Hyperspectral Characteristics Of Typical Subtopical Trees At Different Levels Of Simulated Acid Rain

With the increasing of human activity and fossil fuel’s use, the emission of sulfur, nitrogencompounds has caused acid rain and other environmental stress is more and more serious. Also, it hasaffected the normal growth of plant and aggravate the imbalance of eco-system. This paper would adoptthe method simulating acid rain test under controlled conditions, and use hyperspectral remote sensingtechnology, we evaluated the Spectral reflectance and variation characteristics and law of6typical plant’sleaf in subtropical areas under acid rain in different simulative levels. The experiment shows:⑴There are conspicuous differences between the coniferous and broadleaf in terms of theirsensitivities to the acid rain.3conifers, i.e. Pinus massoniana, Cunninghamia lanceolata and Torreyagrandis are evidently more sensitive to the acid rain than Machilus pauhoi, Cinnamomum camphoraand Myrica rubra，3kinds of broad-leaved trees. For conifer, the chlorophyll content of Pinusmassoniana and Cunninghamia lanceolata was greatly higher than that of Torreya grandis. For thespecies of broad-leaved trees, however, there was no significant difference among the Machilus pauhoi,Cinnamomum camphora and Myrica rubra. Since Pinus massoniana, Cinnamomum camphora andTorreya grandis cannot stand the high level of acid rain, their chlorophyll content at first increaseed andlater declineed, which was contrary to that of Cunninghamia lanceolata. While Myrica rubra couldwithstand long-term acid rain of high level, its chlorophyll content under pH2.5was higher than thatunder pH5.6. As for the Machilus pauhoi, there was no evident law in the changes of chlorophyllcontent of Machilus pauhoi during the4experimental phases.⑵What’s more, the red-edged spectral reflectance positions of the testing plants were substantiallyconsistent with the changing rules of the chlorophyll content. To be more exact, Pinus massoniana andTorreya grandis which belong to the species of coniferous tree mainly showed a "blue shift", whileCunninghamia lanceolata showed "blue shift" first and "red shift" later, which reflected the long-termresistance to the acid rain of high level. Cinnamomum camphora, a type of the broad-leaved treeshowed"red shift" first and "blue shift" later, which was the acceleration and then the resistance to thesimulated acid rain of high level. In the four experiment stages of Myrica rubra, each stages arerelatively flat except the third stage where Myrica rubra‘s first derivative curve has the obviousphenomenon of "blue shift". Combined with the visible spectral reflectance characteristics, we can see Myrica rubra has a strong resistance to the simulation acid rain of high level. Machilus pauhoi showed"red shift" and "blue shift" alternatively, which corresponded to the changes of chlorophyll content andrevealsed its inconspicuous sensitivity to the acid rain.⑶The different vegetation subjected to the acid rain stress has different results while usingdifferent vegetation index. Vegetation index SIPI‘s differences are small under the handle of differentplant and different simulated acid. The SIPI values always float between1~1.05generally, and thevariation hasn’t obvious laws. Other vegetation indexs always performs consistent laws with thechlorophyll content of plant leaf. Besides, through the difference ratio calculation, we can find thatNDVI has a obviously smaller differences comparing with other four vegetation indexs when pH equalsto2.5and5.6. RI and RVI550are better than gNDVI when distinguish the experiment object under thehandle of simulate acid and pH equals to2.5and5.6. While RVI550is relatively better than RI andRVI700on the aspects of distinguish ability.