Associated Changes In Physiolgical Parameter And Spectral Reflectanceindices In Quercus Aquifoliodes Leaves In Response To Water Stress

Quercus aquifoliodes, namely Baron Oak, was a unique species in Northwest Yunnan, Western Sichuan, Southeast Tibet. It was cold-resistant and drought-resistant. Quercus aquifoliodes root system and sprouting ability developed well, played a role in soil conservation and water conservation. Previous studies of Quercus aquifoliodes focused on the classification systematic, biological and ecological research. In this paper, through ASD Field Spectrometer and Photosynthetic apparatus, we studyed Quercus aquifoliodes saplings leaf spectral reflectance in response to different degrees of water stress and change of Quercus aquifoliodes leaf pigments, spectral reflectance in different altitude, it provided guidance to hyperspectral remote sensing technology monitoring vegetation moisture condition. The major results were summarized as follows:(1) Effect of water stress on Quercus aquifoliodes spectral reflectance cunvesQuercus aquifoliodes was drought-tolerant plants, so the length of water stress should be gradual deepening. Under the continuous water stress, the reflectivity of Quercus aquifoliodes spectral reflectance curve in the visible region(VIS) for the first time (Day0) was significantly higher than following spectral reflectance(Day7,Day14,Day21,Day28,Day35,Day42). In the 35th days of water stress, the apparent reflectance spectra significant changes have taken place, the"Green Peak"and"Absorption Valley"in the visible region disappeared, the whole spectrum showed the trend of slowing. All spectral reflectance curves in the 770 nm～1100 nm were lack of regularity.(2) Change of Quercus aquifoliodes photosynthetic rate, transpiration rate and pigment content under water stressBy measuring Quercus aquifoliodes photosynthetic rate, transpiration rate and leaf pigment content, we found that under continuous water stress, Quercus aquifoliodes normal physiological activity was affected due to absence of external water, the photosynthetic rate and transpiration rate has declined, the chlorophyll a, chlorophyll b, carotenoids content in the leaves has decreased with the continuous water stress. In the course of water stress and recovery, Quercus aquifoliodes photosynthetic rate, transpiration rate and pigment content have shown a decline before watering, during recovery phase after rehydration, transpiration rate appeared in a recovery trend at the first measurement, the transpiration rate and pigment content did not immediately respond to rehydration, but after a period of time the recovery trend has appeared.(3) Relationship between spectral index and leaf water content during water stressFrom this study, we found that Water Index(WI), Normalized Difference Vegetation Index(NDVI), Relative Water Content (RWC) and Equivalent Water Thickness(EWT) have shown the same regularity. After watering, these three parameters did not immediately increase but declined, a period of time later the restoration trend began to emerge. This indicated that Quercus aquifoliodes required some time to regulate their own physiological characteristics in order to adapt to change of external environment. From this study, we also can see that the respective variation of spectral index and moisture index was consistent with treatment of each group. In addition, throughout the course of water stress, Water Index(WI) and Normalized Difference Vegetation Index(NDVI) were significantly correlated with moisture index(RWC, EWT), respectively. Correlation analysis showed that: Water Index(WI) and Normalized Difference Vegetation Index(NDVI) have a good validity in describing change of Quercus aquifoliodes leaf relative water content.(4) Relationship between Structural Independent Pigment Index (SIPI) and leaf relative water content, leaf pigment during water stressCorrelation analysis showed that: Structural Independent Pigment Index was significantly correlated with leaf relative water content, when leaf relative water content was high, SIPI almost keep a level and had no significant changes. When leaf relative water content was low, SIPI have showed increasing trend. SIPI also showed a good linear relationship with carotenoid/chlorophyll ratio. With the continuous water stress, due to leaf water consumption, the chlorophyll content decreased, both carotenoid/chlorophyll ratio and SIPI have increased.