Elsevier

Aquatic Botany

Volume 107, May 2013, Pages 39-46
Aquatic Botany

Estimating influence of environmental quality and management of channels on survival of a threatened endemic quillwort

https://doi.org/10.1016/j.aquabot.2013.01.009Get rights and content

Abstract

Isoëtes malinverniana Ces. et De Not. is a narrow endemic quillwort occurring within channels used for rice fields water supply, in the lowland area of North Italy. The range of I. malinverniana is highly fragmented and in the last 10 years the whole population decreased by more than 80%. This strong decline is assumed to be mainly related to the intensification of agricultural practices, which led to decreasing water quality, alteration of flow regimes and mechanized management. In order to highlight which of these factors may affect population performance and fate (persistence vs. extinction) of the species, plant cover, density and leaf length were measured, and a range of water and sediment parameters were analyzed at the plot scale, within the extant populations and in eight historical sites where I. malinvarniana recently disappeared.

At least 4 out of 11 populations, characterized by cover values never exceeding 15% and density hardly approaching 20 plants m−2, revealed scarce chance for survival, under current conditions. On the basis of discriminant analysis, nutrient enrichment did not result the main predictor of Isoëtes decline, as generally noticed for isoetids, since higher water nitrates, P, K and organic C content in the sediments were found in the sites where I. malinverniana showed the highest performance compared to sites of less viable populations. On the other hand, the high water depth, the strong increase of water flow during the rice growing season and the intensive mechanized management of channels, e.g. cutting of aquatic vegetation and dredging using excavators, were among the most important parameters explaining the disappearance of the species.

Our findings may have useful implications for the conservation or restoration of I. malinverniana and other rare aquatic species occurring in running waters of lowland agricultural areas. Hydrological alterations and mechanized maintenance of channels should be restricted where the species still occurs, to improve population performance and seedling survival.

Highlights

► We evaluate the conservation status of the threatened aquatic quillwort I. malinverniana. ► We analyze water, sediment and management to identify the main threats. ► We compare sites with extant populations and sites with extincted populations. ► Higher water level, EC and management characterize the inhospitable space for Isoëtes.

Introduction

Around the world several aquatic species belonging to the ancient relict genus Isoëtes (quillwort) are rare and on the brink of extinction due to water quality deterioration and habitat destruction (Taylor et al., 1993, Leon and Young, 1996, Musselman, 2002, Rhazi et al., 2004, Chen et al., 2005, Kang et al., 2005, Chen et al., 2007, Changkyun et al., 2008). Isoëtes is a cosmopolitan genus of heterosporous lycopsids with fossil records dating back to the Paleozoic (Hoot et al., 2004) and 200 or more living species (Schuettpelz and Hoot, 2006), ranging from perennial aquatics to ephemeral terrestrials (Taylor and Hickey, 1992). Considering the combination of relictual character and the pressures that act detrimentally on their habitats, Isoëtes species are the subject of different conservation measures (Environment Agency of Japan, 2000, Vöge, 2004, USFWS, 1996, IUCN, 2010).

In Italy seven species of quillworts are present (Conti et al., 2005) and all of them are very rare in Italy. In particular, Isoëtes malinverniana is endemic to the Western Po plain and occurs, unlike most of the congenerics, within channels and ditches fed with freshwater deriving from springs and from rivers, mostly used for rice crops water supply and drainage (Soldano and Badino, 1990). Within the genus, I. malinverniana has a high taxonomic significance as it is biogeographically and phylogenetically isolated from other species (Hoot et al., 2006). The range of I. malinverniana is highly fragmented and in the last 10 years the whole population decreased by more than 80% (Barni et al., 2010); at present, only 11 occurrences in very restricted and isolated sites are known.

For these reasons I. malinverniana was listed in the Italian Red Lists (Conti et al., 1997) under the IUCN category Critically Endangered (CR). Moreover I. malinverniana was included in annexes II and IV of the EU “Habitat” Directive 92/43. Although it was designated as a plant species of Community interest in need of strict protection, at the time only one of the extant populations is included in a Site of Community Importance.

As a first approach, the conservation of rare endemic taxa requires insights on their geographic distribution, niche characterization and particularly into limiting environmental factors and impact of activities, both past and present (Bernardos et al., 2006). Up to now, the knowledge on I. malinverniana ecology and causes of population reduction only relied on qualitative observations (Corbetta, 1965, Soldano and Badino, 1990), and overall information based on field measurements is still lacking. The decline of I. malinverniana populations may be due to anthropogenic activities but we are still far from pinpointing which kind of habitat changes, or combined effect of them, caused their deterioration and regression. Isoëtes species and, to a wider extent, isoetids are reported to have morphological and metabolic strategies evolved as adaptations to unproductive oligotrophic environments (Hutchinson, 1975, Chapin, 1980, Vitousek, 1982). Consequently, water pollution and eutrophication by contamination with domestic, agricultural or industrial effluents is generally regarded as the main predictor of Isoëtes and isoetid decline (Smolders et al., 2002, Arts, 2002, Wen et al., 2003, Liu et al., 2005, Pedersen et al., 2006). Therefore, we expected that more viable populations would be found in the most nutrient poor channels with characteristics similar to those reported for most Isoëtes and isoetid natural habitats, and thus with higher conservation values. Besides water deterioration, the mechanized management of channels, intensively maintained by regular cutting of bankside and aquatic vegetation, dredging and re-profiling using excavators, was assumed to play an important role in the decline of I. malinverniana populations.

Therefore, we aimed to (i) evaluate the conservation status of the extant populations of I. malinverniana, (ii) investigate the relationship between population performance and habitat conditions, and (iii) identify which factors among water quality, sediment characteristic and management regime may affect the fate (persistence vs. extinction) of the species. The study of habitat characteristics and management of agricultural channels may clarify aspects of their underestimated role in hosting rare aquatic species and help in preparing technical guidelines for conservation.

Section snippets

Study species

I. malinverniana Ces. et De Not. is an evergreen perennial, submerged quillwort, characterized by a short rhizomatous 3-lobed corm and numerous linear leaves, spirally arranged. Leaves can be 30–100 cm long according to Tutin et al. (1993). The ligules are triangular. Basal sporangia are without velum, megasporangia are usually on outer leaves, microsporangia on inner leaves. The megaspores are white to grey, with a mean diameter of 440–500 μ, with a rounded-triangular profile and an evident

Conservation status

The HCA performed for the 38 ISO plots (Fig. 1) identified three distinct clusters according to the measured structural traits (cover percentage, maximum leaf length and plant density). Two out of three clusters grouped plots belonging to different populations (i.e. channels) (see Appendix I), highlighting the structural heterogeneity within each population. Therefore, in order to find out the relationships between population structure and the associated environmental parameters, analyses were

Discussion

Three different situations can be identified within and among I. malinverniana extant populations. Considering cover, density, and length as diagnostic parameters of plant and population performance (Vöge, 2003) we can assume that a decreasing health status of the plant occurs from populations with ISO-A to populations with ISO-C dominating plots.

Unfortunately we lack quantitative data revealing the Isoëtes growth rates in its original undisturbed habitat, severely altered or destroyed

Acknowledgements

Researches have been carried out within the Project “Biodiversità per tutti” directed by Ente Parco Lame del Sesia and funded by Cassa di Risparmio delle Province Lombarde (CARIPLO).

The authors express their warmest thanks to Daniela Bouvet for technical support and to Adriano Soldano who introduced them into the I. malinverniana research.

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