| Cunninghina lanceolata(Lamb.) Hook.(Taxodiaceae) is the mainly fast-growing commercial timber tree species in China. The establishment and management technique of its seed orchard keep ahead in the system of plant improved variety selection and breeding. At present, though the third-generation orchards of Cunninghina lanceolata had been planted and used in production, the yield of these third-generation orchards are still not enough to satisfy the demands of the market. Because of the first and second generation orchards have stepped into aging and decline period, therefore, the problem that how to take corresponding technical measures to make the declined seed trees rejuvenate and extend operating period of the seed orchard has been the urgent problem to address for forestry scientific and technological workers. Based on the conditions showed above, in this research, the aged seed trees in the first generation seed orchard grafted in 1987 in Xianshui forest farm of Quanzhou county in Guangxi were used as research objects, and the physiological response, rejuvenation effect and economic benefits on aged seed trees after stumping were studied to provide scientific basis for the sustainable management of aged seed orchards in Cunninghina lanceolata. The preliminary conclusions were as follows:(1) All aged seed trees can sprout after stumping, and new branches sprouted after four month of stumping. The high of cut was the chief factor affecting the sprouting of new branches and the sprouting ability of new branches was inversely proportional to the high of cut, the lower the cut, the better the growth of new branches. The fraction surviving of new branches was lifted to 90.8% from 40.0%, was improved more than 1 times by coving the cut with plastic membrane.(2) After stumping, the leaf stomatal characteristics of new branches significantly changed, stomatal length and width significantly increased with the increace of branche age. Comparing with non-stumping trees, when the age of new branches of stumping trees was three, the increase of stomatal length of new branhes was range between 2.2% and 2.8%, and the increase of stomatal width was range between 2.6% and 9.8%. There was positive correlation between chlorophyll content and branch age, the higher the age of branches, the higher the content of chlorophyll. The ages of new branches were decreased after the stumping of aged seed trees, therefore, the chlorophyll contents of new branches from stumped seed trees were lower than old branches from non-stumped seed trees. The contents of soluble sugar, starch and carbohydrate had positive correlation with branch age, separately. The activity of superoxide dismutase(SOD) had positive correlation with branch age and it increased with branch age, by contrast, peroxidase(POD) had negative correlation with branch age. The activities of these two enzyams suppressed each other and the change regulation was that POD declined while SOD activity increased.(3) Photosynthetic capacities of new branches were significantly increased. Comparing with old branches of non-stumping trees, the net photosynthesis rate, stomatal conductance, transpiration rate and and water efficiency of new branches of stumping trees were increased by 123.9%, 84.0%, 51.8% and 22.8%. The result showed that the younger the age, the better the photosynthetic capacities. Leaf net photosynthetic rate, leaf stomatal conductance and leaf transpiration rate of the branches in the east were higher than the branches in the south and west, the branches in the south took the second place, the branches in the west were the worst. Therefore, the attention should be paid on the management of branches in the operation of seed orchard.(4) After stumping, in Agust of fast-growing stage, the contents of N, P, K, Cu, Zn, Fe and B of seed trees were average increased by 15.3%, 17.0%, 27.0%, 239.7%, 62.9%, 45.2% amd 46.3%, respectively; and in December of slow-growing stage, the contents of N, P, K, Cu, Zn and Fe of seed trees were average increased by 15.3%, 17.0%, 27.0%, 239.7%, 62.9%, 45.2% amd 46.3%, respectively. The results above shows that stumping can promote seed trees rejuvenate.(5) Stumping has helped aged seed trees recove or improved the fruiting ability, and has effectively improved the quality of seeds. The yield of stumped seed trees when it fruited for the first time after stumping was higher than the total yield of non-stumped seed trees of recent 3 years, which was increased by 35.6%, length and diameterof cones were respectively increased by 2.9% and 1.6%, and 1000-grain weight, quality,germination potential, germination rate and seedling number were significantly increased by 17.1%, 82.7%, 134.4%, 130.3% and 24.9%, respectively. Contents of gibberellin ofstumped seed trees were higher than non-stumped seed trees, meanwhile the seed germination effects were better. Comparing with non-stumping trees, the seed of stumping trees had higher content of gibberell icacid, which was increased by 12.6%, and had better germination effect.(6) Under the same hereditary basic conditions, the growth of filial generation was affected by seed qualities. The seeds of stumping trees had better quality than of non-stumping trees, and its filial generation had better growth, the amounts of growth on two-years old and three-years stands were increased by 4.6% and 8.7%.(7) The comprehensive evaluation results of the medium and short term economic benefits on three renew methods of non-reform, stumping rejuvenation and reconstruct showed that stumping rejuvenation was the best method. The seed orchared was profitable after four years of stumping and the income higher than no-reform seed orchared year by year. Short term internal rate of return was 33.44%, it was 2.5 times as rejuvenation. It was the most effective means for aged seed orchard rejuvenation in the interim.As suggested above, after the stumping of decland seed trees in aged seed orchard, the new branches were re-younged and leaves physiological characteristics were improved. Not only the yeild of cones and seeds of new branches were increased, but also the seed quality, the effectiveness of seedlings breeding and the growth of stand were enhanced. In short, stumping had positive effectiveness on aged seed trees, this research helps to enrich practical experience and system info of tree seed orchard in China. |
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