When plants are subjected to competition, their physiological behavior changes. To understand the developmental physiology of weeds will subsidize the development of cropping systems which favor the crops plants in detriment of weeds. The objective of this work was to evaluate the physiological behavior of different weed species, growing under intraspecific competition. Greenhouse experiment was conducted in randomized complete block design arranged in factorial scheme 4 × 5 with four replications. Factor A was the weed species [Urochloa plantaginea (Alexandrergrass), Bidens pilosa (hairy beggarticks), Ipomoea indivisa (morningglory) and Conyza bonariensis (hairy fleabane)], and factor B was the plant density of these species (20, 40, 60, 80 or 100 plants m -2 ). The following variables were evaluated: sub-stomatal CO 2 concentration, photosynthesis rate, consumed CO 2 , stomatal conductance, transpiration rate, water use efficiency, plant height, shoot diameter, leaf area, and shoot dry biomass. Alexandergrass relies on the superior control of stomatal opening and high water use efficiency. Hairy beggarticks efficiency in competition lies on its ability to remove water from soil to levels when the other surrounding plant species would undergo stress. Morning glory and hairy fleabane did not present detectable particular features in the study, and their importance as weeds is probably tied to other survival abilities but superior competition. In conclusion, the weed species studied present distinct competitive strategies.
We aimed to evaluate the initial growth and physiological characteristics of rice planted following ryegrass in lowland areas. The experiment was conducted in Capao do Leao, Brazil, in Typic Albaqualf. Ryegrass was planted preceding the experiment installation. Prior to rice planting, the area was burndown with herbicide, when treatments were established: ryegrass plants were cut at 0, 15, 30 or 45 cm above ground, resulting in different mulching levels. Rice was then planted, being managed according to local recommendations for the crop. We evaluated the variation in soil moisture levels, rice establishment in density and seedling height, and physiological parameters: relative fluorescence, chlorophyll, flavonoid a nd nitrogen balance indexes. High mulching levels by ryegrass allowed rice five additional days on a dry season, before harmful soil water tension, compared to bare soil; seedlings able to emerge under the ryegrass mulching, grew without considerable barriers; plant physiology in fields with residual ryegrass mulching was little affected, and ryegrass cut up to 45cm height prior to planting rice seem not to affect it. This corresponds to a maximum of about 4500 kg ha-1 of ryegrass straw on soil surface prior to planting rice to avoid damages to crop establishment.
Since antioxidant enzymes activity affects the end of dormancy stage, it is important to understand the responses given by antioxidant enzymes and their roles in budbreak induction in temperate fruit trees. This research aimed at evaluating the antioxidant enzymes activity at the end of budbreak stage after the inducers application to ‘Castel Gala’ apple trees and their performance in budbreak and blooming. Seven treatments were carried out: Erger® 3% + calcium nitrate 5%; Erger® 5% + calcium nitrate 5%; Erger® 7% + calcium nitrate 5%; garlic extract (GE) 5% + mineral oil (MO) 2%; GE 10% + MO 2%; GE 15% + MO 2%; and the control. Buds were collected one, four and seven days after the application (DAA) of budbreak inducers, and activity of the following enzymes was determined by: superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). Besides that, hydrogen peroxide was quantified. Percentages of budbreak and blooming were evaluated at 32th, 40 th, 45 th and 52 th DAA. The results showed that SOD activity had increased as the dormancy stage reached its end. CAT activity was influenced by the application of budbreak inducers. It decreased significantly throughout the experiment in the most efficient treatment. Percentages of budbreak (61.85%) and blooming (25.44%) showed the highest efficiency in the treatment with Erger® 7% + calcium nitrate 5%, which was the inducer with the highest potential in ‘Castel Gala’ apple trees
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