C3, C4 Photosynthetic Types and C4 Kranz Sub-Types: Occurrence, Distribution, and Photosynthesis

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Imbamba S.K
Macharia J.N.M
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Studies on the occurrence, distribution, and photosynthesis of C3 , C4 photosynthetic systems and C4 Kranz sub-types were carried out from four natural grassland ecosystems located in Masai Mara, Aberdare, Nairobi, and Amboseli National Parks. The four sites differed in several environmental factors including temperature, occurrence and distribution of C, and C4 photosynthetic systems and C4 Kranz sub-types in grasses was examined on the basis of leaf anatomy. Out of 92 grass species studied 87%, 13% were Kranz (C4) and non-Kranz (C3) respectively while 36, 22 and 42% of the C4 species were PEP-ck, NAD-me and NADP-me sub-types respectively. Grasses collected from Masai Mara, Nairobi, and Amboseli were all C" while 65 and 35% of the Aberdare species were C4 and C3 respectively. Thus, the Aberdare site (all >3,000 m) lies in a transitional zone inhabited by both C, and C4 species; the latter being dominated by species in Andropogoneae and Paniceae tribes. C4 species were generally found at lower altitudes while C3 species occupied higher altitudes. An analysis of the distribution of the Kranz sub-types in the grass tribes revealed that species in the Aristideae, Andopogoneae and Arun- dinelleae tribes were NADP-me sub-types while species in Pappophoreae tribe were PEP-ck sub-types. All other tribes were promiscuous; Eragrostideae and Paniceae tribes, for example, contained species with all three Kranz sub-types. Malate formers (NADP-me) were more dominant in areas with high soil moisture while PEP-ck occurred in areas of medium soil moisture; NAD-me were dominant in areas with low soil moisture. CO2 gas exchange studies showed that the C4 species exhibited higher rates than their C3 counterparts. However, C4 species from high altitudes exhibited low CO4 exchange rates than those collected from low altitudes. Measurements in high altitude C" grasses left to adapt at low altitude for one year clearly showed that although the temperature optimum for photosynthesis remained the same (20-2SoC) the maximum rate increased substantially from the original 45-55 mg CO2 dm-2 per hr to 65-75 mg CO2 dm-2 per hr.
East African Agricultural And Forestry Journal, LII (2), p. 88-100