Effects of temperature and moisture treatments on microbial characteristics of arable and grassland soil in dry-hot valley

In order to investigate the influences of temperature and moisture on soil microbial characteristics under different land use types, a laboratory incubation experiment using arable and grassland soils collected from Yuanmou dry-hot valley with a full factorial combination of three temperature levels (15 ℃, 25 ℃ and 35 ℃) and three moisture levels (40%, 60% and 80% water holding capacity-WHC) was conducted. Soil microbial respiration rate, cumulative respiration and microbial metabolic quotient (qCO₂) after 7 d, 14 d and 28 d’s incubations, and soil bacterial community composition after 28 d’s incubation were measured. At each stage of the incubation, microbial respiration rate, cumulative respiration and soil bacterial community diversity (Shannon index) in grassland soil were significantly higher than those in arable soil, while microbial metabolic quotient in grassland soil was significantly lower than that in arable soil (P < 0.05). Soil respiration rate and cumulative respiration in both soils increased significantly with the temperature. The Q₁₀ value at the middle stage of the incubation (14 d) was significantly higher than that at the early (7 d) and late (28 d) stages (P < 0.05). The water treatment had different effects on microbial respirations for different soils, and the cumulative respiration under 60% WHC was larger than those under the other two water treatments. ANOSIM similarity tests suggested that land-use type had a great effect on soil bacterial community composition (r = 0.715, P < 0.01). Compared to arable soil, the bacterial community structure in grassland soil was more sensitive to the temperature and moisture treatments. The relative abundances of dominant groups in grassland and arable soils varied differently with the temperature and water levels.