Effects of vegetational type and soil depth on soil microbial communities on the Loess Plateau of China

Soil microbial communities are very sensitive to changes in land use and are often used as indicators of soil fertility. We evaluated the microbial communities in the soils of four types of vegetation (cropland (CP), natural grassland (NG), broadleaf forest (BF) and coniferous forest (CF)) at depths of 0–10 and 10–20 cm on the Loess Plateau in China using phospholipid fatty acid (PLFA) profiling and denaturing gradient gel electrophoresis (DGGE) of DNA amplicons from polymerase chain reactions. The soil microbial communities were affected more by vegetation type than by soil depth. Total organic carbon, total nitrogen, soil-water content, pH, bulk density (BD) and C:N ratio were all significantly associated with the composition of the communities. Total PLFA, bacterial PLFA and fungal PLFA were significantly higher in the BF than the CP. The DGGE analyses showed that NG had the most diverse bacterial and fungal communities. These results confirmed the significant effect of vegetation type on soil microbial communities. BFs and natural grass were better than the CFs for the restoration of vegetation on the Loess Plateau.     

Interactive effects of elevation and land use on soil bacterial communities in the Tibetan Plateau

The Tibetan Plateau of China is uniquely vulnerable to the global climate change and anthropogenic disturbances. As soil bacteria exert a considerable influence on the ecosystem function, understanding their response to different climates and land-use types is important. Here, we characterized the bacterial community composition and diversity across three major ecosystems (cropland, forest, and grassland) in the Sygera Mountains of Tibet, along a typical elevational gradient (3 300-4 600 m). The abundance of taxa that preferentially inhabit neutral or weak alkaline soil environments (such as Actinobacteria, Thermoleophilia, and some non-acidophilus Acidobacteria) was significantly greater in the cropland than in the forest and grassland. Furthermore, the diversity of soil bacterial communities was also significantly greater in the cropland than in the forest and grassland. We observed a unimodal distribution of bacterial species diversity along the elevation gradient. The dominant phyla Acidobacteria and Proteobacteria exhibited consistent elevational distribution patterns that mirrored the abundance of their most abundant classes, while different patterns were observed for Acidobacteria and Proteobacteria at the class level. Soil pH was the primary edaphic property that regulated bacterial community composition across the different land-use types. Additionally, soil pH was the main factor distinguishing bacterial communities in managed soils (i.e., cropland) from the communities in the natural environments (i.e., forest and grassland). In conclusion, land use (particularly anthropogenic disturbances such as cropping) largely controlled soil environment, played a major role in driving bacterial community composition and distribution, and also surpassed climate in affecting bacterial community distribution.     

Development of soil microbial communities during tallgrass prairie restoration

Soil microbial communities were examined in a chronosequence of four different land-use treatments at the Konza Prairie Biological Station, Kansas. The time series comprised a conventionally tilled cropland (CTC) developed on former prairie soils, two restored grasslands that were initiated on former agricultural soils in 1998 (RG₉₈) and 1978 (RG₇₈), and an annually burned native tallgrass prairie (BNP), all on similar soil types. In addition, an unburned native tallgrass prairie (UNP) and another grassland restored in 2000 (RG₀₀) on a different soil type were studied to examine the effect of long-term fire exclusion vs. annual burning in native prairie and the influence of soil type on soil microbial communities in restored grasslands. Both 16S rRNA gene clone libraries and phospholipid fatty acid analyses indicated that the structure and composition of bacterial communities in the CTC soil were significantly different from those in prairie soils. Within the time series, soil physicochemical characteristics changed monotonically. However, changes in the microbial communities were not monotonic, and a transitional bacterial community formed during restoration that differed from communities in either the highly disturbed cropland or the undisturbed original prairie. The microbial communities of RG₉₈ and RG₀₀ grasslands were also significantly different even though they were restored at approximately the same time and were managed similarly; a result attributable to the differences in soil type and associated soil chemistry such as pH and Ca. Burning and seasonal effects on soil microbial communities were small. Similarly, changing plot size from 300 m² to 150 m² in area caused small differences in the estimates of microbial community structure. In conclusion, microbial community structure and biochemical properties of soil from the tallgrass prairie were strongly impacted by cultivation, and the microbial community was not fully restored even after 30 years.     

Changes of the functional diversity of soil microbial community during the colonization of abandoned grassland by a forest

The impact of secondary succession of grassland communities towards a Norway spruce forest on soil microbial community was studied on a belt transect established in the Pol’ana Mts., Central Europe. Data on understory vegetation, light availability, soil properties and microbial activity were collected on 147 plots distributed over regular grid. Moreover, distributions of functional groups of microorganisms were assessed using BIOLOG analysis on a subset of 27 plots. Mantel partial correlations between microbial community indicators and environmental variables showed that microbial activity generally decreased with increasing tree density and size, whereas it increased with increasing radiation at the soil surface, soil temperature, and cover and diversity of understory vegetation. Functional richness and diversity of microorganisms were positively correlated with solar radiation, but also with plant species richness and diversity. Abundance of several functional groups correlated closely with succession-related variables. Redundance analysis of microbial data provided slightly different outcomes. Forward selection yielded only two environmental variables significantly influencing the composition of the microbial community: tree influence potential and organic carbon content. Abundances of several functional microbial groups correlated with tree influence, documenting that microbial community changes are at least partially driven by the colonization of grassland by trees. Nevertheless, the relative importance of abiotic environment change and plant community succession on microbial community dynamics remains unresolved.     

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

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

Differences in the composition and diversity of bacterial communities from agricultural and forest soils

Differences in the bacterial communities of soils caused by disturbances and land management were identified in rRNA gene libraries prepared from conventional tilled (CT) and no tilled (NT) cropland, a successional forest after 30 y of regrowth (NF) and an old forest of >65 y (OF) at Horseshoe Bend, in the southern Piedmont of Georgia (USA). Libraries were also prepared from forests after 80 y of regrowth at the Coweeta Long Term Ecological Research site (CWT) in the Southern Appalachians of western North Carolina (USA). The composition of the bacterial communities in cropland soils differed from those of the Horseshoe Bend OF and CWT forest soils, and many of the most abundant OTUs were different. Likewise, the diversity of bacterial communities from forest was less than that from cropland. The lower diversity in forest soils was attributed to the presence of a few, very abundant taxa in forest soils that were of reduced abundance or absent in cropland soils. After 30 y of regrowth, the composition of the bacterial soil community of the NF was similar to that of the OF, but the diversity was greater. These results suggested that the bacterial community of soil changes slowly within the time scale of these studies. In contrast, the composition and diversity of the bacterial communities in the Horseshoe Bend OF and Coweeta soils were very similar. Thus, this forest soil bacterial community was widely distributed in spite of the differences in soil properties, vegetation, and climate as well as resilient to disturbances of the above ground vegetation.     

Effects of crop abandonment and grazing exclusion on available soil water and other soil properties in a semi-arid Mongolian grassland

Improper cropping and overgrazing have led to land degradation in semi-arid regions, resulting in desertification. During desertification, vegetation changes have been widely observed, and are likely controlled to some extent by soil water. The purpose of this study was to investigate changes in soil physical properties, organic C, and vegetation induced by land-use changes, with special reference to the dynamics of available soil water. We selected four study sites in a typical Mongolian steppe grassland: grassland protected from grazing, grazed grassland, abandoned cropland, and cultivated cropland. Grazing exclusion increased the cover of perennial grass, with little increase in the root weight. Since there was no difference in available water between the grasslands with and without grazing, there appears to be no serious soil compaction due to overgrazing. On the other hand, vegetation cover and the number of species were poor in both abandoned cropland and cultivated cropland. However, the root weight was greater in abandoned cropland. Although the abandonment of cultivation appeared to increase organic C, available water did not differ significantly in comparison with cultivated cropland. The silt contents were significantly lower in abandoned and cultivated cropland than in both grasslands, suggesting the effects of wind erosion. In addition, the silt contents were positively correlated with the volume fraction of storage pores for available water. Therefore, the lower silt contents may constrain the volume of available water in abandoned cropland. Moreover, the unsaturated hydraulic conductivity results indicated that the diameters of storage pores for available water at the present study sites were smaller than those suggested by previous studies. Although the differences in vegetation cover by different land-use types were observed at every site, differences in the volume of available water were observed at between abandoned cropland and cultivated cropland. The reason why the no differences in available water between grazed grassland and grasslands protected from grazing may be short time of grazing exclusion for 2 years for evaluating the effects of exclusion on soil properties.     

Succession of plant and soil microbial communities with restoration of abandoned land in the Loess Plateau, China

Purpose

There have been a number of studies on the succession of vegetation; however, the succession of soil microbes and the collaborative relationships between microbes and vegetation during land restoration remain poorly understood. The objectives of this study were to characterize soil microbial succession and to explore the collaborative mechanisms between microbes and vegetation during the restoration of abandoned land through quantitative ecology methods.

Materials and methods

The present research was carried out in the succession of a 5-year abandoned land and its conversion to Hippophae rhamnoides shrubs, Larix principis-rupprechtii plantation, and a naturally regenerated forest (mixed forest). Soil bacterial, archaeal and fungal characteristics were tested by real-time quantitative PCR assays and terminal restriction fragment length polymorphism. The richness, diversity, and evenness indices were employed to analyze plant and microbial communities’ structure. The stability of plant and microbial communities was tested using Spearman’s rank correlation. The relationships between the regeneration scenarios and environmental factors were determined through canonical correspondence analysis.

Results and discussion

The aboveground biomass was significantly different among the sites. Soil bacterial, archaeal, and fungal rRNA gene abundances did not increase significantly with increasing soil organic carbon content. There were higher correlation coefficients between plant and total microbial communities on the richness, diversity, and evenness indices and ratios of positive to negative association compared to ones between plant and individual bacteria, archaea, and fungi. Soil bulk density, clay, pH, and litter were the primary significant environmental factors affecting the structure of plant and microbial communities. The positive relationships between plant and soil bacteria, fungi, and total microbe communities, as well as the negative relationships between plant and archaea, were demonstrated.

Conclusions

The results suggested that plants promote the growth of soil bacteria and fungi during the process of community succession on a small scale; however, plants inhibit the growth of soil archaea.     

Long‐term changes of aggregate‐associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey

Soil management systems can have great effect on soil chemical, physical and biological properties. Conversion of forest to grassland and cropland can alter C and N dynamics. The objective of this study was to evaluate the changes in aggregate‐associated and labile soil organic C and N fractions after conversion of a natural forest to grassland and cropland in northern Turkey. This experiment was conducted on plots subject to three different adjacent land uses (forest, grassland and cropland). Soil samples were taken from 0–5, 5–15 and 15–30 cm depths from each land use. Some soil physical (soil texture, bulk density), chemical (soil pH, soil organic matter, lime content, total organic C and N, inorganic N, free and protected organic C) and biological (microbial biomass C and N, mineralizable C and N) properties were measured. The highest and lowest bulk densities were observed in grassland (1.41 g cm⁻³) and cropland (1.14 g cm⁻³), respectively. Microbial biomass C and total organic C in forest were almost twice greater than grassland and four‐times greater than cropland. Cultivation of forest reduced total organic N, mineralizable N and microbial biomass N by half. The great portion of organic C was stored in macroaggregates (>250 µm) in all the three land uses. Free organic C comprised smaller portion of soil organic C in all the three land uses. Thus, this study indicated that long‐term conversion of forest to grassland and cropland significantly decreased microbial biomass C, mineralizable C and physically protected organic C and the decreases were the greatest in cropland. Copyright © 2011 John Wiley & Sons, Ltd.     

Positive relationship between herbaceous layer diversity and the performance of soil biota in a temperate forest

The current decline in biodiversity is particularly pronounced in the herbaceous layer of forest ecosystems. We explored the relationship between a naturally occurring plant diversity gradient in the understory vegetation of a deciduous forest and several above-and belowground ecosystem processes. We show that particularly soil microbial parameters and microarthropod densities are positively correlated with plant species richness. These results confirm recent findings in grassland ecosystems and highlight the intimate interconnectance between the diversity and functioning of above-and belowground compartments. We conclude that irrespective of a potential causal relationship between plant species richness and belowground processes, it is essential to consider the performance of soil biota in order to understand the relationship between herbaceous layer composition and ecosystem function.     

喀斯特峰丛洼地不同植被类型土壤微生物量碳氮磷和养分特征

  目的  探讨桂西北喀斯特峰丛洼地不同植被类型的土壤理化性质和微生物碳(MBC)、微生物氮（MBN）、微生物磷（MBP）含量的变化特征及它们之间的关系。  方法  利用生态化学计量方法和Pearson相关性分析方法研究不同植被类型和土层深度对土壤MBC、MBN、MBP含量和土壤养分含量分布特征的影响。  结果  （1）不同植被类型土壤养分含量和MBC、MBN、MBP含量依次为次生林 > 灌木 > 灌草 > 草地 > 耕地;土壤养分垂直分布表现为随着土层深度加深而下降,不同土层间土壤有机碳（SOC）、全氮（TN）、全磷（TP）含量差异显著,土壤MBC、MBN和MBP含量在不同植被类型和不同土层间差异显著,均表现为MBC > MBN > MBP。（2）不同植被类型土壤MBC/SOC和MBP/TP的值较小,MBN/TN的差异较大。不同植被类型的土壤MBC/MBN差异显著,MBC/MBP变化范围较大,MBN/MBP表现为次生林 > 灌草 > 灌木 > 草地 > 耕地。（3）土壤MBC和MBN与SOC、TN、速效氮和速效钾呈显著或极显著正相关,与土壤容重、pH值表现出不同程度的负相关,表明植被恢复过程中土壤MBC和MBN可作为衡量土壤养分的敏感性指标。  结论  不同植被类型的土壤微生物生物量碳氮磷、养分含量和化学计量特征有明显的表聚效应,随着植被的正向演替,土壤结构、养分和微生物群落功能得到显著提高。     

Decoupling plant-growth from land-use legacies in soil microbial communities

Differences in soil microbial communities between ex-arable and undisturbed soils are often assumed to reflect long-term legacies of agricultural practices. Ex-arable soils, however, are commonly dominated by different plant species than undisturbed soils making it difficult to separate the importance of land-use and plant-growth legacies. In a system where non-native plants dominate ex-arable soils, we decoupled land-use (ex-arable, undisturbed) and plant-growth (native, non-native) effects on soil microbial communities using a factorial sampling design. Soils were removed from 14 sites that formed a 52-year chronosequence of agricultural abandonment. Microbial abundance and composition were measured using whole-soil phospholipid fatty acid analyses and microbial activity was measured in a subset of samples using sole-carbon-source utilization analyses. We found that both non-native-cultivated and ex-arable soils were independently associated with lower microbial abundance and diversity than native and undisturbed soils. We also found a correlation between microbial abundance and age-since-agricultural abandonment in ex-arable/non-native-cultivated soils suggesting that non-native plant effects accumulate over time. Microbial activity was consistent with microbial abundance; microbial communities in non-native-cultivated, ex-arable soils were slow to respire most carbon sources. Our data suggests that agricultural practices create soil conditions that favor non-native plant growth and non-native plants maintain these conditions. Potential mechanisms explaining how non-natives create soils with small microbial communities and how small microbial communities may benefit non-natives are discussed.     

Development of microbial community during primary succession in areas degraded by mining activities

Together with plants, soil microbial communities play an essential role in the development of stable ecosystems on degraded lands, such as postmining spoil heaps. Our study addressed concurrent development of the vegetation and soil fungal and bacterial communities in the course of primary succession in a brown coal mine spoil deposit area in the Czech Republic across a chronosequence spanning 54 years. During succession, the plant communities changed from sparse plants over grassland and shrubland into a forest, becoming substantially more diverse with time. Microbial biomass increased until the 21st year of ecosystem development and later decreased. Although there was a close association between fungi and vegetation, with fungi mirroring the differences in plant community assemblages, the development of the bacterial community was different. The early succession community in the barren nonvegetated soil largely differed from that in the older sites, especially in its high abundance of autotrophic and free‐living N₂‐fixing bacteria. Later in succession, bacterial community changes were minor and reflected the chemical parameters of the soil, including pH, which also showed a minor change with time. Our results show that complex forest ecosystems developed over 54 years on the originally barren soil of the temperate zone and indicate an important role of bacteria in the initial stage of soil development. Although the arrival of vegetation affects substantially fungal as well as bacterial communities, it is mainly fungi that respond to the ongoing development of vegetation.     

Microbial biomass nitrogen pool in soils from a warm temperate grassland,and from deciduous and evergreen forests in Chiba,central Japan

We evaluated the status of the microbial biomass N pool in grassland, and in deciduous and evergreen forest soils in Chiba, central Japan. Microbial biomass N, a labile fraction of total N in the soil, ranged from 6.96 g N m^-2 (15 cm depth) in the grassland to 24.8 g in the deciduous and 20.7 g in the evergreen soils, on a landscape basis. Thus the pattern in the grassland and in the forest soils differed. The N flush measured by a fumigation-incubation method indicated that in the grassland soil microbial biomass N was underestimated by a factor of 2.6 compared with the results from a fumigation-extraction method, because of heavy N immobilization in the microbial biomass. This was in contrast to results from the forest soils, which did not immobilize N. Thus, the forest soils were in a steady-state condition compared with the grassland which formed a seral phase in the ecological succession. Simple correlation coefficients indicated a significant positive relationship between biomass N and organic C in the soil and the N concentration in the litter, the main component of organic matter in the soils of the three ecosystems.     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

Composition of the microbial communities in the mineral soil under different types of natural forest

Phospholipid fatty acid (PLFA) patterns were used to describe the composition of the soil microbial communities under 12 natural forest stands including oak and beech, spruce-fir-beech, floodplain and pine forests. In addition to the quantification of total PLFAs, soil microbial biomass was measured by substrate-induced respiration and chloroform fumigation-extraction. The forest stands possess natural vegetation, representing an expression of the natural site factors, and we hypothesised that each forest type would support a specific soil microbial community. Principal component analysis (PCA) of PLFA patterns revealed that the microbial communities were compositionally distinct in the floodplain and pine forests, comprising azonal forest types, and were more similar in the oak, beech and spruce-fir-beech forests, which represent the zonal vegetation types of the region. In the nutrient-rich floodplain forests, the fatty acids 16:1ω5, 17:0cy, a15:0 and a17:0 were the most prevalent and soil pH seemed to be responsible for the discrimination of the soil microbial communities against those of the zonal forest types. The pine forest soils were set apart from the other forest soils by a higher abundance of PLFA 18:2ω6,9, which is typical of fungi and may also indicate ectomycorrhizal fungi associated with pine trees, and high amounts of PLFA 10Me18:0, which is common in actinomycetes. These findings suggest that the occurrence of azonal forest types at sites with specific soil conditions is accompanied by the development of specific soil microbial communities. The study provides information on the microbial communities in undisturbed forest soils which may facilitate interpretation of data derived from managed or even damaged or degraded forests.     

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.     

Microbial community development and unseen diversity recovery in inoculated sterile soil

Soil is considered as one of the most biodiverse environments on Earth; yet, the taxonomy, occurrence, and role of its different microbial populations are largely unknown. Here, two sterilized soils (from England and Italy) were inoculated with a subsample of their initial microbial communities and/or those from the other soil to study their microbial community evolution. This approach compared two driving factors (original community and soil physico-chemical characteristics) for microbial community definition. After 2 months of incubation and based on metagenomic datasets, the two inoculated communities (from an English grassland and an Italian forest) possessed similar functional and taxonomical structures when inoculated in the same sterile soil. For example, the newly colonized Italian soil was dominated by Actinobacteria related organisms (>66 % of the detected community) with a functional distribution independent of the inoculated soil origin. In addition, some of the organisms that dominated the different inoculated communities after 2 months were similar for a given sterile soil whether they came from the English grassland or the Italian forest, and they had not been detected in the original microbial community from either soil. Thus, similar microorganisms with low representation from the two distinct communities emerged in each sterilized soil, thus increasing the microbial diversity recovered from the microbial community of the donor soil. So far, these observations support the idea that different temperate soil microbial communities have different evenness due to environmental physico-chemical variations, yet have similar community composition (richness), and thus develop similarly when colonizing the same habitat.     

Spatial analysis reveals differences in soil microbial community interactions between adjacent coniferous forest and clearcut ecosystems

Knowledge of how forest management influences soil microbial community interactions is necessary for complete understanding of forest ecology. In this study, soil microbial communities, vegetation characteristics and soil physical and chemical properties were examined across a rectangular 4.57 × 36.58 m sample grid spanning adjacent coniferous forest and clearcut areas. Based on analysis of soil extracted phospholipid fatty acids, total microbial biomass, fungi and Gram-negative bacteria were found to be significantly reduced in soil of the clearcut area relative to the forest. Concurrent with changes in microbial communities, soil macroaggregate stability was reduced in the clearcut area, while no significant differences in soil pH and organic matter content were found. Variography indicated that the range at which spatial autocorrelation between samples was evident (patch size) was greater for all microbial groups analyzed in the clearcut area. Overall, less spatial structure could be resolved in the forest. Variance decomposition using principal coordinates of neighbor matrices spatial variables indicated that soil aggregate stability and vegetation characteristics accounted for significant microbial community spatial variation in analyses that included the entire plot. When clearcut and forest areas were analyzed separately, different environmental variables (pH in the forest area and soil organic matter in the clearcut) were found to account for variation in soil microbial communities, but little of this variation could be ascribed to spatial interactions. Most microbial variation explained by different components of microbial communities occurred at spatial scales other than those analyzed. Fungi accounted for over 50% of the variation in bacteria of the forest area but less than 11% in the clearcut. Conversely, AMF accounted for significant variation in clearcut area, but not forest, bacteria. These results indicate broadly disparate controls on soil microbial community composition in the two systems. We present multiple lines of evidence pointing toward shifts in fungi functional groups as a salient mechanism responsible for qualitative, quantitative and spatial distribution differences in soil microbial communities.     

不同土地利用方式对土壤有机无机碳比例的影响

【目的】 土壤有机碳 (SOC) 和无机碳 (SIC) 对全球碳循环和减缓气候变化具有重要作用,进一步明确二者之间相互转化关系,对准确估算土壤碳储量具有重要意义。现有研究对SOC和SIC相互关系缺乏系统量化,研究结果不一。因此,明确SOC和SIC之间相互关系,可为准确估算和模拟土壤碳的转化过程提供理论基础。 【方法】 本研究搜集了我国1990—2018年已发表的文献共41篇,从不同气候区、不同土地利用方式、不同土层深度探究了SOC和SIC比例的变化,进一步量化了二者之间的相互关系。 【结果】 不同气候区、不同土地利用方式下土壤SOC/SIC值在0—20 cm土层均大于20—100 cm土层。具体来说,在温带大陆性气候区,草地0—20 cm土壤SOC/SIC值最小 (0.53),林地 (0.90) 和农田 (0.80) 土壤较高,且三种土地利用方式下SOC和SIC呈极显著正相关关系;而在温带季风性气候区,0—20 cm土壤SOC/SIC值表现为草地 (0.82) ≈ 农田 (1.05) > 林地 (0.29),且SOC和SIC在林地、农田土壤中呈正相关关系,但在草地土壤中二者为负相关关系。另外,温带大陆性气候区20—100 cm以林地土壤SOC/SIC值最高,草地和农田次之,而在温带季风性气候区三种土地利用方式下无显著差异;SOC和SIC在林地和农田土壤中呈正相关关系,然而在草地土壤中为负相关关系。温带大陆性气候区SOC/SIC值总体以林地较大,农田、草地次之。温带季风性气候区,0—20 cm土层SOC/SIC值以草地较大,农田和林地分别次之。这可能是因为植被覆盖不同,导致了作物碳的归还量不一。同时,不同的植被覆盖还影响了土壤中的各种生物化学进程,改变了碳在土壤中的循环转化过程,进而影响了SOC和SIC含量,使得SOC/SIC值产生较大差异。 【结论】 SOC和SIC之间存在循环转化关系,且不同气候条件、不同土地利用方式、不同土壤类型对SOC和SIC循环转化存在显著影响。不同条件下SOC/SIC值存在显著差异,且二者呈现不同的相关性。本研究结果可为明确土壤碳的循环积累机制,准确估算土壤有机和无机碳库提供理论依据。