Journal APS Oct 2017

J ournal of the A merican P omological S ociety

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Table 4. Hourly photosynthetic rates (Pn, μmol·m -2 ·s -1 ) of four progenies of columnar and standard apple trees F1 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 progeny ACo 7.9±0.59b z 9.8±0.68c 14.4±0.84b 15.7±1.47b 13.8±1.08b 8.3±0.63b 6.8±0.48c 10.8±0.978c 7.7±0.57b 6.2±0.72b 4.8±0.38a ASt 5.3±0.33d 8.6±0.86d 11.3±0.63c 12.9±1.09c 11.9±1.19c 6.8±0.78c 6.4±0.54c 9.5±0.95d 6.6±0.46c 5.1±0.51c 3.3±0.33bc BCo 9.1±0.53a 12.8±0.74a 15.3±1.49a 18.6±1.38a 15.3±0.89a 12±1.40a 10.6±0.61a 15±1.37a 8.9±0.52a 7.6±0.44a 3.8±0.22b BSt 6.2±0.36c 11.1±0.64b 14.2±0.82b 15.2±0.98b 13.9±0.81b 8.2±1.78b 7.6±0.54b 11±1.64bc 8.5±0.49a 7.4±0.43a 2.9±0.17c Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD. Table 5. Hourly transpiration rates (Tr, mmol·m -2 ·s -1 ) of leaves of four progenies of columnar and standard apple trees F1 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 progeny 2.8±0.26a 2.1±0.19b 1.5±0.11c ASt 2.4±0.23c 2.9±0.19c 3.2±0.27c 3.5±0.25d 3.1±0.22b 2.4±0.21c 2.1±0.17d 3.0±0.20c 2.1±0.14bc 2.1±0.18b 1.4±0.10c BCo 3.1±0.27a 3.6±0.35a 4.0±0.18a 4.6±0.35a 3.6±0.16a 3.0±0.23a 2.9±0.26a 3.6±0.26a 2.8±0.25a 2.2±0.20a 1.8±0.15b BSt 2.9±0.28ab 3.0±0.20c 3.5±0.22 b 3.9±0.29bc 2.7±0.26c 2.6±0.27b 2.4±0.18bc 3.2±0.26bc 2.3±0.20b 2.0±0.16b 2.0±0.17a Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD. ACo 2.7±0.28b z 3.3±0.13b 3.7±0.35b 4.2±0.20b 3.6±0.24a 2.8±0.19ab 2.6±0.22b 3.3±0.23b

progenies. In addition, the decrease of Pn from the first peak to the “siesta” at noon was slower for columnar trees than for standard trees, and most obvious in BCo.  Net photosynthetic rate is usually positive- ly related to transpiration rate. The diurnal Tr followed a similar pattern as Pn for both columnar and standard apple trees, showing bimodal curves with a “siesta” phenomenon (Table 5). In the diurnal variation of the day, the two columnar progenies had higher Tr than the two standard progenies. Discussion  The columnar apple tree is a valuable re- source for genetic improvement of new ap- ple cultivars due to its special architecture, which is important for crop yield, quality, and cultivation. Tree architecture also affects root architecture, mineral uptake and pho- tosynthesis of apple trees. Compared with standard trees, columnar trees had more fi- brous roots. The average number of root tips and total root length of columnar trees were 1.22-1.52-fold and 1.18-1.59-fold greater than those of standard apple trees, respec- tively. The root tips contain a large amount

of root hairs and are important for absorp- tion of water and mineral elements. The fact that columnar trees had more root tips provides a foundation for its high efficient absorption of mineral elements. Analyses of root and stem architecture showed that the diameters of root and stem xylem vessels of the columnar trees were greater than those of the standard apple trees. In addition, co- lumnar trees had normal stem xylem vessel morphology, whereas the standard trees had more deformed stem xylem vessels (Zhang et al., 2012a). Stem xylem vessels with larger diameter provide a basis for efficient trans- port of mineral elements in columnar trees (Zhang et al., 2011b). Many factors affect the absorption and uptake of mineral nutri- tion in plants (Zouar, et al., 2016; Quirantes, et al., 2016; Li et al., 2016). The leaf min- eral Ca, Mg, Fe, Cu, Mn and Zn concentra- tions in the columnar trees were significantly higher than those in the standard trees, which might be related to the root architectures as well as the root and stem xylem vessels. In addition, relatively wider xylem vessels in columnar trees may have also enhanced the upward transportation ability, thus result-