Research On Physiological And Ecological Mechanism Response Of Eucalyptus Dunnii Under Low Phosphorus Stress

China has been introduced and planted Eucalyptus for more than 100 years, for developing highly efficient and high quality forestry industry, many forestry workers have been working on the north introduction of eucalyptus in the past 20 years. Fujian is a major province of Forestry, the introduction of the fast-growing eucalyptus in south Fujian are successful, but in northern Fujian region, the majority of fast-growing eucalyptus cannot endure chillness environment.Eucalyptus dunnii is a excellent tree species that with properties of frost-resistant and fast-growing among varieties of eucalyptus, so it has been introduced and cultivated as an important industrial raw materials on a large-scale in our country for a decade. Our country has been substantial at the promotion of Eucalyptus dunnii and it currently becomes an emerging tree species, But at present, little is known about its ecological characteristics. Soil phosphorus deficiency has been commonplace in our country, especially in southern region where is a typical phosphorus deficiency soil, the promotion process of Eucalyptus dunnii growth is bound to encounter the reality of phosphorus deficiency, and the current soil is"Genetics phosphorus deficiency"but not"soil phosphorus deficiency".Excavating the potential ability of crop and potential phosphorus resources of soil is a effective way to solve the contradiction between phosphorus supply and phosphorus loss, and is an available way to prevent phosphorus pollution. So to study Ecophysiological response mechanism of Eucalyptus dunnii under low-phosphorus stress and to explore the potential E.dunnii Phosphorus utilization of genetic characteristics are of great practical significance.In this study, soil culture experiment and nutrient solution were designed.Through the two cultivate ways, the research set eight phosphorus concentration level, measured some typical indicators of morphology and physiology which would easily change under low-phosphorus stress conditions,such as root-crown ratio, acid phosphatase,soil pH, etc. Furthermore,the research did a dynamic follow-up determination on the tree height, diameter, leaf chlorophyll content and acid phosphatase content of E.dunnii. And comparing the different impacts on E.dunnii under the two cultivate ways of low-phosphorus stress test,in order to explore the morphological and physiological response of E.dunnii on low-phosphorus stress.The major findings are as follows:The morphological effects on E.dunnii under low phosphorus stress: soil culture experiment found that the tree height,DBH and the upper part of dry weight of E.dunnii did not significantly increase or decrease with the phosphorus concentration decreased,but a significant reduction in the root dry weight.With the low-phosphorus stress level increased,the root biomass decreased, so was the root-crown ratio.Under low-phosphorus stress conditions, the distribution of dry matter E.dunnii tend to be focused upper the ground; Nutrient solution low-phosphorus stress test found that the root-crown ratio of E.dunnii was different from the rule on soil culture experiment.Comparing with normal phosphorus level,the root-crown ratio of other seven low-phosphorus stress levels were higher,showing an increase rule under severe low-phosphorus stress , but the difference was not significant.With the concentration of phosphorus decreased,the root dry weight, root volume gradually decreased, the total root length also significantly reduced. Root classification results showed that fine roots that less than 1mm diameter were a major component of the root system of E.dunnii, and with the low-phosphorus stress level increased, the diameter class gradually reduced. It showed that phosphorus lack may have a significant impact on root growth and development of E.dunnii.The Physiology effects on E.dunnii under low phosphorus stress: dynamic determination of five months showed that chlorophyll a, chlorophyll b and total chlorophyll content of E.dunnii were significantly increased with phosphorus concentration decreased. The rule of photosynthetic rate changes were the same as chlorophyll changes. But the leaf acid phosphatase of E.dunnii was not increased with the low-phosphorus stress level increased and the low-phosphorus stress treatment time extended. Dealing with different phosphorus concentrations, E.dunnii leaf transpiration rate, stomatal conductance and intercellular carbon dioxide concentration has a similar law that the values are reduced by culture time extended.With the concentration of phosphorus decreased,E.dunnii Root acid phosphatase excreting increased significantly, the result was consistent in nutrient solution phosphorus starvation experiment of root acid phosphatase activity test.The determination on the acid phosphatase activity of the soil of E.dunnii showed that E.dunnii rhizosphere soil acid phosphatase activity was significantly higher than non-rhizosphere acid phosphatase activity by the level of low-phosphorus treatment. With the increase of phosphorus concentration level of treatment, soil rhizosphere phosphatase activity also increased significantly: in the P-deficiency stress, the plant roots induced secretion of acid phosphatase in the soil organic phosphate into inorganic phosphorus for absorption and utilization of plant phosphorus consumption resulted in rhizosphere higher activity of acid phosphatase.Under phosphorus starvation, E.dunnii rhizosphere soil of invertase, urease activity and rhizosphere soil total P content were higher than non-rhizosphere soil; non-rhizosphere and rhizosphere soil urease activity less or the same by the treatment level:Rhizosphere and non-rhizosphere urease activity ratio at between 1.01~1.12.Variance analysis showed that treatment with different phosphorus concentration on E.dunnii sucrase, urease rhizosphere and non-rhizosphere activity are not significantly affected; on soil urease activity significantly impact; on soil enzyme activities of sucrose is not significant. This indicated that the low-phosphorus stress had a greater impact on soil urease activity. Three studies on soil enzyme activity of E.dunnii showed that: Comparing to non-rhizosphere soil,rhizosphere enzymatic process was stronger. which was the same conclusion as correlation study; low-phosphorus stress on soil urease activity and rhizosphere soil acid phosphatase activity significantly affected, which may be associated with in root exudates and rhizosphere microorganisms active activities in rhizosphere soil.Under phosphorus starvation, the rhizosphere soil pH value was slightly lower than non-rhizosphere, with the concentration of phosphorus treatment reduced rhizosphere pH value and non-rhizosphere pH value had an increasing trend, but at the level of non-phosphorus stress (T8) decreased. It may indicate that E.dunnii soil pH had different effectson non-phosphorus environment. Deal with different concentration levels of phosphorus E.dunnii rhizosphere pH value was significantly different; nutrient solution pH value has also increased by nutrient solution experiment.With different phosphorus concentrations, total P content of root, branch and leaf of E.dunnii were significantly reduced. Root dry weight and root phosphorus content was significantly correlated. Results of correlated analysis to all determination indicators showed that indicators such as the rhizosphere soil acid phosphatase, acid phosphatase in leaves, root acid phosphatase, total chlorophyll and photosynthetic rate were closely related under low-phosphorus stress conditions.Generally, comparing a variety of morphological indicators and physiological indicators, We found that in low phosphorus soil E.dunnii able to grow well up;E.dunnii root acid phosphatase in rhizosphere and soil rhizosphere phosphatase activity increased were probably one of E.dunnii response mechanisms under phosphorus starvation and chlorophyll content, photosynthetic rate increased perhaps one of the response mechanisms...