• Energy Research

AbstractBioenergy crop with carbon capture and storage (BECCS) is a key negative emission technology to meet carbon neutrality. However, the biophysical effects of widespread bioenergy crop cultivation on temperature remain unclear. Here, using a coupled atmosphere-land model with an explicit representation of lignocellulosic bioenergy crops, we find that after 50 years of large-scale bioenergy crop cultivation following plausible scenarios, global air temperature decreases by 0.03~0.08 °C, with strong regional contrasts and interannual variability. Over the cultivated regions, woody crops induce stronger cooling effects than herbaceous crops due to larger evapotranspiration rates and smaller aerodynamic resistance. At the continental scale, air temperature changes are not linearly proportional to the cultivation area. Sensitivity tests show that the temperature change is robust for eucalypt but more uncertain for switchgrass among different cultivation maps. Our study calls for new metrics to take the biophysical effects into account when assessing the climate mitigation capacity of BECCS.

AbstractSoils store more carbon than other terrestrial ecosystems1,2. How soil organic carbon (SOC) forms and persists remains uncertain1,3, which makes it challenging to understand how it will respond to climatic change3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss5–7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways4,6,8–11, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.

AbstractTropical forests store about 70% of the total living biomass on land and yet very little is known about changes in this vital carbon reservoir. Changes in their biomass stock, determined by changes in carbon input (i.e., net primary production [NPP]) and carbon turnover time (τ), are critical to the global carbon sink. In this study, we calculated transient τ in tropical forest biomass using satellite‐based biomass and moderate‐resolution imaging spectroradiometer (MODIS) NPP and analyzed the trends of τ and NPP from 2001 to 2012. Results show that τ and NPP generally have opposite trends across the tropics. Increasing NPP and decreasing τ (“N+T−”) mainly distribute in central Africa and the northeast region of South America, while decreasing NPP and increasing τ (“N−T+”) prevail in Southeast Asia and western Amazon forests. Most of the N+T− tropical forest areas are associated with mean annual precipitation (MAP) below 2,000 mm·y−1 and most N−T+ tropical forests with MAP above 2,000 mm·y−1. The τ and NPP trends in the N+T− region are statistically associated with radiation, precipitation and vapor pressure deficit (VPD), while the τ and NPP trends in the N−T+ region are mainly associated with temperature and VPD. Our results inherit the uncertainties from the satellite‐based datasets and largely depend on the carbon use efficiency from MODIS. We thus systematically assessed the robustness of the findings. Our study reveals regional patterns and potential drivers of biomass turnover time and NPP changes and provides valuable insights into the tropical forest carbon dynamics.