宁夏银北盐碱地不同植被光谱特征研究

Spectral characteristics of different vegetations on saline-alkali land in the Northern Yinchuan Plain of Ningxia

【目的】研究不同程度盐碱化土壤上植被的光谱特征,为基于典型植被冠层光谱特征估测宁夏银北地区植被生长状况和土壤盐碱化程度提供理论依据。【方法】于2018年7月中旬,在宁夏银北盐碱地区选取样地,调查不同盐碱化程度土壤的理化性质及其上代表性植被的叶片叶绿素相对含量,分析不同程度盐碱化土壤上代表性植被类型(白刺和芦苇)以及中度盐碱化程度土壤上15种植被(向日葵、芦苇、花花柴、白茎盐生草、西伯利亚滨藜、藜、稗、紫苜蓿、柳枝稷、水稻、砂引草、白刺、槐、赖草、芨芨草)的冠层光谱特征及红边参数变化,研究植被冠层红边参数与土壤pH值、全盐含量以及叶片叶绿素含量的相关性。【结果】不同程度盐碱化土壤的理化性质及其上代表性植被的叶片叶绿素相对含量有明显差异。随着土壤盐碱化程度的增加,在可见光波段(350~760 nm),白刺冠层光谱反射率呈先上升后下降的趋势,芦苇冠层光谱反射率总体上先降低后升高;在760~1400 nm波段,白刺冠层光谱反射率逐渐降低,芦苇冠层反射率先升高后降低;在1400~2500 nm波段,白刺冠层反射率分别是先升高后降低(1400~1900 nm)和持续增加(1900~2500 nm),芦苇冠层反射率先降低后升高。随着土壤盐碱化程度的增加,白刺冠层光谱红边位置、红边斜率、红边峰值面积以及红边斜率与最小振幅的比值均减小;芦苇冠层光谱以上红边参数均先增加后减小。中度盐碱化土壤上,15种植被冠层光谱特征曲线变化趋势相似,但光谱反射率大小存在不同程度差异;除了最小振幅之外,15种植被冠层光谱的红边位置、红边斜率、红边峰值面积以及红边斜率与最小振幅的比值差异较大,故根据光谱特征在野外能够区分典型植被类型。土壤pH值与红边位置、红边斜率和红边峰值面积均呈极显著负相关关系,与红边斜率与最小振幅的比值呈显著负相关关系;土壤全盐含量与红边参数均不相关;叶片叶绿素含量与红边位置之间呈极显著正相关关系,与红边斜率和红边峰值面积之间为显著正相关关系。【结论】在不同程度盐碱化土壤上,不同植被冠层光谱特征变化趋势有差异,根据典型植被冠层光谱特征可以估测宁夏银北地区植被生长状况和土壤pH。

【Objective】The purpose of this study is to provide basis for estimating the vegetation growth status and soil salinity in the Northern Yinchuan Plain of Ningxia by identifying the spectral characteristics of typical vegetation canopies.【Method】In mid-July 2018,the physical and chemical properties of soils with different salinization levels and relative chlorophyll content(SPAD)in leaves of representative vegetations were analyzed.Then,representative plants of different salinization degrees(Nitraria tangutorum and Phragmites australis)and moderately saline-alkali soil(Helianthus annuus,P.australis,Karelinia caspia,Halogeton arachnoideus,Atriplex sibirica,Chenopodium album,Echinochloa crusgalli,Medicago sativa,Panicum virgatum,Oryza sativa,Tournefortia sibirica,N.tangutorum,Sophora japonica,Leymus secalinus,and Achnatherum splendens)were selected and changes in spectral characteristics and red edge parameters were analyzed.Finally,the correlations of red edge parameters with soil pH,total salt content and leaf chlorophyll content was analyzed.【Result】The physical and chemical properties of soils with different salinization levels and leaves SPAD of representative vegetations were significantly different.With the increase of soil salinization degree,in the wavelength of 350-760 nm,the spectral reflectance of N.tangutorum increased first and then decreased,while that of P.australis was opposite.In the range of 760-1400 nm,the spectral reflectance of N.tangutorum gradually decreased,while that of P.australis first increased and then decreased.In the range of 1400-2500 nm,the N.tangutorum reflectance increased first and then decreased(1400-1900 nm)and continuously increased(1900-2500 nm),while that of P.australis first decreased and then increased.As the increase of soil salinity degree,the red edge position,red edge slope and peak area of N.tangutorum canopy spectrum and the ratio of red edge slope to the minimum amplitude all decreased.The red edge parameters above the P.australis canopy spectrum were all decreased after initial increase.The spectral characteristic curves of 15 planted canopies on moderately saline-alkali soils had similar trends with differences in the degree of spectral reflectance.In addition to the minimum amplitude,red edge position,slope,and peak area of the 15 planted canopy spectrum and the ratio of red edge slope to the minimum amplitude were quite different.Thus,typical vegetation types can be distinguished in the field based on spectral characteristics.Soil pH had extremely significant and negative correlation with the position,slope and peak area of red edge,and had significantly negative correlation with the ratio of red edge slope to the minimum amplitude.There was a very significant and positive correlation between chlorophyll content of leaves and position of red edge,and there was a significant and positive correlation between slope and peak area of red edge.【Conclusion】The spectral characteristics of different vegetation canopies on soils with different salinity levels had different changing trends.The vegetation growth conditions and soil pH in Northern Yinchuan Plain of Ningxia can be estimated based on the spectral characteristics of typical vegetation canopies.