Study On The Spectral Characteristics Of Halophytes In Different Seasons In The Ebinur Wetland Nature Reserve

Halophyte is an important life support system in arid area of northwest China,which plays a positive role in maintaining the balance of Xinjiang,saline soil-oasis ecosystem,promoting the development of oasis agricultural economy and improving ecological environment.Research on the regional or landscape ecological environment of Halophyte communities in Ebinur Wetland Nature Reserve requires accurate data sources,and Halophyte data can respond to the biochemical properties of Halophyte communities in spectral information.Therefore,it has a great practical significance to study the spectral characteristics of Halophytes and the changes in the water and salt content of leaves in the northwest arid region.The Ebinur Wetland Nature Reserve was chosen as study area,the spectral reflectance data and the water salt data of Halophytes in May 2016,July 2016,October 2016,May2017 and July 2017,which are selected as the data sources.The effects of soil salinity on the spectral reflectance of Halophyte leaves and the effects of soil moisture on the spectral reflectance of Halophyte leaves were studied by comparing the plant spectra of different communities in the same season and different seasons of the same community.Multivariate linear regression model and BP neural network model were used to analyze the quantitative relationship of published vegetation index and newly constructed vegetation index with vegetation water content and salt ion in leaves.Then author established the estimation model of water and salt in Halophyte,and verified the accuracy of the model,selected the best fitting model.The conclusions are as follows:?1?According to the characteristics of spectral curves of different communities in the same season,the Halophyte with the highest spectral reflectivity in 2016-2017 were Phragmites australis,followed by Populus euphratica,and the Halophyte with low spectral reflectivity were Nitraria tangutorum?Saltwood and Haloxylon ammodendron.According to the characteristics of spectral curves in different seasons of the same community,most Halophytes have the highest spectral reflectance in May 2016 and the lowest spectral reflectivity in summer which may be related to the physiological characteristics of vegetation such as vegetation water content or chlorophyll content and so on.From the first order differential spectrum,the difference is mainly in the corresponding size of“peak”and“valley”near 730 nm,and the corresponding wavelength position is basically the same.The spectral reflectance of Halophytes has gradually increased with the increase of soil water content and salt content.?2?The study on the water content estimation model of Halophytes shows that:the relationship between the newly developed vegetation indices and the vegetation water content was better than that of the published vegetation water indices.And in May 2016,the correlation between vegetation water content and optimization,published indices were the highest.The model R²of the newly developed vegetation indices were above 0.65,the model R²of the published vegetation water indices were higher than that of the other four groups.The performance and stability of models constructed by the author are better than that of the published vegetation water index models.Among them,NDSI_?2201,1870??RSI_?2259,1870??RSI_?1535,549?have good predictive ability for water content during the period,and DVI_?1712,1382??RSI_?1659,699??DVI_?1552,554??NDSI_?1526,570?have a rough estimate of water content during the period.?3?The study on salt ion estimation model of Halophytes shows that:only Na⁺content had the best correlation with the newly developed vegetation indices in the four periods.The author have selected DVI_?1859,1806??DVI_?2086,1643??DVI_?1484,1479??DVI_?1885,1852??NDSI?1980,1733??NDSI?1975,869??NDSI?1968,1072??RSI?2318,1801??RSI?2040,675??RSI?2054,396?as the optimal vegetation indices for Halophytes in July 2016;selected DVI_?1780,1501??DVI?1490,1478??DVI?2123,1852??NDSI?1275,1172??NDSI?703,528??RSI?1275,1172??RSI?704,532?as the optimal vegetation indices for Halophytes in May 2017;selected DVI_?1379,426??DVI_?1786,583??DVI?1418,712??DVI?1409,549??NDSI?1766,583??NDSI?679,669??NDSI?680,660??RSI?1787,583??RSI?679,669??RSI_?680,666?as the optimal vegetation indices for Halophytes in July 2017.The BP estimation model had a good effect on the salt content Halophytes.The coefficient of vegetation index of most construction is greater than 0.5,and the accuracy is higher.Among them,the estimation model constructed in July 2017 was the best,and the optimal vegetation index was Na⁺-NDSI_?1766,583?,Na⁺-RSI_?1787,583?and Ca²⁺-DVI_?1418,712?.