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Although the soils in the Tibetan Plateau shrublands store large amounts of total nitrogen (N), the estimated values remain uncertain because of spatial heterogeneity and a lack of field observations. In this study, we quantified the regional soil N storage, spatial and vertical density distributions, and related climatic controls using 183 soil profiles sampled from 61 sites across the Northeast Tibetan Plateau shrublands during the period of 2011-2013. Our analysis revealed a soil N storage value of 132.40 Tg at a depth of 100 cm, with an average density of 1.21 kg m-2. Soil N density was distributed at greater levels in alpine shrublands, compared with desert shrublands. Spatially, soil N densities decreased from south to north and from east to west, and, vertically, the soil Nin the upper 30 and 50 cm accounted for 42% and 64% of the total soilNstocks in the Tibetan Plateau. However, compared with desert shrublands, the surface layers in alpine shrublands exhibited a larger distribution of soil N stocks. Overall, the soil N density in the top 30 cm increased significantly with the mean annual precipitation (MAP) and tended to decrease with the mean annual temperature (MAT), although the dominant climatic controls differed among shrubland types. Specifically, MAP in alpine shrublands, and MAT in desert shrubland, had a weak effect on N density. Soil pH can significant affect soil N density in the Tibetan Plateau shrublands. In conclusion, changes in soil N density should be monitored over the long term to provide accurate information about the effects of climatic factors. [ABSTRACT FROM AUTHOR]

In this study, we examined the year 2011 characteristics of energy flux partitioning and evapotranspiration of a sub-alpine spruce forest underlain by permafrost on the Qinghai-Tibet Plateau (QPT). Energy balance closure on a half-hourly basis was H + λE = 0.81 × ( Rn − G − S) + 3.48 (W m−2) ( r2 = 0.83, n = 14938), where H, λE, Rn, G and S are the sensible heat, latent heat, net radiation, soil heat and air-column heat storage fluxes, respectively. Maximum H was higher than maximum λE, and H dominated the energy budget at midday during the whole year, even in summer time. However, the rainfall events significantly affected energy flux partitioning and evapotranspiration. The mean value of evaporative fraction (Λ = λE/( λE + H)) during the growth period on zero precipitation days and non-zero precipitation days was 0.40 and 0.61, respectively. The mean daily evapotranspiration of this sub-alpine forest during summer time was 2.56 mm day−1. The annual evapotranspiration and sublimation was 417 ± 8 mm year−1, which was very similar to the annual precipitation of 428 mm. Sublimation accounted for 7.1% (30 ± 2 mm year−1) of annual evapotranspiration and sublimation, indicating that the sublimation is not negligible in the annual water balance in sub-alpine forests on the QPT. The low values of the Priestley-Taylor coefficient ( α) and the very low value of the decoupling coefficient (Ω) during most of the growing season suggested low soil water content and conservative water loss in this sub-alpine forest. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]