Carbon storage and sequestration potential of selected tree species in India

A dynamic growth model (CO2FIX) was used for estimating the carbon sequestration potential of sal (Shorea Robusta Gaertn. f.), Eucalyptus (Eucalyptus Tereticornis Sm.), poplar (Populus Deltoides Marsh), and teak (Tectona Grandis Linn. f.) forests in India. The results indicate that long-term total carbon storage ranges from 101 to 156 Mg C?ha^?1, with the largest carbon stock in the living biomass of long rotation sal forests (82 Mg C?ha^?1). The net annual carbon sequestration rates were achieved for fast growing short rotation poplar (8 Mg C?ha^?1?yr^?1) and Eucalyptus (6 Mg C?ha^?1?yr^?1) plantations followed by moderate growing teak forests (2 Mg C?ha^?1?yr^?1) and slow growing long rotation sal forests (1 Mg C?ha^?1?yr^?1). Due to fast growth rate and adaptability to a range of environments, short rotation plantations, in addition to carbon storage rapidly produce biomass for energy and contribute to reduced greenhouse gas emissions. We also used the model to evaluate the effect of changing rotation length and thinning regime on carbon stocks of forest ecosystem (trees?+?soil) and wood products, respectively for sal and teak forests. The carbon stock in soil and products was less sensitive than carbon stock of trees to the change in rotation length. Extending rotation length from the recommended 120 to 150 years increased the average carbon stock of forest ecosystem (trees?+?soil) by 12%. The net primary productivity was highest (3.7 Mg ha^?1?yr^?1) when a 60-year rotation length was applied but decreased with increasing rotation length (e.g., 1.7 Mg ha^?1?yr^?1) at 150 years. Goal of maximum carbon storage and production of more valuable saw logs can be achieved from longer rotation lengths. ‘No thinning’ has the largest biomass, but from an economical perspective, there will be no wood available from thinning operations to replace fossil fuel for bioenergy and to the pulp industry and such patches have high risks of forest fires, insects etc. Extended rotation lengths and reduced thinning intensity could enhance the long-term capacity of forest ecosystems to sequester carbon. While accounting for effects of climate change, a combination of bioenergy and carbon sequestration will be best to mitigation of CO₂ emission in the long term.     

Long-term (≥20 years) application of fertilizers and straw return enhances soil carbon storage: a meta-analysis

Increasing soil carbon (C) storage is crucial to addressing climate change and ensuring food security. The C sequestration potential of the world’s cropland soil is 0.4–0.8 Pg soil C year^?1, which may be achieved through the adoption of recommended management practices (RMPs), including fertilizer management. This study aimed to quantitatively evaluate the influence of long-term application of different fertilizers and straw retention on soil organic carbon (SOC) storage, to compare the calculated response ratios with Intergovernmental Panel on Climate Change (IPCC)-recommended default relative stock change factors, and to propose recommendations for enhancing SOC sequestration. The meta-analysis indicated that the long-term application of chemical fertilizers (CF), organic fertilizers (OF), combined chemical and organic fertilizers (CFOF), and straw return (SR) significantly enhanced the SOC storage. Response ratios varied significantly (p < 0.05) across different fertilization measures and climatic zones, and was sensitive to the initial SOC content. The mean response ratio was 0.94 for no fertilizer (NF), 1.08 for CF, 1.48 for OF, 1.38 for CFOF, and 1.28 for SR. When IPCC default values for response ratios were applied, SOC storage with OF and CFOF treatments in warm temperate regions with a dry climate was underestimated by 26%, and in the cool temperate region with a moist climate was overestimated by 25% (p < 0.05). Analysis showed that sustained application of organic fertilizers and straw return could be a beneficial measures to mitigate climate change and ensure food security in China. Our findings highlight the importance of deriving SOC stock change factors for a detailed classification of cropland by fertilizer management, climate, and soil types in order to more accurately reflect the effects of policy measures.     

Estimating net primary production and annual plant carbon inputs, and modelling future changes in soil carbon stocks in arable farmlands of northern Japan

Soil C sequestration in croplands is deemed to be one of the most promising greenhouse gas mitigation options for Japan's agriculture. In this context, changes in soil C stocks in northern Japan's arable farming area over the period of 1971-2010, specifically in the region's typical Andosol (volcanic ash-derived) and non-Andosol soils, were simulated using soil-type-specific versions of the Rothamsted carbon model (RothC). The models were then used to predict the effects, over the period of 2011-2050, of three potential management scenarios: (i) baseline: maintenance of present crop residue returns and green manure crops, as well as composted cattle manure C inputs (24-34 Mg ha⁻¹ yr⁻¹ applied on 3-55% of arable land according to crop), (ii) cattle manure: all arable fields receive 20 Mg ha⁻¹ yr⁻¹ of composted cattle manure, increased C inputs from crop residues and present C inputs from green manure are assumed, and (iii) minimum input: all above-ground crop residues removed, no green manure crop, no cattle manure applied. Above- and below-ground residue biomass C inputs contributed by 8 major crops, and oats employed as a green manure crop, were drawn from yield statistics recorded at the township level and crop-specific allometric relationships (e.g. ratio of above-ground residue biomass to harvested biomass on a dry weight basis). Estimated crop net primary production (NPP) ranged from 1.60 Mg C ha⁻¹ yr⁻¹ for adzuki bean to 8.75 Mg C ha⁻¹ yr⁻¹ for silage corn. For the whole region (143 × 10³ ha), overall NPP was estimated at 952 ± 60 Gg C yr⁻¹ (6.66 ± 0.42 Mg C ha⁻¹ yr⁻¹). Plant C inputs to the soil also varied widely amongst the crops, ranging from 0.50 Mg C ha⁻¹ yr⁻¹ for potato to 3.26 Mg C ha⁻¹ yr⁻¹ for winter wheat. Annual plant C inputs to the soil were estimated at 360 ± 45 Gg C yr⁻¹ (2.52 ± 0.32 Mg C ha⁻¹ yr⁻¹), representing 38% of the cropland NPP. The RothC simulations suggest that the region's soil C stock (0-30 cm horizon), across all soils, has decreased from 13.96 Tg C (107.5 Mg C ha⁻¹ yr⁻¹) in 1970 to 12.46 Tg C (96.0 Mg C ha⁻¹ yr⁻¹) in 2010. For the baseline, cattle manure and minimum input scenarios, soil C stocks of 12.13, 13.27 and 9.82 Tg C, respectively, were projected for 2050. Over the period of 2011-2050, compared to the baseline scenario, soil C was sequestered (+0.219 Mg C ha⁻¹ yr⁻¹) by enhanced cattle manure application, but was lost (−0.445 Mg C ha⁻¹ yr⁻¹) under the minimum input scenario. The effect of variations of input data (monthly mean temperature, monthly precipitation, plant C inputs and cattle manure C inputs) on the uncertainty of model outputs for each scenario was assessed using a Monte Carlo approach. Taking into account the uncertainty (standard deviation as % of the mean) for the model's outputs for 2050 (5.1-6.1%), it is clear that the minimum input scenario would lead to a rapid decrease in soil C stocks for arable farmlands in northern Japan.     

The impact of climate change under different thinning regimes on carbon sequestration in a German forest district

The objective of this paper is to assess how much carbon (C) is currently stored in a forest district in Thuringia, Germany, and how the carbon stocks will develop up to the year 2099 with a changing climate and under various management regimes (including no management), with different assumptions about carbon dioxide (CO₂) fertilization effects. We applied the process-based model 4C and a wood product model to a forest district in Germany and evaluated both models for the period from 2002 to 2010, based on forest inventory data for the stands in the district. Then, we simulated the growth of the stands in the forest district under three different realizations of a climate change scenario, combined with different management regimes. Our simulations show that in 2099, between 630 and 1149 t C ha^?1 will be stored in this district. The simulations also showed that climate change affects carbon sequestration. The no management strategy sequestered the highest amount of carbon (8.7 t C ha^?1 year^?1), which was greater than the management regimes. In the model, the possible fertilization effect of CO₂ is an important factor. However, forest management remains the determining factor in this forest district.     

松嫩平原玉米带农田表层土壤有机碳储量和固碳潜力研究

农田土壤有机碳储量和固碳潜力是陆地碳循环和全球气候变化研究中的一个重要问题。论文基于第二次土壤普查数据和实地取样数据,利用土壤类型法估算松嫩平原玉米带农田表层土壤有机碳储量,分析4个县市(德惠市、九台市、农安县、公主岭市)农田表层土壤碳库的饱和水平和固碳潜力,比较旱田与水田土壤固碳潜力的差异。结果表明,1980-2005年间,松嫩平原玉米带农田土壤有机碳储量增加了7.20 TgC。各县市农田土壤碳库的饱和水平以德惠市最大,为4.11 kgC·m^-2,九台市次之,公主岭市最低,为3.14 kgC·m^-2。假设在1980年土地利用方式、耕作措施、施肥水平和气候条件不变的情况下,估算得到松嫩平原玉米带农田土壤的固碳潜力为8.17 TgC。从单位面积固碳潜力看,九台市最高,为0.77 kgC·m^-2,农安县次之,德惠市和公主岭市均低于松嫩平原玉米带。松嫩平原玉米带旱田和水田土壤碳库的饱和水平基本持平。     

Factors affecting CO<Subscript>2</Subscript> efflux rates and the stability of soil organic carbon storage in volcanic soils of the Canary Islands

Because volcanic soils store large amounts of soil organic carbon (SOC), they play a far more important role in the carbon (C) cycle than their limited global coverage suggests. We analysed the C released as CO₂ from a range of volcanic soils under natural conditions and analysed the influence of environmental variables (moisture and temperature), substrate availability (as assessed from the contents of various SOC fractions and the inputs of plant residues from litterfall), respiratory agents (roots, microorganisms and decomposing enzymes) and other pedological features of the topsoils (0–30 cm depth) on the CO₂ efflux rates over a 2-year experimental period. High CO₂ efflux rates (419 g C-CO₂ m^?2 y^?1 as the average for Andisols) were obtained that were related to significant decreases in the amount of SOC stored. CO₂ release was strongly controlled by soil moisture, although it was inhibited in the Andisols with the highest moisture levels (above 50 kg m^?2 in topsoil). It was not responsive to the availability of decomposing microorganisms or enzymes and appeared more related to the inputs of easily decomposable plant residues than to the amount of either labile or recalcitrant SOC. Among the SOC pools, only the water-soluble C in saturated paste extracts (WSC_se) of air-dried soil samples was consistently correlated with the CO₂ efflux rates. The desiccation of Andisols appeared to induce the release of previously stabilised SOC, which was readily mineralised when the moisture conditions became favourable. The results of this study indicate that SOC storage in Andisols is highly vulnerable to drying-wetting processes even in unmanaged natural ecosystems and that microclimate conditions can be critical for successful C sequestration in these soils.     

Management Options to Conserve and Sequester Carbon in the Agricultural Sector of the Former Soviet Union

Several management practices are available to conserve and sequester C in the agricultural sector of the former Soviet Union (FSU). The highest rate of C accumulation would result from the implementation of a no-till management option which will only continue during the first ten years until new C equilibrium is reached. Agroforestry management options provide a longer period for C accumulation, but at a lower rate. It is possible that the longest period of C conservation may be achieved by increasing the area under perennial grasses in the crop rotation. During the first decade of implementation of the management practices, the amount of C conserved or sequestered would be approximately equal to the current rate of net C sequestration in FSU forest sector. At present, agricultural soils and vegetation of the FSU store approximately 120 Pg C; the accumulation of soil organic matter is 0.032 Pg C yr^-1. The annual C loss in the FSU agricultural sector was estimated at 0.21 Pg C yr^-1.     

Mediterranean shrublands carbon sequestration: environmental and economic benefits

To date, only a few attempts have been done to estimate the contribution of Mediterranean ecosystems to the global carbon cycle. Within this context, shrub species, composition and structure of the Mediterranean shrublands developing along the Latium coast (Italy) were analyzed in order to evaluate their contribution to carbon (C) sequestration, also taking into consideration the economic benefits at a national level. The considered shrublands had a shrub density of 1,200?±?500 shrubs ha^?1. Shrubs were classified into small (S), medium (M) and large (L), according to their volume (V) and leaf area index (LAI). The total yearly carbon dioxide (CO₂) sequestration per species (SC_y) was calculated multiplying the total photosynthetic leaf surface area (spt) of each species by the mean yearly photosynthetic rate and the total yearly photosynthetic activity time (in hours). Q. ilex and A. unedo had the highest SC_y (46.2?±?15.8 kg CO₂ year^?1, mean value), followed by P. latifolia (17.5?±?6.2 kg CO₂ year^?1), E. arborea, E. multiflora, C. incanus, P. lentiscus, R. officinalis, and S. aspera (6.8?±?4.2 kg CO₂ year^?1, mean value). The total yearly CO₂ sequestration per shrub (SC_shy) was 149?±?5 kg CO₂ year^?1 in L, decreasing 30 % in M and 80 % in S shrubs. Taking into account the frequency of S, M and L and their SC_shy, the total CO₂ sequestration of the Mediterranean maquis was quantified in 80 Mg CO₂ ha^?1?year^?1, corresponding to 22 Mg C ha^?1?year^?1. From a monetary viewpoint, this quantity could be valued to more than 500 US$ ha^?1?year^?1. Extending this benefit to the Mediterranean shrublands throughout the whole country, we obtained a nationwide estimated annual benefit in the order of $500 million.     

Is CO2 flux from oil palm plantations on peatland controlled by soil moisture and/or soil and air temperatures?

Measurements of carbon dioxide (CO₂) flux at the soil surface of oil palm (Elaeis guineensis Jacq.) plantations on peatlands typically exhibit considerable temporal and spatial variation, which challenges the derivation of emission factors required in land use discussions. We tested 20 cm surface soil moisture content, and the diurnal patterns in soil and air temperatures as CO₂ flux controls during an annual measurement schedule in a 15-year-old oil palm plantation in Jambi Province, Sumatra, Indonesia. A total of 480 CO₂ flux measurements were obtained using an Infrared Gas Analyser (IRGA) at six different time intervals each day. Samples were recorded at 20 observation points distributed along four transects located 15, 42, 50, 70, and 84 m from the edge of the drainage canal. Results showed CO₂ flux exhibited no relationship to soil and air temperature, however values tended to increase with volumetric soil moisture content; the highest annual flux of 55 Mg ha^?1 yr^?1 was observed at mid-day, when air temperature was highest, and lowest at dawn when soil and air temperatures were lowest. CO₂ flux decreased consistent with distance from the drainage canal, suggesting a higher flux with a deeper water table. This result indicates a shallow water table must be maintained. The annual mean CO₂ flux of 46?±?30 Mg CO₂ ha^?1 yr^?1 was comparable to other studies, and can be set as a baseline emissions factor for areas with similar land use and peat characteristics.     

Root- and peat-based CO2 emissions from oil palm plantations

Measured carbon dioxide (CO₂) flux from peat soils using the closed chamber technique combines root-related (autotrophic + heterotrophic where rhizosphere organisms are involved) and peat-based (heterotrophic) respiration. The latter contributes to peat loss while the former is linked to recent CO₂ removal through photosynthesis. The objective of this study was to separate root- from peat-based respiration. The study was conducted on peatland under 6 and 15 year old oil palm (Elaeis guineensis Jacq.) plantations in Jambi Province, Indonesia in 2011 to 2012. CO₂ emissions were measured in the field from 25 cm diameter and 25 cm tall closed chambers using an infrared gas analyser. Root sampling and CO₂ emissions measurements were at distances of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 m from the centre of the base of the palm tree. The emission rate for the six and 15 year old oil palm plantations at ≥3.0 m from the centre of the tree were 38.2?±?9.5 and 34.1?±?15.9 Mg CO₂ ha^?1 yr^?1, respectively. At distances <2.5 m, total respiration linearly decreased with distances from the trees. Heterotrophic respirations were 86 % of the 44.7?±?11.2 and 71 % of 47.8?±?21.3 Mg CO₂ ha^?1 yr^?1 of weighted surface flux, respectively for the 6 and 15 year old plantations. We propose that CO₂ flux measurements in oil palm plantations made at a distance of ≥3 m from the tree centre be used to represent the heterotrophic respiration that is relevant for the environmental impact assessment.     

Potential and sustainability for carbon sequestration with improved soil management in agricultural soils of China

Arable land soils generally have lower organic carbon (C) levels than soils under native vegetation; increasing the C stocks through improved management is suggested as an effective means to sequester CO₂ from the atmosphere. China's arable lands, accounting for 13% of the world's total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application). Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50% of the arable lands and returning 50% of the crop residue to soils would lead to an annual soil C sequestration of 32.5 Tg C, which accounts for about 4% of China's current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect lasted for only 20–80 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in climate, soil conditions and crop productivity.     

An assessment of carbon stock for various land use system in Aravally mountains, Western India

Reducing carbon emissions from deforestation and degradation in developing countries is of the central importance in efforts to combat climate change. A study was conducted to measure carbon stocks in various land-use systems including forms and reliably estimates the impact of land use on carbon (C) stocks in the forest of Rajasthan, western India (23°3′–30°12′N longitude and 69°30′–78°17′E). 22.8% of India is forested and 0.04% is the deforestation rate of India. In Indian forest sector of western India of Aravally mountain range covered large area of deciduous forest and it’s very helpful in carbon sequestration at global level. The carbon stocks of forest, plantation (reforestation) and agricultural land in aboveground, soil organic and fine root within forest were estimated through field data collection. Results revealed that the amount of total carbon stock of forests (533.64?±?37.54 Mg·ha^?1, simplified expression of Mg (carbon) ·ha^?1) was significantly greater (P?<?0.05) than the plantation (324.37?±?15.0 Mg·ha^?1) and the agricultural land (120.50?±?2.17 Mg·ha^?1). Soil organic carbon in the forests (172.84?±?3.78 Mg·ha^?1) was also significantly greater (P?<?0.05) than the plantation (153.20?±?7.48 Mg·ha^?1) and the agricultural land (108.71?±?1.68 Mg·ha^?1). The differences in carbon stocks across land-use types are the primary consequence of variations in the vegetation biomass and the soil organic matter. Fine root carbon was a small fraction of carbon stocks in all land-use types. Most of the soil organic carbon and fine root carbon content was found in the upper 30-cm layer and decreased with soil depth. The aboveground carbon (ABGC): soil organic carbon (SOC): fine root carbon ratios (FRC), was 8:4:1, 4:5:1, and 3:37:1 for the forest, plantation and agricultural land, respectively. These results indicate that a relatively large proportion of the C loss is due to forest conversion to agricultural land.     

黄土丘陵区小流域土壤碳氮比的变化及其影响因素

研究土壤C:N的变化有助于深入理解土壤有机碳氮的积累过程及其土壤质量的变化趋势。以黄土高原丘陵沟壑区砖窑沟小流域为单元,基于地貌类型和土地利用方式两大因素,采集737个土壤样品,研究流域内土壤C:N的变化差异及其影响因素。梁峁坡上,林地和草地0~20 cm土层的土壤C:N分别是农田土壤C:N的1.13和1.03倍;沟坡上,林地、草地和农田土壤的C:N分别为13.88、12.58、9.02。农田条件下,梁峁坡、沟坡和沟谷的土壤C:N分别为10.34、9.02和10.77;林地条件下,沟坡和梁峁坡的土壤C:N分别为13.88、11.67;草地条件下,沟坡土壤C:N是梁峁坡土壤C:N的1.19倍。同一地貌类型或土地利用方式条件下,土壤C:N均呈现表层大于深层的趋势,0~20 cm和20~40 cm土层的土壤C:N分别是40~100 cm土层土壤C:N的1.05~1.17和1.16~1.42倍。     

The potential of world cropland soils to sequester C and mitigate the greenhouse effect

Soil emission of CO₂ is closely linked to soil degradation, decrease in soil organic carbon (SOC) content and decline in soil quality. Enhancing soil quality through adoption of best management practices (BMPs) and soil restoration can increase SOC content and soil productivity, and partially mitigate the greenhouse effect. The C sequestration potential through judicious management of world cropland includes 0.08–0.12 Pg/yr by erosion control, 0.02–0.03 Pg/yr by restoration of severely degraded soils, 0.02–0.04 Pg/yr by reclamation of salt-affected soils, 0.15–0.175 Pg/yr by adoption of conservation tillage and crop residue management, 0.18–0.24 Pg/yr by adoption of improved cropping system and 0.30–0.40 Pg/yr as C offset through biofuel production. The total C sequestration potential of the world cropland is about 0.75–1.0 Pg/yr or about 50% of annual emission of 1.6–1.8 Pg by deforestation and other agricultural activities. This finite soil-C sink could be filled over a 20 to 50-year period, during which energy related emission reductions gradually take effect at global scale. Improving soil quality is a win–win strategy, while increasing productivity it also improves environment and partially mitigates the greenhouse effect. Intensification of farming and increasing biomass production can lead to increased sequestration of C in soils, and to partly meet commitments under the Kyoto Protocol at national and global scales. Global reduction in C emission may have to be substantial if the atmospheric concentration of CO₂ is to be stabilized at 550 ppmv. However, realization of this potential would require developing channels of communication between scientists and land managers and policy makers, and providing economic incentives.     

黄土高原典型土壤有机碳和微生物碳分布特征的研究

以阐明黄土高原典型区域土壤有机碳(SOC)含量和储量及微生物碳(Mc)含量随土壤类型、土层和土地利用方式变异规律为目的,研究了从北向南依次分布的干润砂质新成土(神木)、黄土正常新成土(延安)和土垫旱耕人为土(杨凌)等典型土壤的SOC含量和储量及Mc含量的变化特征。结果表明,不同土壤类型、不同土层SOC和Mc含量存在显著差异。同一土壤类型SOC和Mc含量在0～60cm随土层深度增加下降很明显,60～120cm土层有轻微下降,120cm土层以下低而稳定,同层次土壤从南到北,SOC、Mc和SOC储量含量显著下降,均以土垫旱耕人为土最高,黄土正常新成土次之,干润砂质新成土最低,且差异显著(P<0.05);0～200cm土层SOC总储量也沿土垫旱耕人为土(102.23±30.12t/hm²)、黄土正常新成土(67.78±9.23t/hm²)、干润砂质新成土(27.07±4.59t/hm²)依次下降;土垫旱耕人为土、黄土正常新成土和干润砂质新成土在100～200cm土层SOC累积量分别是0～100cm土层的65%、74%和58%,因此在研究黄土高原SOC贮量时必需考虑深层贮量的贡献。Mc随土壤类型的变化趋势与SOC基本相同,与SOC间存在极显著正相关关系(P<0.01);土壤Mc/SOC比值范围为0.005～0.05,土地利用仅对干润砂质新成土和土垫旱耕人为土SOC含量和储量影响显著(P>0.05),但对3种土壤Mc和Mc/SOC比值均产生显著影响;与农田土壤相比,草地土壤Mc和Mc/SOC比值均明显增加,这一结果说明用Mc和Mc/SOC比值更能有效反映土壤质量的变化。     

Bio-char Sequestration in Terrestrial Ecosystems – A Review

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (< 10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 ^∘C common for pyrolysis). Existing slash-and-burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr⁻¹. Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 Pg C yr⁻¹ if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr⁻¹). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.     

‘Carbon stocks in a Scots pine afforestation under different thinning intensities management’

Thinning, as a forest management strategy, may contribute towards mitigating climate change, depending on its net effect on forest carbon (C) stocks. Although thinning provides off-site C storage (in the form of wood products) it is still not clear whether it results in an increase, a reduction or no change in on-site C storage. In this study we analyze the effect of thinning on C stocks in a long-term experiment. Different thinning intensities (moderate, heavy and unthinned) have been applied over the last 30 years in a Scots pine (Pinus sylvestris L.) stand, with a thinning rotation period of 10 years. The main C compartments were analyzed: above and belowground tree biomass, deadwood, forest floor and upper 30-cm of the mineral soil and tree biomass removed in thinning treatments. The results revealed that unthinned stands had the highest C stocks with 315 Mg C ha^?1, moderate thinning presented 304 Mg C ha^?1 and heavy thinning 296 Mg C ha^?1, with significant differences between unthinned and heavily thinned stands. These differences were mainly due to C stock in live biomass, which decreased with thinning intensity. However, soil C stocks, forest floor and mineral soil, were not influenced by thinning, all of the stands displaying very similar values 102–107 Mg C ha^?1 for total soil; 15–19 Mg C ha^?1 for forest floor; 87–88 Mg C ha^?1 for mineral soil). These results highlight the sustainability of thinning treatments in terms of C stocks in this pinewood afforestation, and provide valuable information for forest management aimed at mitigating climate change.     

黄土高原纬度梯度上的植物与土壤碳、氮、磷化学计量学特征

选取陕西省延安市的富县、甘泉县、安塞县和榆林市的靖边县、横山县、榆阳区为研究区域,测定和分析研究区植物叶片和不同土层土壤碳(C)、氮(N)、磷(P)含量,阐明植物叶片和土壤化学计量学特征随纬度梯度的变化模式,为预测黄土高原植物营养元素的限制情况和生态系统的土壤养分状况提供依据.结果表明:1在35.95°~38.36°N的纬度范围内,植物叶片C、N、P含量的变化范围分别是336.95~477.38、18.09~33.17和1.07~1.73 mg·g-1,平均值分别为442.9、25.79和1.37 mg·g-1,变异系数分别为11.9%、17.4%和13.3%;植物叶片C、N、P含量与纬度之间存在显著的相关关系,但植物叶片C含量与叶片N、P含量随纬度的变化存在差异:随着纬度的升高,植物叶片C含量随之降低;而叶片N、P含量随之升高.植物叶片C∶N、C∶P均随着纬度的升高,呈现减小趋势;而植物叶片N∶P与纬度的相关关系并不显著.20~10、10~20和20~40 cm这3个土层土壤C和N的空间分布具有一致性,均随着纬度的升高呈指数减小的趋势,且含量随着土层的加深逐级递减;土壤P的空间分布与C、N不同,随着纬度的升高呈现先增加后减少的趋势.0~10 cm、10~20 cm土层土壤C∶N随纬度的升高变化不显著,20~40 cm土壤C∶N随纬度的升高明显下降;3个土层的土壤C∶P、N∶P均随纬度的升高呈指数减少.3植物C、C∶N和C∶P与不同土层的土壤C、N、P均呈现显著的相关关系,植物N、P与土壤C、N呈现显著的相关关系,而叶片N∶P与不同土层土壤的C、N、P相关关系均不显著.研究表明,植物C、N、P含量与纬度之间存在一定的相关性,而植物与土壤的C、N、P含量之间的相关性并不一致,且与全球尺度相比,黄土高原地区草本植物生长更易受磷限制.     

黄土塬区小流域深层土壤有机碳变化的影响因素

以黄土高原沟壑区王东沟小流域为对象,研究了地形(塬面、塬坡和沟道)、土地利用(自然草地、人工草地、人工林地、农地和果园)对0～200cm土层内土壤有机碳(soil organic carbon,SOC)垂直分布特征的影响,以揭示黄土高原小流域深层SOC储量及其影响因素.结果表明,SOC含量除表层(0～20cm)沟道(10.0g·kg-1)大于塬面(7.8g·kg-1)和塬坡(8.2g·kg-1)外,塬面底层SOC均显著高于塬坡和沟道;塬坡和沟道SOC含量随深度增加而降低,而塬面上呈现SOC随深度增加降低-升高-降低的变化趋势.塬面上,SOC含量呈现人工草地(5.4g·kg-1)农田(5.2g·kg-1)和果园(5.1g·kg-1)的趋势,影响深度为表层40cm;塬坡上,呈现自然草地(4.3g·kg-1)人工林地(3.8g·kg-1)人工草地(3.3g·kg-1)和果园(3.3g·kg-1)的趋势,影响深度达到100cm;而沟道内,林草地利用方式对整个垂直剖面分布的差异无显著影响.20～100cm土层SOC储量占0～100cm储量的67.6%;100～200cm土层SOC储量占0～200cm储量的37.3%,相当于0～100cm的63.8%.研究结果表明地形、土地利用显著(p0.05)影响SOC垂直分布特征;黄土高原沟壑区深层SOC储量巨大,不容忽视.     

餐厨垃圾生物发酵液对黄土丘陵区土壤质量的影响试验

黄土广泛分布于我国西北地区,因气候干旱和暴雨侵蚀等因素,土壤养分贫瘠、微生物量稀缺且盐碱化严重,限制了土壤生态承载力,是区域土地荒漠化主要成因之一.餐厨垃圾发酵产生的生物发酵液含有大量的有机酸和氮、磷等营养元素,并且可工业化生产和配施,有望成为一种针对黄土特性的土壤调理剂.以我国黄土高原代表性的甘肃兰州地区黄土为研究对象,采集不同发酵液配施后的黄土进行理化性质和微生物分析,发现施用发酵液后,黄土中全氮、有效磷、速效钾和有机质含量分别提升363%、577%、308%和204%;结合白茎盐生草和苜蓿等植被种植后,土壤综合肥力进一步提升,土壤全盐含量年均分别下降2.3 g·kg^-1和1.2 g·kg^-1;黄土的结构得到改善;发酵液能够促进部分微生物生长,细菌和古菌生物量提升了22倍,真菌生物量提升了8.3倍,有利于进一步形成植物-微生物共生体系.餐厨垃圾生物发酵液结合耐盐碱植物种植,能够有效提升黄土地区生态环境质量.