Response of Container-grown Apple Trees to Soil Compaction

Container-grown apple (Malus ×domestica Borkh.) trees were exposed to soil compaction created by changing soil bulk density (SBD) to determine the effect of compaction levels, rootstock, and moisture stress on mineral nutrition, leaf gas exchange, and foliar carbohydrate levels. With SBD of 1.0, 1.2, and 1.4 g·cm-3, there was no interaction of rootstock and soil compaction for growth of `Melrose' trees on nine rootstocks. Trees grown in a SBD of 1.2 g·cm-3 had a greater dry weight than trees at 1.4 g·cm-3 bulk density. Increasing SBD to 1.5 g·cm-3 reduced shoot length, total leaf area, leaf size, and dry weight of leaves, shoots, and roots. The interaction between rootstock and SBD was significant and total dry weight of `B.9', `G.16', `G.30', and `M.7 EMLA' was less influenced by 1.5 g·cm-3 soil than trees on `M.26 EMLA' and `MM.106 EMLA'. Withholding moisture for 10 days at the end of a 70-day experiment caused 8% to 25% reduction in growth in a non-compacted (1.0 g·cm-3) soil with much less effect in a compacted soil. Prior to imposing the moisture stress by withholding water, net photosynthesis (Pn) was reduced 13% and transpiration (E) 19% by increasing bulk density to 1.5 g·cm-3. Following 7 days of moisture stress in non-compacted soil, Pn and E were reduced 49% and 36%, respectively, with no such reductions in the compacted soil. Increasing SBD to 1.5 g·cm-3 caused a decrease in the leaf concentration of quinic acid, myoinositol, and sucrose and an increase in fructose and glucose. Trees growing in 1.5 g·cm-3 had reduced concentrations of N, Ca, Mg, Mn, Na, and Zn, and increased P, K, B, and Fe in leaves.