Contrasting effects of rooting volume and aerial spacing on shoot morphology and reproductive performance of Lupinus angustifolius L. cv. Danja

Abstract

Dry matter production and reproductive performance of sand-cultured, pot-grown plants of Lupinus angustifolius L. cv. Danja were markedly affected by varied aerial density (19, 23, 45 and 90 plants m-2) at constant high rooting volume (4.7 l plants-') or by varied rooting volume (1.1, 2.4 and 4.7 1 plant-1) at constant low aerial density (19 plants m-2). Dry weight of roots decreased markedly with reduced aerial spacing, but not with reduced rooting volume, whereas root:shoot dry weight ratio was affected (increased) only by decreased rooting volume. Above-ground competition reduced fruit and seed number to a relatively greater extent than dry matter production, leading to highest 'reproductive' indices and harvest indices at lowest aerial density and least rooting volume. Decreased rooting volume reduced reproductive yield primarily by decreasing the number of orders of branches, while not affecting numbers of pods and seeds on inflorescences. Increased aerial density specifically reduced fruit set and seed number on all inflorescences. Number of branches in each order of inflorescence was reduced, but not the number of orders of branches. Results are discussed in relation to observed effects of inter-plant competition under field conditions, and to nutritional and hormonal hypotheses concerning reproductive performance.