The Breeding And Regeneration Strategies And Ecological Adaptability Of Terminalia Franchetii In Dry-hot Valley

Terminalia franchetii was an indicative plants in Jinshajiang dry-hot valley, and an endemic plant in the southwest China. T. franchetii community was an important typical natural forest in Jinshajiang River. To evaluate the ecological adaptability of T. franchetii population to dry-hot valley climate, the reproductive biology (e.g. pollination biology, seed development and spread) was investigated in three types of T. franchetii communities, including mingled forest, pure forest and savanna woodland. The influence of environmental factors and human interference to the seedling regeneration and seedling settling was studied. Through typical sampling method, seedling regeneration was investigated in different communities. Soil seed bank, community structure, species diversity and soil moisture were investigated. At last, the natural regeneration and ecological adaptive strategy of different communities were discussed. The results showed as follows:(1) Canopy and soil seed bank existed simultaneously in T. franchetii community. Matured seeds fell off slowly from canopy with wind, especially in March which is of the strongest wind, low rainfall and relative humidity. Canopy seed bank could renew soil seed bank and regulate the time of seed germination. Seed fell off two years later from canopy seed bank could also germinate. Furthermore, seed was small, light, with three big wings with long hairs which contributed to the far spread of seed through strong wind. The result showed that T. franchetii seeds could spread further distance. Seed density was 40 grain/m2 at 11.5 meter far away from mother plant. The most of seed gathered in 3.5 meter far from the root of plant (seed density was 150 grain/m2). Seeds gathered in eastward and northward were more than that in westward and southward, probbably influenced by wind direction.(2) The reproductive characteristics of T. franchetii showed strong ecological adaptability to dry-hot valley climate. Stigma open before stamens, pollen and stigma were separated for long time, the coupling between flowering pattern and visiting path of insects promoted outcross. Meanwhile, long flower longevity ensured the success of pollination. The quality of seed in 2010 was better than seed in 2009, while the relative humidity in 2010 lower than 2009 and the wind power also stronger than 2009. The pollen of wind-pollinated plant was easier to spread with stronger wind in the dry air, which maybe increase pollination rate.(3) Seed germination was regulated by water and temperature at same time. Moisture was the important factor limiting seedling regeneration in dry-hot valley. The most adaptaple soil moisture for germination of T. franchetii seed was 15 to 25% and couldn't germinate below 5% of soil moisture. Temperature also played some role in its seed germination. The suitable temperature for seed gemination was 25 to 30℃. Seedling regeneration of T. franchetii community was in forepart and middle period of rainy season when the soil water content and temperature condition were suitable.(4) Seedling regeneration was remarkably different in different communities. The soil seed bank was the principle factor to seedling regeneration, with the highest in pure forest, followed by that in mingled forest, and in savanna woodland, respectively. Seedling regeneration was influenced greatly by community environment through seed fate experiment. The highest seedling convert ratio (seedling number/seed reserves) was in pure forest, followed by that in mingled forest, and that in savanna woodland in forepart and middle period of rainy season, respectively. Seedling convert ratio in savanna woodland was highest with the end of rainy season and the beginning of dry season, as in savanna woodland>pure forest>mingled forest. Seedling convert ratio in mingled forest was less than 2% with the aggravated drought stress. At last, we suggested that different strategies were to implement according to the specific conditions of different community types because of their different regeneration ability and would help restore native vegetation landscape more successfully.