Growth response of cottonwood roots to varied NH₄:NO₃ ratios in enriched patches

Abstract

Maximization of short-rotation forest plantation yields requires frequent applications of nutriends, especially nitrogen(N). Whole-plant growth is known to be sensitive to teh proportion of ammonium to nitrate (NH₄:NO₃). However, the extent to which N form affects root growth, branching and morphology is poorly understood, and these variables may have substantial impoacts on plant nutrient and water acquisition. We used rooted cuttings of cottonwood (Populus deltoides Bartr. ex Marsh.) to investigate the effect of various NH₄:NO₃ ratios on root growth in N-enriched patches. A sand culture study with split-root systems was carried out in which 1-3% of the total root system of each cutting was supplied with 2 mMN at NH₄:NO₃ ratios of 0:100, 20:80, 40:60, 80:20, and 100:0 (molar basis), with the rest of the plant supplied with 0 mM N, resulting in the whole plant becoming N deficient. During the experiment, while-plant growth was unaffected by the treatments. Of the NH₄:NO₃ ratios tested, greatest total root length, specific root length, and root N concentration of roots in enriched patches occurred in the 20:80 NH₄:NO₃ treatment. The largest response of roots in enriched patches was third- and fourth-order root production. We conclude that N form has a profound effect on root development and morphology in enriched patches.

Citation

Woolfolk, Walter T.M.; Friend, Alexander L. 2003. Growth response of cottonwood roots to varied NH₄:NO₃ ratios in enriched patches. Tree Physiology (2003) 23, 427-432