Microbial functional groups under different land-use types
To study the influence of environmental factors and land-use types on microbial functioning in different river areas, microbial functional groups were predicted based on 16S rRNA gene sequences using FAPROTAX database. Subsequently, Pearson’s correlations between microbial functional groups and environmental factors or land-use types were analyzed. Numerous functional groups were associated with nitrate denitrification, nitrite denitrification, denitrification, N respiration, N fixation, and iron (Fe) and manganese (Mn) respiration in the water of river areas dominated by agricultural land (Weihe River). The predicted functions were significantly positively correlated with multiple environmental factors (e.g., NH4+-N, TP, TN, NO3--N, and NO2--N) and land-use types (agricultural and urbanized land), whereas they had negative correlations with DO, pH, forest land, and shurb land.
There were few denitrification-related functional groups in the water of river areas dominated by forest land (Hanjiang River and Qinling tributaries). However, numerous functional groups were associated with aerobic anoxygenic phototrophy, oxidation, nitrite ammonification, nitrate ammonification, nitrification, aerobic nitrite oxidation, anoxygenic photoautotrophy, and aerobic ammonia (NH3) oxidation in the water of Hanjiang River. The functional groups associated with N fixation were significantly positively correlated with NO2--N, shrub land, and forest land, but negatively correlated with DO, NH4+-N, pH, T, agricultural land, grassland, and urbanized land. Furthermore, there were few functional groups associated with N and P cycles in the water of Qinling tributaries. The relative abundances of N metabolism-related functional groups were significantly higher in the water of Weihe River than in other areas, whereas the relative abundances of carbon metabolism-related functional groups were distinctively higher in the water of Hanjiang River than in the other areas (Fig. 5).