Storage, patterns and controls of soil nitrogen in China

Soil holds the largest nitrogen (N) pool in terrestrial ecosystems, but estimates of soil N stock remain controversial. Storage and spatial distribution of soil N in China were estimated and the relationships between soil N density and environmental factors were explored using data from China's Second National Soil Survey and field investigation in northwest China and the Tibetan Plateau. China's soil N storage at a depth of one meter was estimated at 7.4 Pg, with an average density of 0.84 kg m(-2). Soil N density appeared to be high in southwest and northeast China and low in the middle areas of the country. Soil N density increased from the arid to semi-arid zone in northern China, and decreased from cold-temperate to tropical zone in the eastern part of the country. An analysis of general linear model suggested that climate and vegetation determined the spatial pattern of soil N density for natural vegetation, which explained 75.4% of the total variance.