Toxic levels of aluminum and manganese and variation of nitrogen content in grape leaves.

Abstract

Field and greenhouse studies were carried out to determine the effects of Al and Mn individually or collectively on the growth and elemental composition of various grape cultivars. Soil and plant tissue analyses were evaluated in two vineyard locations on which several grape varieties were established on a White House soil series. Soils at both locations were treated with soil amendments and N fertilizers. The results show that both soils are acidic at the top 30 cm surface and have a high extractable Al, Fe and in some cases Mn content. The field results further indicate that grape varieties respond differently to soil acidity in terms of their mineral composition. High soil Al, Fe and Mn resulted in a higher accumulation of these elements in grape leaves whereas the cation uptake especially P, Ca, Zn, and Cu were reduced. Field plants exhibiting P deficiency symptoms resulting from high soil Al and Fe had a 950 Mg kg⁻¹ Al and 400 mg kg⁻¹ Mn in their leaves. Furthermore, these plants had a deficient range of P, K, Ca and Zn. The Al treatments reduced shoot growth and decreased number of leaves. The growth reduction resulted from higher Al, Mn and Fe content of plant leaves and lower P, Ca and Cu. Furthermore high Al treatments of 30 mg 1⁻¹ and more in the nutrient solution resulted in lower accumulation of P, Ca, K, Mg, Fe and Cu. The different parameters were affected by Al levels to different degrees and were more pronounced at a later stage of growth than the earlier stage of growth. The concentration of Al in plant tops at which Al toxicity symptoms appeared was 800 mg kg⁻¹ Al or more. Mn treatments reduced plant growth, decreased number of leaves and induced toxicity symptoms. The percent reduction of growth parameters was greatest at highest Mn levels. The reduced growth resulted from the deficiency of several mineral elements such as Ca, Fe, Zn and Cu and higher accumulation of Mn in plant tissue. The effect of Mn levels on the elemental composition especially Fe, Zn, Cu, Ca and P increased progressively as plant growth progressed. The 10% reduction in growth occurred when plant had accumulated 400 mg kg⁻¹ Mn in their tops. The accumulation of elements in plant leaves was varied at various stages of growth as a function of time and Mn and/or Al concentration in the nutrient solution. The growth reduction and the severity of toxicity symptoms were proportional to either Al, Mn or Al + Mn concentrations in the nutrient solution as well as their accumulation in plant tops.