Study On The Mechanism Of Calcium Cycle Of Dominant Tree Species In Maolan Karst Forest

Maolan Karst forest is the unique primary karst forest vegetation existing in the same latitude area of the earth as its, called as "the model karst habitat". Moreover, as a forest ecosystem survived on the earth, which is concentrated, stable relatively and has the strong original nature, it has provided a natural laboratory for the karst forest research. this article selects nine dominant tree species in Maolan Karst forest, respectively is:⑴Coniferous tree species Pseudotsuqa breviflia;⑵Evergreen broadleaved tree species Kmeria septentrionalis, Phobe crassipedicella, Pittosporum crispulum, Dendrobenthamia hongkongensis, and Clausena dunniana;⑶Deciduous broadleaved tree species Handeliodendron bodinieri, Carpinus lipoensis and Platycarya longipes. the calcium density in leaves and branches of various tree species was determined by Atomic Absorption Spectrometry, and the seasonal month dynamics of calcium accumulation in different organs of different dominant tree species in Maolan Karst forest have been studied, the calcium cycle mechanism was initially discussed of the dominant tree species. the results show, (1) the calcium density in leaves of all the dominant tree species is higher than that in leaves of the plants on general region vegetations, and that of Dendrobenthamia hongkongensis reaches as high as 7%; (2) The author thinks, the possible special mechanism that dominant tree species adapting karst multicalcium habitat in Maolan Karst forest is: In whole growth period, the dominant tree species inclined to accumulate more calcium in trees, but returns less calcium to the karst forest ecosystem. (3)the calcium cycle mechanisms of the different tree species types is different from each other, and the key differences lie in the different calcium assignment in the branch and the leaves as well as the assignment changes in different growth stage of different tree species. The Ca density in leaves of all evergreen trees is higher than that of the branch, in the whole growth stage, the fluctuation of the seasonal dynamics of the calcium density of the leaves and branches of the evergreen trees is not obvious. Moreover, the evergreen trees prefer to accumulate more calcium in the leaves in the earlier stage, but inclined to distribute more calcium into the branches in the later growth period. However, in the whole growth stage, the fluctuation of the seasonal dynamics of the calcium density of the leaves and branches of the evergreen trees is very big. Moreover, the calcium density of the leaves and branches of the deciduous trees increased continuously in the earlier and middle stages, and prefer to accumulate more calcium to leaves, but in the later growth period, particularly in the deciduous period, a sharp drop appears in the calcium density of the leaves of the deciduous trees, and the speed of distribution into the leaves inclined to become slow. In the whole growth period, the calcium density in the leaves and branches of the coniferous trees is increased and decreased mutually, continuously it maintains a lower level, and the fluctuation is very small. (4) In the deciduous time, the relative calcium transfer ratios present the negative values in the leaves of five tree species (Kmeria septentrionalis, Dendrobenthamia hongkongensis, Handeliodendron bodinieri, Carpinus lipoensis and Platycarya longipes.), but mostly is very low, the lowest is -0.05%, the biggest is -0.15%.