Publications

Abstract We refine the information available through the IPCC AR 5 with regard to recent trends in global GHG emissions from agriculture, forestry and other land uses ( AFOLU ), including global emission updates to 2012. Using all three available AFOLU datasets employed for analysis in the IPCC AR 5, rather than just one as done in the IPCC AR 5 WGIII Summary for Policy Makers, our analyses point to a down‐revision of global AFOLU shares of total anthropogenic emissions, while providing important additional information on subsectoral trends. Our findings confirm that the share of AFOLU emissions to the anthropogenic total declined over time. They indicate a decadal average of 28.7 ± 1.5% in the 1990s and 23.6 ± 2.1% in the 2000s and an annual value of 21.2 ± 1.5% in 2010. The IPCC AR 5 had indicated a 24% share in 2010. In contrast to previous decades, when emissions from land use (land use, land use change and forestry, including deforestation) were significantly larger than those from agriculture (crop and livestock production), in 2010 agriculture was the larger component, contributing 11.2 ± 0.4% of total GHG emissions, compared to 10.0 ± 1.2% of the land use sector. Deforestation was responsible for only 8% of total anthropogenic emissions in 2010, compared to 12% in the 1990s. Since 2010, the last year assessed by the IPCC AR 5, new FAO estimates indicate that land use emissions have remained stable, at about 4.8 Gt CO 2 eq yr −1 in 2012. Emissions minus removals have also remained stable, at 3.2 Gt CO 2 eq yr −1 in 2012. By contrast, agriculture emissions have continued to grow, at roughly 1% annually, and remained larger than the land use sector, reaching 5.4 Gt CO 2 eq yr −1 in 2012. These results are useful to further inform the current climate policy debate on land use, suggesting that more efforts and resources should be directed to further explore options for mitigation in agriculture, much in line with the large efforts devoted to REDD+ in the past decade.

Abstract Bioenergy crops are often classified (and subsequently regulated) according to species that have been evaluated as environmentally beneficial or detrimental, but in practice, management decisions rather than species per se can determine the overall environmental impact of a bioenergy production system. Here, we review the greenhouse gas balance and ‘management swing potential’ of seven different bioenergy cropping systems in temperate and tropical regions. Prior land use, harvesting techniques, harvest timing, and fertilization are among the key management considerations that can swing the greenhouse gas balance of bioenergy from positive to negative or the reverse. Although the management swing potential is substantial for many cropping systems, there are some species (e.g., soybean) that have such low bioenergy yield potentials that the environmental impact is unlikely to be reversed by management. High‐yielding bioenergy crops (e.g., corn, sugarcane, Miscanthus , and fast‐growing tree species), however, can be managed for environmental benefits or losses, suggesting that the bioenergy sector would be better informed by incorporating management‐based evaluations into classifications of bioenergy feedstocks.

Abstract Aim The identification of stoichiometric flexibility is crucial for understanding carbon–nitrogen–phosphorus ( C – N – P ) interactions and ecosystem dynamics under a changing environment. However, current evidence of stoichiometric flexibility mainly comes from manipulation experiments, with little evidence from large‐scale observations. Location Alpine and temperate grasslands across northern C hina. Methods Using soil profiles derived from a historical national soil inventory and a contemporary regional soil survey across C hina's grasslands, we examined temporal changes in topsoil C : N : P ratios over recent decades. Results Topsoil C:N ratios of five major grassland types exhibited some flexibility but did not show significant changes over the sampling interval. Non‐significant changes in topsoil C : N ratios were observed both in alpine grasslands on the T ibetan P lateau and in temperate grasslands on the Inner Mongolian Plateau. Consistent with the relatively stable C : N ratios, the slope of the soil C – N stoichiometric relationship did not differ significantly between the two sampling periods. Soil N:P ratios in the surface layer increased significantly over the sampling interval, however, with an overall increase of 0.60 (95% confidence interval 0.58–0.62). A larger increase in soil N : P ratio was found in temperate grasslands on the I nner M ongolian P lateau than in alpine grasslands on the T ibetan P lateau. Moreover, the slope of the soil N – P stoichiometric relationship in these grassland ecosystems became steeper over the sampling interval. Main conclusions These results demonstrate the stability of topsoil C : N stoichiometry but variability in N : P stoichiometry over broad geographical scales, highlighting that soil C and N are tightly coupled, but N and P tend to be decoupled under a changing environment.

Summary Food systems require reorientation to take greater account of interactions with the environment, economy, health and society. Transitions to agroecological farming practices and systems can connect policy areas and realise environmental, economic and social aims. These transitions provide a lens for reviewing policy, practice and behaviours of actors in farming systems and value chains, identification of barriers to uptake, and policy areas to which they contribute or where there are gaps. Developing social and human capital, and governance structures that enable transitions to agroecology are key to their prospects of success. Education and life‐long learning are key to developing the knowledge and skills of younger generations of land managers and other actors in value chains, throughout their careers. The outcome sought is for a shared understanding of the benefits of agroecological practices and systems, creating opportunities to rebalance policies towards delivering climate neutrality, reversing biodiversity loss, and enhancing rights of citizens. To realise those opportunities policies and strategies should be coherent across territorial and systems levels, and tailored to place, system, people, and stages of transitions. Overall, they should be designed to ensure all citizens are beneficiaries of transitions to agroecological farming systems, over the long term, and that no‐one or place is disadvantaged by the processes of change or the outcome intended.

Abstract It has long been assumed that nitrogen and phosphorus cycles are closely coupled. However, this assumption has not been rigorously examined under global change, limiting the predictive power of nitrogen and phosphorus cycling. We conducted a meta‐analysis of 1341 data points from 107 published articles on the response of leaf nitrogen and phosphorus resorption efficiency to major global change factors (i.e. warming, drought, increased rainfall, elevated CO 2 , nitrogen fertilization and phosphorus fertilization) over the last two decades. We showed contrast responses of plant nitrogen and phosphorus resorption to these global change factors, indicating a decoupling of plant nitrogen and phosphorus cycles in the face of global change. These divergent responses were primarily driven by the shifts in nitrogen and phosphorus limitations induced by global change, suggesting that the decoupling of nitrogen and phosphorus cycles may be a plant adaptation strategy in response to nutrient limitation. Furthermore, multiple global change factors exerted additive effects on nitrogen and phosphorus resorption, with nitrogen fertilization being the most influential among them. Synthesis. Our results highlight that the decoupling of plant nitrogen and phosphorus cycles should be incorporated into ecological models to accurately predict ecosystem responses to global change.