Nutrient deficiency and hypoxia as constraints to Panicum coloratum growth in alkaline soils

Alkaline and saline–alkaline soils impose severe restrictions on plant growth. Panicum coloratum var. coloratum is a perennial C4 forage grass widely used in tropical and subtropical environments. Published information on its responses to alkaline soil conditions is scarce. The objectives of this study were (i) to characterize the effects of alkaline substrates on germination and initial growth in this species, (ii) to assess the influence of high pH in combination with reduced availability of either nutrients or oxygen and salinity, on plant growth and (iii) to evaluate some physiological traits potentially responsible for growth restrictions under alkaline soil conditions. Trials were conducted in a greenhouse. Germination and early plant survival were not affected by alkalinity. To isolate the effects of high pH, reduced nutrient and oxygen availability on growth, plants were grown either in neutral or alkaline soil, in hydroponics, in neutralized alkaline soil (with or without supplementary fertilization), or were flooded to induce hypoxia. Alkalinity effects on growth in hydroponics were milder than in soil. Growth in alkaline soil with nutrient supplement was still significantly lower (by 40%) than in neutral soil. Both alkalinity and hypoxia reduced growth non‐synergistically. These results show that studies of plant response to alkaline substrates carried out in aerated nutrient solutions can only partially address the complexity of this stress. Photosynthesis and PSII activity were among the physiological mechanisms negatively affected by alkalinity and may be partially responsible for the growth limitations observed in P. coloratum under alkaline conditions.