Responses Of Physiological And Biochemical And Leaf Reflectance Spectrum Characteristics Of Phyllostachys Violascens Under Different Water Status

High temperature and dry conditions in summer and autumn of southern China have a great negative impact on the growth of bamboo.Water shortage affects the physiological and biochemical process of bamboo,reduces their photosynthetic capacity,and then affects the output of bamboo forests.The rapid identification of bamboo water status plays an important role for accurate management of bamboo.This study taking an important shoot-use bamboo species Phyllostachys violascens as research object.The changes of leaf water,chlorophyll and osmotic regulator content,membrane lipid peroxidation,antioxidant enzyme and root activity were studied with 2a potted plants and water control methods,so as to select appropriate indicators for different water states of Ph.violascens.The reflectance spectrum characteristics and sensitive bands of canopy leaves with different water and chlorophyll content were calculated and analyzed.The regression equation of spectral indices with leaf water and chlorophyll content were built.The results indicated that:（1）Relative water content（RWC）was a water status indicator of Ph.violascens leaves.The RWC of different water treatments（60-80%of the field water capacity for well-watered,WW;40-60%for moderate drought,MD;20-40%for severe drought,SD）in Ph.violascens leaves decreased compared with control（more than 85%of the field water capacity）.However,different water treatments and different treatment time had different effects on the water content of leaves.The RWC of leaves treated with WW treatment was not significantly different compared with control.The RWC of leaves decreased to less than 79%after 21 days of MD treatment.The RWC of leaves was significantly lower compared with control from the start of SD treatment,then decreased to less than 67%after 21d.（2）The leaf membrane lipid peroxidation level of Ph.violascens leaves with different treatments increased first and then decreased.The malondialdehyde（MDA）content in leaves of Ph.violascens reached the maximum in all treatments.The MDA content in leaves treated with WW,MD and SD increased by 22.8%（P>0.05）,17.7%（P>0.05）and 38.2%（P<0.05）respectively.The activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）in leaves were different with different treatment.The SOD,POD and CAT activities of leaves were negatively correlated with MDA content on the 7th day of water treatment,but only the CAT activity of leaves was positively correlated with RWC.（3）Compared with control,the free proline（Pro）content of leaves of with different treatments increased,and the peak time of Pro content was earlier with the lack of water.At14th of MD treatment,the Pro content of leaves increased significantly by 57.9%compared with control.In the middle and late stages of water treatment,the Pro content of the leaves of all treatment was significantly higher than that of the control.Different water treatment aggravated the fluctuation of soluble sugar and starch content in leaves.At 14th of MD and SD treatment,the root activity of Ph.violascens was significantly lower than that of the control and WW treatment.At 28th of the SD treatment the root activity was significantly lower than other treatments.The correlation between leaf RWC and soluble sugar content was not significant,and it was significantly positively correlated with starch and negatively correlated with free proline content.（4）The chlorophyll content of Ph.violascens leaves with WW,MD and SD treatment decreased by 16.4%,10.3%and 36.5%respectively compared with control.The chlorophyll content of leaves decreased significantly after 21 days of MD and SD treatment.Leaf RWC were positively correlated with chlorophyll a,chlorophyll b and total chlorophyll content,especially significant after 21-28 days of water shortage.（5）The leaf water content and its spectral reflectance were negatively correlated in the near-infrared region.The spectral reflectance sensitivity analysis showed that the spectral reflectance in 1400-1600nm and 1800-2000 nm was significantly changed with the decrease of the leaf water content.m NDVI（740,1450）has higher correlation with leaf RWC.The accuracy of the fitting equation with m NDVI and RWC（y=1.1486x²+1.9763x+0.1002）is better.The results provide a reference to estimate leaf water content in bamboo species.The moisture sensitive bands of the canopy reflectance spectrum are similar between the same species of bamboo.（6）Leaf chlorophyll content（LCC）in Ph.violascens was significantly reduced in SD treatment.In the visible region,the spectral reflectance of leaves increased with the decrease of LCC;the correlation between the first-order differential spectral reflectance with wavelengths of 493nm,639nm,693nm,756nm and LCC was better.The correlation coefficient between LCC and spectral characteristic parameters of Green peak reflectance,Red Valley reflectivity,Blue edge area,and Green peak area were higher.With the increase of LCC,the red edge position of the reflectance spectrum was moved to long wave band.The correlation between the modified vegetation index and LCC was better than that of original vegetation index.The regression equation（y=3.36-1518.2DR493+46.4DR693+72.8DR639+1199.1DR756）based on spectral reflectance and the first-order differential value at four wavelengths（493,639,693,756 nm）together with the modified green normalized vegetation index（m GNDVI）modle(y=6.3866x^0.8829)have higher training precision and higher accuracy in the test sample fitting and verification.They were better estimation models for LCC of Ph.violascens.