Richardson K, Griffiths H, Reed M L, Raven J A, Griffiths N M
Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, Scotland.
Oecologia. 1984 Jan;61(1):115-121. doi: 10.1007/BF00379096.
The inorganic carbon fixation patterns of Isoetes lacustris and Lobelia dortmanna from an oligotrophic Scottish loch have been examined by following titratable acidity changes in plant sap and light/dark CO incorporation by roots and shoots. The diurnal pattern of titratable acidity changes in I. lacustris suggests crassulacean acid metabolism (CAM) while the lack of any change in titratable acidity in L. dortmanna suggests C metabolism. Of the carbon fixed by L. dortmanna, 99.9% was taken up through the roots and fixation occurred primarily during the day. In Isoetes, CO was taken up by both roots and shoots and during both day and night. Regardless of the site of CO uptake, fixation occurred only in the shoots of both plants. Analysis of carbon isotope ratios of plant organic material was used to further investigate the photosynthetic mechanisms of these Isoetids. Considering the absence of a nighttime peak in titratable acidity in L. dortmanna, the ΔC (Δ=δC plant-δC source) value of the shoots of L. dortmanna (-14.2‰) is indicative of C photosynthesis limited by the rate of CO diffusion. The less negative Δ of I. lacustris (-6.0‰) is consistent with both dark acidification of CAM and CO limited C photosynthesis. This is in contrast to the terrestrial Isoetes durieui which is shown to have a Δ value which is similar to a terrestrial C plant. The carbon fixation patterns of these Isoetids suggest that the CO concentration in the loch may be growth limiting, and that root uptake and/or dark acidification are means of optimising CO supply. However, in view of the relatively high levels of CO in sediment and bulk water, it is suggested that low levels of nutrients may also limit growth in these plants.
通过追踪植物汁液中可滴定酸度的变化以及根和茎对光/暗二氧化碳的吸收情况，对来自苏格兰一个贫营养湖泊的湖生水韭和多花水叶柳的无机碳固定模式进行了研究。湖生水韭中可滴定酸度变化的昼夜模式表明其存在景天酸代谢（CAM），而多花水叶柳中可滴定酸度没有任何变化则表明其为C3代谢。多花水叶柳固定的碳中，99.9%是通过根部吸收的，且固定主要发生在白天。在水韭中，二氧化碳在白天和夜间均可被根和茎吸收。无论二氧化碳的吸收部位如何，固定只发生在两种植物的茎中。对植物有机物质的碳同位素比值进行分析，以进一步研究这些水韭类植物的光合机制。考虑到多花水叶柳中可滴定酸度在夜间没有峰值，多花水叶柳茎的Δ13C（Δ=δ13C植物 - δ13C源）值（-14.2‰）表明其C3光合作用受二氧化碳扩散速率限制。湖生水韭较小的负Δ13C值（-6.0‰）与CAM的暗酸化和二氧化碳限制的C3光合作用均一致。这与陆生的杜氏水韭形成对比，杜氏水韭的Δ13C值与陆生C3植物相似。这些水韭类植物的碳固定模式表明，湖泊中的二氧化碳浓度可能是生长限制因素，并且根部吸收和/或暗酸化是优化二氧化碳供应的方式。然而，鉴于沉积物和水体中相对较高的二氧化碳水平，有人认为低水平的养分也可能限制这些植物的生长。
