Symbiosis (2010) 52:113–123 DOI 10.1007/s13199-010-0103-1
Early effects of fire on herbaceous vegetation and mycorrhizal symbiosis in high altitude grasslands of Natural Park of Estrela Mountain (PNSE) Anabela Marisa Azul & Vítor Ramos & Fátima Sales
Received: 1 June 2010 / Accepted: 14 December 2010 / Published online: 19 January 2011 # Springer Science+Business Media B.V. 2011
Abstract Severe fires over the last decade have transformed the high altitude grassland biogenetic reserve in the Natural Park of Estrela Mountain (PNSE) of Portugal. Yet, there is little information about the impacts of the fires above and below ground. We assessed the species composition, richness and frequency of the herbaceous vegetation. We characterized the mycorrhizal symbiosis and analysed the soil properties in three cervunal areas of which one was destroyed by a severe fire in 2003. The results indicate that plant community in high altitude grassland of PNSE are rather poor in species but the number may increase after fire. The most remarkable change in the herbaceous vegetation after fire was the abrupt increase of Festuca trichophylla in the burnt area, to the detriment and abrupt decrease of Nardus stricta. Arbuscular mycorrhizas (AM) were the most widespread symbioses in all three grasslands. AM colonization of F. trichophylla was significantly lower in burnt grassland but the AM colonization in N. stricta increased. There was also a higher phosphorous content in
A. M. Azul (*) : F. Sales CFE, Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, PO Box 3046, 3001–401, Coimbra, Portugal e-mail:
[email protected] V. Ramos Laboratory of Ecotoxicology, Genomics and Evolution, Center for Marine and Environmental Research, University of Porto, 4050-123, Porto, Portugal F. Sales Royal Botanic Garden Edinburgh, EH3 5LR, Scotland, UK
soil of the burnt grassland. We put forward a hypothesis about the impacts of recurrent fires above and below ground and discuss its implications to functioning of high altitude ecosystems. Keywords Biogenetic reserve . High altitude grassland . Mycorrhizal symbiosis . Post-fire herbaceous vegetation
1 Introduction Since the industrial revolution, Europe has experienced higher temperatures; warming being greatest in the southwest, centre and northeast as well as in the mountains (European Environment Agency 2004). Future summer warming (June to August) is projected to be greatest over the Iberian Peninsula, central Europe, eastern Adriatic coastline and southern Greece (Pausas 2004; Kjellström et al. 2007). As a result, the mountains in these areas are among of the most sensitive natural ecosystems in Europe (WBGU 2003) and are already affected by rising temperature and decreasing precipitation (European Environment Agency 2004). The European Directive on aquatic systems only applies to streams and rivers with catchments areas larger than 10 km2 (WFD-System A descriptors). By doing so, it misses most of the aquatic high altitude systems. These consist of network of numerous small streams and areas that are usually not even mentioned on maps. They are understudied, and in many cases, are without legal protection. Nevertheless, these complex high altitude aquatic systems service areas at lower altitudes which largely depend on them. Globally, grasslands are the dominant vegetation at higher altitudes and are particularly sensitive to water availability (Clayton and Renvoize 1986). The high altitude
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grasslands in the Iberian Peninsula are probably be one of the most vulnerable ecosystems in Europe as a result of climate change. The present investigation examined the herbaceous vegetation and the mycorrhizal symbioses of high altitude grasslands in the westernmost high mountain of continental Europe, the Estrela Mountain (C. Portugal), and the consequences of recent fires. This particular ecosystem in Estrela Mountain, named “cervunal”, is characterised by the dominance of N. stricta L. (Poaceae), and involves 10.000 ha of a biogenetic reservation (DL nº 140/99, 24th April— Appendix B-1, 6230) within the Natural Park of Estrela Mountain (PNSE). The PNSE is a catchment area for 3 of the main Portuguese rivers (Mondego, Tejo and Douro), supplies water to local cities and villages and also to Coimbra and even Lisbon. The rivers are also a source of electrical power. Despite its conservation status and the recognition that it is a wet area, the “cervunal” has been only superficially studied (Malato-Beliz 1955; Pereira 1957). N. stricta is native and quite common in N. Europe, but in Estrela Mountain it is restricted to high altitudes (above 1200 m) on poor, acid soils (Malato-Beliz 1955; Pereira 1957; Machado 2008). This grass is resistant to cold and long periods of snow cover, which happens during winter in Estrela Mountain. The species is rather frequent in acid heath-land soils, characterized by low rates of mineralization, high rates of leaching and retention of nitrogen in complex organic forms (Read 1991). The acidic pH of these soils also results in low phosphorus availability (Willard 1979). The woody vegetation that grows at the higher altitudes in Estrela Mountain (e.g., Juniperus communis, Calluna vulgaris, Erica arborea, E. umbellata, E. australis and Halimium lusianthum subsp. alyssoides) has been kept out of the “cervunal” for centuries by grazing and by controlled fires. The latter increases the fertility of the soil for a short period and enables grazing on the resultant grass sward by sheep and goats. At present, grazing management is in decline and the woody species are invading some of the grassland. The greater amount of combustible material in the woody plants has the potential increase the temperature of fires to damaging levels, even in wet areas, compared to the fires by shepherds on the grasslands. A fire in 2003 was particularly destructive and burnt an appreciable area of the biogenetic reserve. The occurrence of fire is likely to alter the dynamic interface root/soil where roots, microorganisms, and abiotic soil factors interact. Mycorrhizas are of particular importance in this context. Their establishment modifies the chemical composition of root exudates, the fungal nutrient uptake, the microbial community interactions and the environmental
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rhizosphere. All these factors influence the structure of the whole plant community (see Smith and Read 2008). N. stricta forms arbuscular mycorrhizas (AM) (Ali 1969; Read et al. 1976). The communities of AM fungi play a crucial role in plant community structure and diversity (van der Heijden et al. 1998a, b; Genney et al. 2001; O’Connor et al. 2002). One of the main mechanisms by which AM fungi benefit the host-plant is by increasing soil exploration and, thus, the uptake of higher amounts of immobile ions, particularly phosphorous (Bolan 1991). The two main objectives of this study were: (1) to characterize the herbaceous vegetation in high altitude grassland of PNSE and evaluate the early effects of fire on plant composition, species richness and frequency; (2) to investigate the early effects of fire on mycorrhizal symbioses and soil properties.
2 Materials and methods 2.1 The sites The research took place at the high altitude grasslands of Natural Park of Estrela Mountain (PNSE), C. Portugal, between May and August 2005. More than 70% of the PNSE region includes natural and semi-natural areas and ca. 0.2% of its area is covered by aquatic systems. Snowfall data available for Estrela Mountain indicate a median of 40 to 50 days per year at 1400–1600 m (Andrade et al. 1992). Snow presence is almost constant from November to April, particularly at high altitude between 1600–1993 m. The high altitude plateaus and small watercourses are covered by ice through the winter. Many streams are intermittent during summer due to low precipitation, but may be maintained where N. stricta is found. These high altitude areas of Estrela Mountain were covered by an ice cap with about 70 km2 area during last glaciation’s (Daveau 1971). Three sites were selected in the higher altitudes of PNSE, one burnt by the severe wildfire in August 2003 and two control areas: Vale do Conde (BURNTVC), at 1600 m altitude, destroyed by fire; Covão das Lapas (UNBCL) just under 1650 m; and Fonte dos Perus (UNBFP), just under 1850 m (Fig. 1). The mean of temperature and precipitation during the summer of the severe fire (2003) and the winter after the sampling (2005), are shown in Figs. 2 and 3, respectively. 2.2 Vegetation assessment Plant community composition and structure was assessed during the peak flowering season. In the three grasslands five parallel square plots, 20×20 m each, were selected using a random design. A check-list of plant species was made from
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Analysis were: particle size distribution by pipette and sieving; total nitrogen by the Kjeldhal method (Page et al. 1982); phosphorous content by the ascorbic acid method; potassium and sodium by flame photometry (Page et al. 1982); calcium and magnesium by atomic absorption spectroscopy in an ammonium acetate extract at pH 7; pH on a 2:1 distilled water/soil suspension; and organic matter determined by Walkley-Black dichromate digestion. Analyses were performed by the laboratory of Direcção Regional de Agricultura de Entre Douro e Minho. 2.4 Mycorrhizal sampling and assessment Fig. 1 Location of the three high altitude grasslands investigated in National Park of Estrela Mountain (PNSE), centre of Portugal: ■ = un-burnt grassland Covão das Lapas (UNBCL); ★ = burnt grassland Vale do Conde (BURNTVC); ▲ = un-burnt grassland Fonte dos Perus (UNBFP)
each of these plots. Within each plot, four smaller subplots (0.5×0.5 m each) were randomly selected to assess the plant species that are commonly easily to underestimate due the dominance of N. stricta and Festuca trichophylla. In these subplots, the plant species frequency of annual herbaceous, perennial herbaceous, occasional woody, and bryophytes was recorded. The identification of vascular plants followed Castroviejo et al. (1986–2007). One voucher specimen per vascular taxon was collected; these specimens are housed in the Coimbra herbarium, COI (Department of Life Sciences, University of Coimbra, Portugal). 2.3 Soil analysis Two soil samples were collected from each 20×20 m plot for a total of 10 samples in the three grasslands. Each sample consisted of a mixture of four evenly spaced subsamples collected from the first 10 cm of soil. Soil samples were sieved through a 2-mm mesh sieve and dried. Fig. 2 Mean of temperature in the three high altitude grasslands between Summer 2003 and Winter 2005
Rhizospheric soil with roots was collected to identify the type of symbiosis present and to determine the degree of the mycorrhizal colonization by arbuscular mycorrhizal fungi (AMF). Sampling was conducted during the flowering period between May and August to make possible the identification of the host species. Rhizospheric soil of 71 accessions corresponding to 33 species was collected from the 20×20 m plots selected in the three grasslands; 5 replicas of each accession were analysed. Roots were extracted from the first 10 cm of soil. Samples were wrapped in newspaper, sealed in plastic bags and stored at +4°C for up 2 weeks until processing. Roots were washed thoroughly in running tap water to remove soil. Clean roots were observed under a dissecting microscope to identify sheathing mycorrhizas (ectomycorrhizas); the diagnostic features to detect the ectomycorrhizas were the presence of a mantle and the Hartig net. Some samples were examined under ultraviolet-light in an epifluorescence microscope (Nikon EFD-3) to detect the arbuscules of AM mycorrhiza in living roots (Ames et al. 1982). However, perennial herbaceous, shrubs and most of annual herbaceous did not exhibit autofluorescing AM arbuscules. Thus, a staining procedure modified from Vierheilig et al. (1998, 2005) was used to observe the endomycorrhizas by light microscopy. Roots were stained Max air temp
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Fig. 3 Mean of precipitation in the three high altitude grasslands between Summer 2003 and Winter 2005
after using lactic acid (5% over-night) at the acidification step followed by ink staining (Blue Quink; Parker, Jansville, WI, USA) (Azul et al. 2008). Roots were stored in ethanol 60% before staining. The assessment of AM colonization followed McGonigle et al. (1990). Four slides of 40×22 mm per sample and a minimum of one hundred interceptions per slide were analysed. 2.5 Data analysis and statistics Species frequency and diversity of vegetation cover were calculated based on sub-plot (0.5×0.5 m) data. Species frequency was estimated as the percentage of a given species in the sub-plot. Diversity of plant community was estimated using different descriptors: (i) species richness, total number of taxa found per plot (S); (ii) ShannonWiener index (H), sensitive to rare species; (iii) Simpson index (λ), is a measure of dominance; and (iv) Equitability (H’), evenness of species (Magurran 1988). Statistical analysis used SPSS 15.0 statistical package (S. P.S.S. 2007). Normality and homoscedasticity were tested by the Kolmogorov-Smirnof and Bartlett tests respectively. Analysis of variance was performed using ANOVA (S.P.S. S. 2007) to compare the three sites and reveal the early effect of fire on herbaceous vegetation cover and mycorrhizal symbiosis. Data on vegetation cover composition, nutrient contents, AM colonization, arbuscules in roots, were analysed using one-way ANOVA and the significant differences (p
