Photosynthetic field capacity of cyanobacteria of a tropical inselberg of the Guiana Highlands

Abstract

Photosynthesis of cyanobacteria is well characterized under laboratory conditIOns. We present a detailed study of photosynthetic capacity of cyanobacterial communities measured under natural conditions using chlorophyll fluorescence techniques. Cyanobacteria of extensive and diverse communities grow epi-and endolithically on the bare rock of inselbergs in the tropics where they are exposed to extreme and rapid fluctuations in irradiance, temperature and water availability. Extreme and rapidly changing environmental conditions impose various stresses on cyanobacteria and lead to small-scale niches of different communities along the furrows of an inselberg in French Guiana. These different cyanobacterial communitIes can easily be separated from each other by their species composition. Moreover, cyanobacteria of these zonal areas show significantly different rates of apparent quantum yield of photosystem II (PSII). are differently adapted to utilize early morning light energy and have different strategies to face rapid cycles of desiccation. These different physiological strategies have led to the development of different cyanobacterial communities in distinct zones which are determined by different resistance to dehydration. water transport and storage capacity. In spite of the extreme environmental condItions with very high solar radiation, predawn measurements of potential quantum yield of PS II showed that they are not photoinhibited. We describe the manifold photosynthetic strategies that have developed in cyanobacteria under these extreme and highly fluctuating natural conditions.

Effect of light and temperature on biomass, photosynthesis and capsular polysaccharides in cultured phototrophic biofilms

“…Both the effective quantum yield of PSII (ΔF/ F m ′) and the relETR max showed increasing values with increasing irradiance in the two experimental runs, indicating biofilm photoacclimation, which has also been observed in natural biofilm assemblages from different environments (Kromkamp et al 1998;Underwood 2002;Barranguet et al 2003;Rascher et al 2003;Serõdio 2003;Lugomela et al 2005). When comparing between the two runs at a specific light intensity the values of ΔF/F m ′ and relETR max were higher at 20°C than at 30°C.…”

Ecophysiological responses of desiccation-tolerant cryptobiotic crusts

“…Despite their importance only a few studies are interested in the ecophysiology of cyanobacterial crust communities of the tropical and subtropical inselberg rock surfaces [7,9,19,21,[26][27][28] and seasonally inundated system of plans and dunes [29,30]. Most studies deal with the photosynthesis of the cryptogamic crusts under laboratory conditions [29] while only few characterize the photosynthesis of free-living cyanobacteria under natural conditions in the tropical field [7,21,28,31] and desert [11,13,30]. In addition, as BSCs dry out more slowly due to their embedment to the rock or soil surfaces (under their natural habitats) and therefore may retain water longer than lichens and mosses.…”

Variation des rapports 87Sr/86Sr dans les sols et les plantes d’un inselberg tropical

“…Rain occurs on average 280 d y −1 , with two drier periods, one from September to October and a shorter one in March. The relative humidity is 20% in the dry season and 100% in the rainy season (Sarthou and Grimaldi, 1992) and the average daily temperature is 25-27 • C. However, the temperature of bare rock surfaces may vary widely (18-55 • C) diurnally (Rascher et al, 2003;Sarthou and Grimaldi, 1992), because of the dark cyanobacteria covering these surfaces.…”

“…The endolithic cyanobacteria Choococcidiopsis sp. (Rascher et al, 2003) (Sarthou and Villiers, 1998). Black organic cyanobacteria residues generally accumulate at the upper edge of these patches (Vaçulik et al, 2004).…”

“…The bare rock is covered by a black continuous crust of cyanobacteria. Species include (Rascher et al, 2003;Sarthou et al, 1995): Scytonema guyanense, S. multiramosum, S. myochrous, Stigonema flexuosum, S. hormoïdes, S. ocellatum, S. panniforme, Hapalosiphon fontinalis, H. luteolu and Gloeocapsa sanguainea, most of which are nitrogen fixers (Dojani et al, 2007). The endolithic cyanobacteria Choococcidiopsis sp.…”