Biodiversity Data Journal :
Research Article
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Corresponding author: Alfredo Maccioni (alfredomaccioni87@gmail.com)
Academic editor: Gianniantonio Domina
Received: 07 Jul 2021 | Accepted: 05 Sep 2021 | Published: 19 Nov 2021
© 2021 Alfredo Maccioni, Luisa Canopoli, Valeria Cubeddu, Elisabetta Cucca, Simone Dessena, Samuele Morittu, Rossella Filigheddu, Bachisio Mario Padedda, Emmanuele Farris
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Maccioni A, Canopoli L, Cubeddu V, Cucca E, Dessena S, Morittu S, Filigheddu R, Padedda BM, Farris E (2021) Gradients of salinity and plant community richness and diversity in two different Mediterranean coastal ecosystems in NW Sardinia. Biodiversity Data Journal 9: e71247. https://doi.org/10.3897/BDJ.9.e71247
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This study aimed to test if differences in soil salinity, plant richness and diversity were significantly affected by habitat, site and distance from the seashore at three sandy and three rocky coastal sites in north-western Sardinia.
Each site has been divided into three belts placed at an equal distance of 50 m from the shoreline. We measured soil salinity using a probe and vascular plants richness and diversity using linear transects at all sites. Average soil salinity varied from 0.115 g/l to 0.180 g/l; it was higher in the rocky habitats than in the sandy ones. A total of 21 species were found per transect/site at the rocky sites and 30 species per transect/site at the sandy sites, with an average of Shannon and Weaver's Diversity Index of 1.8 per each belt at each site. These data confirm that, also in the Mediterranean islands, there are coastal gradients of soil salinity from the seashore to inland areas and that also vascular plant richness and diversity are influenced by the distance from the sea. Soil salinity was strongly affected by the type of habitat, being average at the rocky coasts and negligible at the sandy shores. The site effect was not significant for both soil salinity and plant richness and diversity.
biodiversity, psammophilous vegetation and flora, rocky vegetation and flora, soil salinity, spatial distribution pattern, Sardinia
Studies on the effects of biotic and abiotic factors on biodiversity are a central topic in plant ecology (
Abiotic drivers are recognised to play a major role in determining plant diversity in Mediterranean coastal dunes (
Coastal cliffs and dunes can be considered as a set of different vegetation types which are arranged usually in parallel lines, according to a gradient of distance parallel to the coastline, from the sea to the inland: the zone close to the water edge is usually without vascular plants; a zone occupied host by annual halo-nitrophilous communities follows, then perennial grasslands on dunes or chasmophytic plants on cliffs complete the spatial succession. In a mosaic with the perennial vegetation, annual communities develop, characterised by the presence of small herbs with short life-cycles (
It has been experimentally demonstrated that the different environmental factors that limit the growth of the psammophilous plants (soil moisture and nutrients, exposure to wind, burial, salt spray and salinity of the soil) change along the dunes following the distance from the sea (
Although Mediterranean coastal environments are considered a global biodiversity hotspot (
In this research, therefore, we aimed to: 1) measure soil salinity in sandy and rocky Mediterranean insular coastal environments; 2) verify if also species richness and diversity of vascular plants showed spatial gradients similar to soil salinity; and 3) evaluate if the measured gradients (of soil salinity and plant richness and diversity) are significantly affected by the different habitat (rocky vs. sandy), by the site (three sites per habitat), by the distance from the seashore (three fixed distances) or by a combination of the three factors.
Mediterranean insular systems are considered hotspots of plant biodiversity of global importance (
For this study, we selected three rocky (R) and three sandy (D) sites in north-western Sardinia (Italy, see Fig.
We sampled on a gradual elevation gradient in the sandy sites (0-5 m a.s.l.), whereas in the rocky sites, having a steeper shoreline than dunes, we sampled on the summit plateau and not on the cliffs. Therefore, there were no significant differences in the elevation above the sea amongst the three Belts at each site. Furthermore, differences in average elevations above the sea amongst the rocky sites were negligible (10-30 m a.s.l.). We did not expect any tidal influence on soil salinity, because, in the Mediterranean Basin, average tidal height is about 0.2-0.3 m (
Soil salinity was measured through the use of a probe manufactured by the company HANNA Instruments, model HI 993310. The probe operates in the conductivity range from 0.00 to 19.99 mS/cm and has a resolution of 0.01 mS/cm. The in situ measurements of the conductivity of the upper soil were carried out using the sensor probe following the manufacturer’s instructions, inserting it in the soil after wetting with 0.5 litres of distilled water and at a depth sufficient to ensure adequate soil moisture (up to 4 - 5 cm) and also because of the skeletal nature of the studied rocky soils.
The soil salinity data can be read a few seconds after the measurement on a small display connected with the probe and are given as g/l. To classify the obtained values as low, medium, high or very high, we followed the classification proposed by the
Soil salinity, expressed as g/l, was sampled at the three belts of each site during 2013 in the months of April (T1), August (T2) and December (T3). At each Belt, 10 measurements of soil salinity were taken, for a total of 30 measurements at each study site each time, so overall, we took 540 measurements for this study. All measurements per Belt were performed along the Belt section of 50 m in about an equal distance of no less than 4metres from each other.
We determined species’ richness and community diversity by using the method of linear transects (theoretically, a frame quadrat of an infinitesimally small area, i.e. a point in linear transect), useful to study small size vegetation and especially in cases where it is difficult to distinguish individual plants (
Vegetation data of transects were used to calculate Shannon-Weaver Diversity Index (H';
Table
Soil salinity (g/l) at the six study sites in north-western Sardinia, Italy: three rocky sites (Coscia di Donna - R1; La Frana - R2 and Cala Barca - R3) and three sandy sites (Badesi - D1; Platamona - D2 and Porto Ferro - D3). Three belts per site (B1 = 0-50 m from the sea; B2 = 51-100 m; B3 = 101-150 m) were sampled at three times in 2013 (T1 = April; T2 = August; T3 = December).
1Classification of soil salinity according to U.S. Salinity Laboratory Staff 1954: low= < 0.2 [salt concentration (g/l)] and < 0.25 [electrical conductivity (dS/m)]; medium= 0.2-0.5[salt concentration (g/l)] and 0.25-0.75 [electrical conductivity (dS/m)]; high=0.5-1.5 [salt concentration (g/l)] and 0.75-2.25 [electrical conductivity (dS/m)]; very high= 1.5-3.0 [salt concentration (g/l)] and 2.25-5.50 [electrical conductivity (dS/m)].
T1 |
T2 |
T3 |
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B1 |
B2 |
B3 |
B1 |
B2 |
B3 |
B1 |
B2 |
B3 |
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R1 |
0.44±0.10 |
0.30±0.05 |
0.23±0.03 |
0.55±0.08 |
0.29±0.05 |
0.38±0.04 |
0.22±0.02 |
0.21±0.04 |
0.16±0.02 |
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R2 |
0.40±0.07 |
0.23±0.02 |
0.28±0.05 |
0.29±0.04 |
0.23±0.06 |
0.27±0.04 |
0.26±0.03 |
0.19±0.04 |
0.15±0.02 |
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R3 |
0.42±0.04 |
0.26±0.03 |
0.25±0.03 |
0.42±0.05 |
0.26±0.05 |
0.33±0.02 |
0.24±0.02 |
0.20±0.02 |
0.15±0.02 |
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D1 |
0.05±0.01 |
0.06±0.02 |
0.05±0.01 |
0.05±0.01 |
0.02±0.01 |
0.02±0.00 |
0.01±0.00 |
0.03±0.01 |
0.03±0.00 |
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D2 |
0.02±0.00 |
0.04±0.01 |
0.02±0.01 |
0.01±0.01 |
0.02±0.01 |
0.02±0.01 |
0.05±0.02 |
0.05±0.01 |
0.04±0.01 |
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D3 |
0.03±0.00 |
0.05±0.01 |
0.04±0.00 |
0.03±0.01 |
0.02±0.00 |
0.02±0.01 |
0.03±0.01 |
0.04±0.01 |
0.03±0.01 |
Extreme values ranged from 0.551±0.08 g/l at the Belt 1/site R1/time 2 (classified as “high” according to Table
Soil salinity (g/l) at two habitats (R = rocky; D = sandy); three sites per habitat (R1 = Coscia di Donna; R2 = La Frana; R3 = Cala Barca; D1 = Li Junchi; D2 = Platamona; D3 = Porto Ferro) and three belts per site (Belt 1 = 0-50 m from the sea; Belt 2 = 51-100 m; Belt 3 = 101-150 m), sampled at three times in 2013 (T1 = April; T2 = August; T3 = December). A total of 10 measurements were taken at each combination Time × Habitat × Site × Belt.
1Classification of soil salinity according to U.S. Salinity Laboratory Staff 1954: low= < 0.2 [salt concentration (g/l)] and < 0.25 [electrical conductivity (dS/m)]; medium= 0.2-0.5 [salt concentration (g/l)] and 0.25-0.75 [electrical conductivity (dS/m)]; high=0.5-1.5 [salt concentration (g/l)] and 0.75-2.25 [electrical conductivity (dS/m)]; very high= 1.5-3.0 [salt concentration (g/l)] and 2.25-5.50 [electrical conductivity (dS/m)].
ANOVAs emphasise a significant effect of the habitat and the distance from the sea on the soil salt concentration, whereas the site was not a significant factor at any time (Table
Three-way ANOVAs, testing the differences in soil salinity (g/l) between two habitats (Rocky vs. Sandy), three sites per habitat and three belts per site (Belt 1 = 0-50 m from the sea; Belt 2 = 51-100 m; Belt 3 = 101-150 m) at three sampling times in 2013 (T1 = April; T2 = August; T3 = December). N = 10 measurements were taken at each combination Time × Habitat × Site × Belt. Significant values are shown in bold.
Source of variation |
df |
Time 1 |
Time 2 |
Time 3 |
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MS |
F |
P |
MS |
F |
P |
MS |
F |
P |
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Habitat |
1 |
185.6975 |
311.55 |
0.0001 |
260.9545 |
120.86 |
0.0004 |
103.0304 |
257.81 |
0.0001 |
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Site |
4 |
0.5960 |
0.56 |
0.6976 |
2.1592 |
1.95 |
0.1668 |
0.3996 |
0.68 |
0.6206 |
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Belt |
12 |
1.0687 |
3.04 |
0.0007 |
1.1078 |
2.68 |
0.0026 |
0.5901 |
2.76 |
0.0019 |
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Residual |
162 |
0.3518 |
0.4139 |
0.2137 |
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Transformation |
ArcSin (%) |
ArcSin (%) |
ArcSin (%) |
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Cochran’s C-test |
0.2725 (< 0.01) |
0.1503 n.s. |
0.1377 n.s. |
At the time 1, the SNK test for the factor Habitat (SE = 0.0814) showed that dunes had a significantly lower soil salinity than rocky shores. SNK for the factor Belt (nested in Habitat x Site, SE = 0.1876) highlighted at all the three rocky sites that Belt 1 (0-50 m from the seashore) had a higher salinity than Belt 2 and Belt 3, which showed similar levels (Belt1>Belt2=Belt3), whereas, at the three sandy sites, no significant differences were found in soil salinity amongst the three belts (Belt1=Belt2=Belt3).
At the time 2, the SNK test for the factor Habitat (SE = 0.1549) presented a significantly lower soil salinity in dunes than rocky shores. SNK for the factor Belt (nested in Habitat x Site, SE = 0.2034) at the rocky site R1 showed a higher salinity at Belt 1 (0-50 m from the seashore) than Belt 2 and Belt 3, which showed similar levels (Belt1>Belt2=Belt3), whereas, at the other two rocky sites (R2 and R3) and at the three sandy sites, no significant differences were identified in soil salinity amongst the three belts (Belt1=Belt2=Belt3).
At the time 3, the SNK test for the factor Habitat (SE = 0.0666) showed that dunes had a significantly lower soil salinity than rocky shores. SNK for the factor Belt (nested in Habitat x Site, SE = 0.1462) highlighted at the rocky site R2 that Belt 1 (0-50 m from the seashore) had a higher salinity than Belt 2 and Belt 3, which showed similar levels (Belt1>Belt2=Belt3), whereas, at the other two rocky sites (R1 and R3) and at two sandy sites, no significant differences were found in soil salinity amongst the three Belts (Belt1=Belt2=Belt3). Interestingly, at site D1, Belt1 had a significantly lower soil salinity than the other two Belts (Belt1<Belt2=Belt3).
We obtained a list of 89 vascular plants (floristic data are given in Suppl. material
In the rocky sites (R1, R2 and R3), we found 22, 18 and 23 species, respectively, while in the sandy sites (D1, D2 and D3), we found 33, 30 and 27 species, respectively. We found an average of 21 species per site at the rocky sites and 30 species per site at the sandy sites. The highest average number of species was found in Belt 3 with 10 species/transect (higher value was found in Belt 3/site R2 with 15 species/transect), followed by Belt 2 with 9 species/transect and Belt 1 with 7 species/transect (Fig.
Number of vascular plant species at three rocky (R1 = Coscia di Donna, R2 = La Frana, R3 = Cala Barca) and three sandy (D1 = Li Junchi, D2 = Platamona, D3 = Porto Ferro) sites, censused at three belts (Belt 1 = 0-50 m from the sea; Belt 2 = 51-100 m; Belt 3 = 101-150 m), by means of five point transects (every 100 points) per belt.
Shannon and Weaver's Diversity Index (
Shannon and Weaver Biodiversity Index (H’) of vascular plants at three rocky (R1 = Coscia di Donna, R2 = La Frana, R3 = Cala Barca) and three sandy (D1 = Li Junchi, D2 = Platamona, D3 = Porto Ferro) sites, censused at three Belts (Belt 1 = 0-50 m from the sea; Belt 2 = 51-100 m; Belt 3 = 101-150 m), by means of five point transects (every 100 points) per belt.
ANOVA for the number of species (Table
Three-way ANOVAs, testing the differences in the number of species and the Shannon and Weaver's Diversity Index (H’) between two habitats (D = sandy vs. R = rocky), three sites per habitat (D1 = Li Junchi, D2 = Platamona, D3 = Porto Ferro, for sandy sites; R1 = Coscia di Donna, R2 = La Frana, R3 = Cala Barca, for rocky sites) and three belts per site (Belt 1 = 0-50 m from the sea; Belt 2 = 51-100 m; Belt 3 = 101-150 m). N = 5 point transects (100 points each) were taken at each combination Habitat × Site × Belt. Significant values are shown in bold.
Source of variation |
df |
No. of species |
Shannon and Weaver's Diversity Index (H’) |
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MS |
F |
P |
MS |
F |
P |
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Habitat |
1 |
45.5111 |
4.74 |
0.0952 |
0.0673 |
0.13 |
0.7383 |
|
Site |
4 |
9.6111 |
0.54 |
0.7075 |
0.5243 |
1.51 |
0.2602 |
|
Belt |
12 |
17.7000 |
5.27 |
< 0.0001 |
0.3469 |
7.70 |
< 0.0001 |
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Residual |
72 |
3.3556 |
0.0451 |
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Transformation |
none |
none |
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Cochran’s C-test |
0.1821 n.s. |
0.1680 n.s. |
ANOVA for the Shannon and Weaver’s Diversity Index highlighted the significant effect of the factor Belt (Table
The majority of contributions on soil salinity in Mediterranean coastal environments have dealt with laboratory measurements of conductivity on soil samples collected mainly on dunes (
Soils of the rocky shores have a medium salinity level (following the classification proposed by the
Species number and biodiversity index follows an opposite trend with respect to soil salinity (with the relevant exception for H’ at rocky site R1), both being higher at the vegetation belt more distant from the seashore, where soil salinity is lower. Our results have several implications. First, this work sustains the hypothesis that the spatial soil salinity gradient is maintained throughout the year as here assessed and probably during years since no significant severe dry/wet period variations are currently verified for Sardinia (
In conclusion, our data confirm that, also in insular Mediterranean environments, there are coastal gradients of soil salinity from the seashore to inland areas and that the distance from the coastline is the variable explaining not only the zonation of plant communities, as shown by
The data here presented are part of the Bachelor Thesis in Natural Sciences of L.C., V.C., E.C. and S.M. and of the Masters Thesis in Environmental Management of A.M. and S.D., held at the University of Sassari. Marco Cossu, Valentina Murru, Stefania Pisanu, David Roazzi, Arianna Russu and Debora Terrosu helped us in the fieldwork. The authors are grateful to our esteemed colleague Peter J. de Lange (Unitec Institute of Technology, Auckland, NZ) who kindly reviewed the first version of the manuscript.
This research was funded by the Italian Ministry for Research under Grant PRIN project no. 2010BPMAXP “TETRIS” and Fondo di Ateneo per la Ricerca (FAR) 2019 by University of Sassari for E.F.
Conceptualisation: [Alfredo MACCIONI], [Emmanuele FARRIS]; Methodology: [Alfredo MACCIONI], [Emmanuele FARRIS]; Software: [Alfredo MACCIONI], [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Validation: [Rossella FILIGHEDDU], [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Formal Analysis: [Alfredo MACCIONI], [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Investigation: [Alfredo MACCIONI], [Luisa CANOPOLI], [Valeria CUBEDDU], [Elisabetta CUCCA], [Simone DESSENA], [Samuele MORITTU]; Resources [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Data Curation: [Alfredo MACCIONI], [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Writing-Original Draft Preparation: [Alfredo MACCIONI], [Luisa CANOPOLI], [Elisabetta CUCCA], [Emmanuele FARRIS]; Writing-Review and Editing: [Alfredo MACCIONI], [Luisa CANOPOLI], [Rossella FILIGHEDDU], [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Visualisation: [Alfredo MACCIONI], [Luisa CANOPOLI], [Elisabetta CUCCA], [Emmanuele FARRIS]; Supervision: [Bachisio Mario PADEDDA], [Emmanuele FARRIS]; Project Administration: [Emmanuele FARRIS]; Funding Acquisition: [Emmanuele FARRIS].
All authors have read and agreed to the published version of the manuscript.
The authors declare no conflict of interest.
Frequency of 89 vascular plants in three belts (B1-B3) in three rocky sites (R1-R3) and three dune sites (D1-D3) in NW Sardinia. At each combination of Site x Belt, five transects were carried out, therefore frequency of each species is expressed as follows: 0.2 = presence in one transect; 0.4 = presence in two transects; 0.6 = presence in three transects; 0.8 = presence in four transects; 1 = presence in five transects. Plant names follow the last edition of the Italian Vascular Flora Check-List (Bartolucci et al. 2018). Biological (P = Phanerophytes, NP = Nano-phanerophytes, Ch = Chamaephytes, H = Hemicryptophytes, G = Geophytes and T = Therophytes) and chorologic forms were derived from Pignatti (Pignatti 1982).