Responses of microbial community composition and respiration to soil moisture in eroded soil

Soil moisture (SM) is one of the most limited factors on the Loess Plateau, but its effects on the microbial community and respiration are still unclear. To investigate the effects of stepwise wetting and constant SM on the soil microbial community and respiration rates, eroded soil under afforestation on the Loess Plateau was examined. The soils were sampled and incubated with constant gravimetric SM of 5 %, 30 % and 45 % and wetting treatments with SM increasing from 5 % to 30 % (5-30 %), from 5 % to 30 % to 45 % (5-30-45 %) and from 30 % to 45 % (30-45 %). As shown in the results, bacterial richness and Shannon diversity were lower in the wetting treatments of 5-30 % and 5-30-45 % than those in 5 %, 30 % and 45 % SM constant treatments. Contrary, the values were similar in the 30 % SM constant and the 30-45 % SM wetting treatment, which were the highest among all the treatments. The dominant bacterial species converted from Actinobacteria to Alphaproteobacteria and Acidobacteria with SM increasing. No significant differences were observed in fungal Shannon diversity, richness and communities under varying conditions. Consequently, the wetting treatments influenced the bacteria more significantly than fungi. A greater Birch effect occurred with a two-step increase in SM (i.e., 5-30-45 %) than the one-step wetting treatment (i.e., 30-45 %), while a dampened Birch effect was observed with higher previous soil respiration. However, excessive moisture did not enhance or even inhibit microbial respiration. Our work indicated that even short-term changes in the antecedent SM can significantly affect bacterial communities and dynamic of carbon flux. The responses of microbe and respiration were not only dependent on the current SM but also related to the antecedent SM condition. This study benefits plant-soil-water relationship management during afforestation on the Loess Plateau of China.