The carbon sink capacity of the world's agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossil fuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

Feeding 9-10 billion people by 2050 and preventing dangerous climate change are two of the greatest challenges facing humanity. Both challenges must be met while reducing the impact of land management on ecosystem services that deliver vital goods and services, and support human health and well-being. Few studies to date have considered the interactions between these challenges. In this study we briefly outline the challenges, review the supply- and demand-side climate mitigation potential available in the Agriculture, Forestry and Other Land Use AFOLU sector and options for delivering food security. We briefly outline some of the synergies and trade-offs afforded by mitigation practices, before presenting an assessment of the mitigation potential possible in the AFOLU sector under possible future scenarios in which demand-side measures codeliver to aid food security. We conclude that while supply-side mitigation measures, such as changes in land management, might either enhance or negatively impact food security, demand-side mitigation measures, such as reduced waste or demand for livestock products, should benefit both food security and greenhouse gas (GHG) mitigation. Demand-side measures offer a greater potential (1.5-15.6 Gt CO2 -eq. yr(-1) ) in meeting both challenges than do supply-side measures (1.5-4.3 Gt CO2 -eq. yr(-1) at carbon prices between 20 and 100 US$ tCO2 -eq. yr(-1) ), but given the enormity of challenges, all options need to be considered. Supply-side measures should be implemented immediately, focussing on those that allow the production of more agricultural product per unit of input. For demand-side measures, given the difficulties in their implementation and lag in their effectiveness, policy should be introduced quickly, and should aim to codeliver to other policy agenda, such as improving environmental quality or improving dietary health. These problems facing humanity in the 21st Century are extremely challenging, and policy that addresses multiple objectives is required now more than ever. © 2013 John Wiley & Sons Ltd.

梳理了与土壤生态系统功能相联系的，特别是对固碳减排的土壤有机质本质认识的研究进展及路径，探讨了经典腐殖质学说存在的问题，概述了新近的有机质保护稳定学说及腐殖质组学学说，并追溯了生物标志物有机质分子研究，最后从土壤学的基本理念和理论出发讨论和重新认识土壤有机质的本质及其价值。从形成条件、分离条件和分子鉴定等多方面分析，土壤腐殖质形成和稳定学说越来越显示出局限性；而面向气候变化的碳固定研究可以深入探析土壤有机质的复杂存在状态。越来越认识到土壤有机质是投入土壤的有机物质经不同程度生物利用或降解的产物残留，只是被土壤不同程度地区隔和封闭，本质上仍是分子量变化极大的生命源有机物的集合。因此，可通过生物标志物分子作为靶标在土壤中提取和识别，该技术的发展将孕育萌生土壤有机质分子组学。后者可以用于判读土壤有机质的结构支撑、反应活性和促生功能等方面的本质差别，这些差别可能是由有机分子组成结构及存在状态所决定而不是由有机分子稳定性决定的。从这个概念出发，类似于土壤微生物分子生态，土壤有机质的丰度、组成、结构与功能间的联系可能是土壤有机质本质的核心问题。对这种关系的量化和参数化表征可用以探索土壤有机质永续固定，且可以保持生命活性的土壤有机质的管理策略及技术，并配合土壤的团聚体理论诠释土壤的本质和生态系统功能服务，这将是未来土壤学服务人类可持续发展的理论立足点。

不同耕作方式对土壤水热、养分及生物特性产生的影响不同,实施合理的农田土壤管理措施不仅可以改善土壤理化性状,也可改变农田土壤生态过程.保护性耕作方式不同程度地改善了土壤质量,免耕能有效提高土壤酶活性,免耕和深松耕等能为土壤微生物的生长繁殖提供丰富的可利用资源,免耕、少耕等能减少对土壤动物的扰动,进而影响到土壤动物的数量、多样性及种群结构.本文综述了不同耕作方式下农田土壤理化性质和生物学特性的研究进展,重点分析了不同耕作方式对土壤理化因子、酶活性、微生物多样性和土壤动物的影响,指出了适宜的耕作方式对土壤质量修复的可能性及研究方向.

Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 mu m, 2000-250 mu m, 250-53 mu m, and <53 mu m), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m(2)) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 mu m aggregates but reduced SOC storage in <250 mu m aggregates due to SOC changes in LF and iPOM.

The modification of soil organic matter (SOM) decomposition by plant carbon (C) input (priming effect) represents a critical biogeochemical process that controls soil C dynamics. However, the patterns and drivers of the priming effect remain hidden, especially over broad geographic scales under various climate and soil conditions. By combining systematic field and laboratory analyses based on multiple analytical and statistical approaches, we explore the determinants of priming intensity along a 2200 km grassland transect on the Tibetan Plateau. Our results show that SOM stability characterized by chemical recalcitrance and physico-chemical protection explains more variance in the priming effect than plant, soil and microbial properties. High priming intensity (up to 137% of basal respiration) is associated with complex SOM chemical structures and low mineral-organic associations. The dependence of priming effect on SOM stabilization mechanisms should be considered in Earth System Models to accurately predict soil C dynamics under changing environments.

【目的】在已有团聚体碳氮分布研究的基础上，进一步研究不同施肥处理红壤性水稻土团聚体有机碳矿化特征，并分析有机碳矿化的影响因素，为揭示施肥对土壤肥力的影响及土壤有机碳矿化作用机制提供理论依据。【方法】以长期定位施肥红壤性水稻土为研究对象，包括9个处理：不施肥（CK）、有机质循环（C）、氮肥（N）、氮肥+有机质循环（NC）、氮磷肥（NP）、氮磷钾肥（NPK）、氮磷钾肥+有机质循环（NPKC）、氮钾肥（NK）和氮磷钾肥+1/2秸秆回田（NPKS）。运用湿筛法得到＞2 mm、1&mdash;2 mm、0.25&mdash;1 mm、0.053&mdash;0.25 mm和＜0.053 mm 5个粒级团聚体，观测团聚体和全土有机碳矿化动态变化，测定团聚体中微生物生物量碳含量和转化酶活性。【结果】全土和＞1 mm团聚体有机碳矿化速率在培养前期快速下降，之后逐渐降低至稳定状态，而＜1 mm粒级尤其是0.053&mdash;0.25 mm 团聚体，有机碳矿化速率在培养前期降低幅度减小并更早达到稳定状态。有机碳累积矿化量在＞2 mm和1&mdash;2 mm团聚体中最高，在0.053&mdash;0.25 mm团聚体中最低。与对照相比，施磷肥处理（NP和NPK）各粒级团聚体有机碳累积矿化量平均提高17.0%&mdash;62.1%，施有机肥处理（C、NC和NPKC）则平均提高25.0%&mdash;80.5%。＞2 mm和0.25&mdash;1 mm团聚体对全土有机碳矿化的贡献最大，分别为21.0%&mdash;42.5%和20.6%&mdash;32.7%。＞0.25 mm大团聚体微生物生物量碳含量和转化酶活性均高于＜0.25 mm微团聚体。施磷肥处理各粒级团聚体微生物生物量碳含量较对照平均高73.4%&mdash;92.0%，施有机肥处理平均高60.8%&mdash;99.6%。磷肥和有机肥的施用显著提高＞0.25 mm大团聚体转化酶活性，其中NC处理大团聚体转化酶活性最高，较对照提高46.0%&mdash;135.0%。团聚体有机碳累积矿化量与有机碳、全氮、微生物生物量碳含量及转化酶活性均呈极显著正相关，但与有机碳的相关性最大。【结论】大团聚体在土壤有机碳矿化中发挥主导作用；有机碳含量是影响团聚体有机碳矿化的最主要因素；磷肥和有机肥的施用促进了土壤团聚体有机碳的矿化，是提高红壤性水稻土供肥能力的有效措施。

This study aims to investigate the effect of sieving on ex situ soil respiration (CO2 flux) measurements from different land use types. We collected soils (0–10 cm) from arable, grassland and woodland sites, allocated them to either sieved (4-mm mesh, freshly sieved) or intact core treatments and incubated them in gas-tight jars for 40 days at 10 °C. Headspace gas was collected on days 1, 3, 17, 24, 31 and 38 and CO2 analysed. Our results showed that sieving (4 mm) did not significantly influence soil respiration measurements, probably because micro aggregates (&lt; 0.25 mm) remain intact after sieving. However, soils collected from grassland soil released more CO2 compared with those collected from woodland and arable soils, irrespective of sieving treatments. The higher CO2 from grassland soil compared with woodland and arable soils was attributed to the differences in the water holding capacity and the quantity and stoichiometry of the organic matter between the three soils. We conclude that soils sieved prior to ex situ respiration experiments provide realistic respiration measurements. This finding lends support to soil scientists planning a sampling strategy that better represents the inhomogeneity of field conditions by pooling, homogenising and sieving samples, without fear of obtaining unrepresentative CO2 flux measurements caused by the disruption of soil architecture.

Soil carbon (C) stabilisation is known to depend in part on its distribution in structural aggregates, and upon soil microbial activity within the aggregates. However, the mechanisms and relative contributions of different microbial groups to C turnover in different aggregates under various management practices remain unclear. The aim of this study was to determine the role of soil aggregation and their associated microbial communities in driving the responses of soil organic matter (SOM) to multiple management practices. Our results demonstrate that higher amounts of C inputs coupled with greater soil aggregation in residue retention management practices has positive effects on soil C content. Our results provide evidence that different aggregate size classes support distinct microbial habitats which supports the colonisation of different microbial communities. Most importantly our results indicate that the effects of management practices on soil C is modulated by soil aggregate sizes and their associated microbial community and are more pronounced in macro-aggregate compared with micro-aggregate sizes. Based on our findings we recommend that differential response of management practices and microbial control on the C turnover in macro-aggregates and micro-aggregate should be explicitly considered when accounting for management impacts on soil C turnover.© 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

以乌孙山北坡、科古琴山南坡为例,分析伊犁山地南北坡土壤有机碳的分布特征和影响因素。结果表明：① 0~50 cm范围内,高寒草甸、草甸草原土壤有机碳含量较高,荒漠草原土壤有机碳含量最低。土壤有机碳含量均随土壤深度的增加而降低,高寒草甸随土壤深度的增加土壤有机碳下降幅度最大;② 伊犁山地土壤腐殖化程度高,氮矿化能力强。大部分海拔的土壤碳氮比随土壤深度的增加而减少。河谷南坡碳氮比降低速率要大于河谷北坡。③ 土壤有机碳与全氮、全磷以及土壤含水率表现出良好的正相关性;与pH值表现出较好的负相关性,特别是20~50 cm处。植被类型分布和人类活动影响对土壤有机碳垂直变化影响显著。

Understanding how ecosystems store or release carbon is one of ecology's greatest challenges in the 21st century. Organic matter covers a large range of chemical structures and qualities, and it is classically represented by pools of different recalcitrance to degradation. The interaction effects of these pools on carbon cycling are still poorly understood and are most often ignored in global-change models. Soil scientists have shown that inputs of labile organic matter frequently tend to increase, and often double, the mineralization of the more recalcitrant organic matter. The recent revival of interest for this phenomenon, named the priming effect, did not cross the frontiers of the disciplines. In particular, the priming effect phenomenon has been almost totally ignored by the scientific communities studying marine and continental aquatic ecosystems. Here we gather several arguments, experimental results, and field observations that strongly support the hypothesis that the priming effect is a general phenomenon that occurs in various terrestrial, freshwater, and marine ecosystems. For example, the increase in recalcitrant organic matter mineralization rate in the presence of labile organic matter ranged from 10% to 500% in six studies on organic matter degradation in aquatid ecosystems. Consequently, the recalcitrant organic matter mineralization rate may largely depend on labile organic matter availability, influencing the CO2 emissions of both aquatic and terrestrial ecosystems. We suggest that (1) recalcitrant organic matter may largely contribute to the CO2 emissions of aquatic ecosystems through the priming effect, and (2) priming effect intensity may be modified by global changes, interacting with eutrophication processes and atmospheric CO2 increases. Finally, we argue that the priming effect acts substantially in the carbon and nutrient cycles in all ecosystems. We outline exciting avenues for research, which could provide new insights on the responses of ecosystems to anthropogenic perturbations and their feedbacks to climatic changes.