Winkel Anders, Borum Jens
Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørsgade 51, Hillerød, Denmark.
Ann Bot. 2009 May;103(7):1015-23. doi: 10.1093/aob/mcp036. Epub 2009 Feb 14.
Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO(2) availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana and Hydrocotyle verticillata) are able to support photosynthesis supplied by uptake of CO(2) from the sediment.
Gross photosynthesis was measured in two-compartment split chambers with low inorganic carbon availability in leaf compartments and variable CO(2) availability (0 to >8 mmol L(-1)) in root compartments. Photosynthetic rates based on root-supplied CO(2) were compared with maximum rates obtained at saturating leaf CO(2) availability, and (14)C experiments were conducted for two species to localize bottlenecks for utilization of sediment CO(2).
All species except Hydrocotyle were able to use sediment CO(2), however, with variable efficiency, and with the isoetid, Lobelia, as clearly the most effective and the elodeid, Ludwigia, as the least efficient. At a water column CO(2) concentration in equilibrium with air, Lobelia, Lilaeopsis and Vallisneria covered >75% of their CO(2) requirements by sediment uptake, and sediment CO(2) contributed substantially to photosynthesis at water CO(2) concentrations up to 1000 micromol L(-1). For all species except Ludwigia, the shoot to root ratio on an areal basis was the single factor best explaining variability in the importance of sediment CO(2). For Ludwigia, diffusion barriers limited uptake or transport from roots to stems and transport from stems to leaves.
Submersed plants other than isoetids can utilize sediment CO(2), and small and medium sized elodeids with high root to shoot area in particular may benefit substantially from uptake of sediment CO(2) in low alkaline lakes.
沉水植物有不同的策略来克服无机碳限制。一般认为只有小型莲座状物种（水韭类植物）能够利用沉积物中高浓度的二氧化碳。本研究调查了五种具有不同形态和生长特征的沉水淡水植物（矮慈姑、麦氏草、黄花水龙、美洲苦草和轮叶黑藻）在多大程度上能够通过从沉积物中吸收二氧化碳来支持光合作用。
在两室分隔培养箱中测量总光合作用，叶室中无机碳浓度较低，根室中二氧化碳浓度可变（0至>8 mmol/L）。将基于根系供应二氧化碳的光合速率与在叶片二氧化碳饱和时获得的最大速率进行比较，并对两个物种进行了¹⁴C实验，以确定沉积物二氧化碳利用的瓶颈。
除轮叶黑藻外，所有物种都能够利用沉积物中的二氧化碳，但其效率各不相同，水韭类植物矮慈姑最为有效，伊乐藻属的黄花水龙效率最低。在与空气平衡的水柱二氧化碳浓度下，矮慈姑、麦氏草和美洲苦草通过沉积物吸收满足了>75%的二氧化碳需求，并且在水柱二氧化碳浓度高达1000 μmol/L时，沉积物中的二氧化碳对光合作用有很大贡献。对于除黄花水龙外的所有物种，基于面积的茎根比是解释沉积物二氧化碳重要性变异性的最佳单一因素。对于黄花水龙，扩散障碍限制了从根到茎的吸收或运输以及从茎到叶的运输。
除水韭类植物外的沉水植物可以利用沉积物中的二氧化碳，特别是那些根冠比高的中小型伊乐藻属植物，在低碱性湖泊中可能会从沉积物二氧化碳的吸收中受益匪浅。
