Sulfate Uptake Kinetics of Three Annual Range Species1

Abstract

AbstractThe sulfate uptake rates of roots of three annual forages were found to follow different Michaelis‐Menten kinetics. Depletion of added sulfate from the nutrient medium by intact plants gave more reproduceable results than excised roots. Subclover (Trifolium subterraneumL.) showed the lowest affinity for sulfate but a high maximal rate of sulfate uptake. Soft chess (Bromus mollisL.) showed bimodal behavior either with a very high affinity and a low maximal uptake or low affinity with high maximal uptake, suggesting that two uptake mechanisms operate in this species. Sulfate uptake rates decreased with plant age for all three species. The decrease was greatest with filaree [Erodium botrys(Cav.) Bertol.] and least with soft chess. A root temperature of 4°C reduced sulfate uptake by all species implying that sulfate uptake depends on active metabolism. When returned to 20°C, sulfate uptake rates for subclover and filaree recovered immediately, but soft chess recovered only partially. Reduced O2from aeration with N2gas decreased sulfate uptake rates for subclover and soft chess but not for filaree. Subclover recovered quickly to the uptake rates observed before treatment, but soft chess did not. Selenate and molybdate interfered with sulfate uptake. Molybdate at 20 µMhad rapid deleterious effects on the root systems of all species. Selenate at the 20 µMconcentration showed no effect on soft chess, but sulfate uptake of filaree and subclover was reduced initially and plant death occurred within 24 h. The ecological significance of sulfate uptake kinetics is discussed with respect to botanical composition changes that occur with increased S supplies on deficient rangelands.