Evaluating soil biochemical/microbial indices as ecological indicators of different land use/cover in northern Iran

The objective of the study was to examine changes in microbial parameters have been used to monitor changes in soil quality under different land uses in north of Iran. The microbial parameters included microbial respiration (MR), substrate induced respiration (SIR), carbon availability index (CAI), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), ratio of MBC/MBN, metabolic quotient (qCO₂) and microbial ratio were determined under different land use/cover, i.e. virgin natural forest (VNF), degraded natural forest (DNF), alder plantation (AP), sequoia plantation (SP), improved fallow (IF) and home garden (HG) areas in northern Iran. Five composed samples per land use/cover were taken from the top 10 cm of the soil. MR and SIR (0.45 and 1.66 mg CO₂-C g^?1 day^?1, respectively) were found to be significantly higher under AP land uses than in the other areas. CAI did not differ for the land uses; MBC (591 and 590 mg kg^?1, respectively) had higher significantly under SP and VNF land uses than in the other areas. MBN (64.25 and 62.33, respectively mg kg^?1) was significantly higher in AP and VNF land uses, ratio of MBC/MBN (17.02) was higher in SP land use than other areas, HG had significantly higher qCO₂ (0.0012 μg CO₂-C mg^?1 MBC day^?1) and finally microbial ratio was significantly higher under IF (599.16) in comparison with HG > AP ≈ DNF > VNF > SP areas. Overall, our results indicate that AP land use (Alnus subcordata C. A. Mey.) increase of soil quality and alder plantation is suitable for rehabilitation of degraded natural forests.     

Soil biochemical/microbial indices as ecological indicators of land use change in mangrove forests

The objective of the study was to examine the long-term changes in biochemical/microbial indicators of soil quality due to clear felling of mangroves for establishment of plantations. The biochemical/microbial parameters included dissolved organic-C (DOC) and -N (DON), soil microbial biomass-C (SMBC), -N (SMBN) and -P (SMBP), soil respiration (SR), metabolic quotient (qCO₂), adenylates (ATP, AMP and ADP), adenylate energy charge (AEC), ergosterol and their ratios. Results revealed that the undisturbed mangroves possessed considerably greater amounts of soil organic C, DOC and DON. Consequently, SMBC, SMBN and SMBP showed marked reductions in the plantations suggesting an average loss of 66%, 49% and 75%, respectively due to changed land use. Likewise, SR decreased by 46.4% in the plantations. Enhanced qCO₂ levels in the plantations indicated a microbial community under stress with a high maintenance carbon demand, while lower qCO₂ levels in the mangroves indicated an efficient microbial community and a better use of available organic substrates. The levels of ATP, AMP and ADP followed a trend identical to that of SMB and SR. Greater ergosterol concentration led to greater ergosterol/SMBC ratio suggesting a shift in the microbial community structure from a primarily fungi dominated SMB in the mangroves to a fungi recessive SMB in the plantations.     

Diversity of soil fungal communities of Cerrado and its closely surrounding agriculture fields

Cerrado is a savanna-like region that covers a large area of Brazil. Despite its biological importance, the Cerrado has been the focus of few microbial diversity studies. A molecular approach was chosen to characterize the soil fungal communities in four areas of the Cerrado biome: a native Cerrado, a riverbank forest, an area converted to a soybean plantation, and an area converted to pasture. Global diversity of fungal communities in each area was assessed through Ribosomal intergenic spacer analysis which revealed remarkable differences among the areas studied. Sequencing of approximately 200 clones containing 18S rDNA sequences from each library was performed and, according to the genetic distance between sequences, these were assigned to operational taxonomic units (OTUs). A total of 75, 85, 85, and 70 OTUs were identified for the native Cerrado, riverbank forest, pasture, and soybean plantation, respectively. Analysis of sequences using a similarity cutoff value of 1% showed that the number of OTUs for the native Cerrado area was reduced by 35%; for the soybean plantation, a reduction by more than 50% was observed, indicating a reduction in fungal biodiversity associated with anthropogenic activity. This is the first study demonstrating the anthropogenic impact on Cerrado soil fungal diversity.     

米亚罗林区土地利用变化对土壤有机碳和微生物量碳的影响

为了解土地利用变化对土壤有机碳和微生物量碳的影响,分析了川西米亚罗林区原始冷杉林、20世纪60年代云杉人工林、20世纪80年代云杉人工林和农地的土壤有机碳和微生物量碳状况.结果表明,土地利用变化明显地影响了土壤有机碳和微生物量碳含量.土壤有机碳和微生物量碳含量原始林最高,其次为60年代人工林和80年代人工林,农地最低.农地土壤有机碳含量分别比原始林、60年代人工林和80年代人工林低83%、53%和52%,微生物量碳含量分别低23%、25%和21%.土壤有机碳和微生物量碳含量均随土壤深度的增加而降低,并且两者在不同土地利用类型的变化趋势基本一致.相关分析表明,土壤有机碳和土壤微生物量碳与全氮、水解氮、速效磷呈极显著相关(P＜0.01),说明土壤微生物量碳可作为衡量土壤有机碳变化的敏感指标,而土壤有机碳和微生物量碳含量可作为衡量土壤肥力和土壤质量变化的重要指标.     

Effect of long-term nutrient managements on biological and biochemical properties of semi-arid tropical Alfisol during maize crop development stages

Understanding the influence of organic or inorganic nutrient management on soil biology and biochemistry during crop growth may help to develop more sustainable fertilization strategies. Hence, the biological variables including soil organic carbon (SOC), microbial biomass carbon (MBC), six cultivable microbial communities, five hydrolytic enzymes activity and soil respiratory indices from a long-term fertility experiment field (>100 years) were assessed at different growth stages of maize. The samples were taken from four long-term treatments viz., control (no fertilization), balanced inorganic fertilizers (IC), organic amendments (OM) and integrated nutrient management (INM, organic manure plus chemical fertilizers) at five different stages of maize cropping (S1, pre-cropping; S2, five days after sowing; S3, vegetative; S4, flowering; S5, after harvesting). Responses of most of the assessed parameters to organic fertilization (OM and INM) were significantly higher than those from inorganically managed and control soils. There was significant difference in SOC due to long-term nutrient managements (OM > INM > IC > control) but not due to growth stages of maize. MBC was also higher in OM and INM compared to IC and control and found significantly different at growth stages of maize. Values of microbial counts and assessed enzyme activities were highest at vegetative stage of maize following a declined trend at later stages. The respiration studies indicate a difference between the responses of substrate induced respiration rate (SIR) and metabolic quotient (qCO₂). SIR was more significantly influenced by long-term nutrient managements than crop stages, while qCO₂ was by early stage of maize growth (S2) alone. The principal component analysis (PCA) identifies MBC, qCO₂, SIR, dehydrogenase, phosphatase and aryl sulphatase and counts of Actinobacteria and diazotrophs as major drivers for the variability among the samples. PCA discriminated OM and INM samples from IC and control and vegetative stage of maize from other stages. The interaction effects of long-term nutrient managements and maize growth stages were found significant to MBC, counts of Actinobacteria and diazotrophs and activities of dehydrogenase, acid phosphatase and aryl sulphatase. However, the resilience of semi-arid tropical soil, independent of long-term nutrient management adoptions, was not affected due to maize growth. The present study thus provides some reliable biological indicators to monitor the semi-arid tropical soils, those influenced by nutrient managements.     

Element storage in native,agri-, and silvicultural ecosystems of the Brazilian savanna. II. Metals

Conversion of native savanna in Brazil, the Cerrado, to agri- and silvicultural land use causes changes in metal storages of the ecosystems. To evaluate the sustainability of land use these changes have to be known. Therefore, we examined the Al, Ca, Fe, K, Mg, Mn, Na, and Zn storages in above- and belowground biomass, the organic layer, and the top 2 m of the mineral soil (Anionic Acrustoxes) of three replicate plots in each of six native and land-use systems. The systems were native Cerrado, Pinus caribaea Morelet plantations, productive and degraded Brachiaria decumbens Stapf pastures, and conventional and no-tillage soybean cultivation. The total metal storage varied little among the studied systems except for Ca, K, and Mg. All land-use systems had larger Ca storages (cropping systems 202–205 g m^–2, productive pasture: 112, degraded pasture: 84, Pinus: 81) than the Cerrado (62 g m^–2). The K storage was smaller in the pastures (17–18 g m^–2) than in Cerrado and Pinus stands (22–24) and largest in the cropping systems (26). The Mg storages were largest in the cropping systems (65–69) and productive pasture (59 g m^–2); those in the Pinus stands (52), the degraded pasture (51), and the Cerrado (53) were similar. For most metals, the aboveground biomass contained up to 1% of the total storage including the top 2 m of the soil (<5% if the lower ecosystem boundary was set at 0.3 m soil depth). However, the aboveground biomass stored up to 12% of Ca, K, and Mg down to 2 m soil depth (41% if the lower ecosystem boundary was set at 0.3 m soil depth). In the Pinus stands, the storage of most metals was larger in the below- than in the aboveground biomass; for the other systems the reverse was true. Metal storages in soil were little affected by land use except that liming resulted in increased Ca and Mg storages in the topsoil. The comparison between known inputs of Ca, K, and Mg and mean annual change rates of their storages revealed that there were considerable base metal losses by leaching, grazing, and removal with the harvest. After 12–20 years, the land-use impact on metal storages is restricted to Ca, Mg, and K. Generally, all land-use systems tend to be richer in these nutrients except for the significant depletion in K of the pastures.     

喀斯特峰丛洼地不同土地利用方式土壤肥力特征

基于网格法(5 m×5 m)采样,研究了喀斯特峰丛洼地不同土地利用方式(火烧、刈割、刈割除根、封育、种植玉米、种植牧草)下表层(0～20 cm)土壤肥力特征,利用主成分分析影响土壤肥力的主要因子,典范相关分析探讨土壤养分和土壤微生物的耦合关系.结果表明: 研究区6种土地利用方式土壤呈微碱性,pH 7.83～7.98,不同土地利用方式土壤养分含量不同,分别为有机碳76.78～116.05 g·kg^-1、全氮4.29～6.23 g·kg^-1、全磷1.15～1.47 g·kg^-1、全钾3.59～6.05 g·kg^-1、碱解氮331.49～505.49 mg·kg^-1、有效磷3.92～10.91 mg·kg^-1、有效钾136.28～198.10 mg·kg^-1,除pH呈弱变异外,其他指标均呈中等至强度变异.不同土地利用方式对土壤肥力的影响不同,有机碳、全氮、全磷、碱解氮等主要养分受影响最大,沿封育、火烧、刈割、刈割除根、种植牧草、种植玉米的人为干扰增加梯度而减少;其次是土壤微生物,尤其是放线菌;典范相关分析表明,火烧迹地的全磷与土壤微生物生物量磷,全钾与土壤微生物生物量碳,全氮与放线菌的相互影响最大,刈割、刈割除根、封育、种植玉米、种植牧草土壤全氮与土壤微生物生物量碳,速效磷与土壤微生物生物量氮,pH与土壤微生物生物量碳、真菌,全氮、全钾与土壤微生物生物量磷,pH与真菌、放线菌相互之间的影响最大.土地利用方式的变化改变了喀斯特峰丛坡地土壤肥力特征.在喀斯特地区进行生态恢复与重建时,应采取合理的土地利用方式,提高喀斯特退化生态系统的土壤质量.     

Changes in Diversity, Abundance, and Structure of Soil Bacterial Communities in Brazilian Savanna Under Different Land Use Systems

The Brazilian Savanna, also known as “Cerrado”, is the richest and most diverse savanna in the world and has been ranked as one of the main hotspots of biodiversity. The Cerrado is a representative biome in Central Brazil and the second largest biome in species diversity of South America. Nevertheless, large areas of native vegetation have been converted to agricultural land including grain production, livestock, and forestry. In this view, understanding how land use affects microbial communities is fundamental for the sustainable management of agricultural ecosystems. The aim of this work was to analyze and compare the soil bacterial communities from the Brazilian Cerrado associated with different land use systems using high throughput pyrosequencing of 16S rRNA genes. Relevant differences were observed in the abundance and structure of bacterial communities in soils under different land use systems. On the other hand, the diversity of bacterial communities was not relevantly changed among the sites studied. Land use systems had also an important impact on specific bacterial groups in soil, which might change the soil function and the ecological processes. Acidobacteria, Proteobacteria, and Actinobacteria were the most abundant groups in the Brazilian Cerrado. These findings suggest that more important than analyzing the general diversity is to analyze the composition of the communities. Since soil type was the same among the sites, we might assume that land use was the main factor defining the abundance and structure of bacterial communities.     

A minimum data set and soil quality index to quantify the effect of land use conversion on soil quality and degradation in native rangelands of upland arid and semiarid regions

Conversion of native rangelands to croplands potentially influences soil functions and quality. The aim of the current study was to assess soil quality (SQ) after rangeland conversion and degradation for more than 40 years using an indexing framework and integrated approach. Fifteen soil attributes were measured at two sampling depths (0–20 and 20–40 cm) of paired native undisturbed and adjacent cultivated rangelands at three rangeland sites. The soil organic carbon (OC), electrical conductivity (EC) and arylsulphatase (ARY) activity were found to be the key indicators of the minimum data set and these indicators greatly affected the computed soil quality index (SQI), particularly in the soil surface. The contribution of OC, EC and ARY to the overall SQI was 77, 13 and 10%, respectively. Although rangeland conversion reduced other soil attributes (including aggregate stability, available water capacity, cation exchange capacity, microbial biomass, microbial activity and the activities of urease and invertase enzymes), in particular at the 0–20 cm depth, these variables did not contribute to the estimated SQI values because of their high correlation with OC contents (i.e., strong interdependency). Cultivated rangelands were characterized by a low soil OC content, EC and ARY activity, and consequently a low SQI. A significant decline in SQI value (29–47%) was observed as a result of rangeland conversion to croplands, depending on soil depth considered and scoring function used to compute the SQI. Overall, converting native rangelands to croplands decreased SQ to 52–64% of their potential capacity using a non-linear scoring method. In summary, soil OC, EC and ARY are the most important indicators, which can be used to monitor and asses the degradation of rangeland SQ after conversion to croplands in these arid and semiarid upland environments. This finding is of especial importance because the assessment of SQ allows the successful and straightforward discrimination between rangeland and cropland ecosystems or to quantify land use conversion effects on SQ. It is concluded that the rate of soil changes can be assessed and compared more accurately in the studies of land use conversions in native rangeland ecosystems using the current indexing framework due to its simplicity and quantitative flexibility.     

Effect of Sugarcane Burning or Green Harvest Methods on the Brazilian Cerrado Soil Bacterial Community Structure

Background

The Brazilian Cerrado is one of the most important biodiversity reservoirs in the world. The sugarcane cultivation is expanding in this biome and necessitates the study of how it may impact the soil properties of the Cerrado. There is a lack of information especially about the impacts of different sugarcane management on the native bacterial communities of Cerrado soil. Therefore, our objective was to evaluate and compare the soil bacterial community structure of the Cerrado vegetation with two sugarcane systems.

Methods

We evaluated samples under native vegetation and the impact of the two most commonly used management strategies for sugarcane cultivation (burnt cane and green cane) on this diversity using pyrosequencing and quantitative PCR of the rrs gene (16S rRNA).

Results and Conclusions

Nineteen different phyla were identified, with Acidobacteria (≈35%), Proteobacteria (≈24%) and Actinobacteria (≈21%) being the most abundant. Many of the sequences were represented by few operational taxonomic units (OTUs, 3% of dissimilarity), which were found in all treatments. In contrast, there were very strong patterns of local selection, with many OTUs occurring only in one sample. Our results reveal a complex bacterial diversity, with a large fraction of microorganisms not yet described, reinforcing the importance of this biome. As possible sign of threat, the qPCR detected a reduction of the bacterial population in agricultural soils compared with native Cerrado soil communities. We conclude that sugarcane cultivation promoted significant structural changes in the soil bacterial community, with Firmicutes phylum and Acidobacteria classes being the groups most affected.     

Soil microbial biomass influence on strontium availability in mine soil

Abstract

The main aim of our work was to assess whether strontium (Sr) affects soil microbial biomass size and activity, and the involvement of said biomass in the availability process of the metal. In addition, information concerning the distribution and mobility of the stable element within ecosystems may allow the prediction of the behaviour of its radioisotope counterpart, ⁹⁰Sr. Samples were collected in the surroundings of a strontium mine and characterised for total and diethylene triamine pentaacetic acid (DTPA)-extractable Sr, total organic C (TOC), microbial biomass C (MBC), MBC/TOC ratio and metabolic quotient (qCO₂). Moreover, MBC and DTPA-extractable Sr were measured during a 45-day incubation experiment of samples soils amended with maize. Overall, increased levels of total Sr had a negative effect on both TOC and MBC. DTPA-extractable Sr was significantly correlated to MBC/TOC suggesting a possible role of soil microbial biomass in the mobilisation of the element. The synthesis of new microbial biomass after soil amendment was negatively affected by the initial content of DTPA-extractable Sr. Conversely, there was a linear positive relationship between newly formed MBC and DTPA-extractable Sr during the incubation, indicating that soil microbial biomass may promote the mobilisation of Sr. These findings indicate that soil amendment with easily degradable organic substrate significantly increases Sr mobility and availability.     

哈尼梯田生态系统土壤微生物量碳的影响因素

土壤微生物量碳（MBC,Microbial Biomass Carbon）是土壤微生物量的重要组成部分,也是土壤肥力变化的重要指标之一。哈尼梯田肥沃的土壤对哈尼梯田生态系统的维持与循环起到重要作用。以哈尼梯田水源区（乔木林、灌木林、荒草地）和梯田为研究对象,采用氯仿熏蒸法测定了4种不同土地利用类型0-20、20-40、40-60 cm 3个土层的土壤MBC,并分析了其与季节变化、地上植被及土壤理化性质之间的关系。结果表明：4种土地利用类型土壤MBC 3个土层皆以乔木林最高,其次是灌木林、荒草地、梯田,且4种土地利用类型土壤MBC含量都随土层深度的增加而减少,其中乔木林0-20 cm土层土壤MBC含量是40-60 cm土层的3.19倍。4种土地利用类型土壤MBC含量均具有明显的季节变化,总体呈"夏季偏高冬季偏低"的变化模式。相关分析表明,不同土地利用类型地上植被的多样性指数、盖度、优势种高度、枯落物层厚度与每一土层土壤MBC都具有很强的相互关系。土壤MBC与土壤有机碳和土壤孔隙度呈正相关性,与土壤容重呈负相关性。植被生长情况、土壤有机碳和孔隙度含量及季节变化是导致不同土地利用类型土壤微生物量碳差异的主要因素。     

Land-use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling

Over the past decades, the tropical mountain rainforest of southern Ecuador has been threatened by conversion to cattle pastures. Frequently, these pastures are invaded by bracken fern and abandoned when bracken becomes dominant. Changes in land-use (forest–pasture–abandoned pasture) can affect soil microorganisms and their physiological responses with respect to soil carbon and nutrient cycling. In situ investigations on litter decomposition and soil respiration as well as biogeochemical characterization of the soil were carried out to identify the driving factors behind. The conversion of forest to pasture induced a pronounced increase in CO₂–C effluxes to 12.2 Mg ha^?1 a^?1 which did not decrease after abandonment. Soil microbial activity and biomass showed a different pattern with lowest values at forest and abandoned pasture sites. With 3445 mg kg^?1 (0–5 cm) microbial biomass carbon (MBC by CFE-method), the active pasture had a more than three times higher value than forest and abandoned pasture, which was among the highest in tropical pasture soils. A shift in the microbial community structure (phospholipid fatty acid, PLFA) was also induced by the establishment of pasture land; the relative abundance of fungi and Gram-negative bacteria increased. PLFA fingerprints of the forest organic layer were more similar to pasture than to forest mineral soil. Chemical properties (pH value, exchangeable cations) were the main factors influencing the respective microbial structure. Bracken-invasion resulted in a decrease in the quantity and quality of above- and belowground biomass. The lower organic substance and nutrient availability induced a significant decline in microbial biomass and activity. After pasture abandonment, these differences in soil microbial function were not accompanied by pronounced shifts in the community structure and in soil pH as was shown for the conversion to pasture. A disconnection between microbial structure and function was identified. Similar soil CO₂–C effluxes between active and abandoned pasture sites might be explained by an underestimation of the effluxes from the active pasture site. All measurements were carried out between grass tussocks where fine-root density was about 2.6 times lower than below tussocks. Thus, lower proportions of root respiration were expected than below tussocks. Overall, soil microorganisms responded differently to changes in land-use from forest to pasture and from pasture to abandoned pasture resulting in pronounced changes of carbon and nutrient cycling and hence of ecosystem functioning.     

Relative availability of inorganic N-pools shifts under land use change: An unexplored variable in soil carbon dynamics

Land use change (LUC) may detrimentally affect the soil organic carbon (SOC) within different soil fractions; directly supplemented by significant contribution to soil CO₂ efflux (SCE). To understand the governing mechanism, experimental data were collected for SOC and SCE along with soil physico-chemical, microbial and aggregate characteristics across adjacent secondary forest (SF)-grassland (GL)-cropland (CL) sequence in dry tropical ecosystems. A significant change in SOC and SCE was observed from SF to GL and CL systems, respectively; though moderately from GL to CL system. Respective decrease in SOC (31 and 42%); soil ammonium-N to nitrate-N ratio (ANR; 96 and 86%), microbial biomass C (MBC; 30 and 50%), nitrogen (MBN; 6 and 33%) and MBC/MBN ratio (25 and 24%); whereas increase in SCE (43 and 57%) and soil nitrate-N availability (340 and 592%) was observed from SF to GL and CL systems. Moreover, aggregate physical distribution shifted toward smaller size fractions; whereas aggregate-associated total C and KMnO₄-labile-C concentration and carbon management index (CMI) across aggregate-size fractions decreased linearly with the land use sequence. SOC was majorly governed by macro-aggregate water stability (WAS_macro) and MBC; whereas SCE by CMI of macro-aggregate (CMI_macro) fraction. Furthermore, the ANR showed positive correlation with microbial (i.e. MBC and MBC/MBN ratio) and macro-aggregate physical (i.e. WAS_macro) and chemical stability (i.e. CMI_macro). It indicates that a shift in the microbial community with the land use may affect the relative availability of inorganic N pools and associated aggregate characteristics. Thus, our results indicate that a shift in ANR with LUC may be an unexplored and crucial indicator of soil C dynamics mediating quantitative and qualitative changes in microbial and aggregate characteristics in dry tropical ecosystems. Further, a critical emphasis is needed on the relationship of SOC dynamics with ANR for future studies at various spatiotemporal scales worldwide to recognize its potential role as ecological indicator of SOC dynamics. Also, its inclusion under climatic models may help to better predict the future climate.     

The change of soil carbon stocks and fine root dynamics after land use change from a native pasture to a pine plantation

A published meta-analysis of worldwide data showed soil carbon decreasing following land use change from pasture to conifer plantation. A paired site (a native pasture with Themeda triandra dominant, and an adjacent Pinus radiata plantation planted onto the pasture 16 years ago) was set up as a case study to assess the soil carbon reduction and the possible reason for the reduction under pine, including the change in fine root (diameter <2 mm) dynamics (production and mortality). Soil analysis confirmed that soil carbon and nitrogen stocks to 100 cm under the plantation were significantly less than under the pasture by 20 and 15%, respectively. A 36% greater mass of fine root was found in the soil under the pasture than under the plantation and the length of fine root was about nine times greater in the pasture. Much less fine root length was produced and roots died more slowly under the plantation than under the pasture based on observations of fine root dynamics in minirhizotrons. The annual inputs of fine root litter to the top 100 cm soil, estimated from soil coring and minirhizotron observations, were 6.3 Mg dry matter ha⁻¹ year⁻¹ (containing 2.7 Mg C and 38.9 kg N) under the plantation, and 9.7 Mg ha⁻¹ year⁻¹ (containing 3.6 Mg C and 81.4 kg N) under the pasture. The reduced amount of carbon, following afforestation of the pasture, in each depth-layer of the soil profile correlated with the lower length of dead fine roots in the layer under the plantation compared with the pasture. This correlation was consistent with the hypothesis that the soil carbon reduction after land use change from pasture to conifer plantation might be related to change of fine root dynamics, at least in part.     

九段沙不同演替阶段湿地土壤微生物呼吸的差异性及其影响因素

通过分析九段沙不同演替阶段湿地土壤微生物呼吸及其土壤微环境因子,研究了不同类型湿地土壤微生物呼吸的差异性及其影响因素。结果表明,处于不同植被演替阶段的湿地土壤微生物呼吸具有显著差异(P0.05),海三棱藨草区高于芦苇区,互花米草区最高(0.367 mg.g-1.(24h)-1),互花米草的引种及蔓延增强了入侵区域土壤微生物呼吸。综合考虑不同植被类型湿地土壤微生物呼吸及植被生物量,芦苇区呼吸微弱、植被生物量最高,在理论上具有更高的有机碳碳汇聚能力。通径分析结果显示,影响土壤微生物呼吸强度的主要生物因素有:原核微生物多样性(Shannon指数)和土壤微生物生物量;土壤有机质、硝态氮及土壤含水量对上述微生物活性指标有显著影响,因此也属于土壤微生物呼吸的主要影响因素。     

Element storage in native, agri-, and silvicultural ecosystems of the Brazilian savanna

The expanding agriculture in the Brazilian savanna, the Cerrado, changes C and nutrient storages of the savanna ecosystems thereby affecting the global C budget and the sustainability of the local land use. We examined the biomass and the C, N, P, and S storages in above- and belowground biomass, in the organic layer, and in the top 2 m of the mineral soil (Anionic Acrustoxes) of three replicate plots of each of native Cerrado, Pinus caribaea Morelet plantations, productive and degraded Bracchiaria decumbens Stapf. pastures, and of conventional and no-tillage soybean cultivation. Aboveground biomass – in the cropping systems shortly before harvest – decreased in the order, Pinus (15 kg m^–2) > Cerrado (2.3) > conventional tillage (1.9) > no tillage (1.5) > productive pasture (0.64) > degraded pasture (0.37) and belowground biomass in the order, Pinus (9.1) > Cerrado (3.0) > productive pasture (2.2) > degraded pasture (1.5) > conventional tillage (0.60) > no tillage (0.41). The aboveground biomass contained 1.1 (degraded pasture) to 19% (Pinus) of the total C storage, 0.3 (productive pasture, degraded pasture) to 3.5% of the total N storage, 0.3 (degraded pasture) to 2.1% (no tillage, conventional tillage) of the total P storage, and 0.3 (degraded pasture) to 3.7% (Pinus) of the total S storage of the ecosystems. Total C storage in the ecosystems was significantly larger in the Pinus stands (36 kg m^–2) than in all other systems; differences among Cerrado (20), degraded pasture (19), productive pasture (20), no tillage (19), and conventional tillage (19) were small and not significant. All land-use systems had larger N (Pinus, 1.5; degraded pasture, 1.3; productive pasture, 1.4; no tillage, 1.4; conventional tillage, 1.4 kg m^–2) and S storage (PI, 28; degraded pasture, 33; productive pasture, 34; no tillage, 36; conventional tillage, 38 g m^–2) than the Cerrado (N, 1.2 kg; S, 26 g m^–2). The P storages varied between 17 and 29 g m^–2 and were not significantly different among the studied ecosystems. The N and S accumulations in the 12–20-year-old land-use systems were larger than the cumulative known fertilizer inputs indicating that there were unknown inputs possibly including the exploration of the deeper subsoil by deep-reaching roots and transfer of nutrients to the topsoil. Our results indicate that afforestation with Pinus trees has the potential to sequester large amounts of C while pasture degradation, no tillage, and conventional tillage tended to result in small C losses. Land use resulted in a marked accumulation of N and S relative to the Cerrado.     

Effects of Composts from Agroindustrial Wastes on Microbial Activity of a Typic Xerofluvent Soil Under Mediterranean Conditions,SE Turkey

Supplementing the nutrient requirement of crops through organic manures as compost derived from agroindustrial wastes plays a key role in sustaining soil fertility, and crop productivity and reducing use of chemical fertilizers. Therefore, this work was conducted for investigating the effects of addition of oily cumin compost (CC) and oily oregano compost (OC) (these composts were derived from oily cumin and oily oregano wastes of aromatic plant factory) at rates of 40 t ha^?1 to identify those potential organic amendments that might improve the quality of an Entisol. Additionally, those effects on the biochemical properties of a Typic xerofluvent soil were compared to chemical fertilization (CF) and also control (CT) during a cotton vegetation period under a Mediterranean climatic condition. Soil biological status was evaluated by measuring the soil microbial biomass carbon (MBC), basal soil respiration (BSR), N-mineralization (N_min), soil metabolic quotient (qCO₂) and soil enzymatic activities (dehydrogenase-DHG, urease-UA, protease-PRO, and alkaline phosphate-ALKPA) in soil samples that were collected on the 19th, 78th and 190th days followed by compost application to the experimental soils. The MBC, BSR and qCO₂, as well as soil enzyme activities, increased significantly in the compost-treated soils compared with the CF-treated soil and nontreated soils (CT) with respect mean values. The level of microbial activity of soil applied chemical fertilizer was almost the same to those of control soil. As a result of cumin compost (CC) application 137-1810% increase of the level of microbial activity with respect to the CT and CF, followed by OC, 47-314% occurred at the end of the experiment. Because of this there were no toxic effects caused by composts observed. The application of these composts to the soil resulted in the most increase in DHG activity significantly. The application of CC with a C/N ratio of 23 resulted a more favorable soil biological properties than the application of OC (C/N ratio = 32) during cotton vegetation period (190 days). Results from this study suggest that composted aromatic plant wastes can be used to enhance the soil microbial activity, thereby promoting plant growth.     

不同土地利用方式下喀斯特峰丛洼地土壤微生物群落特征

基于对喀斯特峰丛洼地6种土地利用类型(坡耕地、草丛、灌丛、人工林、次生林、原生林)的土壤微生物、养分、矿物质和植被4组变量35个指标的调查分析,研究了不同土地利用方式下土壤微生物种群数量、微生物生物量C、N、P及其分形特征,以及土壤微生物与植被、土壤养分、矿物质的关系.结果表明:不同土地利用方式下喀斯特峰丛洼地的土壤微生物种群数量及组成不同.微生物种群数量均以原生林和坡耕地最高,人工林最低;3种森林土壤的细菌比率较大,坡耕地、草丛、灌丛的放线菌比率较大,真菌的比率均很小;土壤微生物生物量C、N、P的含量均很高,其中原生林最高;土壤微生物生物量碳与土壤微生物种群数量具有良好的分形关系,而土壤微生物生物量氮、磷与种群数量不存在分形关系;土壤微生物与植被、土壤养分、土壤矿物质显著相关,其中土壤微生物生物量碳与乔木层的Shannon指数、土壤速效氮、Fe₂O₃、CaO含量显著相关.     

Early warning indicators of changes in soil ecosystem functioning

In the last decades, soil is facing numerous environmental threats and climatic changes that are causing a rapid decline of soil fertility and biodiversity. Soil organic matter (SOM), has the most widely recognized influence on soil quality, but it hardly puts in evidence processes associated to the new soil threats, because of its insensitivity in assessing soil quality changes in the short-term. A series of chemical and biochemical analyses were carried out in agricultural and forestry soil ecosystems subjected to different threats, to identify the parameters that better evidence changes in soil characteristics in a short term, but the identification of basic universal indicators and the choice of the number of estimated measures are still under investigation and discussion. The main aim of this paper was to identify biochemical markers to be used routinely and applicable to different soil ecosystems, as early warning indicators of alteration in soil ecosystem functioning. The results obtained allowed to identify three indicators, microbial biomass (MBC), water soluble phenols (WSP), and fluorescein diacetate hydrolase (FDA), as effective tools in the evaluation of soil quality changes in the short term, showing also a threat-indicator specificity. MBC reflected changes mainly induced by abiotic stress, FDA displayed modification caused by climate, and WSP pointed out alteration due to the organic amendment.