不同作物农田的土壤呼吸与高光谱的关系

Relationships between soil respiration and hyperspectrum in different croplands

为研究种植不同作物的农田土壤呼吸与高光谱植被指数的关系,选取3种典型夏熟作物冬小麦、油菜籽、蚕豆,于2018年10月至2019年5月进行田间随机区组试验,观测土壤呼吸、土壤温度、土壤湿度的季节动态,并观测NDVI(归一化植被指数)、DVI(差值植被指数)、RVI(比值植被指数)、EVI(增强植被指数)、PRI(光化学植被指数)5种高光谱植被指数和叶绿素SPAD值。结果表明:冬小麦、油菜籽、蚕豆田土壤呼吸季节平均值分别为1.78±0.15、1.35±0.27、1.61±0.22μmol·m^-2·s-1,冬小麦田土壤呼吸显著高于油菜籽田(P<0.05),冬小麦与蚕豆田以及油菜籽与蚕豆田土壤呼吸无显著差异(P>0.05)。冬小麦田土壤呼吸残差(基于温度指数方程的模拟值与实测值的差值)与NDVI、RVI、EVI、PRI、SPAD值均存在显著(P<0.05)或极显著(P<0.01)的相关关系,蚕豆田土壤呼吸残差与NDVI、DVI、RVI、EVI、PRI均存在极显著(P<0.01)相关关系,而油菜籽田土壤呼吸残差与上述植被指数均不存在显著的相关关系,这可能与油菜籽3-4月份花期叶片退化有关。在冬小麦和蚕豆田,可分别建立基于土壤温度、NDVI、RVI、PRI、SPAD值以及土壤温度、RVI的土壤呼吸模型,而油菜籽田土壤呼吸的季节变化仅与土壤温湿度和SPAD值有关。

In order to investigate the relationship between soil respiration and hyperspectrum, a field randomized block experiment with three crops of winter wheat, rapeseed, and broad bean was performed from October 2018 to May 2019. The changes in soil respiration, soil temperature, and soil moisture dynamics were measured. The normalized difference vegetation index(NDVI), difference vegetation index(DVI), ratio vegetation index(RVI), enhanced vegetation index(EVI), and photochemical reflectance index(PRI)obtained from the hyperspectral method and the SPAD value of chlorophyll were also determined. The results indicated that the seasonal mean soil respiration values were 1.78±0.15, 1.35±0.27 μmol·m^-2·s-1, and 1.61±0.22 μmol·m^-2·s-1 for winter wheat, rapeseed, and broad bean croplands, respectively. Soil respiration was significantly(P<0.05)higher in the winter wheat plots than in the rapeseed plots. There was no significant(P>0.05)difference in soil respiration between the plots of winter wheat and broad bean and between those of rapeseed and broad bean.Residual soil respiration computed as the difference between the modeled soil respiration using the soil temperature and exponential function and the observed soil respiration was significantly(P<0.05)or extremely significantly(P<0.01)correlated with the NDVI, RVI, EVI,PRI, and SPAD values in winter wheat cropland. Residual soil respiration was extremely significantly(P<0.01)correlated with the NDVI,DVI, RVI, EVI, and PRI in broad bean cropland. There was no such correlation between the residual soil respiration and vegetation indexes in the rapeseed cropland owing to the flowering from March to April. A model based on the soil temperature, NDVI, RVI, PRI, and SPAD values and one based on soil temperature and RVI values were established to simulate soil respiration in winter wheat and broad bean croplands, respectively. The seasonal changes in soil respiration were only controlled by the soil temperature, moisture, and SPAD value in rapeseed cropland.