Yak excreta-induced changes in soil microbial communities increased the denitrification rate of marsh soil under warming conditions

Microbial denitrification is a major contributor to the terrestrial production of greenhouse nitrous oxide (N2O). The responses of soil denitrifiers to yak excreta addition in marsh soil under a warming background have not been well evaluated. We investigated the soil physicochemical properties, denitrification rate (DR), enzymes and community of denitrifier genes (nirS and nirK) of marsh soil with different yak excreta additions (dung addition, D; urine addition, U) on the Southeast Qinghai-Tibetan Plateau under three different temperatures (13 degrees C, 19 degrees C and 25 degrees C). Excreta addition significantly increased the DR of marsh soil under different temperatures (P < 0.05). However, as temperature increased, yak excreta addition had no obvious effect on nitrate reductase (NAR) and nitrite reductase (NIR). Excreta addition reduced the diversity of the denitrifier community. nirK was more sensitive to excreta addition and temperature than nirS. For nirK, the proportions of Phyllobacteriaceae and Bradyrhizobiaceae were greater than those of other species and were mainly observed in the control (CK) and U, and Rhizobiaceae was mainly distributed in D. The proportion of Rhizobiaceae increased with increasing temperature, but the proportion of Hyphomicrobiaceae decreased. Unclassified Proteobacteria and unclassified bacteria were the dominant species for nirS. Oxalobacteraceae and Rhodocyclaceae were much more sensitive to temperature changes than other denitrifiers. The nirK community was mainly affected by NO2-N and TOC, but NO2-N and AP had a significant effect on nirS. AP, NO2-N and moisture could affect DR directly or indirectly by affecting the diversity of the denitrifier community and soil enzymes. Our findings suggest that yak excreta addition could profoundly promote DR by regulating the diversity of the denitrifier community of marsh ecosystems under warming conditions.

Automated summary

The addition of yak excreta significantly increased the denitrification rate of marsh soil under different temperatures, but had no obvious effect on nitrate reductase and nitrite reductase as temperature increased. The diversity of the denitrifier community was reduced by excreta addition, with nirK being more sensitive to these additions and temperature changes.