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Investigation of the zinc and manganese status of some stands of tsuga heterophylla in British Columbia Gadziola, Robert


Western hemlock has lower foliar Zn and higher foliar Mn concentrations compared to some other conifers. Existing foliar diagnostic norms for conifers imply a Zn deficiency and possibly a Mn toxicity in many stands of western hemlock. This study was undertaken in order to determine the significance of these foliar levels in the nutrition of western hemlock. The nutrition of hemlock was studied using comparative nutrition and fertilizer screening trials. The screening trials consisted of treatments of Zn and Mn applied as foliar sprays and as soil treatments. Different methods of application were utilized to determine if factors of the plant such as uptake and/or translocation could account for the characteristic foliar zinc and manganese levels in hemlock. In addition, a treatment was applied consisting of a complete fertilizer without Zn and Mn. This "complete-Zn-Mn" treatment was included to investigate the possibility of additional nutrient deficiencies and/or toxicities. In a comparison of total foliar concentrations, hemlock had lower Zn compared to Douglas-fir, amabilis fir and white pine. In contrast, hemlock had higher Mn compared to Douglas-fir, amabilis fir, white pine, red cedar and yellow cedar. Analysis of cellular fractions of foliage produced two results. First, Zn accumulated in the mitochondrial fraction and Mn accumulated in the ribosomal and vacuolar fraction, irrespective of the level of the treatment or the species. Accumulation in certain fractions may indicate a physiological need in that fraction or a tolerance mechanism. Second, comparing hemlock to Douglas-fir, total Zn levels tend to be consistent with levels in different fractions, indicating that total levels may be an adequate indication of physiologically active levels. But comparing hemlock to Douglas-fir, total Mn levels are not consistent with Mn levels in different fractions, indicating that total Mn levels may not be an adequate indication of physiological levels. In the fertilizer screening trials, nutrient uptake and growth responses were dependent upon the site, the level of fertilizer application, and the time since application. Nutrient uptake and positive growth responses were obtained with foliar treatments of Zn and soil treatments of Mn in both the first year and second year following fertilization. Nutrient and growth responses to soil Zn treatments were delayed until the second year following fertilization. Additional evidence supporting a Zn deficiency was indicated by a positive relationship between foliar Zn and height increment, evidence of retranslocation of Zn to new foliage in the second year following foliar Zn treatment, and the high ranking of Zn in the vector analysis from the "complete-Zn-Mn" treatment. Positive growth responses to the "complete-Zn-Mn" treatment were obtained in the first and second years following treatment. Ranking of nutrient response vectors using relative values indicated the existence of other nutrient deficiencies, besides Zn and Mn. Growth response, as measured by shoot increment ratio, was obtained primarily in the second year after treatment with foliar applications of Zn. Shoot increment ratio response occurred to soil Mn treatments in the first year of treatment. For the "complete-Zn-Mn" treatment there was an increase in shoot increment ratio in both the first and second years following treatment. Height increment ratio increased in response to foliar Zn applications in the second year, and to soil Mn treatments in the first year. Foliar Zn and foliar N were positively correlated with each other. Foliar Zn concentrations increased as a result of soil applications of Mn, but applications of Zn had no effect on Mn uptake. Therefore, there was no evidence in this study to suggest that low foliar levels of Zn in hemlock are due to a Mn antagonism. The only interaction obtained with the "complete-Zn -Mn" treatment was a synergism: it caused an increase of foliar Zn. Ingestad's nutrient ratios were calculated for the foliar levels from the control and the "complete-Zn-Mn" treatments. Comparing these ratios to the optimum revealed that most of the nutrients were in balance except for Fe and Mn. Existing diagnostic norms for Zn appear to adequately describe the Zn nutrition of hemlock'. Response to fertilization occurred with control foliar Zn concentrations for hemlock being below the critical level of 15 μg g⁻¹. Diagnostic norms for Mn need to be revised. Response occurred-even though control foliar Mn concentrations for hemlock were well above the critical level of 25 μg g⁻¹. Therefore, total foliar manganese may not be indicative of the physiological manganese status of hemlock. These results for hemlock are discussed in light of existing knowledge from the literature regarding the nutrient strategy of metal tolerant plants and low nutrient adapted plants.

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