Interaction Between Anoxia and Nutrition on Root Traits, Growth and Shoot Nutrients in the Perennial Tropical Grass Urochloa humidicola

The perennial C4 grass Urochloa humidicola is widely planted in low fertility acidic soils of Tropical America. In this region it is expected that waterlogging events will increase in frequency and intensity in the near future. We hypothesized that an increase in the nutrient concentration of the solution would increase the waterlogging tolerance of U. humidicola. Slight increases of the nutrient load of the stagnant solution positively increased the shoot biomass, but higher increase in nutrients did not further increase plant growth. Likewise, shoot biomass was comparable between aerated and stagnant conditions at low nutrition, however, shoot biomass in aerated plants were statistically higher than stagnant plants at high nutrition. Under stagnant solution and low nutrient conditions, longer roots and more root number with higher porosity and smaller stele were developed to improve waterlogging adaptation. Suberized lamella and lignified sclerenchyma were found in roots from all aerated and stagnant treatments. Likewise, a barrier to impede radial oxygen loss was developed in roots in all treatments. The concentration of nutrients (N, P, K, Mg, Ca and S) in leaves increased at higher nutrient concentrations irrespective of the aeration treatment. Significant reductions in leaf concentration of cations K, Mg and Ca were exhibited under stagnant conditions. Under low nutrient conditions, plants invested more resources to root growth than shoot growth, improving the exploration for resources. Therefore, a bigger root system with better capacity for oxygen transport under low nutrition and stagnant conditions is contributing to maintain shoot biomass production at comparable levels to the aerated controls in these low nutrient conditions. In contrast, smaller and less roots were not enough to maintain higher biomass produced at high nutrient conditions. We conclude that roots modification under stagnant low nutrient solutions are contributing to improve plant adaptation to such conditions.