Contribution of rhizomicrobial and root respiration to the CO2 emission from soil (A review)

Separate determination of root respiration and rhizomicrobial respiration is one of the most interesting, important, and methodologically complicated problems in the study of the carbon budget in soils and the subdivision of the CO₂ emission from soils into separate fluxes. In this review, we compare the main principles, the advantages and disadvantages, and the results obtained by the methods of component integration, substrate-induced respiration, respiratory capacity, girdling, isotope dilution, model rhizodeposition, modeling of the ¹⁴CO₂ efflux dynamics, exudates elution, and the δ¹³C measurements of the microbial biomass and CO₂. Summarizing the results of the determinations performed by these methods, we argue that about 40% of the rhizosphere CO₂ efflux is due to root respiration and about 60% of this efflux is due to the respiration of microorganisms decomposing root exudates.     

Experimental assessment of the contribution of plant root respiration to the emission of carbon dioxide from the soil

The contributions of root and microbial respiration to the total emission of CO₂ from the surface of gray forest and soddy-podzolic soils were compared under laboratory and field conditions for the purpose of optimizing the field version of the substrate-induced respiration method. The magnification coefficients of respiration upon the addition of saccharose (k _mic) were first determined under conditions maximally similar to the natural conditions. For this purpose, soil cleared from roots was put into nylon nets with a mesh size of 40 μm to prevent the penetration of roots into the nets. The nets with soil were left in the field for 7–10 days for the compaction of soil and the stabilization of microbial activity under natural conditions. Then, the values of k _mic were determined in the root-free soil under field conditions or in the laboratory at the same temperature and water content. The contribution of root respiration as determined by the laboratory version of the substrate-induced respiration method (7–36%) was lower compared to two field versions of the method (27–60%). Root respiration varied in the range of 24–60% of the total CO₂ emission from the soil surface in meadow ecosystems and in the range of 7–56% in forest ecosystems depending on the method and soil type.     

中国西北棉花根系呼吸对土壤呼吸贡献率的研究

To measure the contribution of root respiration (Rr) to total soil respiration (Rt) in arid cotton fields, eighteen plots, nine for girdling and nine control, were built in an arid cotton field in the Aksu National Experimental Station of Oasis Farmland Ecosystem, Xinjiang of China. Given the difference of soil respiration between girdled plots and non-girdled control plots, the components of soil respiration, root respiration (Rr) and respiration originating from decomposition (Rd) were divided. The temperature sensitivities of R r and R d were analyzed, respectively. The results showed that the average contribution of R r to R t in arid cotton field was about 32% during the study period. The temperature-response curve of R r differed from that of Rd . The dynamic variation of R d was more related to the change of soil temperature as compared to Rr . Rr and Rd had different responses to the variation of environment, and thus new models capable of differentiating between Rr and Rd are needed for evaluating the different factors controlling these two components of soil respiration in arid cotton field.     

水稻土基底呼吸与CO2排放强度的日动态及长期不同施肥下的变化

土壤呼吸排放是陆地生态系统土气交换快速而活跃的途径之一,对大气CO2浓度的变化有显著的影响。本文对太湖地区一个代表性水稻土水稻收割后土壤基底呼吸CO2排放进行了昼夜观测和采样分析。结果表明,不同小区平均土壤呼吸与CO2排放速率在CO2-C.12.2～25.2.mg/(m2h)之间,日排放量在CO2-C.327.2～604.1mg/(m2d)之间,低于文献报道的森林和草地及旱作农田的土壤呼吸;与长期有机-无机配施处理相比,长期单施化肥CO2日排放量提高了55%～85%,并且显著提高了土壤呼吸对土壤(5.cm)温度的响应敏感性。相关分析表明,土壤呼吸CO2排放强度与土壤微生物N(Nmic)、微生物C∶N(Cmic/Nmic)和P的有效性有密切的关系;生物有效N和P的有效性显著地影响着土壤呼吸与CO2的生成和排放。本试验结果进一步支持了水稻土的固碳效应。但是,供试不同小区土壤呼吸排放强度的变异隐含着长期不同施肥处理可能使与高呼吸活性有关的微生物群落发生改变,有待于进一步研究。     

Determination of root and microbial contributions to the CO<Subscript>2</Subscript> emission from soil by the substrate-induced respiration method

The contributions of root and microbial respiration to the CO₂ emission from the surface of gray forest and soddy-podzolic soils under meadow and forest vegetation were determined in field and laboratory experiments. In the field, a new modification of the substrate-induced respiration (SIR) method was applied. According to this method, the contribution of root respiration was estimated at 41–50% for meadow cenoses and 33% for forest cenoses; similar values were obtained in the course of separate incubation of roots and soil in laboratory (42–57% and 29–32%, respectively) and with the use of the laboratory version of the SIR method (35–40% and 21–31%, respectively). The analysis of difference between the values of root respiration and microbial respiration obtained by the field and laboratory methods for the same experimental plots and the comparison of advantages and disadvantages of these methods made it possible to outline the ways for the further improvement of the field version of the SIR method.     

土壤微生物生物量和呼吸强度对大气CO2浓度升高的响应

随着全球环境变化对陆地生态系统的影响逐渐成为公众和科学界关注的热点,CO2作为一种重要的温室气体受到格外重视.大气CO2浓度升高将直接影响陆地植物的光合作用[1].植物的光合产物约有20% ～ 50%被运送到地下,通过根系分泌及死亡输入土壤[2],因此大气CO2浓度升高将会间接影响土壤生态系统.长期以来,关于大气CO2浓度升高对农作物地上部分的研究较多,但关于大气CO2浓度升高对土壤特别是土壤微生物的影响的研究报道较少.     

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.     

秸秆对根区土壤酶活性、无机氮及呼吸量的影响

采用田间小区试验和室内土壤培养相结合的方法,研究了秸秆对根区土壤酶活性、无机氮总量和呼吸量的影响。结果表明:秸秆的加入,使土壤脲酶活性和蔗糖酶活性升高,过氧化氢酶活性与秸秆加入量达显著差异,但其活性随培养时间的延长而逐渐降低;土壤多酚氧化酶活性与其它酶活性变化规律不同,大豆田土壤多酚氧化酶活性高于玉米田多酚氧化酶活性。土壤无机氮含量随培养时间的延长而增加,其中大豆田土壤加入秸秆后,处理间没有显著差异,而玉米田土壤差异显著。各处理间土壤呼吸总量与秸秆加入量均达差异显著水平,玉米田土壤高于大豆田土壤。相关性分析表明,玉米田土壤4种酶活性与无机氮和呼吸量均呈显著相关,而大豆田土壤脲酶、多酚氧化酶活性与土壤无机氮均呈极显著相关。因此,秸秆的加入可以促进土壤微生物的活动,提高了土壤酶活性、无机氮的含量及呼吸量。     

Contribution of plant photosynthate to soil respiration and dissolved organic carbon in a naturally recolonising cutover peatland

The aim of this study was to investigate how three vascular plant species (Calluna vulgaris, Eriophorum angustifolium and Eriophorum vaginatum) colonising an abandoned cutover peatland affect fluxes of recent photosynthate to dissolved organic carbon (DOC), soil and plant respiration and shoot biomass. We used in situ ¹³CO₂ pulse labelling to trace carbon (C) throughout a 65 day pulse chase period. Between 16 and 35% of the pulse of ¹³C remained in shoot biomass after 65 days with significant differences between C. vulgaris and E. angustifolium (P = 0.009) and between C. vulgaris and E. vaginatum (P = 0.04). A maximum of 29% was detected in DOC beneath labelled plants and losses of ¹³C from peat respiration never exceeded 0.16% of the original pulse, showing that little newly fixed C was allocated to this pool. There were no significant differences between the different plant species with respect to ¹³C recovered from DOC or via peat respiration. More C was lost via shoot respiration; although amounts varied between the three plant species, with 4.94–27.33% of the ¹³C pulse respired by the end of the experiment. Significant differences in ¹³C recovered from shoot respiration were found between C. vulgaris and E. angustifolium (P = 0.001) and between E. angustifolium and E. vaginatum (P = 0.032). Analysis of δ¹³C of microbial biomass indicated that recently assimilated C was allocated to this pool within 1 day of pulse labelling but there were no significant differences in the ¹³C enrichment of the microbial biomass associated with the different plant species. The data suggest that peat respiration represents a small flux of recent assimilate compared to other fluxes and pools and that different vascular plant species show considerable variation in the quantities and dynamics of C allocated to DOC.     

Effects of digestate from anaerobically digested cattle slurry and plant materials on soil microbial community and emission of CO2 and N2O

Anaerobic digestion of animal manure and crop residues may be employed to produce biogas as a climate-neutral source of energy and to recycle plant nutrients as fertilizers. However, especially organic farmers are concerned that fertilizing with the digestates may impact the soil microbiota and fertility because they contain more mineral nitrogen (N) and less organic carbon (C) than the non-digested input materials (e.g. raw animal slurry or fresh plant residues). Hence, an incubation study was performed where (1) water, (2) raw cattle slurry, (3) anaerobically digested cattle slurry/maize, (4) anaerobically digested cattle slurry/grass-clover, or (5) fresh grass-clover was applied to soil at arable realistic rates. Experimental unites were sequentially sampled destructively after 1, 3 and 9 days of incubation and the soil assayed for content of mineral N, available organic C, emission of CO₂ and N₂O, microbial phospholipid fatty acids (biomass and community composition) and catabolic response profiling (functional diversity). Fertilizing with the anaerobically digested materials increased the soil concentration of NO₃⁻ ca. 30–40% compared to when raw cattle slurry was applied. Grass-clover contributed with four times more readily degradable organic C than the other materials, causing an increased microbial biomass which depleted the soil for mineral N and probably also O₂. Consequently, grass-clover also caused a ∼10 times increase in emissions of CO₂ and N₂O greenhouse gasses compared to any of the other treatments during the 9 days. Regarding microbial community composition, grass-clover induced the largest changes in microbial diversity measures compared to the controls, where raw cattle slurry and the two anaerobically digested materials (cattle slurry/maize, cattle slurry/grass-clover) only induced minor and transient changes.     

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).     

Contributions of root respiration to total soil respiration before and after frost in Populus euphratica forests

Temporal changes in soil CO₂‐efflux rate was measured by a canopy‐gap method in a Populus euphratica forest located at the both sides of Tarim River banks (W China). Soil CO₂‐efflux rates in situ were correlated with key soil biotic (e.g., fungal, bacterial, and actinomycetes populations) and abiotic (e.g., soil moisture, temperature, pH, organic C) variables. Two kinds of measurement plots were selected: one under the crown of a living Populus euphratica tree and the other under a dead standing Populus euphratica tree. Diurnal variations in soil respiration in these plots were measured both before and after the occurrence of the first frost. Soil respiration of the dead standing Populus euphratica (Rd) was assumed to be a measure of heterotrophic respiration rate (Rh), and root respiration rate (Rr) was estimated as the difference between soil respiration under living (Rl) minus soil respiration under dead standing Populus euphratica. Daily variation of Rr contribution to the total soil respiration in Populus euphratica forests were analyzed before and after the frost. The contribution of root respiration to total soil respiration before and after frost varied from 22% to 45% (mean 30%) and from 38% to 50% (mean 45%), respectively. In addition, Rh was significantly correlated with soil temperature both before and after frost. In contrast, Rr was not significantly correlated with soil temperature. Change in Q₁₀ of Rr was different from that of Rh from before the frost to after the frost. Variation of Q₁₀ of Rr from before the frost to after the frost was larger than that of Q₁₀ of Rh. Thus, the results indicate that different soil respiration models are needed for Rr and Rh because different factors control the two components of soil respiration.     

Separation of soil respiration into CO2 emission sources using 13C natural abundance in a deciduous broad-leaved forest in Japan

Abstract

In determining the soil and ecosystem carbon balance, it is necessary to distinguish between autotrophic respiration and heterotrophic respiration. We attempted to measure the contribution of CO₂ emissions from plant roots (R_RHI), from soil organic matter (R_SOM), and from litter (R_L) to CO₂ emissions from the forest floor (soil respiration; R_S) in a deciduous forest of oak (Quercus serrata Thunb.) and hornbeams (Carpinus laxiflora Sieb. et Zucc. Bl., Carpinus tschonoskii Maxim. and Carpinus japonica Bl.) on Andosols in Japan, using a ¹³C natural abundance technique. The ¹³C natural abundances of roots (δ_RHI), litter (δ_L) and SOM (δ_SOM) in the surface soil were ?28.9, ?30.1 and ?24.3‰, respectively. This means that the differences between δ_SOM and δ_RHI are large enough to calculate the contributions of R_RHI, R_SOM and R_L to R_S based on the mass balance of the CO₂ isotope ratios. R_RHI and R_SOM had close relationships with soil temperature, and R_L was influenced by soil temperature and moisture. In summer, under high soil temperatures, R_RHI and R_SOM were the predominant sources of R_S and the proportion of R_RHI to R_SOM to R_L was 51:44:5. In winter, R_L was predominant and the proportion of R_RHI to R_SOM to R_L was 20:11:69. The estimated annual emissions of R_RHI, R_SOM and R_L were 1.45, 2.10 and 1.30 Mg C ha^?1, respectively; thus, the proportion of R_RHI to R_SOM to R_L was 30:43:27 on a whole-year basis.     

农田土壤呼吸特征及根呼吸贡献的模拟分析

采用静态箱法研究了黄淮海平原典型农田土壤CO2排放通量的日变化、季节变化特征,分析了土壤温度、水分对土壤呼吸的影响;并利用反硝化一分解(DNDC)模型定量化研究了根呼吸对土壤总呼吸的贡献.结果表明,在作物生长季节内棉花地、休闲地和冬小麦/夏玉米地土壤CO2排放均表现出明显的季节变化规律.土壤CO2排放季节变化的总体趋势是夏季高、其他季节低,与对应气温的动态变化基本一致.冬小麦/夏玉米地土壤CO2排放通量高峰值为2324 mg·m-2·h-1,棉花地为1111.9 mg·m-2·h-,休闲地为436.07 mg·m-2·h-1.土壤CO2季节性排放受温度的影响最大,其中与5 cm地温的相关性最好,与土壤湿度的相关性不太明显.同一种种植模式施氮量高的处理CO2平均排放通量大于低的处理.同时根据DNDC模型估算,玉米根际呼吸对土壤呼吸的贡献最大,为91%～95%,棉花和冬小麦根际呼吸比例分别约为70%和80%.施氮不仅影响土壤微生物的呼吸而且还影响到根系呼吸.     

Soil CO2 emission and its relationship to soil properties under different tillage systems

There is a lack of understanding as to which soil property is the most important at regulating the temporal variability of soil CO₂ emissions on China’s Loess Plateau. The objective of this study was to evaluate the CO₂ emissions and their relationships to certain soil properties in a winter wheat (Triticum aestivum L.) field subject to no-till (NT) and conventional tillage (CT) practices. The CO₂ emissions were signi?cantly higher in the CT (257.6 mg CO₂ m^?2 h^?1), compared with the NT (143.8 mg CO₂ m^?2 h^?1), treatment. Soil organic matter content and carbon stock were 8% and 14% higher, respectively, in the NT, compared with the CT, treatment. Regression analyses between the CO₂ emissions and soil properties, including soil temperature and carbon stock, explained up to 88% and 60% of the temporal variability in CO₂ emissions in the NT and CT treatments, respectively. Linear correlations between the soil temperature and CO₂ emissions were recorded in both the NT and CT treatments. Soil temperature was the most important factor in terms of understanding the temporal variability in CO₂ emissions in wheat fields of the study area.     

Oxygen and substrate availability interactively control the temperature sensitivity of CO2 and N2O emission from soil

Biology and Fertility of Soils - We investigated how oxygen availability, substrate amount, and quality affect the temperature dependency of enzymatic processes involved in the production of carbon...     

Short-term CO2 emissions from planted soil subject to elevated CO2 and simulated precipitation

Carbon dioxide emissions from soils beneath canopies of two Mediterranean plants, Artemisia absinthium L. and Festuca pratensis Huds. cv. Demeter, were monitored over a 7-day period that included an artificial precipitation event of 4 cm. The experiments were conducted using 0.2 m³ soil microcosms inside greenhouses with CO₂ concentrations of either 360 or 500 μmol mol⁻¹. Carbon dioxide flux from the soil surface, as calculated using a diffusive transport model agreed well with CO₂ flux measurements made using a dynamic flow system. Soil CO₂ emissions did not differ significantly between the 360 and 500 μmol mol⁻¹ CO₂ treatments when soils were dry (volumetric soil moisture content ≤9%). A simulated precipitation event caused an immediate exhalation of CO₂ from soil, after which CO₂ emissions declined slightly and remained constant for approximately 36 h. CO₂ emissions from soil microcosms with F. pratensis plants growing in 500 μmol mol⁻¹ CO₂ then rose to levels that were significantly greater than CO₂ emissions from soils in the microcosms exposed to 360 μmol mol⁻¹ CO₂. For A. absinthium growing in 500 μmol mol⁻¹ CO₂, the rise in soil CO₂ emissions following the wetting event was not significantly greater than emissions from soils with A. absinthium growing under 360 μmol mol⁻¹ CO₂. A. absinthium above ground biomass increased by 46.1 ± 17.9% (mean ± S.E., n = 4, P ≤ 0.05). Above ground biomass did not significantly increase for F. pratensis (14.4 ± 6.5%, P ≥ 0.10). Root biomass, on the other hand, increased for both species; by 50.6 ± 17.9% (P ≤ 0.05) for A. absinthium and by 55.9 ± 12.7% (P ≤ 0.05) for F. pratensis. Our results demonstrate two events following precipitation onto dry soils, an immediate release of CO₂ followed by a gradual increase from enhanced biological activity The gradual increase was greater for the herbaceous ruderal perennial F. pratensis under elevated CO₂.     

东北黑土区旱作农田土壤CO2排放规律

为研究农田土壤CO2排放规律,调控农田碳平衡,通过对东北黑土区旱作农田土壤CO2排放的定位连续观测,研究了玉米、大豆农田土壤CO2排放的季节变化规律;并估算了农田碳平衡。结果表明:1)农田土壤CO2排放通量随季节呈单峰曲线变化,7月份出现最大值;秸秆覆盖还田明显增加了农田土壤CO2排放;玉米或大豆生长发育对土壤CO2排放影响较小。2)地温的季节变化与土壤CO2排放通量季节变化规律一致,用指数方程和二次方程均可很好地模拟土壤CO2排放通量与地温之间的关系,但指数方程优于二次方程,以20cm土层地温的相关性最高,5cm土层地温的相关性最低。3)玉米、大豆农田在通常情况下为大气CO2的"汇",玉米-玉米-大豆轮作周期(3a)的碳汇年平均为4.53t/hm2,该碳汇可为固碳减排提供参考。     

The interdependent effects of soil temperature and water content on soil respiration rate and plant root decomposition in arid grassland soils

Soil respiration (CO₂ evolution), soil temperature (1 dm) and water content (0–1dm) were determined over a 2 yr period in a grassland soil of the arid shrub-steppe. Respiration was due primarily to decomposition of plant roots by soil organisms. Although respiration rate was generally limited by soil temperature in the fall, winter and early spring and by soil water content in the late spring and summer, temperature and water content were interdependent in their effects on soil respiration rate. Soil organisms responded to changes in soil temperatures at water contents as low as 1–2 per cent (106-88 bar suction). Above approximately 6° C, increased soil water content resulted in increased soil respiration rate. but the extent of the increase was non-linear and dependent upon soil temperature. Respiration rate approached a maximum at soil water contents of 6–10 per cent (35-13 bar suction) depending upon soil temperature and was generally optimum at temperatures above 15° C. The mutual regulation of soil respiration rate by temperature and moisture during this study was best described by a soil temperature-water interaction or multiplicative term, and regression equations which included this term served to accurately predict seasonal changes in soil respiration rate. Using a simple regression equation which included only the interaction term, it was possible to account for 70 per cent of the total variation in soil respiration rate during the monitoring period.