Abstract:【Objective】Microbial biomass carbon(C)metabolism is vital in the formation and stabilization of organic C in soil, constituting a critical parameter in the models of terrestrial ecosystems. Yet, the variances in the microbial C metabolism indices in soils developed from different lithological origins remain undefined. 【Method】To address the scientific gap in the characteristics and driving factors of microbial biomass C metabolism in soils developed from different rocks, we sampled forest soils developed from limestone and clastic rocks as research objects. Using 18O-H2O labeling, we measured the microbial growth rate, respiration rate, carbon use efficiency (CUE), and turnover time. Combined with soil physicochemical properties, soil organic matter mineral protection characteristics, soil enzyme activity, and microbial biomass and community composition, we clarified the influencing mechanism of lithology on forest soil microbial biomass C metabolism. 【Result】The findings indicate that the pH and the 0.002～0.05 mm particle content in limestone-derived soils surpass those in clastic rock-derived soils, whereas soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon(DOC), C: P and N: P ratios were lower in limestone-derived soils (P<0.05). The limestone-developed soils had a higher content of exchangeable calcium and magnesium (Ca/Mg) and free iron and aluminum ((Fe+Al)d) than the clastic rock-developed soils, but the content of amorphous iron and aluminum((Fe+Al)o)was lower than that in the clastic rock-developed soils. Furthermore, the enzyme activity related to C, N, and P cycling in limestone-developed soils was significantly lower than that in clastic rock-developed soils (P< 0.05). In addition, the microbial biomass phosphorus (MBP) in limestone-developed soils was higher than that in clastic rock-developed soils, but microbial biomass carbon(MBC), fungi: bacteria ratio (F: B), and Gram-positive to Gram-negative bacteria ratio (G+: G-)were significantly lower than those in clastic rock-developed soils (P<0.05). The microbial growth rate and turnover rate in limestone-derived soils were significantly higher than in clastic rock-derived soils (P<0.05), but there was no significant difference in the microbial respiration rate and CUE between the two types of soils. Correlation analysis revealed that the soil microbial growth rate and turnover rate were significantly positively correlated with soil pH, (Ca+Mg): (Fe+Al)o, (Ca+Mg): SOC, (Fe+Al)d: SOC, and Gram-negative bacteria(P<0.05), and significantly negatively related to DOC, organic C bound to iron and aluminum, enzyme activity, MBC: MBN, F: B, and G+: G- ratio(P<0.05). The soil CUE was significantly negatively correlated with MBC and MBC: MBN (P<0.05) while microbial respiration rate was only significantly negatively correlated with phenol oxidase activity (P<0.05). In summary, the higher pH, weaker amorphous iron-aluminum mineral protection, lower microbial resource limitation, and larger bacterial biomass (especially Gram-negative bacteria) in limestone-derived soils may lead to greater microbial motility in these soils and stronger substrate availability, resulting in larger microbial growth and turnover rates. However, there was no difference in the soil microbial biomass CUE between the two rock types, which may be due to the similar soil C: N ratio. 【Conclusion】The microbial biomass C metabolism of forest soils developed from two types of rocks is controlled by biological and non-biological factors. These research results provide a new mechanism for explaining the differences in organic carbon pools in forest soils developed from different rocks.

Abstract:[Objective] Soil microbes are an important factor driving turnover of soil organic matter (SOM), through participating in SOM formation, linking aboveground and underground ecosystems in evolution process, and influencing the structure and function of ecosystems. However, it is still a hard nut to evaluate the contribution of soil microbes (especially microbial residues) to SOM, and a hotspot of research in this aspect, due to limitation in technology. In this study, efforts were dedicated to examining (1) how forest secondary succession influences the content of microbial residues and its contribution to soil organic carbon (SOC); (2) how soil depth affects content of microbial residues and its contribution to SOC; and (3) how fungal and bacterial residues regulate the contribution of microbial residues to SOC.[Method] To explore changes in the content of microbial residues and contribution of microbial residues to SOC, soil samples were collected from the topsoil (0-5 cm) and subsoil (5-15 cm) in five plots of secondary forests with different age or succession (i.e. 20 years, 80 years, 120 years, 200 years and ≥ 300 years) in the Changbai Mountain National Nature Reserve, Jilin, Northeast China for analysis of amino sugars, including glucosamine, galactoamine, and muramic acid, as biomarkers for microbial residues. Based on the analysis, contents of fungal and bacterial residues were worked out. Besides, soil organic matter in the sample was analyzed for composition (i.e. aromatic C, aliphatic C and polysaccharides) with fourier transform mid-IR spectroscopy.[Result] Our study showed significant increases in content of microbial residues and contribution of the residues to SOC in both topsoil and subsoil during the period of 80-200 years of the succession, whereas a reverse trend was found after 300 years. Path analysis showed that content of microbial residues was positively related to microbial biomass carbon (MBC) in the two soil layers during the succession, indicating that changes in MBC influence the accumulation of microbial residues. In the soils under secondary forests 80-200 years old, labile SOM (low in aromatic C/polysaccharides ratio) was relatively higher, which was beneficial to utilization of microbial carbon (high in MBC/SOC ratio) and accumulation of microbial residues, and promoted contribution of the residues to SOC, while in the soils under secondary forests >300 years old, recalcitrant SOM (high in aromatic C/polysaccharides ratio) was relatively higher, which inhibited utilization of microbial C, thus leading to decline in content of microbial residues and contribution of the residues to SOC. Content of microbial residues varied with soil depth, being higher in the topsoil than in the subsoil as SOC did. Higher content of SOC in the topsoil induced generation of more microbial biomass, thus leading to higher accumulation of microbial residues, whereas the existence of higher contents of recalcitrant fractions of SOM in the topsoil caused decrease in contribution of the residues to SOC. In addition, the variation of SOM utilization rate from low in the topsoil to high in the subsoil caused decline of fungal residue contribution to SOC, but a reverse trend with bacterial residues.[Conclusion] In summary, changes in availability of carbon resources (i.e. SOC concentration and SOM components) trigger variation of content and accumulation of microbial residues in SOC. All the findings in this study may provide certain theoretical support for us in exploring effects of microbial metabolites on SOM formation from the perspective of microbial ecology. Therefore, this study suggests that the anabolic pathways of soil microbes be integrated into the current terrestrial ecosystem carbon models, which will sure facilitate better prediction and evaluation of SOC response to ecosystem managements.

Abstract:Abstract 【Objective】Soil erosion is a serious problem, causing soil and nutrient losses and altering physical, chemical and biological properties of the soil. Numerous reports have been published on effects of soil erosion on soil physicochemical properties. However, little has been done on quantitative analysis of how soil erosion and deposition affect soil microbial biomass in the black soil region of China. Soil microbial biomass is a sensitive indicator of changes in the environment, compared with soil organic matter. The study on impacts of soil erosion and deposition on soil microbial biomass is expected to be able to provide certain important basis for scientific evaluation of the environmental effects of soil erosion. Therefore, the study was oriented to investigate response of soil microbial biomass carbon and nitrogen to soil erosion and deposition, by analyzing soil microbial biomass carbon, microbial biomass nitrogen and erosion rate of the soils at different locations (the upper stream, middle stream and downstream reaches) in the valley and different positions (the upper, middle, and lower slope position) on a slope. 【Method】The Binzhou River Valley, a typical region of black soil thin in soil layer in Northeast China, was taken as the research area. Contents of microbial biomass carbon and microbial biomass nitrogen in the soils of the sampling sites different in slope position and location in the valley were measured using the chloroform fumigation extraction method and erosion rates of the soils estimated using the 137Cs tracer method. 【Result】Results show significant differences exist between the soils in spatial distribution of soil microbial biomass, and negative relationships of the spatial distributions of soil microbial biomass carbon and microbial biomass nitrogen with that of soil erosion and deposition. On the watershed scale, soil erosion rate declined drastically from the upper stream down to the middle stream and the lower stream, while both soil microbial biomass carbon and microbial biomass nitrogen exhibited a reverse trend, being significantly higher in the downstream than in the upper stream and middle stream. The content of soil microbial biomass carbon was 26.9% and 17.4% lower, respectively, in the upper stream and the middle stream than in the downstream, and the content of soil microbial biomass nitrogen 22.9% and 18.1% lower. On the slope scale, soil erosion rate descended significantly from the middle slope position to the upper slope position and to the lower slope position; but both soil microbial biomass carbon and microbial biomass nitrogen acted reversely, too, beingsignificantly higher at the lower slope than at the middle slope. The content of soil microbial biomass carbon was 13.8% and 20.2%, respectively,lower at the upper slope and the middle slope than at the lower slope, and the content of soil microbial biomass nitrogen 10.0% and 19.5% lower. Regression analysis shows that the contents of soil microbial biomass and nutrient decreased linearly with increasing soil erosion rate. Microbial biomass carbon, microbial biomass nitrogen, organic matter and total nitrogen in the soil were negatively related with soil erosion rate at an extremely significant level (p <0.01), respectively. 【Conclusion】Obviously soil erosion has some profound impacts on spatial distributions of the microbial biomasscarbon and microbial biomass nitrogen in the soil. The removal and redistribution of soil nutrients caused by the processes of soil erosion and deposition is the main reason why spatial distribution of soil microbial biomass differ between erosion and deposition areas.

Abstract:In South China, application of winter green manure crops into the double rice cropping system has been proved to be a high effective rotation pattern in improving soil environments, soil fertility and rice yields，and is very beneficial to the sustainable agriculture. The effects of long-term application of green manure crops on soil microbial biomass carbon, soil microbial biomass nitrogen and the seasonal fluctuation of soil microbial biomass properties in red paddy soil were still not clear enough. Based on a 31-year long-term field experiment on cultivation of double cropping rice and winter green manure in red paddy soil in South China, soil microbial biomass properties were investigated at different stages, aimed to provide a theoretical basis for deliborating mechanism and effects of winter green manure on transformation of soil carbon and nitrogen in the paddy ecosystem. The long-term field experiment includes 4 treatments, i.e., rice-rice-milk vetch (RRV), rice-rice-winter rape (RRP), rice-rice-ryegrass (RRG) and rice-rice-winter fallow (RRF). Soil samples were collected at 4 different typical stages, i.e., flowering stage of winter green manure crop (S1), after the incorporation of green manure (S2), mature stage of early rice (S3), and after the harvest of late rice (S4), for analysis of soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil microbial quotient and soil microbial biomass carbon to nitrogen ratio (SMBC/SMBN). The results showed that the cultivation of green manure crops increased the contents of SMBC, SMBN and soil microbial quotient. Especially at the S4 stage, when soil properties were relatively stable, all the green manure treatments were significantly higher than those in the RRF treatment, and similar trends were observed for the annual mean values. The SMBC and SMBN were most influenced by the leguminous green manure milk vetch. Compared with the RRF treatment，they were increased by 21.12% and 98.45%, respectively, at the S4 stage, and by 15.92% and 3.49% for the annual mean values, respectively. The annual average values of soil microbial quotient in RRV, RRP, RRG were 3.61%, 3.66% and 3.61%, respectively, significantly higher than that in RRF treatment (3.13%). Although the SMBC, SMBN and soil microbial quotient were affected by sampling time profoundly, they all showed similar trends at all the 4 sampling stages, i.e., no significant differences between the stage of S1 and S2, down to the lowest level at the S3 stage, and up again at the S4 stage. The SMBC to SMBN ratio did not vary much among different treatments but fluctuated obviously with the sampling stages, i.e., highest at the S3 stage (when soil being flooded) and lowest at the S4 stage (when soil being non-flooded). It could be concluded that soil microbial properties were improved obviously after the long term cultivation of winter green manure crops in red paddy soil in South China, furtherly supporting that the cultivation of winter green manure crops is an effective way for soil fertilizing in red paddy fields.

Abstract:To explore effect of biological soil crusts (BSCs) on soil microbial biomass carbon（SMBC）and nitrogen（SMBN）, soil of a sand dune covered with BSCs in the artificially revegetated sand zone at the southeastern edge of the Tengger Desert, China was selected as subject of the study. Four sample plots were set different in sand-fixing time (55, 47, 30 and 20 a, separately), and a plot of mobile sand dunes and a plot of natural vegetation as control. Results show that cyanobacteria-lichen and moss crusts significantly increased the contents of SMBC and SMBN in artificially revegetated areas (p<0.05), which was positively related to sand-fixing time（p<0.05). Crust type was also a factor, significantly affecting the content of soil microbial biomass. The contents of SMBC and SMBN under moss crusts were significantly higher than those under cyanobacteria-lichen crusts（p<0.05). In addition, BSCs significantly increased the contents of SMBC and SMBN in the 0~20 cm soil layers（p<0.05）and the effect weakened with increasing soil depth. Moreover, the contents of SMBC and SMBN under BSCs varied seasonally to a significant level, showing a decreasing order of in summer > in spring > in autumn. Heat and water were two main factors controlling the seasonal variation, while BSCs affected soil microbial biomass seasonally by regulating soil temperature and moisture.

Abstract:Changes in soil microbial biomass carbon and enzyme activity in fluvo-aquic soil of the North China Plain were investigated after the soil, with or without cellulose, was amended with inorganic nitrogen and glucose in the experiment of incubation under constant temperature and humidity. The experiment was designed to have 8 treatments, i.e. control (CK), addition of inorganic nitrogen (N), addition of glucose (G), addition of cellulose (C), addition of glucose and inorganic nitrogen (C+N), addition of inorganic nitrogen in soil with cellulose (C+N), addition of glucose treatment in soil with cellulose (C+G), and addition of glucose and inorganic nitrogen in soil with cellulose (C+G+N). Cumulative soil carbon dioxide release, microbial biomass carbon and activities of dehydrogenase, β-glucosidase, catalase, and alkaline phosphatase were measured, separately at various intervals during the 33 days of incubation. Results show that in all microbial parameters no significant difference existed between CK and Treatment C. As against Treatments CK and C, all the treatments displayed a significant increase in cumulative carbon dioxide release, with Treatment C+G+N listed on the topmost. Treatments G, G+N, C+G, and C+G+N all showed an obvious increment in Cmic content and DHD, APH activity, particularly during the first two weeks of the incubation, while Treatments N and C+N displayed similarly like CK result. The findings implied that glucose could significantly increase microbial activity, but inorganic nitrogen could not. The effects of glucose and inorganic nitrogen on GLU and CAT were not obvious and in most cases no significant difference was found between different treatments. Correlation analysis demonstrates that carbon dioxide release rate was always positively related to APH activity, but not to Cmic and other enzymes activities and their relationships varied with the time of incubation, which was probably due to variation of the composition of soil microbial community or the way soil microbs utilize the substrates with the time of incubation. Cluster analysis further indicates that the 8 treatments could be sorted into three groups according to their soil microbial activity. Treatment C+G+N was the only one in the group of the highest activity, which suggests that it is important to amend the soil containing hard-to-decompose cellulose with inorganic nitrogen and readily available organic carbon at the same time for improving its soil microbial activity.

Abstract:A field experiment was carried out in 2005~2008 to a study effects of different tillage methods on soil microbial biomass C, N and P in plough layer of an oat field in Qingshuihe County, Inner Mongolia. The experiment was designed to have five treatments, i.e. non-tillage with short stubbles（NL）, non-tillage with tall stubbles (NH), non-tillage with short stubbles and mulch (NLS), non-tillage with tall stubbles and mulch (NHS) and conventional tillage (T). Results show no much difference between the treatments in trend in interannual variation of soil microbial biomass C, N and P in amount. Both soil microbial biomass C and N followed a double-peak curve. The peaks appreared at the jointing and filling stages, separately in Treatments NLS and NHS, and at booting and filling stages, separately in Treatments NL, NH and T while the peaks of soil microbial biomass N did at the seedling and filling stages, separately. However, the amount of soil microbial biomass P varied following a single-peak curve, with the peak appearing at the filling stage in all the treatments. Regardless of years or growing stages, the treatments followed a decreasing order of Treatment NHS > Treatment NLS > Treatment NH > Treatment NL > Treatment T in amount of soil microbial biomass C, N and P. All the non-tillage treatments affected yield of the crop, which declined first and then rose as compared with CK or Treatment T. Taking 2008 as an example, yield of the crop increased by 22%, 17%, 11% and 5%, respectively, in Treatment NHS, Treatment NLS, Treatment NH and Treatment NL. To sum up, non-tillage especially non-tillage with stubbles and mulch, is conducive to improvement of contents of soil microbial biomass C, N and P, and yield of the crop.

Abstract:PGPR bacterial manure is getting more and more popular in crop and vegetable production, but it has not yet been specialized enough for use in flue-cured tobacco production. In this study, the PGPR bacterial manure used was prepared out of the antibiotic bacteria, nitrogen fixing bacteria, phosphate-dissolving bacteria, and potassium-dissolving bactera screened and isolated from flue-cured tobacco rhizosphere. The experiment was laid out in an experiment field of yellow brown soil, using Yuanyan 89, a common tobacco cultivar. The application rate of the PGPR bacterial manure was set at 30 kg hm-2 when tobacco seedlings was transplanted to the plots randomly arranged. The experiment had four treatments, viz., Treatment I, 100% NPK + PGPR (conventional NPK application rate for tobacco + PGPR bacterial manure), Treatment II, 80% NPK + PGPR (80% the conventional NPK application rate + PGPR), Treatment III, 100% NPK (Conventional NPK application rate) and Treatment IV, 80% NPK (80% of the conventional NPK application rate). Results show that in the PGPR treatments the count of actinomyces in tobacco rhizospheres was reduced by 17% to 27% (p＜0.05), while the content of microbial biomass carbon increased by 3% to 16% during the whole growth period; the count of phosphate-dissolving bacteria at the budding stage increased by 24% (p＜0.05); and the quality of cured leaves was better, as compared to those in the non-PGPR treatments. Comparison between Treatment II and Treatment IV revealed that application of PGPR increased the availability of N, K, Cu, Zn, B, and Fe in tobacco rhizosphere at budding stage by 4.46%~28.87%, while decreased the availability of P, Ca, Mg, and Mn by 2.63%~30.19%, however, it improved yield and net production value of the flue-cured tobacco by 7.53% and 30.05%%, respectively. Compared with Treatment III, Treatment II increased yield and net production value of the flue-cured tobacco by 4.52% and 24.68%. The findings suggest that the use of PGPR bacterial manure is an effective approach to reduction of the application rate of chemical fertilizers in tobacco production and sustainable production of quality and hazard-free flue-cured tobacco leaves.

Abstract:Based on a long-term field experiment initiated in 1989 and conducted in the National Agro-Ecological Experiment Station located in Fengqiu County, Henan Province, China, dynamic changes of microbial biomass C and N, and microbial activity during the growth period of summer maize as related to different continuous fertilization management were investigated in 2007.At the same time, effect of long-term fertilization on microbial biomass and activity and their relationship with soil organic carbon content was also discussed. The experiment was designed to have 7 treatments, i.e. organic manure (OM), half organic manure plus half fertilizer N (1/2OM+1/2NPK), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK).Results show that temporal variation of soil microbial biomass C and N, and microbial activity was significant during the growth period of summer maize. The dynamics of microbial biomass C and microbial activity were consistent, and their extremely positive correlation suggests that microbial biomass C can be used as an indicator of microbial activity.Fertilization significantly affected soil microbial biomass and microbial activity.The 7 treatments generally showed a decreasing order of OM > 1/2OM+1/2NPK > NPK > NP > PK > NK > CK indicating that organic matter was beneficial to soil biochemical environment and soil microbial activity.Compared with Treatment OM, the other chemical treatments revealed a trend of decreasing soil microbial biomass and weakening microbial activity.It was particularly significant in treatments unbalanced in nutrient, with Treatment NK showing the worst effect, probably because element P is an important element for making up cell wall and membrane for most bacteria.Positive relationship of microbial biomass and enzyme activity with soil organic C was also observed.

Abstract:To investigate effects of warming on soil nutrients, microbes and soil enzyme activities in alpine meadow and alpine swamp meadow in the hinterland of the Qinghai-ibet Plateau of China, an experiment was carried out from August 2006 to September 2008 using open-top chambers and capped chambers for comparison.Results show that (1) in alpine swamp meadow, warming increased the average air temperature by 2.4 ℃, and the soil temperature within the depth of 5 cm by 0.8℃ in the open-op chambers and by 4.9℃ and by 14.℃, respectively, in the closed chambers; while in alpine meadow, it increased soil temperature by 0.1℃ and by 3.3℃ in the open-op chambers and closed chambers, respectively.(2) soil nutrients in the two meadows responded differently to warming.In the alpine swamp meadow, soil organic carbon and total nitrogen decreased in the soil layer 0~5 cm in depth, but increased in the soil layer 5~20 cm in depth in both chambers, while in the alpine meadow, they increased in the soil layer 0.cm in depth, but decreased in the soil layer 5~20 cm in depth.(3) warming significantly increased carbon and nitrogen contents in soil microbial biomass, but the greater magnitude of the temperature rise in the closed chambers suppressed metabolism of soil microbes, thus leading to decrease in carbon and nitrogen contents in microbial biomass.(4) The activities of catalase, urease and proteinase increased to a various extent in two meadow soils, but the activity of alkaline phosphatase decreased, and saccharase responded differently between the two meadow soils.The increase in activities of catalase, urease and proteinase and the decrease in saccharase and alkaline phosphatase in the closed chambers were less in magnitude than in the open-op chamber, which is similar to the variation trend of the population of soil microbes.The different responses of soil organic carbon and total N to warming is attributed to difference between the two meadows in soil properties, hydrothermal regime, soil metabolism, vegetation, soil fauna (animal and microbe), population and micro-iodiversity.