Effects of Elevated Aluminum Concentration and Distribution on Root Damage, Cell Wall Polysaccharides, and Nutrient Uptake in Different Tolerant Eucalyptus Clones

Abstract

Aluminized acidic soil can damage Eucalyptus roots and limit tree growth, hindering the productivity of Eucalyptus plantations. At present, the negative impacts of elevated aluminum (Al) on the cell morphology and cell wall properties of Eucalyptus root tip are still unclear. In order to investigate the responses of two different tolerant clones, Eucalyptus urophylla (G4) and Eucalyptus grandis × Eucalyptus urophylla (G9), to Al toxicity, seedling roots were treated hydroponically with an Al solution, and the polysaccharide content in the root tip cell wall and the characteristics of programmed cell death were studied. The results show that the distribution of Al was similar in both clones, although G9 was found to be more tolerant to Al toxicity than G4. The Al3+ uptake of pectin in root tip cell walls was significantly higher in G4 than in G9. The root tip in G4 was obviously damaged, enlarged, thickened, and shorter; the root crown cells were cracked and fluffy; and the cell elongation area was squeezed. The lower cell wall polysaccharide content and PME activity may result in fewer carboxylic groups in the root tip cell wall to serve as Al-binding sites, which may explain the stronger Al resistance of G9 than G4. The uptake of nitrogen and potassium in G4 was significantly reduced after aluminum application and was lower than in G9. Al-resistant Eucalyptus clones may have synergistic pleiotropic effects in resisting high aluminum–low phosphorus stress, and maintaining higher nitrogen and potassium levels in roots may be an important mechanism for effectively alleviating Al toxicity.

Physiological Mechanism through Which Al Toxicity Inhibits Peanut Root Growth

“…Consequently, the root tip expands [ 29 ]. Similar findings have been reported in Eucalyptus clones, in which Al toxicity stress led to taproot enlargement and root tip shortening and thickening [ 30 ]. These changes may be due to alterations in the cell wall cellulose content under Al stress, which causes cell deformation and a shift in growth direction from vertical to horizontal, resulting in the expansion and thickening of the root tip base [ 30 ].…”

Impact of Simulated Acid Rain on Soil Base Cations Dissolution between Eucalyptus Pure Plantations and Eucalyptus–Castanopsis fissa Mixed Plantations

“…In the proton buffering process of red soil, Mg 2+ and Ca 2+ play a major role. This is especially true of Ca 2+ because the amount of Ca 2+ released is much larger than that of Mg 2+ , and the adsorbed Ca 2+ in the cation exchange reaction is easy to decompose and release [44]. Under acid deposition leaching, Ca 2+ can be released from the soil through mineral weathering, thus increasing the amount of Ca 2+ leached [35].…”