The Hyperspectral Diagnosis Model for Acid Stress of Cinnamomum camphora

The hyperspectral technique plays an important role in detecting the response of plant under the acid stress. Taking Cinnamomum camphora as the subject, the hyperspectral information at leaf scale under 419 days of acid disposals was measured. Differing from other kinds of environmental stresses, the responses of plants under acid stress are more complicated due to the fertilizer effect of sulfur and nitrogen. Based on the hyperspectral monitoring on the leaf of Cinnamomum camphora under four grades of acid rains (pH 5. 6, pH 4. 5, pH 3. 0, pH 2. 0), the aim of this study is to find the turning point from promoting to inhibiting growth by acid rain. Based on the 16 terms of hyperspectral data, the pretreatments were firstly conducted and the abnormal values were removed; and then the typical spectrals were selected based on the temporal variations of leaf response (the differences of the spectral values under pH 5. 6 minus those under pH 4. 5, pH 3. 0, pH 2. 0, respectively) under acid stresses; finally the diagnostic models were constructed using the typical spectral. The results showed that the typical bands to reflect the response of Cinnamomum camphora under acid stresses were mainly within 470-520 and 565-700 nm, based on which the difference of blue edge index and the difference of yellow edge index were built. The acid rain with pH 4. 5 and pH 3. 0 first promoted and then inhibited the growth of Cinnamomum camphora, with the turning point at 100 days and 50 days of spraying acid rain, respectively. The acid rain with pH 2. 0 inhibited the growth of Cinnamomum camphora at the beginning of acid treatments, and this inhibition had been strengthened with time increasing. This study showed that the long term of hyperspectral monitoring could indicate the temporal variations of the responses of Cinnamomum camphora under acid treatments. These results could provide scientific information for monitoring the plant responses under acid rain at a regional scale, which also provide scientific suggestions for the government to enact environmental protection plans.