【草原土壤固碳】Dario A. Fornara1* Lindsay Banin12 Michael J. Crawley3. Multi-nutrient vs. nitrogen-only effects on carbon sequestration in grassland soils. Global Change Biology
Abstract
Human activities have greatly increased the availability of biologically active forms of nutrients [e.g. nitrogen (N) phosphorous (P) potassium (K) magnesium (Mg)] in many soil ecosystems worldwide. Multi-nutrient fertilization strongly increases plant productivity but may also alter the storage of carbon (C) in soil which represents the largest terrestrial pool of organic C. Despite this issue is important from a global change perspective key questions remain on how the single addition of N or the combination of N with other nutrients might affect C sequestration in human-managed soils. Here we use a 19-year old nutrient addition experiment on a permanent grassland to test for nutrient-induced effects on soil C sequestration. We show that combined NPKMg additions to permanent grassland have ‘constrained’ soil C sequestration to levels similar to unfertilized plots whereas the single addition of N significantly enhanced soil C stocks (N-only fertilized soils store on average 11 t C ha−1 more than unfertilized soils). These results were consistent across grazing and liming treatments suggesting that whilst multi-nutrient additions increase plant productivity soil C sequestration is increased by N-only additions. The positive N-only effect on soil C content was not related to changes in plant species diversity or to the functional composition of the plant community. N-only fertilized grasslands show however increases in total root mass and the accumulation of organic matter detritus in topsoils. Finally soils receiving any N addition (N only or N in combination with other nutrients) were associated with high N losses. Overall our results demonstrate that nutrient fertilization remains an important global change driver of ecosystem functioning which can strongly affect the long-term sustainability of grassland soil ecosystems (e.g. soils ability to deliver multiple ecosystem services).
【全球气象数据库与作物产量模拟】Justin van Wart Patricio Grassini Kenneth G. Cassman*. Impact of derived global weather data on simulated crop yields. Global Change Biology
Abstract
Crop simulation models can be used to estimate impact of current and future climates on crop yields and food security but require long-term historical daily weather data to obtain robust simulations. In many regions where crops are grown daily weather data are not available. Alternatively gridded weather databases (GWD) with complete terrestrial coverage are available typically derived from: