Cottonwood Fine-Root Turnover in Response to Nitrogen Regimes in a Short Rotation Plantation Study

Abstract

Fine-roots are the most active and absorptive part of the root system. Roots respond to and are controlled in part by the environment. Environmental factors are often correlated with root dynamics including soil moisture, aeration, temperature, and nutrient supply. The mineral nutrient most frequently limiting to plant growth is nitrogen (N). Nitrogen availability is dependent on microbial activity and environmental conditions. Favorable conditions increase N availability and fine-roots take up the available N to meet plant demands. Plant nutrient demands in fast growing Populus spp. (poplar) can be high. Poplar plantations have the potential to absorb excess N in the environment and to be used as buffers along agricultural lands or used for remediation. The fast growth in poplars also has the potential to meet human needs. Correct manipulation of N fertilizer or site selection can induce rapid growth to meet wood resource demands for energy and industry and to sequester CO2 and reduce green house gases. With so many possible uses for poplars and the potential to meet objectives by using N correctly, we tested cottonwood (Populus deltoides) fine-root response to various N fertilizer levels in a short rotation plantation. The plantation was maintained and studied for two years. Fine-root dynamics were controlled largely by temporal effects. Live-root standing crop increased 1.6 fold from the first through the second year. First year roots had longer life spans than second year roots. First year root production also responded to N treatment but no biological implications were found. Change in time with stand age and season had the strongest control over fine-root dynamics of this cottonwood stand under intensive management.