Accuracy of enteric methane emission models for cattle in sub-Saharan Africa: status quo and the way forward.

Cattle emit over 65% of enteric methane (CH4) in sub-Saharan Africa (SSA), making them the focus of many mitigation strategies targeting livestock emissions. Since measured feed intake data are sparse, emission factors for enteric CH4 (EFCH4) are mainly estimated indirectly from gross energy intake (GEI) using the net energy (NE) requirements for different metabolic processes in cattle. However, all NE requirement systems commonly used for cattle in SSA were developed for cattle in temperate regions. Therefore, we assessed the suitability of different enteric CH4 models for estimating the GEI of cattle in SSA. The Intergovernmental Panel on Climate Change (IPCC) and South African models were identified as the main tier 2-based methods used to estimate enteric CH4 emissions from cattle in SSA. In the IPCC model, EFCH4 was estimated as (GEI * [Ym/100])/55.65, where Ym is the conversion factor (%) of gross energy in feed to CH4 and 55.65 the energy content of CH4 (MJ/kg). The GEI was estimated based on NE requirements for different metabolic processes in cattle as per the American National Research Council. In the South African model, EFCH4 was estimated as (Y/100 * GEI/55.22), where Y is the CH4 yield and 55.22 is the energy content of CH4; Y was calculated from the dry matter (DM) digestibility while GEI was calculated by predicting DM intake and multiplying it by 18.4 MJ (gross energy per kilogram DM). Also, the suitability of the British and German NE requirement systems was assessed as alternatives used for cattle nutrition in SSA. These NE systems were implemented in the IPCC model to yield the "AFRC" and "GfE" models, respectively. The four models were then evaluated using an evaluation dataset summarizing feed quality and DM intake results from 21 studies conducted in SSA, with 125 dietary treatments, and 822 cattle observations. The relative prediction error (RPE) and concordance correlation coefficient (CCC) were used to evaluate the models' accuracy. Only the South African model estimated the GEI in dairy cattle with an acceptable RPE (18.9%) and highest CCC (0.87), while the other three models yielded estimates with RPE > 20%. None of the four models we assessed estimated GEI for other cattle (i.e., nondairy) with an RPE < 20% or CCC > 0.30. The inaccuracy in GEI estimates suggests an error of the same magnitude in EFCH4 estimates. Therefore, a concerted effort is needed to improve the accuracy of enteric CH4 estimation models for cattle in SSA.

Accurate estimates of enteric methane (CH4) emissions are needed to ascertain the efficacy of mitigation strategies proposed for cattle in sub-Saharan Africa (SSA). Models used for cattle in SSA were developed using data on metabolic processes measured from cattle in temperate regions which may lead to inaccurate enteric CH4 estimates. Therefore, we assessed the suitability of different enteric CH4 models for estimating the gross energy intake (GEI) of cattle in SSA. The Intergovernmental Panel on Climate Change (IPCC) and South African models were identified as tier 2-based methods for estimating enteric CH4 emissions from cattle in SSA. Also, the British and German net energy systems were implemented in the IPCC model to yield two other models. These four models were evaluated using a dataset summarizing feed quality and intake results from 21 studies conducted in SSA. Only the South African model estimated the GEI of dairy cattle with an error of <20% (acceptable cutoff point), while the other three models yielded estimates with the error of >20%. None of the four models estimated GEI for nondairy cattle with an error of <20%. We provide the first estimate of model uncertainty that may be applied to enteric CH4 estimates from cattle in SSA.

Optimization of Extraction Process and Dynamic Changes in Triterpenoids of Lactuca indica from Different Medicinal Parts and Growth Periods.

In this study, the triterpenoids in the leaves of Lactuca indica L.cv. Mengzao (LIM) were extracted via microwave-assisted ethanol extraction, and the optimum extraction conditions for triterpenoids were determined through single-factor experiments and the Box-Behnken method. The effects of three factors (solid-liquid ratio, microwave power and extraction time) on the total triterpenoids content (TTC) were evaluated. The TTC of different parts (roots, stems, leaves and flowers) of LIM in different growth stages was studied, and the scavenging effects of the highest TTC parts on DPPH, ABTS and hydroxyl free radicals were investigated. The results showed that the optimum extraction conditions for microwave-assisted extraction of total triterpenoids from LIM leaves were as follows: solid-liquid ratio of 1:20 g/mL; microwave power of 400 W; and extraction time of 60 min. Under these conditions, the TTC was 29.17 mg/g. Compared with the fresh raw materials, the TTC of the materials increased after freeze drying. The leaves of LIM had the highest TTC, and the flowering stage was the best time. The triterpenoids from the leaves had a strong ability to eliminate DPPH and ABTS free radicals, and the elimination effect of dried leaves was better than that of fresh leaves, while the elimination effect of hydroxyl free radicals was not obvious. The tested method was used to extract total triterpenoids from LIM using a simple process at low cost, which provides a reference for developing intensive processing methods for L. indica.

Air warming and CO2 enrichment cause more ammonia volatilization from rice paddies: An OTC field study.

Ammonia (NH3) volatilization in rice paddies may be affected by elevated atmospheric CO2 concentration ([CO2]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO2 enrichment and warming on NH3 volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO2 enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO2] had no significant effects on NH3 volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO2 enrichment might offset the possible enhancement on NH3 volatilization, as more soil N was absorbed by plant thus reducing NH3 loss potential. Elevated temperature increased NH3 volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH4+-N) concentration, pH, and urease activity. Combination of CO2 enrichment and warming caused the highest cumulative NH3 loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH4+-N concentration, pH and urease activity were also observed with co-elevation of [CO2] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO2 enrichment cause more NH3 volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH3 losses under future climate change.

Reconsidering the efficiency of grazing exclusion using fences on the Tibetan Plateau.

Grazing exclusion using fences is a key policy being applied by the Chinese government to rehabilitate degraded grasslands on the Tibetan Plateau (TP) and elsewhere. However, there is a limited understanding of the effects of grazing exclusion on alpine ecosystem functions and services and its impacts on herders' livelihoods. Our meta-analyses and questionnaire-based surveys revealed that grazing exclusion with fences was effective in promoting aboveground vegetation growth for up to four years in degraded alpine meadows and for up to eight years in the alpine steppes of the TP. Longer-term fencing did not bring any ecological and economic benefits. We also found that fencing hindered wildlife movement, increased grazing pressure in unfenced areas, lowered the satisfaction of herders, and rendered substantial financial costs to both regional and national governments. We recommend that traditional free grazing should be encouraged if applicable, short-term fencing (for 4-8 years) should be adopted in severely degraded grasslands, and fencing should be avoided in key wildlife habitat areas, especially the protected large mammal species.

Air warming and CO2 enrichment increase N use efficiency and decrease N surplus in a Chinese double rice cropping system.

Effectiveness of N might be modified in rice cultivation under future climate change with elevated atmospheric CO2 concentration ([CO2]). At present, limited information is available to understand how plant N uptake and N use efficiency respond to elevated [CO2] and/or temperature in Chinese double rice cropping systems. A four-year field experiment was therefore conducted using open-top chambers with varying [CO2] (ambient, ambient +60 µmol mol-1) and varying temperature (ambient, ambient +2 °C) in Hubei Province, Central China. Compared with ambient conditions, elevated [CO2] increased plant N uptake and N use efficiency, as measured by fertilizer N recovery efficiency (NRE), N agronomic efficiency (NAE), N physiological efficiency (NPE) and apparent system N use efficiency (NUEsys), in both early rice and late rice. CO2 enrichment tended to decrease soil mineral N concentration since more N was assimilated by plants. Elevated temperature led to lower plant N uptake and decreased NRE and NAE in early rice, due to a reduction in grain yield induced by heat injury. In contrast, warming increased plant N uptake and N use efficiency in late rice as no heat stress existed. Warming tended to increase soil mineral N concentration in early rice but had negligible effects in late rice. When elevated [CO2] and temperature were combined, the positive effects of CO2 enrichment for N utilization were able to compensate for the negative effects of warming in early rice, while the interaction was synergetic in late rice. Hence, co-elevation of [CO2] and temperature led to higher N use efficiency (64.6% for NUEsys across four years) and decreased annual N surplus by 28.6-36.5 kg N ha-1 compared with ambient conditions. Our findings confirm that CO2 enrichment and air warming can improve N use efficiency at both crop level and system level in Chinese double rice cultivation.

Potential Mechanisms of Abiotic Stress Tolerance in Crop Plants Induced by Thiourea.

Abiotic stresses, such as temperature extremes, drought, salinity, and heavy metals are major factors limiting crop productivity and sustainability worldwide. Abiotic stresses disturb plant growth and yield formation. Several chemical compounds, known as plant growth regulators (PGRs), modulate plant responses to biotic and abiotic stresses at the cellular, tissue, and organ levels. Thiourea (TU) is an important synthetic PGR containing nitrogen (36%) and sulfur (42%) that has gained wide attention for its role in plant stress tolerance. Tolerance against abiotic stresses is a complex phenomenon involving an array of mechanisms, and TU may modulate several of these. An understanding of TU-induced tolerance mechanisms may help improve crop yield under stress conditions. However, the potential mechanisms involved in TU-induced plant stress tolerance are still elusive. In this review, we discuss the essential role of TU-induced tolerance in improving performance of plants growing under abiotic stresses and potential mechanisms underlying TU-induced stress tolerance. We also highlight exploitation of new avenues critical in TU-induced stress tolerance.

Effect of grazing on methane uptake from Eurasian steppe of China.

BACKGROUND: The effects of grazing on soil methane (CH4) uptake in steppe ecosystems are important for understanding carbon sequestration and cycling because the role of grassland soil for CH4 uptake can have major impacts at the global level. Here, a meta-analysis of 27 individual studies was carried out to assess the response patterns of soil CH4 uptake to grazing in steppe ecosystems of China. The weighted log response ratio was used to assess the effect size. RESULTS: We found that heavy grazing significantly depressed soil CH4 uptake by 36.47%, but light and moderate grazing had no significant effects in grassland ecosystem. The response of grassland soil CH4 uptake to grazing also was found to depend upon grazing intensity, grazing duration and climatic types. The increase in soil temperature and reduced aboveground biomass and soil moisture induced by heavy grazing may be the major regulators of the soil CH4 uptake. CONCLUSIONS: These findings imply that grazing effects on soil CH4 uptake are highly context-specific and that grazing in different grasslands might be managed differently to help mitigate greenhouse gas emissions.

Stable carbon isotope as a signal index for monitoring grassland degradation.

Grassland degradation due to overgrazing is common in many areas of the world. This study analyzed the potential of the stable carbon isotope (δ(13)C) value as a structural microcosmic index to monitor processes of grassland degradation. The δ(13)C values of plant leaves, roots and soils in non-grazed (NG) and over-grazed (OG) grassland were measured from samples collected from the seven types of grassland in China. We found that the leaf δ(13)C values of palatable species (δ(13)Cleaf) and root δ(13)C values (δ(13)Croot) in OG grasslands were reduced compared with those from NG grasslands. Furthermore, the δ(13)Cleaf and δ(13)Csoil were positive correlation with elevation and latitude, δ(13)Croot was negative correlation with them at high altitude (3000~5000m), and δ(13)Croot and δ(13)Csoil were negative correlation with them at low altitude (0~2000m), respectively. Consequently, tracing of the δ(13)C variations in grassland ecosystem can provide a powerful tool to evaluate the degree of grassland degradation.

Exploring effective sampling design for monitoring soil organic carbon in degraded Tibetan grasslands.

The effects of climate change and human activities on grassland degradation and soil carbon stocks have become a focus of both research and policy. However, lack of research on appropriate sampling design prevents accurate assessment of soil carbon stocks and stock changes at community and regional scales. Here, we conducted an intensive survey with 1196 sampling sites over an area of 190 km(2) of degraded alpine meadow. Compared to lightly degraded meadow, soil organic carbon (SOC) stocks in moderately, heavily and extremely degraded meadow were reduced by 11.0%, 13.5% and 17.9%, respectively. Our field survey sampling design was overly intensive to estimate SOC status with a tolerable uncertainty of 10%. Power analysis showed that the optimal sampling density to achieve the desired accuracy would be 2, 3, 5 and 7 sites per 10 km(2) for lightly, moderately, heavily and extremely degraded meadows, respectively. If a subsequent paired sampling design with the optimum sample size were performed, assuming stock change rates predicted by experimental and modeling results, we estimate that about 5-10 years would be necessary to detect expected trends in SOC in the top 20 cm soil layer. Our results highlight the utility of conducting preliminary surveys to estimate the appropriate sampling density and avoid wasting resources due to over-sampling, and to estimate the sampling interval required to detect an expected sequestration rate. Future studies will be needed to evaluate spatial and temporal patterns of SOC variability.

[Discussion on reduction potential of CH4 emission intensity for early off-take practice of grazing yak].

The case study preliminarily compared the CH4 reduction potential and CH4 emission intensity of 7 year-old and 4 year-old grazing yak after early off-take practice based on the 2006 IPCC GHG inventory guidelines and under the premise of equal herbage consumption. Our results showed that the total CH4 emission was greater by about 86.3 kg for 2.1 4-year yaks compared with 7 years old yak during their life assuming that their total herbage consumption was the same, because total herbage consumption for a 7-year yak was equal to that of 2.1 4-year yaks. However, CH4 emission per unit body weight (1.374 kg x kg(-1)) for a 7-year yak (i. e. emission intensity) was higher than that of 2.1 4-year yaks (0.973 kg x kg(-1)) because total body weight of 2.1 4-year yaks was higher by 192 kg than that of a 7-year yak. According to CH4 emission intensity, change of the early off-take practice from 7-year to 4-year yak could reduce 77 kg CH4 if producing 192 kg body weight through 2.1 4-year yaks compared with a 7-year yak, i. e. reduction potential was about 1 600 kg CO2 equivalent under the same consuming forage. Therefore, for grassland-based animal husbandry, early off-take practice for grazing animals had a great reduction potential in the intensity of greenhouse gases (GHGs) emissions per unit output rather than total emissions of GHGs.

Alpine grassland soil organic carbon stock and its uncertainty in the three rivers source region of the Tibetan Plateau.

Alpine grassland of the Tibetan Plateau is an important component of global soil organic carbon (SOC) stocks, but insufficient field observations and large spatial heterogeneity leads to great uncertainty in their estimation. In the Three Rivers Source Region (TRSR), alpine grasslands account for more than 75% of the total area. However, the regional carbon (C) stock estimate and their uncertainty have seldom been tested. Here we quantified the regional SOC stock and its uncertainty using 298 soil profiles surveyed from 35 sites across the TRSR during 2006-2008. We showed that the upper soil (0-30 cm depth) in alpine grasslands of the TRSR stores 2.03 Pg C, with a 95% confidence interval ranging from 1.25 to 2.81 Pg C. Alpine meadow soils comprised 73% (i.e. 1.48 Pg C) of the regional SOC estimate, but had the greatest uncertainty at 51%. The statistical power to detect a deviation of 10% uncertainty in grassland C stock was less than 0.50. The required sample size to detect this deviation at a power of 90% was about 6-7 times more than the number of sample sites surveyed. Comparison of our observed SOC density with the corresponding values from the dataset of Yang et al. indicates that these two datasets are comparable. The combined dataset did not reduce the uncertainty in the estimate of the regional grassland soil C stock. This result could be mainly explained by the underrepresentation of sampling sites in large areas with poor accessibility. Further research to improve the regional SOC stock estimate should optimize sampling strategy by considering the number of samples and their spatial distribution.

Sound management may sequester methane in grazed rangeland ecosystems.

Considering their contribution to global warming, the sources and sinks of methane (CH4) should be accounted when undertaking a greenhouse gas inventory for grazed rangeland ecosystems. The aim of this study was to evaluate the mitigation potential of current ecological management programs implemented in the main rangeland regions of China. The influences of rangeland improvement, utilization and livestock production on CH4 flux/emission were assessed to estimate CH4 reduction potential. Results indicate that the grazed rangeland ecosystem is currently a net source of atmospheric CH4. However, there is potential to convert the ecosystem to a net sink by improving management practices. Previous assessments of capacity for CH4 uptake in grazed rangeland ecosystems have not considered improved livestock management practices and thus underestimated potential for CH4 uptake. Optimal fertilization, rest and light grazing, and intensification of livestock management contribute mitigation potential significantly.

Climate change adaptation among Tibetan pastoralists: challenges in enhancing local adaptation through policy support.

While researchers are aware that a mix of Local Ecological Knowledge (LEK), community-based resource management institutions, and higher-level institutions and policies can facilitate pastoralists' adaptation to climate change, policy makers have been slow to understand these linkages. Two critical issues are to what extent these factors play a role, and how to enhance local adaptation through government support. We investigated these issues through a case study of two pastoral communities on the Tibetan Plateau in China employing an analytical framework to understand local climate adaptation processes. We concluded that LEK and community-based institutions improve adaptation outcomes for Tibetan pastoralists through shaping and mobilizing resource availability to reduce risks. Higher-level institutions and policies contribute by providing resources from outside communities. There are dynamic interrelationships among these factors that can lead to support, conflict, and fragmentation. Government policy could enhance local adaptation through improvement of supportive relationships among these factors. While central government policies allow only limited room for overt integration of local knowledge/institutions, local governments often have some flexibility to buffer conflicts. In addition, government policies to support market-based economic development have greatly benefited adaptation outcomes for pastoralists. Overall, in China, there are still questions over how to create innovative institutions that blend LEK and community-based institutions with government policy making.

Effect of stocking rate on soil-atmosphere CH4 flux during spring freeze-thaw cycles in a northern desert steppe, China.

BACKGROUND: Methane (CH(4)) uptake by steppe soils is affected by a range of specific factors and is a complex process. Increased stocking rate promotes steppe degradation, with unclear consequences for gas exchanges. To assess the effects of grazing management on CH(4) uptake in desert steppes, we investigated soil-atmosphere CH(4) exchange during the winter-spring transition period. METHODOLOGY/MAIN FINDING: The experiment was conducted at twelve grazing plots denoting four treatments defined along a grazing gradient with three replications: non-grazing (0 sheep/ha, NG), light grazing (0.75 sheep/ha, LG), moderate grazing (1.50 sheep/ha, MG) and heavy grazing (2.25 sheep/ha, HG). Using an automatic cavity ring-down spectrophotometer, we measured CH(4) fluxes from March 1 to April 29 in 2010 and March 2 to April 27 in 2011. According to the status of soil freeze-thaw cycles (positive and negative soil temperatures occurred in alternation), the experiment was divided into periods I and II. Results indicate that mean CH(4) uptake in period I (7.51 µg CH(4)-C m(-2) h(-1)) was significantly lower than uptake in period II (83.07 µg CH(4)-C m(-2) h(-1)). Averaged over 2 years, CH(4) fluxes during the freeze-thaw period were -84.76 µg CH(4)-C m(-2) h(-1) (NG), -88.76 µg CH(4)-C m(-2) h(-1) (LG), -64.77 µg CH(4)-C m(-2) h(-1) (MG) and -28.80 µg CH(4)-C m(-2) h(-1) (HG). CONCLUSIONS/SIGNIFICANCE: CH(4) uptake activity is affected by freeze-thaw cycles and stocking rates. CH(4) uptake is correlated with the moisture content and temperature of soil. MG and HG decreases CH(4) uptake while LG exerts a considerable positive impact on CH(4) uptake during spring freeze-thaw cycles in the northern desert steppe in China.

The melting Himalayas: cascading effects of climate change on water, biodiversity, and livelihoods.

The Greater Himalayas hold the largest mass of ice outside polar regions and are the source of the 10 largest rivers in Asia. Rapid reduction in the volume of Himalayan glaciers due to climate change is occurring. The cascading effects of rising temperatures and loss of ice and snow in the region are affecting, for example, water availability (amounts, seasonality), biodiversity (endemic species, predator-prey relations), ecosystem boundary shifts (tree-line movements, high-elevation ecosystem changes), and global feedbacks (monsoonal shifts, loss of soil carbon). Climate change will also have environmental and social impacts that will likely increase uncertainty in water supplies and agricultural production for human populations across Asia. A common understanding of climate change needs to be developed through regional and local-scale research so that mitigation and adaptation strategies can be identified and implemented. The challenges brought about by climate change in the Greater Himalayas can only be addressed through increased regional collaboration in scientific research and policy making.