Morphophysiology of the passion fruit ‘BRS Rubi do Cerrado’ irrigated with saline waters and nitrogen fertilization

This study aimed to evaluate the gas exchanges and growth of the purple passion fruit cultivar ‘BRS Rubi do Cerrado’ as a function of the salinity levels of the irrigation water and nitrogen fertilization. The research was conducted in pots adapted as drainage lysimeters, placed within a plant nursery, using a Regolithic Neosol of sandy texture, in the municipality of Pombal-PB, Brazil. A randomized block design was used, testing five levels of electrical conductivity of irrigation water (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1) associated with four doses of nitrogen (50, 75, 100, and 125% of the recommendation). The irrigation water salinity above 0.3 dS m-1 compromised the leaf area and the relative water content of the purple passion fruit ‘BRS Rubi do Cerrado’. High doses of nitrogen enhance the deleterious effects of irrigation water salinity on stomatal conductance, transpiration, internal CO2 concentration, CO2 assimilation rate, number of leaves, stem diameter, and height of purple passion fruit plants. When waters with salinity levels of up to 1.3 dS m-1 are used, the dose of 125 mg of N kg-1 of soil is recommendation for providing increases in the CO2 assimilation rate of the purple passion fruit ‘BRS Rubi do Cerrado’ at 70 days after sowing (DAS). Water salinity increases electrolyte leakage, regardless of nitrogen doses.

Intrinsic Fluctuations in Transpiration Induce Photorespiration to Oxidize P700 in Photosystem I

Upon exposure to environmental stress, the primary electron donor in photosystem I (PSI), P700, is oxidized to suppress the production of reactive oxygen species that could oxidatively inactivate the function of PSI. The illumination of rice leaves with actinic light induces intrinsic fluctuations in the opening and closing of stomata, causing the net CO2 assimilation rate to fluctuate. We examined the effects of these intrinsic fluctuations on electron transport reactions. Under atmospheric O2 conditions (21 kPa), the effective quantum yield of photosystem II (PSII) (Y(II)) remained relatively high while the net CO2 assimilation rate fluctuated, which indicates the function of alternative electron flow. By contrast, under low O2 conditions (2 kPa), Y(II) fluctuated. These results suggest that photorespiration primarily drove the alternative electron flow. Photorespiration maintained the oxidation level of ferredoxin (Fd) throughout the fluctuation of the net CO2 assimilation rate. Moreover, the relative activity of photorespiration was correlated with both the oxidation level of P700 and the magnitude of the proton gradient across the thylakoid membrane in 21 kPa O2 conditions. These results show that photorespiration oxidized P700 by stimulating the proton gradient formation when CO2 assimilation was suppressed by stomatal closure.

Shade tree species affect gas exchange and hydraulic conductivity of cacao cultivars in an agroforestry system

Shade tolerance is a widespread strategy of rainforest understory plants. Many understory species have green young stems that may assimilate CO2 and contribute to whole-plant carbon balance. Cacao commonly grows in the shaded understory and recent emphasis has been placed on diversifying the types of trees used to shade cacao plants to achieve additional ecosystem services. We studied three agricultural cacao cultivars growing in the shade of four timber species (Cedrela odorata L., Cordia thaisiana Agostini, Swietenia macrophylla King and Tabebuia rosea (Bertol) A.D.C.) in an agroforestry system to (i) evaluate the timber species for their effect on the physiological performance of three cacao cultivars; (ii) assess the role of green stems on the carbon economy of cacao; and (iii) examine coordination between stem hydraulic conductivity and stem photosynthesis in cacao. Green young stem photosynthetic CO2 assimilation rate was positive and double leaf CO2 assimilation rate, indicating a positive contribution of green stems to the carbon economy of cacao; however, green stem area is smaller than leaf area and its relative contribution is low. Timber species showed a significant effect on leaf gas exchange traits and on stomatal conductance of cacao, and stem water-use efficiency varied among cultivars. There were no significant differences in leaf-specific hydraulic conductivity among cacao cultivars, but sapwood-specific hydraulic conductivity varied significantly among cultivars and there was an interactive effect of cacao cultivar × timber species. Hydraulic efficiency was coordinated with stem-stomatal conductance, but not with leaf-stomatal conductance or any measure of photosynthesis. We conclude that different shade regimes determined by timber species and the interaction with cacao cultivar had an important effect on most of the physiological traits and growth variables of three cacao cultivars growing in an agroforestry system. Results suggested that C. odorata is the best timber species to provide partial shade for cacao cultivars in the Barlovento region in Venezuela, regardless of cultivar origin.

Water status, cell damage and gas exchanges in West Indian cherry (Malpighia emarginata) under salt stress and nitrogen fertilization

This study was conducted to evaluate water status, cell damage and gas exchanges of West Indian cherry grown under saline water irrigation and nitrogen (N) fertilization in the post-grafting stage. The experiment was carried out in drainage lysimeters under greenhouse conditions in Regolithic Neosol with sandy loam texture. Treatments consisted of two levels of electrical conductivity of water (ECw) (0.8 and 4.5 dS m-1) and four N doses (70; 85; 100 and 115% of the N recommendation), arranged in randomized blocks, with three replicates. The dose relative to 100% corresponded to 200 g of N per plant per year. Irrigation with 4.5 dS m-1 electrical conductivity water resulted in a reduction in stomatal conductance, transpiration, CO2 assimilation rate and instantaneous carboxylation efficiency but increased cell damage percentage and internal CO2 concentration in West Indian cherry plants. Inhibition of CO2 assimilation rate in West Indian cherry plants is related to non-stomatal effects. Irrigation with 4.5 dS m-1 water and fertilization with 115% of N recommendation intensified leaf water saturation deficit in the West Indian cherry crop. The BRS Jaburu West Indian cherry was sensitive to 4.5 dS m-1 water salinity.

Effects of water deficit on growth and physiology of young Conocarpus erectus L. and Ficus benjamina L. Saplings

A greenhouse experiment was conducted to investigate the effects of water deficit on growth and physiological parameters of Ficus benjamina and Conocarpus erectus. The results revealed that all growth parameters such as plant height, stem diameter, no. of leaves, no. of branches and chlorophyll contents significantly decreased under water deficit condition. Interestingly, although leaf, stem and total biomass production and allocation decreased significantly under water deficit, but root biomass production and allocation increased significantly. Similarly, stomatal conductance to water vapor decreased significantly and CO2 assimilation rate remained similar to control under water deficit condition. Resultantly, a significant increase in water use efficiency was evident in both species under water deficit condition. These results suggested that, in spite of a significant decrease in biomass production, young Conocarpus erectus and Ficus benjamina can tolerate water deficit which is due to sustained CO2 assimilation rate and increase in root biomass.

Salt tolerance and regulation of gas exchange and hormonal homeostasis by auxin-priming in wheat

The objective of this work was to assess the regulatory effects of auxin-priming on gas exchange and hormonal homeostasis in spring wheat subjected to saline conditions. Seeds of MH-97 (salt-intolerant) and Inqlab-91 (salt-tolerant) cultivars were subjected to 11 priming treatments (three hormones x three concentrations + two controls) and evaluated under saline (15 dS m-1) and nonsaline (2.84 dS m-1) conditions. The priming treatments consisted of: 5.71, 8.56, and 11.42 × 10-4 mol L-1 indoleacetic acid; 4.92, 7.38, and 9.84 × 10-4 mol L-1 indolebutyric acid; 4.89, 7.34, and 9.79 × 10-4 mol L-1 tryptophan; and a control with hydroprimed seeds. A negative control with nonprimed seeds was also evaluated. All priming agents diminished the effects of salinity on endogenous abscisic acid concentration in the salt-intolerant cultivar. Grain yield was positively correlated with net CO2 assimilation rate and endogenous indoleacetic acid concentration, and it was negatively correlated with abscisic acid and free polyamine concentrations. In general, the priming treatment with tryptophan at 4.89 × 10-4 mol L-1 was the most effective in minimizing yield losses and reductions in net CO2 assimilation rate, under salt stress conditions. Hormonal homeostasis increases net CO2 assimilation rate and confers tolerance to salinity on spring wheat.