Photosynthetic responses to light in seedlings of selected Amazonian and Australian rainforest tree species

Abstract

Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy.

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

“…However, with the exception of similar light levels in the studies of Langenheim et al (1984) and Ishida et al (1999), daily and maximum PFD under HL in our experiment were much higher than the high light treatments of those studies. In addition, considering the low values of A max , A sat and chlorophyll a content we have evidence to suggest the occurrence of chronic photoinhibition (Osmond 1994) in H. courbaril under HL and a higher susceptibility of H. courbaril than T. micrantha to this process.…”

“…Apparent quantum yield and F v /F m ratio at midday of both plants studied were very low when compared to rainforest climax species and did not show a complete recover at pre-dawn (Thompson et al 1992, Langenheim et al 1984, Lovelock et al 1994, Zipperlen & Press 1996, Barker et al 1997, Scholes et al 1997. However, with the exception of similar light levels in the studies of Langenheim et al (1984) and Ishida et al (1999), daily and maximum PFD under HL in our experiment were much higher than the high light treatments of those studies.…”

“…stilbocarpa under LL was very high when compared with other semideciduous (Kitajima 1994) and rainforest climax species grown under both high and low light levels (Langenheim et al 1984;Ramos & Grace 1990, StraussDebenedetti & Bazzaz 1991, Turnbull 1991, Thompson et al 1992, Tinoco-Ojanguren & Pearcy 1995, Zipperlen & Press 1996, Barker et al 1997, Sholes et al 1997. It is also interesting to compare the results of H. courbaril var.…”

“…It is also interesting to compare the results of H. courbaril var. stilbocarpa, an endemic semideciduous variety, with the same species from Amazonian rainforest (Langenheim et al 1984). According to Langenheim et al (1984), H. courbaril from Amazonia showed photosynthetic capacity around 5.0 and 3.5 when growing, respectively, Table 2.…”

“…stilbocarpa, an endemic semideciduous variety, with the same species from Amazonian rainforest (Langenheim et al 1984). According to Langenheim et al (1984), H. courbaril from Amazonia showed photosynthetic capacity around 5.0 and 3.5 when growing, respectively, Table 2. Means ± s x -of transpiration rate (E) and stomatal conductance (g s ) in mol m -2 s -1 for seedlings of Trema micrantha (pioneer) and Hymenaea courbaril var.…”