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Features of CAM-cycling expressed in the dry season by terrestrial and epiphytic plants of Clusia arrudae Planchon & Triana in two rupestrian savannas of southeastern Brazil in comparison to the C3-species Eremanthus glomerulatus Less.

 
: Scarano, F.R.; Mattos, E.A. de; Franco, A.C.; Cavalin, P.O.; Orthen, B.; Fernandes, G.W.; Lüttge, U.

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Trees 30 (2016), No.3, pp.913-922
ISSN: 0931-1890
ISSN: 1432-2285
English
Journal Article
Fraunhofer IME ()

Abstract
In rupestrian savannas in southeastern Brazil Clusia arrudae Planchon & Triana in the dry season performed CAM-cycling with very little gas exchange in the early morning followed by a long depression during the rest of the day. CAM-cycling is considered as a survival strategy under drought and the productivity of the plant which is quite abundant must rely on performance of C (3) -photosynthesis in more favorable seasons. In rupestrian savannas in the Serra do Cip (19A degrees 14'48.9aEuro(3)S, 43A degrees 30'36.0aEuro(3)W) at 1300 m a.s.l. and in the Serra de So Jos, (21A degrees 08'S, 44A degrees 17'W) at 1010-1030 m a.s.l. in southeastern Brazil Clusia arrudae Planchon & Triana is abundant. As CAM is frequent in the genus Clusia we supposed that it would perform CAM as a drought adaptation at the very dry rupestrian savanna sites in the dry season. At the Serra do Cip site as control we studied the obligate C-3-species Eremanthus glomerulatus Less. Both species are sympatric at this site. Eremanthus glomerulatus performed C-3-photosynthesis with a midday depression. The patterns of C. arrudae were completely different so that genuine C-3-photosynthesis was excluded, but they were also not typical of CAM. The stomata were almost closed during the night. Some stomatal opening and net CO2 uptake occurred in the early morning hours followed by a long depression with stomatal closure throughout the rest of the day. Nevertheless, photo inhibition was limited and photosynthetic electron transport rate remained high during this time indicating that photosynthetic excitation energy was required and suggesting that CO2 assimilation was continuing behind closed stomata based on internal sources of CO2. There was some nocturnal accumulation of organic acids (malic and citric acids) which could represent a source of CO2 during the light period. Overall, the observations can be best explained by the performance of CAM-cycling by C. arrudae. However, leaf carbon gain of C. arrudae was much inferior to that of E. glomerulatus. CAM-cycling appears to be a strategy for protection from photoinhibitory damage and survival under strong conditions of drought. Steeper more vertical leaf positions observed would assist reducing overheating during stomatal closure at high irradiance. The abundance of C. arrudae suggests that the plant must have other means to sustain productivity such as full C-3-photosynthesis in the more favorable seasons.

: http://publica.fraunhofer.de/documents/N-404225.html