Deleterious interaction of light impairment and organic matter enrichment on Isoetes lacustris (Lycopodiophyta, Isoetales)by Eglantine Chappuis, Ana Lumbreras, Enric Ballesteros, Esperança Gacia

Hydrobiologia

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Year
2015
DOI
10.1007/s10750-015-2321-2
Subject
Pollution / Aquatic Science / Environmental Science (all)

Text

PRIMARY RESEARCH PAPER

Deleterious interaction of light impairment and organic matter enrichment on Isoetes lacustris (Lycopodiophyta,

Isoetales)

Eglantine Chappuis . Ana Lumbreras .

Enric Ballesteros . Esperanc¸a Gacia

Received: 21 October 2014 / Revised: 28 April 2015 / Accepted: 6 May 2015  Springer International Publishing Switzerland 2015

Abstract Light reduction and increased organic matter load often occur together in lakes undergoing eutrophication. We aimed at experimentally testing the relative importance of light availability, organic matter enrichment and their interactions in the collapse of healthy populations of Isoetes lacustris.

We conducted an in situ shading (65 and 35% of incident light) and organic matter enrichment (10% enrichment) experiment in a Pyrenean pond (NE

Spain). We followed plant performance using growth indicators, carbon balance indicators and individual survival. Severe light reduction (35%) resulted in a lengthening of the new leaves and no effects on mortality. Organic matter enrichment resulted in lower production and increased individual mortality. The combination of both stresses resulted in stronger negative effects and the highest mortality rate, which helps explaining I. lacustris die-offs observed after damming. Under severe light reduction (35%), plants used corm starch to keep growing. Consequently, starch percentage decreased and sucrose percentage increased as it was transported to the growing leaves.

The most extreme changes were observed under severe light reduction and fertilization, which extremely increased the ratio between sucrose and total non-structural carbohydrates (TNC). Thus, I. lacustris sucrose:TNC ratio is a good indicator of light reduction and organic matter enrichment stresses.

Keywords Nutrient enrichment  Carbohydrate 

Oligotrophic soft-water lakes  Sucrose  Starch 

Aquatic macrophytes

Introduction

Local and regional eutrophication are at the origin of major biodiversity loss for submerged aquatic vegetation due to both, organic matter (OM) load to sediments and light environment deterioration (Hautier et al., 2009; Moss et al., 2013, among others). Softwater oligotrophic lakes from Northern and Central

Europe (e.g. Denmark and the Netherlands) have experienced eutrophication at a regional scale derived by intensive agriculture, which peaked during the late twentieth century (Portielje & Van der Molen, 1998;

Baastrup-Spohr et al., 2013), with consequent major impacts for aquatic macrophytes (e.g. Sand-Jensen et al., 2000; Arts, 2002; Pulido et al., 2012). Further

Handling editor: Sidinei Magela Thomaz

E. Chappuis (&)  A. Lumbreras  E. Ballesteros 

E. Gacia

Centre d’Estudis Avanc¸ats de Blanes (CEAB-CSIC), Ctra. d’acce´s a la Cala St. Francesc 14, 17300 Blanes, Spain e-mail: chappuis@ceab.csic.es

Present Address:

A. Lumbreras

Instituto de Cieˆncias Agra´rias e Ambientais

Mediterraˆnicas (ICAAM), Universidade de E´vora,

Nu´cleo da Mitra, 7000 E´vora, Portugal 123

Hydrobiologia

DOI 10.1007/s10750-015-2321-2 appropriate management has resulted in a significant improvement of water quality. Also, some projects have focused on restoration actions devoted to improve and, whenever possible, recover some of these ecosystems and its endangered flora (i.e. isoetids

Lobelia dortmanna, Littorella uniflora and Isoetes spp.; Pulido et al., 2011a, b; Baastrup-Spohr et al., unpublished data). However, isoetid plant recovery has been found to be low and requires further research.

The Pyrenean high mountain range (Southern

Europe) holds hundreds of soft-water oligotrophic lakes and ponds that shelter an important representation of European isoetids in its southern geographical limit of distribution (Gacia et al., 1994; Murphy, 2002). Signs of regional increase in N deposition (Catalan et al., 1994) and shifts towards lake P eutrophication have been detected within the last decades in the Pyrenees (Camarero & Catalan, 2012), while livestock farming and damn construction have locally threatened few of those systems (Gacia &

Ballesteros, 1996, 1998; Chappuis et al., 2011).

Isoetes lacustris L. is a rather common aquatic perennial quillwort present in soft-water oligotrophic lakes throughout Europe. This species plays a key role in the systems it colonizes by increasing redox potential and subsequently oxidizing the soluble nitrogen forms found in sediment pore water due to high root oxygen loss (Smolders et al., 2002; Gacia et al., 2009). This increase in the redox potential leads to an enhancement of denitrification (RisgaardPetersen & Jensen, 1997) and phosphorous immobilization that fosters the recovery to oligotrophic conditions (Jones et al., 1994). Moreover, I. lacustris has a CAM photosynthetic pathway (Gacia & Ballesteros, 1993a), which is a carbon dioxide concentrating mechanism that diminishes the threat of carbon starvation in soft-water lakes (Keeley, 1998).

Light is an essential resource for plant photosynthesis that can often limit growth and reproduction.

Variation of irradiance results in changes from the physiological up to the community level. In aquatic systems, light may be strongly reduced by water column characteristics (i.e. water colour, suspended solids concentration and plankton) and by epiphytes presence (Bornette & Puijalon, 2001). A way to bypass a reduced irradiance income is to increase the photosynthetic surface area, a response already described for I. lacustris (Gacia & Ballesteros, 1993b).

However, when light irradiance is below the compensation point, I. lacustris declines rapidly and many plants die after 2 months (Rorslett & Johansen, 1995).

Sediment organic matter is also an important factor that influences the growth and distribution of aquatic plants (e.g. Barko & Smart, 1983, 1986; Sousa et al., 2009). Specifically, I. lacustris thrives in oligotrophic lakes, where growth can be nutrient limited (Gacia &

Ballesteros, 1994). Previous in situ experiments showed that fertilized plots produced more leaves and lost fewer leaves than unfertilized plots (Gacia, 1992). However, I. lacustris populations decline and disappear if nutrient increase persists and reaches eutrophic conditions (Arts, 2002; Salgado et al., 2010;