Amino acid nutrition in short-rotation tree production: The effects on soil nutrient dynamics, microbial interactions, and tree physiology

Plants have the ability to assimilate and use amino acids as part of their nitrogen (N) nutrition. This has been observed in boreal, temperate, tundra, and alpine ecosystems, but further studies are needed to elucidate amino acid nutrition in forestry and agricultural production systems. This research evaluates the effects of amino acid nutrition on soil nutrient dynamics, microbial interactions, and tree physiology in short-rotation tree production of three economically important tree species. Two conifer species---Fraser fir (Abies fraseri [Pursh] Poir.) and Red pine ( Pinus resinosa Aiton)---and one hardwood, hybrid poplar ( Populus nigra L. x Populus maximowiczii A. Henry 'NM6') were fertilized with varying rates (0, 50, 100, 200, and 300 lbs N ac-1) of an amino acid fertilizer containing arginine. Results indicate that competition may be occurring in the year of establishment, as arginine applications rates two to three times greater than the inorganic control were necessary to achieve similar growth and foliar N. In subsequent research, similar biomass and nutrient partitioning and no improvements in NUE were observed, indicating that nutrients are not severely limiting likely because arginine is functioning as a slow release fertilizer. CEC and microbial activity were not improved, likely due to the short duration of the study. Results also indicate that photosynthesis is likely more affected by biochemical processes than nutrient availability or microbial interactions. We suggest that amino acids have the potential to be a viable, alternative nutrient source, though further research should continue to elucidate the effects of amino acid nutrition in production systems.