Abstract
An experiment was conducted to determine the effects of nutritional level and flower location on factors related to flower, pollen, and ovule production, and to determine what developmental patterns would be modified to mediate any observed changes. Plants subjected to high nutrient levels developed larger leaves, more branches, more flowers on both the main stem and the branches, and opened their first flowers 6 days sooner than plants at lower levels of nutrients. Total flower number increased from 72.2 to 626.8 per plant, with most of the increase produced on the primary branches. The number of pollen grains in the entire androecium averaged 14,685, but significantly increased with higher nutrient levels and decreased with the stage of plant maturity (nodal position on the plant). The number of ovules also increased with nutrient level and decreased with maturity stage. Average ovule number decreased from about 129 in flowers at nodes produced early in the growth cycle to about 100 in flowers produced at later nodes. Despite highly significant plasticity in numbers of both pollen and ovules, the Pollen/Ovule Ratio (average 132.7) did not vary significantly with either nutrient level or plant maturity stage. Path analysis, which decomposes correlation coefficients into direct and indirect effects of factors influencing development, indicated that nutrient level had a very strong direct effect on the number of primary branches and on the number of primary-branch flowers, as well as very strong indirect effects on the latter. The primary-branch flowers directly determined over 67% of the total flower number, and indirectly determined about 24% jointly with secondary-branch flowers, and over 3% jointly with main-stem flowers. The direct effects of secondary-branch flowers and mainstem flowers were 3.8% and 0.3%, respectively. The relationship among components of yield is slightly additive. Direct determination of yield was 74.6% by the number of flowers per plant, 0.6% by the number of ovules per flower, 3.8% by the number of seeds per ovule, and 1.1 % by the weight per seed. The proportion of yield jointly determined by flower number and the developed seeds per ovule was 15.3%. It was concluded that allocation of resources increases to both male and female functions under conditions of high nutrient levels, and pollen/ovule ratios are consistent within a plant despite significant plasticity in numbers of pollen grains and ovules.
Highlights
Energy allocation patterns of plant species to activities such as growth, maintenance, and reproduction have been the subject of many studies (Kawano and Masuda 1980; Charlesworth and Charlesworth 1981; Goldman and Willson 1986)
Experimental plants of Clarkia unguiculata were grown in a University of California greenhouse in Riverside, California, from seeds collected in the Caliente Hills, Kern County, California
Our four objectives were to determine whether flower number and other components of growth and reproduction increased with nutrient level, what developmental patterns would be modified to accomodate observed increases, what effects nutritional level and flower location have on pollen and ovule production in individual flowers, and whether consistency of the pollen/ ovule ratio might be affected by variation in the production of pollen and ovules
Summary
Energy allocation patterns of plant species to activities such as growth, maintenance, and reproduction have been the subject of many studies (Kawano and Masuda 1980; Charlesworth and Charlesworth 1981; Goldman and Willson 1986). Reproductive effort in plants is commonly defined in terms of seed production and is described by components of yield, i.e., the mass of seeds produced can be determined by multiplying together the numbers ofinflorescences per plant, fruits per inflorescence, seeds per fruit, and the weight per seed (Primack 1978; Adams 1967; and others). Increased production of flowers or fruit, etc., may be inhibited or even reversed at some high or moderately high level of nutrients, depending on the species or cultivar (Flint and Asen 1953; Arthur and Hedley 1976; Breen and Martin 1981; Maynard et al 1962)
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