The Effect Of Nitrogen On Photosynthesis And Nutrient Utilization Of Populus×Euramericana Seedlings

Populus is one of the most important timber species planted in north China plain areas.Fertilization is an important management measures in Populus plantation due to the rapid growth rate and nutrient consumption characteristics of Populus. Nitrogen, as one of the essential nutrient played an important role in the growth and productivity of Populus. Therefor, it is of great significance in improving productivity of Populus plantation and enriching silviculture to study the effect of nitrogen application on nitrogen assimilation and utilization and growth of Populus.To clarify the mechanism of nitrogen application on the productivity of Poplar seedlings, Populus xeuramericana (Dode) Guiner CV.’74/76’and Populus xeuramericana (Dode) Guiner CL.’Zhonglin-46’are cultured at different nitrogen condition through combining research methods of field and potted testing. The effects of nitrogen addition on growth, biomass partition, source-sink relationship, distribution of carbohydrates, nutrient and light utilization of one-year old Populus xeuramericana seedlings are studied. The results of the study are summarized as follows:(1) Nitrogen application significantly increased the whole leaf area of two Populus xeuramericana seedlings during the growth stage, but the effect of nitrogen application on root morphological parameters was significant at the early growth stage. Additional nitrogen supply significantly increased the whole plant biomass of two seedlings, especially for clone107. At the end of the growth stage, whole plant biomass of clone107and clone46reached the highest value899.04g-plant-1and540.81g-plant-1separately under N2treatment.(2) With the increase of nitrogen supply, stem biomass accumulation increased during the fast-growing period, while root biomass accumulation and its allocation increased significantly at the end of the growing period. Nitrogen application decreased the total non-structural carbohydrates content of two seedlings and promoted the transportion of non-structural carbohydrates from leaves to stems and roots.(3) At the intrial stage of the growing season, seedlings absorbed nitrogen mostly from the soil, accounting for more than70%. With the growth of seedlings,15N content in seedlings accounted for more than50%of the total nitrogen content to the late growing season. Nitrogen application significantly increases the uptaken of total nitrogen and15N, especially for roots. Nitrogen uptake efficiency of two seedlings is higher under Nl treatment (35%～45%), but there is no significant difference in nitrogen utilization efficiency between N treatments.(4) Nitrogen application improved quantum yield (AQY), carboxylation efficiency (CE), the soluble protein content and the PS II efficieney of two seedlings at the fast-growing stage, so the net photosynthetic rate increased. At the end of the growing stage, respiration rate increased while photosynthetic energy and electronic transformation efficiency of clone46decreased under N2treatment which leads to the decrease of net photosynthetic rate. Compared to clone46, the light-saturated photosynthetic rate of clone107is stabilized around20μmolCO2·m-2·S-1.(5) Comprehensive evaluation of productivity of two seedlings shows that the growth index and biochemical index are of great signifcance in seedlings biomass accumulation. Biomass fitted values of all nitrogen treatment ranked in the order of N2> N1> N0. Biomass fitted values of clone107are higher than that of clone46under each nitrogen treatment and reached the higest value122.09g-plant-1under N2treatment (10g N-plant-1).