Mineral Toxicity and Physiological Functions in Tree Seedlings Irrigated with Effluents of Varying Chemistry in Sandy Soil of Dry Region

Abstract

Effluents namely canal water as control (T₁); municipal effluent (T₂); textile effluent (T₃); steel effluent (T₄); textile + municipal effluent in 1:1 ratio (T₅); steel + municipal effluent in 1:2 ratio (T₆); steel + municipal + textile in 1:2:2 ratio (T₇); and steel + textile in 1:2 ratio (T₈) were added to the seedlings of Acacia nilotica and Eucalyptus camaldulensis. The aim was to monitor the toxic effect of the accumulated mineral ions on the physiological functions and ultimately to utilize these effluents in tree plantation. Foliage mineral concentration, leaf water potential (LWP), rate of photosynthesis (P _n ), rate of transpiration (T) and stomatal conductance (g) were recorded. Mineral accumulation increased in the seedlings of T₂ treatment. However, the accumulation of Mn, Fe, Cu and Zn was the highest (p<0.001) in the seedlings of T₄, T₆, T₇, and T₈ treatments affecting N, P, K, Ca, Mg, and Na concentration. The seedlings of T₃ treatment had less Mg, Mn, Fe, Cu, and Zn and medium N, Ca, and P concentration, which were negatively correlated with Na concentration in foliage and the amount added through effluent irrigation. Concentration of N, K, Ca, Mg, and Na was higher in the foliage of A. nilotica whereas P, Mn, Fe, Cu, and Zn were high in E. camaldulensis. Early two months data showed reduction (p<0.01) in P _n (87%), T (81%), g (67%), and LWP as a result of metal stresses (toxicity) in T₆, T₇, and T₈ seedlings. E. camaldulensis maintained high LWP and P _n and low T and g compared to A. nilotica. High LWP in the seedlings of T₂ was associated (p<0.05) high P _n , T, and g. However, these physiological parameters lowered in the seedlings of T₃ and T₅. Seedlings of T₁, T₂, and T₅ maintained high LWP, P _n , T, and g throughout the experimental period. These parameters however, decreased (p<0.01) in the seedlings of T₃ treatment subsequently through Na induced deficiency of Mg, Ca, Mn, Fe, Cu, and Zn. The enhanced physiological functions in T₅ treatment were probably the result of ameliorative effect of municipal effluent through increased mineral status. The study suggests that excess accumulation of Na, Mn, Fe, Cu, and Zn leads to metal toxicity that adversely affects physiology of the tree seedlings. Mixing of effluents and/or removal of excess would ameliorate these toxic effects and could be the better management practices for their use in tree irrigation.

Keywords:

• Arid region
• Effluent irrigation
• Gas exchange
• Leaf water potential
• Metal toxicity

Acknowledgments

Authors are thankful to the Director, Arid Forest Research Institute, Jodhpur for providing research facilities. One of us (MB) thanks ICFRE, Dehradun for the award of JRF/SRF.