盐分对土壤呼吸和有机质动力学的影响与土壤电导率相关，而与渗透势的关系更为密切

Osmotic potential (OP) of soil solution may be a more appropriate parameter than electrical conductivity (EC) to evaluate the effect of salts on plant growth and soil biomass.However,this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture.This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture.Four non-saline and non-sodic soils differing in texture (S-4,S-13,S-24 and S-40 with 4％,13％,24％ and 40％ clay,respectively) were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions,resulting in EC (1:5 soil:water ratio) between 0.4 and 5.0 dS m-1 with two levels of sodicity (sodium absorption ratio (SAR) ＜ 3 (non-sodic) and 20 (sodic),1:5 soil:water ratio).Adjusting the water content to levels optimal for microbial activity,which differed among the soils,resulted in four ranges of OP in all the soils:from-0.06 to--0.24 (controls,without salt added),-0.55 to-0.92,-1.25 to-1.62 and-2.77 to-3.00 Mpa.Finely ground mature wheat straw (20 g kg-1) was added to stimulate microbial activity.At a given EC,cumulative soil respiration was lower in the lighter-textured soils (S-4 and S-13) than in the heavier-textured soils (S-24 and S-40).Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils,with a greater decrease on Day 40 than on Day 10.Cumulative soil respiration was greater at SAR =20 than at SAR ＜ 3 only at the OP levels between-0.62 and-1.62 MPa on Day 40.In all the soils and at both sampling times,concentrations of dissolved organic C and N were higher at the lowest OP levels (from-2.74 to-3.0 MPa) than in the controls (from-0.06 to-0.24 MPa).Thus,OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.     

Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan (Carya illinoinensis) orchards in the southwestern region of the United States. Given the paucity of data regarding the effect of indaziflam on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effects of different application rates of indaziflam on soil microbial activity, diversity, and biochemical processes related to nitrogen (N) cycling. During two consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown and treated with indaziflam applied at two different rates (25 and 50 g active ingredient (ai) ha^-1, with the higher rate being slightly lower than the recommended field application rate of 73.1 g ai ha^-1). Soil samples were collected approximately one week before and one week after herbicide application for determination of soil microbial biomass and diversity, N mineralization, and β-glucosaminidase activity. Soil samples collected from the control mesocosms without herbicide application were treated in the laboratory with two rates of indaziflam (75 and 150 g ai ha^-1) to determine the immediate effect on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. The results showed a slight to moderate decrease in microbial diversity (7% in 2015 and 44% in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed in soils from the mesocosms (33%) and soils treated with indaziflam in the laboratory (45%). The mineral N pool was generally dominated by ammonium after indaziflam application, which was consistent with the drastic decrease (75%) in nitrification activity measured in the laboratory experiment. The results of this study indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on soil microbial activity, but may affect N cycling processes.     

土壤微生物多样性研究方法综述

Soil microorganisms play a central role in decomposing organic matter, in determining the release of mineral nutrients, and in nutrient cycling. Recently, extensive studies have focused on soil microbial diversity. However, understanding the diversity of this complex microbial community in the soil environment is a challenging task. Thus, it is important to master and comprehend appropriate methods for studying soil microbial diversity. Concepts of soil microbial diversity and major methods of study are briefly introduced in this paper. Then, the application of biochemical-based and molecular-based techniques in this area, and their advantages and disadvantages are evaluated. Based on recent related research, perspectives for studying microbial diversity in soils are presented.     

不同土地利用方式下上壤微生物群落水平生理图谱(CLP)与土壤碳、氮有效性之间的相互关系（英文）

The goal of this work was to assess soil microbial respiration,determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate(O2-CLPP),in response to endogenous C and several individual C substrates in the soils with different organic C contents(as a function of soil type and management practice).We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition.A respiratory quotient(RQ) was calculated based on the ratio of the response to endogenous soil C vs.each C-only substrate,and was related to total organic carbon(TOC).For assessing N availability for microbial activity,the effect of N supplementation on soil respiration,expressed as N_(ratio),was calculated based on the response of several substrates to N addition relative to the response without N.Soils clustered in 4 groups after a principal component analysis(PCA),based on TOC and their respiratory responses to substrates and endogenous C.These groups reflected differences among soils in their geographic origin,land use and C content.Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates.TOC was negatively correlated with RQ(r = —0.65),indicating that the soils with higher organic matter content increased respiratory efficiency.The N addition in the assay in the absence of C amendment(i.e.,only endogenous soil C present) had no effect on microbial respiration in any soil,indicating that these soils were not intrinsically N-limited,but substrate-dependent variation in N_(ratio) within soil groups was observed.     

水分含量对秸秆还田土壤碳矿化和微生物特性的影响

An 80-d incubation experiment was conducted to investigate straw decomposition,the priming effect and microbial characteristics in a non-fertilized soil(soil 1) and a long-term organic manure-fertilized soil(soil 2) with and without13 C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect,microbial biomass C(Cmic),and β-glucosidase activity,and more abundant populations of bacteria and fungi than the soil 1. Also,soil CO2 emission,Cmic,β-glucosidase activity,and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw,the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity(WHC) were significantly higher by 31% and 17%,respectively,compared to those at 25% of WHC. In contrast,β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmicdecreased as straw availability decreased,which was mainly attributed to the reduction of straw-derived Cmic. Amended soils,except the amended soil 2 at 25% of WHC,had a more abundant fungal population as straw availability decreased,indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.     

连续三年添加制革厂堆肥后土壤微生物生物量研究

Brazilian industry produces huge amounts of tannery sludge as residues, which is often disposed by landfilling or land application. However, consecutive amendment of such composted industrial wastes may cause shifts in soil microbial biomass （SMB） and enzyme activity. This study aimed to evaluate SMB and enzyme activity after 3-year consecutive composted tannery sludge （CTS） amendment in tropical sandy soils. Different amounts of CTS （0.0, 2.5, 5.0, 10.0, and 20.0 t ha-1） were applied to a sandy soil. The C and N contents of SMB, basal and substrate-induced respiration, respiratory quotient （qCO2）, and enzyme activities were determined in the soil samples collected after CTS amendment for 60 d at the third year. After 3 years, significant changes were found in soil microbial properties in response to different CTS amounts applied. The organic matter and Cr contents significantly increased with increasing CTS amounts. SMB and soil respiration peaked following amendment with 10.0 and 20.0 t ha-1 of CTS, respectively, while qCO2 was not significantly affected by CTS amendment. However, soil enzyme activity decreased significantly with increasing CTS amounts. Consecutive CTS amendment for 3 years showed inconsistent and contrasting effects on SMB and enzyme activities. The decrease in soil enzyme activities was proportional to a substantial increase in soil Cr concentration, with the latter exceeding the permitted concentrations by more than twofold. Thus, our results suggest that a maximum CTS quantity of 5.0 t ha-1 can be applied annually to tropical sandy soil, without causing potential risks to SMB and enzyme activity.     

玉米秸秆质量和土壤水分对土壤活性有机碳组分和微生物性质的影响

Investigating the effects of residue chemical composition on soil labile organic carbon(LOC) will improve our understanding of soil carbon sequestration.The effects of maize residue chemical composition and soil water content on soil LOC fractions and microbial properties were investigated in a laboratory incubation experiment.Maize shoot and root residues were incorporated into soil at 40%and 70% ?eld capacity.The soils were incubated at 20?C for 150 d and destructive sampling was conducted after 15,75,and 150 d.Respiration,dissolved organic carbon(DOC),hot-water extractable organic carbon(HEOC),and microbial biomass carbon(MBC)were recorded,along with cellulase and β-glucosidase activities and community-level physiological pro?les.The results showed that the cumulative respiration was lower in root-amended soils than in shoot-amended soils,indicating that root amendment may be bene?cial to C retention in soil.No signi?cant differences in the contents of DOC,HEOC and MBC,enzyme activities,and microbial functional diversity were observed between shoot- and root-amended soils.The high soil water content treatment signi?cantly increased the cumulative respiration,DOC and HEOC contents,and enzyme activities compared to the low soil water content treatment.However,the soil water content treatments had little in?uence on the MBC content and microbial functional diversity.There were signi?cantly positive correlations between LOC fractions and soil microbial properties.These results indicated that the chemical composition of maize residues had little in?uence on the DOC,HEOC,and MBC contents,enzyme activities,and microbial functional diversity,while soil water content could signi?cantly in?uence DOC and HEOC contents and enzyme activities.     

Soil physicochemical and microbial drivers of temperature sensitivity of soil organic matter decomposition under boreal forests

Soil organic matter(SOM)in boreal forests is an important carbon sink.The aim of this study was to assess and to detect factors controlling the temperature sensitivity of SOM decomposition.Soils were collected from Scots pine,Norway spruce,silver birch,and mixed forests(O horizon)in northern Finland,and their basal respiration rates at five different temperatures(from 4 to 28℃)were measured.The Q_(10) values,showing the respiration rate changes with a 10℃ increase,were calculated using a Gaussian function and were based on temperature-dependent changes.Several soil physicochemical parameters were measured,and the functional diversity of the soil microbial communities was assessed using the MicroResp?method.The temperature sensitivity of SOM decomposition differed under the studied forest stands.Pine forests had the highest temperature sensitivity for SOM decomposition at the low temperature range(0–12℃).Within this temperature range,the Q_(10) values were positively correlated with the microbial functional diversity index(H'_(mic))and the soil C-to-P ratio.This suggested that the metabolic abilities of the soil microbial communities and the soil nutrient content were important controls of temperature sensitivity in taiga soils.     

Responses of soil microbial communities and functions associated with organic carbon mineralization to nitrogen addition in a Tibetan grassland

Alpine grasslands with a high soil organic carbon(SOC)storage on the Tibetan Plateau are experiencing rapid climate warming and anthropogenic nitrogen(N)deposition;this is expected to substantially increase the soil N availability,which may impact carbon(C)cycling.However,little is known regarding how N enrichment influences soil microbial communities and functions relative to C cycling in this region.We conducted a 4-year field experiment on an alpine grassland to evaluate the effects of four different rates of N addition(0,25,50,and 100 kg N ha^-1 year^-1)on the abundance and community structure(phospholipid fatty acids,PLFAs)of microbes,enzyme activities,and community level physiological profiles(CLPP)in soil.We found that N addition increased the microbial biomass C(MBC)and N(MBN),along with an increased abundance of bacterial PLFAs,especially Gram-negative bacterial PLFAs,with a decreasing ratio of Gram-positive to Gram-negative bacteria.The N addition also stimulated the growth of fungi,especially arbuscular mycorrhizal fungi,reducing the ratio of fungi to bacteria.Microbial functional diversity and activity of enzymes involved in C cycling(β-1,4-glucosidase and phenol oxidase)and N cycling(β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase)increased after N addition,resulting in a loss of SOC.A meta-analysis showed that the soil C/N ratio was a key factor in the response of oxidase activity to N amendment,suggesting that the responses of soil microbial functions,which are linked to C turnover relative to N input,primarily depended upon the soil C/N ratio.Overall,our findings highlight that N addition has a positive influence on microbial communities and their associated functions,which may reduce soil C storage in alpine grasslands under global change scenarios.     

亚热带土壤不同矿物组分中铬的吸附

Safe application of chromium (Cr)-containing organic industrial wastes to soil requires considering the ability of the soil to adsorb Cr.In this study,the maximum Cr adsorption capacity was assessed for the bulk samples and their clay and iron-free clay fractions of four subtropical soils differing in mineralogy.To this end,the samples were supplied with Cr(Ⅲ) nitrate solutions at pH 4.5 or 5.5.The results of Cr(Ⅲ) adsorption fitted to a Freundlich equation and the adsorption capacity was positively correlated with soil organic matter and iron oxide contents.The clay fractions adsorbed more Cr per unit mass than the bulk soils and the iron-free clay fractions.The Cr(Ⅲ) adsorption capacity increased with increasing soil pH due to more charges on adsorbing surfaces.Our results suggest that the soils rich in organic matter and iron oxides and having a pH above 4.5 are suitable for application of Cr(Ⅲ)-loaded industrial wastes.     

Short-Time Response of Microbial Communities to Waste Compost Amendment of an Intensive Cultivated Soil in Southern Italy

In an intensely cultivated soil in southern Italy, the effects of municipal waste compost on soil activities (basal respiration, β-glucosidase, and fluorescein diacetate (FDA) hydrolysis), Biolog functional diversity, pH, and electrical conductivity (EC) were estimated in a short period following amendment. Treatment with compost at 30 t ha^?1 (dry matter) was compared to mineral fertilization and untreated soil. In these poor soils, organic amendment allowed the rapid recovery of an active and biodiverse soil community. While the addition of compost increased all microbial activities and EC, the pH did not change. Conversely, metabolic activity that was positively correlated to FDA hydrolysis rate initially was enhanced by compost but decreased with time and disappeared at the end of the incubation. Results indicated that waste compost amendments affected microbial activities, both at global and functional levels, favoring a rapid return of biological factors of fertility.     

The influence of different types of urban land use on soil microbial biomass and functional diversity in Beijing,China

Soil microbes in urban ecosystems are affected by a variety of abiotic and biotic factors resulting from changes in land use. However, the influence of different types of land use on soil microbial properties and soil quality in urban areas remains largely unknown. Here, by comparing five types of land use: natural forest, park, agriculture, street green and roadside trees, we examined the effects of different land uses on soil microbial biomass and microbial functional diversity in Beijing, China. We found that soil properties varied with land uses in urban environments. Compared to natural forest, soil nutrients under the other four types of urban land use were markedly depleted, and accumulation of Cu, Zn, Pb and Cd was apparent. Importantly, under these four types of land use, there was less microbial biomass, but it had greater functional diversity, particularly in the roadside‐tree soils. Furthermore, there were significant correlations between the microbial characteristics and physicochemical properties, such as organic matter, total nitrogen and total phosphorus (P < 0.05), suggesting that lack of nutrients was the major reason for the decrease in microbial biomass. In addition, the larger C/N ratio, Ni concentration and pool of organic matter together with a higher pH contributed to the increase in microbial functional diversity in urban soils. We concluded that different land uses have indirect effects on soil microbial biomass and microbial community functional diversity through their influence on soil physicochemical properties, especially nutrient availability and heavy metal content.     

Long‐term effects of leguminous cover crops on microbial indices and their relationships in soils of a coconut plantation of a humid tropical region

In this study, leguminous crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides, and Pueraria phaseoloides. grown as soil cover individually in the interspaces of a 19‐yr‐old coconut plantation in S. Andaman (India) were assessed for their influence on various microbial indices (microbial biomass C, biomass N, basal respiration, ergosterol, levels of ATP, AMP, ADP) in soils (0–50 cm) collected from these plots after 10 years. The effects of these cover crops on . CO₂ (metabolic quotient), adenylate energy charge (AEC), and the ratios of various soil microbial properties viz., biomass C : soil organic C, biomass C : N, biomass N : total N, ergosterol : biomass C, and ATP : biomass C were also examined. Cover cropping markedly enhanced the levels of organic matter and microbial activity in soils after the 10‐yr‐period. Microbial biomass C and N, basal respiration, . CO₂, ergosterol and levels of ATP, AMP, ADP in the cover‐cropped plots significantly exceeded the corresponding values in the control plot. While the biomass C : N ratio tended to decrease, the ratios of biomass N : total N, ergosterol : biomass C, and ATP : biomass C increased significantly due to cover cropping. Greater ergosterol : biomass C ratio in the cover‐cropped plots indicated a decomposition pathway dominated by fungi, and high . CO₂ levels in these plots indicated a decrease in substrate use efficiency probably due to the dominance of fungi. The AEC levels ranged from 0.80 to 0.83 in the cover‐cropped plots, thereby reflecting greater microbial proliferation and activity. The ratios of various microbial and chemical properties could be assigned to three different factors by principal components analysis. The first factor (PC1) with strong loadings of ATP : biomass C ratio, AEC, and . CO₂ reflected the specific metabolic activity of soil microbes. The ratios of ergosterol : biomass C, soil organic C : total N, and biomass N : total N formed the second factor (PC2) indicating a decomposition pathway dominated by fungi. The biomass C : N and biomass C : soil organic C ratios formed the third principal component (PC3), reflecting soil organic matter availability in relation to nutrient availability. Overall, the study suggested that Pueraria phaseoloides. or Atylosia scarabaeoides were better suited as cover crops for the humid tropics due to their positive contribution to soil organic C, N, and microbial activity.     

Soil fertility and bacterial community composition in a semiarid Mediterranean agricultural soil under long-term tillage management

This research attempted to investigate a part of the United Nations sustainable development goal 15, dealing with preventing land degradation and halting the loss of microorganisms’ diversity. Since soil deterioration and biodiversity loss in the Mediterranean area are occurring because of intensive management, we evaluated some biochemical and microbiological parameters and bacterial biodiversity under long-term conventional tillage (CT) and no-tillage (NT) practices, in Basilicata, a typical Region of Southern Italy, characterized by a semiarid ecosystem. The highest biological fertility index (BFI) (composed of soil organic matter, microbial biomass C, cumulative microbial respiration during 25 days of incubation, basal respiration, metabolic quotient and mineralization quotient) was determined for the 0–20 cm of NT soil (class V, high biological fertility level). The analysis of the taxonomic composition at the phylum level revealed the higher relative abundance of copiotrophic bacteria such as Proteobacteria, Actinobacteria and Bacteroidetes in the NT soil samples as compared to the CT soil. These copiotrophic phyla, more important decomposers of soil organic matter (SOM) than oligotrophic phyla, are responsible of a higher microbial C use efficiency (CUE) in tilled soil, being microbial community composition, C substrates content and CUE closely linked. The higher Chao1 and Shannon indices, under the NT management, also supported the hypothesis that the bacterial diversity and richness increased in the no-till soils. In conclusion, we can assume that the long-term no-tillage can preserve an agricultural soil in a semiarid ecosystem, enhancing soil biological fertility level and bacterial diversity.     

Biochemical quality of organic amendments affects soil fungistasis

Soilborne plant pathogens are among the most important limiting factors for the productivity of agro-ecosystems. Identifying reliable and effective control methods is crucial for efficient biological control. Soil fungistasis is the capability of soils to inhibit the germination and growth of soil-borne fungi in presence of optimal abiotic conditions. The aim of this study is to clarify the relationships between soil amendments with plant residues spanning a wide variety of biochemical quality and soil fungistasis. Microcosms experiments were performed with 42 different plant residues and the effect on soil fungistasis was assessed by using four different fungi (Aspergillus niger, Botrytis cinerea, Pyrenochaeta lycoperici and Trichoderma harzianum). We measured soil respiration and FDA enzymatic activity and compared classic litter proximate chemical analysis with ¹³C-CPMAS NMR spectroscopy. Results showed that quality of organic amendments is a major controlling factor of soil fungistasis. The dramatic relief of soil fungistasis when soil was amended with lignin poor, but labile C rich, substrates gives strong support to the competition-based hypothesis. The positive correlation between soil respiration and fungal growth further supports the competition hypothesis. Finally, ¹³C NMR results showed a relationship between soil fungistasis and the biochemical quality of plant residues, and provided a quantitative assessment of the time required for fungistasis restoration after organic materials application.     

Soil microbial activity after restoration of a semiarid soil by organic amendments

Unsuitable agricultural practices together with adverse environmental conditions have led to degradation of soil in many Mediterranean areas. One method for recovering degraded soils in semiarid regions, is to add organic matter in order to improve soil characteristics, thereby enhancing biogeochemical nutrient cycles. In this study, the effect of adding the organic fraction of urban wastes (both fresh and composted) on different carbon fractions and on microbiological and biochemical parameters (microbial biomass C, basal respiration and different enzymatic activities) of a degraded soil of SE Spain has been assessed in a 2 year experiment. Three months after the addition of the organic material, spontaneous plant growth occurred and the plant cover lasted until the end of the experiment. Organic soil amendment initially increased the levels of soil organic matter, microbial biomass, basal respiration and some enzyme activities related to the C and N cycles These values decreased but always remained higher than those of the unamended soil. The results indicate that the addition of urban organic waste is beneficial for recovering degraded soils, the microbial activity of which clearly increases with amendment. The incorporation of compost seemed to have a greater positive effect on the soil characteristics studied than the incorporation of fresh organic matter.     

Effects of straw amendment and moisture on microbial communities in Chinese fluvo-aquic soil

Purpose

Returning crop straw into fields is a typical agricultural practice to resolve an oversupply of straw and improve soil fertility. Soil microorganisms, especially eukaryotic microorganisms, play a critical role in straw decomposition. To date, microbial communities in response to straw amendment at different moisture levels in Chinese fluvo-aquic soil are poorly understood. The aim of this study was to explore the effects of straw amendment and moisture on microbial communities in Chinese fluvo-aquic soil.

Materials and methods

Two soils (one was applied with organic manure, and the other was not applied with any fertilizer) from a long-term field experiment in the North China Plain were collected. Soils with and without straw amendment at 25 and 55 % of the average water-holding capacities of the two soils were incubated at 25 °C for 80 days. All treatments were sampled 20 and 80 days after the start of incubation. Microbial biomass and community structure were analyzed by phospholipid fatty acids (PLFA) assay, and the eukaryotic diversity and community composition were assessed via barcoded pyrosequencing of the 18S ribosomal RNA (rRNA) gene amplicons.

Results and discussion

PLFA analysis showed that straw amendment increased the biomass of Gram-positive bacteria, Gram-negative bacteria, actinobacteria, and fungi and shifted microbial community structure. The varied straw availability resulted in a large variation in microbial community structure. In the presence of straw, actinobacterial and fungal biomass both decreased under high moisture content. 18S rRNA gene pyrosequencing indicated that straw amendment decreased eukaryotic diversity and richness and probably restructured the eukaryotic community. Under identical moisture content, long-term organic manure-fertilized soil had higher eukaryotic diversity and richness than the unfertilized soil. In the amended soils under high moisture content, the relative abundance of dominant fungal taxa (Dikarya subkingdom, Ascomycota phylum, and Pezizomycotina subphylum) decreased.

Conclusions

Straw amendment increases microbial biomass, shifts microbial community structure, and decreases eukaryotic diversity and richness. High moisture content probably has a negative effect on fungal growth in the amended soils. In conclusion, microbial communities in Chinese fluvo-aquic soil are significantly affected by straw amendment at different moisture levels.     

不同培肥管理措施对土壤微生物生态特征的影响

本文研究了厩肥区、秸杆区、化肥区和无肥对照区四种不同培肥管理措施对土壤微生物生态特征的影响,结果表明,施入厩肥、化肥或秸杆还田均能明显增加土壤微生物生物量及呼吸量;土壤微生物生物质量、土壤呼吸及代谢商等微生物指标均与土壤有机质的变化呈相同的变化趋势;BIOLOG生态盘测试亦揭示了培肥管理措施能明显影响土壤微生物的群落结构。     

不同土地利用方式下土壤微生物群落水平生理图谱(CLP)与土壤碳、氮有效性之间的相互关系

The goal of this work was to assess soil microbial respiration, determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate (O₂-CLPP), in response to endogenous C and several individual C substrates in the soils with different organic C contents (as a function of soil type and management practice). We also used the O₂-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition. A respiratory quotient (RQ) was calculated based on the ratio of the response to endogenous soil C vs. each C-only substrate, and was related to total organic carbon (TOC). For assessing N availability for microbial activity, the effect of N supplementation on soil respiration, expressed as N_ratio, was calculated based on the response of several substrates to N addition relative to the response without N. Soils clustered in 4 groups after a principal component analysis (PCA), based on TOC and their respiratory responses to substrates and endogenous C. These groups reflected differences among soils in their geographic origin, land use and C content. Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates. TOC was negatively correlated with RQ (r = - 0.65), indicating that the soils with higher organic matter content increased respiratory efficiency. The N addition in the assay in the absence of C amendment (i.e., only endogenous soil C present) had no effect on microbial respiration in any soil, indicating that these soils were not intrinsically N-limited, but substrate-dependent variation in N_ratio within soil groups was observed.     

双季稻田土壤微生物群落对连续5年施有机肥和石灰的响应差异

  目的  土壤微生物是土壤健康的敏感“指示器”,但不同的土壤微生物类群对连续施用有机肥和石灰的响应规律及不同指标的敏感性仍不明确。  方法  本文选取中亚热带双季稻区的紫泥田作为研究对象,研究连续5年施用有机肥或石灰后,土壤微生物“黑箱指标”（微生物生物量碳氮、微生物熵和土壤呼吸速率）和土壤活体微生物（PLFAs）组成的响应规律与差异。  结果  与对照相比,连续施用有机肥后,土壤微生物生物量碳（MBC）、氮（MBN）含量和土壤呼吸速率分别提高37%、28%和44% ~ 59%,微生物多样性也显著提高,土壤细菌结构发生改变,尤其是革兰氏阴性菌（G?）的PLFAs绝对量提高了100%,但真菌类群的响应不敏感。相反,连续施用石灰5年后,土壤微生物生物量碳、氮含量均呈下降趋势,微生物熵和土壤呼吸速率分别降低11%和26% ~ 52%,微生物多样性显著降低,细菌、放线菌和绝大多数真菌类群PLFAs绝对量下降30% ~ 58%。相关性分析结果表明,土壤有机质含量与土壤微生物总PLFAs和细菌PLFAs含量呈显著正相关关系;而土壤pH仅与Simpson多样性指数呈显著正相关关系。施有机肥显著提高了土壤有机质含量进而导致细菌MBC、MBN、G?和土壤呼吸速率显著增加;而施石灰后土壤微生物群落结构及活性降低与土壤pH有关。  结论  连续5年施用有机肥、石灰后,土壤微生物指标分别表现为正面、负面响应。与“黑箱指标”相比,某些特定微生物类群（如G?）的敏感性指数值更高,在土壤健康评价中极具应用潜力。