龟裂碱土对植被冠层光谱特征及长势预测的影响

Effect of takyr solonetzs on vegetation canopy spectral characteristics and growth prediction

为了通过统一土壤背景来量化龟裂碱土对其上覆植被冠层光谱的影响,通过野外原位测定,系统分析了龟裂碱土上覆植被在自然和覆盖条件下5个典型生育期冠层光谱特征、光谱反射率与叶片叶绿素值和叶面积指数(leafarea index,LAI)之间的关系,进而建立了不同条件下2个生理指标的预测模型。结果表明:覆盖条件下向日葵三对叶期冠层光谱反射率较自然条件下在400～520和1027～1130nm平均降低了0.10,在521～1026nm平均降低了0.18;其他生育期覆盖条件下冠层光谱反射率较自然条件下在可见光波段下降,在近红外区域增加(其中七对叶期在720～1050nm平均增幅为11.29%)。自然条件下三对叶期冠层光谱反射率与叶绿素值和LAI平均相关系数分别为0.68和0.47,开花期、乳熟期光谱反射率与叶绿素值和LAI与三对叶期相关性相似;其他2个生育期冠层光谱反射率自然条件下在可见光波段与2个生理指标平均相关系数分别为-0.27和-0.52,在近红外区域分别为0.53和0.69,覆盖条件下相关系数明显高于自然条件。三对叶期建立的叶片叶绿素值和LAI预测方程决定系数最小,现蕾期最大。除三对叶期外,其他时期对2个生理指标的预测模型的拟合度都较高(RSPAD为0.61～0.88,RLAI为0.72～0.92),预测能力也较强;引入土壤pH值可以增强模型的稳定性和预测能力。研究结果可为该地区龟裂碱土上覆植被长势估测提供理论依据。

In order to quantify the effect of takyr solonetzs on canopy spectral of above vegetation （sunflower） via unifying soil background, the characteristics of canopy spectral, the relationship of spectral reflectance with SPAD value and leaf area index （LAD were analyzed during five typical growth stages. Then, models for SPAD value and LAI prediction were established based on canopy spectral reflectance of sunflower and soil background pH value. The results showed that the tendency of SPAD value was similar to LAI of sunflower. There were increased then decreased with the advance of growth stages; they were the maximum value at budding stage and anthesis stage, respectively. Canopy spectral reflectance of sunflower in strongly alkaline soil were higher in the visible light and lower in near infrared region than reflectance of sunflower in slightly and moderately soil. Canopy spectral reflectance of sunflower at 3-1eaves stage decreased by 0.10 at the wavelength of 400-520 nm and 1027-1130 nm when the soil was covered with black cloth compared to its natural conditions; meanwhile, the reflectance decreased by 0.18 at 521-1026 nm. The reflectance at other growth stages decreased in visible-light range and increased in near-infrared when the soil was covered in contrast with its natural conditions （the canopy reflectance increased by 0.059 in 720-1050 nm and its amplification was 11.29% at 7-1eaves stage）. The spectral reflectance of sunflower at the natural state showed a positive correlation with the SPAD value and LAI at 3-1eaves stage, and the average correlation coefficients between the reflectance and SPAD value, LAI were 0.68 and 0.47, respectively. Anthesis and filling stages were same as 3-1eaves stage. The average correlation coefficients between the spectral reflectance at other stages and two agronomy parameters in visible range were -0.27 and -0.52 in visible range, and the average correlation coefficients between them were 0.53 and 0.69 in near-infrared, respectively, the correlation coefficients between them were maximum values in near-infrared at budding stage. When soil was covered, the correlation coefficient was comparatively higher than its natural condition. The minimum and maximum values of determination coefficients of the models for SPAD value and LAI were predicted based on canopy spectral appeared at 3-1eaves and budding stages, respectively. The effect of polynomial equations of SPAD value and LAI predicted were better than other equations at large, however, exponent and power equations of LAI predicted were the best at 3-1eaves, 7-1eaves and anthesis stage. The models had higher precision and capacity of predicting at all growth stage （RsPADwere 0.61-0.88, RLAiwere 0.72-0.92） except 3-1eaves stage. Therefore, models involved with pH value could effectively reduce the interference of soil background on the prediction of SPAD value and LAI of sunflower.