Carlos Henrique B. A. Prado

Seasonal leaf gas exchange and water potential in a woody cerrado species community

Predawn leaf water potential (Ypd) and morning values of leaf gas exchange, as net photosynthesis (A), stomatal conductance (gs), transpiration (E), and morning leaf water potential (Ymn) were determined seasonally in 22 woody cerrado species growing under natural conditions. Despite the lower mean values of Ypd in the dry season (-0.35 ± 0.23 MPa) compared to the wet season (-0.08 ± 0.03 MPa), the lowest Ypd in the dry season (-0.90 ± 0.00 MPa) still showed a good nocturnal leaf water status recovery for all species studied through out the year. Mean gs values dropped 78 % in the dry season, when the vapor pressure of the air was 80% greater than in the wet season. This reduction in gs led to an average reduction of 33% in both A and E, enabling the maintainance of water use efficiency (WUE) during the dry season. Network connectance analysis detected a change in the relationship between leaf gas exchange and Ymn in the dry season, mainly between gs-E and E-WUE. A slight global connectance value increase (7.25 %) suggested there was no severe water stress during the dry season. Multivariate analysis showed no link between seasonal response and species deciduousness, suggesting similar behavior in remaining leaves for most of the studied species concerning leaf gas exchange and Ymn under natural drought.

Photosynthesis and Water Use Efficiency in Twenty Tropical Tree Species of Differing Succession Status in a Brazilian Reforestation

Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (PNA) or a dry mass (PNM) basis, differed among species. PNA and PNM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 μmol m−2 s−1) for PNA, and 5-fold (from 50 to 275 μmol kg−2 s−1) for PNM. The highest PNA (23 μmol m−2 s−1) and PNM (275 μmol kg−2 s−1) values were recorded in PS Croton urucurana, while the lowest PNA (7 μmol m−2 s−1) and PNM (50 μmol kg−2 s−1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (gs), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest gs and E. PNM was highly correlated with ALM in both PS and LS (r=−0.75 and −0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUEi) were also observed in the PS when compared with the LS.

Ecophysiology of coconut palm under water stress

O coqueiro apresenta grande importância economica e social para milhoes de pessoas nos tropicos e subtropicos. A seca e um dos fatores ambientes que mais limitam a produtividade do coqueiro. Nessa revisao, apresentam-se dados fisiologicos e morfologicos sob uma perspectiva integrada, de modo a ter-se uma visao holistica acerca do comportamento do coqueiro frente a deficiencia hidrica em campo e em condicoes controladas. A elevada capacidade de produzir raizes homorrizicas, a capacidade dessas raizes em prospectar continuamente agua e nutrientes e a elevada tolerância protoplasmatica nas folhas permitem ao coqueiro superar o deficit hidrico. Elevada estabilidade das membranas, osmoprotecao, osmoregulacao, e aumento da atividade de enzimas antioxidantes sao caracteristicas usualmente observadas nas folhas do coqueiro sob deficit hidrico. Informacoes sobre as trocas gasosas foliares, potencial hidrico foliar, eficiencia do uso da agua e o comportamento estomatico foram compiladas, destacando-se as diferencas entre cultivares e hibridos sob estresse hidrico. As diferentes caracteristicas morfofisiologicas de genotipos de coqueiro geralmente guardam correspondencia com as observacoes agronomicas em campo.

CARBON GAIN IN COFFEA ARABICA DURING CLEAR AND CLOUDY DAYS IN THE WET SEASON

Three cultivars of Coffea arabica , Catuai Vermelho IAC 81, Icatu Amarelo IAC 2944 and Obata IAC 1669–20, were evaluated in relation to leaf gas exchange and potential photochemical efficiency of photosystem II under field conditions on clear and cloudy days in the wet season in southeast Brazil. Independent of levels of irradiance, leaf water potential (υ leaf ) values were always higher than the minimum required to affect daily net photosynthesis (P N ). P N , stomatal conductance (g s ), leaf transpiration (E) and the index of photochemical efficiency (F v /F m ) declined on a clear day in all cultivars. The depression of leaf gas exchange and F v /F m (specially around midday) caused a strong decrease (about 70 %) in daily carbon gain on a clear day. Under cloudless conditions, g s and P N were correlated with the air vapour pressure deficit (VPD air ), but not with photosynthetic photon flux density (PPFD) values. On a cloudy day, the daily carbon gain was barely limited by PPFD below 800 μmol m −2 s −1 , the F v /F m values showed a slight decrease around midday, and g s and P N were positively correlated with PPFD but not with VPD air . By contrast, irrespective of the contrasting irradiance conditions during the day, P N and E were correlated with g s .

The influence of vapour pressure deficit on leaf water relations of Cocos nucifera in northeast Brazil.

Daily courses of leaf gas exchange and leaf water potential (psi(leaf)) of green dwarf coconut palm (Cocos nucifera) were measured in irrigated plantations on the wet coastal plateau and in a dry semi-arid area of northeast Brazil. At both sites, significant correlations were obtained between stomatal conductance (gs) and vapour pressure deficit (VPD(air)), psi(leaf) and VPD(air), leaf transpiration (E) and gs, and E-Ψ(leaf). Despite these similar relationships between sites, stronger correlations involving gs-VPD(air) and E-Ψ(leaf) were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPD(air). In addition, at the semi-arid site, only, the net photosynthesis (P(N)) was not correlated with E and Ψ(leaf), and the intrinsic water use efficiency (WUEi) was disconnected from VPD(air) and Ψ(leaf). The different behaviour of leaf gas exchange and Ψ(leaf) between sites was probably caused by low gs in response to high VPD(air) at the semi-arid site. Our results indicate potential for significant alterations in the pattern of leaf gas exchange during future climatic changes with increasing temperature and concomitant increases in VPD(air). The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψ(leaf), gs, gp, and VPD(air)), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as P(N)-E, P(N)-Ψ(leaf), WUEi-VPD(air) and WUEi-Ψ(leaf).

Growth and photosynthetic capacity in two woody species of cerrado vegetation under different radiation availability

Seedlings of two woody species of cerrado vegetation, Copaifera langsdorffii and Eriotheca gracilipes, were studied under three different radiation availability (100, 80 and 30% transmittance). Full solar radiation brought about more biomass, higher total leaf area, higher maximal photosynthesis per crown on area or on mass bases and higher photosynthetic capacity on area bases. Only the photosynthetic capacity values on leaf mass bases were higher in both species under low radiation availability (80 and 30% transmittance). The differences of accumulated biomass appeared more clearly after 4 months of sowing but the root/shoot dry biomass ratio and height were maintained constant for both species independently of the available radiation. Cultivated under full solar radiation both species will be able to cover more suitable the two processes during seedlings phase: growth and defense.

Comportamento sazonal do potencial hídrico e das trocas gasosas de quatro variedades de coqueiro-anão

Leaf gas exchange and water potential (Yl) were assessed daily and seasonaly in four varieties of dwarf coconut (Cocos nuficera L.) under field conditions: Cameroon Red Dwarf (CRD), Gramame Red Dwarf (GRD), Gramame yellow Dwarf (GYD) and Jiqui Green Dwarf (JGD). All varieties showed strong reduction of stomatal conductance (gs) values in the dry season. At this period, transpiration (E) and net photosynthesis (A) rates decreased largely in JGD and in GRD, when both genotypes presented greater values of intrinsic water use efficiency (A/gs) than in wet season, specially JGD. Taking in account all genotypes studied in wet season, the leaf gas exchange was conditioned by photosynthetic photon flux density (PFFD) and by gs values. On the other hand, during the dry season, leaf gas exchange was correlated only with gs values. The variety CRD did not restrict E in dry season, showing the lowest Yl but holding the highest A values per day among genotypes under drought. Contrastingly, the genotype JGD could control efficiently E intensity, maintaining the highest A/gs ratio despite of reduced A values in dry season. In dwarf coconut plantations with high technical management such as in irrigated areas, the CRD could be the most suitable variety to achieve favorable carbon balance during the year.

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.