ABSTRACT The lack of information on the growth of forage grasses in semi-arid environment, especially from the perspective of irrigation, is one of the obstacles to regular forage supply, as well as to the rational use of irrigation water. The objective with this study was to evaluate the leaf gas exchanges, biomass flow and structural characteristics of buffel grass cultivar Gayndah under different water supplies (30, 60, 90 and 120% of the reference evapotranspiration - ETo) during the dry season and dry-rainy season, in completely randomized design in a split-plot scheme with three repetitions. The experiment was conducted in Sobral, CE, Brazil (3° 45’ 00.77” S and 40° 20’ 38.55” W, altitude of 101 m) from September 2015 to January 2016. A higher photosynthetic rate was verified during the dry season, evidencing the adaptability of buffel grass to environments with water restriction. Overall, the best morphogenic and structural characteristics and the biomass production were observed in the dry season. The 90% ETo regime leads to maximum amount of forage accumulation, whereas the 30% ETo allows the maintenance of the cultivar Gayndah of buffel grass in a state of latency during the dry season.

ABSTRACT This study aimed to evaluate the growth and physiology of citrus scion/rootstock combinations irrigated with saline water until the pre-flowering stage. The experiment was conducted in drainage lysimeters with capacity for 150 dm3, in randomized block design in a 2 x 10 factorial scheme, corresponding to two electrical conductivities of water (S1 = 0.3 and S2 = 3.0 dS m-1) and ten scion/rootstock combinations (nine hybrids and one commercial variety) grafted with Tahiti lime, in three repetitions and one plant per plot. Grafted seedlings were transplanted one year after sowing, subjected to salt stress from 15 days after transplanting until the pre-flowering period, and evaluated for gas exchanges and growth. The irrigation with 3.0 dS m-1 saline water did not influence the photosynthetic activity of the studied citrus scion/rootstock combinations until the pre-flowering. The genotype Santa Cruz Rangpur lime (LCRSTC) was more sensitive to irrigation water salinity in terms of growth. The least sensitive combinations to salinity were Tahiti lime grafted onto TSKFL x (LCR x TR) - 018, TSKFL x TRBK - 011 and TSKFL x TRBK - 30.

Abstract Cowpea is a crop with great economic, social and food importance in semi-arid regions, but its production is drastically reduced by the water deficit in these regions, requiring better management strategies that allow the crop’s production. This study therefore aimed to evaluate the photosynthetic efficiency and production of cowpea cultivars under deficit irrigation replacement levels. The experiment tested three cowpea genotypes (G1 = ‘BRS Aracé’, G2 = ‘BR 17 Gurguéia’ and G3 = ‘BRS Marataoã’) and four irrigation depths (40, 60, 80 and 100% of ETc), resulting in a 3 x 4 factorial scheme, arranged in randomized complete blocks design with four replicates. During the experiment, the gas exchanges, chlorophyll a fluorescence and production of the cowpea genotypes under deficit irrigation were evaluated. Carbon fixation in the photosynthetic metabolism of cowpea plants was reduced by accentuated water deficit, regardless of the genotype. The low stress severity was indicated by the lack of effects on chlorophyll fluorescence, indicating that the reduction in the rate of carbon assimilation was due to the stomatal effects. The irrigation with 80% of ETc can be used in the cultivation of the respective cultivars, but with small losses in the production. Among the genotypes, ‘BRS Marataoã’ stands out with respect to yield, with higher values for weight of pods and green beans.

ABSTRACT: Stress caused by extreme temperatures is one of the main elements that limit the geographical distribution and the seasonal growth of several plants, causing a severe delay in their development, reducing the photosynthetic rate and signaling the synthesis of defense compounds. Considering the current environmental changes and the damages that these changes can cause in plant physiology and growth, the objective of this work was to understand the interactions between temperature, physiology and growth, and to characterize the impact of temperature changes on the initial development of Vernonia ferruginea Less. Seedlings of this species were conditioned in germination chambers at previously adjusted constant temperatures (10, 20, 25, 30, and 35 oC) for sixty days, in order to evaluate physiological and growth parameters. The optimum temperature range for the initial growth of V. ferruginea is between 25 and 30 oC. The stress caused by sub-optimal and over-optimal temperatures affected cell homeostasis and caused a delay in the growth and development of seedlings. In stressful situations, growth inhibition and the activation of response mechanisms were observed for the adaptation and maintenance of cellular homeostasis through the accumulation of the proline osmoprotectant and soluble carbohydrates. Additionally, plants presented a normal development within a wide temperature range, despite the development delay, the change in gas exchanges and the synthesis of substances related to the defense system.

This study tested the hypothesis that dissipative efficiency of tropical tree species could be an ecological advantage in the forest succession process. Daily leaf gas exchanges of a pioneer species (Guazuma ulmifolia) and a late successional species (Cariniana legalis) were evaluated under well-irrigated conditions and by withholding irrigation. Analyses of network connectance (Cg) and plant autonomy (At) were carried out in order to assess metabolic network changes in response to environmental perturbation. As a global estimation of latent heat dissipation, the capacity to both maintain and cool leaf temperature in response to air temperature changes (deltaT = TºCair - TºCleaf) was evaluated. The changes observed in both the systemic parameters (Cg and At) and the physiological ones brought about by water deficit, associated with discrepant growth rates between both species, suggested that the initial formation of gap canopies composed by pioneer species could simply be a result of the higher photosynthetic rates of these species, and not necessarily because late successional species cannot cope with such a heterogeneous environment as that of a gap. Our results indicate that, in the absence of water constraints, the highest CO2 assimilation rates of pioneer species are supported by the efficiency of the whole dissipative structure, involving both degradation and dissipative processes. As a practical result, our study suggests the deltaT analysis in order to evaluate the efficiency of dissipative structures and as a aid in characterizing functional groups.

The most widely standard used for powdery mildew control on cucurbitaceas is the use of resistant cultivars and systemic fungicides, even though nutrition has been an option. The supply of silicon is benefic to many vegetable species, stimulating growth, yield, photosynthesis and regulation of transpiration; besides, its deposition in the epidermis avoids the invasion of fungus, bacteria and sucking insects. The aim of this experiment was to evaluate the influence of potassium silicate on powdery mildew control, development and yield of zucchini squash, cultivar Caserta. The experiment was conducted at Universidade Estadual Paulista, in greenhouse conditions and with a randomized design, divided in four replications, 11 plants per plot and five treatments: control (water), chemical treatment with fenarimol (2.4 g a.i. 100 L-1) and potassium silicate, in doses 1.5 L ha-1; 2.0 L ha-1 and 2.5 L ha-1. We evaluated the disease severity; gas exchange (net CO2 assimilation rates, transpiration, stomatal conductance and water use efficiency); growth (leaf area ratio, relative growth rate, absolute growth rate, net assimilation rate and specific leaf mass) and yield. The results showed that the foliar application of potassium silicate and fenarimol controlled powdery mildew and had no influence on plant growth. Therefore, the potassium silicate may be used as alternative for control of fungal pathogens and reduced application of chemical products, which provides a greater environmental sustainability. However, it is necessary to be careful with high doses because it was observed that 2.5 L h-1 was harmful to fruit production and gas exchange, despite being effective in controlling powdery mildew. According to this study it is recommended using 2.0 L ha-1 for control of powdery mildew to zucchini squash, and can replace the use of fenarimol, without affecting productivity and development of plants.

Tendo em vista que a Caatinga é um bioma fortemente antropizado e influenciado pela salinidade, é imperativo elucidar as respostas fornecidas a esse estresse por espécies pioneiras com potencial para recuperação de áreas degradadas durante as fases iniciais do desenvolvimento. Nesse sentido, o objetivo desse trabalho foi verificar o efeito da salinidade sobre o crescimento, o status hídrico, a partição de Na+ e K+ e as trocas gasosas em plântulas de Erythrina velutina Wild. durante o estabelecimento tardio. Sementes coletadas de dez árvores matrizes foram escarificadas, desinfestadas e geminadas em papel toalha sob condições controladas e as plântulas foram cultivadas hidroponicamente em água destilada em casa de vegetação por 8 d. O meio hidropônico foi trocado por NaCl 100 mM ou água destilada para o controle, mantendo as plântulas sob as mesmas condições por 3 d. O tratamento salino não foi capaz de causar mortalidade das plântulas de E. velutina, porém estas apresentaram três respostas morfológicas distintas, incluindo a aparente redução da altura, a murcha ou o aparecimento de manchas necróticas, acompanhadas pela diminuição da massa seca e do conteúdo relativo de água nas folhas cordiformes. O estresse salino causou a acumulação de Na+ e alterou a partição de K+ nas diferentes partes da plântula, mas a relação K+/Na+ se manteve mais próxima de 1,0 apenas nos cotilédones. A exposição à salinidade também reduziu a condutância estomática, a assimilação liquida de CO2 e a transpiração, além de aumentar a temperatura e a concentração de CO2 subestomático nas folhas cordiformes durante o curso diário. Diante dos danos observados, não é recomendado o uso dessa espécie para a recuperação de áreas degradadas que apresentem elevada salinidade, visto que esse estresse pode levar à mortalidade das plântulas por efeitos osmóticos e iônicos que podem propiciar privação de carbono.

Abstract Atriplex nummularia L. is one of the most studied halophytes in research on phytoremediation of salt-affected soils. However, the optimization of biomass requires studies that indicate the appropriate way to evaluate the photosynthesis. The objective of this study was to investigate the photosynthetic efficiency of A. nummularia irrigated with saline water in order to indicate the best range of photosynthetically active radiation (PAR) that should be used. Plants were subjected to daily irrigations (0, 50, 100, 200, 250 and 300 mmol L-1 of NaCl). The light curves were determined at 15 and 84 days applying twenty light intensities (2000, 1750, 1500, 1250, 1000, 750, 500, 250, 200,175, 150, 125, 100, 75, 50, 25, 15, 10, 5, 0 μmol m-2 s-1 PAR). The highest values of photosynthesis rate were observed at PAR of 2000 μmol m-2 s-1 and of 800 μmol m-2 s-1 to 15 and 84 days of evaluation, independent of the NaCl concentration. The present study provides data that support the choice of the ideal PAR in evaluations of gas exchange in A. nummularia.

Understanding the dynamics of physiological changes involved in the acclimation responses of plants after their exposure to repeated cycles of water stress is crucial to selecting resilient genotypes for regions with recurrent drought episodes. Under such background, we tried to respond to questions as: (1) Are there differences in the stomatal-related and non-stomatal responses during water stress cycles in different clones of Coffea canephora Pierre ex A. Froehner? (2) Do these C. canephora clones show a different response in each of the two sequential water stress events? (3) Is one previous drought stress event sufficient to induce a kind of “memory” in C. canephora? Seven-month-old plants of two clones (’3V’ and ‘A1’, previously characterized as deeper and lesser deep root growth, respectively) were maintained well-watered (WW) or fully withholding the irrigation, inducing soil water stress (WS) until the soil matric water potential (Ψmsoil) reached ≅ −0.5 MPa (−500 kPa) at a soil depth of 500 mm. Two sequential drought events (drought-1 and drought-2) attained this Ψmsoil after 19 days and were followed by soil rewatering until a complete recovery of leaf net CO2 assimilation rate (Anet) during the recovery-1 and recovery-2 events. The leaf gas exchange, chlorophyll a fluorescence, and leaf reflectance parameters were measured in six-day frequency, while the leaf anatomy was examined only at the end of the second drought cycle. In both drought events, the WS plants showed reduction in stomatal conductance and leaf transpiration. The reduction in internal CO2 diffusion was observed in the second drought cycle, expressed by increased thickness of spongy parenchyma in both clones. Those stomatal and anatomical traits impacted decreasing the Anet in both drought events. The ‘3V’ was less influenced by water stress than the ‘A1’ genotype in Anet, effective quantum yield in PSII photochemistry, photochemical quenching, linear electron transport rate, and photochemical reflectance index during the drought-1, but during the drought-2 event such an advantage disappeared. Such physiological genotype differences were supported by the medium xylem vessel area diminished only in ‘3V’ under WS. In both drought cycles, the recovery of all observed stomatal and non-stomatal responses was usually complete after 12 days of rewatering. The absence of photochemical impacts, namely in the maximum quantum yield of primary photochemical reactions, photosynthetic performance index, and density of reaction centers capable of QA reduction during the drought-2 event, might result from an acclimation response of the clones to WS. In the second drought cycle, the plants showed some improved responses to stress, suggesting “memory” effects as drought acclimation at a recurrent drought.