Root Hydraulic Conductance of Four Cotton Genotypes Grown with and without N Fertilizer.

Nitrate concentration in soil has been shown to influence hydraulic conductivity of plant roots in controlled environments. This research was conducted to evaluate the influence of N fertilizer rate and genotype on cotton (Gossypium hirsutum L.) root hydraulic conductance under field conditions. Four cotton genotypes that were developed in diverse environments were grown with 0 or 112 kg N ha^-1 in Florence, SC and Stoneville, MS in 2009 and 2010. The four genotypes were AGC 85 (developed in Arizona), PD-2 (developed in South Carolina), Siokra L-23 (developed in Australia), and Tamcot 22 (developed in Texas). Root hydraulic conductance was measured with a high pressure flow meter about six weeks after emergence when soil water was not limiting. At the same time, plant stems were collected and analyzed for nitrate concentration. Hydraulic conductance of roots was higher in Stoneville than in Florence; interactions among locations, N rates, and genotypes were not significant. Stem nitrate concentrations were higher for plants in plots receiving N fertilizer, but no differences between fertilizer rates occurred for root hydraulic conductance. Similarly, no differences occurred among these diverse genotypes for root hydraulic conductance in either location in either year. Results agree with previous research that N does not influence hydraulic conductance under field conditions.