2.2 Field sampling
All the three sampling sites were located on flat ground with
representative native steppe communities. The sites were fenced to
exclude animal grazing at the beginning of the plant growing season in
2016, and plant and soil samples were collected from these sites at the
end of August. At each site, five quadrates of 1m ×1m were set up at the
center and four corners of a delineated area of 20 m×20 m, and all
standing live and dead vascular plants (that was obviously produced
during the current season) in these quadrats were harvested at ground
level species by species, dried to a constant weight at 65℃ and weighed.
The dry mass of all plant species per quadrat averaged over five
replicates was used to determine the aboveground plant biomass at peak
plant biomass time, and this was also used to approximate ANPP of the
grassland (Scurlock et al., 2002). The belowground biomass and its
distribution profile (0-70 cm) were measured using the soil coring
method, and BNPP (during the plant growing season from May to October)
of the studied grassland was obtained from previous studies (Chai et
al., 2014; Hou et al., 2014).
Whole plants of dominant species at each site were collected by digging
up each individual to a depth of 20 cm below ground level, and then each
individual was cut into two parts: aboveground part (shoots) and
belowground part (noted as roots, but it includes plant roots and
rhizomes as well as shoot stumps buried below the soil surface). A
sample of about 300g dry matter of the shoots and the roots of each
plant species was collected in each of the three plots at each site. The
samples were washed with deionized water, dried at 65℃ and then cut into
pieces (<5mm) for phytolith analysis.
The soil bulk density and moisture content were obtained by the
cutting-ring method and the oven drying method (at 105℃). The soil
samples were collected using soil cores (diameter =7cm) and air dried at
ambient temperature in laboratory.