Soil Microbial Respiration Rate Research Articles

Physical, chemical, and biological properties of soil under soybean cultivation and at an adjacent rainforest in Amazonia

Land-use change in the Amazon basin has occurred at an accelerated pace during the last decade, and it is important that the effects induced by these changes on soil properties are better understood. This study investigated the chemical, physical, and biological properties of soil in a field under cultivation of soy and rice, and at an adjacent primary rain forest. Increases in soil bulk density, exchangeable cations and pH were observed in the soy field soil. In the primary forest, soil microbial biomass and basal respiration rates were higher, and the microbial community was metabolically more efficient. The sum of basal respiration across the A, AB and BA horizons on a mass per area basis ranged from 7.31 to 10.05 Mg CO2-C ha-1yr-1, thus yielding estimates for total soil respiration between 9.6 and 15.5 Mg CO2-C ha-1yr-1 across sites and seasons. These estimates are in good agreement with literature values for Amazonian ecosystems. The estimates of heterotrophic respiration made in this study help to further constrain the estimates of autotrophic soil respiration and will be useful for monitoring the effects of future land-use in Amazonian ecosystems.

Effect of heat-disturbance on microbial biomass carbon and microbial respiration in Chinese fir (Cunninghamia lanceolata) forest soils

Prescribed fire has now become the usual management practice in the Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation in southern China. Heat generated during fire may affect carbon (C) dynamics in soils. We investigated the microbial biomass C (MBC) and microbial respiration in two Chinese fir forest soils (one is not exposed to fire for the past 88 years, and the other is recently exposed to prescribed fire) after soil heating (100 and 200 °C) under three moisture regimes [25, 50 and 75 % of water holding capacity (WHC)]. For both soils, significant reduction in MBC with increasing heating temperature was found. Soils without exposing to fire previously had significantly greater MBC concentration than the fire-exposed soils when heated at 100 or 200 °C. Lower soil water content resulted in higher MBC concentrations in both soils. In contrast, both soils had the highest soil microbial respiration rate at 50 % WHC. Soils without exposing to fire previously had the greatest microbial respiration rates at 200 °C, while the fire-exposed soils when heated at 100 °C had greatest microbial respiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 °C and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.

Long-term conservation tillage influences the soil microbial community and its contribution to soil CO2 emissions in a Mollisol in Northeast China

Conservation tillage can significantly affect the biological, chemical, and physical properties of soil. This study aimed to determine the effect of conservation tillage on the soil microbial community and respiration and on soil CO2 emissions. In this study, the effects of 10 years of conservation tillage (no-till: NT and ridge tillage: RT) on soil CO2 fluxes and soil microbial communities were assessed in a black soil in Northeast China. The annual soil CO2 emissions were higher under moldboard plow (MP) than under NT by 7.8 % (P < 0.05). The average soil microbial respiration rate from RT was higher than that from MP by 11 % (P < 0.05). Soil microbial respiration under NT (65 %) and RT (64 %) contributed more to soil CO2 emissions than MP (54 %). Total soil bacterial and fungal phospholipid fatty acids (PLFAs) were 1.6 times and 2.6 times greater under NT and RT, respectively, than under MP in the 0–5 cm layer, whereas they decreased by 21–47 % under NT and 26–41 % under RT in the 5–10, 10–20, and 20–30 cm layers. The F:B (the ratio of soil fungal PLFAs to bacterial PLFAs) varied with soil depth (0–10 cm) between conservation tillage (NT and RT) and MP. Conservation tillage induced the stratification of the soil microbial community on the vertical profile. RT increased soil microbial respiration, soil organic carbon (SOC) concentration, and soil microbial PLFAs at the 0–5 cm depth, whereas it did not influence the annual soil CO2 emissions compared to MP with a similar carbon input. These results suggested that RT might be an appropriate tillage practice for providing a better habitat for soil microbes and SOC sequestration in Northeast China.

Salinity influence on soil microbial respiration rate of wetland in the Yangtze River estuary through changing microbial community

Estuarine wetland, where freshwater mixes with salt water, comprises different regions (rivers and marine ecosystems) with significantly varying tidal salinities. Two sampling areas, ZXS and JS, were selected to investigate the effect of tidal salinity on soil respiration (SR). ZXS and JS were located in Zhongxia Shoal and Jiangyanan Shoal of Jiuduansha Wetland respectively, with similar elevation and plant species, but significantly different in salinity. The results showed that with almost identical plant biomass, the SR and soil microbial respiration (SMR) of the tidal wetland with lower salinity (JS) were significantly higher than those of the tidal wetland with higher salinity (ZXS) (p<0.05). However, unlike SMR and SR, the difference in the soil microbial biomass (SMB) was not significant (p>0.05) with the SMB of ZXS a little higher than that of JS. The higher SMR and SR of JS may be closely connected to the soil microbial community structures and amount of dominant bacteria. Abundant β- and γ-Proteobacteria and Actinobacteria in JS soil, which have strong heterotrophic metabolic capabilities, could be the main reason for higher SMR and SR, whereas a high number of ε-Proteobacteria in ZXS, some of which have carbon fixation ability, could be responsible for relatively lower carbon output. Path analysis indicated that soil salinity had the maximum negative total influencing coefficient with SMR among the various soil physical and chemical factors, suggesting that higher soil salinity, restricting highly heterotrophic bacteria, is the principle reason for lower SMR and SR in the ZXS.

Microbial Respiration in Arctic Upland and Peat Soils as a Source of Atmospheric Carbon Dioxide

Knowledge on soil microbial respiration (SMR) rates and thus soil-related CO2 losses from Arctic soils is vital because of the crucial importance of this ecosystem within the global carbon (C) cycle and climate system. Here, we measured SMR from various habitats during the growing season in Russian subarctic tundra by applying two different approaches: 14C partitioning approach and root trenching. The variable habitats encompassed peat and mineral soils, bare and vegetated surfaces and included both dry and moist ones. The field experiment was complemented by laboratory studies to measure bioavailability of soil carbon and identify sources of CO2. Differences in bioavailability of soils, measured in the laboratory as basal soil respiration rates, were generally greater than inter-site differences in SMR rates measured in situ, suggesting secondary constraints at field conditions, such as soil C content. There was a tendency towards lower SMR in vegetated peat plateaus compared to upland mineral tundra (on average 137 vs. 185 g CO2 m−2 growing season−1, respectively), but no significant differences were found. Surprisingly, the bare surfaces (peat circles) with 3500-year-old C at the surface exhibited about the largest SMR among all sites as shown by both methods. This was related to the general development of peat plateaus in the region, and uplifting of deeper peat with high C content to the surface during the genesis of peat circles. This observation is particularly relevant for decomposition of deeper peat in vegetated peat plateaus, where soil material similar to the bare surfaces can be found. The data indicate that the large stocks of C stored in permafrost peatlands are principally available for decomposition despite old age.

水分和温度对若尔盖湿地和草甸土壤碳矿化的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 水分和温度对若尔盖湿地和草甸土壤碳矿化的影响 DOI: 10.5846/stxb201302030230 作者: 作者单位: 重庆西南大学地理科学学院,重庆西南大学地理科学学院,华中农业大学资源与环境学院;华中农业大学资源与环境学院,四川省草原科学研究院,中国科学院地理科学与资源研究所 生态系统网络观测与模拟重点实验室,中国科学院地理科学与资源研究所 生态系统网络观测与模拟重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(31270519, 31070431) The effect of moisture and temperature on soil C mineralization in wetland and steppe of the Zoige region, China Author: Affiliation: College of Geographical Science,Southwest University,College of Geographical Science,Southwest University,College of Resources and Environment,Huazhong Agricultural University,Wuhan,,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤碳矿化及其温度和水分敏感性是研究生态系统碳循环的重要指标。以若尔盖高寒湿地和草甸为对象,在不同水分(70%,100%,130%饱和含水量(SSM))和温度(5,10,15,20,25 ℃)培养下定期测定土壤碳矿化速率(或土壤微生物呼吸速率),探讨水分和温度对高寒湿地和草甸土壤碳矿化的影响,为揭示未来暖干化对若尔盖地区碳贮存及其碳汇功能的潜在影响提供科学依据。实验结果表明:增温显著促进了高寒湿地和草甸土壤碳矿化,而水分过高会抑制土壤碳矿化;此外,高寒湿地土壤碳矿化速率高于高寒草甸。土壤水分和草地类型对土壤碳矿化温度敏感性(Q10)的影响比较复杂。高寒草甸Q10随水分升高而显著升高,培养7 d时的Q10变化趋势为70% SSM(1.21)< 100% SSM(1.76)< 130% SSM(2.80),培养56 d的Q10从1.17上升为4.53。高寒湿地的Q10在培养7 d差异不显著,但整个56 d培养期内Q10随水分升高而显著增加。在评估暖干化对若尔盖地区碳贮量和碳汇功能的影响时,应更加重视高寒草甸和高寒湿地Q10对水分和温度变化的不同响应。 Abstract:Soil carbon (C) mineralization and its response to temperature and moisture are important components of an ecosystem's C cycle. In this study, soils of alpine wetlands and meadows in the Zoige region were incubated at various temperatures (5, 10, 15, 20, and 25℃) and soil moisture regimes (70%, 100%, and 130% saturated soil moisture (SSM)). Soil C mineralization rate (or soil microbial respiration rate) was measured regularly. The main objectives were to (1) explore whether the responses of soil C mineralization and in particular, its temperature sensitivity (Q10), are different between alpine wetland and meadow soil types, and (2) to reveal impact of warming and drying scenarios on soil C storage and C sequestration in alpine wetlands and steppe environments. The results showed that soil C mineralization increased significantly with increasing incubation temperature, but excessive soil moisture depressed soil C mineralization. The soil C mineralization capacity in the alpine wetland soil was higher than that of the alpine meadow, regardless of soil moisture. Moreover, soil water content and grassland types interactively influenced Q10 of soil C mineralization (F=14.79,P < 0.001). In the meadow, the values of Q10 increased significantly with increasing water content, as follows: 70% SSM (1.21) < 100% SSM (1.76) < 130% (2.80) in the 7-day incubation experiment, and rose from 1.17 to 4.53 in the 56-day incubation experiment. The Q10 values were not significantly different in the wetland under different soil moisture in the 7-day incubation experiment; but the Q10 values increased significantly with increasing soil moisture in the 56-day incubation experiment. On the basis of the different Q10 values, we concluded that soil C mineralization of the meadow soil is more sensitive to future regional warming and drying scenarios than that of the alpine wetland. When evaluating the effect of warming and drying scenarios on soil C storage and sequestration within alpine wetland and steppe environments, the phenomenon that the Q10 responds differently to changes in soil moisture and temperature in the alpine meadow and alpine wetland ecosystems should be considered. 参考文献 相似文献 引证文献

Thermal response of soil microbial respiration is positively associated with labile carbon content and soil microbial activity

The rate of substrate availability in mediating the response of soil microbial respiration rate (SMRR) relative to temperature was investigated using soils from southern Inner Mongolia. Two independent experiments were performed: the first one was to provide natural soils with different soil water contents (non-incubation experiments), and the second one was to incubate soils under two temperature regimes (10°C and 30°C) and two moisture regimes (35% and 75% water holding capacity) (incubation experiments). The temperature sensitivity of soil microbial respiration rate (Q10) varied from 1.76 to 2.25 for the non-incubated soils and was similar to the incubated soils, which ranged from 1.77 to 2.43. In the non-incubation experiments, the greatest dissolved organic carbon (DOC) values (0.57mgg−1) occurred in the soils with moderate soil moisture, then followed by the wet soils (0.31mgg−1), and lastly (0.18mgg−1) by the dry soils; in the incubation experiment, the DOC was significantly (P<0.05) greater at 10°C (0.28mgg−1) than that incubated at 30°C (0.20mgg−1).The regression results showed that the soil water-soluble carbon content was the main factor that had a significant (P<0.01) influence on the temperature sensitivity of soil microbial respiration in both experiments. It is concluded that substrate availability controls temperature sensitivity of soil microbial respiration in the grassland soils. The variations of the Q10 and its dependence on substrate availability have important implications for regional and global ecosystem carbon modeling, specifically in predicting the response of terrestrial ecosystems to future global warming.

Reclamation of a Petroleum-Contaminated Calcareous Soil Using Phytostimulation

Soil contamination by hydrocarbons poses a threat to groundwater and food chains. Hence, the elimination of these compounds from contaminated soil is vital. In this study, we investigated the degradation of total petroleum hydrocarbons (TPHs) in the rhizosphere of tall fescue (Festuca arundinacea L.), agropyron (Agropyron smithii L.), safflower (Carthamus tinctorius L.), and sunflower (Helianthus annus L.) at three soil contamination levels, denoted as C0 (<50 mg kg-1 TPH), C1 (40360 mg kg-1 TPH), and C2 (69760 mg kg-1 TPH). The dry matter yield decreased with increasing contamination level in all four plant species. Safflower seedlings grew poorly and died within 10 to 11 weeks at the highest contamination level. Soil microbial respiration rate increased by 77 and 80% in the rhizosphere soil of tall fescue and agropyron, respectively, in the C1 treatment as compared to the control. The TPH concentration decreased by 71 and 69% in the C1 treatment and by 45 and 42% in the C2 treatment in the rhizosphere soil of agropyron and tall fescue, respectively. Sunflower had no significant effect on the degradation of the contaminating petroleum hydrocarbons in comparison to plant-free control. According to these results, agropyron and tall fescue appear to be suitable choices for the phytoremediation of investigated petroleum-contaminated soils.

The Influence of Aromatic Plants on Microbial Biomass and Respiration in a Natural Ecosystem

The influence of three aromatic plant species, laurel (Laurus nobilisL.), myrtle (Myrtus communisL.), and French lavender (Lavandula stoechasL.), on top soil microbial biomass, respiration rates, and bacterial colonies was investigated. Fresh, mature plant material was introduced into a typical Mediterranean habitat in Northern Greece. The essential oil chemical compositions from the aromatics used in the study were evaluated by GC-MS analysis. The major compounds constitutingL. nobilisessential oil were 1,8-cineole (48.1%), eugenol (12.3%), and α-pinene (6.0%);M. communisoil consisted of α-pinene (31.2%), myrtenyl acetate (19.3%), and 1,8-cineole (16.1%); andL. stoechasconsisted of fenchone (46.7%), camphor (9.9%), and 1,8-cineole (9.0%).L. nobilispresented the highest inhibition against bacterial colonies (44.9%) and lowered soil respiration and microbial biomass when compared to control soils. In contrast,M. comunnisandL. stoechaswere found to augment bacterial activity by 85.9% and 63.8%, respectively, and to increase soil respiration (1.5-fold) and microbial biomass (2.5-fold) compared to control soil samples. These two plants are proposed for further investigations in biodegradation programs.

Wood‐feeding beetles and soil nutrient cycling in burned forests: implications of post‐fire salvage logging

Rising economic demands for boreal forest resources along with current and predicted increases in wildfire activity have increased salvage logging of burned forests. Currently, the ecological consequences of post‐fire salvage logging are insufficiently understood to develop effective management guidelines or to adequately inform policy decision‐makers. We used both field and laboratory studies to examine the effects of post‐fire salvage logging on populations of the white‐spotted sawyer Monochamus scutellatus scutellatus (Say) (Coleoptera: Cerambycidae) and its ecological function in boreal forest. Monochamus s. scutellatus adults were relatively abundant in both burned and clear‐cut logged sites but were absent from salvage logged sites. An in situ mesocosm experiment showed that the abundance of M. s. scutellatus larvae in burned white spruce bolts was linked to changes in total organic nitrogen and carbon in mineral soil. Organic nutrient inputs in the form of M. s. scutellatus frass increased mineral soil microbial respiration rates by more than three‐fold and altered the availability of nitrogen. Changes in nitrogen availability corresponded with decreased germination and growth of Epilobium angustifolium and Populus spp. but not Calamagrostis canadensis. Although the present study focused on local scale effects, the reported findings suggest that continued economic emphasis on post‐fire salvage logging may have implications beyond the local scale for biodiversity conservation, nutrient cycling and plant community composition in forest ecosystems recovering from wildfire.

Soil organic carbon and biological indicators in an Acrisol under tillage systems and organic management in north-eastern Brazil

No-tillage and organic farming are important strategies to improve soil quality. This study aimed to quantify the effects of the tillage systems and organic management on total organic carbon (TOC), labile C (CL), and biological indicators in an Acrisol in north-eastern Brazil. Five systems were studied: NV, native vegetation; NT/ORG, no-tillage plus organic fertiliser; NT/CHE, no-tillage plus chemical fertiliser; NT/CHE/ORG, no-tillage plus organic and chemical fertiliser; CT/CHE, conventional tillage plus chemical fertiliser. Soil samples were collected in the 0–0.10 and 0.10–0.20 m depths. TOC stocks were higher in NT/CHE/ORG (0–0.10 m, 14.0 Mg/ha; 0.10–0.20 m, 13.0 Mg/ha) and NT/ORG (0–0.10 m, 12.6 Mg/ha; 0.10–0.20 m, 11.6 Mg/ha) than in CT/CHE and NV systems. CL stocks were higher in NT/ORG (3.61 Mg/ha) at 0–0.10 m and in NT/ORG, NT/CHE, and NT/CHE/ORG at 0.10–0.20 m. At 0–0.10 m, microbial biomass C content was higher in the NT/CHE/ORG (190 mg/kg) and NT/ORG (155 mg/kg). Soil microbial respiration rate was similar in all systems. However, qCO2 was higher in the NT/CHE and CT/CHE systems, suggesting a stress in the soil microbial biomass. No-tillage and organic management promoted positive changes in soil organic carbon and soil microbial properties and improved soil quality.

Microbial and enzyme properties of apple orchard soil as affected by long-term application of copper fungicide

Copper-based fungicides have been applied in apple orchards for a long time, which has resulted in increasing soil Cu concentration. However, the microbial and enzyme properties of the orchard soils remain poorly understood. This study aimed to evaluate the effect of long-term application of Cu-based fungicides on soil microbial (microbial biomass carbon (C mic), C mineralization, and specific respiration rate) and enzyme (urease, acid phosphatase, and invertase activities) properties in apple orchards. Soil samples studied were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil as for reference. The mean Cu concentrations of orchard soils significantly increased with increasing orchard ages ranging from 21.8 to 141 mg kg −1, and the CaCl 2-extractable soil Cu concentrations varied from 0.00 to 4.26 mg kg −1. The soil mean C mic values varied from 43.6 to 116 mg kg −1 in the orchard soils, and were lower than the value of the reference soil (144 mg kg −1). The ratio of soil C mic to total organic C (C org) increased from 8.10 to 18.3 mg C mic g −1 C org with decreasing orchard ages, and was 26.1 mg C mic g −1 C org for the reference soil. A significant correlation was observed between total- or CaCl 2-extractable soil Cu and soil C mic or C mic/C org, suggesting that the soil Cu was responsible for the significant reductions in C mic and C mic/C org. The three enzyme activity assays also showed the similar phenomena, and declined with the increasing orchard ages. The mean soil C mineralization rates were elevated from 110 to 150 mg CO 2–C kg −1 soil d −1 compared with the reference soil (80 mg CO 2–C kg −1 soil d −1), and the mean specific respiration rate of the reference soil (0.63 mg CO 2–C mg −1 biomass C d −1) was significantly smaller than the orchard soils from 1.19 to 3.55 mg CO 2–C mg −1 biomass C d −1. The soil C mineralization rate and the specific respiration rate can be well explained by the CaCl 2-extractable soil Cu. Thus, the long-term application of copper-based fungicides has shown adverse effects on soil microbial and enzyme properties.

Root and Microbial Contributions to Soil Respiration during a Soybean Growing Season

Soil respiration is an important process for carbon geochemical cycling. Based on our five long‐term fertilizer experiments, soil respiration was measured using pot experiments with or without planting soybean. Soil respiration rates and soybean root biomass were determined at different observation times. Soil respiration rates due to soil microbial activity could be estimated by extrapolating a newly derived regressive equation at zero root biomass. Soil microbial respiration rates in the control were also observed directly, ranging from 16.0 to 42.7 mg carbon (C) m−2 h−1. Average soil microbial respiration rates from the regression analyses and direct observations were 32.9 and 27.8 mg C m−2 h−1, respectively. The average proportions of soil respiration rates due to the soybean growth were 63.0% using the regressive equation and 69.8% from direct observation. Therefore, the application of these two methods could provide new insight for separating plant root respiration from soil microbial respiration, which is important for estimating their individual contributions to atmospheric carbon dioxide.

Non-target effects of entomopathogenic nematodes on soil microbial community and nutrient cycling processes: A microcosm study

Under microcosm conditions, changes in the soil microbial biomass, respiration rates, and nitrogen pools as indicators of potential non-target effects of entomopathogenic nematodes on soil, were evaluated. Two tests were conducted using soil collected from the field with no history of entomopathogenic nematode application. Treatments consisted of applications of Steinernema carpocapsae All strain in the presence or absence of the wax moth Galleria mellonella larva as a target insect host, compared with the untreated control (soil only). In the second experiment an insecticide treatment (trichlorfon) was added. Microbial biomass (total nitrogen), and mineral nitrogen (NH 4-N, NO 3-N) were measured using standard methods up to 32 days and soil respiration up to 64 days in both experiments. No negative effect was detected in the soil microbial biomass, respiration and nitrogen pools after application of S. carpocapsae. However, a significant increase in ammonium was measured during almost the entire period of the test in the nematode plus larva treatment, not shown in the other treatments. This high level of ammonium in the nematode plus larva treatment showed that entomopathogenic nematodes can indirectly affect system-level processes in soil and adds evidence on the importance of indirect interactions affecting functions in soil food webs. The application of the insecticide trichlorfon significantly suppressed the microbial biomass and nitrification process.

Biochemical parameters and bacterial species richness in soils contaminated by sludge-borne metals and remediated with inorganic soil amendments

The effectiveness of two amendments for the in situ remediation of a Cd- and Ni-contaminated soil in the Louis Fargue long-term field experiment was assessed. In April 1995, one replicate plot (S1) was amended with 5% w/w of beringite (B), a coal fly ash (treatment S1+B), and a second plot with 1% w/w zerovalent-Fe iron grit (SS) (treatment S1+SS), with the aim of increasing metal sorption and attenuating metal impacts. Long-term responses of daily respiration rates, microbial biomass, bacterial species richness and the activities of key soil enzymes (acid and alkaline phosphatase, arylsulfatase, β-glucosidase, urease and protease activities) were studied in relation to soil metal extractability. Seven years after initial amendments, the labile fractions of Cd and Ni in both the S1+B and S1+SS soils were reduced to various extents depending on the metal and fractions considered. The soil microbial biomass and respiration rate were not affected by metal contamination and amendments in the S1+B and S1+SS soils, whereas the activity of different soil enzymes was restored. The SS treatment was more effective in reducing labile pools of Cd and Ni and led to a greater recovery of soil enzyme activities than the B treatment. Bacterial species richness in the S1 soil did not alter with either treatment. It was concluded that monitoring of the composition and activity of the soil microbial community is important in evaluating the effectiveness of soil remediation practices.

Responses of soil microbial biomass and N availability to transition strategies from conventional to organic farming systems

Abstract Organic farming can enhance soil biodiversity, alleviate environmental concerns and improve food safety through eliminating the applications of synthetic chemicals. However, yield reduction due to nutrient limitation and pest incidence in the early stages of transition from conventional to organic systems is a major concern for organic farmers, and is thus a barrier to implementing the practice of organic farming. Therefore, identifying transition strategies that minimize yield loss is critical for facilitating the implementation of organic practices. Soil microorganisms play a dominant role in nutrient cycling and pest control in organic farming systems, and their responses to changes in soil management practices may critically impact crop growth and yield. Here we examined soil microbial biomass and N supply in response to several strategies for transitioning from conventional to organic farming systems in a long-term field experiment in Goldsboro, NC, USA. The transitional strategies included one fully organic strategy (ORG) and four reduced-input strategies (withdrawal of each or gradual reduction of major conventional inputs—synthetic fertilizers, pesticides (insecticides/fungicides), and herbicides), with a conventional practice (CNV) serving as a control. Microbial biomass and respiration rate were more sensitive to changes in soil management practices than total C and N. In the first 2 years, the ORG was most effective in enhancing soil microbial biomass C and N among the transition strategies, but was accompanied with high yield losses. By the third year, soil microbial biomass C and N in the reduced-input transition strategies were statistically significantly greater than those in the CNV (averaging 32 and 35% higher, respectively), although they were slightly lower than those in the ORG (averaging 13 and 17% lower, respectively). Soil microbial respiration rate and net N mineralization in all transitional systems were statistically significantly higher than those in the CNV (averagely 83 and 66% greater, respectively), with no differences among the various transition strategies. These findings suggest that the transitional strategies that partially or gradually reduce conventional inputs can serve as alternatives that could potentially minimize economic hardships as well as benefit microbial growth during the early stages of transition to organic farming systems.

Partitioning root and microbial contributions to soil respiration in Leymus chinensis populations

Based on the enclosed chamber method, soil respiration measurements of Leymus chinensis populations with four planting densities (30, 60, 90 and 120 plants/0.25 m 2) and blank control were made from July 31 to November 24, 2003. In terms of soil respiration rates of L. chinensis populations with four planting densities and their corresponding root biomass, linear regressive equations between soil respiration rates and dry root weights were obtained at different observation times. Thus, soil respiration rates attributed to soil microbial activity could be estimated by extrapolating the regressive equations to zero root biomass. The soil microbial respiration rates of L. chinensis populations during the growing season ranged from 52.08 to 256.35 mg CO 2 m −2 h −1. Soil microbial respiration rates in blank control plots were also observed directly, ranging from 65.00 to 267.40 mg CO 2 m −2 h −1. The difference of soil microbial respiration rates between the inferred and the observed methods ranged from −26.09 to 9.35 mg CO 2 m −2 h −1. Some assumptions associated with these two approaches were not completely valid, which might result in this discrepancy. However, these two methods' application could provide new insights into separating root respiration from soil microbial respiration. The root respiration rates of L. chinensis populations with four planting densities could be estimated based on measured soil respiration rates, soil microbial respiration rates and corresponding mean dry root weight, and the highest values appeared at the early stage, then dropped off rapidly and tended to be constant after September 10. The mean proportions of soil respiration rates of L. chinensis populations attributable to the inferred and the observed root respiration rates were 36.8% (ranging from 9.7 to 52.9%) and 30.0% (ranging from 5.8 to 41.2%), respectively. Although root respiration rates of L. chinensis populations declined rapidly, the proportion of root respiration to soil respiration still increased gradually with the increase of root biomass.

Liming and nitrogen fertilization affects phosphatase activities, microbial biomass and mycorrhizal colonisation in upland grassland

We have studied the effects of factorial combinations of lime and N additions on soil microbial biomass, respiration rates and phosphatase activity of an upland grassland. We also used an Agrostis capillaris seedling bioassay to assess the effect of the treatments on the activity of arbuscular-mycorrhizal (AM) fungi and root surface phosphatase enzymes and the concentrations of N and P in the bioassay plant shoots. In the F and H horizons, soil microbial biomass carbon (Cmic) decreased in response to the liming, while addition of lime and N together reduced basal respiration rates. In the Ah horizon, Cmic was unaffected by the treatments but basal respiration rates decreased in the plots receiving nitrogen. Soil phosphatase activity decreased only in the Ah horizon in plots receiving lime, either in combination with N or alone. The mass of root fwt. colonized by AM fungi increased in response to the treatments in the order nitrogen<lime<N plus lime. In contrast, root surface phosphatase activity decreased only in response to additions of nitrogen. A positive linear relationship was observed between root surface phosphatase activity and the P concentration of the plant shoots (R2=28.7%, P=0.004). The results demonstrate the sensitivity of both free-living heterotrophic microorganisms and symbiotic mycorrhizal fungi to short-term (2 years) applications of lime and N to long-term upland grassland, particularly in relation to the key P cycling activities undertaken by these organisms.

Soil microbial responses to experimental warming and clipping in a tallgrass prairie

AbstractGlobal surface temperature is predicted to increase by 1.4–5.8°C by the end of this century. However, the impacts of this projected warming on soil C balance and the C budget of terrestrial ecosystems are not clear. One major source of uncertainty stems from warming effects on soil microbes, which exert a dominant influence on the net C balance of terrestrial ecosystems by controlling organic matter decomposition and plant nutrient availability. We, therefore, conducted an experiment in a tallgrass prairie ecosystem at the Great Plain Apiaries (near Norman, OK) to study soil microbial responses to temperature elevation of about 2°C through artificial heating in clipped and unclipped field plots. While warming did not induce significant changes in net N mineralization, soil microbial biomass and respiration rate, it tended to reduce extractable inorganic N during the second and third warming years, likely through increasing plant uptake. In addition, microbial substrate utilization patterns and the profiles of microbial phospholipid fatty acids (PLFAs) showed that warming caused a shift in the soil microbial community structure in unclipped subplots, leading to the relative dominance of fungi as evidenced by the increased ratio of fungal to bacterial PLFAs. However, no warming effect on soil microbial community structure was found in clipped subplots where a similar scale of temperature increase occurred. Clipping also significantly reduced soil microbial biomass and respiration rate in both warmed and unwarmed plots. These results indicated that warming‐led enhancement of plant growth rather than the temperature increase itself may primarily regulate soil microbial response. Our observations show that warming may increase the relative contribution of fungi to the soil microbial community, suggesting that shifts in the microbial community structure may constitute a major mechanism underlying warming acclimatization of soil respiration.

Soil Microbial Biomass, Respiration Rate, and Temperature Dependence on a Successional Glacier Foreland in Ny-Ålesund, Svalbard

We examined soil microbial activities, i.e., biomass, respiration rate, and temperature dependence of the respiration on a glacier foreland in Ny-Ålesund, Svalbard, Norway. We collected soil samples from 4 study sites that were set up along a primary succession (Site 1, the youngest, to Site 4, the oldest). Microbial biomass measured with the SIR method increased with successional age (55 to 724μg Cbiomass g−1 soil d.w. from Site 1 to Site 4). The microbial respiration rate of the soil was measured in a laboratory with an open-flow infrared gas-analyzer system, changing the temperature from 2° to 20°C at 3–4° intervals. The microbial respiration rate increased exponentially with the temperature at all sites. The temperature dependence (Q10) of the microbial respiration rate ranged from 2.2 to 4.1. The microbial respiration rates at a given temperature increased with succession as a step change (0.48, 0.43, 1.26, and 1.29μg C g−1soil h−1 at 8°C from Site 1 to Site 4, respectively). However, the substrate-specific respiration rate (respiration rate per gram soil carbon) decreased with successional age (0.034 to 0.006μg C mg−1Csoil h−1 from Site 1 to Site 4). A comparison of these respiratory properties with other ecosystems suggested that soil microorganisms in arctic soils have a high potential for decomposition when compared to those of other temperate ecosystems.