GROWTH, RESPIRATION, ION UPTAKE AND CARBON PARTITIONING OF PHASEOLUS VULGARIS L. ROOT SYSTEMS EXPOSED TO LOCALIZED ANOXIA

Soil aeration may vary widely in space and time within compacted, poorly drained and even some well drained soil environments. The analysis of root responses to variations in soil aeration could contribute to our understanding of root growth under field conditions.; Split root cultures were used to simulate conditions of localized anoxia within the root systems of (Phaseolus vulgaris L.) genotypes. Aeration treatments included an aerated control, a nonaerated control and a localized anoxia treatment where half of the root system was aerated and the remaining half nonaerated. A modified infrared gas analyzer method was developed to measure the CO(,2) respiration of root systems. Root growth during the 72 hour treatment period was determined using a staining technique.; Root growth did not occur in the nonaerated environments. Localized anoxia stimulated root growth in the aerated portion of the root system with values ranging from 150 to 185% of the aerated control. An experimental line partitioned the compensatory growth into roots which were present before the treatment period. A stress resistant variety partitioned the extra growth into lateral roots which emerged during the treatment. Compensatory root growth was associated with an increase in the number of elongating lateral root tips which emerged during the treatment.Localized anoxia stimulated the absorption of K('+) ions per unit of root weight in one genotype.; Aerated root systems accumulated between 40 to 60% of the ('14)C-sucrose translocated from the source leaf in a 2 h labeling period. Localized anoxia resulted in the greater translocation of ('14)C-sucrose to the elongating root tips of a stress line while the label accumulated in the nongrowing portions of the stress susceptible root system.; Oxygen stress within a portion of the root system appeared to increase root growth, ion uptake, respiration and modified the carbon accumulation in the nonstressed portion of the root system. These varied responses of the genotypes to localized anoxia suggests that the adaptation of genotypes to specific soil environments combined with the development of soil management techniques designed to produce an improved root environment could contribute substantially to the utilization of marginal soils.