基于IPCC的河北省2005年森林碳储量

基于IPCC的方法,对河北省2005年森林及其它木质生物质碳储量进行了研究.结果表明,河北省2005年森林和其它木质生物质总碳储量为6 111.96万t,折合固定CO2的量为22 410.52万t.现有林以幼、中龄林为主,林分平均碳密度较低,仅为10.32 t·hm-2;按优势树种(树种组)排序,最大的5个碳库为桦树、...     

紫外光辐照浸渍纸颜色与碳的价态变化

用X射线光电子能谱仪与分光光度计,分析浸渍纸受到紫外光辐照后,颜色及碳价态的变化情况.结果表明:浸渍纸在受到紫外光辐照过程中,颜色变化规律分3个阶段,两端变化大,且呈现黄蓝轴色品指数的增强,中间变化较小;同时,碳价态也发生了显著的改变,高结合能含量增加.结合其变色规律,推断出其表面形成了比较稳定的"膜"结构.     

浅谈森林碳汇对我国林业发展的意义

本文对我国森林生态系统固碳功能和碳储量研究,碳汇合作项目及其对我国林业发展的意义进行了概括。     

浙北平原区土壤碳源/汇分布研究

根据2002～2008年浙江省土壤地球化学调查数据,计算不同时期的土壤有机碳密度,初步在浙江省嘉善县、慈溪市两地区圈定了土壤有机碳源区47.18 km2、碳汇区306.81 km2,为其他地区开展同类研究提供了参考研究思路,也为浙江省土地规划、节能减碳和经济发展战略研究提供参考.     

洞庭湖地区长期施肥条件下双季稻田生态系统净碳汇效应及收益评估

以农业部望城红壤水稻土生态环境重点野外观测试验站的长期定位肥力效应试验稻田为研究对象,利用历年作物产量、凋落物固碳和农田CO2排放等观测资料及生态系统的物质和管理投入等调查资料,估算了年碳汇平衡和经济收益,以及不同施肥处理的固碳速率、潜力及表土碳密度。结果表明,不同施肥处理下年碳汇量介于0．82～4．70tC·hm^-2·a^-1,增施有机肥（猪粪、稻草）的处理NPK＋RS、NK＋PM和NP＋RS的碳汇量分别是相应的仅施化肥处理NPK、NK和NP的1．1、1．7和1-4倍。不同处理生态系统物质投入的碳成本介于0．03-0．65tC·hm^-2．a^-1,人工管理的碳成本介于1．42—1．48tC·hm^-2·a^-1,年经济收益介于1．17×10^3～8．71×10^3 CNY·hm^-2·a^-1,有机肥配施的经济效益是单施化肥的1．1～1．6倍。不同施肥处理固碳速率介于25．83—51．98kg·hm^-2·a^-1,不同施肥处理表土碳密度介于29．21～43．24t·hm^-2,增施有机肥能够提高土壤固碳速率和表土碳密度。与单施化肥相比,有机无机配施处理的生态系统生产力较高,也表现出较高的碳汇效应和经济收益,是促进土壤固碳减排的一项重要措施。     

Role of organic fractions on C decomposition and N mineralization of animal wastes in soil

The relative contributions of water-soluble, water-non-soluble, Van Soest-soluble, and neutral detergent fiber (NDF) fractions of pig slurry (PS), cattle slurry (CS), cattle farmyard manure (FYM), and composted cattle farmyard manure (CFYM) to the overall C and N mineralization of the raw wastes were studied by incubating treated soil for 107 days at 15°C under non-limiting N conditions. The C or N mineralization of soluble fractions was calculated from the difference between C or N mineralization of the raw and non-soluble fractions. The organic N content of raw wastes ranged from 15 to 32 mg N g⁻¹ dry matter and organic C to organic N ratio from 13 to 29. The water-soluble fraction (SOL_W) was close to 100 mg C g⁻¹ raw waste C for CS, FYM, and CFYM but reached 200 mg C g⁻¹ for PS. The Van Soest-soluble fraction (SOL_VS) was the main fraction for PS, CS, and CFYM (>500 mg C g⁻¹ raw waste C) but only 303 mg C g⁻¹ raw waste C for FYM. Both soluble and non-soluble fractions contributed to C decomposition of slurries, with half to more than half of the decomposed C derived from the degradation of soluble compounds. Most of the C decomposed from FYM was derived from the large NDF fraction, but the contribution from the water-soluble C to the decomposition was also significant. Carbon mineralization of CFYM was due to the degradation of the NDF fraction, whereas soluble C did not contribute. Amounts of N mineralized or immobilized by raw wastes and non-soluble fractions at the end of incubation were significantly correlated (P < 0.01) with their organic C to organic N ratio. The contribution of the Van Soest-soluble fraction to N mineralization varied greatly between the four wastes. Finally, large differences in the C degradability and N availability of the water and Van Soest-soluble fractions were demonstrated.     

Impacts of management on decomposition and the litter-carbon balance in irrigated and rainfed no-till agricultural systems

The litter carbon (C) pool of a single litter cohort in an agroecosystem is the difference between net primary productivity and decomposition and comprises 11–13% of the total C pool (litter and soil 0–15 cm depth) post-harvest. This litter-C pool is highly dynamic and up to 50% can be decomposed in the first 12 months of decomposition. Thus, understanding litter-C dynamics is key in understanding monthly and annual total ecosystem carbon dynamics. While the effects of management practices such as irrigation and fertilization on productivity are well understood, the effects on decomposition are less studied. While irrigation and fertilization increase productivity, this will only lead to increased litter-C residence time and litter-C pool accretion if these techniques do not also result in equivalent or greater increases in decomposition. Management could potentially have impacts on litter-C accretion by increasing litter inputs, changing plant-C allocation, plant tissue quality, or decomposition rates. We examined carbon loss of one annual cohort of maize litter using in situ nylon litter bags for 3 years in three no-till fields with differing management regimes: irrigated continuous maize with a pre-planting fertilization application and two fertigation events, irrigated maize–soybean rotation with the same fertilization regime as the irrigated continuous maize management regime, and rainfed maize–soybean rotation with a single pre-planting fertilization event. We addressed the effects of these different management regimes on net primary productivity and litter inputs, litter nitrogen (N) concentrations and carbon quality measures, plant C allocation, decomposition rates and the potential changes in the overall litter-C balance. We found that irrigation/fertigation management increased litter inputs, led to changes in plant tissue quality, had no effect on carbon allocation, and increased decomposition rates. This balance of both greater litter inputs and outputs of C from the irrigated management regimes led to a similar litter-C balance for this litter cohort in the irrigated and rainfed management regimes after 3 years of decomposition. Our data clearly show that merely increasing litter-C inputs through irrigation/fertigation practices is not sufficient to increase litter-C residence time because decomposition rates also increase. Therefore, close monitoring of decomposition rates is essential for understanding litter-C pool dynamics.     

Protein breakdown represents a major bottleneck in nitrogen cycling in grassland soils

Proteins represent the dominant input of organic N into most ecosystems and they also constitute the largest store of N in soil organic matter. The extracellular protease mediated breakdown of proteins to amino acids therefore represents a key step regulating N cycling in soil. In this study we investigated the influence of a range of environmental factors on the rate of protein mineralization in a grazed grassland and fallow agricultural soil. The protein turnover rates were directly compared to the rates of amino acid mineralization under the same conditions. Uniformly ¹⁴C-labelled soluble protein and amino acids were added to soil and the rate of ¹⁴CO₂ evolution determined over 30 d. Our results indicate that the primary phase of protein mineralization was approximately 20 ± 3 fold slower that the rate of amino acid mineralization. The addition of large amounts of inorganic NO₃⁻ and NH₄⁺ to the soil did not repress the rate of protein mineralization suggesting that available N does not directly affect protease activity in the short term. Whilst protein mineralization was strongly temperature sensitive, the presence of plants and the addition of humic and tannic acids had relatively little influence on the rate of soluble protein degradation in this fertile grassland soil. Our results suggests that the extracellular protease mediated cleavage of proteins to amino acids rather than breakdown of amino acids to NH₄⁺ represents the limiting step in soil N cycling.     

Soil resource heterogeneity in terms of litter aggregation promotes nitrous oxide fluxes and slows decomposition

To better understand the role of resource heterogeneity in decomposition and nitrous oxide (N₂O) flux we systematically altered the degree of plant litter aggregation in soil, from uniformly distributed to highly aggregated. In laboratory incubations, we distributed 4.5 g of dried clover shoots (Trifolium pratense L.) in two particle sizes (1 or >5 mm) into 1, 3, or 9 patches versus uniformly distributed. Soil moisture content was also varied to manipulate soil oxygen (O₂) concentrations. In moist soil (50% water-filled pore space, WFPS), litter aggregation delayed the peak litter decomposition rate by 3-5 days compared to uniformly distributed litter regardless of the litter particle size. In contrast, under near-saturated soil conditions (80% WFPS) litter aggregation suppressed decomposition throughout the 26-day incubation period. This significant interaction between litter aggregation and soil moisture treatments suggests that diffusion of soil resources (likely O₂) plays an important role in the influence of litter aggregation on decomposition. Specifically, O₂ diffusion may more adequately meet O₂ consumption rates when litter is distributed than when aggregated. In contrast to the temporary influence of aggregation on litter decomposition, N₂O fluxes under 50% WFPS conditions were consistently greater and on average 7.9, 7.2, and 4.7-fold greater than fine aggregated litter (1, 3, and 9 patches, respectively) than when uniformly distributed. Coarse litter aggregation also stimulated N₂O emissions, but not as much as fine litter. Under field conditions with growing maize (Zea mays L.), litter aggregation also stimulated N₂O emissions. The results suggest that litter aggregation plays a role in N₂O flux from agricultural soils and it might be manipulated to provide an additional N₂O mitigation strategy.     

Low levels of nitrogen addition stimulate decomposition by boreal forest fungi

Climate warming and associated increases in nutrient mineralization may increase the availability of soil nitrogen (N) in high latitude ecosystems, such as boreal forests. These changes in N availability could feed back to affect the decomposition of litter and organic matter by soil microbes. Since fungi are important decomposers in boreal forest ecosystems, we conducted a 69-day incubation study to examine N constraints on fungal decomposition of organic substrates common in boreal ecosystems, including cellulose, lignin, spruce wood, spruce needle litter, and moss litter. We added 0, 20, or 200 μg N to vials containing 200 mg substrate in factorial combination with five fungal species isolated from boreal soil, including an Ascomycete, a Zygomycete, and three Basidiomycetes. We hypothesized that N addition would increase CO₂ mineralization from the substrates, particularly those with low N concentrations. In addition we predicted that Basidiomycetes would be more effective decomposers than the other fungi, but would respond weakly or negatively to N additions. In support of the first hypothesis, cumulative CO₂ mineralization increased from 635 ± 117 to 806 + 108 μg C across all fungal species and substrates in response to 20 μg added N; however, there was no significant increase at the highest level of N addition. The positive effect of N addition was only significant on cellulose and wood substrates which contained very little N. We also observed clear differences in the substrate preferences of the fungal species. The Zygomycete mineralized little CO₂ from any of the substrates, while the Basidiomycetes mineralized all of the substrates except spruce needles. However, the Ascomycete (Penicillium) was surprisingly efficient at mineralizing spruce wood and was the only species that substantially mineralized spruce litter. The activities of β-glucosidase and N-acetyl-glucosaminidase were strongly correlated with cumulative respiration (r = 0.78 and 0.74, respectively), and Penicillium was particularly effective at producing these enzymes. On moss litter, the different fungal species produced enzymes that targeted different chemical components. Overall, our results suggest that fungal species specialize on different organic substrates, and only respond to N addition on low N substrates, such as wood. Furthermore, the response to N addition is non-linear, with the greatest substrate mineralization at intermediate N levels.