Using Boron Isotope (IUB) to Study Boron Uptake and Translocation by Peach and Plum Trees Grown in Sandy and Calcareous Soils Under Different Levels of Calcium

摘要

The objective of this study was to investigate boron (B) uptake and translocation using boron-10 (10B), in response to calcium (Ca) supplementation of the substrate in an attempt to understand B function in plant metabolism. A pot experiment was designed using two-year old Marianna plum and Lovell peach trees. They were grown in 20 litre (L) pots filled with sandy or calcareous soil. Treatments included two concentrations of B (2.5 and 5.0 mg/kg) and three concentrations of Ca (80, 200 and 400 mg/kg). Boron was applied as H3B03 enriched in 10B and Ca as (CH3COO)2 Ca.H20. The pots were arranged in a completely randomized design. Leaf, stem, fine root, root tip and root tip cell wall samples were collected at the end of the growing season for determination of total B, 10B and Ca. Plant samples were extracted using 0.20 N HNO3 and analysed using an inductively coupled plasma mass spectrometer (ICP/MS). Cell wall extraction was performed on 0.5-1.0 g fresh weight of the root tips. Results indicated that in sandy soil, there was an inverse relationship between B concentration in the nutrient solution and plant dry weight. However, as Ca concentration in the nutrient solution increased the dry weight increased. Analysis of variance showed that both B and Ca in the irrigation solution had significant effects on B partitioning in the three plant organs. Calcium application at 200 and 400 mg/kg reduced the B concentration significantly in the leaf and stem but linearly increased B concentration in the fine root. Under calcareous soil, less B was recorded in the leaf and stem but more in the fine root compared with its concentrations in the plants grown in sandy soil. The root tips maintained the highest B concentration. In both peach and plum the 10B:11Bratio increased as B concentration in the nutrient solution increased. However, Ca application decreased the,0B:11B ratio in the leaf indicating less B was translocated to the leaf. There were significant differences between B concentrations in Lovell peach and Marianna plum trees. Marianna accumulated less B than Lovell in the leaf and stem but more B in the root tips. Under calcareous soil, less B was translocated to the shoot than under sandy soil. The lower B translocation to the shoot system couldbe explained by the high fixation capacity (precipitation and adsorption) of calciumcarbonate to B under calcareous soil. Boron and Ca levels in the root tip cell wall showed that Ca followed the same pattern as B. As Ca concentration in the irrigation solution increased (400 mg/kg), significant increases occurred in the B concentrationin root tip cell walls. The percent increase of B in the cell wall reached about five- and seven-fold of its concentration at low Ca level (80 mg/kg) in sandy and calcareous soil, respectively.