Relationship Between Soil Microbial Biomass C and N and Mineralizable Nitrogen in Some Arable Soils on Loess Plateau

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC)and N (SMBN) in 16 loessial soils sampled from Ausai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg Cg-1 with an average of 206.1 μg C g-1, accounting for 1.36%～6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g-1 with an average of 29.4 μg N g-1, accounting for 0.20%～5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.

Seasonal variation in soil microbial biomass carbon and nitrogen in an artificial sand-binding vegetation area in Shapotou, northern China

In this study, seasonal variation characteristics of surface soil microbial biomass carbon （MBC） and soil microbial biomass nitrogen （MBN） of an artificial vegetation area located in Shapotou for different time periods were studied using the chloroform fumigation method, and the results were compared with those of near-natural vegetation areas and mobile dunes. Results showed that the MBC and MBN levels in the 0-5 cm soil layer were higher in autumn than in summer and spring. As the prolongation of vegetation restoration raised the MBC and MBN levels in summer and autumn, no clear variation was found in spring. However, the MBC and MBN in 5-20 cm had no obvious seasonal variation. During summer and autumn, the variation trend of MBC and MBN in the vertical direction was shown to be 0-5 〉 5-10 〉 10-20 cm in the vegetation area, while for mobile dunes, the MBC and MBN levels increased as the depth increased. The natural vegetation area was shown to possess the highest MBC and MBN levels, and yet mobile dunes have the lowest MBC and MBN levels. MBC and MBN levels in artificial sand-binding vegetation increased with the prolongation of vegetation restoration, indicating that the succession of sand-binding vegetation will result in the ac- cumulation of soil carbon and nitrogen, as well as the restoration of soil fertility.

Effects of Carbon and Nitrogen Additions on Soil Microbial Biomass Carbon and Enzyme Activities Under Rice Straw Returning

The effects of different amounts of carbon and nitrogen sources on the soil microbial biomass carbon,dissolved organic carbon and related enzyme activities were studied by the simulation experiment of rice straw returning to the field,and the mechanism of the decomposition of rice straw returning to the field was discussed.Completely randomized experiment of the two factors of the three levels was designed,and a total of nine treatments of indoor soil incubation tests were conducted.Full amount of rice straw was applied to the soil in this simulation experiment and different amounts of brown sugar and urea were added in the three levels of 0(no carbon source and nitrogen source),1(low levels of carbon and nitrogen sources)and 2(high levels of carbon and nitrogen sources),respectively.The results showed that the addition of different amounts of carbon and nitrogen sources to the rice straw could increase the soil carbon content.Compared with T0N0,the microbial biomass carbon of T2N2 was increased significantly by 170.48%;the dissolved organic carbon content of T1N2 was significantly increased by 58.14%and the free humic acid carbon contents of T0N2,T1N1 and T2N0 were significantly increased by 56.16%and 45.55%and 47.80%,respectively;however,there were no significant differences among those of treatments at later incubation periods.The addition of different carbon and nitrogen sources could promote the soil enzyme activities.During the incubation period,all of the soil enzyme activities of adding sugar and urea were higher than those of T0N0 treatment.Therefore,the addition of different amounts of carbon and nitrogen sources to rice straw returning could improve soil microbial biomass carbon content,dissolved organic carbon and soil enzyme activities.

Effects of Soil Salinity on Microbial Biomass Nitrogen of Landscape Soil

Soil salinization can limit the development of agriculture in the Yellow River Delta.In this paper,saline and alkaline farmland in the Yellow River Delta was chosen as the research object,and effects of soil salinity on soil microbial biomass nitrogen(SMBN) under different conditions were investigated to study the response of soil nitrogen turnover to salt stress.There were four salinity gradients(S1:0.1%;S2:0.5%;S3:0.9%;S4:1.3%),and four substrates were added to the soil.The results showed that after the addition of various substrates,SMBN in treatments with high soil salinity(S3 and S4) was obviously lower than that in treatments with low soil salinity(S1 and S2).In comparison with treatment S1,the average of SMBN in treatments S3 and S4 decreased by 35.8% and 46.7% respectively when there was no substrate added to them;it declined by 55.6% and 56.1% respectively as the carbon source was added to them;it reduced by 24.6% and 28.3% when the nitrogen source was added to them;it dropped by 43.8% and 57.0% respectively as the carbon and nitrogen source were added to them.Compared with treatments without substrates,the addition of the nitrogen source could not improve SMBN;the addition of the carbon source or carbon and nitrogen source could enhance SMBN obviously,and it increased by 60.9% and 66.1%(or 110.8% and 140.2%) in treatments with low soil salinity(S1 and S2),while it changed slightly in treatments with high soil salinity(S3 and S4).In order to increase SMBN,it is needed to apply organic fertilizer or chemical fertilizer and organic fertilizer to maintain or improve soil fertility.

Effects of Different Land Cover Types on Soil Microbial Biomass Carbon and Nitrogen in the Lower Reaches of Niyang River

[Objectives]To comprehensively and deeply explore the effects of different land cover types in the lower reaches of Niyang River on soil microbial biomass carbon and nitrogen,and to provide a scientific basis for the rational use and sustainable management of land resources in this area.[Methods]Taking the 3 types of land cover(cultivated land,grass land and forest land)in the lower reaches of Niyang River in Tibet as the research object,the contents,distribution characteristics and relationships of soil organic carbon,organic nitrogen,microbial biomass carbon,microbial biomass nitrogen and readily oxidizable organic carbon,and their relationships were studied in 0-10,10-20,20-40,40-60,and 60-100 cm soil depth.[Results]The soil organic carbon content of forest land was higher than that of grass land and cultivated land;the vertical change trend of soil organic carbon content decreased with the increase of depth(P<0.05),and it was mainly concentrated in the soil with a depth of 0-20 cm.The soil organic carbon content was significantly different among forest land,grass land and cultivated land(P<0.05),but there was no significant difference between cultivated land and grass land(P>0.05).The soil organic nitrogen content was significantly different among cultivated land,grass land,and forest land(P<0.05),but there was no significant difference between grass land and forest land(P>0.05).The readily oxidizable organic carbon,microbial biomass carbon and nitrogen in forest land were higher than that in cultivated land and grass land.The change trend of soil readily oxidizable organic carbon,microbial biomass carbon and microbial biomass nitrogen was similar to the change of soil organic carbon content,showing a significant positive correlation.In addition to being subject to land cover,soil microbial biomass carbon and nitrogen content were also subject to the interaction of factors such as soil temperature,humidity,pH and vegetation types.[Conclusions]Changes in land cover significantly affect soil organic carbon and nitrogen,readily oxidizable organic carbon,microbial biomass carbon and nitrogen content.

Seasonal dynamics of soil microbial biomass C and N of Keteleeria fortunei var. cyclolepis forests with different ages

Soil microbial biomass is an important indicator to measure the dynamic changes of soil carbon pool.It is of great signifi cance to understand the dynamics of soil microbial biomass in plantation for rational management and cultivation of plantation.In order to explore the temporal dynamics and infl uencing factors of soil microbial biomass of Keteleeria fortunei var.cyclolepis at diff erent stand ages,the plantation of diff erent ages(young forest,5 years;middle-aged forest,22 years;mature forest,40 years)at the Guangxi Daguishan forest station of China were studied to examine the seasonal variation of their microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)by chloroform fumigation extraction method.It was found that among the forests of diff erent age,MBC and MBN diff ered signifi cantly in the 0–10 cm soil layer,and MBN diff ered signifi cantly in the 10–20 cm soil layer,but there was no signifi cant diff erence in MBC for the 10–20 cm soil layer or in either MBC or MBN for the 20–40 cm soil layer.With increasing maturity of the forest,MBC gradually decreased in the 0–10 cm soil layer and increased fi rstly and then decreased in the 10–20 cm and 20–40 cm soil layers,and MBN increased fi rstly and then decreased in all three soil layers.As the soil depth increased,both MBC and MBN gradually decreased for all three forests.The MBC and MBN basically had the same seasonal variation in all three soil layers of all three forests,i.e.,high in the summer and low in the winter.Correlation analysis showed that MBC was signifi cantly positively correlated with soil organic matter,total nitrogen,and soil moisture,whereas MBN was signifi cantly positively correlated with soil total nitrogen.It showed that soil moisture content was the main factor determining the variation of soil microbial biomass by Redundancy analysis.The results showed that the soil properties changed continuously as the young forest grew into the middle-aged forest,which increased soil microbial biomass and enriched the soil nutrients.However,the soil microbial biomass declined as the middle-age forest continued to grow,and the soil nutrients were reduced in the mature forest.

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Introduction of Dalbergia odorifera enhances nitrogen absorption on Eucalyptus through stimulating microbially mediated soil nitrogen-cycling

Background:There is substantial evidence that Eucalyptus for nitrogen(N)absorption and increasing the growth benefit from the introduction of N-fixing species,but the underlying mechanisms for microbially mediated soil N cycling remains unclear.Methods:We investigated the changes of soil pH,soil water content(SWC),soil organic carbon(SOC),total N(TN),inorganic N(NH_(4)^(+)-N and NO_(3)^(-)-N),microbial biomass and three N-degrading enzyme activities as well as the biomass and N productivity of Eucalyptus between a pure Eucalyptus urophylla×grandis plantation(PP)and a mixed Dalbergia odorifera and Eucalyptus plantation(MP)in Guangxi Zhuang Autonomous Region,China.Results:Compared with the PP site,soil pH,SWC,SOC and TN in both seasons were significantly higher at the MP site,which in turn enhanced microbial biomass and the activities of soil N-degrading enzymes.The stimulated microbial activity at the MP site likely accelerate soil N mineralization,providing more available N(NH_(4)^(+)-N in both seasons and NO_(3)^(-)-N in the wet-hot season)for Eucalyptus absorption.Overall,the N productivity of Eucalyptus at the MP site was increased by 19.7% and 21.9%,promoting the biomass increases of 15.1% and 19.2% in the drycold season and wet-hot season,respectively.Conclusion:Our results reveal the importance of microbially mediated soil N cycling in the N absorption on Eucalyptus.Introduction of D.odorifera enhances Eucalyptus biomass and N productivity,improve soil N availability and increased soil C and N concentration,which hence can be considered to be an effective sustainable management option of Eucalyptus plantations.

Assessment of soil quality using soil organic carbon and total nitrogen and microbial properties in tropical agroecosystems

Assessment of soil quality is an invaluable tool in determining the sustainability and environmental impact of agricultural ecosystems. The study was conducted to assess the quality of the soils under arable cultivation, locally irri-gated and non-irrigated, forestry plantations of teak (Tectona grandis Lin.) and gmelina (Gme- lina arborea Roxb.), and cashew (Anacardium occidentale Lin.) plantation agro ecosystems using soil organic carbon (SOC), soil total ni-trogen (STN) and soil microbial biomass C (SMBC) and N (SMBN) at Minna in the southern Guinea savanna of Nigeria. Soil samples were collected from soil depths of 0-5 cm and 5-10 cm in all the agro ecosystems and analyzed for physical, chemical and biological properties. All the agro ecosystems had similar loamy soil texture at both depths. The soils have high fer-tility status in terms of available phosphorus and exchangeable calcium, magnesium and po- tassium. The irrigated arable land had significantly (P 6.6 suggesting fungal domination in all the agroecosystems. The forestry plantation soils had higher SMBC and SMBN as a per-centage of SOC and STN respectively than the cultivated arable land soils. Burning for clearing vegetation and poor stocking of forestry planta-tions may impair the quality of the soil. The study suggests that the locally irrigated agro- ecosystem soil seems to be of better quality than the other agroecosystem soils.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods(continuous flooding(CF), continuous flooding and aeration(CFA), and alternate wetting and drying(AWD)). The abundances of amoA ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering(S1), heading(S2), and ripening(S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon(MBC) and soil microbial biomass nitrogen(MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

Soil Microbial Activity During Secondary Vegetation Succession in Semiarid Abandoned Lands of Loess Plateau

To show the vegetation succession interaction with soil properties, microbial biomass, basal respiration, and enzyme activities in different soil layers （0-60 cm） were determined in six lands, i.e., 2-, 7-, 11-, 20-, and 43-year-old abandoned lands and one native grassland, in a semiarid hilly area of the Loess Plateau. The results indicated that the successional time and soil depths affected soil microbiological parameters significantly. In 20-cm soil layer, microbial biomass carbon （MBC）, microbial biomass nitrogen （MBN）, MBC/MBN, MBC to soil organic carbon ratio （MBC/SOC）, and soil basal respiration tended to increase with successional stages but decrease with soil depths. In contrast, metabolic quotient （qCO2） tended to decrease with successional stages but increase with soil depths. In addition, the activities of urease, catalase, neutral phosphatase, β-fructofuranosidase, and earboxymethyl cellulose （CMC） enzyme increased with successional stages and soil depths. They were significantly positively correlated with microbial biomass and SOC （P 〈 0.5）, whereas no obvious trend was observed for the polyphenoloxidase activity. The results indicated that natural vegetation succession could improve soil quality and promote ecosystem restoration, but it needed a long time under local climate conditions.

Microbial Activity in a Temperate Forest Soil as Affected by Elevated Atmospheric CO_2

Microorganisms play a key role in the response of soil ecosystems to the rising atmospheric carbon dioxide （CO2） as they mineralize organic matter and drive nutrient cycling. To assess the effects of elevated CO2 on soil microbial C and N immobilization and on soil enzyme activities, in years 8 （2006） and 9 （2007） of an open-top chamber experiment that begun in spring of 1999, soil was sampled in summer, and microbial biomass and enzyme activity related to the carbon （C）, nitrogen （N） and phosphorus （P） cycling were measured. Although no effects on microbial biomass C were detected, changes in microbial biomass N and metabolic activity involving C, N and P were observed under elevated CO2. Invertase and .dehydrogenase activities were significantly enhanced by different degrees of elevated CO2. Nitrifying enzyme activity was significantly （P 〈 0.01） increased in the August 2006 samples that received the elevated COs treatment, as compared to the samples that received the ambient treatment. Denitrifying enzyme activity was significantly （P 〈 0.04） decreased by elevated COs treatments in the August 2006 and June 2007 （P 〈 0.09） samples, β-N-acetylglucosaminidase activity was increased under elevated CO2 by 7% and 25% in June and August 2006, respectively, compared to those under ambient CO2. The results of June 2006 samples showed that acid phosphatase activity was significantly enhanced under elevated CO2. Overall, these results suggested that elevated CO2 might cause changes in the belowground C, N and P cycling in temperate forest soils.

Relationship Between Microbial Community and Soil Properties During Natural Succession of Abandoned Agricultural Land

The changes of microbial biomass carbon (MBC) and nitrogen (MBN) and microbial community in the topsoil of the abandoned agricultural land on the semi-arid Loess Plateau in China during the natural succession were evaluated to understand the relationship between microbial community and soil properties. MBC and MBN were measured using fumigation extraction, and microbial community was analyzed by the method of fatty acid methyl ester (FAME). The contents of organic C, total N, MBC, MBN, total FAME, fungal FAME, bacterial FAME and Gram-negative bacterial FAME at the natural succession sites were higher than those of the agricultural land, but lower than those of the natural vegetation sites. The MBC, MBN and total FAME were closely correlated with organic C and total N. Furthermore, organic C and total N were found to be positively correlated with fungal FAME, bacterial FAME, fungal/bacterial and Gram-negative bacterial FAME. Natural succession would be useful for improving soil microbial properties and might be an important alternative for sustaining soil quality on the semi-arid Loess Plateau in China.

Soil carbon and nitrogen dynamics linked to Piliostigma species in ferugino-tropical soils in the Sudano-Sahelian zone of Burkina Faso, West Africa

In the Sudano-Sahelian zone of Burkina Faso, Piliostigma reticulatum （DC） Hochst and Piliostigma thonningii （Schumach） are precursor species of fallow land colonization and they are used by rural villagers. The present study aimed to assess the contribution of Piliostigma species to soil quality improvement. We quantified organic carbon, total nitrogen, soil microbial biomass, soil basal respiration and metabolic quotient from soil samples taken under and outside Piliostigma canopies. We used one-way ANOVA to test for differences in the above parameters between locations （beneath and outside Piliostigma canopies）. We recorded increased total organic carbon under Piliostigma from 31%–105% and in total nitrogen from 23%–66%. Microbial biomass was 13%–266% higher beneath canopies as compared to outside canopies. Basal respiration was also higher beneath canopies. The chemical elements varied by class of soil texture. Metabolic quotient （qCO2） was significantly correlated to clay （r = 0.80） and silt （r = 0.79） content. Piliostigma stands produced abundant litter due to their leaf biomass. Thus, they contribute to improved total organic carbon and total nitrogen content in the different phytogeographic zones and improve soil fertility.

Nitrogen in soils beneath 18 65 year old stands of subtropical evergreen broad-leaved forests in Laoshan Mountains in Eastern China

Monitoring of soil nitrogen （N） cycling is useful to assess soil quality and to gauge the sustainability of management practices. We studied net N mineralization, nitrification, and soil N availability in the 0-10 cm and 11-30 cm soil horizons in east China during 2006-2007 using an in situ incubation method in four subtropical evergreen broad-leaved forest stands aged 18-, 36-, 48-, and 65-years. The properties of surface soil and forest floor varied between stand age classes. C：N ratios of surface soil and forest floor decreased, whereas soil total N and total organic C, available P, and soil microbial biomass N increased with stand age. The mineral N pool was small for the young stand and large for the older stands. NO3^--N was less than 30% in all stands. Net rates of N mineralization and nitrification were higher in old stands than jn younger stands, and higher in the 0-10 cm than in the 11-30 cm horizon. The differences were significant between old and young stands （p 〈 0.031） and between soil horizons （p 〈 0.005）. Relative nitrification was somewhat low in all forest stands and declined with stand age. N trans- formation seemed to be controlled by soil moisture, soil mierobial biomass N, and forest floor C：N ratio. Our results demonstrate that analyses of N cycling can provide insight into the effects of management disturbances on forest ecosystems.

Soil microbial biomass carbon and nitrogen in forest ecosystems of Northeast China:a comparison between natural secondary forest and larch plantation

Aims Natural secondary forest(NSF)and larch plantation are two of the predominant forest types in Northeast China.However,how the two types of forests compare in sustaining soil quality is not well understood.This study was conducted to determine how natural secondary forest and larch plantation would differ in soil microbial biomass and soil organic matter quality.Methods Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),soil organic carbon(SOC)and total nitrogen(TN)in the 0-to 15-cm and 15-to 30-cm soil layers were investigated by making chemical and biological measurements in the montane region of eastern Liaoning Province,Northeast China,during the growing season of 2008 in stands of NSF and Larix olgensis plantation(LOP).Important Findings We found that soil MBC and MBN were significantly lower in the LOP than in the NSF.Both MBC and MBN declined significantly with increasing soil depth in the two types of stands.The ratios of MBC to SOC(MBC/SOC)and MBN to TN(MBN/TN)were also significantly lower in the LOP than in the NSF.Moreover,the values of MBC,MBC/SOC,and MBN/TN significantly varied with time and followed a similar pattern during the growing season,all with an apparent peak in summer.Our results indicate that NSF is better in sustaining soil microbial biomass and nutrients than larch plantation in the temperate Northeast China.This calls for cautions in large-scale conversions of the native forests to coniferous plantations as a forest management practice on concerns of sustaining soil productivity.

Effect of vegetation type, wetting intensity, and nitrogen supply on external carbon stimulated heterotrophic respiration and microbial biomass carbon in forest soils

By using packed soil-core incubation experiments, we have studied stimulating effects of addition of external carbon （C） （glu- cose, 6.4 g C m 2） on heterotrophic respiration and microbial biomass C of a mature broadleaf and Korean pine mixed forest （BKPF） and an adjacent white birch forest （WBF） soil under different wetting intensities （55% and 80% WFPS, water-filled pore space） and nitrogen （N） supply （NH4C1 and KNO3, 4.5 g N m-e） conditions. The results showed that for the control, the cumulative carbon dioxide （CO2） flux from WBF soil during the 15-day incubation ranged from 5.44 to 5.82 g CO2-C m-2, which was significantly larger than that from BKPF soil （2.86 to 3.36 g CO2-C m 2）. With increasing wetting intensity, the cumulative CO2 flux from the control was decreased for the WBF soil, whereas an increase in the CO2 flux was observed in the BKPF soil （P 〈 0.05）. The addition of NH4C1 or KNO3 alone significantly reduced the cumulative CO2 fluxes by 9.2%-21.6 % from the two soils, especially from WBF soil at low wetting intensity. The addition of glucose alone significantly increased soil heterotrophic respiration, microbial biomass C （MBC）, and microbial metabolic quotient. The glucose-induced cumulative CO2 fluxes and soil MBC during the incubation ranged from 8.7 to 11.7 g CO2-C m-2 and from 7.4 to 23.9 g C m-2, which are larger than the dose of added C. Hence, the addition of external carbon can increase the decomposition of soil native organic C. The glucose-induced average and maximum rates of CO2 fluxes during the incubation were significantly in- fluenced by wetting intensity （WI） and vegetation type （VT）, and by WIxVT, NH4ClxVT and WIxVTxNH4C1 （P〈0.05）. The addition of NH4C1, instead of KNO3, significantly decreased the glucose-induced MBC of WBF soil （P〈0.05）, whereas adding NH4C1 and KNO3 both significantly increased the glucose-induced MBC of BKPF soil at high moisture （P〈0.05）. According to the differences in soil labile C pools, MBC and CO2 fluxes in the presence and absence of glucose, it can be concluded that the stimulating effects of glucose on soil heterotrophic respiration and MBC under temperate forests were dependent on vegetation type, soil moisture, and amount and type of the N added.

南亚热带常绿阔叶林土壤微生物生物量碳氮年际动态特征及其影响因子

土壤微生物是土壤有机质和养分循环的主要驱动者,研究土壤微生物生物量碳氮变化、稳态特征及其对环境因子内在的长期响应机理具有重要意义。以南亚热带常绿阔叶林土壤为对象,对土壤微生物生物量碳和氮(MBC和MBN)、土壤有机碳(SOC)、总氮(TN)、总磷(TP)、可溶性碳(ROC)、速效氮(AN)、pH、土壤温度(ST)和土壤含水量(SWC)进行连续10年监测;应用方差分析、相关性和回归分析及稳态分析等探究MBC和MBN的年际变化和稳态特征及主要影响因素。研究结果表明:(1)旱季MBC和MBN含量分别在171.32—358.45和25.90—54.08 mg/kg区间波动,雨季分别在394.01—507.97和68.40—88.05 mg/kg区间波动;旱、雨季的MBC含量年际间变化显著(P<0.05),但MBN含量仅在旱季变化显著(P<0.05)。雨季MBC和MBN含量均显著高于旱季(P<0.01),且雨季的MBC和MBN含量是旱季的2倍以上。(2)旱、雨季的MBC与MBN之间均呈显著正相关(P<0.05)。在旱季,MBC和MBN均与ROC和AN含量显著正相关(P<0.05),此外,MBN含量也与TP(P<0.05)和SOC(P<0.01)显著正相关。在雨季,仅SOC与MBN呈显著正相关(P<0.05)。(3)在旱季,MBC含量变化主要受ROC(P<0.05)和AN(P<0.001)影响,MBN则受AN控制(P<0.05)。在雨季,AN(P<0.05)主导了MBC的变化,TP(P<0.05)和SOC(P<0.05)是MBN变异的主导因子。AN(P<0.001)和SOC(P<0.001)是旱、雨季土壤MBC和MBN变化的主导因子。(4)土壤MBC和MBC/MBN稳态指数在年际间均为绝对稳态型(P>0.05);雨季的MBN(P=0.685)为绝对稳态型,但旱季为非稳态(P<0.01,H>1)。雨季微生物熵显著高于旱季(P<0.01),表明土壤有机质质量及养分利用效率更高。综上,MBC和MBN含量受季节更替显著影响,且主要受土壤SOC和AN的影响;受旱季水分限制,MBN的稳态更差。

Effects of acetylene at low concentrations on nitrification, mineralization and microbial biomass nitrogen concentrations in forest soils

Temperate forest surface soils at the varying distances from main trunks (e.g., Pinus koraiensis and Quercus mongolica) were used to study the effects of acetylene (C2H2) at low concentrations on nitrification, mineralization and microbial biomass N concentrations of the soils, and to assess the contribution of heterotrophic nitrification to nitrous oxide (N2O) emissions from soils. The use of acetylene at partial pressures within a range from 10 to 100 Pa C2H2 in headspace gas gave a significant decrease in N2O emission at soil moisture of c. 45% water-filled porosity space, and the decrease was almost the same in each soil after exposure of C2H2 at low concentrations. Heterotrophic nitrification could account for 21%―48% of total N2O emission from each soil; the contribution would increase with increasing distances from the Pinus koraiensis trunks rather than from the Quercus mongolica trunks. Under the experimental conditions, the use of C2H2 at low concentrations showed no significant influ- ence on soil microbial biomass N, net N mineralization and microbial respiration. However, 100 Pa C2H2 in headspace gas could reduce carbon dioxide (CO2) emissions from soils. According to the rapid consumption of 10 Pa C2H2 by forest soils and convenience for laboratory incubations, 50 Pa C2H2 in headspace gas can be used to study the origin of N2O emissions from forest soils under aerobic con- ditions and the key associated driving mechanisms. The N2O and CO2 emissions from the soils at the same distances from the Quercus mongolica trunks were larger than those from the Pinus koraiensis trunks, and both emissions decreased as the distances from trunks increased. The stepwise regression analysis showed that 95% of the variability in soil CO2 emissions could be accounted for by the concentrations of soil total C and water soluble organic C and soil pH, and that 72% of the variability in soil N2O emissions could be accounted for by the concentrations of soil total N, exchangeable NH+4-N and microbial biomass N and 25% of the variability in heterotrophic nitrification by the soil microbial biomass N concentration. The emissions of N2O and CO2 from forest soils after exposure of C2H2 at low concentrations were positively related to the net nitrification of the soils.

不同耕作及秸秆还田方式对土壤养分及微生物生物量碳氮的影响

为促进作物稳产增产,采用田间定位试验,研究不同耕作[免耕(NT)、浅耕(ST)、深耕(DT)]及秸秆还田方式[秸秆还田(-T)、秸秆离田]下,黑土区土壤剖面(0~10 cm、10~20 cm、20~30 cm、30~40 cm)养分及微生物量碳、微生物量氮的变化。结果表明,不同耕作方式处理的土壤理化性质存在显著差异,在各耕层中土壤有机质含量最高的处理依次为NT-T、DT、ST-T和DT;全氮含量最高的处理依次为ST-T、DT、NT-T和NT-T;速效氮含量最高的处理依次为DT-T、DT-T、DT和NT;土壤各耕层pH均为ST处理最高;土壤含水率在0~10 cm土层中NT-T处理最高,其他土层中均为ST-T处理显著高于其他处理;土壤微生物生物量碳、氮含量均表现为ST-T处理最高。不同的耕作方式下,土壤有机质、速效氮、含水率在秸秆还田方式下表现最高;而土壤微生物生物量碳氮含量无论在秸秆是否还田下,浅耕和深耕的方式均优于免耕。