Sensitivity of global soil carbon stocks to combined nutrient enrichment

Soil stores approximately twice as much carbon as the atmosphere and fluctuations in the size of the soil carbon pool directly influence climate conditions. We used the Nutrient Network global change experiment to examine how anthropogenic nutrient enrichment might influence grassland soil carbon storage at a global scale. In isolation, enrichment of nitrogen and phosphorous had minimal impacts on soil carbon storage. However, when these nutrients were added in combination with potassium and micronutrients, soil carbon stocks changed considerably, with an average increase of 0.04 KgCm−2 year−1 (standard deviation 0.18 KgCm−2 year−1). These effects did not correlate with changes in primary productivity, suggesting that soil carbon decomposition may have been restricted. Although nutrient enrichment caused soil carbon gains most dry, sandy regions, considerable absolute losses of soil carbon may occur in high‐latitude regions that store the majority of the world's soil carbon. These mechanistic insights into the sensitivity of grassland carbon stocks to nutrient enrichment can facilitate biochemical modelling efforts to project carbon cycling under future climate scenarios

Effect of age on bone density and bone turnover in men

ObjectiveLittle is known about the pattern of age-related bone loss in men, and although androgens are required for optimum bone mass it is not clear whether the fall in bone mass with age in men is related to falling androgens.DesignCross-sectional measurement of bone density, at five sites, and markers of bone resorption and formation in 147 normal volunteers aged 20-83 years.SubjectsHealthy laboratory workers, hospital staff, their relatives, and husbands of women attending our osteoporosis clinic.MeasurementsForearm density (fat corrected), spine L2-L4, femoral neck, Ward's triangle and trochanter density; serum procollagen I C-terminal extension peptide, osteocalcin, bone alkaline phosphatase and collagen I C-terminal telopeptide; fasting urine hydroxyproline/creatinine, pyridinoline/creatinine and deoxy-pyridinoline/creatinine; and free androgen index (FAI), measured as serum testosterone/sex hormone binding globulin.ResultsBone loss accelerated at most sites after age 50. There was a significant fall in FAI from the third decade onwards. The levels of all bone markers fell with age.ConclusionsBone loss in men appears to accelerate from age 50 and is associated with decreased bone formation which may be associated with falling levels of free androgen