Genotypic Differences in Physiological Integration, Morphological Plasticity and Utilization of Phosphorus Induced by Variation in Phosphate Supply in Trifolium Repens

Abstract

1 A large-leafed and a small-leafed genotype of Trifolium repens were grown with homogeneous low or high phosphate (P) supply, or with heterogeneous P supply so that the plant grew from a low P patch into a high P patch. Intraplant distribution of recently acquired P-32, morphological and physiological characteristics and biomass allocation were measured so that genotypic variation in physiological integration for P and its implications for growth could be assessed. 2 Low vs, high homogeneous P supply induced differing proportional reductions in the values of plant characteristics with magnitude for percentage of branching of nonrooted ramets > leaf size > petiole length > internode length > stolen diameter and rate of ramet production. 3 In homogeneously supplied plants, only 5% of P-32 exported from a single root was transported to proximal ramets. Genotypes differed in physiological integration: under heterogeneous P supply 50% of P-32 exported from the first root of the high P patch was transported basipetally in the small-leafed compared with only 3% in the large-leafed genotype. 4 Despite the genotypic difference in P-32 distribution under heterogeneous P supply, the dry mass and morphology of proximal ramets supplied with low P were unaffected by P supply to distal ramets in both genotypes. 5 The size of distal ramets in heterogeneously supplied plants was smaller than in plants with homogeneous high P supply. Consequently, in both genotypes placement of ramets and ramet size were influenced by both the local environment and by the environment of proximal ramets (i.e. by the nutritional status of the whole plant). 6 Compared to the large-leafed genotype, the small-leafed genotype had less rapid production of biomass, smaller responses of relative growth rates to different rates of P supply, more ramets with leaves when grown in low P supply, and, when exposed to heterogenous P supply, an elevated tissue concentration of phosphorus in leaves. It was concluded that the genotypes differed in growth strategy in a manner consistent with predictions based on fertility level within their habitat of origin and that thorough assessment of physiological integration of P nutrition within genotypes of T. repens required measurement of al the processes involved in acquisition, allocation and utilization of P.