Uncertainty of Climate Response to Natural and Anthropogenic Forcings Due to Different Land Use Scenarios

The A.M.Obukhov Institute of Atmospheric Physics,Russian Academy of Sciences (IAP RAS) climate model (CM) of intermediate complexity is extended by a spatially explicit terrestrial carbon cycle module.Numerical experiments with the IAP RAS CM are performed forced by the reconstructions of anthropogenic and natural forcings for the 16th to the 20th centuries and by combined SRES (Special Report on Emission Scenarios) A2-LUH (Land Use Harmonization) anthropogenic scenarios for the 21st century.Hereby,the impact of uncertainty in land-use scenarios on results of simulations with a coupled climate-carbon cycle model is tested.The simulations of the model realistically reproduced historical changes in carbon cycle characteristics.In the IAP RAS CM,climate warming reproduced in the 20th and 21st centuries enhanced terrestrial net primary production but terrestrial carbon uptake was suppressed due to an overcompensating increase in soil respiration.Around year 2100,the simulations the model forced by different land use scenarios diverged markedly,by about 70 Pg (C) in terms of biomass and soil carbon stock but they differed only by about 10 ppmv in terms of atmospheric carbon dioxide content.     

Impacts of climate change on primary production and carbon sequestration of boreal Norway spruce forests: Finland as a model

The aim of this study was to estimate the potential impacts of climate change on the spatial patterns of primary production and net carbon sequestration in relation to water availability in Norway spruce (Picea abies) dominated forests throughout Finland (N 60°–N 70°). The Finnish climatic scenarios (FINADAPT) based on the A2 emission scenario were used. According to the results, the changing climate increases the ratio of evapotranspiration to precipitation in southern Finland, while it slightly decreases the ratio in northern Finland, with regionally lower and higher soil water content in the south and north respectively. During the early simulation period of 2000–2030, the primary production and net carbon sequestration are higher under the changing climate in southern Finland, due to a moderate increase in temperature and atmospheric CO₂. However, further elevated temperature and soil water stress reduces the primary production and net carbon sequestration from the middle period of 2030–2060 to the final period of 2060–2099, especially in the southernmost region. The opposite occurs in northern Finland, where the changing climate increases the primary production and net carbon sequestration over the 100-year simulation period due to higher water availability. The net carbon sequestration is probably further reduced by the stimulated ecosystem respiration (under climate warming) in southern Finland. The higher carbon loss of the ecosystem respiration probably also offset the increased primary production, resulting in the net carbon sequestration being less sensitive to the changing climate in northern Finland. Our findings suggest that future forest management should carefully consider the region-specific conditions of sites and adaptive practices to climate change for maintained or enhanced forest production and carbon sequestration.     

Agroecological measures and circular economy strategies to ensure sufficient nitrogen for sustainable farming

Sustainable food systems face trade-offs between demands of low environmental pressures per unit area and requirements of increasing production. Organic farming has lower yields than conventional agriculture and requires the introduction of nitrogen (N) fixing legumes in crop rotations. Here we perform an integrated assessment of the feasibility of future food systems in terms of land and N availability and the potential for reducing greenhouse gas (GHG) emissions. Results show that switching to 100% organic farming without additional measures results in N deficiency. Dietary change towards a reduced share of animal products can aggravate N limitations, which can be overcome through the implementation of a combination of agroecological, circular economy and decarbonization strategies. These measures help to recycle and transfer N from grassland. A vegan diet from fully decarbonized conventional production performs similarly as the optimized organic scenario. Sustainable food systems hence require measures beyond the agricultural sector.     

Sensitivity of the Carbon Storage of Potential Vegetation to Historical Climate Variability and CO2 in Continental China

The interest in the national levels of the terrestrial carbon sink and its spatial and temporal variability with the climate and CO2 concentrations has been increasing. How the climate and the increasing atmospheric CO2 concentrations in the last century affect the carbon storage in continental China was investigated in this study by using the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM). The estimates of the M-SDGVM indicated that during the past 100 years a combination of increasing CO2 with historical temperature and precipitation variability in continental China have caused the total vegetation carbon storage to increase by 2.04 Pg C, with 2.07 Pg C gained in the vegetation biomass but 0.03 Pg C lost from the organic soil carbon matter. The increasing CO2 concentration in the 20th century is primarily responsible for the increase of the total potential vegetation carbon. These factorial experiments show that temperature variability alone decreases the total carbon storage by 1.36 Pg C and precipitation variability alone causes a loss of 1.99 Pg C. The effect of the increasing CO2 concentration alone increased the total carbon storage in the potential vegetation of China by 3.22 Pg C over the past 100 years. With the changing of the climate, the CO2 fertilization on China's ecosystems is the result of the enhanced net biome production (NBP), which is caused by a greater stimulation of the gross primary production (GPP) than the total soil-vegetation respiration. Our study also shows notable interannual and decadal variations in the net carbon exchange between the atmosphere and terrestrial ecosystems in China due to the historical climate variability.     

Greenhouse gas emissions from Mediterranean agriculture: Evidence of unbalanced research efforts and knowledge gaps

Designing effective mitigation policies for greenhouse gas (GHG) emissions from agriculture requires understanding the mechanisms by which management practices affect emissions in different agroclimatic conditions. Agricultural GHG emissions and carbon sequestration potentials have been extensively studied in the Mediterranean biome, which is a biodiversity hot spot that is highly vulnerable to environmental changes. However, the absolute magnitude of GHG emissions and the extent to which research efforts match these emissions in each production system, are unknown. Here, we estimated GHG emissions and potential carbon sinks associated with crop and livestock production systems in the Mediterranean biome, covering 31 countries and assessing approximately 10,000 emission items. The results were then combined with a bibliometric assessment of 797 research publications to compare emissions estimates obtained with research efforts for each of the studied items. Although the magnitude of GHG emissions from crop production and the associated carbon sequestration potential (261 Tg CO₂eq yr⁻¹) were nearly half of those from livestock production (367 Tg CO₂eq yr⁻¹), mitigation research efforts were largely focused on the former. As a result, the relative research intensity, which relates the number of publications to the magnitude of emissions, is nearly one order of magnitude higher for crop production than for livestock production (2.6 and 0.4 papers Tg CO₂eq⁻¹, respectively). Moreover, this mismatch is even higher when crop and livestock types are studied separately, which indicates major research gaps associated with grassland and many strategic crop types, such as fruit tree orchards, fiber crops, roots and tubers. Most life cycle assessment studies do not consider carbon sequestration, although this single process has the highest magnitude in terms of annual CO₂eq. In addition, these studies employ Tier 1 IPCC factors, which are not suited for use in Mediterranean environments. Our analytical results show that a strategic plan is required to extend on-site field GHG measurements to the Mediterranean biome. Such a plan needs to be cocreated among stakeholders and should be based on refocusing research efforts to GHG balance components that have been afforded less attention. In addition, the outcomes of Mediterranean field studies should be integrated into life cycle assessment-based carbon footprint analyses in order to avoid misleading conclusions.     

Carbon Sequestration and Turnover in Semiarid Savannas and Dry Forest

Data on carbon and biomass budgets under different land use in tropical savannas and some dry forests are reviewed. Global data show wide ranges of biomass carbon stocks (20-150 Mg C ha-1), net primary production (2-15 Mg C ha-1y-1) and litter production (2-10 Mg C ha-1y-1) for the semiarid tropics. Although ranges for soil carbon are also wide, an average figure for the top 20 cm is probably 10 g C kg-1, or about 25 Mg C ha-1. In order to arrive at a better understanding of C budgets and their controls, two regional reviews are presented for NE Brazil and W. Africa.In NE Brazil approximately 40% of the lands have "near-climax" native vegetation. Less than 10% of the area is planted annually, but about 3-4 times that area is affected by shifting cultivation which has an average cycle of 5 y arable use followed by 20 y or more recovery. Standing biomass of native caatinga shows nearly the full global range with 2-50 Mg C ha-1. Litter fall around 1-2 Mg C ha-1y-1 is partly decomposed and partly consumed by animals, resulting in low average soil C levels near 8 g kg-1, or 20 Mg C ha-1. Under cultivation, C sequestration is decreased, and soils lose approximately half their C stocks before being abandoned.In W. Africa between 50-70% of the land is under a management regime with minimal C returns to the soils. Overgrazing and over-exploitation for fuel wood has resulted in land degradation. Short fallow periods on cultivated lands have caused serious declines in soil C stocks. Both C sequestration and stocks are therefore lower in W. Africa than in NE Brazil.Improvements in the C sequestration in these semi arid regions depend on an increase in crop production under suitable rotations, improved fallow and animal husbandry, and a limitation on biomnass burning. Use of fertilizer is required for improved productivities but socioeconomic constraints largely prevent such improvements, resulting in a very limited scope for changes in soil C management.     

Impacts of urban expansion on nitrogen and phosphorus flows in the food system of Beijing from 1978 to 2008

Rapid growth of metropolitan areas is associated with increased flows of nitrogen (N) and phosphorus (P) in the food production–consumption system. However, quantitative analyses of these flows during urban expansion and information about their controlling factors are scarce.Here, we report on N and P flows in the food system of Beijing, which experienced a remarkable growth in population number between especially 1978–2008, using a combination of statistical data bases, surveys and the NUFER model (nutrient flow in the food system, environment and resource). The N (or P) cost of food is defined as the amount of ‘new’ N (or P) used in food production for the delivery of 1 kg N (or P) in the food entering household. ‘New’ N (P) includes fertilizer N (P), biological N fixation, atmospheric N deposition, and imports of N (P) via feed and food. Recycled N (P) includes N (P) in crop residues, manures and wastes.We found that the rapid increase in temporary migrants greatly increased food imports to Beijing metropolitan areas and thereby led to an apparent decrease of the N and P cost of food. The input of ‘new’ N to the food system of Beijing metropolitan areas increased from 180 to 281 Gg, and for P from 33.5 to 50.4 Gg during 1978–2008, as a result of increases in population and changes in food consumption patterns per capita. The food and feed imports in per cent of total ‘new’ N and P inputs increased from 31 to 63% for N and from 18 to 46% for P during 1978–2008. The N and P cost of the food was relatively low compared to the mean of China, and decreased over time. About 52% of the new N input and 85% of the new P input was not recycled in 2008, it accumulated as wastes (in crop residues, animal excreta, and human excreta and household wastes). The N and P use efficiencies in crop and animal production were low, i.e., only 17% for N and 11% for P in 2008. Total losses of ammonia (NH₃) and nitrous oxide (N₂O) to air and of N to groundwater and surface waters increased by a factor of about 3, and losses of P to groundwater and surface waters increased by a factor of 37 in the period 1978–2008.Key measures for decreasing N and P accumulation and losses are (1) developing satellite towns, (2) expelling animal production to rural areas, and (3) effective collection of the wastes and animal manure, and the utilization of these in rural areas outside Beijing. These findings may also portend changes in other metropolitan areas in China and elsewhere in the rapidly developing world.     

Tropical soils could dominate the short-term carbon cycle feedbacks to increased global temperatures

Results of a simple model of the effects of temperature on net ecosystem production call into question the argument that the large stocks of soil carbon and greater projected warming in the boreal and tu ndra regions of the world willlead to rapid efflux of carbon from these biomes to the atmosphere. We show that low rates of carbon turnover in these regions and a relatively greater response of net primary production to changes in temperature may lead to carbon storage over some limited range of warming. In contrast, the high rates of soil respiration found in tropical ecosystems are highly sensitive to small changes in temperature, so that despite the less pronounced warming expected in equatorial regions, tropical soils are likely to release relatively large amounts of carbon to the atmosphere. Results for high-latitude biomes are highly sensitive to parameter values used, while the net efflux of carbon from the tropics appears robust.     

A global model of changing N2O emissions from natural and perturbed soils

A high resolution global model of the terrestrial biosphere is developed to estimate changes in nitrous oxide (N₂O) emissions from 1860–1990. The model is driven by four anthropogenic perturbations, including land use change and nitrogen inputs from fertilizer, livestock manure, and atmospheric deposition of fossil fuel NO _x . Global soil nitrogen mineralization, volatilization, and leaching fluxes are estimated by the model and converted to N₂O emissions based on broad assumptions about their associated N₂O yields. From 1860–1990, global N₂O emissions associated with soil nitrogen mineralization are estimated to have decreased slightly from 5.9 to 5.7 Tg N/yr, due mainly to land clearing, while N₂O emissions associated with volatilization and leaching of excess mineral nitrogen are estimated to have increased sharply from 0.45 to 3.3 Tg N/yr, due to all four anthropogenic perturbations. Taking into account the impact of each perturbation on soil nitrogen mineralization and on volatilization and leaching of excess mineral nitrogen, global 1990 N₂O emissions of 1.4, 0.7, 0.4 and 0.08 Tg N/yr are attributed to fertilizer, livestock manure, land clearing and atmospheric deposition of fossil fuel NO _x , respectively. Consideration of both the short and long-term fates of fertilizer nitrogen indicates that the N₂O/fertilizer-N yield may be 2% or more.C. NBM Definitions AET _mon (cm H₂O) = monthly actual evapotranspiration - AET _ann (cm H₂O) = annual actual evapotranspiration - age _h (years) = stand age of herbaceous biomass - age _w (years) = stand age of woody biomass - atmblc (gC/m²/month) = net flux of CO₂ from grid - biotoc (gC/g biomass) = 0.50 = convert g biomass to g C - beff _h = 0.8 = fraction of cleared herbaceous litter that is burned - beff _w = 0.4 = fraction of cleared woody litter that is burned - bfmin = 0.5 = fraction of burned N litter that is mineralized or converted to reactive gases which rapidly redeposit. Remainder assumed pyrodenitrified to N₂. + N₂O - bprob = probability that burned litter will be burned - burn _h (gC/m²/month) = herbaceous litter burned after land clearing - burn _w (gC/m²/month) = woody litter burned after land clearing - cbiomsh (gC/m²) = C herbaceous biomass pool - cbiomsw (gC/m²) = C woody biomass pool - clear (gC/m²/month) = woody litter C removed by land clearing - clearn (gN/m²/month) = woody litter N removed by land clearing - cldh (month^–1) = herbaceous litter decomposition coefficient - cldw (month^–1) = woody litter decomposition coefficient - clittrh (gC/m²) = C herbaceous litter pool - clittrw (gC/m²) = C woody litter pool - clph (month^–1) = herbaceous litter production coefficient - clpw (month^–1) = woody litter production coefficient - cnrath (gC/gN) = C/N ratio in herbaceous phytomass - cnrats (gC/gN) = C/N ratio in soil organic matter - cnratt (gC/gN) = average C/N ratio in total phytomass - cnratw (gC/gN) = C/N ratio in woody phytomass - crod (month^–1) = forest clearing coefficient - csocd (month^–1) = actual soil organic matter decompostion coefficient - decmult decomposition coefficient multiplier; natural =1.0; agricultural =1.0 (1.2 in sensitivity test) - fertmin (gN/m²/month) = inorganic fertilizer input - fleach fraction of excess inorganic N that is leached - fligh (g Lignin/ g C) = lignin fraction of herbaceous litter C - fligw (g Lignin/ g C) = 0.3 = lignin fraction of woody litter C - fln2o = .01–.02 = fraction of leached N emitted as N₂O - fnav = 0.95 = fraction of mineral N available to plants - fosdep (gN/m²/month) = wet and dry atmospheric deposition of fossil fuel NO _x - fresph = 0.5 = fraction of herbaceous litter decomposition that goes to CO₂ respiration - fresps = 0.51 + .068 ^* sand = fraction of soil organic matter decomposition that goes to CO₂ respiration - frespw = 0.3 ^* (^* see comments in Section 2.3 under decomposition) = fraction of woody litter decomposition that goes to CO₂ respiration - fsoil = ratio of NPP measured on given FAO soil type to NPF_miami - fstruct = 0.15 + 0.018 ^* ligton = fraction of herbaceous litter going to structural/woody pool - fvn2o = .05–.10 = fraction of excess volatilized mineral N emitted as N₂O - fvol = .02 = fraction of gross mineralization flux and excess mineral N volatilized - fyield ratio of total agricultural NPP in a given country in 1980 to total NPP_miami of all displaced natural grids in that country - gimmob _h (gN/m²/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of herbaceous litter - gimmob _s (gN/m²/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of soil organic matter - gimmob _w (gN/m²/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of woody litter - graze (gC/m²/month) = C herbaceous biomass grazed by livestock - grazen (gN/m²/month) = N herbaceous biomass grazed by livestock - growth _h (gC/m²/month) = herbaceous litter incorporated into microbial biomass - growth _w (gC/m²/month) = woody litter incorporated into microbial biomass - gromin _h (gN/m²/month) = gross N mineralization due to decomposition and burning of herbaceous litter - gromin _s (gN/m²/month) = gross N mineralization due to decomposition of soil organic matter - gromin _w (gN/m²/month) = gross N mineralization due to decomposition and burning of woody litter - herb herbaceous fraction by weight of total biomass - leach (gN/m²/month) = leaching (& volatilization) losses of excess inorganic N - ligton (g lignin-C/gN) = lignin/N ratio in fresh herbaceous litter - LP _h (gC/m²/month)= C herbaceous litter production - LP (gC/m²/month) = C woody litter production - LPN _h (gN/m²/month) = N herbaceous litter production - LPN _W (gN/m²/month) = N woody litter production - manco2 (gC/m²/month) = grazed C respired by livestock - manlit (gC/m²/month) = C manure input (feces + urine) - n2oint (gN/m²/month) = intercept of N₂O flux vs gromin regression - n2oleach (gN/m²/month) = N₂O flux associated with leaching and volatilization of excess inorganic N - n2onat (gN/m²/month) = natural N₂O flux from soils - n2oslope slope of N₂O flux vs gromin regression - nbiomsh (gN/m²) = N herbaceous biomass pool - nbiomsw (gN/m²) = N woody biomass pool - nfix (gN/m²/month) = N₂ fixation + natural atmospheric deposition - nlittrh (gN/m²) = N herbaceous litter pool - nlittrw (gN/m²) = N woody litter pool - nmanlit (gN/m²/month) = organic N manure input (feces) - nmanmin (gN/m²/month) = inorganic N manure input (urine) - nmin (gN/m²) = inorganic N pool - NPP _acth (gC/m²/month)= actual herbaceous net primary productivity - NPP _actw (gC/m²/month) = actual woody net primary productivity - nvol (gN/m²/month) = volatilization losses from inorganic N pool - plntnav (gN/m²/month)= mineral N available to plants - plntup _h (gN/m²/month) = inorganic N incorporated into herbaceous biomass - plntup _w (gN/m²/month) = inorganic N incorporated into woody biomass - precip _ann (mm) = mean annual precipitation - precip _mon (mm) = mean monthly precipitation - pyroden _h (gN/m²/month) = burned herbaceous litter N that is pyrodenitrified to N₂ - pyroden _w (gN/m²/month) = burned woody litter N that is pyrodenitrified to N₂ - recyc fraction of N that is retranslocated before senescence - resp _h (gC/m²/month) = herbaceous litter CO₂ respiration - resp _s (gC/m²/month) = soil organic carbon CO₂ respiration - resp _w (gC/m²/month) = woody litter CO₂ respiration - sand sand fraction of soil - satrat ratio of maximum NPP to N-limited NPP - soiloc (gC/m²) = soil organic C pool - soilon (gN/m²) = soil organic N pool - temp _ann (°C) = mean annual temperature - temp _mon (°C) = mean monthly temperature Now at the NOAA Aeronomy Laboratory, Boulder, Colorado.     

Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning

In order to estimate the production of charcoal and the atmospheric emissions of trace gases volatilized by burning we have estimated the global amounts of biomass which are affected by fires. We have roughly calculated annual gross burning rates ranging between about 5 Pg and 9 Pg (1 Pg = 10¹⁵ g) of dry matter (2–4 Pg C). In comparison, about 9–17 Pg of above-ground dry matter (4–8 Pg C) is exposed to fires, indicating a worldwide average burning efficiency of about 50%. The production of dead below-ground dry matter varies between 6–9 Pg per year. We have tentatively indicated the possibility of a large production of elemental carbon (0.5–1.7 Pg C/yr) due to the incomplete combustion of biomass to charcoal. This provides a sink for atmospheric CO₂, which would have been particularly important during the past centuries. From meager statistical information and often ill-documented statements in the literature, it is extremely difficult to calculate the net carbon release rates to the atmosphere from the biomass changes which take place, especially in the tropics. All together, we calculate an overall effect lof the biosphere on the atmospheric carbon dioxide budget which may range between the possibilities of a net uptake or a net release of about 2 Pg C/yr. The release of CO₂ to the atmosphere by deforestation projects may well be balanced by reforestation and by the production of charcoal. Better information is needed, however, to make these estimates more reliable.Now at the Max-Planck-Institute for Chemistry, Mainz, FRG.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Satellite-derived estimates of potential carbon sequestration through afforestation of agricultural lands in the United States

Afforestation of marginal agricultural lands represents a promising option for carbon sequestration in terrestrial ecosystems. An ecosystem carbon model was used to generate new national maps of annual net primary production (NPP), one each for continuous land covers of ‘forest’, ‘crop’, and ‘rangeland’ over the entire U. S. continental area. Direct inputs of satellite “greenness” data from the Advanced Very High Resolution Radiometer (AVHRR) sensor into the NASA-CASA carbon model at 8-km spatial resolution were used to estimate spatial variability in monthly NPP and potential biomass accumulation rates in a uniquely detailed manner. The model predictions of regrowth forest production lead to a conservative national projection of 0.3 Pg C as potential carbon stored each year on relatively low-production crop or rangeland areas. On a regional level, the top five states for total crop afforestation potential were: Texas, Minnesota, Iowa, Illinois, and Missouri, whereas the top five states for total rangeland afforestation potential are: Texas, California, Montana, New Mexico, and Colorado. Afforestation at this level of intensity has the capacity to offset at least one-fifth of annual fossil fuel emission of carbon in the United States. These projected afforestation carbon gains also match or exceed recent estimates of the annual sink for atmospheric CO₂ in currently forested area of the country.     

Seasonal and interannual variations of carbon exchange over a rice-wheat rotation system on the North China Plain

Rice-wheat (R-W) rotation systems are ubiquitous in South and East Asia, and play an important role in modulating the carbon cycle and climate. Long-term, continuous flux measurements help in better understanding the seasonal and interannual variation of the carbon budget over R-W rotation systems. In this study, measurements of CO2 fluxes and meteorological variables over an R-W rotation system on the North China Plain from 2007 to 2010 were analyzed. To analyze the abiotic factors regulating Net Ecosystem Exchange (NEE), NEE was partitioned into gross primary production (GPP) and ecosystem respiration. Nighttime NEE or ecosystem respiration was controlled primarily by soil temperature, while daytime NEE was mainly determined by photosythetically active radiation (PAR). The responses of nighttime NEE to soil temperature and daytime NEE to light were closely associated with crop development and photosynthetic activity, respectively. Moreover, the interannual variation in GPP and NEE mainly depended on precipitation and PAR. Overall, NEE was negative on the annual scale and the rotation system behaved as a carbon sink of 982 g C m-2 per year over the three years. The winter wheat field took up more CO2 than the rice paddy during the longer growing season, while the daily NEE for wheat and rice were -2.35 and -3.96 g C m-2, respectively. After the grain harvest was subtracted from the NEE, the winter wheat field became a moderately strong carbon sink of 251-334 g C m-2 per season, whereas the rice paddy switched to a weak carbon sink of 107-132 per season.     

Laboratory studies of some environmental variables controlling sulfur emissions from plants

Several trace sulfur gases that can have a significant influence on atmospheric chemistry are emitted from biological systems. In order to begin to address biological questions on the mechnisms of production of such gases, laboratory-scale experiments have been developed that reproduce such emissions under controlled conditions. Using a flux chamber technique, flats containing soil, or soil plus plants were sampled for the net fluxes of sulfur gases. The major sulfur gas emitted from all the plants tested (corn, alfalfa, and wheat) was dimethyl sulfide (DMS). Alfalfa and wheat also emitted lesser amounts of methanethiol, variable amounls of hydrogen sulfide, and in some experiments wheat emitted carbon disulfide. The use of a plant incubator allowed a systematic study of the effects of variables such as temperature, photon flux, and carbon dioxide levels, on these emissions. Fluxes of all the emitted sulfur gases increased exponentially with increasing air temperature, and increased with increasing photon flux up to a saturation level of \~300 E/m^–2 sec^-1. Three to four-fold changes in DMS flux were observed during light to dark or dark to light transitions. By varying the CO₂ content of the chamber flush gas, it was shown that the observed sulfur fluxes from corn and alfalfa were not related to the CO₂ concentration. Growing these crop plants through holes in a Teflon soil-covering film allowed a separate determination of soil and foliage emissions and substantiation of the light dependent uptake of COS by growing vegetation observed in previous field studies.     

农田生态系统温室气体排放研究进展

自1985年起,中国科学院大气物理研究所利用自行设计制造的自动观测仪器系统,历时十六年先后对我国四大类主要水稻产区的甲烷排放规律及其与土壤、气象条件和农业管理措施的关系进行了系统野外观测实验,并对稻田甲烷产生、转化和输送机理进行了理论研究,探讨了控制稻田甲烷排放的实用措施,建立了估算和预测稻田甲烷排放的数值模型.在甲烷排放的时空变化规律和转化率研究方面有一系列新的发现,在稻田甲烷产生率、排放率及其与环境条件的关系方面取得一系列新的成果,以充分证据改变了国际上关于全球和中国稻田甲烷排放总量的估算.在对稻田甲     

春玉米生长发育、产量和籽粒品质对减量施氮的响应

针对当前东北地区过量施氮的问题,研究减量施氮对春玉米生长发育、产量及籽粒品质的影响,对优化氮肥的科学管理技术,促进春玉米生产绿色高效发展具有重要意义。本研究以丹玉405为试验材料,通过大田播种的方式,以农民习惯性施氮量为对照,设置11.1%、55.5%和100%三个水平减量施氮试验,分析春玉米生长发育、产量和籽粒品质对减量施氮的响应机制。结果表明：玉米苗期,减氮导致生长发育指标（株高、茎粗、叶面积指数、生物量干、鲜重、叶片比重等）均减少,不利于地上部的生长和干物质向叶片分配,随着减氮量的增加,减少幅度增加。苗期以后,适量减氮促进玉米地上部的生长,株高、茎粗、叶面积指数、生物量和叶片占比等生物学性状有增加趋势。适量减氮导致果穗长、果穗粗、百粒重、理论产量、籽粒含水量和淀粉含量增加,籽粒脂肪含量减少,氨基酸和粗蛋白含量呈先增加后减少。随着减氮量的增加,果穗长、果穗粗、百粒重和理论产量增加幅度均减小,籽粒含水量和淀粉含量增加幅度增大,脂肪含量减少幅度减小。减氮11.1%时,果穗长、果穗粗和理论产量增加幅度最大,分别为1.9%、3.7%和11.5%。当施氮量为240 kg·hm^-2（减氮11.1%）时,玉米产量达到最大,为945.4 g·m^-2,籽粒脂肪含量最少,为2.4 g·100 g^-1;氨基酸含量最大,为83.9 μmol·g^-1;粗蛋白含量最高,为6.8%。研究结果可为当地的玉米生产提供更加完善的施肥管理,指导农户科学施肥。     

Modeling N_2O Emissions from Agricultural Fields in Southeast China

l.Intr0ductionWiththedevelopmentofeconomy,theenvironmentalproblemsarebec0mingincreasinglyserious.Am0ngthem,theenhancementofgreenh0useeffectsandglobalwarm-ingaretwoimPOrtantonesthathavear0usedwideattention.Nitrousoxide(N,O)isanim-POrtantgreenhousegasandplayingagreatroleinthesetwoprocesses.SincetheIndustrialRevolution,theatmosphericN2Oconcentrationhasincreasedbyaboutl5%(IPCC,l995).Inthelast4Oyears,itincreasedrapidlyatarateof0.2%ro.3%yr-'(IPCC,l99O).Ifitin-creasesatthisrate,theatmospheri…     

Influences of international agricultural trade on the global phosphorus cycle and its associated issues

Industrial phosphorus (P) fertilizer has substantially improved global food production, but has also led to environmental impacts. Intensive global agricultural trade has increased and the impacts of trade on aggravating or alleviating future P scarcity must be examined, especially for the most vulnerable countries. We combined data to estimate the global P trade among countries and its impacts on global P flows, based on global agricultural trade, cropland soil P budgets and crop P fertilizer footprints (the amount of industrial P fertilizer applied for producing one unit of P in the harvested crop). The global agricultural P trade represented a fraction of 16% of P in harvested crops in 2014, half of which was exported from the United States of America, Brazil and the European Union and one fifth imported by China. Virtual P fertilizer flows (about 2.60 Tg P y^-1) referred to industrial P fertilizers applied to traded crops by exporting countries; thus, 1/3 of global virtual P fertilizer flows were associated with the international soybean trade. P use efficiency (PUE), the ratio of the harvested crop-P to the total external P inputs, is a larger problem for tropical than temperate countries. Global crop trade had brought in a net 0.2 Tg P y^-1 savings of industrial P fertilizers globally, compared to crop production in export and import countries. >0.50 Tg y^-1 of the gross global accumulation of soil P and P in freshwater were associated with global agricultural trade. Global PUE, however, could be improved considerably, and thus global cooperation and improving PUE could help to solve the problem of future P scarcity. Vulnerable countries should also propose urgent national plans to address their own situations of P scarcity or low PUE.     

土壤微生物生物量研究进展

综述了近年来国内外土壤微生物量包括微生物碳、微生物氮、微生物磷和微生物硫及其与碳、氮、磷和硫循环方面的研究进展,着重论述了土壤微生物量C,N,P,S在土壤养分转化循环中的重要性,并就种植、轮作、施肥等农业措施和土壤微生物量与环境的关系包括重金属和农药污染对土壤微生物量的影响进行了探讨。同时,就今后土壤微生物量的研究重点提出了展望。     

The carbon cost of agricultural production in the global land rush

Increases in the number of large-scale land transactions (LSLTs), commonly known as ‘land grabbing’ or ‘global land rush,’ have occurred throughout the lower- and middle-income world over the past two decades. Despite substantial and continuing concerns about the negative socio-environmental impacts of LSLTs, trade-off analysis on boosting crop yield and minimizing climate-related effects remains limited. Our study makes use of a global dataset on LSLTs for agricultural production to estimate potential carbon emissions based on different scenarios of land cover change and fertilizer use, as well as potential value of agricultural production on transacted land. We show that, if fully implemented on ∼ 38 M ha of transacted land, 2.51 GtC will be emitted during land conversion, with another 24.2 MtC/year emitted from fertilizer use, assuming farming technology of investors’ origin is adopted on transacted land. Comparison of different combinations of forest protection policies and agricultural intensification levels reveals that enforcing strict deforestation regulation while promoting fertilizer use rate improves the carbon efficiency of agricultural production. Additionally, positive spillovers of investors’ farming technology on existing arable lands of host countries can potentially double their crop yield. Our analyses thus suggest that fostering agricultural intensification and technology spillovers under strict regulation on land allocation to investors to protect forests would allow for boosting agricultural yield while minimizing carbon emissions.