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 (CO and NO) 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 CO and lower NO 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.
Research Highlights: Intensive nitrogen (N) application for agricultural purposes has substantially increased soil nitrous oxide (N2O) emissions. Agricultural soil has great potential in the reduction of N2O emissions, and applications of biochar and nitrification inhibitors may be useful for mitigating agricultural soil N2O emissions. Background and Objectives: Camellia oleifera Abel. is an important woody oil plant in China. However, intensive N input in C. oleifera silviculture has increased the risk of soil N2O emissions. As an important greenhouse gas, N2O is characterized by a global warming potential at a 100-year scale that is 265 times that of carbon dioxide. Thus, mitigation of soil N2O emissions, especially fertilized soils, will be crucial for reducing climate change. Materials and Methods: Here, we conducted an in situ study over 12 months to examine the effects of C. oleifera fruit shell-derived biochar and dicyandiamide (DCD) on soil N2O emissions from a C. oleifera field with intensive N application. Results: A three-fold increase of cumulative soil N2O emissions was observed following N application. Cumulative N2O emissions from the field with N fertilization were reduced by 36% and 44% with biochar and DCD, respectively. While N2O emissions were slightly deceased by biochar, the decrease was comparable to that by DCD. Conclusions: Results indicated that biochar may mitigate soil N2O emissions substantially and similarly to DCD under specific conditions. This result should be examined by prolonged and multi-site studies before it can be generalized to broader scales.
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