Response of Potted Pear Trees to Increasing Copper Concentration in Sandy and Clay-Loam Soils

ABSTRACT

The response of potted pear trees grafted on quince (Cydonia oblonga Mill.) Sydo stock to increasing concentrations (0, 50, 100, 200, 400, 600, 800, and 1000 mg kg⁻¹) of copper (Cu) in sandy and clay-loam soils were evaluated and crop toxicity thresholds and symptoms were determined. Reductions of shoot growth and leaf area were observed only for pear grown in sandy soil with more than 400 mg Cu/kg. During the growing season, carbon assimilation and soil microbial biomass were reduced as concentration of soil Cu increased. However, the effect was always stronger in sandy than clay-loam soil. Copper accumulated in roots, with response to soil Cu additions described by a linear and a quadratic function for sandy and clay-loam soil, respectively. A possible antagonism was observed between Cu and zinc (Zn) in the roots. Root Zn concentration decreased as soil Cu concentration increased.

Keywords:

• carbon assimilation
• CaCl₂-extractable Cu
• DTPA-extractable Cu
• microbial biomass
• toxicity threshold

ACKNOWLEDGMENTS

This study was supported by Regione Emilia-Romagna (legislation 28/98) - CRPV (Cesena) and PROBER (Bologna). We thank Dr. E. Muzzi for his help in statistical data analysis and Lobietti farm (Comacchio, Ferrara, Italy) for providing the sandy soil.

Notes

^zCation exchange capacity.