Effect of Temperature and Light Intensity Early in Ontogeny on Growth of Pinusresinosa Seedlings

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Abstract
Low temperature or low light intensity following germination of Pinusresinosa seeds greatly suppressed subsequent seedling development, with cotyledon expansion inhibited more than root expansion. A strong influence of shoot environment early in ontogeny was demonstrated on initiation of all but a few early-formed primary needle primordia and on expansion of all primary needles, including those formed early. Low temperatures or low light intensities during the cotyledon stage of development prevented initiation of most of the normal complement of primary needles. However, when seedlings were placed in a favorable environment following prolonged exposure to low temperature or low light intensity, primordia of primary needles formed readily and subsequently expanded. Following seed germination, the young seedling is a system of competing carbohydrate sinks. Early development of the seedling is an integrated continuum with the source of growth requirements shifting during ontogeny, from megagametophytes to cotyledons, to primary needles, to secondary needles. The importance of cotyledons and primary needles to early seedling development is emphasized.

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