Abstract
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 N in the upper 30 and 50 cm accounted for 42% and 64% of the total soil N stocks 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.
Highlights
Nitrogen (N) is a significant stimulant of plant growth [1,2] and an important limiting element in terrestrial ecosystems [3]
In the Northeast Tibetan Plateau shrublands, the total soil N storage within a 100 cm depth was estimated at 132.40 Tg
We investigated the soil total N storage, spatial and vertical density patterns, and related environmental factors using 183 soil profiles collected across the Northeast Tibetan Plateau shrublands
Summary
Nitrogen (N) is a significant stimulant of plant growth [1,2] and an important limiting element in terrestrial ecosystems [3]. The levels of anthropogenic reactive nitrogen in the terrestrial ecosystem have increased in recent decades [4,5], and the accelerated industrialization and use of N fertilizer have significantly affected N cycles [1,6,7]. The increase in N deposition is expected to continue [7,10], and reports suggest that soil may function as an N sink in terrestrial ecosystems [11,12]. The dynamics of soil N determine whether the terrestrial ecosystem functions as a N sink or source [14], but can even alter the biogeochemical cycles of other
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