Experimental design, materials and methods
Description of the sites
This experiment was conducted at an alpine meadow in the Haibei
Alpine Meadow Ecosystem Research Station of Chinese Academy of
Science, which is located in a large valley surrounded by the Qilian
Mountain of the northeast of Qinghai-Tibet Plateau (37°
37′N, 101°
12E′)
in Qinghai province. It has a typical highland continental climate with
cold and long winter but cool and short summer. The annual mean air
temperature recorded at the station is −1.7 °C [2]. The day/night temperature
variation is substantial due to strong sun radiation. The annual
mean precipitation is 560 mm and 85% of rainfall is within the growing
season from May to September [3].
The dominant soil type at the station is Mat Cryic Cambisols (a typical
alpine grassland soil) and its pH values are 7.3 and 7.4 at depths of
10 and 20 cm, respectively. Aboveground plant biomass increases
from May to July, reaches the maximum level in late July and early
August, and withers in early October. Over 80% of vegetation species
use C3 photosynthetic pathway for carbon fixation [3].
This experiment, designed to study the effects of climate changes
with the space-substitutes-time strategy, was set at four sites/elevations