Physio-biochemical Response And Its Mechanism Of Pinus Yunnanensis Attacked By Xylophagous Insects

Applying insects as bio-indicators to monitor and assess forest health indicated that insect species and population fluctuations can be used to make a rapid assessment of forest health, but how to apply this theory to forest protection , further studies were needed for the mechanism of insect's damages to trees. The weakness of forests is often followed by xylophagous insects, and the woods health situation is directly to its physiological metabolism. In this dissertation, it was investigated on physiological and biochemical responses of Pinus yunnanensis Franch. after the attacking by xylophagous insects such as Tomicus yunnanensis and Monochamus alternatus, mainly concerned about photosynthetic-physiological indexes, activities of the protective enzymes, contents of the related active substances and changes of volatiles. By the analysis of relations between the xylophagous insects damage and the pine trees health, it was willing to found indexes system scientifically for judging forest health by the indication from xylophagous insects . The main results of the study were showed as the follows:1.Trees'responses of photosynthetic-physiological indexes after attacking(1) After shoot stress from Tomicus yunnanensis , net photosynthetic rate, transpiration rate, stomatal conductance and other photosynthetic indexes decreased significantly (p<0.01), so did the chlorophyll contents of needle leaves. The pines'photosynthesis procedure during the daytime changed greatly. It was a single peak curve for the day-round of net photosynthetic rate with the summit time at 12:00 in the noon, that was 2 hrs ahead of those of undamaged pines, and the peak value was cut down at the rate of 45%. Photosynthesis of the damaged trees happened mainly in the morning. Compared with the undamaged, the day average net photosynthetic rate of the damaged decreased significantly (p<0.01) and the day-round assimilation amount of CO2 decreased by 55.9%.The corresponding analysis showed that net photosynthetic rate of the undamaged was influenced mainly by the photosynthetic active radiation and with its poor relation to environmental factors on transpiration rate. But for the damaged, the influence factors of net photosynthetic rate and transpiration rate increased, and the trees were sensitive to environmental moisture changes. It can be inferred that the shoot damage lead to the decrease of resistance, and the weakness of pine trees was eventually occurred as their normal growth was affected easily by the changes of environmental factors.(2) Regarding the stress from Monochamus alternatus, during the period of feeding and nutrition supplying, it was showed that decreases were happened after the xylophagous insects feeding, dynamically on trees'photosynthetic-physiological indexes such as net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration . The longer and the stronger the xylophagous insects fed, the lower the indexes went. On the contrary, the water use efficiency went down previously but rose gradually during feeding period. It indicated that the pines were able to handle stress from the xylophagous insects'feeding by improving the water usr efficiency during a certain period.2. Changes of activities of the protective enzymes and contents of the related active substances followed damaging: although it was various for SOD, POD and CAT activities and MDA, proline and total protein contents when the trees were damaged by Tomicus yunnanensis and fed by Monochamus alternatus, there were some changes seemed with same regularities.(1) Induced after damaged or fed, the pines were found with changes of activities of enzymes and contents of active substances both in leaves and phloems by the comparison of those from unattacked trees. But it was more considerable in leaves rather than in phloems of the changes. It should be selected for investigations on the activities and contents to the responses of damaging and feeding with leaf materials determined, due to their sensitive to stress from the two insects, easiness to regularity finding and quickness to reaction.(2) Except protein content, activities of enzymes and contents of active substances in leaves of the damaged or the fed pines increased differently at some extent by the comparison of the undamaged. But during the observing period, some of the activities and contents decreased rapidly and the other of them maintained in high level. Such increase was obviously the outcome of responses answered by the plants themselves to irritation from outside. Variations of some decrease mentioned above both in time and rate were probably due to their characteristics. Maybe it was just not found during the observing period for the decrease of those maintaining-high-level enzymes and active substances. For the reason of protein decrease, it seemed that most of the protein without links to the response-answer reactions denatured and disappeared because of the transfer of inner-cell circummustances such as water and electricity potentials in leaves followed by the damaging. In a word, regular changes were found in these activities and contents so that they were available to indicating the extent of beetle damaging. And SOD, POD and MDA were more sensitive to the damaging or feeding from the two insects than other indexes, thus they were taken as ideal indexes for insects damaging indication. SOD is also known as an important index to vegetable health recognition, then, it become a tie between the damaging extent and plant health level.3. Changes of constituents and relative contents of volatiles released from damaged pine trees(1) It was similar in the day-round changes as the regularity for volatile varieties to both damaged and undamaged pines, even a few differs in amount, but the consists of volatiles varied greatly. These different substances, especially volatiles from Tomicus yunnanensis shoot bored Pinus yunnanensis Franch., were probably related to tree's defensive mechanism or information transportation.(2) Compared with the undamaged, the varieties and amounts of volatiles from damaged or fed pines changed in some extent. During the period, constituents in kinds and amounts related to xylophagous insects damaging extent were probably key chemicals such asα-pinene,β-pinene andα-phellandrene. For relatively high contents in volatiles, they caused constituents changes of the pine tree volatiles, either affected xylophagous insects'behavior as they were easy to receive and recognised.(3 )Damaged by different xylophagous insects and in different feeding parts, it was large variation of the relative contents ofα-pinene andβ-pinene. And the ratios ofα-pinene versus toβ-pinene were all lower than those in undamaged trees. It was proofed by studies that the smaller the ratio was, the weaker the trees got. The xylophagous insects damaging lead to the worsening of pine tree health, so the xylophagous insects could be indicative insects for health judging to Pinus yunnanensis Franch.