Study On Physiological And Ecological Mechanism Of Eucalyptus Grandis×E. Urophylla Adaptability To Karst Habitat And Non-karst Habitat

In order to study the photosynthetic capacity and adaptation strategies of E. grandis x E. urophylla both in karst hibitat and non-karst hibitat by using the open exchange system Li-6400portable photosynthesis system, diurnal and seasonal dynamics of photosynthesis and photo-response curve of E. grandis x E. urophylla were measured in Guilin karst habitat and non-karst habitat under the clear weather condition in March (spring), July (summer), October (autumn) and December (winter) of2011. Besides, chlorophyll content, leaf area, leaf thickness, specific leaf area, leaf dry matter content and the morphological anatomy structure of leaves of E. grandis×E. urophylla were measured. Based on the study, the physiological and ecological mechanism of Eucalyptus grandis×E. urophylla adaptive to karst habitat could be revealed. Furthermore, the results provided important reference value to the vegetation restoration and reconstruction when selected suitable species to grow on karst hills. The main results obtained were as follows:(1) The diurnal change of net photosynthetic rate, transpiration rate and stomatal conductance of E. grandis×E. urophylla were "single peak" curves in four seasons. The net photosynthetic rate of E. grandis×E. urophylla in karst habitat was higher than some tree species in karst hill, though the net photosynthetic rate of E. grandis×E. urophylla in karst habitat was lower than that in non-karst habitat. The water use efficiency of E. grandis×E. urophylla in karst habitat was lower than that in non-karst habitat in four seasons. The maximum (5.052/μmol·mmol-1) and minimum (1.406μmol·mmol-1) of the water use efficiency of E. grandis×E. urophylla among four seasons appeared in winter and autumn respectively. The water use efficiency of E. grandis×E. urophylla in autumn was higher than Sapindu smukorossi (1.28μmol·mmol-1) though it was the lowest among four seasons. The E. grandis×E. urophylla in karst habitat can adjust its water use efficiency to adapt the arid environment of karst hill.(2) In spring, the main influencing factors of E. grandis x E. urophylla in karst habitat in were the stomatal conductance and transpiration rate, while the main influencing factors of E. grandis×E. urophylla in non-karst habitat were the vapor pressure deficit based on leaf temp, water use efficiency and photosynthetic active radiation. In summer, the main influencing factors of E. grandis×E. urophylla in karst habitat were the stomatal conductance, vapor pressure deficit based on leaf temp and atmospheric relative humidity, while the main influencing factors of E. grandis×E. urophylla in non-karst habitat were the stomatal conductance, water use efficiency and air CO2concentration.In autumn, the main influencing factors of E. grandis×E. urophylla in karst habitat were the stomatal conductance and water use efficiency, while the main influencing factors of E. grandis×E. urophylla in non-karst habitat were the stomatal conductance, limitation of stoma and vapor pressure deficit based on leaf temp. In winter, the main influencing factors of E. grandis×E. urophylla in karst habitat were the intercellular CO2concentration, air CO2concentration and limitation of stoma, while the main influencing factors of E. grandis×E. urophylla in non-karst habitat were the stomatal conductance and atmospheric relative humidity.(3) The maximum net photosynthetic rate, apparent quantum yield, light compensation point and light saturation point of E. grandis×E. urophylla in karst habitat were17.89μmol·m-2·s-1,0.06mol·mol-1,14.68μmol·m-2·s-1and1344μmol·m-2·s-1respectively. The maximum net photosynthetic rate, apparent quantum yield, light compensation point and light saturation point of E. grandis×E. urophylla in non-karst habitat were22.977μmol·m-2·s-1,0.065mol·mol-1,15.833μmol·m-2·s-1and1400μmol·m-2·s-1respectively. The E. grandis×E. urophylla in non-karst habitat are of high light saturation point and low light compensation point, thus having certainly adaptability to strong light and weak light.(4) The specific leaf area of E. grandis×E. urophylla in karst habitat was lower than it in non-karst habitat, while, the leaf dry matter content of E.grandis×E. urophylla in karst habitat was higher than it in non-karst habitat. The stomas mainly distributed in the lower epidermis of leaves. The stomata density and stomata index of E. grandis×E. urophylla in karst habitat were higher than that in non-karst habitat. The morphology and anatomy characteristic of E. grandis×E. urophylla in karst habitat was typical xeromorphism, with well differentiated palisade and spongy tissue, highly density of leaf venation and developed vascular system. These structures of leaf were very typical character of adaptation to arid environment. Moreover, that the chlorophyll a/b in karst habitat was higher than it in non-karst habitat, showed that the activity of photochemical reaction center of E. grandis x E. urophylla was high.(5) The adaptive mechanism of E. grandis x E. urophylla to adapt the environment in karst habitat in four seasons were as follows:in spring, the high stomatal conductance improved transpiration rate and was helpful for pushing CO2into the blade, thus making net photosynthetic rate increase; in summer, the stomatal conductance declined, the vapor pressure deficit based on leaf temp achieved the maximum of the year making stomatal limitation increase, so net photosynthetic rate showed a downward trend; in autumn, the stomatal conductance and transpiration rate decreased, making net photosynthetic rate decrease; in winter, the temperature, photosynthetic active radiation, transpiration rate and stomatal conductance of E. grandis x E. urophylla all dropped down to the lowest of the year, the limitation of stoma prevented CO2from entering cells, so net photosynthetic rate dropped down to the lowest of the year.(6) The adaptive mechanism of E. grandis x E. urophylla to adapt the environment in non-karst habitat in four seasons were as follows:in spring, the high vapor pressure deficit based on leaf temp and stomatal conductance would help to increase water use efficiency, the photosynthetic active radiation was helpful to increase net photosynthetic rate; in summer, the stomatal conductance was high although it was lower than that in spring, the transpiration rate and photosynthetic active radiation were high, making net photosynthetic rate achieve the maximum of the year; in autumn, the vapor pressure deficit based on leaf temp was higher than it in winter, the stomatal conductance decreased,so the net photosynthetic rate decreased; in winter, the photosynthetic active radiation and transpiration rate of E. grandis×E. urophylla both dropped down to the lowest of the year, so the net photosynthetic rate dropped down to the lowest of the year.In conclusion, the high light saturation point and water use efficiency of E. grandis×E. urophylla in karst habitat indicated that E. grandis×E. urophylla had the characteristic being suitable to the karst hills or the tactics avoiding drought. The low specific leaf area and high leaf dry matter content of E. grandis×E. urophylla in karst habitat withstand high temperature drying environment. We can plant E. grandis×E. urophylla appropriately on karst hills in Guilin. The higher net photosynthetic rate and water use efficiency of E. grandis x E. urophylla in non-karst habitat than that in karst habitat indicated that E. grandis x E. urophylla had the characteristic being suitable to the non-karst habitat.