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Objective. 'lo agronomically and physiologically evaluate the development of lettuce cultivars under protected conditions. Materials and methods. Under a completely randomized block design, the growth, agronomic and physiological characteristics of five lettuce cultivars were evaluated in two protected agriculture systems and in open field conditions. Results. The cultivars White Boston and Romana Parris Island Coss in house mesh and open field had the highest values in physiological variables (Photosynthesis close to 25.00/¿mol CO2 m2/s, transpiration greater than 7.00 mmol water m2/s and stomatai conductance greater than 1.50 mmol water mmol agua m2/s), which caused the highest values in fresh biomass area and root (95.90 and 3.55 g). The photosynthesis variable in plants sown in the open field reached values of22.29/¿mol CO2 m2/s, compared with house mesh and greenhouse with 17.14 and 14.16/¿mol CO2 m2/s. Conclusions. The ability of these lettuce cultivars to tolerate heat stress was due to morphological and physiological mechanisms, including long-lived leaf, stomatai control, and high photosynthetic potential. [ABSTRACT FROM AUTHOR]

The use of conglomerate for the development of mycorrhizal inoculants is very important to develop a variety of commercial products made from these microorganisms. According to this a experiment was conducted in order to compare the effect of two mycorrhizal inoculants on growth, development and gasses interchange of maize plants. The experiment was developed under a completely randomized design and the inoculants proved were the first constituted by Glomus cubense specie and the other one was a conglomerate of species (Consorcio Selva). Different mycorrhizal (intensity and frecuence), physiological (stomatal conductance, photosynthetic rate) and growth (height, stem diameter and dry mass) indicators were evaluated. Not differences were detected among the inoculants employed on growth indicators, but in mycorrizal parameters the conglomerate (Consorcio Selva) presented the highest values of the indicator; however, an interesting behavior was observed using Glomus cubense inoculants due to the values obtained for this inoculants were comparable to control, but the effect of this specie was the best obtained on gas exchange variable. These results point to the highest efficiency of this specie and to the functional differences between species on ecological point of view, and they open the possibility of using of cluster in field's condition. [ABSTRACT FROM AUTHOR]

In order to study the ecophysiological relations that affect the growth of B. decumbens in monocrop (MO) and associated withZ. leucocephala (AS), evaluations of photosynthetic active radiation (PAR), assimilation (A) stomatic conductance (Gs), transpiration (E), relative humidity (RH), water potential (0h), differential of steam pressure (DSP) and leaf area index (LAI) were made in a tropical humid forest zone. The evaluations were made 5,10 and 22 days after grazing under both conditions (MO and AS). The most positive values of 0h (P<0,05) were found in AS, as well as the lowest values of PAR (P<0,05) in all the evaluated dates. RH and DSP did not show differences (P 0,05). The gas exchange parameters (E, Gs and A) showed significantly higher values in MO (P<0,05) in all dates. LAI was higher in MO after 10 and 22 days of evaluation. Due to the limitation of the photosynthetic capacity exerted by the light decrease on the grass, that PAR is concluded to be the most important factor that determine growth and development of B. decumbens in AS. [ABSTRACT FROM AUTHOR]

This research work was aimed at determining the effect of high temperatures on some growth variables and gas exchange in tomato plants of Amalia cv. Plants were grown in pots containing silica sand, which were put in trays adding Hoagland's nutrient solution to them. Treatments consisted of a control having a temperature of 25 gC during the day and 18 gC in the dark period, another treatment in which day and night temperatures increased 5 gC every four days up to 40 with 33 gC and a variant where plants were subjected to a heat shock of 40/33 gC day/night respectively for a period of four days. Once treatment application was concluded, plants were placed under the same conditions of the control treatment for 12 days, to evaluate their recovery. Evaluations on biomass, stomatal conductance and CO2 assimilation rate were recorded at the end of every period of heat treatment and recovery. Data analysis made evident a depressive effect of different variables evaluated when increasing environmental temperature; such effect was not eliminated in some indicators after the recovery period. [ABSTRACT FROM AUTHOR]