Research On Carbon Exchange Of Double-cropping Rice Ecosystem And Its Response To Winter Use In Paddy Field

In the double cropping rice ecosystem,there is a significant amount of photosynthetic carbon sequestration in the rice growing season,which may mitigate the global warming.The carbon sequestration and emission of the winter fallow paddy field which last for 4 to 6months have a great effect on the annual carbon balance of the double cropping rice ecosystem.The characteristics of carbon exchange in ecosystems are of great significance to the estimation of regional carbon balance.In this study,the carbon flux of the double-cropping rice ecosystems were monitored by eddy covariance techniques in Liuyang City,Hunan Province.The seasonal characteristics of carbon exchange were analyzed,in order to explore the effects of carbon sequestration and emission of winter fallow paddy field on annual carbon balance of the double-cropping rice ecosystem.In addition,two trials were conducted for"planting grass and rearing chicken-double rice crop"system and"rearing chicken and biochar apply-double rice crop”system in Yun Park base of Hunan Agricultural University,in order to evaluate the effect of two use patterns of paddy field in winter on carbon exchange.The main results are summarized as follows:?1?The net carbon exchange of the double cropping rice ecosystem estimated by both eddy covariance and chamber methods were 778.4 gC·m^-2,which were comprised of the early rice by 147.7 gC·m^-2,the late rice by 127.4 gC·m^-2and the winter fallow by 503.3gC·m^-2.The annual GPP of the double cropping rice ecosystem was 1643.7 gC·m^-2 and the R_eco was 2425.8 gC·m^-2.The contribution rates of NEE,GPP and R_eco by paddy field in winter were 64.7%,17.4%and 31.9%,respectively.The potential of carbon sequestration in the winter paddy field ecosystem was great for its NEE contributed was beyond 50%.The cumulative discharge of CH₄ in the double cropping rice ecosystem was 13.8 g·m^-2 in winter paddy field,86.1 g·m^-2 in early rice growth period,95.9 g·m^-2 in late rice growth period,and the proportion of CH4 emissions in each period was 7.06%,43.98%and 48.96%,respectively,which means that cultivating rice will increase the emission of methane.The SOC have reduced for 1.9g·kg^-1.?2?In the experiment of planting grass and rearing chicken,compared with the control,the treatments of plant grass winter paddy field and plant grass and rearing chicken promoted the carbon emission and the sequestration of photosynthetic carbon in the double cropping rice ecosystem.Among them,the treatments of planting Milkvetch and planting Milkvetch combined with rearing chickens increased the carbon emission and carbon sequestration greatly.The R_eco and GPP the two treatments increased by 42.8%,32.5%and 41.9,32.1%,respectively.Plant Milkvetch and ryegrass may make the double cropping rice ecosystem become weak carbon sinks,at least to reduce the amount of CO₂ emitted by the double cropping rice ecosystem in the winter.The CH₄ emission in the early rice was increased by20%compared with the control in the treatments of planting Milkvetch combined with rearing chicken in winter paddy field.The total CH₄ emission was higher than that of the control by 60.4%in planting Milkvetch treatment.The SOC have improve by 13²0%comparing with the control.?3?Compared with the control,the treatment of rearing chickens with biochar application improved the annual carbon uptake and photosynthetic carbon sequestration of the double cropping rice ecosystem,and the annual NEE increased by 53.9¹05.9%.The treatments of rearing chicken and rearing chicken with biochar application improved the soil organic carbon content up to 12.2²0.4%and 31.1⁶7%.Rearing chicken and rearing chicken with biochar application will also increase the CH₄ emission of early rice ecosystem,and the emission increased by 38%compared with the control.But the total emissions with the addition of biochar will reduce the ecological system CH₄ emissions by 30.6%.The SOC have improve by 33⁶6%comparing with the control.?4?Soil respiration is a major component of carbon emissions from double cropping rice ecosystems,while rice discharges are a major part of CH₄ emissions from double cropping rice ecosystems.For the control group,the soil CO₂ emission in the growth season of the double cropping system accounted for 59%of the total ecosystem carbon emissions,and the soil CH₄ emissions accounted for 43%of the total ecosystem emissions in the trial of rearing chicken with biochar application.The addition of biochar in paddy field in winter could inhibit soil respiration and soil CH₄ emission,and the reduction ratio was 7%and 38%respectively,which indicated that biochar addition is a good mitigation measure for both CO₂ and CH₄.