The Effects Of Phenolic Acids Concentration And Ammonium To Nitrate Ratio On Photosynthesis And Nitrogenous Metabolism Of Populus × Euramericana ‘Neva’

The declines of soil fertility and forestland productivity of continuously cropped poplar plantations were closely related to the phenolic acids accumulated in the soil. Nitrogen is vital element for plants living. Some questions are raised: do phenolic acids impact on nitrogenous metabolism of poplar? Is this effect the main cause of continuous cropping obstacle of poplar?What is the rate of ammonium nitrogen to nitrate nitrogen fertilized impacting on process of photosynthesis and nitrogen metabolism of poplar under different conditions of phenolic acids? Would the ratio of ammonium nitrogen to nitrate nitrogen adjusted enhance the resistance capability of poplar to phenolic acids? To answer these questions, According to the contents of 5 types phenolic acids(X, X= 247 mg·L-1 p-hydroxybenzoic acid + 11 mg·L-1 vanillin + 7 mg·L-1 ferulic acid + 54 mg·L-1 benzoic acid + 2 mg·L-1 cinnamic acid) in the soil of second generation poplar plantation and the absorption rates of the acids, some experiments were conducted in 2014 and 2015. In 2014, completely random factorial experiment with two factors and three levels(0X*1:14, 0.5X*1:14, 1.0X*1:14, 0X*1:7, 0.5X*1:7, 1.0X*1:7, 0X*1:3, 0.5X*1:3, 1.0X*1:3) were designed using three kinds of phenolic acid gradients(0X, 0.5X, 1.0X) and three nitrogen form ratios(NH4+-N:NO3--N=1:3, 1:7, 1:14), then poplar(Populus × euramericana ‘Neva’) were planted into pots with vermiculite. Photosynthetic gas exchange and chlorophyll fluorescence parameters of leaves of poplar, such as the total nitrogen, biomass and the activities of nitrate reductase(NR), nitrite reductase(Ni R), glutamine nynthetase(GS) and glutamate synthas(GOGAT) of root and leaves were determined. In 2015, six phenolic acid gradients(0X, 0.5 X, 1.0 X, 1.5 X, 2.0 X, 3.0 X) were set and cultured by Hoagland nutrient solution, of which the ammonium were labeled with 15 N. The abundances of 15 N in root, stem and leaves of poplar, photosynthetic gas exchange and chlorophyll fluorescence parameters of leaves, the total nitrogen, biomass, the activities of nitrate reductase(NR), nitrite reductase(Ni R), glutamine nynthetase(GS) and glutamate synthas(GOGAT) of root and leaves were determined in order to reveal the mechanism that phenolic acids reduce productivity of poplar and find out the methods to increase the productivity of poplar. The results are as follows:1. The effects of phenolic acids concentrations and nitrogen forms on photosynthetic gas exchange of Populus × euramericana ‘Neva’.In 9 kinds of interactions of phenolic acids and nitrogen forms, with the increase of PAR, the PN of all treatments increased before reaching the light saturation point, while after that, the trends were different. When the ratio of NH4+-N to NO3--N was 1:14, PN of 0.5X and 1.0X was decreased with the increase of PAR. When the nitrogen ratio was increased, the ratio of NH4+-N to NO3--N reached 1:7 or 1:3, PN of 0.5X and 1.0X was not obvious with the increase of PAR.Photosynthetic gas exchange parameters on light saturation point(PAR=1500μmol·m-2·s-1): The net photosynthetic rate of poplar leaves decreased with the increase of phenolic acid concentrations, and increased with the increase of the ratio of NH4+-N to NO3--N. It had a significant impact on the interaction effects of phenolic acids and nitrogen forms on net photosynthetic rate(PN), intercellular CO2 concentration(Ci), transpiration rate(Tr), stomatal conductance(Gs), stomatal limitation(Ls), and water-use efficiency(WUE) of leaves(P < 0.05). When the ratio of NH4+-N to NO3--N was 1:14, the main reason for the decline of PN was the non-stomatal factors, while when the ratio was 1:3, the main reason changed to the stomatal factor. Under the condition of phenolic acids, when the ratio of NH4+-N to NO3--N was increased, the increase of PN of poplar was larger than that under non-phenolic acid condition. The PN of poplar was the highest with 0X*1:3 and 0.5X*1:3 treatments. Therefore, ammonium nitrogen fertilizer was recommended to increase for dealing with the issue of the degradation of continuous cropping poplar plantations.2. The Effects of phenolic acids concentrations and ntrogen forms on chlorophyll fluorescence of Populus × euramericana ‘Neva’With the increase of the concentration of phenolic acids, Fm, Fv/Fm, ΦPSⅡ, and qP decreased, while F0 and NPQ increased. When the content of ammonium nitrogen increased, the reduction extents of Fm, Fm/Fv, and qP decreased and were influenced by the interaction effects of phenolic acids and nitrogen forms, significantly(P < 0.01), and F0, ΦPSⅡ and NPQ were beneficial to photochemical reactions of poplar.3. The Effects of phenolic acids concentrations and nitrogen forms on biomass of Populus × euramericana ‘Neva’With the increase of the concentrations of phenolic acids, the total biomass of poplar decreased, the R/S increased. When the ratio of NH4+-N to NO3--N was increased, the total biomass increased, and the root-shoot ratio decreased. The distribution patterns of aboveground and underground parts of the poplar were influenced by phenolic acids and nitrogen forms. The biomass of underground parts increased with the increase of the concentration of phenolic acids. The biomass of aboveground parts increased with the ratio of NH4+-N to NO3--N. The interaction effects of phenolic acids and nitrogen forms on biomass and R/S had a significant influence(P < 0.01). Under the condition of phenolic acids, increasing the ratio of NH4+-N to NO3--N reduced the decreasing amplitude of biomass and the increasing amplitude of R/S.4. The Effects of phenolic acids concentrations and nitrogen forms on nitrogenous metabolism of Populus × euramericana ‘Neva’With the increase of the concentration of phenolic acids, the content of total nitrogen in roots stems and leaves decreased, but the content of total nitrogen increased when the ratio of NH4+-N to NO3--N was increased. The interaction effects of phenolic acids and nitrogen forms had a significant impact on total nitrogen content. The content of total nitrogen in root, stem, and leaf of poplar with 1.0X*1:3 treatment was the highest, and it was 1.07, 1.08 and 1.03 times than those with 0X*1:14 treatment, respectively.About 90% of the nitrogen used by poplar is from the absorption of nitrate ions and the rest is derived from the absorption of ammonium ions. Of the total nitrogen uptake, 28%-36% was assigned to the root, 45%-54% was distributed to the leaves, and 17%-19% was assigned to the stem only. The absorbed ammonium nitrogen had 34%-45% distribution to the root, 35%-50% was assigned to the leaves, and 15%-21% was assigned to the stem; 27%-35% of the uptake of nitrate nitrogen was assigned to the root, 46%-55% was assigned to the leaves, and 16%-19% was assigned to the stem. With the increase of the concentration of phenolic acids, the contents of total nitrogen, nitrate nitrogen, and ammonium nitrogen in root were increased, but the contents of total nitrogen, nitrate nitrogen, and ammonium nitrogen in leaf were decreased. In addition, the content of ammonium nitrogen in the stem was increased, and the contents of total nitrogen and nitrate did not change. Phenolic acids could reduce the total amounts of ammonium nitrogen and nitrate uptake in poplar, and the higher concentration of phenolic acids was, the less amount of ammonium nitrogen and nitrate uptake would be. The largest decrease in ammonium nitrogen uptake was between 0X-1.5X; and the largest decrease in nitrate nitrogen uptake was between 1.0X-2.0X.The activities of NR, GS, and GOGAT in the roots and leaves of poplar decreased with the increase of the concentration of phenolic acids, and increased with the increase of the ratio of NH4+-N to NO3--N. The interaction effects of phenolic acids and nitrogen forms had a significant influence on the activities of NR, GS, and GOGAT in poplar(P < 0.01). Under phenolic acid environment, when the ratio of ammonia to nitrate was increased, the increase rates of the activities of NR, GS, and GOGAT in roots and leaves were higher than those in the non-phenolic acid environment. The activities of NR, GS, and GOGAT in leaves were much higher than those in roots, and the uptake of ammonium by poplar was mainly in the leaves.