Distribution characteristics of soil nitrogen during the greening period of forageunder different alpine grasslands in the eastern Qilian Mountain

Abstract

Abstract: Seven different alpine grassland types [Rhododendrons brushland (DJ), Salix cupularis brushland (GL), Potentilla fruticosa brushland (JL), Polygonum viviparum grassland (ZY), Grass steppe (HC), Swamp grassland (ZZ) and Kobresia grassland (SC)] in the eastern Qilian Mountains of the Qinghai-Tibetan Plateau, west China, were investigated for their soil nitrogen [Including microbial biomass nitrogen (MBN), soil total nitrogen, K₂SO₄-extractable nitrogen, alkali-hydrolysable nitrogen and nitrogen density] and their co-relationships. Soil total nitrogen, alkali-hydrolysable nitrogen, and nitrogen density varied from 4.2 to 7.9 g/kg, 104.1 to 234.0 mg/kg, and 0.38 to 0.61 kg/m², respectively. In 2005 and 2006, K₂SO₄-extractable nitrogen ranged from 3.4 to 11.4 mg/kg and 1.8 to 13.9 mg/kg, respectively. The contribution of K₂SO₄-extractable nitrogen to MBN varied from 3.93% to 11.62% in 2005 and 3.88% to 15.37% in 2006. MBN ranged from 49.0 to 143.0 mg/kg in 2005 and 35.9 to 171.7 mg/kg in 2006. MBN showed a significant positive correlation at P<0.05 with K₂SO₄-extractable carbon under brushland and a significant positive correlation at P<0.01 with K₂SO₄-extractable carbon under grassland. It also showed a significant positive correlation at P<0.01 with K₂SO₄-extractable nitrogen under DJ and GL, and a significant positive correlation at P<0.05 with K₂SO₄-extractable nitrogen under JL, ZY, HC, ZZ and SC. With the exception of SC, MBN showed a significant positive correlation at P<0.01 with MBC or MBP. The contribution of K₂SO₄-extractable nitrogen or MBN to soil total nitrogen varied from 0.07% to 0.16% and 1.16% to 1.93% respectively in 2005. In the eastern Qilian Mountains of the Qinghai-Tibetan Plateau, the values of total nitrogen, K₂SO₄-extractable nitrogen, and alkali-hydrolysable nitrogen were differed between the different types of grassland. Furthermore, the type of grassland was the deciding factor for quantity and ecological distribution of soil MBN and plant communities, and was the important factor influencing their quantity and ecological distribution, and the co-relationship between MBN and K₂SO₄-extractable nitrogen or K₂SO₄-extractable carbon. The co-relationship between MBN and MBC or MBP was decided by soil microorganism communities or their community structure.

CLC Number:

YANG Cheng-de, CHEN Xiu-rong, LONG Rui-jun, MAN Yuan-rong, ZHANG Jun-zhong. Distribution characteristics of soil nitrogen during the greening period of forageunder different alpine grasslands in the eastern Qilian Mountain[J]. Acta Prataculturae Sinica, 2010, 19(1): 67-74.

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