Fig. 1. Location of sampling points (Fig. A). Each grassland
type includes a paired no-grazing and grazing site. Fig. B shows a
temperate desert sample site; Fig. C shows a temperate grassland sample
site; Fig. D shows a montane meadow sample site. Fig. E shows the sample
layout.
2.2. Experimental design and field sampling
In July 2021, three areas (Fukang city, Mubi County and Qitai County) on
the eastern section of the northern slope of Tianshan were selected.
Each area corresponded to one grassland type: temperate desert,
temperate steppe and mountain meadow. The test sites were all located
within the national fixed monitoring sites and have been fenced since
2012. The fenced areas are surrounded by spring and autumn grazing areas
for sheep, and the grazing intensity is moderate (0.6-1.0 sheep/ha). At
each site, paired plots (a long-term grazing plot and a grazing
exclusion plot) were sampled. All paired plots shared soil type and
geographical conditions, including slope, elevation, and topography.
Three sample lines were set up at 50-m intervals in each of the grazing
exclusion and grazing areas, and three 1 m × 1 m herb samples were laid
out at approximately 50-m intervals on each sample line (total of 54
small samples). If there were shrubs in the plot, 5 additional shrub
plots (10 m×10 m) were measured. The plant species present in each
square were recorded. For each plant species, its cover, average height,
density and biomass were documented. Plant coverage was measured by the
projection method; natural heights were measured using a ruler, and
individual quantities (densities) of each species were recorded with the
help of statistical methods. The aboveground biomass of each species was
estimated in each sampling plot by clipping the plant from the soil
surface using scissors. The collected plant material was brought back to
the laboratory for treatment (dried at 80 °C for 24 h to a constant
weight). All the plant data are presented in Supplementary Table 1. Soil
samples were collected at two depths: 0-5 cm and 5-10 cm. The samples
from the same sample line and depth were mixed and placed in sealed
bags. The samples were taken back to the laboratory in a vehicle
refrigerator (-20 °C). Half of the samples were stored at 4 °C, while
the rest were air-dried at room temperature. Plant roots, gravel, and
other debris were removed from the air-dried samples. The remaining soil
was ground, mixed, and sieved through 1-mm and 0.25-mm sieves for
analysis.
2.3. Plant community diversity measurement
According to Whittaker’s scientific and comprehensive discussion on an
evaluation index of plant diversity, the α-diversity index is often used
to study the species diversity within a community caused by the
differentiation of interspecific niches within a community and is a
commonly used evaluation index in ecological research (Whittaker, 1977).
This study used the method proposed by Whittaker. The community
structure attributes were characterized by the importance value (IV),
Patrick richness index (R), Simpson dominance index (D), Shannon‒Wiener
diversity index and Pielou index (E)(Wu et al., 2009), and they were
calculated as follows:
Importance value (IV): (1)
Patrick richness index (R): (2)
Simpson dominance index (D): (3)