Root damage affects nitrogen uptake and growth of young Fuji/M.26 apple trees

Summary

Effects of root damage during the transplant process on growth and nitrogen (N) uptake were studied with one-year-old bench-grafted Malus domestica Borkh ‘Fuji’ on M.26 rootstock apple nursery plants. Plants were potted after grafting and grown outside for one season. At the end of the season uniform trees were selected and randomly divided into four groups. One group of plants were moved into a 2°C cold room with soil and container intact (IR Treatment). Plants in other groups were removed from pots and stored as bareroot in the same cold room for three months. In the spring, bareroot plants were either: (1) transplanted with about 10% of the root system damaged during transplant (TP Treatment and Control-CK); or (2) root pruned by 25% (by volume) prior to transplant (RP treatment). Five trees from each treatment received 1 g of ¹⁵NH₄¹⁵NO₃ at 12, 41 and 76 d after repotting. Control (CK) trees received no N. Trees were harvested 10 d after each N application, and plant growth and total N and ¹⁵N content of different tissues were determined. Root pruning reduced plant total biomass and root biomass at the first two harvests, but the plants from the RP treatment had highest total plant biomass and root biomass at the third harvest. There was no significant difference in the new stem and leaf growth among IR, RP and CK treatments at harvests but the TP treatment reduced new shoot biomass. Plants with intact roots (IR) had the higher total N content while control plants (CK) had the lowest. Root pruning reduced ¹⁵N uptake rate at the first two harvests but promoted it at the third harvest. Our results suggest that plant growth and nutrient uptake was suppressed by root pruning/damage during transplanting only in the early season, and the negative effects on growth and N uptake were offset later in the season by compensative root regeneration.