Effects of Mineral Nutrition on Components of Reproduction in Clarkia ungucilata

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.

Effects of Soil Nitrogen on Pollen Production, Pollen Grain Size, and Pollen Performance in Cucurbita pepo (Cucurbitaceae)

“…In other species, pollen production per flower and/ or pollen grain size are known to vary within and among plants in a population, and some of this variation appears to be due to environmental conditions affecting the pollenproducing plant (Willson and Burley, 1983;Stanton and Preston, 1986;McKone and Webb, 1988;Cruzan, 1990;Young and Stanton, 1990b;Nakamura and Wheeler, 1992). For example, pollen production per flower and/or mean pollen grain size typically decreases over the course of the growing season as the number of prior flowers and fruits on the plant increases (e.g., Vasek et al, 1987;Cruzan, 1990;Young and Stanton, 1990b; but see Devlin, 1989). Because our study uses inbred lines of plants and an experimental garden design, it clearly demonstrates that a common environmental factor (differences in soil nitrogen availability) can influence both the size and number of pollen grains/flower that a plant produces.…”

“…It is, therefore, reasonable to expect that the conditions under which the sporophyte is growing may influence both the quantity and quality of the pollen it produces. Only recently, however, have the growing conditions of the sporophyte been shown to affect pollen production (Freeman and Vitale, 1985;Vasek et al, 1987), pollen viability (Freeman and Vitale, 1985;Vasek et al, 1987), and pollen germination (Schlichting, 1986). Environmentally determined differences in pollen performance (speed of germination and/or pollen tube growth rate) are potentially important because they could lead to nonrandom fertilization under conditions of pollen competition (more pollen tubes in the style than ovules in the ovary).…”

Characteristics of pollen production in a population of New Zealand snow‐tussock grass (Chionochloa pallens Zotov)

“…Few other species have been investigated in this regard. In Clarkia unguiculata, both pollen production and ovule number are reduced in flowers from later inflorescence nodes; however, these differences cancel each other so that the pollen-ovule ratio is unchanged (Vasek et al, 1987).…”

Testing Evolutionary and Ecological Hypotheses Using Path Analysis and Structural Equation Modelling

“…Arnold * Present address: Dr R. J. Mitchell, Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA. 1972;Maddox & Antonovics 1983;Mitchell-Olds 1987;Vasek et al 1987;Schemske & Horvitz 1988;Crespi & Bookstein 1989;Crespi 1990;Farris & Lechowicz 1990). Yet this revival has not exploited fully the powerful methodological advances introduced by behavioural and social scientists, whose experimentally intractable systems parallel our own (but see Maddox & Antonovics 1983).…”