Effects Of Defoliating The Growth Of Poplar Seedlings By Simulated Nitrogen Deposition

As one kind of global environmental change,atmospheric nitrogen deposition has a direct impact on plant physiological functions and photosynthesis,and it also has an important impact on plant energy distribution and overall growth and development.Because of the redundant growth of the leaves,the plants consume a lot of energy to supply redundant organs for growth and development.Therefore,under the background of atmospheric nitrogen deposition,it has important theoretical significance to study whether reducing the growth redundancy artificially affects the aboveground and underground growth of plants.In this study,we used Populus × euramericana 107 as the test material,apply different concentrations of nitrogen fertilizer to poplar to simulate nitrogen deposition environment,study the impact of leaf redundancy on the physiological function of poplar,explore the plant’s own response to atmospheric nitrogen deposition and other environmental changes Compensatory physiological effects and adjustment of growth strategies.From this research,we find that:(1)Both nitrogen and defoliation has increased the leaf chlorophyll content and leaf specific weight,it indicates that adding nitrogen and removing leaf will increase the photosynthetic rate and biomass accumulation of plants,but the high nitrogen content in the external environment will lead to the growth of redundancy poplar,and it is not conducive to be useful timber.The artificial removal of leaves facilitates the removal of growth redundancy,and then increases the accumulation and utilization of photosynthetic products.Therefore,a certain degree of atmospheric nitrogen deposition is conducive to the growth and development of the aerial parts of plants,and on this basis the low-intensity defolioation is conducive to the redistribution of nitrogen in the plant,which tends to balance,and can also reduce the adverse effects of growth redundancy.(2)The nitrogen-phosphorous ratio in leaves of plants showed an increasing trend under both low and medium nitrogen conditions.However,when the nitrogen content was too high,the nitrogen-phosphorous ratio of plants was significantly inhibited,indicating that the relevance between leaf growth and nitrogen conditions wealcened under high nitrogen conditions.Defoliation also brings about a decrease in the nitrogen-phosphorous ratio in leaf,which is due to the change of the plant’s own growth strategy.The leaves need morephosphorus for regrowth,and the plants compensate for the growth by increasing the growth rate of the leaf.(3)Defoliation of Poplar under the condition of external nitrogen application can significantly promote the growth of above-ground and underground parts.It showed that under simulated atmospheric nitrogen deposition,it does exist the growth redundancy in poplar leaves,and defoliation operation helped remove growth redundancy.The defoliation operation also significantly reduced the average diameter of the poplar root system(p < 0.05),indicating that the removal of leaves has an inhibitory effect on the energy transport capacity of the underground part of the poplar.(4)The root length,surface area and specific root weight of poplar 1-3 fine roots were significantly higher than that of the control group under different leaf defoliation strengths,and the root length and surface area of 1-2 orders roots showed The increasing trend with the enhanced strength removal of defoliation operation.The increasing trend indicated that different poplars have different coping strategies on different fine roots under different levels of defoliation stress.In the case of serious damage to the aerial parts of the leaves,the root selected strengthen the root surface area with the root length of 1-2 order roots to get greater absorption capacity.Regardless of the nitrogen concentration,the cross-sectional diameter of poplar 1-3 fine roots appeared with the increase of defoliation strength.The rate of energy absorption and material transport of plants to the external environment increases gradually with the increase of the defoliation in strength,which indicated that the rate of energy absorption and material transpirt of plants to the external environment is suppressed.This showed that changes in plant growth strategies are affected by growth redundancy.