Corresponding author: Edy Fantinato ( edy.fantinato@unive.it ) Academic editor: Simonetta Bagella
© 2020 Mattia Baltieri, Edy Fantinato, Silvia Del Vecchio, Gabriella Buffa.
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:
Baltieri M, Fantinato E, Del Vecchio S, Buffa G (2020) Intraspecific variability of leaf traits and functional strategy of Himantoglossum adriaticum H. Baumann. Plant Sociology 57(2): 105-112. https://doi.org/10.3897/pls2020572/03
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Trait-based studies have become extremely common in plant ecology. In this work we analysed intraspecific trait variation of Himantoglossum adriaticum, a European endemic orchid species of Community interest, to investigate whether different populations growing on managed and abandoned semi-natural dry grasslands show differences in the CSR strategy. In seven populations occurring in Veneto Region (NE Italy), we measured H. adriaticum maximum vegetative height, leaf traits (LA, LDMC, SLA) and calculated the CSR strategy. Through CCA we investigated the relationship between plant traits and both plant community attributes (cover and height of herbs and shrubs), and geomorphologic features (aspects and slope). PERMANOVA test was used to investigate if the CSR strategy of H. adriaticum varied according to the management regime. Results showed that individuals of H. adriaticum develop different strategies when growing in different habitats. Specifically, individuals growing in managed fully sunny dry grasslands reached higher vegetative height (MH), had lower values of SLA and a higher relative contribution of the C parameter than individuals growing in abandoned dry grasslands, which, on the contrary, were shorter, had higher values of SLA (and correspondingly lower values of LDMC) and a higher relative contribution of the R parameter. Further data on reproductive traits (e.g. fruit and seed-set) may corroborate our results. Although the number of individuals addressed in this study is rather low, and our conclusions may not be considered of general validity for the species, our study demonstrated the applicability of the CSR strategy scheme in detecting functional strategies at intraspecific level.
CSR plant strategy theory, dry grasslands, Himantoglossum adriaticum, intraspecific trait variation, land-use change, plant traits
Trait-based studies have become extremely common in plant ecology (
Although species identity provides major information for ecological studies, the traditional taxonomic description becomes less effective when we are to understand plant reactions to environmental changes, e.g. climate or natural/anthropogenic disturbance, and the processes behind them (
Several studies suggest the existence of sets of plant traits that co-vary, thereby allowing the identification of syndromes that affect survival (e.g.
In light of the above, this study aims at investigating whether populations of the Adriatic Lizard Orchid (Himantoglossum adriaticum H. Baumann), growing on managed and abandoned semi-natural dry grasslands show differences in the CSR strategy. The evaluation of intraspecific trait variability might be the key to understanding the interactions between H. adriaticum and the extant community and reveal its ability to respond to environmental variations.
The study took place on two hilly massifs of the Veneto Region (NE Italy): the Berici Hills (N 45.443.909; E 11.516.229) and the Euganei Hills (N 45.315.955; E 11.702.056), originated from volcanic (basaltic and rhyolitic) bedrock (
Sampling sites were represented by small- to medium-sized (0.2–2 ha) dry grasslands, dispersed in an agricultural landscape among forests and arable fields. Created by low-intensity agricultural land use, semi-natural dry grasslands represent unique and species-rich plant assemblages. Temperate dry grasslands are maintained by traditional management practices as mowing, pasturing and haymaking (
Himantoglossum adriaticum is a European endemic species of priority interest (Directive 92/43/ EEC, Annex II), suffering population decline in many European countries (
H. adriaticum is a robust, perennial, tuberous, orchid with an over-wintering rosette composed of lanceolate, pale green basal leaves. The generative shoots are on average 40–80 cm tall, but they can reach 120 cm. The inflorescence is elongate and lax, composed of several (15–40) flowers and typically 14–24 cm in length (
We selected seven populations of H. adriaticum; three at the Euganei Hills and four at the Berici Hills. Between the 1st and the 10th of June, we placed a plot of 2 m × 2 m at the core of each population. In each plot, the plant community attributes were described by recording the composition of vascular plant species and visually estimating the percentage cover and average height of the herb and shrub layer (Ch and Cs; Hh and Hs, respectively). To account for geomorphic variability, in each plot topographic data were collected: aspect (AS), expressed in degrees clockwise from the North and slope (SL), measured in percentage steepness with respect to the horizontal plane (steepness = 0%).
Given the threatened status of the species, we restricted the sampling to a low number of individuals per population (less than 15% of the overall individuals’ abundance) in order to avoid negative impacts on the populations’ persistence (
LA, LDMC and SLA provide strong indications about vascular plant adaptations under different environmental conditions and are at the basis of the calculation of the CSR strategies (
- Leaf area (LA): it is the size of the photosynthetic organ. It measures how much a plant invests in the photosynthesis. The leaf area is directly linked to the plant capacity to intercept light, and hence to the plant productivity. Leaf area can vary with changes in climate, altitude, and stress, such as soil aridity. LA decreases under increasing stressful conditions (
- Leaf dry matter content (LDMC): it quantifies leaf tissue density and nutrient retention capacity. High values of LDMC indicate a preference in conserving nutrients. Species with high level of LDMC show tough leaves, highly resistant to hazards (
- Specific leaf area (SLA): it is defined as the ratio of total leaf area to total leaf dry mass. In other words, it describes the amount of leaf area for light capture per unit of biomass invested. High SLA values are generally recorded in resource-rich environments, while low values in resource-poor environments (
We used the canonical correspondence analysis (CCA) to study the relationship between plant traits, plant community attributes and plot geomorphological features. In the CCA ordination, the sample units were the individuals of H. adriaticum collected in each population. We used values of LDMC, SLA and the maximum height of the whole foliage (MH) as dependent variables, while the percentage cover and average height of the herb and shrub layer (Ch and Cs; Hh and Hs), plot aspect (AS) and slope (SL) as predictor variables. We used 1,000 Monte Carlo permutations to assess statistical significance of the association between plant traits, plant community attributes and plot geomorphological features. To define the groups in the CCA diagram we performed a cluster analysis on the plots × plant community attributes (using average-linkage method and Bray–Curtis distance).
The relative contribution (%) of C, S, and R parameters to the tertiary CSR strategy was automatically calculated and represented by a ternary plot using the spreadsheet provided by
We sampled 29 individuals of H. adriaticum. The number of sampled individuals varied from 1 to 15, with an average number of 4.5 ± 5.2 (mean ± SD) individuals per population (Table
Plant community attributes and geomorphological features of sampled populations.
Population ID | Sampling site | Total number of individuals | Number of sampled individuals | Aspect (degrees) | Slope (%) | Herb layer cover (%) | Shrub layer cover (%) | Herb height (cm) | Shrub height (cm) | Management regime |
1 | Euganei | 15 | 2 | 315 | 5 | 70 | - | 20 | 0 | Managed |
2 | Euganei | 115 | 13 | 45 | 5 | 40 | - | 25 | 0 | Managed |
3 | Euganei | 96 | 3 | 0 | 0 | 90 | 30 | 20 | 300 | Abandoned |
4 | Berici | 15 | 2 | 90 | 35 | 100 | 28 | 70 | 200 | Abandoned |
5 | Berici | 23 | 1 | 135 | 20 | 65 | 50 | 40 | 250 | Abandoned |
6 | Berici | 62 | 3 | 135 | 15 | 80 | 65 | 40 | 180 | Abandoned |
7 | Berici | 101 | 3 | 135 | 10 | 75 | 50 | 30 | 400 | Abandoned |
The two CCA axes explained 88.81% (p = 0.018) and 11.19% (p = 0.002) of the variance, respectively (Trace = 0.021; P < 0.001). The first CCA axis was strongly positively related to the percentage cover of the herb (Ch; 0.71) and shrub layer (Cs; 0.63), to the average high of the shrub layer (Hs; 0.62) and to the plot slope (SL; 0.53). The largest loadings on the second axis were from plot aspect (AS; -0.27) and slope (SL; 0.25). The CCA revealed a strong positive relationship between SLA, community attributes (i.e., Ch, Cs, Hh and Hs) and plot geomorphological features (i.e., AS and SL; Fig.
Scatterplot of the canonical correspondence analysis (CCA) utilized to investigate the relationship between plant traits (blue triangles), plant community attributes and plot geomorphological features (red lines). Different symbols indicate individuals of H. adriaticum growing in managed (black dots) or in abandoned grasslands (black stars), as revealed by the cluster analysis.
The overall strategy of H. adriaticum obtained by averaging single individual strategy irrespectively of the habitat type was CR (C:S:R; 60:0:40 %). Significant differences in the CSR strategy of H. adriaticum growing in managed vs. abandoned dry grasslands were revealed by PERMANOVA (F= 28.4; d.f. = 40.71; P < 0.0001). Tukey test revealed that individuals of H. adriaticum growing in managed dry grasslands showed a significantly higher percentage of the C parameter (P < 0.0001; Fig.
In other words, our results suggest that individuals of H. adriaticum show different strategies when growing in different habitats (Fig.
Managed grasslands | ||||||||
ID | Maximum vegetative height (cm) | LA (mm2) | LDMC (%) | SLA (mm2 mg-1) | %C | %S | %R | Tertiary strategy |
1 | 22.7 | 2.347.033 | 9.937 | 17.685 | 77.43 | 0 | 22.57 | C/CR |
2 | 27.4 | 1.935.357 | 11.290 | 20.531 | 67.94 | 0 | 32.06 | C/CR |
6 | 38.7 | 1.869.641 | 11.597 | 21.933 | 64.49 | 0 | 35.51 | C/CR |
7 | 45.2 | 1.766.543 | 10.141 | 23.411 | 61.14 | 0 | 38.86 | C/CR |
17 | 40.6 | 2.936.839 | 12.720 | 12.847 | 95.71 | 4.29 | 0 | C |
18 | 31.1 | 1.346.199 | 10.101 | 24.798 | 56.52 | 0 | 43.48 | CR |
19 | 33.9 | 1.804.074 | 11.796 | 16.346 | 81.46 | 0 | 18.54 | C |
20 | 33.7 | 2.301.610 | 12.784 | 14.276 | 89.15 | 4.69 | 6.159 | C |
21 | 35.2 | 1.091.375 | 12.789 | 15.440 | 79.25 | 5.38 | 15.37 | C |
22 | 24.2 | 1.315.645 | 13.901 | 17.281 | 67.44 | 10.9 | 21.7 | C/CR |
23 | 45.6 | 1.672.339 | 13.610 | 14.696 | 80.97 | 10.1 | 8.909 | C |
24 | 34.0 | 1.755.570 | 12.237 | 18.075 | 73.72 | 1 | 25.28 | C/CR |
25 | 35.8 | 1.650.154 | 9.290 | 20.705 | 66.4 | 0 | 33.6 | C/CR |
26 | 36.0 | 2.073.885 | 11.139 | 16.157 | 82.95 | 0 | 17.05 | C |
27 | 49.1 | 2.709.226 | 12.363 | 14.069 | 93.29 | 1.94 | 4.776 | C |
28 | 32.7 | 1.809.762 | 11.325 | 19.574 | 70 | 0 | 30 | C/CR |
29 | 28.5 | 1.531.902 | 10.782 | 18.836 | 71.08 | 0 | 28.92 | C/CR |
Abandoned grasslands | ||||||||
ID | Maximum vegetative height (cm) | LA (mm2) | LDMC (%) | SLA (mm2 mg-1) | %C | %S | %R | Tertiary strategy |
3 | 29.4 | 2.381.676 | 9.724 | 21.063 | 68.02 | 0 | 31.98 | C/CR |
4 | 29.4 | 2.067.571 | 9.769 | 26.650 | 57.07 | 0 | 42.93 | CR |
5 | 27.0 | 1.934.965 | 9.010 | 22.896 | 62.78 | 0 | 37.22 | C/CR |
8 | 38.7 | 1.547.654 | 9.624 | 30.906 | 49.52 | 0 | 50.48 | CR |
9 | 45.2 | 854.140 | 7.471 | 40.698 | 35.96 | 0 | 64.04 | R/CR |
10 | 41.2 | 1.018.072 | 10.568 | 40.301 | 37.84 | 0 | 62.16 | R/CR |
11 | 32.3 | 2.131.742 | 9.468 | 23.533 | 62.28 | 0 | 37.72 | C/CR |
12 | 39.5 | 868.181 | 8.752 | 35.873 | 39.62 | 0 | 60.38 | R/CR |
13 | 33.4 | 1.184.001 | 9.111 | 23.704 | 57.33 | 0 | 42.67 | CR |
14 | 37.4 | 1.404.920 | 11.609 | 32.653 | 46.9 | 0 | 53.1 | CR |
15 | 37.2 | 1.273.419 | 13.051 | 28.582 | 48.44 | 4.23 | 47.33 | CR |
16 | 27.2 | 2.379.992 | 15.152 | 22.667 | 56.45 | 12.7 | 30.87 | C/CR |
Plant traits are increasingly used to detect plant responses to changes in environmental conditions, since they allow to determine species ecological roles in the environment (
According to
Overall, H. adriaticum exhibited a Competitive-Ruderal (CR) secondary strategy, incorporating substantial competitive and, to a lesser extent, ruderal features. Interestingly, neither the species nor the two groups of individuals showed the stress-tolerant component. This low inclination for the S- strategy may be explained by the particular phenology of H. adriaticum. Contrary to other dry grassland orchid species, its growing period starts in late spring, and the time of flowering is usually around late May or June. The capsules mature in 4–6 weeks, and seeds are shed rather quickly, in July or August (
Despite these general characteristics, the CCA ordination showed that specific leaf area (SLA) and leaf dry matter content (LDMC) of H. adriaticum varied along with community attributes and plot geomorphological features, reaching, respectively, the highest and the lowest values in partially shaded, sloping grasslands encroached by shrubs. These traits are known to reflect crucial life history trade-offs between the investment of resources in further resource acquisition vs. conservation (
We are aware that the number of individuals addressed in this study is rather low, and that our conclusions may not be considered of general validity for the species. However, as reported by