Abstract
The cycle of key nutrient elements nitrogen (N) and phosphorus (P) has been massively altered by anthropogenic activities. Little is known about the impacts on greenhouse gas (GHG) emission of the large nutrient additions occurring in the alpine grasslands of the Tibetan Plateau. We investigated soil surface emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) under control, N, P and combined nitrogen and phosphorus (NP) additions from July 2011 to September 2012. Compared to the control, CO2 flux significantly increased by 14.6% and 27.4% following P and NP addition, respectively. The interaction of NP addition had a significant influence on CO2 flux during the non-growing season and the spring thaw period. Compared to the control, CH4 flux decreased by 9.9%, 23.2% and 26.7% following N, P and NP additions, respectively, and no interactive effect of NP addition was found in any period. Soil N2O flux was significantly increased 2.6 fold and 3.3 fold, following N and NP addition treatments, respectively, and there was no interaction effect of NP addition together. The contribution of cumulative CO2 emission during the non-growing season was less than 20% of the annual budget, but cumulative CH4 and N2O emissions during the same period can account for 37.3–48.9% and 44.7–59.5% of the annual budget, respectively. Methane and N2O emissions did not increase greatly during the spring thawing period, with contributions of only 0.4–3.6% and 10.3–12.3% of the annual budget, respectively. Our results suggest that N and P addition could increase CO2 and N2O emissions and reduce CH4 emission. Furthermore, although the non-growing season is very cold and long, cumulative CH4 and N2O emissions are considerable during this period and cannot be neglected by future studies evaluating the greenhouse gas emission budget in the Tibetan plateau.
Highlights
Global warming is a major issue of common concern for the international community and can be attributed to anthropogenic emissions of greenhouse gases (GHG)
Our results suggest that in the non-growing season, N2O emission from the alpine grassland on the plateau contributes >40% to the annual budget and a greater contribution of N2O emissions during the spring thawing period accounts for more than 10% of the annual budget
The nutrient addition tended to inhibit the flux of CH4 for all periods and P addition significantly altered the sink or source patterns of CH4 during the spring thawing period, meaning that the fertilized alpine grassland was a limited source of CH4
Summary
Global warming is a major issue of common concern for the international community and can be attributed to anthropogenic emissions of greenhouse gases (GHG). With the intensification of global warming, it is necessary to accurately estimate the regional budgets of GHG emissions in the world. Nitrogen and P addition has proved to increase yield and quality of forage and improve the soil availability of farming and animal husbandry [6] but has caused vegetation succession and pasture degradation [7] and extensively influenced the GHG budget [8,9,10]. The influence of P addition on GHG emission has rarely been considered It remains unclear how soil N and P enrichment due to anthropogenic activities affect the Plateau’s GHG budget and its components in alpine grasslands and whether the response of GHG to N is distinct from the response of GHG to P addition
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