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Plants that grow well while accumulating and transporting less potassium (K) perform better than more-sensitive plants when under deifciency conditions, which makes low-K-input and environmentally friendly agriculture possible. We conducted hydroponics and sand culture experiments to evaluate the efifciency of various apple (Malus domestica Borkh) rootstocks in their K uptake and utilization. Five genotypes were selected which are widely used in China-M. hupehensis Rehd,M. prunifolia Borkh, M. robusta Rehd,M. sieversii Roem, andM. rockii Rehd. Plant heights, root and shoot dry weights, and K concentrations were recorded. These genotypes differed markedly in dry weights, absolute and relative K concentrations, absolute and relative K accumulations, and their K efifciency ratio under deifcient K conditions. The last parameter, expressed as relative shoot dry weight, was strongly and positively correlated with the other four parameters in each genotype. Therefore, we suggest that this parameter could serve as an index when selecting K-efifcient genotypes. In this study, we have determined thatM. sieversii andM. rockii are K-inefifcient genotypes;M. prunifolia is K-efifcient genotype;M. hupehensis andM. robusta have moderate levels of potassium efifciency.