Zinc Uptake and Shoot Partitioning Between Zinc Efficient and Inefficient Exacum Genotypes

Interspecific hybrids of exacum (Exacum L.) display variable responses to zinc nutrition. Our research compared two genotypes with contrasting zinc efficiency phenotypes in terms of root cation exchange capacity (CEC), whole plant 65Zn uptake, and the effects of Cu+2 and Mg+2 on 65Zn uptake and partitioning to shoot tissues. Results show that the zinc efficient and inefficient genotypes had significantly different root CEC [27.2 and 16.9 cmol(+)·kg-1 root dry weight (DW), respectively] and whole plant 65Zn uptake rates (0.048 and 0.026 μmol·h-1·g-1 DW, respectively). In equimolar concentrations to Zn+2, Cu+2 reduced Zn+2 uptake by approximately 50% in both genotypes while supplemental Mg+2 enhanced Zn+2 uptake. In addition, Mg+2 facilitated a larger proportion of absorbed 65Zn to the upper shoot of the efficient genotype. We conclude zinc is absorbed through a specific Zn+2/Cu+2 transporter and that zinc efficiency in exacum is based on a combination of apoplastic and symplastic traits. In addition, a secondary Mg+2 × Zn+2 interaction may contribute to the zinc efficiency phenotype.

Mycorrhizal Infection Reduces Shortterm Aluminum Uptake and Increases Root Cation Exchange Capacity of Highbush Blueberry Plants

Aluminum (Al) uptake by and root cation exchange capacity (CEC) of mycorrhizal (M) and nonmycorrhizal (NM) blueberry (Vaccinium corymbosum L.) plants were studied. Root CEC was higher in M plants than in NM plants, but total and root Al contents were higher in NM plants. Leaf Al content was higher in NM than in M plants after 1 and 5 hours of exposure. The aurintriboxylic acid stain for Al indicated the presence of Al in the M symbiont. Despite a larger root system and higher root CEC, regression analysis indicated roots of M plants absorbed less Al in the first 5 hours, suggesting that Al sequestration in the M symbiont is responsible for reduced total Al uptake. Differences in dry matter partitioning between M and NM plants were also observed.

Managing soil acidity: old solutions can cause new problems

Acid and moderately acid soils (pH 5-6) are widespread in the farmed areas of New Zealand. Application of limestone to raise soil pH has been a common practice and re-acidification of soils requires that this be done regularly. The impact of liming and re-acidification cycles on soil chemistry is discussed and examples presented using a Southland soil: Waimumu silt loam. Wide ratios of Ca:Mg develop in the soil and further lime application is shown to damage growth of white clover but not Grasslands Tama ryegrass. Differences in surface chemistry of roots of legumes and grasses are discussed and the implications of the interactions between changes in soil chemistry and plant roots considered. Keywords acidification, calcium, magnesium, cation ratio, root CEC