Mineralization of sulfur from organic residues assessed by inverse isotope dilution

Sulfur (S) deficiency in soils is increasingly recognized in agricultural systems. The quantification of S mineralization/immobilization processes after incorporation of organic materials into soils is a key factor to predict the availability of S to growing plants. However, immobilization and mineralization occur simultaneously making the quantification of the magnitude of each process difficult. We used the inverse isotope (³⁵SO₄) dilution technique to quantify immobilization and mineralization fluxes after incorporation of two organic residues with contrasting C/S ratio's (cabbage or wheat straw) into a sandy soil in planted and unplanted soils (pot trial with ryegrass and incubation). The soil was labeled with ³⁵SO₄ and incubated for 63 days prior to the application of residues. The specific activity (SA) of soil-extractable SO₄ did not change significantly in the control soil during the subsequent experimental period despite significant net mineralization, illustrating that labile-S in soil was homogenously labeled. Application of residues decreased the SAs during the incubation due to the dilution with unlabeled-S from the residues. A three-compartment dynamic model was fitted to the SA data predicting that gross mineralization of residue-S was almost complete over 43 days incubation although this release was not matched by the increase in soil SO₄ due to immobilization reactions. Soil-extractable SO₄ was significantly increased in the cabbage-treated soil while the reverse was true in the wheat straw amended soil in which the S-immobilization was almost twice the gross mineralization of residue-S. The SA of S in ryegrass were maximally 15% lower than in corresponding soil extracts suggesting that residue mineralization was similar in planted and unplanted soils. The inverse isotope dilution method offers potential for screening S release of different residues; however the details of the dynamics of soil-S isotopes show that the individual fluxes are not constant during the incubation.     

Small amounts of ammonium (NH$ _4^+ $) can increase growth of maize (Zea mays)

Nitrate (NO$ _3^ - $ ) and ammonium (NH$ _4^+ $ ) are the predominant forms of nitrogen (N) available to plants in agricultural soils. Nitrate concentrations are generally ten times higher than those of NH$ _4^+ $ and this ratio is consistent across a wide range of soil types. The possible contribution of these small concentrations of NH$ _4^+ $ to the overall N budget of crop plants is often overlooked. In this study the importance of this for the growth and nitrogen budget of maize (Zea mays L.) was investigated, using agriculturally relevant concentrations of NH$ _4^+ $ . Maize inbred line B73 was grown hydroponically for 30 d at low (0.5 mM) and sufficient (2.5 mM) levels of NO$ _3^ - $ . Ammonium was added at 0.05 mM and 0.25 mM to both levels of NO$ _3^ - $ . At low NO$ _3^ - $ levels, addition of NH$ _4^+ $ was found to improve the growth of maize plants. This increased plant growth was accompanied by an increase in total N uptake, as well as total phosphorus, sulphur and other micronutrients in the shoot. Ammonium influx was higher than NO$ _3^ - $ influx for all the plants and decreased as the total N in the nutrient medium increased. This study shows that agriculturally relevant proportions of NH$ _4^+ $ supplied in addition to NO$ _3^ - $ can increase growth of maize.     

The environmental prospects of cultured meat in China

To deal with concerns in China about environmental degradation and a growth in population accompanied by increased consumption of livestock products, a meat alternative is required. This study compared the environmental impacts of producing different protein sources for nutrition, including crops, livestock products, and cultured meat. The results showed that cultured meat has the lowest land use per unit of protein and unit of human digestible energy. China’s crops have the lowest energy use and greenhouse gas(GHG) emissions per unit of energy and protein. The energy use in cultured meat production is slightly higher than that of current pork production in China, whereas GHG emissions are lower. It is concluded that the overall impact of replacing livestock products with cultured meat would be beneficial for China’s environment and would potentially improve food security because less land is needed to produce the same amount of protein and energy.     

海南岛橡胶林生态系统碳通量及其影响因子研究

以位于海南岛西北部儋州地区的橡胶林为研究对象,采用涡度相关技术进行长期CO2通量观测,获得海南岛橡胶林生态系统碳通量的动态特征,并分析其对各影响因子的响应情况。结果表明:(1)橡胶林生态系统净碳交换量(NEE)日动态均为"U"型曲线,白天均为碳吸收(NEE为负值),夜间均为碳排放(NEE为正值);全年各月除2月外,NEE月总值均为负值,吸收碳,雨季4~10月各月NEE值均较大,旱季1~3月、11~12月,各月NEE值均较小;橡胶林年固碳能力强大,超过11.0 t C/(hm2·a)。(2)橡胶林生态系统NEE与光合有效辐射(PAR)、冠层内大气平均温度(Ta)、地下5 cm土壤温度(T_-5 cm)和饱和水汽压差(VPD)及地下5 cm土壤含水量(VWC_-5 cm)等均负相关,但影响强度不同,其中PAR影响最为显著;另外NEE还与橡胶林本身林分状况及周围大气环境CO2浓度等相关。     

The physicochemical and microbiological status of a restored bog in Québec: Identification of relevant criteria to monitor success

The Bois-des-Bel Sphagnum peatland (Rivière du Loup, QC) was restored in 1999 after 20 years of abandonment. Restoration work included not only the blockage of drainage ditches, but also the reintroduction of plant material including Sphagnum remains. Following restoration, the physicochemical and microbial characteristics (biomass, activity and composition) of the peat were analysed. The goal was to investigate the functional status of the restored ecosystem. The high N:P (>20) and N:K (>15) ratios indicated possible K and P deficiencies in the restored and the cutover sites, which is mainly associated with the intense leaching and the high degree of decomposition of the peat in these sites. The concentrations of , P and K in the top layer of the restored site were closer to those of the natural site, which indicated a possible effect of restoration on the physicochemistry of the restored site. Microbial biomass values derived from the FE technique followed a gradient natural>restored>cutover through the profile, which was not the case with the SIR technique. Values from SIR varied overall between 0.19 and 4.88 mg C g⁻¹ and were significantly higher in the natural site. The natural peatland site had significantly (P<0.05) greater cumulative C-CO₂ production (surface aerobic: 4.5-8.7 μg C-CO₂ g⁻¹ h⁻¹). The poor organic matter quality was the main explanation for the low respiration rates of the surface layer in the restored and the cutover site. All CO₂ respiration data were plotted against time and the resulting curves were successfully fitted to a global kinetic model. Methane production was detected at low but measurable rates in the natural and the restored samples, but not in the cutover peat. Overall, the results confirmed the existence of a lag between the positive response of vegetation to restoration and that of the microbial compartment. This study also pointed out that some physicochemical dysfunctions remained even after three growing seasons following restoration in the subsurface horizons studied.     

地球温暖化国际森林政策比较与我国的对策

针对防止地球温暖化《京都议定书》签约国家的履约现状,在分析国际上有代表性的发达国家——美国、日本和瑞典等国所采取的森林政策的基础上,提出了我国应对这一国际形势的对策。     

东北日光温室葡萄园水热通量特征及其对气象因子的响应

运用温室葡萄水热平衡观测资料,分析了东北日光温室葡萄的能量平衡和能量分量日变化、生育期变化以及分配规律,同时也分析了潜热通量(λET)对环境因子的响应。结果表明:水热通量各分量在整个生育期日变化总体上呈现为单峰趋势,净辐射(R_n)的峰值最大为618.75 W·m^-2,λET峰值最大为242.73 W·m^-2,感热通量(H)峰值最大为327.93 W·m^-2;在新梢生长期,白天λET较小,为34.55 W·m^-2,随着生育期推进,λET逐渐增大,在果实着色成熟期达到最大值(78.49 W·m^-2)之后减小;H在各生育期能量中均占了绝大部分;白天潜热通量占净辐射的比例(λET/R_n)在新梢生长期最小,为25.28%,在果实着色成熟期最大,为44.17%;感热通量占净辐射比例(H/R_n)整个生育期几乎都达50%以上,土壤热通量占净辐射比例(G/R_n)相对较小,变化范围为4.46～12.32 W·m...     

我国农业农村减排固碳标准现状与体系构建

农业农村是温室气体排放源之一，也是固碳增汇的重要方面，我国农业农村领域仍存在减排固碳底数不清、监测方法和核算标准体系不健全、认证缺乏指导依据等问题，因此，亟需构建农业农村减排固碳技术标准体系，充分发挥标准基础性、引领性作用，提升农业农村减排固碳技术水平和管理效能。本文对国内外农业农村领域碳排放、碳减排、固碳等相关标准进行梳理，分析现阶段标准现状和存在的问题，明确建立农业农村减排固碳标准体系的思路及整体框架，加快关键领域标准制定与实施，重点围绕稻田甲烷、农田氧化亚氮、反刍动物肠道甲烷、畜禽粪污管理、秸秆露天焚烧及农村生活用能等“排放源”，农田和渔业“碳汇源”，以及可再生能源替代“减排源”等主要领域，研编一批国家、行业、地方标准，提出标准体系建设有关建议，为推进农业农村领域建立健全统一的碳排放数据监测计量、核算、报告、核查等技术规范体系，推进农业农村绿色发展提供技术支撑。