Responses of soil respiration to shrub introduction in the desert steppe of the eastern Ningxia

We aimed to study the responses of soil respiration to shrub introduction in the desert steppe of eastern Ningxia. We selected an enclosed grassland, grazing grassland, and Caragana korshinskii shrubland of different shrub years (22, 12, 3 a) and intervals (40, 6, 2 m) to study the association between soil respiration, moisture, carbon, nitrogen, and microorganisms during grassland grazing and shrub introduction. The results showed that the soil’s moisture in 0 – 10 cm layer had obvious seasonal dynamics, and the introduction of shrubs could consumed much more water in deeper soil. The seasonal changes of soil respiration had correspondence with surface soil moisture. Soil respiration decreased after the introduction of shrubs, and there was no significant difference in different shrub years between the enclosed and grazing grassland, but there were significant differences with the decrease of intervals. Soil’s organic carbon decreased with the deeper soil layer, which decreased with the increasing shrub year and decreasing shrub interval. Soil’s total nitrogen in enclosed grassland was higher than that in shrublands, while that of grazing grassland was comparatively lower. The total nitrogen content increased with increasing shrub year and decreasing shrub interval, but there was no significant difference (P > 0.05). The introduction of shrubs caused significant increase in the number of each microbial community (P < 0.05), but significantly decreased when the planting intervals are 2 m. After the introduction of shrubs, the quantity of microorganisms significantly increased, but significantly decreased with the high density. Soil’s microbial biomass carbon decreased with the introduction of shrubs and increased with the growth of years and reduced with the decreasing shrub interval after growth in certain years. The qCO₂ level decreased with the extension of years and increased with the decrease of intervals. Soil respiration was positively correlated with soil moisture and soil microbial carbon quantity. Soil respiration had significant positive correlation with soil moisture (P < 0.01), negative correlation with soil organic carbon, total nitrogen, and microbial quantity, and the differences significantly negatively correlated between soil respiration and actinomycetes (P < 0.05).