Trocas gasosas foliares de variedades crioulas de milho sob estresse salino
Ana Célia da Costa Barroso
UFERSA
Miguel Ferreira Neto
Francisco Vanies da Silva Sá
Rayane Amaral de Andrade
Ricardo André Rodrigues Filho
Palavras-chave: Zea mays (L.), Salinidade, Variedades crioulas, Irrigação, Estresse salino, Produtividade
Resumo
Soil salinization represents one of the main limiting factors for agricultural productivity, directly affecting plant physiology and the sustainability of crops. That said, maize (Zea mays L.) is considered a crop of high economic importance, showing moderate sensitivity to salinity, with critical limits of 1.1 dS m⁻¹ for irrigation water and 1.7 dS m⁻¹ for the soil saturation extract. In this context, traditional maize varieties stand out for their genetic diversity and greater capacity to adapt to adverse environments. In this regard, the present study evaluated the effects of irrigation with low and high salinity water, with levels for irrigation water of 0.5 dS m⁻¹ and 5.5 dS m⁻¹, respectively. For this purpose, eight traditional maize varieties were used, namely: Santana do Mato, Grão do Sertão, Pela, Sol da Manhã, Índio, Jaboatão, Pontinha, and Logradouro. The experiment was conducted in a greenhouse at the Department of Agronomic and Forest Sciences of UFERSA Mossoró campus, located in the state of Rio Grande do Norte. The leaf gas exchanges of maize were measured at the flowering stage, between 6 and 9 a.m. Additionally, the evaluations were carried out on mature leaves located in the upper third of each plant, using a portable infrared gas analyzer (IRGA), model LCPro+ Portable Photosynthesis System®. From the analyses conducted during this experiment, it was observed that the maize varieties, when subjected to saline stress, showed restricted stomatal opening, as well as reduced CO2 diffusion in the mesophyll and net carbon assimilation. The CO2 assimilation rate decreased by 50.2% in response to increased electrical conductivity of the irrigation water. Similarly, stomatal conductance was reduced by 40.4% under higher salinity. Furthermore, for transpiration, internal CO₂ concentration, and vapor pressure deficit, decreases of 33.1%, 23.9%, and 9.5% were observed, respectively, highlighting the deleterious effects of salinity on the physiological performance of the plants. Nevertheless, the reduction of VPD with increased salts in the irrigation water indicates that the increase in the electrical conductivity of the irrigation water intensified the plant's adaptive responses (stomatal closure and reduced transpiration), which, by lowering microclimatic VPD and CO₂ intake, contributed to the reduction in net carbon assimilation. Consequently, it was found that the heirloom maize varieties subjected to saline stress exhibited an adaptive response to unfavorable conditions, as the osmotic potential was altered to reduce water loss through transpiration.