Variation of Mechanical Composition, Nutrition and Microbial Activity of Alpine Meadow Soil in Greenhouses With Cultivation Age on the Qinghai-Tibet Plateau

An investigation was conducted to explore variation of soil mechanical composition, soil nutrition and microbial activity in alpine meadow soil under greenhouse with cultivation age on the eastern Qinghai-Tibet Plateau. Three greenhouses different in cultivation age, 5, 10 and 15 years, and an open tract of natural meadow were selected for comparison. Results show that: (1) With greenhouse cultivation going on, soil particle size tended to be smaller. Compared to CK, the open tract of natural meadow, in the greenhouse that had been operating for 5, 10 and 15 years, the fraction <10 μm in soil particle size increased by 8.5, 19.3 and 20.3 percentage points, respectively. (2) The contents of all soil nutrients, soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), nitrate (NO₃^--N), soil total phosphorus (TP), and available phosphorus (PO₄^3--P),except ammonia (NH₄⁺-N), and cation exchange capacity (CEC) increased with rising cultivation age, showing a significant tendency of accumulation. In the greenhouse 10 years in cultivation history, TP and PO₄^3--P contents peaked, being 1.4 g·kg^-1 and 80.8 mg·kg^-1, respectively; and in the greenhouse 15 years in cultivation history, SOC, TN, AN, NO₃^--N and CEC increased by 55.1%, 93.8%, 48.5%, 138.3% and 81.8%, respectively, over that in CK. And (3) Soil microbial activity in the greenhouse soils also increased with cultivation age. Compared to CK, the soil in the greenhouse 5 years in cultivation history, was 46.2% and 41.7% higher in the activity of urease and acid phosphatase, respectively; the soil in the greenhouse 10 years in cultivation history was 66.7% and 26.6% higher in content of soil microbial biomass nitrogen and activity of invertase, respectively; and the soil in the greenhouse 15 years in cultivation history was 50.3% and 100.0% higher in content of soil microbial biomass carbon and activity of catalase, respectively. Obviously, sun-light greenhouse cultivation improves physic-chemical properties of the alpine meadow soil and soil enzyme activity, too.