Monday, November 13, 2006
61-1
Effects of Stress on Respiratory Carbon Efflux from two Maize Inbreds and their Hybrid.
Hugh Earl, Weidong Liu, and Matthijs Tollenaar. Univ. of Guelph, Dept. Plant Agriculture, Guelph, ON N1G 2W1, Canada
Respiratory carbon losses represent a major fraction of the total carbon balance for field crops, but for most crops there is little information on how respiration may vary by genotype, or how respiration is affected by environmental stresses. We monitored pre-dawn respiration rates in two maize inbred lines and their hybrid, grown in an outdoor hydroponic system. Stress treatments were imposed during the period from one week pre-silking to two weeks post-silking (stress period 1) or from two weeks to five weeks post-silking (stress period 2). Light stress was imposed as a 55% reduction in incident light via shade cloth, water stress by restricting irrigation to 50% of daily transpirational water use of control plants, and N stress by withholding N fertilizer from the nutrient solution. Pre-dawn respiration of shoots and washed roots was measured at 20°C in a whole plant gas exchange system at the beginning and end of each stress period, and was expressed in terms of daily fractional loss of existing dry matter (specific respiration, RDW). Genotype by treatment interactions were generally non-significant for RDW. Under control (unstressed) conditions, no significant genotype effect on RDW of roots was found, and RDW of roots was relatively constant across measuring dates, declining from 2.5% d-1 one week pre-silking to 2.1% d-1 by five weeks post-silking. By contrast, RDW of shoots declined from 2.6 to 1.2% DW d-1 over the same period, and by five weeks post-silking was 15% lower in the hybrid than in either inbred. Water stress reduced RDW of shoots during stress period 1. During stress period 2, all three stresses significantly reduced RDW of roots, and all but the N stress reduced RDW of shoots.