| Potassium (K) is one of the three major nutrients in soil-applied fertilizers.Apple-producing areas of the loess plateau is one of the preponderant apple production area inour country, and famous for its good apple quality, but drought and improper fertilizationresulting in lack of orchards potassium, hindering the further improvement in yield andquality of apple. So, plants that grow well while accumulating and transporting less potassium(K) perform better than more-sensitive plants when under deficiency conditions, making thisa cost-effective and environmentally friendly approach for practicing low-K-input agriculture.We conducted hydroponics and sand culture experiments to evaluate the efficiency of variousapple (Malus domestica Borkh) rootstocks in their K uptake and utilization. Five genotypeswere selected what are widely used in China–M. hupehensis Rehd, M. prunifolia Borkh, M.robusta Rehd, M. sieversii Roem, and M. rockii Rehd. Plant heights, root and shoot dryweights, K concentrations, K accumulation, relative K concentrations, relative Kaccumulation and enzymatic activity of antioxidant system were recorded. The main resultsare as follows:1. In both experiments, the lack of a sufficient K supply (K:0.1mM) had significanteffects (P <0.05) on shoot, root, and whole-plant dry matter yields for all five genotypes. Butthe declining level of dry weight under the lack of a K supply is different in genotypes ofapple stock. Here, M. sieversii and M. rockii had much higher relative decline of dry weightper plant; Both M. prunifolia had a smaller relative decline of dry weight per plant comparedwith other four genotypes.2. Root/shoot ratios tended to rise under the K deficiency, although those differenceswere not significant for most of the tested genotypes and the extent of those differences variedin two experiments. Root/shoot ratios in the sand culture experiment is much higher thanroot/shoot ratios under the hydroponics environment. This may have resulted from thedifferent environment provided for root development in each scenario, i.e., sand-culturing wasmore conducive to root growth.3. Compared with a sufficient K supply (K:3.0mM), significantly reduce of the Kconcentration and accumulation was occurred under the K insufficient conditions. But thedeclining extent of the K concentration and accumulation under insufficient K supply is different in apple rootstock genotypes. M. prunifolia had a larger relative K accumulation anda mid-range relative K concentration compared with other four genotypes, showing a strongability to accumulate and use potassium.4. K efficiency ratio, expressed as relative shoot dry weight, was positively correlatedwith RKC, RKA as well as KC and KA in K2, recognized as the important index to chooseK-efficient genotypes. Significantly differences were founded in different apple rootstockgenotypes in our study. For example, M. prunifolia had the highest ratio and was insensitiveto deficiency conditions while both M. sieversii and M. rockii had the smallest ratios,implying that they were sensitive to this source of stress. Potassium efficiency ratio underhydroponic conditions: M. prunifolia (0.71)> M. robusta (0.59)> M. hupehensis (0.58)> M.sieversii (0.45)> M. rockii (0.43); potassium efficiency sand culture conditions ratio: M.prunifolia (0.82)> M. robusta (0.81)> M. hupehensis (0.80)> M. rockii (0.64)> M. sieversii(0.55).5. Compared with the control, the activity of SOD, POD, CAT, APX, MDHAR, DHARfrom different apple rootstocks genotypes were significantly affect by K insufficient treatment.But the enzyme changed significantly is not same in different apple rootstocks genotypes. Theactivity of CAT of M. robusta, POD and DHAR of M. prunifolia under K insufficienttreatment were significantly increased by55.56%,44.83%and86.11%respectively, while theactivity of other enzymes did not change significantly. This may be due to the different applerootstocks genotypes generating different antioxidase when exposed to low potassium stress.6. Five apple rootstock genotypes differed markedly in dry weights, absolute andrelative K concentrations, absolute and relative K accumulations, and their K efficiency ratiounder deficient K conditions. The last parameter, expressed as relative shoot dry weight, wasstrongly 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-efficient genotypes.In this study, we have determined that M. sieversii and M. rockii are K-inefficient genotypes;M. prunifolia is K-efficient genotype; M. hupehensis and M. robusta have moderate levels ofpotassium efficiency. |
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