The Regulation Patterns And Technology Of Tree Structure In Camellia Oleifera

Camellia oleifera is a group of camellia species from whose seeds an edible oil with a very high content of unsaturated fatty acids can be extracted. Biologically, oil-tea trees are small and shrubby in tree form, and bloom abundantly twice every year, with the simultaneity of blooming and fruiting in Autumn. Unfortunately, however, the economic production of oil-tea plantations on a large scale is low due to poor management, the disorder of the tree structure, and the insufficient utility of the solar energy. Theory and practice have proved that rationally controlling the tree structure through pruning is an effective way to increase the photosynthetic efficiency and hence the fruit yield, but with thousands of hectares of established orchards tree regulation is complicated and intensive management is no easy job. In this dissertation, the author has piloted four pruning methods in four test plots of Camellia oleifera with different planting densities, hoping to create simple and practicable tree structures aiming at prolificacy. The study concentrated on the three aspects of introducing the system of indicators for high-yield tree structures on the basis of analyzing the characteristics of natural oil-tea tree structures; investigating the response of tree growth and fruiting to pruning; and establishing tree regulation patterns relative to regulation mechanism from the point of view of tree growth and development, photosynthetic features of the tree canopy, and tree nutrition physiology. The research findings are as follows.I. Response of tree growth and development to pruningFour methods of pruning were tried, including branching angle adjustment, shoot retraction, artificial injury, and cut-back. It was found that:i) adjusting the angle of the lateral shoots affected the growth of new sprouts and the photosynthesis, but showed no significant influence on floral and fruit development. When the angle was45degrees, the best effect was achieved in terms of floral bud differentiation, fruit set, shoot length, and utility rate of light, as compared to the treatments of90degrees and the check, ⅱ) shoot retraction posed a marked impact on tree growth and development. Slight retraction gave the best performance in shoot growth, and the number of shoots generated, shoot length, and shoot diameter increased by36.05%,108.60%, and 35.90%, respectively, than the check. Medium retraction resulted in the highest photosynthetic rate. iii) both girdling and bud cutting inhibited the shoot growth to some extent, but improved the net photosynthetic rate and the rate of light utility. The wider the girdling was, the worse the shooting percentage and shoot quality became. When the ringing was0.6cm in width, the highest net photosynthetic rate (11.59μ molCO2/m2·s) appeared. Bud cutting promoted shoot sprouting above the bud, and the sprouts were short and thick, iv) cutting back of different typed shoots and on different positions of the crown produced significant effects on the tree growth and development, and the photosynthesis was also remarkably affected. While cutting back of enriching shoots induced long and thin shoots, cutting back of weak shoots generated short and stout sprouts. Cutting back of shoots at the middle part of the crown increased the shooting quantity and quality; however, working with the outside shoots of the crown led to little shooting, although the shoots thus produced were thick with the highest net photosynthetic rate.II. Tree growth and development as affected by tree structure controlFour tree body regulation treatments were conducted, i.e. intensive pruning, simplified pruning, casual pruning, and non-pruning (as for check). It was found that: i) simplified pruning was favorable for Spring shooting and the shoot quality; the effect of both intensive and casual prunings was more or less the same, but both treatments were better than the Check non-pruning in terms of shooting percentage and quality; and intensive pruning was most ideal for Autumn shooting and growth, ii) Tree structure regulation promoted the growth of new leaves, with intensive pruning being the best, followed by simplified pruning, iii) pruned trees were better in increasing the number of floral buds than that of the Check, and simplified pruning resulted in bud formation and differentiation in the most positive degree, with the mean number of376floral buds and55.26%bud differentiation, which is14.56%higher than the Check, ⅳ) simplified pruning produced the highest yield of fruit of6.74kg per individual tree, which is1.6and1.2times more than that of the intensive and casual prunings, respectively. However, with intensive pruning the economic characters of individual fruit ranked the first, ⅴ) tree shape regulation improved the tree structure, and lowered the leaf area coefficient. The leaf area coefficient of intensive, simplified, casual prunings, and non-pruning was3.83,4.77,6.89, and7.56, respectively. Intensive and simplified prunings noticeably lessened the number of leading shoots, minimized the tree height, and raised the branching height of the primary shoots.Ⅲ. Canopy photosynthetic properties as regulated by tree structure controlThe crown photosynthesis was studied with four treatments of intensive pruning, simplified pruning, casual pruning, and non-pruning (as for Check). It was found that: i) The pattern of change in net photosynthetic rate, transpiration rate, stomatal limitation value, stomatal conductance, water use efficiency, and efficiency for solar energy utilization by intensive, simplified, and casual prunings was basically the same as that of the Check, but they varied in logarithm value, among which net photosynthetic rate, water use efficiency, and efficiency for solar energy utilization showed significant variation. With the four regulation patterns, the impact of regulation followed the pattern in the descending order of simplified pruning, casual pruning, intensive pruning, and non-pruning. Correlation analysis revealed that the tree structure regulation in oil-tea camellia was completed through the chang of net photosynthetic rate via regulation of the light output and air humidity, ii) more weak light as well as strong light were utilized through tree structure control, and better effects were achieved with simplified and intensive prunings. At the stages of fresh shoot growth and fruit development, the light compensation point was33with simplified pruning and35with intensive pruning, whereas the light saturation point was810and715, respectively, iii) the pattern of net photosynthetic rate with the four regulation treatments was regular at both the shoot growing stage and the fruit development stage. The value of net photosynthetic rate followed the descending order of simplified, casual, non-, and intensive prunings. At both stages the efficiency for solar energy utilization coincided with net photosynthetic rate. Tree structure regulation increased the net photosynthetic rate in the annual life cycle of oil-tea camellia, but each treatment as not closely correlated with the utility efficiency of solar energy, iv) tree shape regulation could well improve the relative lighting intensity of the crown canopy. Comparative analysis indicated that the effect of improvement of intensive pruning was largely the same as simplified pruning, the overall distribution of light intensity on the crown fell in the shape of a funnel, with lighting intensified from top and north to bottom and south of the canopy layer. The diurnal change of relative lighting intensity by different treatments demonstrated a single curve, the peak value came at12:00, and the value increased with the enhancement of the pruning intensity.Ⅳ. The physiological foundation of tree structure regulation in Camellia oleiferaThe nutritional condition and enzyme activity of the trees in the test plot whose tree structure was regulated by either intensive pruning, simplified pruning, casual pruning, or non-pruning were analyzed. Results showed that:i) the soluble sugar, soluble starch, and soluble protein in the tree under different pruning treatments followed basically the same pattern of change. While the content of soluble sugar and soluble protein presented a single curve with the peak appearing at the fruit growth stage, the content of soluble starch was in the Ⅴ shape with the lowest content recorded at the fruit development stage. The three nutritional elements were all higher in content with the pruning treated trees than the non-pruned trees. Simplified pruning induced the highest nutritional content in different growth and development stages, followed by intensive and casual prunings whose nutritional content was almost identical, ⅱ) three nutritional elements by content were significantly in positive correlation with the length of the fresh shoots both at the shoot growing and fruit enlargement stages, but this was not true of the shoot size at varied growth periods. With shoot growth the content of nutrients posed an enormously positive correlation to the shoot size; however, fruit growth was only significantly correlated to the content of soluble protein, ⅲ) measurement of activity of superoxide dismutase, nitrate reductase, sucrose synthetase, and amylase showed that different regulation treatments presented activity in the descending order of simplified, casual, non-, and intensive prunings. The activity of all enzymes was the highest with simplified pruning, and the lowest with intensive pruning, indicative of the fact that moderate pruning could increase the enzyme activity, whereas excessive pruning could lower the enzyme activity.