Studies On The Technology And Effects Of Promoting Trunk Extension Of Paulownia By Pruning

The dissertation aims to develop technology of promoting trunk extension of Paulownia by pruning,reveal its dynamic effects and mechanism.The dynamic effects of pruning with different intensities and methods to 2 to 4 years old Paulownia fortunei 'Yulinensis 1' trees on the growing indicators of the trunks,branches and leaves and their relative growing relationship were studied based on continuous eight years' measurements.Futhermore,their effects on the characteristics of photosynthesis,transpiration and water use efficiency of Paulownia were also investigated in the first year of pruning.The research achievements are as follows:(1) The key points of the technology of promoting trunk extension of Paulownia by pruning are to prune the top branches and part of under-layer branches from Paulownia trees without natural trunk extension in the spring of the third year after plantation with optimum pruning intensity of 50～70%, remain 2～3 rounds of the lower-layer branches which removed totally next year,pay much more attention to nurturing management measures such as bud picking,normal bud seleting,trunk extension developing from the middle ten days of April to the middle ten days of May in the pruning year,and enhance water and fertilizer management from the previous month.(2) The growth effects of this technology were reflected in the growth and dynamic changes from each growing indicator of Poulownia's trunks,branches and leaves,together with their relative growing relationship.①It had no significant effects on the original trunk growth,but very significantly promoted the growing of the extended trunk and the total volume of the trunk(V_t).Meanwhile,it reduced the taper of the original trunk to a certain degree and kept the form quotient of the extended trunk and the breast height form factor of the original trunk in a rather high level continuously.The successful rate of Paulownia trunk extension was about 97.5%,with the extending height of 5.73 m～ 5.75 m and the main trunk of 9.44 m～9.57 m.Because each trunk indicator had comparatively higher average day increment(A_m),maximum day increment(AGR_max) and/or comparatively longer fast-growing period(T) and growing period(D_g) in the pruning year and higher average annual increment,maximum annual increment in the eight years after pruning,the annual increment of the 5 growing indicators of the original main trunk decreased slightly in 4a,but began to revive and increase in 5a,and advanced rapidly in 6a and 7a,their total increment and the cumulated increment after pruning were near to those of CK respectively from 6a,meanwhile,the annual increment and total increment of the diameter,sectional area and volume of the extending trunk were comparatively higher in every year.Thus the total V_t increment in 11a and the accumulated V_t increment from 4a to 11a were 77.61%～79.12%and 96.85%～98.74%higher than those of CK respectively.②It had the effect of promoting the growth of the upper crown of trunk extension and the lower branches,enhancing the annual increment of base cross section area(S_b) of the crown layer and the whole tree branches to make the total S_b close to that of CK obviously.Because each indicator had comparatively higher A_m,AGR_max and/or longer T and D_g,the annual increment of the base diameter(D_b) of the extension branch from the upper crown and S_b were relatively the highest while that of D_b of the lower crown didn't grow so fast with the relatively higher annual increment of the crown layer S_b.The annual S_b increment of the whole tree was significantly 55.32%～56.89%higher than that of CK,therefore the total S_b was close to CK.It also improved the increment of the unit area of lower branches for S_b in the middle and the lower stem, cross section area and the original trunk volume and that of the upper branches to keep the growth of the original trunk,thus significantly improved the total volume of the main trunk.③It obviously increased the single leaf dry weight(LDW) and the leaf area(LA),improved the growth of leaves on the under-layer of a single branch and avoid leaves' growth of the whole crown severely falling.In the pruning year,the number of lateral branches decreased 51.53%,but the number of leaves in the lower crown decreased only 16.45%,and the LDW and LA of the lower crown increased 12.22%and 11.61% respectively,thereby the total LQ,LDW and LA of the whole tree decreased only by 32.29%,22.88% and 20.59%.As a result,the growth and development of the lateral branch were kept on high level by improving the increment of the lateral branch of unit volume leaf blade,thereby the volume of the trunk and V_t of unit volume leaf blade could be enhanced significantly without obviously reducing the growth of the diameter of the total trunk. (3) The pruning technique improved the light environment and ventilation condition greatly, hence promoted the photosynthetic potential of Paulownia leaves.①It improved the photosynthetic ability of leave blades both on lower crown and on the total plant,further reduced the difference between the upper and the lower crown.Compared with CK from May to August in the pruning year, the maximum photosynthetic rate,light saturation point,light compensation point and photosynthetic range of lower crown were increased by 27.70%,36.74%,34.22%and 36.80%,respectively,while those of upper crown were raised by 0.72%,1.75%,26.11%and 1.11%,thus those of the total tree were increased by 9.27%,12.56%,16.36%and 12.46%,the total amounts of the maximum and average photosynthetic yield were only decreased by 13.22%,14.98%.②The transpiration rate (Tr) which increased with increasing photosynthetic photon flux density(PPFD) and its increasing amplitude were enhanced when the PPFD was zero.The average Tr per unit LA of the upper,lower and whole crown were 11.65%,16.62%and 14.15%higher than those of CK respectively.Compared with CK,the total amount of average Tr were decreased by 48.00%in the upper crown,increased by 30.15% in the lower crown and decreased by 8.31%for the whole crown due to the effect of the pruning measures on the leaves.③Compared with that of CK,the average efficiency of water use(WUE) of Paulownia leaves was decreased by 4.21%in the upper crown,increased by 9.60%and 1.51%in the lower and the whole crown respectively because of the effects of the pruning measures on the correlation parameters of WUE to PPFD and the related main indicators.The results showed that the pruning technique could enhance the WUE to a certain degree and it had more obvious effects on the lower crown than on the upper,meanwhile,it significantly reduced WUE differences between the upper and the lower crown.