Uptake and translocation of manganese in seedlings of two varieties of Douglas fir (Pseudotsuga menziesii var. viridis and glauca)

Douglas fir (Pseudotsuga menziesii) variety glauca (DFG) but not the variety viridis (DFV) showed symptoms of manganese (Mn) toxicity in some field sites. We hypothesized that these two varieties differed in Mn metabolism. To test this hypothesis, biomass partitioning, Mn concentrations, subcellular localization and 54Mn-transport were investigated. Total Mn uptake was three-times higher in DFG than in DFV. DFV retained > 90% of 54Mn in roots, whereas > 60% was transported to the shoot in DFG. The epidermis was probably the most efficient Mn barrier since DFV contained lower Mn concentrations in cortical cells and vacuoles of roots than DFG. In both varieties, xylem loading was restricted and phloem transport was low. However, sieve cells still contained high Mn concentrations. DFV displayed higher biomass production and higher shoot : root ratios than DFG. Our results clearly show that both varieties of Douglas fir differ significantly in Mn-uptake and allocation patterns rendering DFG more vulnerable to Mn toxicity.     

The influence of the ectomycorrhizal fungus Rhizopogon subareolatus on growth and nutrient element localisation in two varieties of Douglas fir (Pseudotsuga menziesii var. menziesii and var. glauca) in response to manganese stress

Acidification of forest ecosystems leads to increased plant availability of the micronutrient manganese (Mn), which is toxic when taken up in excess. To investigate whether ectomycorrhizas protect against excessive Mn by improving plant growth and nutrition or by retention of excess Mn in the hyphal mantle, seedlings of two populations of Douglas fir (Pseudotsuga menziesii), two varieties, one being menziesii (DFM) and the other being glauca (DFG), were inoculated with the ectomycorrhizal fungus Rhizopogon subareolatus in sand cultures. Five months after inoculation, half of the inoculated and non-inoculated seedlings were exposed to excess Mn in the nutrient solution for further 5 months. At the end of this period, plant productivity, nutrient concentrations, Mn uptake and subcellular compartmentalisation were evaluated. Non-inoculated, non-stressed DFM plants produced about 2.5 times more biomass than similarly treated DFG. Excess Mn in the nutrient solution led to high accumulation of Mn in needles and roots but only to marginal loss in biomass. Colonisation with R. subareolatus slightly suppressed DFM growth but strongly reduced that of DFG (-50%) despite positive effects of mycorrhizas on plant phosphorus nutrition. Growth reductions of inoculated Douglas fir seedlings were unexpected since the degree of mycorrhization was not high, i.e. ca. 30% in DFM and 8% in DFG. Accumulation of high Mn was not prevented in inoculated seedlings. The hyphal mantle of mycorrhizal root tips accumulated divalent cations such as Ca, but not Mn, thus not providing a barrier against excessive Mn uptake into the plants associated with R. subareolatus.     

Morphotype community structure of ectomycorrhizas on Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings grown under elevated atmospheric CO2 and temperature

Mycorrhizas alter the acquisition of carbon and nutrients, thereby affecting numerous plant and ecosystem processes. It is important, therefore, to determine how mycorrhizal populations will change under possible future climate conditions. Individual and interactive effects of elevated atmospheric CO₂ concentration and atmospheric temperature were assessed in a 2×2 factorial design [ambient and elevated (200 ppm above ambient) CO₂ concentrations, and ambient and elevated (4°C above ambient) temperatures]. In June 1993, 2-year-old Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings were planted in 12 environment-tracking chambers (n=3) containing reconstructed, low-nitrogen, native forest soil. Climate treatments were imposed shortly thereafter, and the seedlings grew until June 1997. Soil cores were taken twice per year during the exposure period. We present findings on changes in the community structure of ectomycorrhizal (ECM) root tips, categorized into morphotypes using gross morphological traits. A diverse and stable community of morphotypes (a total of 40) was encountered; no more than 30 of which were seen at any sampling time. In the first sample, there were only 15 morphotypes found in the 12 chambers. Morphotype numbers increased during the first half of the experiment, remaining fairly constant thereafter. Near the end of the exposure, elevated-temperature treatments maintained more morphotypes than ambient treatments. However, overall, absolute measures (number of ECM tips) were affected primarily by CO₂ treatment, whereas proportional measures (e.g., Simpson’s index) were affected primarily by temperature. While some morphotypes were negatively affected seasonally by higher temperatures (putative Rhizopogon group), others (Cenococcum) seemed to thrive. Underlying the dominant patterns of change in diversity, driven by the Rhizopogon group, subdominant populations responded slightly differently. Community diversity through time tended to increase at a greater rate for all subdominant populations compared with the rate when dominant populations were included. Received: 16 August 1999 / Accepted: 2 March 2000     

微地形对江西武夷山南方铁杉针阔混交林幼树更新的影响

为探讨江西武夷山南方铁杉针阔混交林内不同微地形中幼树更新特征的差异,明晰不同微地形生境对幼树天然更新的影响。以江西武夷山国家级自然保护区内海拔约1800m的南方铁杉针阔混交原始林为研究对象,基于在其中建立的中亚热带南方铁杉针阔混交林动态监测固定样地首次调查数据,将固定样地中160个20m×20m的样方根据其海拔、凹凸度和坡度3种地形参数通过C-均值模糊聚类划分成不同的微地形生境,比较这不同微地形下的更新幼树种类组成及幼树更新特征,包括幼树密度,幼树平均胸径、平均高、平均冠幅,空间分布格局,分析不同微地形下幼树更新特征与地形因子、林分因子之间的关系。结果显示：(1)通过聚类分析,最终将固定样地的微地形生境划分成4类,分别为陡坡、凹地、凸地、缓坡。(2)4类微地形更新幼树优势种组成类似,但优势程度存在差异。闽皖八角幼树在4类微地形中的重要值皆为第一,均大于43%。建群种南方铁杉的幼树在凸地的重要值为9.09%,具有一定优势;在陡坡的重要值为0.62%,优势程度较差。(3)陡坡的更新幼树密度最高,为399株/hm~2,高于凹地,凸地和缓坡;幼树平均胸径和平均高的大小表现为：缓坡>凸地&...