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

Researchers led by Prof. LIU Wenzhi from the Wuhan Botanical Garden of the Chinese Academy of Sciences (CAS) 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 results provided new 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 was significantly higher in rhizosphere soils sediments. However, bacterial amoA gene abundance was higher in sediments than in rhizosphere soils.

In the vertical dimension, both nitrification and denitrification rates in riparian zones were both the highest in surface soils (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 highlights the central role of the riparian rhizosphere as a hotspot of nitrogen transformation and removal in riverine 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 need to consider multiple scale factors when predicting the function and structure of nitrifying and denitrifying communities.

The results were 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 CAS.