Study of functional and physiological response of co-occurring shrub species to the Mediterranean climate

Abstract

The Mediterranean basin is characterised by increasingly dry summers and the study of the adaptive traits developed by plants living in this stressful environment is of great interest, also in relation to climate projections for this area. Cistus monspeliensis, Myrtus communis and Phillyrea angustifolia are three co-occurring shrubs typical of the Mediterranean maquis. Their functional and physiological parameters were studied in spring, summer and autumn in order to highlight adjustments of these traits and to test eventual different adaptive strategies. Soil and leaf chemical characteristics were determined in the different seasons. Leaf area, specific leaf area, leaf dry matter content, succulence index, pigment contents hydric status and main markers of oxidative stress and antioxidant response were detected. The stressful summer season induced disturbance in hydric balance, decrease in succulence index and chlorophyll content and high contents of hydrogen peroxide. Thanks to higher enzymatic activities and total glutathione content, in the two evergreen species M. communis and P. angustifolia oxidative damage remained at levels equal to or lower than the other seasons. Only in the semideciduous C. monspeliensis both functional and biochemical traits showed a higher stress condition in summer. The higher stability of functional traits in the two evergreen species may be explained by the sclerophyllous nature of their leaves. Four environmental variables - Tmax, Tmin, soil conductivity and organic matter - mostly influenced NMDS segregation of these species.

Keywords: Antioxidants; Functional traits; Hydric balance; Hydrogen peroxide; Non-Metric Multidimensional Scale (NMDS); Oxidative stress.

Fig. 1

Photo of the experimental field: Castellare Mount (43° 45′ N, 10° 27′ E, Pisa, Italy).

Fig. 2

Relative water content (RWC) in spring, summer and autumn leaves of Cistus monspeliensis, Myrtus communis and Phillyrea angustifolia. Data are mean of 3–9 replicates ± SE for each species. Means followed by the same letters are not significantly different at 5% according to the Kruskal-Wallis test.

Fig. 3

Hydrogen peroxide and TBA-reactive substances (TBARS) in spring, summer and autumn leaves of Cistus monspeliensis, Myrtus communis and Phillyrea angustifolia. Data are mean of 3–9 replicates ± SE for each species. Means followed by the same letters are not significantly different at 5% according to the Kruskal-Wallis test.

Fig. 4

Dendrogram obtained by average-linkage cluster analysis based on the Euclidean distance of the matrix samples x morphological, biochemical, and physiological traits. Species abbreviations: Cmon, Cistus monspeliensis; Mcom, Myrtus communis; Pang, Phillyrea angustifolia; au, autumn leaves; sp, spring leaves; su, summer leaves.

Fig. 5

NMDS diagram based on the dissimilarity (measured by the Euclidean distance) occurring in the three species measuring morphological, biochemical, and physiological traits. Four environmental variables have a Spearman correlation coefficient >0.6 with the two axes. Variables abbreviations: cond, conductivity; orgmat, organic matter content; Tmax, maximum temperature; Tmin, minimum temperature. Species abbreviations: Cmon, Cistus monspeliensis; Mcom, Myrtus communis; Pang, Phillyrea angustifolia; au, autumn leaves; sp, spring leaves; su, summer leaves.