Quantifying root growth dynamics and nutrient uptake in apple trees

[摘要] ENGLISH SUMMARY: The dynamics of white roots were quantified using minirhizotrons (MR) over two consecutive seasons in four apple orchards in the Elgin-Vyeboom region of the Western Cape, South Africa. The cultivars monitored in this study were as follows: young, non-bearing 'Corder Gala'/M7; young, bearing 'Fuji'/M793; mature, bearing 'Golden Delicious'/M793 and 'Cripps Pink'/M793. Root growth patterns were related to soil water and temperature dynamics to determine the influence of the soil environment on white root dynamics. Changes in photosynthesis for the non-bearing 'Corder Gala' and bearing 'Golden Delicious' orchards were also quantified in order to determine possible correlation between white root activity and tree physiology.Nutrient uptake and distribution in relation to white root dynamics and established uptake periods were also investigated for one-year-old potted 'Golden Delicious'/M7 trees (glasshouse) and for mature bearing 'Golden delicious'/M793 (field). In the potted trial, the effect of timing and application rate of soil applied Ca(NO3)2 was evaluated with reference to Ca concentration and distribution amongst the roots, trunk and new growth. In the field trial, the effect on fruit tree performance was evaluated following the soil application of Ca(NO3)2 during white root flushes (determined by MR images) compared to recommended phenological based timmings (90 % petal drop and post-harvest).A bimodal white root growth pattern was confirmed for the bearing orchards with the first root flush in summer and a second, often longer flush, in winter. The winter root flush during tree dormancy is unique compared to existing literature on apple root growth dynamics and is attributed to the warmer winter climate of our region. For the non-bearing orchard, no defined white root growth pattern was observed. It appears that white root production occurs throughout the growing season in varying quantities from spring until autumn.White root growth dynamics in this study was not determined by the seasonal variation in soil temperature, although soil environmental conditions did play a role. The consistent white root growth flush for bearing orchards during winter indicate suitable environmental soil conditions for root growth - which is in contrast to climatic regions where winter temperatures result in cold (<5C) soils supressing root growth. Similarly, soil water fluctuation did not appear to influence the timing of the flushes, especially for the bearing 'Golden Delicious' orchard. Soil water and temperature in this study was therefore condusive to root growth throughout the year. This suggests that other factors e.g. endogenous tree physiological factors probably control the temporal pattern of white root production in these orchards. Changes in white root numbers and photosynthesis from spring to autumn indicated a possible relationship in the non-bearing orchard, but was not evident in the mature bearing orchard.In the potted trial, both the timing and concentration of soil applied Ca(NO3)2 affected Ca distribution in roots and new growth. The effect of application time significantly influenced the Ca concentration of both the roots and new growth and confirmed previous findings, whereas the effect of application rate only influenced the Ca concentration of the new aerial growth. Higher rates of Ca(NO3)2 in summer was neccesary to significantly increase the Ca concentration of new arial growth, whereas the standard rate was suffice in autumn for significant increases in the root system. In the field trial however, no significant affect of additional Ca(NO3)2 for the applied rates was observed as quantified by leaf and fruit mineral analysis or fruit yield and quality.

[发布机构] Stellenbosch University