Research On Responses Of CO₂Flux In Honghe Wetland

Wetlands are important ecosystems on earth, in addition to the forests and oceans called theworld’s three major ecosystems. The wetland contains rich flora and fauna and microbial resources,it is affectionately known as "the human gene pool" and "Cradle of Humankind". Wetlandecosystems functions significantly in regulating climate, cleaning up the environment, conservingeater, homogenizing flood, recharging groundwater, controlling soil erosion, protection of speciesgenes, biological diversity and other functions, to protect the global climate and ecologicalenvironment plays a vital role, is known as the "kidney of the earth". Sanjiang Plain is China’slargest swamp distribution zone, and the wetland of Sanjiang Plain plays an important role inregulation of surrounding climatic conditions and ecological environment. Honghe Wetland wasconsidered as the most accurate remaining representatives of the pristine landscape of the thisreserve.From May to October of2011, the CO₂flux of wetland was measured monthly over thegrowing seasons with the closed-chamber technique in Honghe Nature Reserve of the SanjiangPlain. CO₂fluxes over the different water treating fields, different N-treatments and straw-returnwere compared and analyzed, the effect of different water levels, nitrogen application andstraw-return CO₂emission from Honghe wetland of the Sanjiang Plain was further discussed.Discussed the influence relations between CO₂flux and meteorological factors. In this study, PPRmethod was applied to predict the CO₂flux in wetland of the Sanjiang Plain.The main conclusions are as follows:（1） In the growth season CO₂flux was highest in July and in lowest in October. CO₂fluxvariation range was463.5mg/（m²Â·h）—1118.2mg/（m²Â·h） in growing season of2011in HongheWetland of Sanjiang Plain.（2） The CO₂flux was more positively correlated with soil temperature of5cm depth than airtemperature and the others at0cm depth,10cm depth,15cm depth, and20cm depth, there wasexponential relationship between CO₂flux and the soil temperature （5cm）. The expression betweenCO₂flux and soil temperature at5cm depth was Y=312.^8e0.05x（R²=0.77）.（3） The CO₂flux showed clear temporal and spatial variations, showing that the emission rateof CO₂was higher in July, and the CO₂fluxes were negatively significantly correlated withstanding water depth. The highest emission flux was at the water depth of20cm, with an average944.3±181.9mg/（m²Â·h）, followed by40cm（799.6±202.8）, and60cm（504.9±166.8）. （4） There was a binomial relationship between CO₂flux and the soil temperature （5cm）. Theapplication of nitrogen fertilizer can improve CO₂flux; ecosystem respiration increased with theincrease of nitrogen amount, the maximum soil respiration rate was at N2PK level, andstraw-return would decrease the CO₂fluxes of N2PK level.（5） In the wetland of Sanjiang Plain during the period of1961-2011, the annual temperatureof the recent51years was increasing at speed of0.32℃/10a; the annual precipitation showed anobvious fluctuations, and decreased by2.65mm/10a without significant; change trend of the annualaverage relative humidity was fluctuate increasing, and the climate trend rate was0.18%/10awithout significant; a significant declining trend of sunshine hours and wind velocity existed, atthe rate of approximately-13.3h/10a and-0.26m/（s·10a）.（6） Correlative correlation analysis indicates that the correlative sequence of the CO₂fluxwith meteorological elements is air temperature> wind speed> sunshine hours> relative humidity> precipitation. There was a relationship of R-square>0.9between the above five factors and CO₂flux. Based on projection pursuit regression（PPR） model, which projects high-dimensional dataonto low-dimensional subspaces and analyses the structure of the data on low-dimension. PPRmodel could access a satisfied prediction being a potential method on the CO₂flux.