Photosynthetic induction in saplings of three shade-tolerant tree species: comparing understorey and gap habitats in a French Guiana rain forest

Abstract

The photosynthetic induction response under constant and fluctuating light was examined in naturally occurring saplings (about 0.5-2 m in height) of three shade-tolerant tree species, Pourouma bicolor spp digitata, Dicorynia guianensis, and Vouacapoua americana, growing in bright gaps and in the shaded understorey in a Neotropical rain forest. Light availability to saplings was estimated by hemispherical photography. Photosynthetic induction was measured in the morning on leaves that had not yet experienced direct sunlight. In Dicorynia, the maximum net photosynthesis rate (A ) was similar between forest environments (ca 4 µmol m s), whereas for the two other species, it was twice as high in gaps (ca 7.5) as in the understorey (ca 4.5). However, the time required to reach 90% of A did not differ among species, and was short, 7-11 min. Biochemical induction was fast in leaves of Pourouma, as about 3 min were needed to reach 75% of maximum carboxylation capacity (V); the two other species needed 4-5 min. When induction continued after reaching 75% of V , stomatal conductance increased in Pourouma only (ca 80%), causing a further increase in its net photosynthesis rate. When fully induced leaves were shaded for 20 min, loss of induction was moderate in all species. However, gap saplings of Dicorynia had a rapid induction loss (ca 80%), which was mainly due to biochemical limitation as stomatal conductance decreased only slowly. When leaves were exposed to a series of lightflecks separated by short periods of low light, photosynthetic induction increased substantially and to a similar extent in all species. Although A was much lower in old than in young leaves as measured in Dicorynia and Vouacapoua, variables of the dynamic response of photosynthesis to a change in light tended to be similar between young and old leaves. Old leaves, therefore, might remain important for whole-plant carbon gain, especially in understorey environments. The three shade-tolerant species show that, particularly in low light, they are capable of efficient sunfleck utilization.

Links between tree structure and functional leaf traits in the tropical forest tree Dicorynia guianensis Amshoff (Caesalpiniaceae)

“…Changes in LMA were caused by changes in leaf thickness but not in density. Increases in LMA with increasing tree age or size are well documented [26,56,60,74,89]. Variations in LMA related to changes in leaf thickness have been also reported in numerous species [58].…”

“…Classical patterns of response of leaves to changing light conditions were observed between trees at low and medium irradiance [1,12,21,26,39,46,57,58,61,63,66,67,74,86,90]. Leaf thickness and density, leaf dry mass per area and stomatal density increased with increasing irradiance pointing out the large leaf plasticity of the species.…”

“…Each A-PPFD curve consisted of eight measurements at decreasing PPFD obtained by placing neutral filters between the bulb and the cuvette: values close to 1 050, 700, 400, 150, 100, 50, 30 and 0 µmol m -2 s -1 were used. The time needed for photosynthetic induction and foliage acclimation between two measurements was about 15 min [74] and 5 min, respectively.…”

“…It is likely that the increase in leaf thickness in the understorey results from the light acclimation process to low irradiance. D. guianensis, like numerous other tropical species [67,86], increases its leaf life-span in the understorey (mean leaf life span of saplings in understorey ranging from 3 to 4 years [5,74] vs. 18 months in clearings [5]. This results in a greater biomass accumulation and provides a means to compensate for the leaf construction costs over time [6,73,83], and to enable the construction of an efficient foliar display for light interception [30,68,87].…”

Photosynthetic performance and anatomical adaptations in Byrsonima sericea DC. under contrasting light conditions in a remnant of the Atlantic forest

“…Photosynthetic induction occurs rapidly, in minutes (Rijkers et al, 2000), whilst photosynthetic adjustments can take days (Cai et al, 2005) and morphological alterations are observed after weeks or months (Ackerly, 1997). Within the plasticity possible for each successional state, plants adjust their pigments, photosynthesis, ultra-structure and anatomy in response to light (Oguchi et al, 2003;Rozendaal et al, 2006;Terashima et al, 2006;Sarijeva et al, 2007).…”