Heat stress due to high daytime temperatures is one of the main limiting factors in rice (Oryza sativa L.) yield in Colombia. Thus, the objective of the present research was to analyze the effect of three different daytime temperatures (25, 35, and 40 °C) on the physiological responses of three Colombian rice cultivars (F60, F733, and F473), thereby contributing to the knowledge of rice acclimation mechanisms. For 10 d, eight plants of each of the three cultivars were subjected daily to 5 h periods of 35 and 40 °C. The control treatment corresponded to normal growth conditions (25 °C). Thermal stress was assessed based on a series of physiological and biochemical parameters. The 35 °C treatment produced photosynthetic and respiratory differences in all three cultivars. At 40 °C, ̔F60̓ displayed the lowest photosynthetic rate and the highest respiratory rate. Although this cultivar experienced particularly strong electrolyte leakage and changes in proline when subjected to the high-temperature treatments, similar trends were observed in ̔F733̓ and ̔F473̓. At 40 °C, the concentration of malondialdehyde (MDA) was lower in ̔F473̓ than in the other cultivars. These results may explain the poor agronomic performance of ̔F60̓ in the field under daytime heat stress. The methodologies employed in the present work may be useful in Colombian rice breeding programs, particularly for the selection of heat-tolerant breeding stocks.

The use of biostimulants is an agronomic tool to improve plant tolerance to abiotic stress in plants. This study explored the effect of foliar biostimulants sprays such as brassinosteroids (BR), amino acids (AA), nitrophenolates (NP) or a biostimulant based on botanical extracts (BE) on leaf gas exchange parameters [photosynthesis (PN), stomatal conductance (gs) and transpiration (E)], leaf photosynthetic pigments, lipid peroxidation of membranes and proline content of two commercial rice genotypes [‘Fedearroz 67’ and ‘Fedearroz 60’] under heat stress conditions. The established treatments were: i) plants without heat stress and foliar applications of biostimulants (C), ii) plants under heat stress and without foliar applications of biostimulants (HT), and iii) plants with heat stress and three foliar applications with BR (1 mL·L-1), AA (30 mL·L-1), NP (15 mL·L-1) or BE (15 mL·L-1). The results showed that the application of BR, AA, NP or BE increased the values ​​of PN (~14.5 µmol CO2·m-2·s-1), gs (~0.46 mmol·m-2·s-1) and E (~43.9 H20 day-1·plant-1) compared to plants (both genotypes) not treated with biostimulants under heat stress (9.9 µmol CO2·m-2·s-1 for PN, 0.31 mmol·m-2·s-1 for gs, and 27.3 H20 day-1·plant-1 for E). Foliar biostimulant sprays also caused a lower malondialdehyde and proline production in rice genotypes under heat stress. In conclusion, the biostimulants BR, AA, NP, or BE can be considered an agronomic strategy to help mitigate the adverse effects of heat stress in rice areas where periods of high temperatures are expected during the day in Colombia.

No abstract

The objective of this review is to show in a general way how biochar (BC) can be obtained and its effects on the physicochemical properties of soils and physiological behavior of cultivated plants. BC is a product rich in carbon that comes from the pyrolysis of biomass, generally of vegetable origin. BC is obtained by the decomposition of organic matter exposed to temperatures between 200-900 ºC in an atmosphere with low oxygen availability (pyrolysis), which can be slow, intermediate or fast. Depending on the biomass and the temperature used in its production, BC can contain high levels of elements such as carbon, nitrogen, oxygen, hydrogen, sulfur, among others. The main sources to produce biochar are forest, agroindustrial and manure residues. BC quality and physical-chemical characteristics will depend not only on the type of waste or plant material for production, but also on the plant photosynthetic apparatus. The high carbon contents present in organic matter, which are more resistant to biological and chemical decomposition, are stabilized by the pyrolysis process. When incorporated into the soil, BC remains stable for longer periods of time and is not volatilized into the atmosphere; this allows BC to be considered as an important compound for the mitigation of the impacts of polluting substances. Additionally, it has been found that BC application improves the physicochemical characteristics of the soil, including fertility. This improvement generates positive responses in the physiological behavior of cultivated plants such as the increase of germination, accumulation of dry matter, photosynthetic rate, yield and quality of the harvested organ. BC use opens important doors for the sustainable management of agriculture in Colombia. It can be considered in production systems exposed to heavy metals such as vegetables and perennial species, in order to reduce the impact of these substances on human health.

No abstract