The effects of phenolic acids and nitrogen form on poplar saplings

• 1、College of Forestry, Shandong Agriculutral University, Taian city, 271018

Abstract：The relationship between nitrogen form and tree growth need to be further investigated and it is still unclear that how the tree biomass allocation and fine roots growth are affected by the ratio of ammonium to nitrate in phenolic acid environments. The study focused on the response of the biomass allocation of stem, leaf and roots of poplar saplings (Populus × euramericana \'Neva\') to different NH4:NO3 ratios in simulated phenolic acid environments, and examined the response of root morphology and carbon and nitrogen concentration in roots to ammonium:nitrate ratio based on root order. The objective is to provide theoretical foundation for further study on the relationship between the characteristics of root and soil interface and the tree growth. The results showed that: (1) Treated with different NH4:NO3 ratio, the poplar saplings demonstrated the significantly different allocation pattern of roots biomass (P < 0.05). Phenolic acid reduced the biomass of poplar saplings, but it was significant and also did not change the distribution pattern of above- and below-ground biomass. (2) Treated with different NH4:NO3 ratios, root diameter, root dry weight and specific root length of poplar saplings were significantly different (P < 0.05). the dry weight of fine root was significantly increased under the 1: 3 NH4:NO3 ratio (P < 0.05). however, the 4-5 order fine root diameter was significantly inhibited but the specific root length was increased under 1: 7 NH4:NO3 ratio. Phenolic acid and NH4:NO3 ratio significantly affected the diameter of fine roots (P = 0.012), root dry weight (P = 0.011) and specific root length (P = 0.008). The interaction between phenolic acid and NH4:NO3 ratio had a decisive effect on fine roots hierarchy. (3) Phenolic acids and NH4:NO3 ratio had a significant interactive effect on the concentration of carbon and nitrogen in 4-5 order fine roots. Under 1:14 NH4:NO3 ratio, phenolic acids significantly increased the carbon concentration in 4-5 order roots. (4) The principal component analysis (PCA) showed that there were significant differences in the morphological characteristics and the carbon and nitrogen concentration of root orders. Four principal components explained 80.8% of all variation in the morphological and chemical traits of poplar roots. Roots order has 0.892 loading value in the first principal component, and phenolic acids have 0.768 loading in the second principal component, and nitrogen (NH4:NO3 ratio) has 0.944 loading value in the fourth principal component. All the results indicated that the mineral nitrogen forms had a significant effect on the poplar biomass allocation, phenolic acids and NH4:NO3 ratio had a significant interactive effect on the morphology of fine roots and the concentration of carbon and nitrogen in roots. Therefore, a reasonable ratio of inorganic nitrogen during fertilization has great practical significance for improving the poplar plantation productivity.

Keywords： fine roots morphology biomass allocation phenolic acids NH4:NO3 ratio root order