Mineral Soil Respiration Research Articles

Simultaneous Measurements of Dissolved Organic Carbon and Soil Respiration Reveal Reduced Soil Carbon Loss Under Nitrogen Addition in a Montane Forest

AbstractA major uncertainty in the estimation of soils acting as net carbon (C) sinks or sources stem from the effects of anthropogenic nitrogen (N) input on the balance between plant C input and soil C loss. In contrast to the generally observed increasing pattern of plant C input, the response of soil C loss to increased N deposition remains elusive, largely due to its large temporal variation. Here simultaneous measurements of two major soil C loss pathways, including dissolved organic carbon (DOC) leaching and soil respiration, were conducted for 5 and 3 yr, respectively, to assess the effects of N addition on soil C loss in an N‐limited montane forest. The effects were seasonal, depth and N level dependent and the two pathways responded asynchronously to N addition. Significant decreases in DOC concentrations and fluxes in leachates from the organic layer were observed during autumn/winter under a high N addition rate (40 kg N/ha/yr). No significant impact of N addition on DOC concentrations or fluxes was observed for leachates from the mineral soil horizon. Biodegradability was low for DOC from both soil layers and was not consistently influenced by N addition. Soil respiration was significantly decreased under high N addition. Annual soil C loss (estimated by summing DOC leaching from the mineral horizon and soil respiration) showed that N addition reduced soil C loss consistently over years, implying that the forest soil is likely a C sink under excess N deposition, which should be confirmed with longer term monitoring.

Potential Effects of Biochar Application for Improving Wheat (Triticum aestivum L.) Growth and Soil Biochemical Properties under Drought Stress Conditions

Different soil amendments are applied to improve soil properties and to achieve higher crop yield under drought conditions. The objective of the study was to investigate the role of biochar for the improvement of wheat (Triticum aestivum L.) growth and soil biochemical properties under drought conditions. A pot experiment with a completely randomized design was arranged with four replications in a wire house. Drought was imposed on two critical growth stages (tillering and grain filling) and biochar was applied to the soil 10 days before sowing at two different rates (28 g kg−1 and 38 g kg−1). Soil samples were collected to determine the soil properties including soil respiration and enzymatic parameters after crop harvesting. Results showed that water stress negatively affects all biochemical properties of the soil, while biochar amendments positively improved these properties. Application of biochar at 38 g kg−1 provided significantly higher mineral nutrients, Bray P (18.72%), exchangeable-K (7.44%), soil carbon (11.86%), nitrogen mineralization (16.35%), and soil respiration (6.37%) as a result of increased microbial activities in comparison with the 28 g kg−1 rate.

Contribution of above ground litterfall and roots to the soil CO2 efflux of two sub-tropical Cunninghamia lanceolata and Castanopsis carlesii forests

Soil respiration (RS) is the largest terrestrial carbon (C) flux to the atmosphere, and it can be influenced by changing input of plant C from above- and/or below ground. Especially in tropical and sub-tropical ecosystems, the contributions of litter respiration (RL), autotrophic respiration (RA) and mineral soil respiration (RM) are still poorly understood. In the present study, RS was measured under untreated control (CT), root exclusion (NR), litterfall exclusion (NL), and combined litterfall and root exclusion (NRNL) in a subtropical Cunninghamia lanceolata plantation and a secondary Castanopsis carlesii forest for three years. In addition, litter input, litter and soil chemistry, and microbial biomass and community structure (PLFAs) were assessed. RS was significantly higher in the C. carlesii forest than in the coniferous C. lanceolata forest. RL and RA were significantly higher in the C. carlesii forest than in the C. lanceolata forest, while there was no significant difference in RM. RM, RA, and RL contributed 55%, 29%, and 16% to RS under C. lanceolata, and 39%, 32%, and 29% under C. carlesii, respectively. Above ground litter input and microbial biomass were lower in the coniferous C. lanceolata forest. Soil microbial biomass was significantly lower in NL, NR and NRNL in both forests. NL had most pronounced effects on the microbial community composition in the C. carlesii soil, whereas NR and NRNL affected the community composition in C. lanceolata soil. Overall, the unexpectedly small and only insignificant additive effects of litter exclusion and root exclusion in the combined treatment (NRNL) suggest that yet unresolved interactions had accelerated the decomposition of mineral soil organic matter and RM under this lowest plant C-input scenario. Hence, in the case that above and below ground plant C inputs change simultaneously, effects on RS and its components might be more complex than suggested by single-C-source manipulation studies.

Short Term Effects of a Changing Carbon Input on the Soil Respiration of Picea schrenkiana Forests in the Tianshan Mountains, Xinjiang

The impact of exogenous carbon input changes on forest soil respiration provides the basis for an intensive analysis of the forest carbon cycle. Based on a plant residue addition and removal control experiment, this study investigated the short-term soil respiration response to carbon input changes of Picea schrenkiana on the Tianshan Mountains during their growing season with five different carbon input treatments:control, double litter, no root, no litter, and no input. The results revealed that, during the entire observation period, the cumulative soil respiration rates were 3.38, 3.94, 2.65, 2.87, and 2.01 μmol·(m2·s)-1 in the double litter, control, no litter, no root, and no input treatments, respectively. Compared with the control treatment, the cumulative soil CO2 efflux increased by 402.65 g·m-2 in the double litter treatment, whereas it decreased by 515.00, 354.73, and 967.15 g·m-2 in the no litter, no root, and no input treatments, respectively. The mineral soil respiration, litterfall respiration, and root respiration contributed 59.46%, 21.49%, and 14.79%, respectively, to the total soil respiration rate. PCA analysis revealed that the soil respiration rate was positively correlated with the soil temperature, soil moisture, soil total phosphorus content, pH, and soil organic carbon content, and negatively correlated with the soil bulk density, while the soil total nitrogen content, carbon nitrogen ratio, and soil electrical conductivity had no effect on the soil respiration rate.

Forest Floor and Mineral Soil Respiration Rates in a Northern Minnesota Red Pine Chronosequence

We measured total soil CO2 efflux (RS) and efflux from the forest floor layers (RFF) in red pine (Pinus resinosa Ait.) stands of different ages to examine relationships between stand age and belowground C cycling. Soil temperature and RS were often lower in a 31-year-old stand (Y31) than in 9-year-old (Y9), 61-year-old (Y61), or 123-year-old (Y123) stands. This pattern was most apparent during warm summer months, but there were no consistent differences in RFF among different-aged stands. RFF represented an average of 4–13% of total soil respiration, and forest floor removal increased moisture content in the mineral soil. We found no evidence of an age effect on the temperature sensitivity of RS, but respiration rates in Y61 and Y123 were less sensitive to low soil moisture than RS in Y9 and Y31. Our results suggest that soil respiration’s sensitivity to soil moisture may change more over the course of stand development than its sensitivity to soil temperature in red pine, and that management activities that alter landscape-scale age distributions in red pine forests could have significant impacts on rates of soil CO2 efflux from this forest type.

Depth heterogeneity of soil organic carbon dynamics in a heavily grazed alpine meadow on the northeastern Tibetan Plateau: A radiocarbon-based approach

A deep understanding of soil organic carbon (SOC) dynamics on the Tibetan Plateau is crucial for predicting the response of the alpine carbon pool to future climate changes. Here we present information about SOC stocks and turnover time in a heavily grazed alpine meadow on the Tibetan Plateau based on radiocarbon (14C) measurements and inverse modeling. Our results reveal that the alpine meadow soil is composed of three distinct carbon pools. The topsoil represents the active carbon pool, which has a carbon inventory-weighted mean turnover time of 64 years. The CO2 efflux due to the mineral soil respiration from this pool is ca. 48.45 g C m-2 yr-1, accounting for 91 % of the total heterotrophic soil respiration. The intermediate carbon pool has an inventory-weighted mean turnover time of 780 years and the rate of mineral soil respiration in this pool is an order of magnitude lower than that in the active carbon pool. The parental materials feature the passive carbon pool, which has millennia-long turnover time and the mineral soil respiration is trivial. Comparing our results with other 14C-based studies suggests that grazing intensity may alter not only the SOC stocks but also the soil respiration rate in the alpine grassland ecosystem. The heavily grazed alpine meadow broadly fits the exponential relationship between turnover time and mean annual air temperature identified by meta-analysis of published data from the Tibetan Plateau, alpine grassland, and forest sites elsewhere.

应用高频观测探讨不同森林经营方式下矿质土壤呼吸的昼夜动态特征

PDF HTML阅读 XML下载 导出引用 引用提醒 应用高频观测探讨不同森林经营方式下矿质土壤呼吸的昼夜动态特征 DOI: 10.5846/stxb201608191698 作者: 作者单位: 福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,三明市三元区林业局,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点资助项目（31130013）；国家自然科学基金资助项目（31500407）；福建省教育厅B类科技资助项目（JB14025） High-frequency analysis of the diel patterns of mineral soil respiration under different forest management Author: Affiliation: College of Geographical Science,Fujian Normal University; State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geographical Science,Fujian Normal University; State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),,,,,,,, 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:矿质土壤呼吸是森林生态系统土壤碳库损失的重要途径之一，也是森林生态系统碳（C）平衡估算中的关键因子。了解矿质土壤呼吸在不同时间尺度上的变化，对理解森林生态系统C循环应对全球变化的响应至关重要，而高频观测是探讨矿质土壤呼吸在不同时间尺度变化的重要手段之一。通过高频自动观测系统与Li-8100土壤CO2通量测量系统，对福建省三明市陈大镇国有林场的米槠（Castanopsis carlesii）次生林在不同森林经营方式下（CK对照，RR皆伐，RB火烧）的矿质土壤呼吸与土壤温度和含水量的昼夜动态进行分析，并比较2种采样策略下矿质土壤呼吸的年、日均通量差异。结果表明：1）不同森林经营方式的矿质土壤呼吸与土壤温度和土壤含水量均存在着明显的季节动态，矿质土壤呼吸速率年均值表现为CK（2.18 μmol m-2 s-1） > RB（1.93 μmol m-2 s-1） > RR（1.89 μmol m-2 s-1）。2）在不同森林经营方式下，采用手动观测的矿质土壤呼吸年平均日通量显著低于高频观测结果，而采用高频观测09：00-11：00时间段内观测数据计算日通量与高频自动观测系统全天（24h）结果无显著差异；3）不同森林经营方式下的林地，土壤水热条件的变化是影响矿质土壤呼吸的重要因素之一。双因子模型拟合结果表明，土壤温度和含水量共同解释了CK、RR和RB矿质土壤呼吸速率的年变化的96.8%，62.8%，95.4%，拟合结果明显优于以温度为单因子的指数模型。因此，未来气候变化背景下，为准确评估和预测不同森林经营方式对土壤与大气间碳通量交换的影响，采用高频自动观测技术观测矿质土壤呼吸，将有利于提高碳通量估算精度。 Abstract:Mineral soil respiration is an important route for the loss soil carbon (C) in forest ecosystems, and it is a key factor for estimating the forest ecosystem carbon balance. Making sense of mineral soil respiration variation on temporal and spatial scales is a critical component of understanding forest ecosystem C cycle responses to climate change. Thus, high-frequency measurements have become one of the primary tools used to measure mineral soil respiration on both temporal and spatial scales. The objective of this study was to compare a manual system (Li-8100A) with an automated system for measuring mineral soil respiration in a subtropical forest. We carried out the study in a secondary Castanopsis carlesii forest with different forest management (Control, CK; Residual retention after clear cutting, RR; Residual burning after clear cutting, RB) in Sanming, Fujian. The results obtained were as follows. (1) The mineral soil respiration flux, soil temperature, and soil moisture content under different forest managements all showed obvious seasonal dynamics, and mineral soil respiration rates were in the order of CK (2.18 μmol m-2 s-1) > RB (1.93 μmol m-2 s-1) > RR (1.89 μmol m-2 s-1). (2) The annual flux determined using high-frequency measurement was significantly higher than that determined using the manual system, whereas there was no difference between the soil respiration rate calculated between 09:00 and 11:00 (high-frequency data) for different forest managements. (3) Soil hydrothermal condition is one of the important factors affecting mineral soil respiration under different forest management. A two-factor model show that included soil temperature and moisture explained the annual variation of mineral soil respiration rate as 96.8%, 62.8% and 95.4% in CK, RR, and RB treatments, respectively. The double factors model demonstrated that combined with soil temperature and moisture was explained the annual variation of mineral soil respiration rate 96.8%, 62.8% and 95.4% in CK, RR and RB, respectively. The results obtained using this model were better than those obtained using a single-factor model. Therefore, in order to accurately assess and predict the effects of different forest management on the C flux exchange between the soil and atmosphere under future climate change, high-frequency measurements should be considered. 参考文献 相似文献 引证文献

马尾松林土壤呼吸组分对不同营林措施的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 马尾松林土壤呼吸组分对不同营林措施的响应 DOI: 10.5846/stxb201503020398 作者: 作者单位: 中国林业科学研究院森林生态环境与保护研究所 国家林业局森林生态环境重点实验室,中国林业科学研究院森林生态环境与保护研究所 国家林业局森林生态环境重点实验室,中国林业科学研究院森林生态环境与保护研究所 国家林业局森林生态环境重点实验室,中国林业科学研究院森林生态环境与保护研究所 国家林业局森林生态环境重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级公益性科研院所基本科研业务费专项（CAFRIFEEP201101）；林业公益性行业科研专项（201104008） Responses of soil respiration and its components to forest management in Pinus massoniana stands Author: Affiliation: Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, State Forestry Administration Key Laboratory of Forest Ecology and Environment;National Forest Ecosystem Station of Three Gorges Reservoir in Zigui County,,Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, State Forestry Administration Key Laboratory of Forest Ecology and Environment;National Forest Ecosystem Station of Three Gorges Reservoir in Zigui County, 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:针对不同营林措施（对照、除灌、采伐1（15%）、采伐2（70%）后的三峡库区马尾松飞播林，采用LI-8100对其土壤呼吸组分的呼吸速率和土壤温度、湿度进行为期1年的连续观测分析表明，不同营林措施对土壤呼吸组分的影响不同。1）观测期内，各营林措施下凋落物层呼吸速率差异并不显著，对照、除灌、采伐1、采伐2的根呼吸速率均值分别为：1.00、0.83、0.86、1.11μmolCO2m-2s-1；采伐处理下矿质土壤呼吸显著高于对照和除灌（P<0.05）；2）与对照相比，营林措施并未显著改变凋落物呼吸对于土壤总呼吸的贡献率（18.78%-23.70%），但降低了根呼吸的贡献率，其中以采伐1最为显著（P<0.05）；除灌的矿质土壤呼吸贡献率（37.00%）与对照（38.32%）相近，而采伐1（45.63%）和采伐2（43.07%）均显著增加了矿质土壤呼吸的贡献率，矿质土壤呼吸的变化是造成采伐措施下土壤呼吸变化的主要土壤呼吸组分；3）营林后仅采伐2措施下土壤温湿度显著高于对照，土壤温湿度双因子模型较单因子模型能更好的解释土壤呼吸组分变化，但仅能解释其部分变化（4.6%-59.3%），仍需对营林后其他相关因子进行深入的综合研究。 Abstract:Forest soils play a critical role in the carbon cycle and carbon sequestration at both global and local scales, and forest management practices (e.g., harvesting, burning, and thinning) influence soil carbon processes by altering organic matter quality and quantity, key microclimatic conditions, microbial communities, and other factors. However, the effects of forest management on soil carbon effluxes in different ecosystems are still largely unknown, despite being critical to estimate global carbon fluxes. Quantifying the responses of soil respiration and its components to forest management is vital to accurately evaluate forest carbon balance. Thus, an aerially seeded Pinus massoniana forest was chosen in the Three Gorges reservoir area to evaluate the effects on soil respiration of different forest management practices (i.e., control; shrub-cutting:harvesting all shrubs and removing all harvest residues. Harvest strategy 1%-15% harvest intensity and removing main harvest residues without leaves and small branches; Harvest strategy 2%-70% harvest intensity and the same harvest residue management as that in harvest 1). All experimental treatments were located in similar habitats and consisted of three 20 m×20 m plots. The treatments were conducted in October 2013. A combination of trenching and litter removing methods were employed in order to partition soil respiration into components of litter layer respiration, root respiration, and mineral soil respiration. The soil temperature, soil moisture, and rate of soil respiration and its components were observed continuously for one year (from November 2013 to October 2014) using a Li-8100 system. Management did not affect litter layer respiration within the measuring period. Root respiration in the control, shrub-cutting, harvest strategy 1, and harvest strategy 2 treatments were 1.00, 0.83, 0.86, and 1.11 μmol CO2 m-2 s-1, respectively. The mineral soil respiration of harvested stands was significantly higher than that of control and shrub-cutting stands (P < 0.05). The proportion of litter layer respiration to total respiration was not significantly influenced by forest management (18.78%-23.70%), but the contribution of root respiration to total respiration was reduced, especially in the harvest strategy 1 treatment (P < 0.05). The contribution of mineral respiration to total respiration significantly increased in harvested stands, which was mainly attributed to the decrease in total soil respiration. Management effects on soil temperature and soil moisture were only observed in the stands of harvest strategy 2. A two-factor model that included soil temperature and moisture better explained the variations in soil respiration (4.6%-59.3%) than that by a model using temperature (4.2%-59.1%) or moisture (0.3%-23.5%) alone. Other factors that influence soil respiration and its components need to be further elucidated. 参考文献 相似文献 引证文献

Carbon input manipulation affects soil respiration and microbial community composition in a subtropical coniferous forest

We determined the effects of aboveground and belowground C inputs on soil CO2 efflux and microbial community composition by phospholipid fatty acids using aboveground litter addition or removal and root trenching in a subtropical forest in Southern China. From January 2011 to December 2011, soil respiration varied with the seasonal changes in soil temperature and water content, but its pattern was not altered by C input manipulation. The effects of C input manipulation on the temperature sensitivity of soil respiration was season-dependent, which were greater in the dormant season than in the growing season. Litter addition increased the soil respiration by 33% compared with the control, whereas litter removal decreased it by 22.6%. Root trenching decreased soil respiration by 20.4%. Aboveground litter decomposition, root and rhizosphere respiration, and mineral soil respiration contributed to 22.3%, 20.1%, and 57.6% of total soil CO2 efflux, respectively. We also found that increase in soil CO2 efflux induced by litter addition was 10.4% greater than decrease by litter removal. Litter removal increased 21.6% of the concentration of Gram-positive bacteria and decreased 32.8% of the bacteria to fungi ratio, compared with the control. Root trenching increased the concentrations of bacteria, fungi, and actinomycetes by 28.8%, 161.2% and 32.5%, respectively, but decreased the Gram-negative to Gram-positive bacteria and the bacteria to fungi ratios by 57.4% and 107.9%. C input treatment did not increase the Gram-positive bacteria but nor decreased the Gram-negative to Gram-positive bacteria ratio. The concentration of the 16:0 PLFA and the Gram-negative to Gram-positive bacteria ratio were significantly correlated with soil respiration. These results suggest that root C input has greater influence on soil microbial community composition than the aboveground litter C input.

Decreased carbon limitation of litter respiration in a mortality-affected piñon–juniper woodland

Abstract. Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon–juniper ecosystems in southwestern North America, may affect C substrate availability in several ways, for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon–juniper sites in central New Mexico, USA: one with a recent (&lt; 1 yr), experimentally induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon–juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) piñon mortality reduces the C limitation of litter respiration; and (3) piñon mortality enhances the C limitation of mineral soil respiration. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Consistent with hypothesis 2, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Applications to the mineral soil showed evidence of reduction in CO2 flux on the girdled site and a non-significant increase on the control. We speculate that the reduction may have been driven by water-induced carbonate dissolution, which serves as a sink for CO2 and would reduce the net flux. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.

Influence of long-term thinning on the biomass carbon and soil respiration in a larch (Larix gmelinii) forest in Northeastern China.

Thinning management is used to improve timber production, but only a few data are available on how it influences ecosystem C sink capacity. This study aims to clarify the effects of thinning on C sinks of larch plantations, the most widespread forests in Northeastern China. Both C influx from biomass production and C efflux from each soil respiration component and its temperature sensitivity were determined for scaling-up ecosystem C sink estimation: microbial composition is measured for clarifying mechanism for respiratory changes from thinning treatment. Thinning management induced 6.23 mol C m−2 yr−1 increase in biomass C, while the decrease in heterotrophic respiration (R h) at the thinned sites (0.9 mol C m−2 yr−1) has enhanced 14% of this biomass C increase. This decrease in R h was a sum of the 42% decrease (4.1 mol C m−2 yr−1) in litter respiration and 3.2 mol C m−2 yr−1 more CO2 efflux from mineral soil in thinned sites compared with unthinned control. Increases in temperature, temperature sensitivity, alteration of litters, and microbial composition may be responsible for the contrary changes in R h from mineral soil and litter respiration, respectively. These findings manifested that thinning management of larch plantations could enhance biomass accumulation and decrease respiratory efflux from soil, which resulted in the effectiveness improvement in sequestrating C in forest ecosystems.

Rainfall pulse primarily drives litterfall respiration and its contribution to soil respiration in a young exotic pine plantation in subtropical China

Although litterfall respiration (RL) is a key process of soil carbon dynamics in forests, factors that drive RL and its contribution to soil respiration (RS) have not been sufficiently studied. Using a litter removal method, we researched RL and the ratio of RL:RS in a 20-year-old exotic slash pine ( Pinus elliottii Englem.) plantation in subtropical China. Soil temperature explained 67%, 78%, and 25% of variation in RS, mineral soil respiration (RS-L), and RL, respectively, but had little impact on RL:RS. To study influences besides temperature, measured RS and RS-L were normalized using the Arrhenius equation. Even though this subtropical plantation was characterized by a humid climate with abundant precipitation, a rainfall pulse induced increase in soil moisture primarily drove RL and its contribution to RS but depressed RS-L. The response of RL to rainfall and soil moisture was significantly more sensitive than that of RS-L. Furthermore, the effects of rainfall and soil moisture on RS, RL, and RL:RS were higher during the dry season (July–December) than during the wet season (January–June). In the context of climate change, RL and its contribution to RS are expected to decrease because of the predicted decrease in rainfall amount and frequency in subtropical regions.

Dissecting soil CO 2 fluxes from a subtropical forest in China by integrating field measurements with a modeling approach

Terrestrial carbon sequestration involves a series of processes, including photosynthesis, plant autotrophic respiration and soil microbial heterotrophic respiration. Field measurements of carbon dioxide (CO 2) using either eddy covariance or chamber methods usually provide bulk CO 2 fluxes from more than one sink or source. For the purpose of estimating the C budget in ecosystems, it is inherently important to determine the individual sinks or sources. This report describes how we tested the Forest-DNDC model using a dataset collected at a subtropical forest site in Sichuan Province, China. One-year field measurements were conducted using a chamber method at four plots with different treatments that were specifically designed to distinguish the CO 2 fluxes produced from three sources: root respiration, forest floor respiration and mineral soil respiration. The obtained datasets were utilized to verify the modeled CO 2 fluxes from the corresponding sources for the tested forest ecosystem. Results from the tests indicated that Forest-DNDC was capable not only of quantifying the total CO 2 emissions but also of distinguishing their sources related to plant autotrophic and soil microbial heterotrophic respiration. Because measuring root respiration is always difficult in field investigations, adopting Forest-DNDC for quantifying root respiration represents an appropriate complement to most field measurements.

Effects of changes in the soil environment associated with heavy precipitation on soil greenhouse gas fluxes in a Siberian larch forest near Yakutsk

A future increase in heavy precipitation events is predicted in boreal regions. An irrigation experiment was conducted in Taiga forest in eastern Siberia to evaluate the effect of heavy precipitation on greenhouse gas ([GHG] CO2, CH4, and N2O) fluxes in the soil. The GHG fluxes on the soil surface were measured using a closed-chamber method and GHG production rates in the mineral soil were estimated using the concentration–gradient method based on Fick’s law. Irrigation water (20 mm day−1) was applied continuously for 6 days (120 mm in total; the same amount as summer precipitation in this region). Greenhouse gas production rates in the organic layer (O-layer) were defined as the difference between the GHG fluxes and the GHG production rates in the mineral soil. Carbon dioxide flux was measured both in root-intact (R s ) and trenched plots (R mw ). The root respiration rate (R r ) was calculated as the difference between R s and R mw . Considering the root distribution in the soil, we regarded the CO2 production rate in the mineral soil to be the microbial respiration rate in the mineral soil (R mm ) and microbial respiration rate in the O-layer (R mo ) as the difference between R mw and R mm . Irrigation increased both soil temperature and moisture in the irrigated plot. The R s , CH4 flux and N2O flux during the irrigation period were higher in the irrigated plot than that in the non-irrigated plot (P < 0.05; mean R s ± standard deviation [SD] (mg C m−2 h−1) were 171 ± 20 and 109 ± 11, mean CH4 flux ± SD (μg C m−2 h−1) were −5.4 ± 4.1 and −14.0 ± 6.5, and mean N2O flux ± SD (μg N m−2 h−1) were 1.6 ± 1.6 and 0.2 ± 1.1, respectively). Soil moisture had a positive effect on R mm and CH4 production rate in the O-layer, a negative effect on R r , and did not affect R mo , the CH4 production rate in the mineral soil or the N2O production rates in both the O-layer and the mineral soil. Soil temperature had a positive effect on R r and R mo . The increment of global warming potential of the soil mainly resulted from an increase in microbial respiration rates. Future changes in precipitation patterns in this region would accelerate decomposition of the soil organic matter.

Leaf litter is an important mediator of soil respiration in an oak-dominated forest

The contribution of the organic (O) horizon to total soil respiration is poorly understood even though it can represent a large source of uncertainty due to seasonal changes in microclimate and O horizon properties due to plant phenology. Our objectives were to partition the CO(2) effluxes of litter layer and mineral soil from total soil respiration (SR) and determine the relative importance of changing temperature and moisture mediating the fluxes. We measured respiration in an oak-dominated forest with or without the O horizon for 1 year within the Oak Openings Region of northwest Ohio. Mineral soil and O horizon respiration were subtracted from mineral soil respiration (MSR) to estimate litter respiration (LR). Measurements were grouped by oak phenology to correlate changes in plant activity with respiration. The presence of the O horizon represented a large source of seasonal variation in SR. The timing of oak phenology explained some of the large changes in both SR and LR, and their relationship with temperature and moisture. The contribution to SR of respiration from the mineral soil was greatest during pre-growth and pre-dormancy, as evident by the low LR:MSR ratios of 0.65 +/- 0.10 (mean +/- SE) and 0.69 +/- 0.03, respectively, as compared to the other phenophases. Including moisture increased our ability to predict MSR and SR during the growth phenophase and LR for every phenophase. Temperature and moisture explained 85% of the variation in MSR, but only 60% of the variation in LR. The annual contribution of O horizon to SR was 48% and the ratio of litter to soil respiration was tightly coupled over a wide range of environmental conditions. Our results suggest the presence of the O horizon is a major mediator of SR.

Soil carbon dioxide efflux in pure and mixed stands of oak and beech

Total Soil Respiration (TSR) was measured in pure and mixed stands of oak and beech and was partitioned into two contributions using the forest floor removal technique: Mineral Soil Respiration (MSR) and Forest Floor Respiration (FFR). In addition, laboratory incubations of the forest floor and the Ah horizon were performed to evaluate the heterotrophic respiration and the DOC production of these horizons. The relationships between soil temperature and the various soil respiration contributions in the three stands were compared using Q(10) functions. In situ, significant differences (alpha = 0,05) between stands were observed for the R-10 parameter (respiration rate at 10 degrees C) of the TSR, MSR and FFR contributions, while only the temperature sensitivity (Q(10)) of TSR was significantly affected by stand composition. The effect of soil water content was only significant on MSR and followed different patterns according to stand composition. Under controlled conditions, the R-10 of the forest floor and of the Ah horizon varied with stand composition and the Q(10) of the forest floor decreased in the order: oak (2.27) > mixture (2.01) > beech (1.71).

Change in soil carbon cycling for stand development of Japanese cedar (Cryptomeria japonica) plantations following clear‐cutting

Soil carbon cycling was studied in Japanese cedar plantations with different stand ages after clear‐cutting and was analyzed by a compartment model. The amount of biomass and the litterfall rate increased rapidly with the growth of Japanese cedar, which were approximated by a simple logistic function of stand age. The accumulation of A0 layer decreased from 21 t ha−1 to 5 t ha−1 during the 10 years following clear‐cutting, and then recovered to nearly the same level as before clear‐cutting within 20 years after clear‐cutting, although the amount of soil carbon in the mineral soil recovered more than 40 years after clear‐cutting. The total and mineral soil respiration rates increased rapidly after clear‐cutting and gradually decreased in young stands and stabilized in old stands. The relative decomposition rate of the A0 layer and organic matters in mineral soil was high in the young stands because of the relatively high soil temperature rather than the soil moisture content. After the closing up of the canopy, the relative decomposition rates of the A0 layer and humus in the mineral soil stabilized at 0.14 to 0.16 y–1 and 0.005 to 0.013 y−1, respectively. Consequently, soil carbon cycling was strongly affected by clear‐cutting. The amount of soil carbon rapidly decreased because of the cessation of litterfall and the increase of the relative decomposition rate of the A0 layer and humus, and recovered gradually to the level before clear‐cutting with the growth of the cedar plantation. The change in soil carbon cycling with stand development was partly caused by the change in soil temperature and moisture content but was mainly caused by the amount of cedar litterfall which changed significantly in the early stage of the stand following clear‐cutting, and became slower and leveled off in the late stage with stabilization of the environmental conditions and litterfall rate.

Biotic and abiotic factors controlling soil respiration rates in Picea abies stands

The response of soil respiration to varying environmental factors was studied in four Picea abies stands (47-, 87-, 111- and 146-year old) during the 1998 growing season. While within-site variations of soil CO 2 efflux (up to 1.6 μmol CO 2 m −2 s −1 ) were larger than their diurnal variability (<0.25 μmol CO 2 m −2 s −1 ), spatial variations within a site were smaller than seasonal changes in soil respiration rates (up to 4.4 μmol CO 2 m −2 s −1 ). Highest within-site variability of soil efflux was generally found during the summer months when maximum flux rates of 4–6 μmol CO 2 m −2 s −1 were reached (coefficient of variation 40%). Soil temperatures (in the O f and O h layers, and A h horizon) showed a pronounced seasonal course, in contrast to soil moisture. An exponential equation best described the relationships between soil temperature in the O f layer and soil CO 2 efflux ( r 2 between 0.75 and 0.81). However, an Arrhenius type equation always resulted in lower r 2 values (0.52–0.71). The Q 10 values ranged between 2.39 (146-year old stand) and 3.22 (87-year old stand), averaging 2.72 for the P. abies stands within the watershed. The removal of litter and organic layers generally affected soil CO 2 efflux negatively. In three of the four P. abies stands (47-, 87-, 146-year old stands), soil respiration rates were reduced by 10–20% after removal of the L and O f layer, and by 30–40% after removal of the L and most of the O f and O h layers. Thus, mineral soil respiration seemed to contribute a major fraction to the total soil CO 2 flux (>60%). Trenching shallow fine roots during collar insertion and mechanical inhibition of root in-growth during the following months allowed fine root respiration to be separated from microbial respiration only in times of highest root growth. Microbial respiration seemed to dominate the respiratory CO 2 loss from the forest floor (>70%). The comparison of the annual soil CO 2 efflux in the 47-year old P. abies stand (about 710 g C m −2 yr −1 ) with annual litterfall and root net primary productivity estimates supported this conclusion.

Forest Harvesting Effects on Soil Temperature, Moisture, and Respiration in a Bottomland Hardwood Forest

The effect of forest disturbance on C cycling has become an issue, given concerns about escalating atmospheric C content. We examined the effects of harvest intensity on in situ and laboratory mineral soil respiration in an East Texas bottomland hardwood forest between 6 and 22 mo after harvesting. Treatments included a clearcut, a partial cut wherein approximately 58% of the basal area was removed, and an unharvested control. The soda-lime absorption technique was used for in situ respiration (CO 2 efflux) and the wet alkali method (NaOH) was used for laboratory mineral soil respiration. Soil temperature and moisture content were also measured. Harvesting significantly (P = 0.05) increased in situ respiration during most sampling periods. This effect was attributed to an increase in live root and microflora activity associated with postharvesting revegetation. In situ respiration increased exponentially (Q 10 relationship) as treatment soil temperatures increased (mean range 8.3-29.1°C), but followed a parabolic-type pattern through the range of soil moisture measured (mean range 10.4-31.5% Mean rates of laboratory mineral soil respiration measured during the study were unaffected by cutting treatment for most sampling sessions. Overall, the mean rate of CO 2 efflux in the clearcuts (7.15 g CO 2 m -2 d -1 ) was significantly higher than that in the partial cuts (5.95 g CO 2 m -2 d -1 ), which in turn was significantly higher than that in the controls (4.95 g CO 2 m 2 d -1 ). Mass balance estimates indicate that these treatment differences will have little or no long-term effect on C sequestration of these managed forests.

Carbon dioxide and methane fluxes by a forest soil under laboratory-controlled moisture and temperature conditions

Carbon dioxide and methane are important greenhouse gases whose exchange rates between soils and the atmosphere are controlled strongly by soil temperature and moisture. We made a laboratory investigation to quantify the relative importance of soil moisture and temperature on fluxes of CO 2 and CH 4 between forest soils and the atmosphere. Forest floor and mineral soil material were collected from a mixed hardwood forest at the Harvard Forest Long-Term Ecological Research Site (MA) and were incubated in the laboratory under a range of moisture (air-dry to nearly saturated) and temperature conditions (5–25°C). Carbon dioxide emissions increased exponentially with increasing temperature in forest floor material, with emissions reduced at the lowest and highest soil moisture contents. The forest floor Q 10 of 2.03 (from 15–25°C) suggests that CO 2 emissions were controlled primarily by soil biological activity. Forest floor CO 2 emissions were predicted with a multiple polynomial regression model ( r 2=0.88) of temperature and moisture, but the fit predicting mineral soil respiration was weaker ( r 2=0.59). Methane uptake was controlled strongly by soil moisture, with reduced fluxes under conditions of very low or very high soil moisture contents. A multiple polynomial model accurately described CH 4 uptake by mineral soil material ( r 2=0.81), but only weakly ( r 2=0.45) predicted uptake by forest floor material. The mineral soil Q 10 of 1.11 for CH 4 uptake indicates that methane uptake is controlled primarily by physical processes. Our work suggests that inclusion of both moisture and temperature can improve predictions of soil CO 2 and CH 4 exchanges between soils and the atmosphere. Additionally, global change models need to consider interactions of temperature and moisture in evaluating effects of global climate change on trace gas fluxes.