João Paulo Souza

Shoot-foliage relationships in deciduous, semideciduous, and evergreen cerrado tree species

The morphology and the biomass allocation in shoots and leaves were investigated in 15 cerrado tree species with distinct leaf phenology growing under natural conditions. Higher values of leaf/shoot ratio on mass base, individual leaf area, leaf area per shoot, leaf display index, and leaf number per shoot length were found in deciduous than in evergreen species. The differences about shoot-foliage relationship across leaf phenological groups could be explained by plagiotropic shoots on deciduous and by erect shoots in semideciduous and evergreen species. Plagiotropic shoots allow similar irradiance along shoots and high biomass allocation in favor of leaves without foliage self-shading in deciduous tree species. The structural differentiation between short and long shoots was indicated by an exponential relationship between leaf display index and shoot length in all deciduous, in three semideciduous, and in two evergreen species. Therefore, especially in deciduous, the short shoots had higher leaf area per unit of length than the long shoots. The differentiation between short and long shoots depends on the shoot length in deciduous because of the leaf number on shoot is predetermined in buds. Contrastingly, the leaf neo-formation in semideciduous and in evergreen tree species keeps the shoot-leaf relationship per shoot length more constant, because of the foliage being produced according to the shoot growth during the year. In conclusion, the foliage persistence, the shoot inclination, the type of leaf production and the resources allocation between autotrophic and heterotrophic vegetative canopy parts are interdependent in cerrado tree species across different leaf phenological groups.

Network analysis of tree crowns distinguishes functional groups of Cerrado species

Deciduous, semideciduous and evergreen leaf phenological groups of Cerrado trees were studied using a representative network composed of nodes and links to uncover the structural traits of the crown. A node denotes the origin of a branch, and a link represents the branch emerging from a lateral bud. The network representation usually resulted in a graph with three links per node and twice as many links as nodes for each leaf phenological group. It was possible to identify four kinds of nodes according to the position and the number of links: initial, regular, emission and final nodes. The numbers of links and nodes and the distance between two kinds of nodes decreased from evergreen to deciduous species. A crown with a few nodes and links and a short distance between the kinds of nodes could facilitate the unfolding of foliage on leafless branches at the end of the dry season in deciduous trees. In contrast, foliage persistence in evergreens could facilitate the mass flow to new leaves produced during the entire year in a crown with a high number of links and nodes and with a large distance between nodes. There is a clear interdependence between the degree of leaf deciduousness and the crown structural traits in Cerrado tree species. Therefore, there are functional groups of trees in Cerrado vegetation that are characterized by a set of structural traits in the crown, which is associated with leaf deciduousness.

Influence of shoot inclination on irradiance and morphophysiological leaf traits along shoots in cerrado trees with distinct leaf deciduousness

This study investigated the relationship among shoot inclination, irradiance and morphophysiological traits of basal (BL) and distal (DL) leaves in six cerrado trees with distinct leaf deciduousness. Deciduous species showed plagiotropic shoots (44o) and larger leaf area than semideciduous and evergreen species, which showed orthotropic shoots (56o and 63o, respectively). Despite larger leaf area, irradiance at shoot base in deciduous was around 85% in relation to full irradiance, while in semideciduous and evergreen only 23% of irradiance reached on BL. Likewise, maximum net photosynthesis (Pnmax) was similar between BL and DL in deciduous. Contrastingly, semideciduous and evergreen showed significant decreasing of Pnmax in BL. Plagiotropic shoots of deciduous allow similar irradiance along shoots, resulting in similar Pnmax along shoot. On the other hand, orthotropic shoots of semideciduous and evergreen resulted in shading and decreasing of Pnmax on BL. However, considering BL and DL together, there was not significant difference of leaf-life-span or Pnmax among deciduous, semideciduous and evergreen. Therefore, shoot inclination and shading among leaves on same shoot should be significant influencing leaf morphophysiological traits along shoots in cerrado trees. On the other hand, similar leaf-life-span among phenological groups resulted in absence of Pnmax differences when BL and DL were considered together.

Comparison between canopy trees and arboreal lower strata of urban semideciduous seasonal forest in Araguari - MG

The present study intended to determine the phytosociological characteristics of the tree elements on the lower strata and the canopy of a semideciduous seasonal forest. The trees (> 15 cm circumference at breast height) were sampled in 40 plots of 10m x 20m. The individuals in the lower strata (> 1m up to 15 cm of circumference in the base of the stem) were sampled in plots of 10m x 10m. Licania apetala and Micrandra elata obtained the first and second places in the two strata. Among the species with the highest value of importance on the canopy, Alchornea glandulosa, Pimenta pseudocaryophyllus, Copaifera langsdorffii, Heisteria ovata and Didymopanax morototoni presented a ratio of less than one individual in the lower strata when compared to the canopy. However, there was a high floristic similarity between the lower strata and the canopy.

GRAFTING FOR IMPROVING NET PHOTOSYNTHESIS OF COFFEA ARABICA IN FIELD IN SOUTHEAST OF BRAZIL

Leaf gas exchange and leaf water potential (Ψleaf) were measured seasonally on non-grafted and grafted Coffea arabica on Coffea canephora in the field to investigate whether grafting would be able to protect the carbon balance against the rise of in vapour pressure deficit (VPD) and air temperature (Tair) under future climate change. The net maximum photosynthetic rate obtained from the net photosynthesis (PN) curve as a function of photosynthetic photon flux density (PPFD) in wet and dry periods was used to estimate the integrated potential diurnal net CO2 assimilation (IPPN) around midday. The difference between IPPN and the integrated values of PN during diurnal courses (IPN) was measured to test grafting as suitable practice for minimizing midday depression of PN. Higher values of PN in grafted plants around midday showed that grafting was important even when environmental conditions were favourable in field conditions. Reduced susceptibility of grafted plants to midday depression was revealed by lower values of Ψleaf associated with higher values of PN and leaf transpiration (E) on sunny days in summer and spring, and by higher values of stomatal conductance (gs) around midday in autumn, winter and spring. The differences of E, gs, PN and Ψleaf between non-grafted and grafted plants were higher in dry periods in winter and spring. In addition, the ratio IPN/IPPN in grafted was double that in non-grafted plants around midday in sunny summer and in spring. Indeed, PN and gs of non-grafted plants showed higher dependence on VPD than grafted ones. The lower susceptibility of grafted plants to water stress demonstrated the graft efficiency for increasing positive components of leaf carbon balance of C. arabica in the field, especially under high VPD in projected future climate conditions.

Responses of woody Cerrado species to rising atmospheric CO2 concentration and water stress: gains and losses

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 (430mgdm-3) or elevated [CO2] (700mgdm-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.

Improving the development of Coffea arabica after changing the pattern of leaf gas exchange by watering cycles.

Hardening of Coffea arabica saplings by watering cycles (WCs) might be a suitable practice to achieve higher tolerance to low leaf water potential (Ψ leaf ) before transplanting to the field. As a consequence, hardening could promote growth and biomass gain during the initial development of C. arabica in the field. Thus, the less interrupted initial growth in a changing environment should confer higher flowering intensity in hardened than in control plants. The aim of this work was to verify if leaf gas exchange and Ψ leaf behaviour of C. arabica saplings grafted on C. canephora showed consistent alterations during hardening by WCs and if this was effective to improve vegetative and reproductive growth under field conditions. For these reasons, saplings of the Mundo Novo cultivar of C. arabica grafted on C. canephora were submitted to seven WCs over 35 days. Each WC was completed when net photosynthesis was close to zero. The pattern of leaf gas exchange, mainly stomatal conductance (g s ), was modified permanently after three WCs and the new pattern of leaf gas exchange could result in a more positive water balance and less interrupted development of C. arabica saplings in the field, particularly due to permanent low values of g s . After field transplantation, hardened plants showed greater height and stem diameter, more leaves and branches, and superior biomass production in leaves, stem and roots than control plants in dry and wet periods. The number of flowers was also significantly higher in hardened than in control plants. On the other hand, similar values were found between control and hardened plants in the leaf area ratio and the shoot/root ratio. Therefore, previous hardening by WCs was effective in improving leaf gas exchange, vegetative and reproductive development under field conditions and maintained the original biomass partitioning among the main plant compartments in dry and wet periods.

Rising [CO2] changes competition relationships between native woody and alien herbaceous Cerrado species

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] (380ppm and 700ppm) 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.