The Regulation Of Nitrogen And Phosphorus Nutrition On Growth Of Larch Seedling

Larch(Larix gmelinii) is the one of the most important timber species in northeastern China,and its growth is often limited by nitrogen and phosphorus shortage because slow decomposition rate of litter results by low temperature and long winter in boreal forest. Therefore,it is important practice and theory significance of improving productivity of larch forest and enriching silviculture to study the effect of nitrogen and phosphorus supply level on assimilation and utilization of nitrogen and phosphorus in larch.In this study,the experiment was conducted in green house,the Larch seedlings were cultured in sand to supplied with different levels of nitrogen and phosphorus.The growth index of Larch seedlings on the condition of different levels of nitrogen and phosphorus supply was determined,and the process of assimilation and accumulation of nitrogen and phosphorus in larch seedlings was analysed.The results of the study were summarized as follows:(1) The relationship·between nitrogen and phosphorus supply with accumulation and translocation of nitrogen and phosphorus in larch seedling.Additional nitrogen supply significant increased needle,stem and root nitrogen concentration in larch seedling,and needle nitrogen concentration was highest and have the most change extent with the increase of nitrogen supply.Phosphorus supply level has no effect on the nitrogen absorption of larch seedling.Low phosphorus supply didn't decrease the needle phosphorus concentration,but it did indue a decline of stem and root phosphorus concentration,these suggested that insufficient phosphorus supply decreased the phosphorus assimilation of larch seedling. Inereasing the phosphorus supply may increase stem and root phosphorus concentration.The value of nitrogen translocation amount,nitrogen translocation efficiency and nitrogen contribution in roots were higher than shoots,and which in shoots were higher than needles with different nitrogen supply,and all raised with the increase in nitrogen supply.The value of nitrogen translocation amount,nigrogen translocation efficiency and nitrogen contribution in roots and shoots were the highest with the 0.5 mmol·L^-1 phophorus supply same as the translocation amount and nitrogen translocation efficiency in needles,however the value of the nitrogen contribution in needles was the highest with the 1.0 mmol·L^-1 phosphorus supply,and the related values above all declined while increasing or decreasing phosphorus supply.The value of nitrogen harvest index(NHI) of needles was the highest,and which of the roots take the second place,which of the shoots was lowest;the value of NHI of needles was increased with the increase in phosphorus supply while which of the roots declined,however which of effects on shoots was no significant.(2) The effect of nitrogen and phosphorus supply levels on accumulation and allocation of carbon and nitrogen in larch seedlings root.The results showed that with the increase in nitrogen supply,the carbon concentration in the larch roots were declined,while the carbon accumulation amount and carbon harvest index were increased;The carbon concentration and accumulation were increased with the nitrogen supply increasing while the root order ascending;The carbon accumulation,nitrogen accumulation in whole root of larch seedlings were up with the increase in nitrogen supply;meanwhile the biomass of whole root were raised. Nitrogen accumulation amount increased significantly while the nitrogen supply level increased to highest(supplied with the nitrogen supply level of 32 mmol·L^-1).Same as the carbon harvest index,the nitrogen harvest index in larch roots were raised with the nitrogen supply increasing.However,the C/N ratio in roots were declined with increase in nitrogen supply.The phophorus translocation amount and harvest index of root was higher than needle and shoot with the different level of nitrogen supply,and the value above of the shoot was lowest.While the value of phosphorus contribution and efficiency of root was higer than shoot,and the value of shoot was higer than needle.The effect of phosphorus supply on phosphorus translocation amount,translocation contribution and phosporus harvest index was not significant while was significant with root and needle.(3)The effect of nitrogen and phosphorus nutrition on biomass and carbon distribution in larch seedlings.Deficient nitrogen and phosphorus supply significant restrained shoot growth of larch seedlings,but had no effect on root growth.Increased nitrogen and phosphorus supply obviously improved the shoot growth of larch seedlings,and excessive phosphorus supply restrained growth of seedlings.Partitioning of carbon to roots was enhanced in order to inerease root growth and enlarge absorption surface to nutrition with the deficient nitrogen and phosphorus supply,It maybe a adaptive strategy of larch seedling to low nutrition supply.The effect of phophorus supply on carbon concentration of larch seedling was not significant,and the carbon accumulation was increased from root order 2 to order 5.The carbon accumulation of higer order and low order root were different while the phosphorus supply was 1 mmol·L^-1.The nitrogen concentration of larch seedling was higest with the normal phosphorus supply;The nitrogen harvest index of order 1 root of seedling was higest with the different phosphorus supply.(4) The relationship between nitrogen and phosphorus nutrition with photosynthesis of larch seedlings.There was a strong correlation between nitrogen supply and photosynthesis of larch seedlings,deficient nitrogen supply reduced chlorophyll content,carotenoid content total soluble protein content of needle of larch seedling and result in light-saturated net photosynthetic rate(Pmax) which reflect plant photosynthetic ability decreased,the Fv/Fm and Φ_PSⅡ decreased significantly.Whereas increased nitrogen supply can significantly improve photochemistry efficiency and alleviate photoinhibition.In addition,with the decease of nitrogen supply level,qP of larch seedling also decrease,and this change was accompanied by a increase of NPQ,these suggest that under nitrogen deficiency,the light energy which have been captured by plant can not be used effcetively,but more of them is dissipated in heat. Compared with the effect of nitrogen,phosphorus had little effect on photosynthesis of larch seedling.Phosphorus defieieney didn't indue in deceased of photosynthetic pigment content and to total soluble protein content,and P_max only decrease slightly.On the other hand, phosphorus supply level either had a significant effect on chlorophyll fluorescene parameters, it also indicated that the effect of phosphorus on photosynthetic characteristics of lareh seedling is slight.