Drought Resistance And Evaluation Of Afforestation Species In Karst Rocky Desertification Areas Of Guangdong Province

During the process of adaption to the environment, plants can gradually develop drought resistance ability via natural selection. Plants are often under water stress at the karst rocky desertification areas of Guangdong province, which will directly affect various physiological activities. The drought resistance of common afforestation species were analyzed and evaluated in this study, which aims to provide reference for selecting drought-tolerant plants. Six common afforestation tree species were collected, and they were Aleurites montana Lour., Ilex rotunda Thunb., Elaeocarpus sylvestris(Lour.) Poir., Liquidambar Linn., Cinnamomum Camphora(L.) Presl. and Magnoliaceae glanca Blume. The main results were listed as follows:(1) The water consumption, the highest and the average water consumption rate(WCR) per hour in daytime of the seedlings of six species showed a downward trend in drought stress. Before severely drought stress, Ilex rotunda Thunb, maintained high daily water consumption, which showed strong adatbility to arid environmental conditions. The highest average WCR were observed at Magnoliaceae glanca Blume. and Cinnamomum camphora(L.) Presl, decreasing slowly at the end of water stress during the day. Daily variation of the WCR increased at first, but decreased later. Generally, the highest WCR occurred during the period of 12:00 ~ 16:00, which indicated that these plants may show the maximum water consumption during this period, and plants may also advanced or delayed the time of the maximum WCR with the extension of drought stress. In this experiment, Ilex rotunda and Cinnamomum camphora showed strong ability of controlling water.(2) During the drought stress, the photosynthetic rate(Pn), transpiration rate(Tr) and stomatal conductance(Cond) of six species all declined obviously. However, the intercellular CO2 concentration(Ci) and the water use efficiency(WUE) showed different changes, the Ci fell after rose, the WUE showed downward trend but with some fluctuation. At first, the Tr, Cond and Ci of Ilex rotunda showed high values. Under severe stress, although the value of these three indexes declined rapidly but still high, indicating Ilex rotunda with better ability of drought resistance. The WUE of Cinnamomum Camphora was relatively stable before experiencing severe drought stress. Cinnamomum Camphora presented positive strategy against drought stress.(3) During drought stress, the soluble starch contents of six plant species all decreased, however, and soluble sugars contents increased. Ilex rotunda and Aleurites montana could significantly improve the soluble sugar content so that they could endure drought stress. The methane dicarboxylic aldehyde(MDA) content of six species increased remarkably under the drought treatment. Compared with other tree species, the difference of MDA content of Ilex rotunda between drought stress and normal water supply was minimum, which only increased 0.22?mol·g-1. And this difference for Magnoliaceae glance followed. Our study revealed these two species could maintain the stabilization of the plasma membrane. The leaf soluble protein content of Ilex rotunda, Magnoliaceae glance and Elaeocarpus sylvestris all reduced at first, but then increased. Compared with other species, these three species were able to retain higher content of leaf soluble protein, which showed greater ability of osmotic adjustment.(4) Plant leaf organs develop different strategies to adapt to the drought environment. Both Ilex rotunda and Magnoliaceae glance have thicker cuticle and leaf thickness, well-developed spongy tissue and palisade tissue, thinly leathery leaf blade, which can protect the mesophyll and enhance the ability of drought resistance.(5) Principal component analysis was used to select the physiological indexes which would be obviously affected by drought stress, including photosynthetic rate, leaf soluble protein content, the highest WUR, the thickness of leaves, spongy tissue thickness, epidermal thickness, cuticle thickness and WUE. The results of the principal component analysis indicated that these species varied in the ability of drought resistance. And the rank order of drought resistance ability of the species from the strongest to the weakest was listed as follows: Ilex rotunda > Magnoliaceae glanca > Cinnamomum Camphora > Elaeocarpus sylvestris > Aleurites montana > Liquidambar.