Szabó Sándor, Koleszár Gergő, Zavanyi Györgyi, Nagy Péter Tamás, Braun Mihály, Hilt Sabine
Department of Biology, University of Nyíregyháza, Nyíregyháza, Hungary.
Department of Tisza Research, Centre for Ecological Research, Debrecen, Hungary.
Front Plant Sci. 2022 Oct 31;13:963579. doi: 10.3389/fpls.2022.963579. eCollection 2022.
Free-floating and rootless submerged macrophytes are typical, mutually exclusive vegetation types that can alternatively dominate in stagnant and slow flowing inland water bodies. A dominance of free-floating plants has been associated with a lower number of aquatic ecosystem services and can be explained by shading of rootless submerged macrophytes. , high pH and competition for several nutrients have been proposed to explain the dominance of rootless submerged macrophytes. Here, we performed co-culture experiments to disentangle the influence of limitation by different nutrients, by pH effects and by allelopathy in sustaining the dominance of rootless submerged macrophytes. Specifically, we compared the effects of nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) deficiencies and an increased pH from 7 to 10 in reducing the growth of free-floating by the rootless . These macrophyte species are among the most common in highly eutrophic, temperate water bodies and known to mutually exclude each other. After co-culture experiments, additions of nutrients and pH neutralisation removed the growth inhibition of free-floating plants. Among the experimentally tested factors significantly inhibiting the growth of , an increase in pH had the strongest effect, followed by depletion of P, N and Fe. Additional field monitoring data revealed that in water bodies dominated by , orthophosphate concentrations were usually sufficient for optimal growth of free-floating plants. However, pH was high and dissolved inorganic N concentrations far below levels required for optimal growth. Low N concentrations and alkaline pH generated by dense stands are thus key factors sustaining the stable dominance of rootless submerged vegetation against free-floating plants. Consequently, N loading from e.g. agricultural runoff, groundwater or stormwater is assumed to trigger regime shifts to a dominance of free-floating plants and associated losses in ecosystem services.
漂浮且无根的沉水植物和扎根的沉水植物是典型的、相互排斥的植被类型，它们可交替在静止和缓流的内陆水体中占主导地位。漂浮植物占优势与较少的水生生态系统服务相关，这可以通过无根沉水植物被遮蔽来解释。高pH值以及对几种养分的竞争被认为可以解释无根沉水植物占优势的现象。在此，我们进行了共培养实验，以厘清不同养分限制、pH值影响和化感作用在维持无根沉水植物优势方面的影响。具体而言，我们比较了氮（N）、磷（P）、铁（Fe）和锰（Mn）缺乏以及pH值从7升高到10对无根沉水植物抑制漂浮植物生长的影响。这些大型植物物种是富营养化温带水体中最常见的物种，并且已知它们相互排斥。共培养实验后，添加养分和中和pH值消除了对漂浮植物生长的抑制。在实验测试的显著抑制漂浮植物生长的因素中，pH值升高的影响最强，其次是P、N和Fe的耗尽。额外的实地监测数据显示，在以无根沉水植物为主的水体中，正磷酸盐浓度通常足以支持漂浮植物的最佳生长。然而，pH值较高，溶解无机氮浓度远低于最佳生长所需水平。因此，密集的无根沉水植物群落产生的低氮浓度和碱性pH值是维持无根沉水植被相对于漂浮植物稳定优势的关键因素。因此，例如农业径流、地下水或雨水带来的氮负荷被认为会引发向漂浮植物占优势的状态转变以及相关的生态系统服务损失。
