Reciprocal transfer effects on denitrifying community composition and activity at forest and meadow sites in the Cascade Mountains of Oregon

In order to examine the effects of disturbance, vegetation type, and microclimate on denitrification and denitrifier community composition, experimental plots were established at the H. J. Andrews Experimental Forest in the Cascade Mountains of Oregon. Soil cores were reciprocally transplanted between meadow and forest and samples were collected after 1 and 2 years. Denitrifying enzyme activity (DEA) was measured using the acetylene block assay and terminal restriction length polymorphism profiles were generated with nosZ primers that target the gene coding for nitrous oxide reductase. Nitrate concentrations, C mineralization, and water content were measured to gain additional insights into soil properties controlling DEA. Meadow soils were significantly higher in DEA than forest soils, and the highest DEA levels were observed in cores transferred from the meadow into the forest. Nitrate concentrations were also different between forest and meadow soils, but did not correlate to DEA. DEA was higher in open versus closed cores, suggesting an association between denitrification and the rhizosphere. Denitrifier communities of undisturbed forest and meadow soils shifted through a 4-year period but remained distinct from each other. Similarly, denitrifier communities clustered by vegetation type of origin regardless of manipulation, suggesting that the overall denitrifier communities are well buffered against environmental changes.     

不同人为干扰尺度对米槠群落外貌特征影响研究

从群落外貌探讨不同人为干扰尺度对福建武平米槠林的影响。结果表明:随着人为干扰尺度(CK对照、A级择伐更新、B级天然更新、C级人工促进天然更新和D级杉木林)的加大藤本植物、地面芽植物、地上芽植物、中型叶、草质叶、复叶和落叶的种类逐渐上升或呈“S”型上升,而高芽位植物、小型叶、革质叶、全缘叶、单叶和常绿的种类逐渐下降或呈“S”下降;CK、A级、B级和C级的外貌是由革质、单叶、小型叶为主的常绿高位芽植物所决定的,而D级由草质、单叶、中型叶为主的常绿高位芽植物所决定的。     

田林老山南坡森林植被的生态学研究 Ⅰ.森林植被主要类型和分布

田林老山南坡位于桂西北田林县境,主峰海拔2062.5m,面积约350km~2。该区木本植物79科210属452种。其植物区系特点为:区系成分起源古老,特有种较多,成分复杂,地理替代和垂直带替代明显,热带、亚热带性质强。主要森林类型有:杜鹃、吊钟、红果树等组成的山顶矮林;稠、栲、木荷、木莲、水青冈、枫香等组成的常绿落叶阔叶混交林;栲、石栎、楠、润楠、茶等组成的常绿阔叶林;桦木、马尾树、拟赤杨、枫香、桤木、栋、山柳等组成的次生落叶阔叶林;黄杞、浆果楝、扁担杆、水锦树等组成的常绿阔叶灌丛;山柳、南烛、木姜子等组成的落叶阔叶灌丛;平脉椆、红荷木、海南蒲桃等组成的谷地常绿、半常绿阔叶林;细叶云南松、矩鳞油杉等组成的南亚热带针叶林;以及人工栽培的松、杉等组成的亚热带针叶林。森林植被垂直带谱是:海拔250～800m,南亚热带季风常绿阔叶林带(由于人为干扰剧烈,已消失);海拔800～1500m,山地常绿阔叶林带;海拔l500～1900m,常绿落叶阔叶混交林带;海拔1900m以上,山顶矮林带。     

植被恢复演替初期对模拟降雨产流特征的影响

利用模拟降雨装置,研究了演替恢复初期不同植被覆盖以及不同处理下坡面降雨的产流过程和人渗率。实验研究结果表明,植被演替开始之初,由于地表土壤的土质比较疏松,土壤的人渗率比较大。随着植被演替的进行,土壤中有机质等物质的逐渐累积,土壤的理化性质发生了变化,土壤的人渗特征也随之降低。剪草降雨小区的实验研究结果说明,在降雨的初期,土壤的人渗性能相对较低,随着实验的进行,在雨滴的打击下,部分结皮被破坏,土壤的人渗率也随之增大。说明地表生物结皮的存在,降低了土壤的人渗性能。采取适当的措施破坏地表生物结皮,有利于提高土壤的人渗性能,增加干旱半干旱地区对降雨的利用程度。     

建立坡面植被恢复群落质量评价体系的探讨

利用构建AHP评判矩阵计算各评价指标的权重,根据对专家建议值的统计,确定4个分时期对整个坡面植被恢复群落质量的影响权重,并计算出坡面植被质量的最终值,然后根据给出的值域进行植被恢复群落质量等级划分。     

Hydrolase activity, microbial biomass and community structure in long-term Cd-contaminated soils

Long-term effects of high Cd concentrations on enzyme activities, microbial biomass and respiration and bacterial community structure of soils were assessed in sandy soils where Cd was added between 1988 and 1990 as Cd(NO₃)₂ to reach concentrations ranging from 0 to 0.36 mmol Cd kg⁻¹ dry weight soil. Soils were mantained under maize and grass cultivation, or ‘set-aside’ regimes, for 1 year. Solubility of Cd and its bioavailability were measured by chemical extractions or by the BIOMET bacterial biosensor system. Cadmium solubility was very low, and Cd bioavailability was barely detectable even in soils polluted with 0.36 mmol Cd kg⁻¹. Soil microbial biomass carbon (B_C) was slightly decreased and respiration was increased significantly even at the lower Cd concentration and as a consequence the metabolic quotient (qCO₂) was increased, indicating a stressful condition for soil microflora. However, Cd-contaminated soils also had a lower total organic C (TOC) content and thus the microbial biomass C-to-TOC ratio was unaffected by Cd. Alkaline phosphomonoesterase, arylsulphatase and protease activities were significantly reduced in all Cd-contaminated soils whereas acid phosphomonoesterase, β-glucosidase and urease activites were unaffected by Cd. Neither changes in physiological groups of bacteria, nor of Cd resistant bacteria could be detected in numbers of the culturable bacterial community. Denaturing gradient gel electrophoresis analysis of the bacterial community showed slight changes in maize cropped soils containing 0.18 and 0.36 mmol Cd kg⁻¹ soil as compared to the control. It was concluded that high Cd concentrations induced mainly physiological adaptations rather than selection for metal-resistant culturable soil microflora, regardless of Cd concentration, and that some biochemical parameters were more sensitive to stress than others.     

退化生态系统植被恢复过程中土壤微生物群落活性响应

通过分析退化生态系统中主要植被恢复类型对土壤微生物群落活性的影响,探讨敏感和可靠的微生物群落活性响应指标,揭示适合当地生态条件的植被恢复类型。结果表明,沙米荒地、白沙蒿、柠条、沙冬青和人工乔木林地土壤微生物量C,N,P和微生物商、蔗糖酶、脲酶、过氧化氢酶、碱性磷酸酶均表现出显著差异(P<0.05)。在土壤各层内,除上层人工乔木林地土壤微生物量N相对较高外,柠条恢复草地土壤微生物量C,N,P都相对较高,沙米荒地均较低;土壤微生物商没有明显的趋势;人工乔木林地蔗糖酶和柠条恢复草地脲酶活性相对较高,过氧化氢酶和碱性磷酸酶活性没有明显的变化趋势,沙米荒地的蔗糖酶、脲酶和过氧化氢酶活性以及白沙蒿草地碱性磷酸酶活性较低。方差分析(ANOVA)显示,蔗糖酶、脲酶、过氧化氢酶和碱性磷酸酶与土壤有机质、全氮以及微生物量C,N,P之间呈显著相关关系;主成分分析(PCA)表明,土壤微生物量N,C,P和蔗糖酶、土壤微生物商基本反映了研究区植被恢复中土壤微生物群落活性的响应信息。不同植被恢复类型草地中土壤微生物群落活性的变化表明,柠条和人工乔木林是研究区域内适合当地生态条件的植被恢复类型。     

Soil microbial communities resistant to changes in plant functional group composition

The soil community is an often ignored part of research which links plant biodiversity and ecosystem functioning despite their influence on numerous functions such as decomposition and nutrient cycling. Few consistent patterns have been detected that link plant and soil community composition. We used a removal experiment in a northern Canadian grassland to examine the effects of plant functional group identity on soil microbial community structure and function. Plant functional groups (graminoids, legumes and forbs) were removed independently from plots for five growing seasons (2003-2007) and in the fifth year effects on the soil microbial community were examined using substrate-induced respiration (SIR - a measure of metabolic diversity) and phospholipid fatty acid analysis (PLFA - a measure of microbial community composition). Removal treatments were also crossed with both a fertilizer treatment and a fungicide treatment to determine if effects of functional group identity on the soil community were context dependent. Plant functional group identity had almost no effect on the soil microbial community as measured by either SIR or PLFA. Likewise, soil properties including total carbon, pH, moisture and nutrients showed a limited response to plant removals in the fifth year after removals. We found a direct effect of fertilizer on the soil community, with fertilized plots having decreased metabolic diversity, with a decreased ability to metabolize amino acids and a phenolic acid, but there was no direct soil microbial response to fungicide. We show that in this northern Canadian grassland the soil microbial community is relatively insensitive to changes in plant functional group composition, and suggest that in northern ecosystems, where plant material is only slowly incorporated into the soil, five growing seasons may be insufficient to detect the impact of a changing plant community on the soil microbes.     

Land-use history has a stronger impact on soil microbial community composition than aboveground vegetation and soil properties

The response of soil microbial communities following changes in land-use is governed by multiple factors. The objectives of this study were to investigate (i) whether soil microbial communities track the changes in aboveground vegetation during succession; and (ii) whether microbial communities return to their native state over time. Two successional gradients with different vegetation were studied at the W. K. Kellogg Biological Station, Michigan. The first gradient comprised a conventionally tilled cropland (CT), mid-succession forest (SF) abandoned from cultivation prior to 1951, and native deciduous forest (DF). The second gradient comprised the CT cropland, early-succession grassland (ES) restored in 1989, and long-term mowed grassland (MG). With succession, the total microbial PLFAs and soil microbial biomass C consistently increased in both gradients. While bacterial rRNA gene diversity remained unchanged, the abundance and composition of many bacterial phyla changed significantly. Moreover, microbial communities in the relatively pristine DF and MG soils were very similar despite major differences in soil properties and vegetation. After >50 years of succession, and despite different vegetation, microbial communities in SF were more similar to those in mature DF than in CT. In contrast, even after 17 years of succession, microbial communities in ES were more similar to CT than endpoint MG despite very different vegetation between CT and ES. This result suggested a lasting impact of cultivation history on the soil microbial community. With conversion of deciduous to conifer forest (CF), there was a significant change in multiple soil properties that correlated with changes in microbial biomass, rRNA gene diversity and community composition. In conclusion, history of land-use was a stronger determinant of the composition of microbial communities than vegetation and soil properties. Further, microbial communities in disturbed soils apparently return to their native state with time.     

Plot-scale manipulations of organic matter inputs to soils correlate with shifts in microbial community composition in a lowland tropical rain forest

Little is known about the organisms responsible for decomposition in terrestrial ecosystems, or how variations in their relative abundance may influence soil carbon (C) cycling. Here, we altered organic matter in situ by manipulating both litter and throughfall inputs to tropical rain forest soils, and then used qPCR and error-corrected bar-coded pyrosequencing to investigate how the resulting changes in soil chemical properties affected microbial community structure. The plot-scale manipulations drove significant changes in microbial community composition: Acidobacteria were present in greater relative abundance in litter removal plots than in double-litter plots, while Alphaproteobacteria were found in higher relative abundance in double-litter and throughfall reduction plots than in control or litter removal plots. In addition, the bacterial:archaeal ratio was higher in double-litter than no-litter plots. The relative abundances of Actinobacteria, Alphaproteobacteria and Gammaproteobacteria were positively correlated with microbial biomass C and nitrogen (N), and soil N and C pools, while acidobacterial relative abundance was negatively correlated with these same factors. Bacterial:archaeal ratios were positively correlated with soil moisture, total soil C and N, extractable ammonium pools, and soil C:N ratios. Additionally, bacterial:archaeal ratios were positively related to the relative abundance of Actinobacteria, Gammaproteobacteria, and Actinobacteria, and negatively correlated to the relative abundance of Nitrospira and Acidobacteria. Together, our results support the copiotrophic/oligotrophic model of soil heterotrophic microbes suggested by Fierer et al. (2007).