Publications

Climate change affects the amount of plant litter inputs to soils around the world, with cascading effects on soil respiration (SR). Soil extracellular enzymes catalyze the rate-limiting steps in soil organic matter decomposition, and can be considered as proxies for SR. Soil cellulase and ligninase are two dominant carbon (C)-degrading enzymes, targeting the decomposition of readily decomposable and structurally complex C pools, respectively. However, whether and how changes in aboveground plant litter inputs influence soil cellulase and ligninase activities as well as the implications for SR remains poorly understood. We conducted a global meta-analysis on the responses of soil cellulase and ligninase activities and SR to litter addition or removal by synthesizing data from 55 studies with the aim of linking soil enzyme activity to SR. Litter addition significantly increased cellulase activity by 25.2%, whereas litter removal significantly decreased it by 25.9%. In contrast, neither litter addition nor removal influenced ligninase activity. The changes in cellulase activity correlated positively with changes in SR, but no such relationship was found for ligninase activity. In addition, the effects of litter addition and removal on cellulase activity decreased with treatment duration. These results indicate that litter alterations affect SR primarily by controlling the microbial decomposition of readily decomposable rather than structurally complex C pools. Altogether, we suggest that the total and long-term effects of litter alterations on SR might be smaller than previously thought.

Abstract. Soil organic carbon sequestration (SOCseq) is considered the most attractive carbon capture technology to partially mitigate climate change. However, there is conflicting evidence regarding the potential of SOCseq. The additional storage potential on existing global cropland is missing. SOCseq is region-specific and conditioned by management but most global estimates use fixed accumulation rates or time frames. Here, we show how the SOC storage potential and its steady state varies globally depending on climate, land use and soil. Using 83,416 soil observations, we developed a quantile regression neural network that quantifies the SOC variation within soils with similar characteristics. This allows us to identify similar areas that present higher SOC with the difference representing an additional storage potential. The estimated additional SOC storage potential of 29 to 67 Pg C in the topsoil of global croplands equates to only 2 to 5 years of emissions offsetting and 32 % of agriculture's 92 Pg historical carbon debt estimate due to conversion from natural ecosystems. Since SOC is temperature-dependent, this potential is likely to reduce by 18 % by 2040 due to climate change.

Abstract Since 1990, the Intergovernmental Panel on Climate Change (IPCC) has produced five Assessment Reports (ARs), in which agriculture as the production of food for humans via crops and livestock have featured in one form or another. A constructed database of the ca. 2,100 cited experiments and simulations in the five ARs was analyzed with respect to impacts on yields via crop type, region, and whether adaptation was included. Quantitative data on impacts and adaptation in livestock farming have been extremely scarce in the ARs. The main conclusions from impact and adaptation are that crop yields will decline, but that responses have large statistical variation. Mitigation assessments in the ARs have used both bottom‐up and top‐down methods but need better to link emissions and their mitigation with food production and security. Relevant policy options have become broader in later ARs and included more of the social and nonproduction aspects of food security. Our overall conclusion is that agriculture and food security, which are two of the most central, critical, and imminent issues in climate change, have been dealt with an unfocussed and inconsistent manner between the IPCC five ARs. This is partly a result of not only agriculture spanning two IPCC working groups but also the very strong focus on projections from computer crop simulation modeling. For the future, we suggest a need to examine interactions between themes such as crop resource use efficiencies and to include all production and nonproduction aspects of food security in future roles for integrated assessment models.