Is stomatal conductance of Central Amazonian saplings influenced by circadian rhythms under natural conditions?

• Published in: Theoretical and experimental plant physiology Vol. 26; no. 2; pp. 115 - 125
• Main Authors: Mendes, K. R., Marenco, R. A.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-08-2014
• Subjects: Biomedical and Life Sciences; Life Sciences; Biological clock; Stomatal patchiness; Diurnal photosynthesis
• ISSN: 2197-0025; 2197-0025
• DOI: 10.1007/s40626-014-0010-6

Stomata control CO
2
uptake and transpirational water loss, and their functioning is closely regulated by external factors, such as light, CO
2
concentration, air vapor pressure deficit, and temperature. In addition, endogenous factors (e.g. biological clock) also affect stomatal movement. In comparison with ambient factors, internal factors have received less attention in Amazonian tree species. The aim of this study was to determine how stomatal functioning and photosynthesis respond to continuous light exposure during a circadian cycle. We collected data from July to September 2010 in four saplings of
Amphirrhox surinamensis
. Stomatal conductance (
g
s50
) and photosynthesis at a constant photosynthetically active radiation of 50 µmol m
−2
s
−1
(
P
N50
) were measured continuously during a circadian period (24 h, day and night) under a [CO
2
] of 380 µmol mol
−1
, temperature of 25 ± 2 °C, air relative humidity of 73 ± 3 %. The highest values of
g
s50
and
P
N50
were observed before 02:00 pm. Values of these parameters decreased toward the end of the afternoon and night until reaching steady state around midnight. Stomatal reopening (inferred by the increase in
g
s
values) began after midnight (01:00 am–02:00 am) when lower temperatures were recorded. Cooler temperatures observed after midnight and higher vapor pressure deficit values recorded early in the morning should promote closing rather than stomatal opening. Stomatal reopening in the early predawn hours suggests the involvement of an endogenous timer (circadian clock) in stomatal functioning.