黑土区大豆基因型的根际细菌群落结构时空动态变化

The dynamics of rhizosphere microbial communities is important for plant health and productivity, and can be influenced by soil type, plant species or genotype, and plant growth stage. A pot experiment was carried out to examine the dynamics of microbial communities in the rhizosphere of two soybean genotypes grown in a black soil in Northeast China with a long history of soybean cultivation. The two soybean genotypes, Beifeng 11 and Hai 9731, differing in productivity were grown in a mixture of black soil and siliceous sand. The bacterial communities were compared at three zone locations including rhizoplane, rhizosphere, and bulk soil at the third node (V3), early flowering (R1), and early pod (R3) stages using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA. The results of principal component analyses (PCA) showed that the bacterial community structure changed with growth stage. Spatially, the bacterial communities in the rhizoplane and rhizosphere were significantly different from those in the bulk soil. Nevertheless, the bacterial communities in the rhizoplane were distinct from those in the rhizosphere at the V3 stage, while no obvious differences were found at the R1 and R3 stages. For the two genotypes, the bacterial community structure was similar at the V3 stage, but differed at the R1 and R3 stages. In other words, some bacterial populations became dominant and some others recessive at the two later stages, which contributed to the variation of the bacterial community between the two genotypes. These results suggest that soybean plants can modify the rhizosphere bacterial communities in the black soil, and there existed genotype-specific bacterial populations in the rhizosphere, which may be related to soybean productivity.     

日本湿润的温带草地根际和微生物呼吸对土壤CO2排放的贡献及环境影响因素

Soil CO2 efflux, root mass, and root production were investigated in a humid temperate grassland of Japan over a growing season (Apr. to Sep.) of 2005 to reveal seasonal changes of soil CO2 efflux, to separate the respective contributions of root and microbial respiration to the total soil CO2 efflux, and to determine the environmental factors that control soil respiration. Minimal microbial respiration rate was estimated based on the linear regression equations between soil CO2 efflux and root mass at different experimental sites. Soil CO2 efflux, ranging from 4.99 to 16.29 μmol CO2 m-2 s-1, depended on the seasonal changes in soil temperature. The root mass at 0--10 cm soil depth was 0.82 and 1.27 kg m-2 in Apr. and Sep., respectively. The root mass at 0--10 cm soil depth comprised 60% of the total root mass at 0--50 cm soil depth. The root productivity at 0--30 cm depth varied from 8 to 180 g m-2 month-1. Microbial and root respiration rates ranged from 1.35 to 5.51 and 2.72 to 12.06 μmol CO2 m-2 s-1, respectively. The contribution of root respiration to the total soil CO2 efflux averaged 53%, ranging from 33% to 72%. The microbial respiration rate was exponentially related to soil temperature at 10 cm depth (R2 = 0.9400, P = 0.002, n = 6), and the root respiration rate was linearly related to the root production at 0--30 cm depth (R2 = 0.6561, P = 0.042, n = 6).     

镉胁迫系统中土壤氮循环微生物活性随大豆生育期变化的动态效应研究

The potential influences of cadmium （Cd） on the biochemical processes of the soil nitrogen （N） cycle, along with the dynamics of ammonification, nitrification, and denitrification processes in the rhizosphere and non-rhizosphere （bulk soil）, respectively, were investigated in a Cd-stressed system during an entire soybean growing season. In terms of Cd pollution at the seedling stage, the ammonifying bacteria proved to be the most sensitive microorganisms, whereas the effects of Cd on denitrification were not obvious. Following the growth of soybeans, the influences of Cd on ammonification in the bulk soil were： toxic impacts at the seedling stage, stimulatory effects during the early flowering stage, and adaptation to the pollutant during the podding and ripening stages. Although nitrification and den itrification in the bulk soil decreased throughout the entire growth cycle, positive adaptation to Cd stress was observed during the ripening stage. Moreover, during the ripening stage, denitrification in the bulk soil under high Cd treatment （20 mg kg^-1） was even higher than that in the control, indicating a probable change in the ecology of the denitrifying microbes in the Cd-stressed system. Changes in the activity of microbes in the rhizosphere following plant growth were similar to those in the non-rhizosphere in Cd treatments; however, the tendency of change in the rhizosphere seemed to be more moderate. This suggested that there was some mitigation of Cd stress in the rhizosphere.     

长白山岳桦-暗针叶林过渡带根系呼吸对土壤总呼吸的贡献

Total and root-severed soil respiration rates for five plots set up 50 m apart in a Betula ermanii Cham.-dark coniferous forest ecotone on a north-facing slope of the Changbai Mountains, China, were measured to evaluate the seasonal variations of soil respiration, to assess the effect of soil temperature and water content on soil respiration, and to estimate the relative contributions of root respiration to the total soil respiration. PVC cylinders in each of 5 forest types of a B. ermanii-dark coniferous forest ecotone were used to measure soil respirations both inside and outside of the cylinders. The contribution of roots to the total soil respiration rates ranged from 12.5% to 54.6%. The mean contribution of roots for the different plots varied with the season, increasing from 32.5% on June 26 to 36.6% on August 3 and to 41.8% on October 14.In addition, there existed a significant （P 〈 0.01） logarithmic relationship between total soil respiration rate and soil temperature at 5 cm soil depth. Also, a similar trend was observed for the soil respiration and soil water content at the surface （0-5 cm） during the same period of time.     

稻麦轮作系统中大气CO2浓度升高对冬小麦生长季土壤呼吸的影响

Studies on the effect of elevated CO2 on C dynamics in cultivated croplands are critical to a better understanding of the C cycling in response to climate change in agroecosystems. To evaluate the effects of elevated CO2 and different N fertilizer application levels on soil respiration, winter wheat （Triticum aestivum L. cv. Yangmai 14） plants were exposed to either ambient CO2 or elevated CO2 （ambient [CO2] ＋ 200 μmol mol-1）, under N fertilizer application levels of 112.5 and 225 kg N ha-1 （as low N and normal N subtreatments, respectively）, for two growing seasons （2006-2007 and 2007-2008） in a rice-winter wheat rotation system typical in China. A split-plot design was adopted. A root exclusion method was used to partition soil respiration （RS） into heterotrophic respiration （RH） and autotrophic respiration （RA）. Atmospheric CO2 enrichment increased seasonal cumulative RS by 11.8% at low N and 5.6% at normal N when averaged over two growing seasons. Elevated CO2 significantly enhanced （P 〈 0.05） RS （12.7%）, mainly due to the increase in RH （caused by decomposition of larger amounts of rice residue under elevated CO2） during a relative dry season in 2007-2008. Higher N supply also enhanced RS under ambient and elevated CO2. In the 2007-2008 season, normal N treatment had a significant positive effect （P 〈 0.01） on seasonal cumulative RS relative to low N treatment when averaged across CO2 levels （16.3%）. A significant increase in RA was mainly responsible for the enhanced RS under higher N supply. The correlation （r2） between RH and soil temperature was stronger （P 〈 0.001） than that between RS and soil temperature when averaged across all treatments in both seasons. Seasonal patterns of RA may be more closely related to the plant phenology than soil temperature. The Q10 （the multiplier to the respiration rate for a 10 ℃ increase in soil temperature） values of RS and RH were not affected by elevated CO2 or higher N supply. These results mainly suggested that the increase in RS at elevated CO2 depended on the input of rice residue, and the increase in RS at higher N supply was due to stimulated root growth and concomitant increase in RA during the wheat growing portion of a rice-winter wheat rotation system.     

茶树种植对中国东部黄棕壤酸化的影响

Soil acidification is an important process in land degradation around the world as well as in China. Acidification of Alfisols was investigated in the tea gardens with various years of tea cultivation in the eastern China. Cultivation of tea plants caused soil acidification and soil acidity increased with the increase of tea cultivation period. Soil pH of composite samples from cultivated layers decreased by 1.37, 1.62 and 1.85, respectively, after 13, 34 and 54 years of tea plantation, as compared to the surface soil obtained from the unused land. Soil acidification rates at early stages of tea cultivation were found to be higher than those at the later stages. The acidification rate for the period of 0-13 years was as high as 4.40 kmol H⁺ ha^-1 year^-1 for the cultivated layer samples. Soil acidification induced the decrease of soil exchangeable base cations and base cation saturation and thus increased the soil exchangeable acidity. Soil acidification also caused the decrease of soil cation exchange capacity, especially for the 54-year-old tea garden. Soil acidification induced by tea plantation also led to the increase of soil exchangeable Al and soluble Al, which was responsible for the Al toxicity to plants.     

黄土和塿土中Fe, Mn, Cu和Zn向植物根部移动的机理

The pot experiments were conducted in the artificial climate laboratories to determine the relative importance of mass flow and diffusion in supplying Fe, Mn, Cu and Zn to wheat, soybean and maize plants growing in loessal soil and lou soil. It was found that the calculated relative contribution of mass flow of iron, manganese, copper and zinc to plant uptake varied from 5% to more than 100%, depending on the crop species and soil types as well as plant growth stage, soil moisture, atmosphere humidity, etc. The results also showed that the major transportation mechanisms of these micronutrients in soil-root system varied with the crop and its growth, climate and soil, significantly. In general, mass flow was more important for Cu and Zn and diffusion was more significant for Fe and Mn at the seedling stage.     

Mechanisms for the Movement of Fe,Mn,Cu and Zn to Plant Roots in Loessal Soil and Lou Soil

The pot experiments were conducted in the artificial climate laboratories to determine the relative importance of mass flow and diffusion in supplying ,Fe,Mn,Cu,and Zn to wheat,soybean and maize plants growing in loessal soil and lou soil.It was found that the calculated relative contribution of mass flow of iron,manganese,copper and zinc to plant uptake varied from 5% to more than 100%,depending on the crop species and soil types as well as plant growth stage,soil moisture,atmosphere humidity,etc.The results also showed that the major transportation mechanisms of these micronutrients in soil-root system varied with the crop and its growth,climate and soil,singnificantly,In general,mass flow was more important for Cu and Zn and diffusion was more significant for Fe and Mn at the seedling stage.     

Phenological Stage, Plant Biomass, and Drought Stress Affect Microbial Biomass and Enzyme Activities in the Rhizosphere of Enteropogon macrostachyus

Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon(C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities(β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyus was grown under controlled conditions. Drought stress(partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d(seedling stage), 70 d(elongation stage), and 80 d(simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyus invested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.     

盐度和氮素对向日葵(Helianthus annuus L.)光合速率和生长状况的影响

Understanding the interactions between salinity and fertilizers is of significant importance for enhancing crop yield and fertilizeruse efficiency. In this study a complete block design experiment was performed in the Hetao Irrigation District of Inner Mongolia,China, to evaluate the effects of interactions between soil salinity and nitrogen(N) application rate on sunflower photosynthesis and growth and to determine the optimum N application rate for sunflower growth in the district. Four levels of soil salinity expressed as electrical conductivity(0.33–0.60, 0.60–1.22, 1.2–2.44, and 2.44–3.95 dS m-1) and three application rates of N fertilization(90, 135,and 180 kg ha-1) were applied to 36 micro-plots. Soil salinity inhibited the photosynthetic rate, stomatal conductance, transpiration rate, plant height, leaf area, and aboveground dry matter of sunflowers. The intercellular CO2 concentration first decreased and then increased with increasing soil salinity in the seedling stage, and the instantaneous leaf water-use efficiency fluctuated with soil salinity. The stomatal and non-stomatal limitations of sunflowers alternated in the seedling stage; however, in the bud, blooming,and mature stages, the stomatal limitation was prevalent when the salinity level was lower than 2.44 dS m-1, whereas the nonstomatal limitation was predominant above the salinity level. The application of N fertilizer alleviated the adverse effects of salinity on sunflower photosynthesis and growth to some extent. During some key growth periods, such as the seedling and bud stages, a moderate N application rate(135 kg ha-1) resulted in the maximum photosynthetic rate and yielded the maximum dry matter. We suggest a moderate N application rate(135 kg ha-1) for the Hetao Irrigation District and other sunflower-growing areas with similar ecological conditions.     

Carbon Dioxide Emission from Black Soil as Influenced by Land‐Use Change and Long‐Term Fertilization

Land‐use change and soil management play a vital role in influencing losses of soil carbon (C) by respiration. The aim of this experiment was to examine the impact of natural vegetation restoration and long‐term fertilization on the seasonal pattern of soil respiration and cumulative carbon dioxide (CO₂) emission from a black soil of northeast China. Soil respiration rate fluctuated greatly during the growing season in grassland (GL), ranging from 278 to 1030 mg CO₂ m^?2 h^?1 with an average of 606 mg CO₂ m^?2 h^?1. By contrast, soil CO₂ emission did not change in bareland (BL) as much as in GL. For cropland (CL), including three treatments [CK (no fertilizer application), nitrogen, phosphorus and potassium application (NPK), and NPK together with organic manure (OM)], soil CO₂ emission gradually increased with the growth of maize after seedling with an increasing order of CK < NPM < OM, reaching a maximum on 17 August and declining thereafter. A highly significant exponential correlation was observed between soil temperature and soil CO₂ emission for GL during the late growing season (from 3 August to 28 September) with Q₁₀ = 2.46, which accounted for approximately 75% of emission variability. However, no correlation was found between the two parameters for BL and CL. Seasonal CO₂ emission from rhizosphere soil changed in line with the overall soil respiration, which averaged 184, 407, and 584 mg CO₂ m^?2 h^?1, with peaks at 614, 1260, and 1770 mg CO₂ m^?2 h^?1 for CK, NPK, and OM, respectively. SOM‐derived CO₂ emission of root free‐soil, including basal soil respiration and plant residue–derived microbial decomposition, averaged 132, 132, and 136 mg CO₂ m^?2 h^?1, respectively, showing no difference for the three CL treatments. Cumulative soil CO₂ emissions decreased in the order OM > GL > NPK > CK > BL. The cumulative rhizosphere‐derived CO₂ emissions during the growing season of maize in cropland accounted for about 67, 74, and 80% of the overall CO₂ emissions for CK, NPK, and OM, respectively. Cumulative CO₂ emissions were found to significantly correlate with SOC stocks (r = 0.92, n = 5, P < 0.05) as well as with SOC concentration (r = 0.97, n = 5, P < 0.01). We concluded that natural vegetation restoration and long‐term application of organic manure substantially increased C sequestration into soil rather than C losses for the black soil. These results are of great significance to properly manage black soil as a large C pool in northeast China.     

Changes of microbial properties in (near-) rhizosphere soils after phytoextraction by Sedum alfredii H: A rhizobox approach with an artificial Cd-contaminated soil

The ultimate goal of soil remediation is to restore soil health. Soil microbial parameters are considered to be effective indicators of soil health. The aim of this study was to determine the effects of phytoextraction on microbial properties through the measurement of soil microbial biomass carbon, soil basal respiration and enzyme activities. For this purpose, a pre-stratified rhizobox experiment was conducted with the Cd hyperaccumulator Sedum alfredii H. for phytoextraction Cd from an artificial contaminated soil (15.81 mg kg⁻¹) under greenhouse conditions. The plant and soil samples were collected after growing the plant for three and six months with three replications. The results indicated that the ecotype of S. alfredii H. originating from an ancient silver mining site was a Cd-hyperaccumulator as it showed high tolerance to Cd stress, the shoot Cd concentration were as high as 922.6 mg kg⁻¹ and 581.9 mg kg⁻¹ at the two samplings, and it also showed high BF (58.4 and 36.8 after 3 and 6 months growth), and TF (5.8 and 5.1 after 3 and 6 months growth). The amounts of Cd accumulated in the shoots of S. alfredii reached to an average of 1206 μg plant⁻¹ after 6 months growth. Basal respiration, invertase and acid phosphatase activities of the rhizosphere soil separated by the shaking method were significantly higher (P < 0.01) than that of the near-rhizosphere soil and the unplanted soil after 3 months growth, so were microbial biomass carbon, urease, invertase and acid phosphatase activities of the rhizosphere soil after 6 months growth. Acid phosphatase activity of the 0–2 mm sub-layer rhizosphere soil collected by the pre-stratified method after 3 months growth was significantly higher (P < 0.05) than that of other sub-layer rhizosphere soils and bulk soil, and so were microbial biomass carbon, basal respiration, urease, invertase and acid phosphatase activities of the 0–2 mm sub-layer rhizosphere soil after 6 months growth. It was concluded that phytoextraction by S. alfredii could improve soil microbial properties, especially in rhizosphere, and this plant poses a great potential for the remediation of Cd contaminated soil.     

Plant roots are more important than temperature in modulating carbon release in a limed acidic soil

Lime is a common amendment to overcome soil acidity in agricultural production systems. However, plant root effects on lime and soil carbon (C) dynamics in acidic soils under varied temperature remain largely unknown. We monitored root effects of soybean on the fate of lime applied to an acidic soil at 20 and 30°C in growth chambers. Soil respired CO₂ was continuously trapped in columns without and with plants until the final stage of vegetative growth. Lime‐derived CO₂ was separated from total respired CO₂ based on δ¹³C measurements in CO₂. Leaching was induced at early and late vegetative growth stages, and the leachates were analysed for dissolved organic (DOC) and inorganic C (DIC) concentrations. Soil respiration significantly increased with lime addition at both temperatures (p < 0.001). The presence of soybean doubled the recovery of lime‐derived CO₂‐C at 20°C at the early growth stage; however, by the end of the experiment, the contribution of lime‐derived CO₂‐C to soil respiration was negligible in all treatments, indicating that the contribution of lime to soil respiration was shortlived. In contrast, DIC and DOC concentrations in leachates remained elevated with liming and were greater in the presence of soybean. We observed no main temperature effects and no interactive effects of temperature and soybean presence on lime‐derived CO₂‐C, DIC and DOC. These results highlight the role of plant‐modulated processes in CO₂ release and C leaching from lime in acidic soils, whereas an increase in temperature may be less important. Temperature and plant roots alter the rate of key processes controlling C dynamics in a limed acidic soil. Lime‐derived CO₂‐C, DIC and DOC increased more in the presence of plants than with increased temperature. Root effects are more important than temperature for inorganic and organic carbon dynamics in limed acidic soils.     

外源放线菌对谷子生长和成熟期根际可培养微生物的影响

为研究外源放线菌对谷子生长及成熟期根际可培养微生物的影响，本研究通过盆栽和田间试验分析施加放线菌微白黄链霉菌（Streptomyces albidoflavus，T4）和密旋链霉菌（Streptomyces pactum，Act12）后成熟期谷子生物量、产量形成指标及根际可培养微生物结构组成的差异，并对谷子生长与根际微生物之间相互关系进行分析。结果表明，①T4促进了盆栽和田间试验中谷子生物量的增加，而T4和Act12也使田间试验中单株谷子籽粒干重和产量增加了13.7%～22.6%。②对于根际微生物，T4处理使培养箱盆栽试验中谷子根际可培养细菌（B）、真菌（F）、放线菌（A）及微生物总数量增加了29.5%～56.9%。T4和Act12使室外盆栽试验中根际真菌数量分别提高了73.3%和222.0%，A/F和B/F降低了34.7%～72.4%。③相关分析表明，成熟期谷子茎叶干重、单株谷子籽粒干重与根际B、F、A和总微生物数量显著正相关（r = 0.748～0.971，P < 0.01），而与A/F和B/F显著负相关（r = -0.764 ～ -0.906，P < 0.01）。综上，供试放线菌通过调整根际可培养微生物群落结构促进了谷子生长，增加了谷子产量。因此，通过外源施加放线菌优化根际可培养微生物群落结构是谷子促生增产的可行途径之一。     

保护性耕作下大豆农田土壤呼吸及影响因素分析

为了探讨保护性耕作对旱作农田土壤呼吸的影响,采用LI6400-09仪器(LI6400便携式光合作用系统连接6400-09呼吸室)在重庆北碚西南大学试验农场对平作(T)、垄作(R)、平作+覆盖(TS)、垄作+覆盖(RS)、平作+覆盖+秸秆速腐剂(TSD)、垄作+覆盖+秸秆速腐剂(RSD)6种处理下的西南紫色土丘陵区小麦/玉米/大豆套作体系中大豆生长季节的土壤呼吸及其水、热、生物因子进行测定和分析,探讨西南丘陵区保护性耕作下大豆农田土壤呼吸及其影响因素。结果表明,大豆整个生育期内土壤呼吸先缓慢增强,到开花期开始增长迅速,成熟期明显下降。不同处理土壤呼吸速率存在差异,表现为TTSD>TS、R>RSD>RS,土壤呼吸的土温敏感指标Q10值排序为TS>TSD>RS=R>T>RSD。秸秆覆盖处理的土壤呼吸对于土壤温度敏感性较高,垄作则降低了土壤温度敏感性。5 cm土层的土壤含水量高低排序为TSD>RSD>TS>RS>T>R。本研究中土壤呼吸与土壤水分呈抛物线函数关系,垄作处理下土壤呼吸与土壤水分正相关,达到显著水平;其他处理均表现负相关,其中TS达到极显著水平。在大豆农田生态系统中优势类群有弹尾目、螨目和双翅目,干漏斗法、陷阱法捕获的土壤动物与土壤呼吸均没有显著的相关关系,两种方法所得土壤动物数量加总与土壤呼吸进行相关分析,发现处理T相关系数达到显著水平,r=0.901,P=0.037。     

施氮量对玉米/大豆套作系统土壤微生物数量及土壤酶活性的影响

为揭示玉米/大豆套作体系下土壤氮素转换的调控机理和根际微生态效应,以种植模式为主因素[设玉米单作(MM)、大豆单作(SS)和玉米/大豆套作(IMS)3种处理],以玉米、大豆施氮总量(玉米、大豆施氮比例为3∶1)为副因素[设不施氮(NN,0 kg?hm~(-2))、减量施氮(RN,180 kg?hm~(-2))和常量施氮(CN,240 kg?hm~(-2))3个处理],研究了玉米/大豆套作系统下不同施氮量对作物根际土壤微生物数量及土壤酶活性的影响。结果表明:与相应单作相比,套作下玉米根际土壤真菌、放线菌数量分别提高25.37%和8.79%;套作大豆根际土壤真菌、放线菌、固氮菌数量高于单作大豆;套作玉米根际土壤蛋白酶、脲酶活性和套作大豆根际土壤蛋白酶活性均显著升高。各施氮水平间,减量施氮下玉米、大豆根际土壤真菌数量较常量施氮和不施氮均有所提高;施氮提高了玉米、大豆根际土壤放线菌数量;大豆根际土壤固氮菌数量以减量施氮最高,比不施氮和常量施氮高17.78%和5.67%;玉米根际土壤蛋白酶活性、脲酶活性和大豆根际土壤脲酶活性均以减量施氮为最高。适宜的施氮量不仅能增加玉米/大豆套作土壤中真菌、放线菌、固氮菌的数量,还能提高土壤蛋白酶、脲酶活性,调节土壤氮素的转化,促进玉米/大豆对土壤中氮素的吸收,实现节能增效。     

Integrated diurnal soil respiration model during growing season of a typical temperate steppe: Effects of temperature, soil water content and biomass production

Soil respiration was measured with the enclosed chamber method in an ungrazed Leymus chinensis steppe during the growing seasons of 2001 and 2002. Soil respiration rate (R_S) was significantly influenced by air temperature (T) at the diurnal scale, and could be described by Van't Hoff's equation (R_S = R₁₀ exp(β(T − 10))). At the seasonal scale, the normalized soil respiration rate at 10 °C (R₁₀) was mainly controlled by soil water content (R² = 0.717, P < 0.001), while the sensitivity of soil respiration to temperature (Q₁₀) was partially affected by absolute growth rate (R² = 0.482, P = 0.004). Thus, soil respiration could be described as R_S = (20.015W − 84.085) (0.103AGR + 1.786)^(T−10)/10 during the growing seasons, integrating soil water content (W) and absolute growth rate (AGR) into the temperature-dependent soil respiration equation. It was validated by the observed soil respiration rates in this study (R² = 0.890, P < 0.001) and observations from near-field experiment (R² = 0.687, P = 0.011). It implied that accurately evaluating annual soil respiration should include the effects of plant biomass production and other abiotic factors besides air temperature.     

Experimental Warming Effects on Soil Respiration,Nitrification, and Denitrification in a Winter Wheat-Soybean Rotation Cropland

A field experiment was conducted to examine responses of soil respiration, nitrification, and denitrification to warming in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation cropland. The results showed that seasonal variations in soil respiration were positively related to seasonal fluctuations in soil temperature. Seasonal mean soil respiration rates for the experimental warming (EW) and control (CK) plots were 3.98 ± 0.43 and 2.54 ± 0.45 μmol m^?2 s^?1, respectively, in the winter wheat growing season, and they were 4.59 ± 0.16 and 4.36 ± 0.08 μmol m^?2 s^?1, respectively, in the soybean growing season. There was a marginally significant level (p = 0.097) for mean nitrification rates between EW and CK plots. Soil temperature and moisture accounted for 58.2% and 58.1% of the seasonal variations observed in the winter wheat and soybean plots, respectively.     

Response of mycorrhizal, rhizosphere and soil basal respiration to temperature and photosynthesis in a barley field

The mycorrhizal, rhizosphere and basal components of soil respiration were partitioned in a barley field experiment with the main objective of determining the controlling effects of photosynthetic activity and temperature on soil respiration sources. Micro-pore meshes were used to create both root and mycorrhiza-free soil cores over which collars for soil respiration measurements were inserted. Differences between mesh treatments were used to determine the contribution of each component. With a focus on the growing season, we analyzed the response of respiration sources to photosynthesis, temperature and moisture, as well as changes in microbial biomass, mineral nitrogen and carbon-nitrogen ratios responding to treatment and time of year. Results gave clear differences between sources in their response to both temperature and photosynthetic activity and showed that several processes are involved in determining respiration rates as well as apparent temperature relations. In particular, the respiration of arbuscular mycorrhizal hyphae was seen to be a significant amount of root derived carbon respiration (25.3%) and consequently of total assimilated carbon (4.8%). This source showed a stronger response to photosynthetic activity than the rhizosphere component (r²=0.79, p<0.001 and r²=0.324, p=0.53, respectively). Q₁₀ values—the increase in respiration rates with a 10 °C increase in temperature—changed seasonally and showed temperature relations being dependent on the presence of mycorrhizal and rhizosphere respiration sources, as well as on plant development. Respiration from mycorrhizal hyphae and the rhizosphere showed no response (r²=0, p<0.99) or low response (r²=0.14, p<0.01) to temperature, respectively. We conclude that the potential importance and controls of mycorrhizal fungi respiration in croplands are comparable to those observed in other ecosystems, and that temperature response curves should be carefully interpreted given that substrate availability and plant dynamics strongly regulate respiration rates in ecosystems.     

土地利用方式对酸性红壤丛枝菌根真菌群落的影响

为了研究土地利用方式对酸性红壤丛枝菌根真菌(arbuscular mycorrhizal fungi, AMF)群落的影响,调查了酸性红壤4种土地利用方式(草地、玉米、花生和大豆)下非根际和根际土壤AMF群落多样性和组成结构。结果表明：土地利用方式显著影响了AMF群落优势属球囊霉属(Glomus)和巨孢囊霉属(Paraglomus)的相对丰度,但是根际作用影响不明显。土地利用方式而非根际作用显著影响了AMF群落香农指数和物种丰富度,其中大豆地表现出最低的香农指数和物种丰富度。土地利用方式和根际作用都显著影响AMF群落组成结构,但是土地利用方式的作用强度明显高于根际作用。球囊霉属主要解释了不同土地利用方式之间的AMF群落组成差异。土壤p H是影响土壤AMF群落结构的最关键因子。因此,土地利用方式比根际作用表现出对酸性红壤AMF群落更大的影响,展现了土地利用变化在影响土壤AMF群落方面的重要作用。