Effect of phosphorus availability on basal root shallowness in common bean

Abstract

Root gravitropism ma y be an importantelementof plant r esponseto phosphorusavailabilit ybecauseit determine s root foraging in fertile t opsoil horizon s, a nd thereb y phosphoru s ac quisition. In thi s study we seek t o test this hypothesisin both t wo dimensionalpaper growth pouch and three-dimen sional s olid media of sand and soil cultures. Fi ve common bean (Phaseo lus vulgaris L.) genotypeswith contrasting ad aptationto low phosphorus availability w ereevaluatedin growth pouches ove r 6 days of growth,and in sand cultureand soil culture o ver 4 weeks of growth. Inall thre e media,phosphorusavailabilit yregulatedthe gravitropic r esponse ofbasal rootsin a genotype-dependent mann er.In pouches, s and,and soil, the phosphorus-inefficient ge notype DOR 364 had deeper roots with phosphorus stress, whereas the ph osphoru s-efficient ge notype G 198 33 respondedto phosphorus s tress by producing shallower ro ots.Genotype sweremostresponsiveto phosphorus s tress insand culture,where rel ative root allocationto the 0-3-and 3-6-cm horizonsincreased50% with phosphorus s tress,and varied 300% (3-6 cm) to 500% (0-3 em) among genotypes. Our re sultsindicatethat(1) phosphorusavailabilit yregulates roo tgravitropic growth in both paper and solid media , (2) responses o bservedin young seedlingscontinue thr oughout ve getative growth,(3) the r esponseof rootgravitropi smto phosphorus av ailabilityvaries amon g genotypes, and (4) genotypic adaptation t o low phosphorus a vailability i s correlated with the ability t o allocate root s to shallowsoil horizons under phosphoru s stress.