The Variations And Impacting Factors Of Water And Carbon Fluxes In A Rain-fed Maize Cropland

Farmland ecosystem is an important component of the terrestrial ecosystems. Analyzing thevariations and controlling mechanisms of water and carbon cycles is significant for understanding ofmaterial cycles of the terrestrial ecosystems. There are fewer observations of carbon and water fluxes indryland agricultural ecosystem than that in other ecosystems. The study area was located on theexperimental station in Shouyang county, Shanxi province. Based on manipulation experiment andin-situ observation, the impact of rainfall and re-watering after drought on soil respiration were detectedby using LI-8100and LI-8150automated soil CO2flux systems in a rain-fed maize ecosystem. At thesame time, water and carbon fluxes of the rain-fed maize ecosystem were observed continuously byusing two eddy covariance systems in the plastic film mulching and un-mulching fields, respectively. Influxes observation fields, the growth of maize, soil water content and temperature, meteorologicalfactors were observed and measured at the same time. The results showed that:1. Compared with un-mulching treatment, plastic film mulching treatment increased soilvolumetric water content and soil temperature at the early growth period. The germination rate washigher and the growth period was shorter in mulching treatment than that in the un-mulching treatment.The green leaf area index of mulching treatment was higher in the early and middle growth stages andlower in the late growth stage. Plastic film mulching treatment raised plant height, abovegroundbiomass, underground biomass and economic yield by10cm,269.7g·m-2,38.6g·m-2and1348kg·ha-1compared with un-muching treatment, respectively.2. There was a good linear relationship between net carbon flux and green leaf area index. Whenphotosynthetically active radiation and air temperature were less than300μmol·m⁽-2（·s^<sub>-1）and15℃, theywere the limiting factors on variations of net carbon flux. Plastic film mulching suppressed soilrespiration so that it enhanced the soil carbon storage. The net carbon flux in the un-mulching field waslower by0.04mgCO^-2·m·s^-1than that in plastic film mulching field in the early and middle growthstages, however, it was higher by0.02mgCO22·m^-2·s^-1in the late growth stage. The total carbonaccumulation of un-mulching treatment and plastic film mulching treatment were596gC·m^-2and506gC·m^-2, respectively.3. The rainfall affects on water and carbon fluxes significantly. Water and carbon fluxes decreasedduring the rainfall and increased after rainfall, however, the increase range of water flux was higher thanthat of carbon flux. If the soil was drought, the rainfall stimulated soil respiration and the soil respirationdecreased after the rainfall. However, the rainfall inhibited soil respiration if the soil volumetric watercontent was higher than27%and the soil respiration increased after the rainfall.4. There was a good linear relationship between evapotranspiration and green leaf area index.When photosynthetically active radiation was less than400μmol·m^{-2（·s）-1}, it was the limiting factor onvariations of evapotranspiration. Compared with the un-mulching treatment, the mulching treatmentdecreased evapotranspiration by3.32×10^-6mm·s^-1in average between May1and June19; it raisedevapotranspiration by3.09×10^-6mm·s^-1in average between June20and July31; it raised only by 0.14×10^-6mm·s^-1in average between August1and August31; it decreased by0.14×10^-6mm·s^-1inaveage between September1and October8. The total evapotranspiration of un-mulching treatment andplastic film mulching treatment were384mm and376mm respectively.5. At the day-scale and the whole growth period, the variations of water and carbon fluxes bothshowed single peak curve. In day-scale, month-scale and the whole growth period, there were all goodlinear relationships between water and carbon fluxes, and the water use efficiency could be expressedby the slope of the line. At the whole growth period, the water use efficiency of plastic film mulchingtreatment and un-mulching treatment were10.9gCO₂^-2·mm^-1H₂O and9.8gCO₂·mm^-1H₂O, respectively.Plastic film mulching suppressed soil respiration and soil surface evaporation and improved water useefficiency and carbon sequestration in soil.