The Greenhouse Gas Emissions From The Herbaceous Peatland In The Sanjiang Plain And The Responses To Climate Change

Peatlands, the primary pool of organic carbon in the earth, are extended over vast areas in the northern hemisphere. The carbon sink of peatlands has changed or will change, which is affected by future climatic variability and the increasingly human disturbance(especially in the temperate climate zone). Therefore that will have the feedback to the climate changes. Deeply understanding the dynamic and control mechanism of greenhouse gases is important to accurately estimate carbon emissions and predict the changes in the contact of climate change. In this study, we monitored the temporal dynamics of greenhouse gas emissions from a Carex lasiocarpa dominated peatland in the field of the Sanjiang Plain. We synchronously investigated the influence of precipitation and climate changes on controlling greenhouse gases emissions. The main conclusions are that:(1) The greenhouse gas emissions of herbaceous peatland in the Sanjiang Plain showed significant temporal patterns. Water table and temperature are the main factors controlling the greenhouse gas emissions. The mean values of CH4 emissions in 2012 to 2014 are 5.41±1.01, 9.03±2.21 and 0.31±0.26 mg C m-2 h-1; CO2 fluxes are 261.75 ± 20.61, 166.54 ± 17.72 and 168.39 ± 27.75 mg C m-2 h-1; N2 O emissions are 46.04±6.24, 24.46±3.6, and 0.13±0.03 μg N m-2 h-1. Through step-wise regression, variations in water table, soil temperature at 25 cm depth and soil’s water-filled pore space together explained 66.7% of the observed temporal variation of CH4 fluxes; Variations in soil temperature at 10 cm depth alone explained 73.7% of ecosystem respiration; there was weak relation between N2 O emissions and environmental factors.(2) There were significantly differences dissolved porewater methane concentration in the vertical profile. There was good relation between the methane concentrations in surface layer(5-10cm) and CH4 emissions. The CH4 concentration in the top layer, at the 5 and 10 cm depth, showed significantly lineal relationship correlated with the plant height(R2=0.6, P=0.005) and soil’s water-filled pore space(R2=0.36, P=0.01). The methane concentrations in surface layer controlled 26-60% of the seasonal variations in methane emissions. Meanwhile, rapid and short-lived precipitation events might have no immediate influence on CH4 concentration.(3) The mean Q10 values ranged from 2.1 to 2.9 depending on the choice of depth where soil temperature was measured(5cm, 10 cm, 15 cm, 20 cm and 25cm). Soil respiration played a major role in peatland carbon balance in our study and amounted to 57% of ecosystem respiration in 2012 and 2013. The Q10 value at the 10 cm depth(2.9) appears to be a good representation for herbaceous peatland in the Sanjiang Plain when applying field-estimation based Q10 values to current terrestrial ecosystem models due to the most optimized regression coefficient(73.7%).(4) Alternation between drying and wetting simulated CH4 emission pulses in the two drying-wetting cycles. Emission pulses were observed on the first or third day after water table increasing, which also explained the time lag of CH4 emissions after rapid and short-lived precipitation events in the field. Our study illustrates that CH4 fluxes in the mesocosms exposed to periodic wetting and drying increase the variability and emissions compared with those in constant water table. Peak pulse emissions significantly increased by 46% in peatland and 116% in gley marsh after rewetting as compared to that in the steady 10 cm water table treatment.Peatland had higher CH4 and N2 O emissions than gley marsh under steady water table treatments(P<0.01).(5) The warm had no significant influence on greenhouse gas emissions in the Carex Lasiocarpa-dominated peatland(P>0.05). This may be explained by the signicant changes of soil moisture in the open top chamber, which may cover the differences in CH4 emissions inside and outside the open top chamber. The fire increased 54% of the aboveground biomass of Carex Lasiocarpa. Therefore, it increased the ecosystem respiration. The fire decreased the CH4 emissions although not significantly(P>0.05).(6) The potential CH4 production and oxidation in the different periods after converting peatland to cultivated soil increased along the incubation time and then decreased. The peak values occurred in the fourth or fifth day. The potential CH4 production in natural peatland(1.68 μg g-1 d-1) was larger than that in drainage peatland(1.04μg g-1 d-1), than that in the 7-year cultivation to paddy field(0.04μg g-1 d-1), than that in the 1 year cultivation to soybean field(4.86 ×10-5μg g-1 d-1). There were significant relations among different land use(P<0.001), except that between paddy field and soybean field(P = 0.616). In addition, the drainage peatland had high potential CH4 production after rewetting.