散射辐射对鄱阳湖平原典型稻田总初级生产力的影响

Effects of Diffuse Radiation on Gross Primary Productivity of Typical Paddy Fields in Poyang Lake Plain

探明散射辐射变化对稻田生态系统总初级生产力(Gross primary productivity,GPP)的影响可为稻田碳汇能力评估和产量估算提供参考。本研究以鄱阳湖平原双季稻田为研究对象,利用涡度相关(Eddy covariance,EC)系统对稻田CO_(2)通量进行了连续两年(2017—2018年)的定位观测,选取水稻生育中期数据,按照散射辐射比例(Diffuse fraction,DF)进行分段,分析了散射辐射对稻田GPP的影响,探明并量化了不同DF条件下散射辐射与其他气象因素对稻田GPP的影响机制。结果表明:不同类型辐射对GPP的影响存在差异,GPP随着直接光合有效辐射(Direct photosynthetically active radiation,PAR_(dir))的增加先迅速增长,随后达到饱和;在不同DF条件下,早晚稻GPP随着散射光合有效辐射(Diffuse photosynthetically active radiation,PAR_(dif))的变化趋势存在差异,当DF为0.1~0.4时,早稻GPP随PAR_(dif)无明显变化趋势,晚稻GPP随PARdif呈上升趋势(决定系数R^(2)为0.23),当DF为0.4~0.7时,早晚稻GPP随PAR_(dif)呈下降趋势(R^(2)为0.38、0.02),当DF为0.7~1.0时,早晚稻GPP随PAR_(dif)呈明显上升趋势(R2为0.32、0.89),可见PAR_(dif)是影响水稻GPP的重要因素。早晚稻GPP与DF呈二次曲线关系(R^(2)为0.45、0.67),早晚稻光能利用效率(Light use efficiency,LUE)则与DF呈显著的线性正相关关系(R^(2)为0.68、0.82),早晚稻最优DF为0.48和0.40。DF变化同时引起气温(Air temperature,T_(a))和饱和水汽压差(Water vapor pressure deficit,VPD)的变化,进而对水稻GPP产生协同影响。气象因素与水稻GPP的通径分析结果表明:不同DF条件下,气象因素对水稻GPP的影响存在明显差异。总体而言,T_(a)和VPD升高分别对水稻GPP起促进和抑制作用,当DF为0.1~0.4、0.4~0.7和0.7~1.0时,影响早稻GPP的主要气象因素为T_(a)、PAR_(dir)和PAR_(dif),影响晚稻GPP的主要气象因素则为PAR_(dif)、PAR_(dir)和PAR_(dif)。

Exploring the impact of diffuse radiation changes on the gross primary productivity(GPP)of paddy ecosystem can provide a reference for the assessment of paddy carbon sink capacity and yield estimation.The eddy covariance(EC)system was used to measure the CO2 flux in the double-cropping paddy field in the Poyang Lake Plain for two consecutive years(2017—2018).The data from the mid-season period of rice was segmented according to the diffuse fraction(DF),and the effect of diffuse radiation and other meteorological factors on GPP under different DF conditions were explored.The results showed that the effects of different types of radiation on GPP were different.For both the early rice and the late rice,GPP and PAR showed a quadratic curve relationship(R^(2) was 0.49 and 0.70).Under different DF conditions,the variation trend of GPP of early and late rice with diffuse photosynthetically active radiation(PAR_(dif))was different.When DF was 0.1~0.4,GPP of early rice did not change significantly with PAR_(dif),GPP of late rice was increased with PAR_(dif)(R^(2)=0.23),and GPP of early and late rice was decreased when DF was 0.4~0.7(R^(2) was 0.38 and 0.02).When DF was 0.7~1.0,GPP of early and late rice showed a significant upward trend with PAR_(dif)(R^(2) was 0.32 and 0.89),indicating that PAR_(dif) was an important factor affecting GPP of rice.As for the direct photosynthetically active radiation(PAR_(dir)),when PAR_(dir) was between 0~10 mol/(m^(2)·d),GPP was increased rapidly with the increase of PAR_(dir),and then tended to be stable.With the increase of DF,GPP and DF showed a quadratic curve relationship(R^(2) was 0.45 and 0.67),while the light use efficiency(LUE)and DF showed a significant linear positive correlation(R^(2) was 0.68 and 0.82).The optimal DF of the early and the late rice were 0.48 and 0.40,respectively.The changes of DF caused the changes of meteorological factors such as air temperature(T_(a))and water vapor pressure deficit(VPD),which had a synergistic effect on rice GPP.The results of path analysis between meteorological factors and GPP showed that the effects of meteorological factors on GPP varied under different DF conditions.Overall,the increase of T_(a) and VPD had positive and negative effects on rice GPP,respectively.T_(a),PAR_(dir) and PAR_(dif) were the main meteorological factors affecting GPP for the early rice,and PAR_(dif),PAR_(dir) and PAR_(dif) were the main meteorological factors for the late rice when DF was 0.1~0.4,0.4~0.7 and 0.7~1.0,respectively.