Species differences in seedling growth and leaf water response to light quality

Abstract

For the majority of forest species slight canopy opening reduces light limitations suggesting that light quality often measured as red:far red ratio (R:FR) plays a significant role in the development of seedlings. The effect of different levels of R:FR was studied on seedlings of four Ghanaian timber species of different ecological guilds to assess their growth and leaf water response to changes in R:FR. The experiment was conducted in shade houses of varying light qualities (0.30, 0.46 and 0.76 R:FR) achieved with the use of bamboo slats, green filter and white cotton cloth. Relative height growth of all species declined in high R:FR with Guarea cedrata and Celtis mildbraedii, shade bearers, having a slower decline of height growth with increasing R:FR than Terminalia ivorensis, pioneer, and Albizia zygia non-pioneer light demander. Relative diameter growth on the other hand increased in higher R:FR treatments except for G. cedreta. Relative biomass growth was not significantly affected by R:FR. Leaf area ratio did not vary in different R:FRs for G. odorata but for the other species it was lower in higher R:FRs. Specific leaf area was also not affected by R:FR except in G. cedreta where it dropped with increase in R:FR. The diurnal pattern of change in stomatal conductance and leaf water potential of T. ivorensis and G. cedrata were similar in lower R:FR ratio but opposite in higher R:FR. This results show that the response of seedlings to changes in R:FR is different for different species and is more of morphological change rather than growth (biomass accumulation). Pioneers are more sensitive to these changes than non-pioneers.

Keywords: Red:far-red ratio, light quality, seedlings growth response, leaf water status, morphological change