Riparian wetland is a hot area where the nitrogen cycle process occurs, but the multidimensional spatial patterns of the function and structure of nitrogen-cycling microorganisms in rivers at a large scale remain unclear.

Researchers led by Prof. LIU Wenzhi from Wuhan Botanical Garden characterized the distribution of the nitrification and denitrification rates and their communities in channel sediments, riparian rhizosphere soils, and riparian bulk soils (0-20, 40-60, and 160-180 cm) in 30 nitrogen-polluted rivers along a latitudinal gradient across China.

The findings revealed novel insights into the spatial distribution of the nitrification and denitrification rates and their communities in different soil types. At the regional scale, river denitrification rates but not nitrification rates were positively correlated with latitude. In the lateral dimension, the potential denitrification rate was significantly higher in rhizosphere soils than in riparian bulk soils, and the archaeal amoA gene abundance in rhizosphere soils was notably higher than that in sediments. However, the bacterial amoA gene abundance in sediments was greater than that in rhizosphere soils. In the vertical dimension, the nitrification and denitrification rates in riparian zones were both the highest in surface soil (0-20 cm) and decreased with soil depth, and the surface bulk soils in riparian zones generally harbored more and more diverse denitrifying microbes than subsurface bulk soils.

This study underscores the pivotal role of the riparian rhizosphere as a hotspot of nitrogen transformation and removal in river ecosystems. These results not only fill a critical gap in the understanding of the multidimensional spatial patterns of nitrogen-cycling processes in rivers, but also highlight the necessity of considering multiple scale factors in predicting the function and structure of the nitrifiers and denitrifiers communities.

The relevant research results have been published in Water Research entitled “Activity and community structure of nitrifiers and denitrifiers in nitrogen-polluted rivers along a latitudinal gradient”. This work was supported by the China Postdoctoral Science Foundation and the Youth Innovation Promotion Association of Chinese Academy of Sciences.