The influence of simulated shadelight and daylight on growth, development and photosynthesis of Pinus radiata, Agathis australis and Dacrydium cupressinum

Abstract

Juvenile seedlings, tnicropropagated plantlets, and adult rooted cuttings of Pinus radiata, together with seedlings of Agathis australis and Dacrvdium cupres.sitium, were grown under either high (670/nnoltn's') or low (200/nnol tn's ') photosynthetic photon flux density (PPFD) and, at low PPFD, under three red:far-red (R/FR) conditions, approxitnately simulating canopy shadelight, daylight and one intertnediate value. In all types of P. radiata, a shade-intolerant species, stetn height and diatneter, stetn and needle dry weight, and apical dotninance wete tnarkedly increased by a reduction in R:FR ratio while fascicle density was decreased. In eonttast, these increases were considerably less for the shade-tolerant D. eupres.simitn and tnoderately tolerant A. australis. With the exception of the P. radiata seedlings, height growth was gteatest in all speeies under high compared to low PPFD for daylight R:FR tatio conditions. Total shoot (or plant) dty weight was increased approximately two-fold in all species and types by the higher PPFD. Shoot extension tates were negatively cortelated with calculated phytochrotne photoequilibriutn with P. radiata, the n-iost shade-intoletant species, having the highest change in tate per unit change in photoequilibriutn (i.e. very responsive), and D. eupressinum, the tnost shade toletant species evaluated, having the stnallest change (i.e. largely untesponsive). Within the specttal quality treattnents at low PPFD, it is suggested that higher rates of dry tnatter aecumulation under the low R:FR ratio were the result of reduced mutual shading of adjacent leaves as a consequence of pholotnorphogenically-conttoiled internode lengths rather than of enhanced photosynthesis per .sc. The significance of the tesults is diseussed in relation to planting stock tnanagetnent in nurseries, the management of forest canopies for understotey seedling growth, and to the construction of representative growth sitnulation tnodels. Consequences for controlled environment lighting are also cotisidered.

Responses of growth, photosynthesis, and leaf conductance to white light irradiance and end‐of‐day red and far‐red pulses in Fuchsia magellanica Lam.

“…Morgan & Smith (1979) found under a relatively high /of 180 //mol m^" s'' that stem extension rate was only slightly affected by R: FR in herbaceous species from closed canopy habitats, but increased markedly in those from open canopy habitats. Warrington et al (1989) observed that for three tree species the responsiveness to R: FR at 200 //mol m"' s"ŵ as inversely related to their shade tolerance. In short term experiments, Impatiens parvifiora (an annual shade tolerator) shows a large increase in stem extension in response to low R: FR under / = 13 //mol m"'^ s^^ (Whitelam & Johnson, 1982).…”

Morphological Responses of Wheat to Changes in Phytochrome Photoequilibrium

“…Past research has relied mainly on an approximation of'P, called the v ratio, which is based on the relative amounts of radiation at the peak absorption wavelengths for each form of phytochrome, generally considered to be centered around 660 nm for Pr and 730 nm for Pfr. However, exact values for these peak absorbances can vary, and different researchers have used v to represent a range of ratios (5,7,11,17,20,26). In this paper, v represents the ratio of radiation at 660:730 nm unless otherwise specified.…”

“…Lowering of v by either means results in the morphological responses of increased stem elongation (17,18,24,26) and reduced tillering (6,20 x 100 mm) and germinated at 23°C in a multisectioned, controlled-environment growth chamber. All plants in trials 1 to 3 were cv Fielder.…”

Elongation of Scots pine seedlings under blue light depletion

“…Simulated shade, i.e. a low red to far-red (R/FR; 660 nm/730 nm) ratio also elongates pine trees (Warrington et al 1988). Consistently, pine trees produce tall and straight trunks in dense stands, as pine is a shade-avoiding species.…”