Multistate assessment of wetland restoration on CO2 and N2O emissions and soil bacterial communities

Over the last 200 years, wetlands have been converted to other land uses leading to the loss of approximately 53% of wetlands in the continental United States. In the late 1980's, policies were instated to mitigate further wetland loss through wetland creation and restoration. Restored wetlands provide important ecosystem services, such as filtration of nutrients and wildlife habitat. However, these benefits could be offset by increased greenhouse gas production. We assessed the impact of wetland conversion to agriculture and restoration on CO₂ and N₂O emissions and microbial communities in three land use types: wetlands with native vegetation (natural); wetlands converted to agricultural management (converted); and restored wetlands (restored). Soil properties varied among land use types. Most notably, soils from restored and converted sites had the lowest C and N, and higher pH. Multivariate analysis of soil properties showed the pocosin wetlands in North Carolina separating from all other locations, regardless of land use. Soil bacterial communities showed a similar trend with communities from North Carolina soils separating from the others with no significant effect of land use or season. Furthermore, land use did not have a significant effect on CO₂ or N₂O emissions, although there was significant temporal variation in CO₂ emissions. These findings indicate that while wetland conversion and restoration may alter some soil properties, these alterations do not appear to be great enough to override the underlying geographic and edaphic influences on soil bacterial communities. Furthermore, wetland restoration did not lead to increased N₂O emission at the dates sampled.     

Microbial community structure in restored riparian soils of the Canadian prairie pothole region

In the Prairie Pothole Region (PPR) of Canada, wetlands once utilized for agricultural purposes are restored through the placement of a ditch plug to return them to their pre-existing hydrological state. The overall objective of this research was to assess differences in riparian soil microbial community structure between reference wetlands, those which had never been utilized for agricultural purposes, and restored wetlands, of varying times since restoration. Soil samples (0-6 cm) were taken from 15 reference and 28 restored wetlands. The soil microbial community was characterized using phospholipid fatty acid (PLFA) analysis. Data were analyzed using non-metric multidimensional scaling, multivariate regression trees (MRT) and indicator species analysis. The microbial community of younger restored soils (1-3 and 4-6 yrs) differed significantly from the reference soils, with reference soils having higher microbial biomass, evenness, and diversity. Richness showed an increasing trend with time since restoration. Results from the MRT underlined the importance of climatic factors, specifically precipitation - potential evapotranspiration (P-PE) in explaining the variation found in the microbial community. More specifically, drier sites had strong indicator species values associated with PLFAs of actinomycetal origin and fungal origin. Within the wetter sites, it was found that the older restored sites (7-11 yrs) and reference sites had strong indicator species values associated with PLFAs of Gram negative and fungal origin. The similarities in microbial community composition and biomass of the older restored sites (7-11 yrs) and the reference sites indicate that this component of the wetland ecosystems begins to recover within this time period.     

黄河三角洲退化湿地微生物群落特性研究

Five different sites with a soluble salt gradient of 3.0--17.7 g kg-1 dry soil from the coast to the inland were selected, and the microbial population size, activity and diversity in the rhizospheres of five common plant species and the adjacent bulk soils (non-rhizosphere) were compared in a degraded wetland of the Yellow River Delta, Shandong Province, China to study the effects of soil environment (salinity, seasonality, depth, and rhizosphere) on microbial communities and the wetland’s ecological function, thus providing basic data for the bioremediation of degraded wetlands. There was a significant negative linear relationship between the salinity and the total number of microorganisms, overall microbial activity, or culturable microbial diversity. Salinity adversely affected the microbial community, and higher salinity levels resulted in smaller and less active microbial communities. Seasonal changes were observed in microbial activity but did not occur in the size and diversity. The microbial size, activity and diversity decreased with increasing soil depth. The size, activity and diversity of culturable microorganisms increased in the rhizospheres. All rhizospheres had positive effects on the microbial communities, and common seepweed had the highest rhizosphere effect. Three halophilic bacteria (Pseudomonas mendocina, Burkholderia glumae, and Acinetobacter johnsonii) were separated through BIOLOG identification, and common seepweed could be recommended for bioremediation of degraded wetlands in the Yellow River Delta.     

氧调控下人工湿地微生物群落结构变化研究

运用磷脂脂肪酸（PLFAs）技术研究了氧调控下复合垂直流人工湿地（IVCW）微生物群落结构及活性变化,结果表明,不曝气IVCW基质表层以好氧微生物为优势种群,但绝大部分微生物都集中在0～20 cm基质层,系统的净化空间受到限制;氧调控下微生物群落向基质纵深发展,表征好氧微生物的单不饱和脂肪酸的含量显著增加,曝气系统下行池表层各类群微生物的生物量为不曝气系统的2～6倍,表征微生物活性的PLFAs总不饱和度水平也明显升高;革兰氏阴性细菌成为曝气IVCW基质微生物群落的优势种群,群落具有更高的活性和专一性,提高了污染物的去除效果。因此,进一步研究微生物的这种适应机制可以为优化湿地系统提供一定的理论基础。     

Land-use intensification and agroforestry in the Kenyan highland: Impacts on soil microbial community composition and functional capacity

This study investigates microbial communities in soil from sites under different land use in Kenya. We sampled natural forest, forest plantations, agricultural fields of agroforestry farms, agricultural fields with traditional farming and eroded soil on the slopes of Mount Elgon, Kenya. We hypothesised that microbial decomposition capacity, biomass and diversity (1) decreases with intensified cultivation; and (2) can be restored by soil and land management in agroforestry. Functional capacity of soil microbial communities was estimated by degradation of 31 substrates on Biolog EcoPlates™. Microbial community composition and biomass were characterised by phospholipid fatty acid (PLFA) and microbial C and N analyses. All 31 substrates were metabolised in all studied soil types, i.e. functional diversity did not differ. However, both the substrate utilisation rates and the microbial biomass decreased with intensification of land use, and the biomass was positively correlated with organic matter content. Multivariate analysis of PLFA and Biolog EcoPlate™ data showed clear differences between land uses, also indicated by different relative abundance of PLFA markers for certain microorganism groups. In conclusion, our results show that vegetation and land use control the substrate utilisation capacity and microbial community composition and that functional capacity of depleted soils can be restored by active soil management, e.g. forest plantation. However, although 20–30 years of agroforestry farming practises did result in improved soil microbiological and chemical conditions of agricultural soil as compared to traditional agricultural fields, the change was not statistically significant.     

Responses of nitrogen cycling and related microorganisms to brackish wetlands formed by evapotranspiration

Elevated evapotranspiration due to warmer air temperature could raise salinity and nutrient levels of some inland wetlands, potentially impacting nitrogen cycling. To characterize the impact of high evapotranspiration on soil microbial nitrogen cycling in inland wetlands, we compared freshwater and brackish marsh(or non-marsh) wetlands in terms of sediment ammonia-oxidizing rate(AOR), denitrifying rate(DR), and related microbial communities in a typical inland basin, the Hulun Lake basin, in Chi...     

Microbial communities responsible for the decomposition of rice straw compost in a Japanese rice paddy field determined by phospholipid fatty acid (PLFA) analysis

To identify the microbial communities responsible for the decomposition of rice straw compost in soil during the rice cultivation period, phospholipid fatty acid (PLFA) composition of rice straw compost was determined by periodically sampling the compost from a Japanese rice field under flooded conditions. About 21% of the compost was decomposed within a period of 3 months. The total amount of PLFAs, as an indicator of microbial biomass, was significantly lower under drained conditions than under flooded conditions and was relatively constant during the flooding period. This indicates that the microbial biomass in the compost samples did not increase during the gradual decomposition of rice straw compost under flooded conditions. The proportion of branched-chain PLFAs (biomarker of Grampositive and anaerobic Gram-negative bacteria) slightly decreased during the early period after placement, and increased gradually afterwards. Among the branched-chain PLFAs, i15:0, ail5:0, i16:0 and i17:0 PLFAs predominated and their proportions increased gradually except for i16:0. The proportion of straight mono-unsaturated PLFAs (biomarker of Gramnegative bacteria) was almost constant throughout the period, and 18:1ω9 and 18:1ω7 PLFAs predominated. The proportion of straight poly-unsaturated PLFAs as a biomarker of eukaryotes including fungi was also constant throughout the period, except for a decrease under drained conditions. Straight poly-unsaturated PLFAs consisted mainly of 18:2ω6c PLFA. Therefore, these results suggest that the proportions of Gram-positive and anaerobic Gram-negative bacteria increased during the decomposition of rice straw compost in flooded paddy field. Statistical analyses enabled to divide PLFA patterns of microbiota in the rice straw compost into two groups, one group consisting of rice straw compost samples collected before mid-season drainage and the other of samples collected after mid-season drainage. Small squared distances among samples in cluster analysis indicated that the community structure of microbiota was similar to each other as a whole. These results suggest that the microbial communities changed gradually during the period of placement, and that mid-season drainage may have affected the community structure of microbiota. Principal component analysis of the PLFA composition suggested that the succession of microbiota along with the decomposition in flooded soil was similar between rice straw compost and rice straw and that the changes in the community structure during the decomposition in flooded soil were more conspicuous for rice straw than for rice straw compost.     

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.     

土地耕作后微生物量碳和水溶性有机碳的动态特征

采用野外观测与室内模拟试验相结合的方法,研究了湿地土壤和垦殖10年的农田耕作后土壤呼吸通量、微生物量碳、土壤基础呼吸、土壤qCO2值、水溶性有机碳的动态特征。研究结果表明:小叶章湿地耕作后,土壤含水量明显下降(p<0.05);土壤CO2通量在最初的1~2 d形成一个排放高峰,农田耕作土壤CO2通量一直显著高于未耕作土壤(p<0.01)。农田土壤微生物量碳含量显著低于小叶章湿地(p<0.001)。在耕作后最初的1~3 d,湿地和农田土壤微生物量碳均没有显著的变化;之后,土壤微生物量碳迅速增加,显著高于未耕作土壤。观测时间内,耕作农田土壤微生物量碳含量始终显著高于未耕作土壤(p<0.01)。垦殖10年农田土壤耕作后,对土壤水溶性有机碳含量无显著影响。湿地耕作后,土壤水溶性有机碳迅速增加。在耕作后80 d内,土壤水溶性有机碳含量显著高于未耕作土壤(p<0.01)。之后,则低于未耕作土壤。     

胶州湾滨海湿地土壤溶解性有机碳淋溶特征

[目的]在山东省青岛市胶州湾滨海湿地采集光滩、碱蓬、芦苇和米草4种不同植被类型土壤,探究滨海湿地土壤溶解性有机碳淋溶特征。[方法]通过室内土柱淋溶试验,测定土壤淋出液溶解性有机碳(DOC)浓度,利用紫外—可见分光光度法对土壤淋出液DOC结构进行分析。[结果]土壤淋出液DOC浓度随土层深度增加而增加;芦苇湿地的土壤淋出液DOC浓度最高,为23.12mg/L,其次分别为碱蓬湿地,米草湿地和光滩湿地,分别为15.22mg/L,14.44mg/L与8.38mg/L。4种土壤淋出液DOC光谱特征值存在一定的差异性,碱蓬湿地土壤淋出液DOC的芳香性和腐殖化程度最高,米草湿地土壤淋出液DOC的分子量和团聚化最大;随土层深度的增加土壤淋出液DOC的芳香性、腐殖化程度增大,分子量以及团聚化程度逐渐减小。[结论]植被残体的分解以及土壤的解吸附能力的差异是造成不同土层土壤淋出液DOC浓度差异的主要原因;而植被类型是影响土壤淋出液DOC结构变化的关键因素。     

Soil morphology,depth and grapevine root frequency influence microbial communities in a Pinot noir vineyard

The composition of microbial communities responds to soil resource availability, and has been shown to vary with increasing depth in the soil profile. Soil microorganisms partly rely on root-derived carbon (C) for growth and activity. Roots in woody perennial systems like vineyards have a deeper vertical distribution than grasslands and annual agriculture. Thus, we hypothesized that vineyard soil microbial communities along a vertical soil profile would differ from those observed in grassland and annual agricultural systems. In a Pinot noir vineyard, soil pits were excavated to ca. 1.6–2.5 m, and microbial community composition in ‘bulk’ (i.e., no roots) and ‘root’ (i.e., roots present) soil was described by phospholipid ester-linked fatty acids (PLFA). Utilization of soil taxonomy aided in understanding relationships between soil microbial communities, soil resources and other physical and chemical characteristics. Soil microbial communities in the Ap horizon were similar to each other, but greater variation in microbial communities was observed among the lower horizons. Soil resources (i.e., total PLFA, or labile C, soil C and nitrogen, and exchangeable potassium) were enriched in the surface horizons and significantly explained the distribution of soil microbial communities with depth. Soil chemical properties represented the secondary gradient explaining the differentiation between microbial communities in the B-horizons from the C-horizons. Relative abundance of Gram-positive bacteria and actinomycetes did not vary with depth, but were enriched in ‘root’ vs. ‘bulk’ soils. Fungal biomarkers increased with increasing depth in ‘root’ soils, differing from previous studies in grasslands and annual agricultural systems. This was dependent on the deep distribution of roots in the vineyard soil profile, suggesting that the distinct pattern in PLFA biomarkers may have been strongly affected by C derived from the grapevine roots. Gram-negative bacteria did not increase in concert with fungal abundance, suggesting that acidic pHs in lower soil horizons may have discouraged their growth. These results emphasize the importance of considering soil morphology and associated soil characteristics when investigating effects of depth and roots on soil microorganisms, and suggest that vineyard management practices and deep grapevine root distribution combine to cultivate a unique microbial community in these soil profiles.     

Incorporation of 13C-labelled rice rhizodeposition carbon into soil microbial communities under different water status

The overall processes by which carbon is fixed by plants in photosynthesis then released into the soil by rhizodeposition and subsequently utilized by soil micro-organisms, links the atmospheric and soil carbon pools. The objective of this study was to determine the plant derived ¹³C incorporated into the phospholipid fatty acid (PLFA) pattern in paddy soil, to test whether utilization of rice rhizodeposition carbon by soil micro-organisms is affected by soil water status. This is essential to understand the importance of flooded conditions in regulating soil microbial community structure and activity in wetland rice systems. Rice plants were grown in soil derived from a paddy system under controlled irrigation (CI), or with continuous waterlogging (CW). Most of the ¹³C-labelled rice rhizodeposition carbon was distributed into the PLFAs 16:0, 18:1ω7 and 18:1ω9 in both the CW and CI treatments. The bacterial PLFAs i15:0 and a15:0, both indicative of gram positive bacteria, were relatively more abundant in the treatments without rice plants. When rice plants were present rates of ¹³C-incorporation into i15:0 and a15:0 was slow; the microbes containing these PLFAs may derive most of their carbon from more recalcitrant C (soil organic matter). PLFAs, 18:1ω7 and 16:1ω7c, indicative of gram negative bacteria showed a greater amount incorporation of labelled plant derived carbon in the CW treatment. In contrast, 18:2ω6,9 indicative of fungi and 18:1ω9 indicative of aerobes but also potentially fungi and plant roots had greater incorporation in the CI treatment. The greater root mass concomitant with lower incorporation of ¹³C into the total PLFA pool in the CW treatment suggests that the microbial communities in wetland rice soil are limited by factors other than substrate availability in flooded conditions. In this study differing soil microbial communities were established through manipulating the water status of paddy soils. Steady state ¹³C labelling enabled us to determine that the microbial community utilizing plant derived carbon was also affected by water status.     

三江平原环型湿地土壤养分的空间分布规律

以三江平原环型湿地作为研究对象，对其环带状植被区湿地土壤的有机碳、全氮、全磷和全钾的空间分布规律进行了初步研究。结果表明，环型湿地土壤有机碳、全氮、全磷和全钾具有明显的空间水平分异规律，有机质、全氮、全磷的含量由环型湿地中心向边缘逐渐减少，全钾的含量和碳氮比逐渐增加。土壤有机碳、全氮、全磷和全钾在垂直方向上具有明显的分层和富聚现象，自上而下，有机质的含量逐渐降低；全氮含量除漂筏苔草群落外，其他各群落土壤全氮含量呈先增加后减少的分布；大部分植物群落全磷含量呈先减后增的“V”型分布；全钾含量呈表层和底层较高、中间层较低的“中空”状分布。通过相关分析表明，环型湿地土壤有机碳与全氮具有相似的空间分布规律，全钾与有机碳、全氮具有相异的空间分布规律，而全磷具有自己独特的空间分布规律。环型湿地土壤的有机碳、全氮、全磷和全钾的空间分布主要受植物体元素含量、生物过程和水文地貌过程影响，它通过过程影响湿地的功能。研究环型湿地的有机碳、全氮、全磷和全钾的空间分布规律不仅有助于完善湿地土壤形成和发育的理论，探明湿地的生态过程和功能，而且为合理利用和保护湿地提供科学依据。     

生物炭、秸秆和有机肥对砂姜黑土改性效果的对比研究

砂姜黑土是广泛分布于我国黄淮海平原、具有多种障碍因子的典型中低产土壤。本研究通过小麦和玉米轮作盆栽试验,研究了生物炭、秸秆和有机肥3种有机物料对砂姜黑土性质的改良效果。结果表明:添加秸秆能显著提高土壤微生物生物量碳(MBC)和可溶性有机碳(DOC)含量,减小土壤线性延展系数(COLE);添加生物炭对砂姜黑土MBC和DOC影响不显著,但显著减小土壤COLE。对土壤磷脂脂肪酸(PLFA)含量的分析发现,添加秸秆显著提高了小麦灌浆期和玉米抽雄期土壤总磷脂脂肪酸、细菌、真菌、放线菌和腐生真菌的含量,而添加生物炭和有机肥对土壤总磷脂脂肪酸、细菌、真菌、放线菌、腐生真菌和真菌/细菌影响不显著。综上,生产实践中3种有机物料添加应根据各地砂姜黑土主要障碍因子不同而灵活选择。     

模拟氮沉降对滨海湿地土壤微生物功能多样性的影响

为全面了解大气氮沉降条件下滨海湿地土壤微生物碳源利用特点,本研究在江苏盐城滨海湿地建立模拟氮沉降实验平台,设置N1(N,0 g/(hm~2·a),对照)、N2(N,3 g/(hm~2·a),低氮)和N3(N,6 g/(hm~2·a),高氮)3个处理,采用Biolog微平板法,分析了土壤微生物功能多样性在不同氮处理下的变化规律和特点。结果表明:不同氮沉降处理间土壤微生物功能多样性差异显著,AWCD值随培养时间延长而增加;Shannon和Mc Intosh多样性指数也随施氮增加呈现升高的趋势,且不同处理间多样性指数差异显著;物种多样性和功能多样性表现出相同的变化规律。土壤微生物对6大类碳源利用强度存在差异,各处理间土壤微生物对碳水化合物类碳源利用率最高,为优势碳源;主成分分析结果显示,不同处理间土壤微生物在碳源利用上有明显的空间分异,土壤微生物功能多样性的差异主要体现在对羧酸类、酚酸类和胺类碳源的利用上,其中胺类尤为突出;此外,对不同施氮处理土壤微生物群落功能多样性与土壤理化因子进行相关分析,结果显示全氮、铵态氮、全磷会对滨海湿地土壤微生物组成和功能活性产生重要影响。     

黄河三角洲冲积平原湿地土壤酶活性与养分相关性研究

对黄河三角洲冲积平原湿地酶活性与土壤养分相关性做了研究.结果表明:随着离海距离的增加,土壤有机质及各养分表现出有规律的变化,土壤脲酶、过氧化氢酶活性沿湿地演替的方向活性升高,过氧化物酶活性降低.土壤有机质和各养分与酶活性相关性达极显著和显著水平,不同土壤酶活性之间也有显著的相关性.3种酶可以作为评价黄河三角洲冲积平原湿地土壤肥力的指标.     

小兴安岭森林沼泽湿地土地利用变化对土壤活性碳组分的影响

[目的]以小兴安岭森林沼泽为研究对象,研究湿地经过人类活动开垦为农田,和排水造林,以及弃耕地的土壤活性碳组分,为深入了解土壤活性碳组分动态变化及其可能影响全球变暖的机制研究提供科学依据。[方法]选择小兴安岭森林沼泽湿地4种土地利用方式(天然沼泽、排水湿地、弃耕地、农田)为研究对象,在野外调查和室内分析的基础上,对比分析土壤有机碳(SOC)、溶解性有机碳(DOC)、微生物碳(MBC)、易氧化碳(EOC)、轻组有机碳(LFOC)、颗粒有机碳(POC)的含量变化和比例关系,并用相关分析法分析土壤有机碳各活性组分之间的关系。[结果]不同土地利用方式土壤有机碳含量随土层深度增加而降低,总体上,在土壤剖面上,天然沼泽的SOC含量大于其他土地利用方式,其他3种土地利用方式之间差异不显著(p0.05)。不同土地利用方式下土壤活性碳组分(DOC,MBC,EOC,POC,LFOC)含量在垂直分布上均呈现出随土壤深度的增加而降低的趋势,土壤活性碳组分含量顺序总体上呈:天然沼泽排水湿地弃耕地农田。4种土地利用类型土壤DOC占SOC的比例,在垂直剖面上,无明显规律变化。土壤SOC含量与DOC,MBC,EOC,POC,LFOC之间的相关性均达到显著水平(p0.05)。土壤DOC和MBC之间呈显著性正相关(p0.05),LFOC和POC之间呈极显著性正相关(p0.05),EOC与其他活性碳组分相关性均不显著(p0.05)。[结论]土地利用变化会对小兴安岭森林沼泽土壤活性碳组分产生影响,应该合理开发小兴安岭森林沼泽湿地。     

黄河三角洲冲积平原湿地土壤酶活性与养分相关性研究

对黄河三角洲冲积平原湿地酶活性与土壤养分相关性做了研究。结果表明,随着离海距离的增加,土壤有机质及各养分表现出有规律的变化,土壤脲酶、过氧化氢酶活性沿湿地演替的方向活性升高,过氧化物酶活性降低。土壤有机质和各养分与酶活性相关性达极显著和显著水平,不同土壤酶活性之间也有显著的相关性。三种酶可以作为评价黄河三角洲冲积平原湿地土壤肥力的指标。     

三江平原湿地不同土地利用方式对土壤养分及酶活性的影响

以中国科学院三江平原湿地生态试验站为对象,研究了不同利用方式（湿地草甸、旱田系统、退耕成草、退耕成林）对土壤酶活性分布特征及相关因子的影响。结果表明:土壤利用方式不同,土壤酶活性（转化酶、脲酶、磷酸酶和过氧化氢酶）、有机碳含量和土壤养分含量有较大差异。土壤有机碳、全氮、全钾、速效磷、碱解氮、微生物量碳和氮均呈现出一致的变化规律,依次表现为湿地草甸 > 退耕草地 > 退耕林地 > 旱田系统,也即由湿地草甸退化过程中,土壤养分含量逐渐降低,其中不同土地利用方式下土壤全磷含量差异不显著（p>0.05）,在湿地的退化过程中,土壤全磷并没有发生显著的变化。与湿地草甸相比,土壤蔗糖酶、脱氢酶、脲酶和酸性磷酸酶活性均显著降低,其活性分别降低了32.69%,36.71%,50.00%,44.28%,由旱田系统恢复为湿地草甸系统后,土壤各种酶活性均显著增加,其中土壤蔗糖酶、脱氢酶、脲酶和酸性磷酸酶活性分别比旱田系统增加了26.68%,31.51%,48.19%,43.84%;表明由湿地草甸开垦为耕地和由耕地恢复为湿地草甸和林地,发生着两种不同的生物学过程,前者为微生物降解过程,而后者则为微生物累积过程。相关性分析表明SOC,TN和SMBC对土壤蔗糖酶、脱氢酶、脲酶和酸性磷酸酶活性的贡献为正,对土壤酶活性起到主导作用。主成分分析表明影响土壤酶活性最主要的因子为SOC,TN和SMBC。     

Variations in microbial community composition through two soil depth profiles

Soil profiles are often many meters deep, but with the majority of studies in soil microbiology focusing exclusively on the soil surface, we know very little about the nature of the microbial communities inhabiting the deeper soil horizons. We used phospholipid fatty acid (PLFA) analysis to examine the vertical distribution of specific microbial groups and to identify the patterns of microbial abundance and community-level diversity within the soil profile. Samples were collected from the soil surface down to 2 m in depth from two unsaturated Mollisol profiles located near Santa Barbara, CA, USA. While the densities of microorganisms were generally one to two orders of magnitude lower in the deeper horizons of both profiles than at the soil surface, approximately 35% of the total quantity of microbial biomass found in the top 2 m of soil is found below a depth of 25 cm. Principal components analysis of the PLFA signatures indicates that the composition of the soil microbial communities changes significantly with soil depth. The differentiation of microbial communities within the two profiles coincides with an overall decline in microbial diversity. The number of individual PLFAs detected in soil samples decreased by about a third from the soil surface down to 2 m. The ratios of cyclopropyl/monoenoic precursors and total saturated/total monounsaturated fatty acids increased with soil depth, suggesting that the microbes inhabiting the deeper soil horizons are more carbon limited than surface-dwelling microbes. Using PLFAs as biomarkers, we show that Gram-positive bacteria and actinomycetes tended to increase in proportional abundance with increasing soil depth, while the abundances of Gram-negative bacteria, fungi, and protozoa were highest at the soil surface and substantially lower in the subsurface. The vertical distribution of these specific microbial groups can largely be attributed to the decline in carbon availability with soil depth.