Fosfato natural reativo e microrganismos promotores do crescimento de plantas em zea mays l. cultivado sob déficit hídrico: mecanismos bioquímicos

Abstract

The state of Rio Grande do Sul in Brazil is directly influenced by the Amazon climate, which brings air masses that generate either droughts or rainfall. Natural phosphate serves as an alternative source of phosphorus, an essential element for plants, commonly used in organic agriculture and agroecology. The Mata Atlântica (Atlantic Forest), predominantly found in the northeastern region of Rio Grande do Sul, stores a significant amount of carbon in its soil. However, with rising temperatures, decomposition processes may reduce this carbon storage, leading to increased carbon dioxide emissions. Additionally, corn (Zea mays L.) is highly sensitive to water stress, which disrupts both growth and biochemical processes in the plant. Natural phosphate provides an alternative phosphorus source, promoting robust root growth, aiding soil pH correction, enhancing nutrient availability, and improving plant resilience under water stress conditions. The objective of this study was to evaluate the effects of applying reactive natural phosphate and plant growth-promoting microorganisms (MPCP) during corn cultivation under water deficit conditions. Greenhouse experiments were conducted, with plants grown in pots and subjected to either 50% or 100% of pot capacity (50% CP and 100% CP, respectively) for 16 days after sowing. Different combinations of MPCP and natural phosphate were applied. At 35 days after sowing, plant samples were collected and analyzed for antioxidant enzyme activity (guaiacol peroxidase, GPOD), proline content, total protein quantification, and lipid peroxidation (TBARS). The study results revealed that root protein levels increased in plants exposed to water deficit, regardless of the treatments used, compared to the average of control treatments (averaged between 100% CP and 50% CP). Furthermore, root protein levels were higher (4.75 mg mL-1) under water deficit conditions than in non-stressed plants (13.59 mg mL-1). In corn plants subjected to water deficit (50% CP), GPOD activity increased with the application of all bioinputs. Additionally, GPOD activity in Z. mays leaves was higher for these treatments compared to plants treated with 100% CP. Regarding proline levels at 100% CP, the treatment resulting in the highest accumulation was reactive natural phosphate combined with Biomaphos (FNR+BsBm). However, under water restriction (50% CP), BsBm induced the greatest proline accumulation in leaves, being 3.7 times higher than the control treatment (50% CP without bioinput). The highest TBARS levels were observed in Z. mays leaves in the control treatment, as well as in plants treated with Azospirillum, BsBm, or FNR+BsBm under 100% CP, compared to the same treatments under water deficit conditions (50% CP). In roots, there was a difference in mean values between 100% CP and 50% CP, with the former being 1.4 times higher than the latter. In conclusion, the use of natural phosphate and MPCP offers a sustainable and efficient approach to mitigate the effects of water deficit in corn, providing accessible and cost-effective technologies for farmers, especially in the context of climate change and reduced precipitation.