Effects of moso bamboo (Phyllostachys edulis) invasions on soil nitrogen cycles depend on invasion stage and warming

Plant invasions may alter soil nutrient cycling due to differences in physiological traits between the invader and species they displace as well as differences in responses to anthropogenic factors such as nitrogen deposition and warming. Moso bamboo is expanding its range rapidly around the world, displacing diverse forests. In addition, near expansion fronts where invasions are patchy, moso bamboo and other species each contribute soil inputs. Nitrogen transformations and greenhouse gas (GHG) emissions are important processes associated with nutrient availability and climate change that may be impacted by bamboo invasions. We collected soils from uninvaded, mixed, and bamboo forests to understand bamboo invasion effects on carbon and N cycling. We incubated soils with warming and N addition and measured net nitrification and N mineralization rates and GHG (CO₂ and N₂O) emissions. Mixed forest soils had higher pH and total N and lower total organic carbon and C/N than either uninvaded or bamboo forest soils. Bamboo forest soils had higher total carbon, dissolved organic carbon, and ammonium N but lower total and nitrate N than uninvaded forest soils. Soil GHG emissions did not vary among forest types at lower temperatures but bamboo forest soils had higher CO₂ and lower N₂O emissions at higher temperatures. While net N transformation rates were lower in bamboo and uninvaded forest soils, they were highest in mixed forest soils, indicating non-additive effects of bamboo invasions. This suggests that plant invasion effects on N transformations and GHG emissions with global change in forests partially invaded by bamboo are difficult to predict from only comparing uninvaded and bamboo-dominated areas.