximately 300 m from the invaded site and a distinct invasion front between sites was present. Along the invasion front, the biomass of the forest floor was negatively correlated with earthworm abundance and biomass. There was no significant difference between litterfall, microbial litter decay, and TSR between the invaded and uninvaded sites, but fine root biomass was approximately 30% lower at the invaded site. There was no significant difference in total soil C pools (0–30 cm) between the invaded and uninvaded sites. Despite profound impacts on forest floor soil C pools, earthworm invasion does not significantly increase TSR, most likely because increased heterotrophic respiration associated with earthworms is largely offset by a decrease in autotrophic respiration caused by lower fine root biomass.     

凋落物和根系去除对滨海沙地土壤微生物群落组成和功能的影响

通过在亚热带滨海防护林湿地松、尾巨桉、纹荚相思和木麻黄人工林中设置去除凋落物、去除根系和对照处理,分析改变地上、地下碳输入对沙地人工林土壤微生物生物量、群落结构和功能的影响.2015年9月,在处理设置一年后采集各处理样方0～10 cm土壤样品,分别采用磷脂脂肪酸分析方法和微孔板酶检测技术对土壤样品的微生物群落组成和6种酶活性进行测定.结果表明: 碳输入处理对土壤微生物生物量的影响因树种而异,并主要取决于凋落物和根系的质量.在尾巨桉林中,去除根系使得脂肪酸总量、革兰氏阳性细菌、革兰氏阴性细菌、真菌和放线菌生物量分别显著减少了31%、30%、32%、36%和26%,去除凋落物使得革兰氏阳性细菌、真菌和放线菌生物量显著减少了24%、27%和24%,而其他树种处理对微生物生物量无显著影响.碳输入处理对土壤微生物群落结构的影响主要表现为真菌丰度下降而放线菌丰度上升.不同树种的土壤酶活性对处理的响应表现不一致:湿地松、纹荚相思和木麻黄林分去除凋落物显著降低土壤中纤维素水解酶、β-葡萄糖苷酶、酸性磷酸酶和乙酰氨基葡萄糖苷酶活性,去除根系仅分别降低和提高了湿地松和纹荚相思林β-葡萄糖苷酶的活性;湿地松、木麻黄人工林去除凋落物显著降低了多酚氧化酶和过氧化物酶活性;去除根系对所有树种土壤氧化酶活性影响不显著.不同树种的凋落物、根系特性是影响土壤微生物群落组成和酶活性的重要因子,碳输入处理造成的土壤温度、水分等微环境的改变也是土壤微生物性质变化的重要驱动力.     

氮肥添加对高寒藏嵩草(Kobresia tibetica)沼泽化草甸和土壤微生物群落的影响

以藏嵩草沼泽化草甸为研究对象,利用磷脂脂肪酸(PLFA)技术,研究连续6年N素添加对地上植被群落数量特征、土壤微生物群落结构的影响。结果表明:①藏嵩草沼泽化草甸群落生物量、枯枝落叶对施肥处理无明显响应,且莎草科植物对土壤氮素的吸收和利用率较低。②施肥增加了0-10 cm土壤微生物类群PLFAs丰富度尤其细菌和革兰氏阳性菌PLFAs,降低了10-20 cm PLFAs丰富度;③磷脂脂肪酸饱和脂肪酸/单烯不饱和脂肪酸、细菌PLFAs/真菌PLFAs的比值随土壤层次增加而增加;④0-10 cm土层革兰氏阳性菌、真菌PLFAs含量与pH、土壤速效磷、速效氮、土壤有机质显著正相关(P0.05或P0.01);10-20 cm土层,细菌、革兰氏阳性菌、真菌和总PLFAs含量与土壤有机质含量显著正相关(P0.05或P0.01)。表明藏嵩草沼泽化草甸微生物PLFAs含量和丰富度对施肥的响应存在明显的土层梯度效应,土壤微生物PLFAs含量和丰富度主要受表层土壤初始养分含量的影响。     

Root controls on soil microbial community structure in forest soils

We assessed microbial community composition as a function of altered above- and belowground inputs to soil in forest ecosystems of Oregon, Pennsylvania, and Hungary as part of a larger Detritus Input and Removal Treatment (DIRT) experiment. DIRT plots, which include root trenching, aboveground litter exclusion, and doubling of litter inputs, have been established in forested ecosystems in the US and Europe that vary with respect to dominant tree species, soil C content, N deposition rate, and soil type. This study used phospholipid fatty-acid (PLFA) analysis to examine changes in the soil microbial community size and composition in the mineral soil (0–10 cm) as a result of the DIRT treatments. At all sites, the PLFA profiles from the plots without roots were significantly different from all other treatments. PLFA analysis showed that the rootless plots generally contained larger quantities of actinomycete biomarkers and lower amounts of fungal biomarkers. At one of the sites in an old-growth coniferous forest, seasonal changes in PLFA profiles were also examined. Seasonal differences in soil microbial community composition were greater than treatment differences. Throughout the year, treatments without roots continued to have a different microbial community composition than the treatments with roots, although the specific PLFA biomarkers responsible for these differences varied by season. These data provide direct evidence that root C inputs exert a large control on microbial community composition in the three forested ecosystems studied.     

Response of Microbial Community Composition and Function to Soil Climate Change

Soil microbial communities mediate critical ecosystem carbon and nutrient cycles. How microbial communities will respond to changes in vegetation and climate, however, are not well understood. We reciprocally transplanted soil cores from under oak canopies and adjacent open grasslands in a California oak–grassland ecosystem to determine how microbial communities respond to changes in the soil environment and the potential consequences for the cycling of carbon. Every 3 months for up to 2 years, we monitored microbial community composition using phospholipid fatty acid analysis (PLFA), microbial biomass, respiration rates, microbial enzyme activities, and the activity of microbial groups by quantifying ¹³C uptake from a universal substrate (pyruvate) into PLFA biomarkers. Soil in the open grassland experienced higher maximum temperatures and lower soil water content than soil under the oak canopies. Soil microbial communities in soil under oak canopies were more sensitive to environmental change than those in adjacent soil from the open grassland. Oak canopy soil communities changed rapidly when cores were transplanted into the open grassland soil environment, but grassland soil communities did not change when transplanted into the oak canopy environment. Similarly, microbial biomass, enzyme activities, and microbial respiration decreased when microbial communities were transplanted from the oak canopy soils to the grassland environment, but not when the grassland communities were transplanted to the oak canopy environment. These data support the hypothesis that microbial community composition and function is altered when microbes are exposed to new extremes in environmental conditions; that is, environmental conditions outside of their “life history” envelopes.     

Characterization of Microbial Consortia in Paddy Rice Soil by Phospholipid Analysis

Abstract Microbial biomass and community structure in paddy rice soil during the vegetation period of rice were estimated by analysis of their phospholipid fatty acids (PLFA), hydroxy fatty acids of lipopolysaccharides (LPS-HYFA), and phospholipid ether lipids (PLEL) directly extracted from the soil. A clear change in the composition of the community structure at different sampling periods was observed, indicated by the principal component analysis of the PLFA. A dramatic decline of ester-linked PLFA was observed in the soil samples taken at the second sampling time. In contrast to the ester-linked PLFA, the non-ester-linked PLFA composition did not change. The hydroxy fatty acids of lipopolysaccharides as well as ether lipids decreased consecutively during the observation period. Total microbial abundance was estimated to be (4.1–7.3) × 10⁹ cells g^-1 soil (dry weight). About 44% account for aerobic and 32% for facultative anaerobic bacteria, and 24% for archaea, on average. According to the profile and patterns of PLFA in the soil sample, it may be suggested that the paddy soil at the August sampling period contained more abundant facultative anaerobic bacteria (ca. 36%) and archaea (ca. 37%), but the total microbial biomass was significantly lower than in the remaining sampling periods. As the plant approached maturity, the microbial community structure in the soil changed to contain more abundant Gram-negative bacteria and methanotrophs. Received: 23 September 1999; Accepted: 28 February 2000; Online Publication: 12 May 2000     

亚热带常见造林树种对土壤细菌及微生物功能群的影响

为揭示亚热带人工林常见造林树种对森林土壤微生物群落的影响,本研究选取马尾松、米老排、枫香、冬青、火力楠、麻栎和光皮桦7个树种为研究对象,采用16S rRNA高通量测序和实时荧光定量PCR技术,探究不同树种土壤细菌的多样性、群落构成以及微生物功能群基因丰度。结果表明: 变形菌门、酸杆菌门和放线菌门是亚热带造林树种的优势细菌门,不同树种细菌多样性和丰富度指数无显著差异。冗余分析表明,土壤容重、土壤C/N、凋落物氮和凋落物C/N是影响土壤细菌组成的主要环境因子。不同造林树种土壤中氨氧化古菌、氨氧化细菌和完全氨氧化菌amoA基因丰度均具有显著差异。完全氨氧化菌在数量上占据优势地位,但只有氨氧化古菌amoA基因丰度与土壤硝态氮呈显著正相关关系,表明氨氧化古菌在亚热带酸性森林土壤自养硝化作用中可能发挥主要作用。相关分析表明,凋落物氮是不同树种影响氨氧化微生物丰度变化的关键驱动因子。本研究表明,土壤微生物功能群对树种的响应比细菌群落结构更加敏感,未来应从微生物功能群角度深入探究不同造林树种对森林生态系统功能的影响机制。     

Effects of wear and above ground forest site type characteristics on the soil microbial community structure in an urban setting

We studied the effects of wear on the understorey vegetation and the soil microbial community structure (phospholipid fatty acid pattern) in urban forests of medium fertility and of varying size in the capital area of Finland, Helsinki. These forests are important sites of recreation for a large number of residents. Consequently, the cover of understorey vegetation is affected by trampling. In the study, the cover of ground layer plant species (mosses) was found to be lower than in rural reference areas. We found that microbial activity, measured as soil respiration, was lower in the most worn forest patches as compared to less worn sites. Further, the microbial community structure of the humus layer changed due to the effects of wear. By comparing the PLFA pattern in trampled and un-trampled forest patches, we found out that the most important factors affecting the structure of microbial community were the dominant tree species (the proportion of broad-leaved tree species in relation to conifers), and the composition of the understorey vegetation. Thus, we could conclude that wear affects the microbial community structure through changes in vegetation, in the quality of litter shed, and through resultant changes in the humus pH, rather than only through soil compaction.     

Changes in Soil Microbial Community Structure Influenced by Agricultural Management Practices in a Mediterranean Agro-Ecosystem

Agricultural practices have proven to be unsuitable in many cases, causing considerable reductions in soil quality. Land management practices can provide solutions to this problem and contribute to get a sustainable agriculture model. The main objective of this work was to assess the effect of different agricultural management practices on soil microbial community structure (evaluated as abundance of phospholipid fatty acids, PLFA). Five different treatments were selected, based on the most common practices used by farmers in the study area (eastern Spain): residual herbicides, tillage, tillage with oats and oats straw mulching; these agricultural practices were evaluated against an abandoned land after farming and an adjacent long term wild forest coverage. The results showed a substantial level of differentiation in the microbial community structure, in terms of management practices, which was highly associated with soil organic matter content. Addition of oats straw led to a microbial community structure closer to wild forest coverage soil, associated with increases in organic carbon, microbial biomass and fungal abundances. The microbial community composition of the abandoned agricultural soil was characterised by increases in both fungal abundances and the metabolic quotient (soil respiration per unit of microbial biomass), suggesting an increase in the stability of organic carbon. The ratio of bacteria:fungi was higher in wild forest coverage and land abandoned systems, as well as in the soil treated with oat straw. The most intensively managed soils showed higher abundances of bacteria and actinobacteria. Thus, the application of organic matter, such as oats straw, appears to be a sustainable management practice that enhances organic carbon, microbial biomass and activity and fungal abundances, thereby changing the microbial community structure to one more similar to those observed in soils under wild forest coverage.     

Soil Moisture Alters the Response of Soil Organic Carbon Mineralization to Litter Addition

Increasing rainfall and longer drought conditions lead to frequent changes in soil moisture that affect soil organic carbon (SOC) mineralization. However, how soil moisture affects response of SOC mineralization to litter addition in forest ecosystems remains unexplored. We added ¹³C-labeled litter to subtropical forest soils with three mass water contents (L, 21%; M, 33%; H, 45%). Carbon dioxide production was monitored, and the composition of soil microbial communities was determined by phospholipid fatty acid (PLFA). When no litter was added, SOC mineralization was greater in the M-treated soil. Litter addition promoted SOC mineralization, but this promotion was altered by soil moisture and litter type. Priming effects induced by P. massoniana leaf litter in the M-moistened soil were significantly (P < 0.05) higher than those in other treatments. Litter-derived C was approximately 55% incorporated into 18:1ω9c and 16:0 PLFAs, and this proportion was not significantly affected by soil moisture. Soil moisture affected the distribution of litter-¹³C in i15:0, i17:0, and cy19:0 individual PLFAs. The primed C evolution was significantly related to the ratio of Gram-positive to Gram-negative bacteria. These results suggest that changes in soil moisture could affect SOC mineralization in forest ecosystems.     

亚热带森林转换对土壤无脊椎动物群落结构的影响

受人类活动干扰的增加,亚热带森林频繁转换为次生林和人工林,可能显著影响土壤无脊椎动物群落结构及其生态功能,但当前的认识并不一致。因此,于2022年7月调查了亚热带天然常绿阔叶林转换为次生林、米槠人工林、杉木人工林后土壤无脊椎动物群落结构特征。共捕获土壤无脊椎动物659只,丰度为26540只/m²,隶属1门6纲13目59科,其中蚁科和球角 虫 兆 科为优势类群。森林转换改变了土壤无脊椎动物群落组成和多样性。天然林向米槠人工林和杉木人工林转换后,土壤无脊椎动物丰度和类群均明显降低,其中大型土壤无脊椎动物丰度的响应更为敏感,在2种林型中分别显著降低了33.58%和36.53%。尽管林型转换对土壤无脊椎动物群落多样性指数无显著影响,但改变了土壤无脊椎动物群落组成,其中天然林与杉木人工林群落组成极不相似(J ＜ 0.25),等节 虫 兆 科为杉木人工林优势类群,占比达到59.84%。冗余分析显示,土壤湿度、凋落物现存量和凋落物磷含量是影响土壤无脊椎动物群落的主要因子,对土壤无脊椎动物群落的解释率为69.30%。可见,林型转换可能通过改变土壤理化性质和凋落物质量,调控土壤无脊椎动物群落结构。     

Leaf Litter Mixtures Alter Microbial Community Development: Mechanisms for Non-Additive Effects in Litter Decomposition

To what extent microbial community composition can explain variability in ecosystem processes remains an open question in ecology. Microbial decomposer communities can change during litter decomposition due to biotic interactions and shifting substrate availability. Though relative abundance of decomposers may change due to mixing leaf litter, linking these shifts to the non-additive patterns often recorded in mixed species litter decomposition rates has been elusive, and links community composition to ecosystem function. We extracted phospholipid fatty acids (PLFAs) from single species and mixed species leaf litterbags after 10 and 27 months of decomposition in a mixed conifer forest. Total PLFA concentrations were 70% higher on litter mixtures than single litter types after 10 months, but were only 20% higher after 27 months. Similarly, fungal-to-bacterial ratios differed between mixed and single litter types after 10 months of decomposition, but equalized over time. Microbial community composition, as indicated by principal components analyses, differed due to both litter mixing and stage of litter decomposition. PLFA biomarkers a15∶0 and cy17∶0, which indicate gram-positive and gram-negative bacteria respectively, in particular drove these shifts. Total PLFA correlated significantly with single litter mass loss early in decomposition but not at later stages. We conclude that litter mixing alters microbial community development, which can contribute to synergisms in litter decomposition. These findings advance our understanding of how changing forest biodiversity can alter microbial communities and the ecosystem processes they mediate.