Nutrient Use Physiology and Morphological Response of Short Rotation Trees Under Amino Acid Fertilization

Plants have the ability to uptake and utilize amino acids as a primary nitrogen source in forest and agricultural ecosystems.  This process has been reported in the arctic, boreal and temperate forests, and in controlled environments where plants are raised in containers. We report on a two-year study that aimed to understand the nutrient use physiology and morphological response of short rotation trees to amino acid fertilization. Conifer transplants (Fraser fir [Abies fraseri] and red pine [Pinus resinosa]) and hardwood cuttings (hybrid poplar) were installed in a nursery bed and treated with varying rates (0, 50, 100, 200, and 300 lbs N/acre) of an amino acid fertilizer containing arginine as a nitrogen source and other plant-essential nutrients. Granular ammonium sulfate applied at 100 lbs N/acre was used as a positive control. Suction lysimeters were installed below the root zone and leachate was collected regularly for chemical analyses. Parameters monitored include morphological response, biomass accumulation, nutrient content in various tree tissues (N, P, K, Ca, Mg), and nutrient leaching below the root zone (N, K, Ca, Mg).  Results obtained indicate that amino acid treatment tended to have a significant effect on morphological responses (height and diameter growth) in conifers and the hardwood, especially in the first year of the study.  This result was suggested to be due to competition with soil microbial communities for arginine following transplant. Morphological response in high rate amino acid treatments tended to be enhanced or similar to the positive control for conifers and the hardwood.  Biomass production and nutrient accumulation were significantly affected by amino acid treatment in the hardwood hybrid and both conifer species.  The enhanced morphological response and biomass production in the hybrid poplar compared to the conifer species is explained by the greater nutrient use efficiency and nutritional needs.  Nutrient losses in amino acid treatments were similar to control treatments in the second year of the study, suggesting that applied amino acid fertilizer was either uptaken by tree roots, bonded to soil exchange sites, or fixed in microbial biomass.  Additional studies are underway to confirm these hypotheses.