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Cultivated Vaccinium species (e.g. highbush blueberry, Vaccinium corymbosum, or cranberry, V. macrocarpon) commonly require acidic soil (pH 4.5 to 5.5) for optimum growth. Under these conditions, ammonium (NH4 +) is the dominant form of inorganic N. In contrast, V. arboreum, the sparkleberry can tolerate higher-pH mineral soils, where nitrate (NO3 -) is typically the predominant inorganic N form. This tolerance may be related to increased ability to acquire and utilize NO3—N. Measurements of 15NO3 - and 15NH4 + influx kinetics in excised roots of V. arboreum, V. corymbosum, and V. macrocarpon did not support this hypothesis. NO3 - influx kinetics measured from 10 micromolar to 200 micromolar NO3 - were similar among all three species. NO3 - influx was consistently lower than NH4 + influx at all concentrations for all three species.
Although ericoid mycorrhizal fungi improve nitrogen (N) nutrition of cranberry (Vaccinium macrocarpon Ait.) and other Ericaceae in their native habitat, the prevalence of ericoid mycorrhizal colonization in cranberry has not been widely examined. The authors measured ericoid mycorrhizal colonization of cranberry root samples from 13 cultivars growing in cranberry beds in Wisconsin. Mycorrhizal colonization was present in all samples. Bed age had a slight but statistically significant negative effect on mycorrhizal colonization. Neither cultivar, bed substratum, nor soil pH had a significant effect on mycorrhizal colonization. Fungicide treatment for fruit diseases did not appear to affect mycorrhizal colonization of cranberry roots. Soil layering in the root zone incited by regular sanding had a significant effect on mycorrhizal colonization; colonization decreased with increasing depth in the root zone soil. Leaf litter was more decomposed in deeper soil layers, with a lower carbon-to-N ratio. Given the consistent presence of ericoid mycorrhizal fungi in cultivated cranberry, it is possible that they may play a role in N nutrition of the cranberry agroecosystem.
Wisconsin cranberry growers report that fruit production by the cranberry cultivar `Ben Lear' (Vaccinium macrocarpon Ait.) is low in beds with poor drainage, while the cultivar `Stevens' is less sensitive to these conditions. We hypothesized that `Ben Lear' and `Stevens' would differ in their root growth and mortality response to variation in soil water potential. Rooted cuttings of each cultivar were grown in a green-house in sand-filled pots with three different soil water potentials which were regulated by a hanging water column below a fritted ceramic plate. A minirhizotron camera was used to record root growth and mortality weekly for five weeks. Root mortality was negligible (2% to 6%). Whole plant relative growth rates were greatest for both cultivars under the wettest conditions. Rooting depth was shallowest under the wettest conditions. Whole-plant relative growth rates of `Ben Lear' were higher than `Stevens' at all soil water potentials. `Stevens' plants had significantly higher root to shoot ratios and lower leaf area ratios than `Ben Lear' plants, and produced more total root length than `Ben Lear' at all soil water potentials. Shallow rooting, high leaf area ratio, and low allocation to root production by `Ben Lear' plants may lead to greater susceptibility to drought stress than `Stevens' plants in poorly drained cranberry beds.
Cranberry (Vaccinium macrocarpon) plants colonized with ericoid mycorrhizal fungi are capable of utilizing organic nitrogen sources that are unavailable to non-mycorrhizal plants. Despite the importance of mycorrhizal colonization in the nitrogen nutrition of wild cranberry, almost all measurements of cranberry nitrogen uptake and assimilation have been carried out with non-mycorrhizal plants. We have found that cranberry can be inoculated directly in solution culture. We cultured the ericoid mycorrhizal fungus Hymenoscyphusericaein liquid culture, harvested and rinsed hyphae, and added ≈200 mg fresh weight hyphae per rooted cranberry cutting (cv. Stevens) growing in a modified Johnson's solution. After 6 weeks, newly developed roots were most heavily colonized. We examined the effects of NH4 + concentration (5, 10, 20, 50, 100, and 500 μm NH4 +) in solution on colonization rates. Colonization (% root length) increased with increasing ammonium concentration in solution, with maximum colonization at 50 and 100 μm NH4 +; colonization was much lower at 500 μm NH4 +. Cranberry inoculated with H. ericaein solution culture will be used for analysis of the effects of mycorrhizal colonization on uptake kinetics of NH4 +, NO3 -, and amino acids.
Air excavation is commonly used to expose structural roots of trees, but its suitability for sampling fine roots for research has not been closely examined. We compared damage and root-diameter class distribution in roots sampled by air excavation with roots sampled by hydropneumatic elutriation of soil cores. We collected samples from six different tree species with a range of fine root diameters: Amur corktree (Phellodendron amurense Rupr.), apple [Malus sylvestris var. domestica (Borkh.) Mansf.], river birch (Betula nigra L.), striped maple (Acer pensylvanicum L.), swamp white oak (Quercus bicolor Willd.), and western redcedar (Thuja plicata D. Don). Root-diameter class distributions for each species were the same for samples collected by either air excavation or by elutriation. Median root diameter was greatest for Amur corktree and western redcedar (≈0.5 mm), intermediate in striped maple and oak, and least in river birch and apple (≈0.2 mm). Root damage was primarily due to loss of root tips. Although species varied in their susceptibility to root damage and whether air excavation caused more damage than elutriation, root diameter was not a good predictor of damage during sampling. Air excavation caused ≈26% greater damage to root samples of river birch and western redcedar than did elutriation. Both sampling methods caused equivalent root damage in all other species. Root anatomy influenced susceptibility to damage during sampling. Epifluorescence microscopy revealed a root hypodermis in all species except Amur corktree and western redcedar. Without the mechanical support of this suberized layer, the cortex of Amur corktree was easily stripped from the stele, leading to extensive damage by both sampling methods. Hydropneumatic root elutriation conferred some protection to roots relative to air excavation (in two of six species); final choice of root sampling method must depend upon the requirements of the individual study and characteristics of the site.
`McIntosh' apple trees [Malus ×sylvestris (L.) Mill. Var domestica (Borkh.)] on five semidwarfing rootstocks (CG.4814, CG.7707, G.30N, M.7 EMLA, and Supporter 4) were planted at 10 locations (MA, MI MN NS 2 in NY ON PA VT and WI) under the direction of the NC-140 Multistate Research Project. After four growing seasons (through 2002), trees on CG.7707, G.30N, Supporter 4, and M.7 EMLA were significantly larger than those on CG.4814. Cumulative root suckering was most from trees on M.7 EMLA, and least from trees on CG.7707, G.30N, and Supporter 4. Yield per tree in 2002 and cumulatively was greatest from trees on G.30N and least from trees on CG.7707 and M.7 EMLA. In 2002 and cumulatively, CG.4814 resulted in the greatest yield efficiency, and M.7 EMLA resulted in the lowest. In 2002, fruit from trees on M.7 EMLA were largest, and those from trees on CG.4814 were smallest. On average, M.7 EMLA resulted in the largest fruit, and G.30N resulted in the smallest. Limited data will be presented on CG.6210, CG.8, G.30T, and M.26 EMLA, which are planted only at some locations. Data for the fifth season (2003) will be presented.
`McIntosh' apple trees [Malus ×sylvestris (L.) Mill. Var domestica (Borkh.)] on 10 dwarfing rootstocks (CG.3041, CG.4013, CG.5179, CG.5202, G.16N, G.16T, M.9 NAKBT337, Supporter 1, Supporter 2, and Supporter 3) were planted at 10 locations (MA, MI MN NS 2 in NY ON PA VT and WI) under the direction of the NC-140 Multistate Research Project. After four growing seasons (through 2002), trees on CG.5202 and CG.4013 were significantly larger than those on all other rootstocks. Smallest trees were on M.9 NAKBT337. Trees on other rootstocks were intermediate. Rootstock did not influence cumulative root suckering. Yield per tree in 2002 was greatest from trees on CG.4013 and lowest from trees on M.9 NAKBT337; however, cumulatively, trees on M.9 NAKBT337 and CG.4013 yielded the most. Yield efficiency in 2002 was not affected by rootstock. Cumulatively, rootstock had very little effect, but trees on CG.5202 were the least efficient. In 2002, M.9 NAKBT337, CG.3041, and Supporter 2 resulted in the largest fruit, and CG.5179 resulted in the smallest. On average, M.9 NAKBT337 resulted in the largest fruit, and G.16T resulted in the smallest. Limited data will be presented on CG.5935 and M.26 EMLA, which are planted only at some locations. Data for the fifth season (2003) will be presented.