2.3 | Field sampling and laboratory analysis
We randomly harvested 30 bunches of C. songorica in each plot in
late August of 2018, corresponding to peak biomass time. Each bunch of
plants with soil were dug out to a depth of 15 cm, with approximately
90% of the roots harvested. The non-rhizosphere soil was defined as
those shaken off from the roots while the rhizosphere soil as those that
adhere to the roots tightly and cannot be shaken off (Chaudhary et al.,
2015). Plants of C. songorica were separated into shoots and
roots, and oven-dried at 65°C for 72 h and weighed. Soil samples from
the same plot were mixed to form a composite sample, thus, we obtained
12 rhizosphere and 12 non-rhizosphere composite soil samples (4
treatments × 3 replications).
Each composite soil sample was equally separated into three portions:
one air-dried, one kept fresh at 4°C, and one stored at -80 °C. The
fresh sample was used to determine the soil moisture and inorganic
nitrogen concentration. Concentrations of ammonium nitrogen and nitrate
nitrogen were measured using a continuous flow analyzer (Auto Analyzer
III, Bran+Luebbe, Germany), and the inorganic nitrogen was their sum.
The air-dried samples were used to determine the concentrations of total
carbon, total nitrogen, total phosphorus, available phosphorus, and the
pH values. Concentrations of total carbon and total nitrogen in
soil/root samples were determined by an element analyzer (Elementar
Vario Micro Cube, Germany), whereas soil total phosphorus and available
phosphorus by a spectrophotometer. Soil pH was measured by a pH meter.
The frozen samples were used to extract DNA for evaluating the richness
and composition of microbial communities.