Comparative Gas Exchange Performance During The Wet Season Of Three Brazilian Styrax Species Under Habitat Conditions Of Cerrado Vegetation Types Differing In Soil Water Availability And Crown Density

We studied the influence of environmental conditions in different vegetation types of the Brazilian savanna (cerrado s.l.) on CO2 assimilation and water use efficiency of Styrax ferrugineus, S. camporum and S. pohlii, which are morphologically similar but have distinct distribution patterns. We measured leaf gas exchange and water relations in adult and young plants. Adult plants of S. ferrugineus were measured in the cerrado s. str.; plants of S. camporum at the edge of cerradão, a woodland vegetation; and in a riparian forest those of S. pohlii. Eight-month-old young plants were planted in the cerrado s. str., at the edge and in the understory of the cerradão, and in the understory of the riparian forest. For young plants, the high light availability in the cerrado s. str. resulted in a threefold greater CO2 assimilation rate (A) compared to the other sites. A of adult plants under full irradiation (1800μmolphotonsm-2s-1) was significantly lower in S. pohlii compared to S. ferrugineus and S. camporum. Although sufficient soil water was available at every site at the end of the wet season, the extreme high water content in the riparian forest soil led to increased stomatal conductance (gs) and transpiration rate (E) for young plants of S. camporum and S. pohlii, but not of S. ferrugineus. However, the large gs in S. pohlii and S. camporum young plants did not result in higher A rates. The differences may indicate some specialization of S. ferrugineus to best growth in open savanna and of S. pohlii in riparian forest habitats. The high water use efficiency of S. camporum young plants in the understory of cerradão seems not yet sufficient to emphasize that this species benefits from this particular habitat. 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An\ue1lise comparativa da anatomia foliar de Melastomataceae em ambiente de vereda e cerrado sensu stricto

Este trabalho descreve a anatomia das lâminas foliares de três espécies de Melastomataceae, Lavoisiera bergii Cogn., Macairea radula (Bonpl.) DC. e Trembleya parviflora (D. Don) Cogn. que estão colonizando a zona alagável e aberta de fundo de vereda e de M. radula e T. parviflora que ocorrem no cerrado sensu stricto da Estação Ecológica de Águas Emendadas, Planaltina/DF. Os dados estruturais mostrados pelas três espécies indicam escleromorfia com características particulares a cada uma delas, como projeções nas células epidérmicas de L. bergii, diferentes tipos e localização de emergências formadas por esclereídes em L. bergii e M. radula, e evaginações na epiderme de T. parviflora. A caracterização anatômica das folhas de M. radula e T. parviflora não difere entre os ambientes. No entanto, as lâminas foliares dos indivíduos encontrados na vereda apresentaram plasticidade com valores significativamente (P< 0,05) maiores para espessura do mesofilo e do parênquima para massa foliar e massa foliar específica em relação aos indivíduos do cerrado sensu stricto. Esta relação é inversa para valores de área foliar específica. A capacidade de apresentar plasticidade estrutural, juntamente com a escleromorfia, pode ter sido relevante para o comportamento invasivo destas espécies na zona de fundo da vereda como destacado na discussão. Além deste ponto, o texto também apresenta uma breve discussão sobre outros aspectos relacionados à importância de estruturas anatômicas na taxonomia e ecologia destas espécies