Root-zone hypoxia reduces growth of the tropical forage grass Urochloa humidicola in high-nutrient but not low-nutrient conditions. uri icon

abstract

  • Background and Aims The perennial C4 grass Urochloa humidicola is widely planted on infertile acidic and waterlogging-prone soils of tropical America. Waterlogging results in soil anoxia, and O-2 deficiency can reduce nutrient uptake by roots. Interestingly, both nutrient deficiencies and soil waterlogging can enhance root cortical cell senescence, and the increased gas-filled porosity facilitates internal aeration of roots. We tested the influence of nutrient supply and root-zone O-2 on root traits, leaf nutrient concentrations and growth of U. humidicola.
  • Conclusions Under low-nutrient conditions, plant growth in stagnant solution was equal to that in aerated solution, whereas under higher-nutrient regimes growth increased but dry mass in stagnant solution was less than in aerated solution. Slow growth in low-nutrient conditions limited any further response to the low O-2 treatment, and greater porosity and smaller stele size in roots would enhance internal O-2 movement within roots in the nutrient-limited stagnant conditions. A constitutive barrier to radial O-2 loss and aerenchyma facilitates O-2 movement to the tips of roots, which presumably contributes to maintaining nutrient uptake and the tolerance of U. humidicola to low O-2 in the root-zone.
  • Key Results Shoot dry mass was reduced for plants in stagnant compared with aerated conditions at high, but not at low, levels of mineral nutrition. In low-nutrition stagnant solution, roots were shorter, of greater porosity and had smaller radial thickness of the stele. Suberized lamellae and lignified sclerenchyma, as well as a strong barrier to radial O-2 loss, were documented for roots from all treatments. Leaf nutrient concentrations of K, Mg and Ca (but not N, P and S) were higher in aerated than in stagnant conditions.
  • Methods Plants were grown in pots in a completely randomized design under aerated or stagnant deoxygenated hydroponic conditions and six nutrient regimes, with low to high concentrations of all essential elements, for 28 d in a controlled-temperature greenhouse. The standard acid solution (SAS) used was previously designed based on infertile acidic soils of the tropical America savannas, and step increases in the concentration of SAS were used in aerated or deoxygenated 0.1 % agar solution, which mimics changes in gas composition in waterlogged soils. Measurements included shoot and root growth, root porosity, root anatomy, radial O-2 loss, and leaf tissue nutrient concentrations.

publication date

  • 2019
  • 2019