Dry semideciduous and deciduous forests occur only on calcium-rich soils and occupy almost 20% of the 200 million ha of the cerrado region of central Brazil. Other savanna physiognomies of woodlands and grasslands, and gallery forests generally occur on acid soils with low calcium levels. The literature on phytosociological aspects of such cerrado physiognomies is quite abundant whereas there is very little information on deciduous forests. Also lacking is information on soil fertility and its influence on species distribution. The objective of the present study was to study the distribution of native species within a dry deciduous forest in the Araguari river valley, Uberlâ ndia, Minas Gerais as related to soil properties. A 1-ha sampling area, with no apparent difference in physiognomy, was divided into fifty 10 m · 20 m plots arrayed in 10 · 5 grid and all trees with a minimum circumference of 15 cm at 1.30 m height were surveyed. A composite soil sample was collected from 0 to 10 cm depth in each plot and soil pH, organic C and nutrient availability were determined. Cluster analysis based on soil chemical properties showed the existence of two distinct groups of plots. Further field examinations revealed that the forest was situated in an area of transition between mica schist and basalt parent materials, without any apparent difference in the forest physiognomy. The basalt-derived soil in 23 plots had significantly higher availability of Ca (47.0 cmol(+) kg -1 soil), Mg (2.59), and K (0.96) than the mica schist derived soil (Ca-18.4, Mg-1.29, and K-0.66) in the remaining 27 plots, though both soils would be classified as eutrophic. A total of 59 species belonging to 27 families were encountered in the area as a whole, of which 36 were common to both soils. In total, 16 species occurred exclusively on the mica schist soil and 7 on the basaltic soil. Myracrodruon urundeuva Allem. (Anacardiaceae) and Tabebuia roseo-alba (Ridl.) Sandwith (Bignoniaceae) were species with high importance values in the forest as a whole. Though there was no significant difference in the diversity index between the two soils, the importance values of these species was larger in the basalt-derived soil with higher nutrient availability.Joã o Paulo De Souza is a scholarship holder of CNPq.

The rise in atmospheric CO2 concentration ([CO2]) has been accompanied by changes in other environmental factors of global climate change, such as drought. Tracking the early growth of plants under changing conditions can determine their ecophysiological adjustments and the consequences for ecosystem functions. This study investigated long-term ecophysiological responses in three woody Cerrado species: Hymenaea stigonocarpa Mart. ex Hayne, Solanum lycocarpum A. St.-Hil. and Tabebuia aurea (Silva Manso) Benth. and Hook. f. ex S. Moore, grown under ambient and elevated [CO2]. Plants were grown for 515 days at ambient (430 mg dm–3) or elevated [CO2] (700 mg dm–3). Some plants were also subjected to water stress to investigate the synergy between atmospheric [CO2] and soil water availability, and its effect on plant growth. All three species showed an increase in maximum net photosynthesis (PN) and chlorophyll index under high [CO2]. Transpiration decreased in some species under high [CO2] despite daily watering and a corresponding increase in water use efficiency was observed. Plants grown under elevated [CO2] and watered daily had greater leaf area and total biomass production than plants under water stress and ambient [CO2]. The high chlorophyll and PN in cerrado plants grown under elevated [CO2] are an investment in light use and capture and higher Rubisco carboxylation rate, respectively. The elevated [CO2] had a positive influence on biomass accumulation in the cerrado species we studied, as predicted for plants under high [CO2]. So, even with water stress, Cerrado species under elevated [CO2] had better growth.

ABSTRACT. Enterolobium contortisiliquum occurs in native forests formations from southeast to northeast Brazil, and too in Argentina, Bolivia and Paraguay. The objective of this study was to evaluate shading effects in the early growth of E. contortisiliquum plants. We measured leaf gas exchange, chlorophyll content index, biomass allocation and leaf development in plants in sunny and shaded areas. The experiment was performed in Universidade Federal de Viçosa, campus Florestal, Minas Gerais, Brazil. To determine the effects of different light regimes (full sunlight and shade) on the growth of E. contortisiliquum plants, we divided plants into two groups: plants grown in a greenhouse under full sunlight, and plants grown under 70% shade tissue. E. contortisiliquum plants grown in full sunlight showed an increase in maximum net photosynthesis, root, stem, and leaf dry mass, root length, root/stem ratio, and length of the stem. However, E. contortisiliquum under shade showed larger specific leaf area, leaf area ratio, chlorophyll content, long leaf life span, and slow growth. These ecophysiological adjustments in sunny and shaded areas may explain the wide geographical distribution of E. contortisiliquum in many vegetation types.Keywords: leaf area, leaf development, maximum net photosynthesis.Efeitos do sombreamento sobre o tempo de vida foliar e características funcionais na espécie com ampla distribuição Enterolobium contortisiliquum (Vell.) Morong RESUMO. Enterolobium contortisiliquum ocorre em formações florestais nativas do sudeste ao nordeste do Brasil e também na Argentina, Bolívia e Paraguai. O objetivo deste estudo foi avaliar os efeitos do sombreamento no crescimento inicial de E. contortisiliquum. As trocas gasosas foliares, o índice de conteúdo de clorofila, a alocação de biomassa e o desenvolvimento foliar foram avaliados em plantas sob sol pleno e sombra. O experimento foi realizado na Universidade Federal de Viçosa, campus Florestal, Minas Gerais, Brasil. Para determinar os efeitos de diferentes regimes de luz sobre o crescimento das plantas de E. contortisiliquum, dividimos as plantas em dois grupos: plantas que cresceram em estufa a pleno sol e plantas que cresceram sob sombrite 70%. As plantas de E. contortisiliquum que cresceram em pleno sol apresentaram aumento na fotossíntese líquida máxima, massa seca de raiz, de caule e folhas, comprimento de raiz, razão massa de raiz/caule e comprimento do caule. Entretanto, plantas de E. contortisiliquum sob sombra apresentaram maior área foliar específica, razão de área foliar, conteúdo de clorofila, tempo de vida foliar e crescimento lento. Esses ajustes ecofisiológicos em áreas sob sol e sombra podem explicar a ampla distribuição geográfica de E. contortisiliquum em muitos tipos vegetacionais.Palavras-chave: área foliar, desenvolvimento foliar, fotossíntese líquida máxima.

Growth and leaf nutrient content were compared in young potted plants of Copaifera langsdorffii in sunny and shaded areas without water stress. Besides, carbon assimilation and leaf water relations were evaluated by net photosynthesis, potential photochemical efficiency and leaf water potential during daily courses in dry and rainy periods under natural conditions in both contrasting irradiances. Higher values of total biomass, height and leaf area occurred in sunny than in shaded area. On the other hand, all young plants survived in shade under natural water stress probably by reason of fast and intense biomass accumulation in favor of roots in early development. There was no significant difference about nutrient concentration in leaves between plants growing in sunny and shaded areas. Net photosynthesis in shade increased occasionally when bunches of direct light reached the leaves. Theses sunflecks took place more frequently and at high intensity in dry period but they were more effective for net photosynthesis in rainy period. The ability of young plants to persist under natural conditions in contrasting irradiance up to 1,230 days after sowing could explain the wide distribution of C. langsdorffii in Cerrado physiognomies and in different types of forest.Key words: Cerrado, biomass partitioning, chlorophyll fluorescence, leaf gas exchange, irradiance, sunflecks. resUMoO crescimento e o conteúdo de nutrientes nas folhas foram comparados em plantas jovens envasadas de Copaifera langsdorffii crescendo em área sob irradiância total e em área sombreada sem estresse hídrico. A assimilação de carbono e as relações hídricas foram avaliadas por meio da fotossíntese líquida, da eficiência fotoquímica potencial e do potencial hídrico foliar durante cursos diários no período seco e chuvoso nas duas áreas com irradiâncias contrastantes. Maiores valores de biomassa total, altura e área foliar ocorreram na área sob irradiância plena. As plantas jovens sobreviveram sob estresse hídrico em condições naturais na área sombreada provavelmente em função do rápido e intenso acúmulo de biomassa nas raízes logo no início do desenvolvimento. Não houve diferença significativa em relação à concentração de nutrientes entre as plantas crescendo sob diferentes regimes de iluminação. A fotossíntese líquida sob sombreamento aumentou ocasionalmente quando feixes de luz que atravessaram as copas atingiram diretamente as folhas de C. langsdorffii. Esses feixes de luz ocorreram com maior intensidade e mais freqüentemente no período seco, mas foram mais efetivos para a assimilação líquida no período chuvoso. A habilidade das plantas jovens persistirem em condições naturais sob os dois regimes contrastantes de irradiância até 1.230 dias após a semeadura pode explicar a vasta distribuição de C. langsdorffii nas diferentes fisionomias do Cerrado e em outras formações florestais. palavras-chave: Cerrado, feixes de irradiância, fluorescência da clorofila, partição da biomassa, sobrevivência, trocas gasosas foliares.

The structure of the Cerrado may be explained by the competition between woody and herbaceous species. However, the rising CO2 concentration ([CO2]) predicted under current climatic change may modify the ecophysiological responses of woody and herbaceous species owing to functional traits of each group, which may in turn modify vegetation structure as competitive relationships change among species. In this study we examined ecophysiological responses and competition between two cerrado species under elevated [CO2]. We selected an herbaceous alien grass (Melinis minutiflora P. Beauv.) and an endemic woody cerrado species (Hymenaea stigonocarpa Mart. ex Hayne). Hymenaea stigonocarpa individuals were maintained in three plots with different M. minutiflora densities: 0, 50 and 100% in two different [CO2] (380 ppm and 700 ppm) in open-top chambers. Leaf gas exchange, effective quantum efficiency of PSII, chlorophyll content, and growth increased in H. stigonocarpa plants under high [CO2]. The competition with M. minutiflora under elevated [CO2] led to an increase in specific leaf area, leaf area ratio and biomass allocation to shoots in H. stigonocarpa. In contrast, M. minutiflora had a delayed leaf development and high stem dry mass under elevated [CO2]. These changes in growth patterns under elevated [CO2] will modify allocation of resources, improving the competition potential of the woody species over the alien grass species in the Cerrado.