Mesophyll conductance variations in response to diurnal environmental factors in Myrcia paivae and Minquartia guianensis in Central Amazonia

Abstract

Mesophyll conductance (g m ) is essential to determine accurate physiological parameters used to model photosynthesis in forest ecosystems. This study aimed to determine the effects of time of day on photosynthetic parameters, and to assess the effect of using either intercellular CO 2 concentration (C i ) or chloroplast CO 2 concentration (C c ), on maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), V cmax . We used Amazonian saplings of Myrcia paivae and Minquartia guianensis. Photosynthetic parameters were measured using an infrared gas analyzer (IRGA); g m was determined using both gas exchange and chlorophyll (Chl) a fluorescence and gas-exchange data alone. Leaf thickness (L T ) and specific leaf area (SLA) were also measured. Air temperature, relative humidity or understory light did not correlate with g m and on average daily IRGA-fluorometer-determined g m was 0.04 mol(CO 2 ) m -2 s -1 for M. paivae and 0.05 mol(CO 2 ) m -2 s -1 for M. guianensis. Stomatal conductance (g s ), g m , electron transport rate (J F ), and light-saturated net photosynthetic rate (P Nmax ) were lower in the afternoon than in the morning. However, no effect of time of day was observed on V cmax . L T and SLA did not affect any of the examined parameters. IRGAdetermined g m was almost the double of the value obtained using the IRGA-fluorescence method. V cmax values determined using C c were about 25% higher than those obtained using C i , which highlighted the importance of using C c in V cmax calculation. Decline in P Nmax at the end of the afternoon reflected variations in g s and g m rather than changes in V cmax . Diurnal variation in g m appeared to be associated more with endogenous than with atmospheric factors.

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

“…PPF and air temperature values recorded in this study are similar to those reported previously for the same region (Nascimento and Marenco, 2013). Shuttleworth et al (1984) also found that radiation above the canopy is only 40 % of extra-terrestrial radiation, about Leaf traits and sapling growth Although there was variation in soil water content and  leaf across rainfall season, neither sapling growth rates nor the leaf traits (photosynthetic parameters, LT, SLA, and the relative chlorophyll content) were affected by rainfall seasonality (p > 0.05).…”

“…V cmax and J max data were standardized to 25 ºC (Nascimento and Marenco, 2013). V cmax and J max were obtained after measuring photosynthesis at CO 2 concentrations of 50 to 2000 µmol mol −1 and saturating light intensity (1000 µmol m −2 s −1 ).…”

Photosynthetic parameters and growth in seedlings of Bertholletia excelsa and Carapa guianensis in response to pre-acclimation to full sunlight and mild water stress

“…This suggests that the biochemical properties of the leaf can be affected by the water stress, as suggested by Tezara et al (1999). The low photosynthetic rates observed under low light intensity is in agreement with the results reported by Nascimento and Marenco (2013) for saplings grown at the forest understory under natural conditions. In Tabebuia rosea, a tropical tree, A max values were 8.94 and 3.96 µmol m -2 s -1 in sun and shade plants, respectively (Kitajima and Hogan 2003), which is within the range reported in this study.…”

Crescimento e eficiência fotossintética de uso do nitrogênio e fósforo em espécies florestais da Amazônia na fase juvenil

“…Vários estudos em florestas tropicais têm relatado diversos efeitos da luminosidade nos processos fisiológicos (DENSLOW et al, 1990;MARENCO, 2010;MARENCO, 2013). Entretanto, não se sabe como mudanças da luminosidade no sub-bosque da floresta podem influenciar nas concentrações de N e P foliar e na eficiência do uso do N e P foliar na Amazônia Central.…”

“…Os valores de irradiância no sub-bosque observados neste estudo são similares aos descritos em outros trabalhos (MOLION, 1987;MARENCO, 2013), que relataram que a luz no sub-bosque da floresta é inferior a 2% de irradiância registrada acima do dossel da floresta. Nas florestas tropicais úmidas, as baixas taxas de crescimento (diâmetro e altura) nas espécies de sub-bosque estão relacionadas à baixa luminosidade a que as árvores são expostas na fase juvenil.…”