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1.
Controls on soil respiration in semiarid soils   总被引：2，自引：0，他引：2  
Soil respiration in semiarid ecosystems responds positively to temperature, but temperature is just one of many factors controlling soil respiration. Soil moisture can have an overriding influence, particularly during the dry/warm portions of the year. The purpose of this project was to evaluate the influence of soil moisture on the relationship between temperature and soil respiration. Soil samples collected from a range of sites arrayed across a climatic gradient were incubated under varying temperature and moisture conditions. Additionally, we evaluated the impact of substrate quality on short-term soil respiration responses by carrying out substrate-induced respiration assessments for each soil at nine different temperatures. Within all soil moisture regimes, respiration rates always increased with increase in temperature. For a given temperature, soil respiration increased by half (on average) across moisture regimes; Q10 values declined with soil moisture from 3.2 (at −0.03 MPa) to 2.1 (−1.5 MPa). In summary, soil respiration was generally directly related to temperature, but responses were ameliorated with decrease in soil moisture.  相似文献   

2.
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.  相似文献   

3.
Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during most of the growing season and peak aboveground biomass production (253.9 g m−2) in 2002 was 60% higher than in 2001. Maximum respiration rates were approximately 9 μmol m−2 s−1 in 2002 while only approximately 5 μmol m−2 s−1 in 2001. Large diurnal variation in TER, which occurred during times of peak biomass and adequate soil moisture, was primarily controlled by changes in temperature. The temperature sensitivity coefficient (Q10) for ecosystem respiration was on average 1.83 ± 0.08, and it declined in association with reductions in soil moisture. Approximately 94% of the seasonal and interannual variation in R10 (standardized rate of respiration at 10 °C) data was explained by the interaction of changes in soil moisture and aboveground biomass, which suggested that plant aboveground biomass was good proxy for accounting for variations in both autotrophic and heterotrophic capacity for respiration. Soil moisture was the dominant environmental factor that controlled seasonal and interannual variation in TER in this grassland, when variation in temperature was held constant. We compared respiration rates measured with chambers and that determined from nighttime eddy covariance (EC) measurements. Respiration rates measured by both techniques showed very similar seasonal patterns of variation in both years. When TER was integrated over the entire growing season period, the chamber method produced slightly higher values than the EC method by approximately 4.5% and 13.6% during 2001 and 2002, respectively, much less than the estimated uncertainty for both measurement techniques. The two methods for calculating respiration had only minor effects on the seasonal-integrated estimates of net ecosystem CO2 exchange and ecosystem gross photosynthesis.  相似文献   

4.
《Applied soil ecology》2006,33(3):284-292
We examined the response of the temperature coefficient (Q10) for soil respiration to changes in soil temperature and soil moisture through a laboratory incubation experiment. Two types of soils differing in vegetation and moisture status were collected and incubated under two temperatures (10 and 30 °C) and two soil moisture regimes (35 and 75% of water holding capacity, WHC) for 5 weeks. Before and after the incubation experiment, the temperature coefficient of soil respiration was measured using soda-lime method by changing temperature in a water bath. For both soils, the mean Q10 values of the respiration rate were 2.0 in the 30 °C and 2.3 in the 10 °C soil treatments. Higher temperature with lower soil moisture treatment significantly decreased the Q10 value, whereas lower temperature with higher soil moisture treatment significantly enhanced the Q10 value (ANOVA, p < 0.05). These results indicate that soils became less sensitive to temperature when incubated under higher temperature with higher moisture conditions, and more sensitive in lower temperature with higher moisture conditions.There was a significant correlation (r2 = 0.67, p < 0.05) between water-soluble carbon (WSC) and soil respiration rate. However, the correlation between soil respiration rate and microbial biomass carbon (MBC) was weak (r2 = 0.27, p > 0.05). Although incubation temperature and moisture accounted for 40 and 29% (as r2 × 100%), respectively, of variations in Q10, soil water-soluble carbon content alone could have explained 79% of the variation, indicating that the availability of respiratory substrate, rather than the pool of soil microorganisms, played a crucial role in the response of the temperature coefficient to environmental factors. These results suggest that biotic factors should also be taken into consideration when using the Q10 function to predict the response of soil respiration to global warming.  相似文献   

5.
Through their effects on microbial metabolism, temperature and moisture affect the rate of decomposition of soil organic matter. Plant roots play an important role in SOM mineralization and nutrient cycling. There are reports that rhizosphere soil exhibits higher sensitivity to temperature than root-free soil, and this can have implications for how soil CO2 efflux may be affected in a warmer world. We tested the effects of 1-week incubation under different combinations of temperature (5, 15, 30 °C) and moisture (15, 50, 100% WHC) on the respiration rate of soil planted with Scots pine and of unplanted soil. Soil respiration in both soils was the highest at moderate moisture (p < 0.0001) and, increased with temperature (p < 0.0001). There was also marginally significant effect of soil kind on respiration rate (p < 0.055), but the significant interaction of temperature effect with soil kind effect, indicated, that soil respiration of planted soil was higher than unplanted soil only at 5 °C (p < 0.05). The soil kind effect was compared also as Q10 coefficients for respiration rate, showing the relative change in microbial activity with increased temperature. However, there was no difference in the thermal sensitivity of soil respiration between planted and unplanted soils (p = 0.99), irrespective of the level of soil moisture. These findings were similar to the latest studies and confirmed, that in various models, being useful tools in studying of soil carbon cycling, there is no need to distinguish between planted and unplanted soil as different soil carbon pools.  相似文献   

6.
Forest ecosystems on the Loess Plateau are receiving increasing attention for their special importance in carbon fixation and conservation of soil and water in the region. Soil respiration was investigated in two typical forest stands of the forest-grassland transition zone in the region, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest, in response to rain events (27.7 mm in May 2009 and 19 mm in May 2010) during the early summer dry season. In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4 μmol CO2 m−2 s−1 in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, being consistent with the differences in C, N contents and fine root mass on the forest floor and in soil between the two stands. However, root respiration (Rr) per unit fine root mass and microbial respiration (Rm) per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Respiration by root rhizosphere in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.  相似文献   

7.
Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (Rs), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of Rs. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO2 efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO2 efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m−2 s−1 in the forest, abandoned field and olive grove, respectively. Rs was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds Rs was controlled by soil moisture. Exponential and linear models adequately described Rs responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of Rs in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO2 efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO2 efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.  相似文献   

8.
Abstract

Tree clearing is a topical issue the world over. In Queensland, the high rates of clearing in the past were mainly to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties, i.e. total soil respiration, root respiration, microbial respiration, and microbial biomass (C and N), and the response of soil respiration to change in temperature.

In-field and laboratory (polyhouse) experiments were undertaken. For in-field studies, paired cleared and uncleared pasture plots were selected to represent three major tree communities of the region, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11–13, and 33 years; n=18 for cleared and uncleared plots) to determine the temporal impact of clearing on soil biological properties. Experiments were conducted in the polyhouse to study in detail the response of soil respiration to changes in soil temperature and soil moisture, and to complement in-field studies for estimating root respiration.

The average rate of CO2 emission was 964 g CO2/m2/yr, with no significant difference (P<0.05) among cleared and uncleared sites. Microbial respiration and microbial biomass were greater at uncleared compared with those at cleared sites. The Q 10-value of 1.42 (measured for different seasons in a year) for in-field measurements suggested a small response of soil respiration to soil temperature, possibly due to the limited availability of soil moisture and/or organic matter. However, results from the polyhouse experiment suggested greater sensitivity of root respiration to temperature change than for total soil respiration. Since root biomass (herbaceous roots) was greater at the cleared than at uncleared sites, and root respiration increased with an increase in temperature, we speculate that with rising ambient temperature and consequently soil temperature, total soil respiration in cleared pastures will increase at a faster rate than that in uncleared pastures.  相似文献   

9.
Soil respiration of a desert soil was measured at the New Mexico State University Ranch in Southern New Mexico. Respiration rates were highest during late July and August after summer rains. Soil respiration data were used to estimate soil organic matter turnover which was 54 yr using summer data and 20 yr using both summer and winter data. The long turnover estimate for summer measurements resulted from temperatures above optimum in June and July. Diurnal soil respiration was also measured after a simulated 2.54 cm rain event. For both wetted and dry soils, temperature controlled the patterns of soil respiration with an optimum of near 41°C. Activation energy values decreased from 84.91 to 39.5 kJ mol?1 when the soil was wetted. A light-dark container method was tested as a possible means of estimating algal uptake of CO2, however, the method was not feasible for desert soils.  相似文献   

10.
Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha−1, while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha−1, was approximately twice that of the LG site. Soil respiration measurements showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q10 value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m−2 y−1 to the atmosphere, which was about one third more than the 1530 g CO2 m−2 y−1 released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem.  相似文献   

11.
不同覆盖条件下旱作农田土壤呼吸及其影响因素   总被引：7，自引：3，他引：4  
利用田间试验研究了不同覆盖条件下旱作农田冬小麦土壤呼吸及其水热状况。设4个处理,即无覆盖处理（CK）、 小麦全年 4500 kg/hm2秸秆覆盖（M4500）、 9000 kg/hm2秸秆覆盖（M9000）和地膜覆盖（PM）。结果表明, 土壤呼吸在作物生育期呈单峰曲线变化,PM 处理峰值出现在拔节期,其余处理推迟至抽穗期; CK、 M4500、 M9000、 PM处理呼吸速率均值分别为CO2 1.54、 1.44、 1.45、 1.75 mol /(m2s),其中PM与CK处理差异显著（P0.05）; 生育期内土壤呼吸温度敏感性（Q10值）在1.86~2.39之间; 土壤温度低于5℃时,Q10值较高,而当土温高于5℃时,土壤呼吸的温度控制作用较弱; 土壤水分对土壤呼吸的限制作用不大。多元线性回归分析表明,05cm土层温度和水分形成的双因子模型可以更好地解释土壤呼吸速率变异,各处理的决定系数分别为CK 0.827、 M4500 0.816、 M9000 0.896、 PM 0.729（P0.01）。  相似文献   

12.
Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO2 budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO2 m–2 h–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO2 m–2 day–1, while values below 300 mg CO2 m–2 day–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO2 g–1 dry weight h–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q10 values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q10 values. Within the temperature interval between 20°C and 30°C, Q10 values were around 2 while the Q10 values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account.  相似文献   

13.
[目的] 揭示中国极端干旱区甘肃省石羊河流域储水灌溉与季节性冻融叠加作用下对土壤呼吸的影响,为进一步提高极端干旱区灌溉水资源利用效率和节约灌溉水源提供理论基础和技术支撑。[方法] 按照1 199.4 m3/hm2低灌溉定额分为灌水和非灌水处理,将冻融循环分为冻结期、冻融期和解冻期3个时间段,采用LI-8100土壤碳通量全自动测量系统对各处理地块的土壤呼吸速率进行观测与分析。[结果] 极端干旱区储水灌溉在季节性冻融作用下农田生态系统土壤呼吸速率增强,土壤碳排放量增加,农田生态系统碳循环被改变,有利于作物的生长和提高粮食产量。不同土地利用方式下土壤呼吸速率对水分和温度的响应程度不同。整个冻融过程中土壤呼吸速率呈现出：解冻期>冻结期>冻融期的规律。冻结期、冻融期和解冻期3个时期的土壤CO2都表现为源,但在夜间极低温度时土壤CO2由源转化为汇。[结论] 储水灌溉调控了整个冻融期土壤呼吸的过程,改变了极端干旱区农田生态系统的碳循环。在水分与季节性冻融叠加作用下,储水灌溉地块土壤呼吸速率相对未储水地块随温度的波动更为剧烈,但与温度的变化趋势一致,水分加剧了其随温度的波动。  相似文献   

14.
Climate change scenarios predict increases in temperature, changes in precipitation patterns, and longer drought periods in most semi-arid regions of the world. Ecosystems in these regions are prone to land degradation, which may be aggravated by climate change. Soil respiration is one of the main processes responsible for organic carbon losses from arid and semi-arid ecosystems. We measured soil respiration over one year in two steppe ecosystems having different degrees of land degradation under three ground-covers: with vegetation, bare soil, and an intermediate situation between plants and bare soil.The largest differences in soil respiration rates between the sites were observed in spring, coinciding with the highest level of plant activity. The degraded site had drier and hotter soils with less soil water availability and a longer drought period. As a result, vegetation on the degraded site did not respond to spring rainfall events. Soil respiration showed a strong seasonal variability, with average annual rates of 1.1 and 0.8 μmol CO2 m−2 s−1 in the natural and degraded sites, respectively. We did not observe significant differences in soil respiration rates associated with ground-cover i.e., the temporal variation was much larger than the spatial variation. At both sites, soil moisture was the controlling driver of soil respiration for most of the year, when temperatures were above 20 °C and constrained the response to temperature for the few months when the temperature was below 20 °C. An empirical model based on soil temperature and soil moisture explained 90% and 72% of the seasonal variability of soil respiration on the natural and degraded sites, respectively. For the first time, this study suggests that land degradation may alter the carbon balance of these ecosystems through changes in the temporal dynamics of soil respiration and plant productivity, which have important negative consequences for ecosystem functioning and sustainability.  相似文献   

15.
Soil respiration (Rs) is the second-largest source of CO2 to the atmosphere in terrestrial systems. In tropical savannas seasonal moisture availability and frequent fires drive ecosystem dynamics and may have a considerable impact on soil carbon (C) cycling, including Rs. In order to test the effect of fire on soil C cycling we measured Rs in annually burnt and unburnt plots in wet and dry seasons at a long-term fire experiment established in savanna woodlands of northern Australia. There was a significant interaction between season and fire, with highest rates of daily Rs (722 mmol CO2 m−2 d−1) observed in the wet season on unburnt, leaf litter patches. The three fold higher Rs rate on unburnt plots in the wet season was due to greater root-derived respiration (Rroot: 356 mmol CO2 m−2 d−1), while smaller changes to soil-derived respiration (Rsoil: 51 mmol CO2 m−2 d−1) were simply the result of C moving through decomposition rather than combustion pathways. Relationships between instantaneous Rs and soil temperature showed hysteresis with variable direction, suggesting that season and fire treatment also influence the soil depth at which CO2 is produced. We suggest that (1) changes to fire regimes, through active management or climate change, in tropical savannas could have an impact on Rs, and (2) the direct effect of fire on soil C cycling is limited to the removal of aboveground litter inputs.  相似文献   

16.
[目的]探讨不同水土保持措施对红壤坡地柑橘林土壤呼吸的影响,为科学评价水土保持生态建设在应对气候变化方面的作用提供基础数据。[方法]采用试验观测和对比分析的方法研究横坡间作+等高草带、横坡间作、顺坡间作和清耕对照4种处理对柑橘林土壤呼吸速率的动态变化及其对土壤温度、土壤水分的响应。[结果]4个不同处理的柑橘林土壤呼吸速率均呈明显的单峰曲线变化,峰值出现在7月;各处理的土壤呼吸速率季节动态变化一致,采取横坡间作+等高草带和横坡间作两种水保措施均一定程度上增加了土壤呼吸速率;土壤呼吸速率与土壤温度呈显著正相关;横坡间作+等高草带和横坡间作处理的土壤呼吸的温度敏感性指数Q10较柑橘清耕和顺坡间作处理Q10值略有增加。[结论]红壤柑橘林采取水土保持措施后,土壤呼吸速率增强,且其对温度的响应增加。  相似文献   

17.
Spatial and temporal patterns of soil respiration rates and controlling factors were investigated in three wet arctic tundra systems. In situ summer season carbon dioxide fluxes were measured across a range of micro-topographic positions in tussock tundra, wet sedge tundra, and low-centre polygonal tundra, at two different latitudes on the Taimyr Peninsular, central Siberia. Measurements were carried out by means of a multi-channel gas exchange system operating in continuous-flow mode.Measured soil respiration rates ranged from 0.1 g CO2-C m?2 d?1 to 3.9 g CO2-C m?2 d?1 and rate differences between neighbouring sites in the micro-topography (microsites) were larger than those observed between different tundra systems. Statistical analysis identified position of the water table and soil temperature at shallow depths to be common controls of soil respiration rates across all microsites, with each of these two factors explaining high proportions of the observed variations.Modelling of the response of soil respiration to soil temperature and water table for individual microsites revealed systematic differences in the response to the controlling factors between wet and drier microsites. Wet microsites – with a water table position close to the soil surface during most of the summer – showed large soil respiration rate changes with fluctuations of the water table compared to drier microsites. Wet microsites also showed consistently higher temperature sensitivity and a steeper increase of temperature sensitivity with decreasing temperatures than drier sites. Overall, Q10 values ranged from 1.2 to 3.4. The concept of substrate availability for determining temperature sensitivity is applied to reconcile these systematic differences. The results highlight that soil respiration rates in wet tundra are foremost controlled by water table and only secondarily by soil temperature. Wet sites have a larger potential for changes in soil respiration rates under changing environmental conditions, compared to drier sites.It is concluded that understanding and forecasting gaseous carbon losses from arctic tundra soils and its implication for ecosystem-scale CO2 fluxes and soil organic matter dynamics require good knowledge about temporal and spatial patterns of soil water conditions. The water status of tundra soils can serve as a control on the temperature sensitivity of soil respiration.  相似文献   

18.
Knowledge of seasonal trends and controls of soil CO2 emissions to the atmosphere is important for simulating atmospheric CO2 concentrations and for understanding and predicting the global carbon cycle. This is particularly the case for high arctic soils subject to extreme fluctuating environmental conditions. Based on field measurements of soil CO2 efflux, temperature, water content, pore gas composition in soil and frozen cores as well as detailed temperature experiments performed in the laboratory, we evaluated seasonal controls of CO2 effluxes from a well-drained tundra heath site in NE-Greenland. During the growing season, near-surface temperatures correlated well with observed CO2 effluxes (r2>0.9). However, during intensive thawing of near-surface layers we observed up to 1.5-fold higher effluxes than expected due to temperature alone. These high rates were consistent with high CO2 concentrations in frozen soil (>10% CO2) and suggested a spring burst event during soil thawing and a corresponding trapping of produced CO2 during winter. Laboratory experiments revealed that microbial soil respiration continued down to a least −18 °C and that up to 80% of the produced CO2 was trapped in soil at temperatures between 0 and −9 °C. The trapping of CO2 in frozen soil was positively correlated with soil moisture (r2=0.85) and led to an abrupt change of the temperature sensitivity (Q10) observed for soil CO2 release at 0 °C with Q10 values below 0 °C being up to 100-fold higher than above 0 °C. The results of sub-zero CO2 production allowed us to predict the microbial soil respiration throughout the year and to evaluate to what extent burst events during thawing can be explained by the release of CO2 being produced and trapped during winter. Taking only the upper 20 cm of the soil into account, winter soil respiration accounted for about 40% of the annual soil respiration. At least 14% of the winter CO2 production was trapped during the winter 2000-2001 and observed to be released upon thawing. Thus, the site-specific winter soil respiration is an important part of the annual C cycle and CO2 trapping should be accounted for in future field and modelling studies of soil respiration dynamics in arctic ecosystems. In conclusion, we have discovered a soil moisture dependent uncoupling of CO2 production and release in frozen soils with important implications for future field studies of Arctic C cycling.  相似文献   

19.
 Soils are a major source of atmospheric NO and N2O. Since the soil properties that regulate the production and consumption of NO and N2O are still largely unknown, we studied N trace gas turnover by nitrification and denitrification in 20 soils as a function of various soil variables. Since fertilizer treatment, temperature and moisture are already known to affect N trace gas turnover, we avoided the masking effect of these soil variables by conducting the experiments in non-fertilized soils at constant temperature and moisture. In all soils nitrification was the dominant process of NO production, and in 50% of the soils nitrification was also the dominant process of N2O production. Factor analysis extracted three factors which together explained 71% of the variance and identified three different soil groups. Group I contained acidic soils, which showed only low rates of microbial respiration and low contents of total and inorganic nitrogen. Group II mainly contained acidic forest soils, which showed relatively high respiration rates and high contents of total N and NH4 +. Group III mainly contained neutral agricultural soils with high potential rates of nitrification. The soils of group I produced the lowest amounts of NO and N2O. The results of linear multiple regression conducted separately for each soil group explained between 44–100% of the variance. The soil variables that regulated consumption of NO, total production of NO and N2O, and production of NO and N2O by either nitrification or denitrification differed among the different soil groups. The soil pH, the contents of NH4 +, NO2 – and NO3 –, the texture, and the rates of microbial respiration and nitrification were among the important variables. Received: 28 October 1999  相似文献   

20.
Getting a better understanding of CO2 efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS = black spruce; TA = trembling aspen) or in mixtures (MW = BS + TA mixedwood), on total (RS), heterotrophic (RH) and autotrophic soil respiration (RA) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand-specific soil respiration–temperature models were developed to estimate annual soil CO2 efflux. Soil temperature was the main factor explaining RS and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual RS and RH were significantly greater in MW and TA than in BS, whereas annual RA was greater in BS and MW than in TA. Temperature sensitivity (Q10) of both RS and RH was significantly higher in BS than in MW and TA, suggesting that CO2 efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO2 efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO2 efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC.  相似文献   

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