Mechanism Affects Of Nitrogen And Phosphorus On Productivity Of Populus×euramericana Cv. "74/76" Plantation

D-optimal regression design with quadratic saturation and The quadratic normal and rotary experiment design of four factors with five levels were applied to study the effects of nitrogen and phosphorus fertilization on growth of seedling Populus×euramericana cv."74/76"trees in terms of leaf photosynthesis, chlorophyⅡ fluorescence,biomass distribution pattern, root morphology, The results showed that:(1)Biomass of the seedling trees were enhanced by fertilizing nitrogen and phosphorus, above-ground part biomass obviously increased by nitrogen addition, underground partion biomass obviously increased by phosphorus addition. As young trees of one year, the total biomass were biggest when 15 milligram of nitrogen per kilogram of soil treated. The proportion of branch biomass were biggest when application quantity of nitrogen/ phosphorus is 2.88.(2)Compared with control group.The Peak value of Pn and Tr appearanced advancing by notrogen and phosphorus supplying. The daily mean of evaporation rate was obviously reduced by high nitrogen supplying. and increased by nitrogen and phosphorus supplying. Stomatal conductance was on the trend of decreasing linearly especially treated by nitrogen and phosphorus in whole-day. The water use efficiency was increased by nitrogen and phosphorus supplying.(3)Leaf area(p<0.0001), content of Chla were obviously increased by nitrogen addition, but the effect with Pn and PhiPS Ⅱ were not obviously. Pn and PhiPS Ⅱ were obviously increased by phosphorus addition. in general, 86% of the biomass variation was caused by photosynthetic yield which was the product of leaf net photosynthetic rate multiplying total leaf area per trees, the affect intensity of total leaf area per trees on biomass accumulation was up to 82% but the affect of leaf net photosynthetic rate on biomass accumulation was not obviously.(4)Root length and root surface were obviously decerased by nitrogen or phosphorus supplying, root volumes was increased by nitrogen and phosphorus supplying. The carbon assimilation exporting prefer to fine root as nitrogen or phosphorus treated. Negative relationshio between biomass and that root length , root surface, root volumes which diameter less than two millimeter and more than ten millimeter. Positive relationship between biomass and the root parameter which diameter more than two millimeter and less than ten millimeter.(5)For seedling trees of three years, fertilizing with nitrogen of 400 gram per basin, phosphorus of 350 gram per basin at September 7th and June 13th is the optimal scheme in plant density with 2m×3m.fertilizing with nitrogen of 200 gram per basin, phosphorus of 175 gram per basin at September 21th and June 13th is the optimal scheme in plant density with 2m×6m.