Plant nutrient changes in a semi-arid Mediterranean shrubland after fire

Abstract. Alkaline xeric soils from SE Spain weathered from kakiritized dolomitic rocks and subjected to recurrent fires, show phosphorus immobilization, low nutrient availability and high cation content, which might affect plant nutrition. Currently, Ulex shrubland, with a variety of dolomitophilous endemics, is colonizing eroded areas and replacing the original shrubland communities. Variation in nutrient content during post-fire regeneration was studied in six species which differ widely in their successional status. All species showed a high consumption of nutrients immediately after the fire. A pattern of decline in internal nutrient levels, especially P, with time since fire was detected in mid-to-late successional shrubs: Juniperus oxycedrus, Genista spartioides, and to a lesser extent in Rosmarinus officinalis, a shrub species of intermediate successional status. This pattern of decline may represent a progressive change towards a metabolism with a low turnover along the age gradient. Early successional shrub species behaved in a different way. Cistus clusii showed a nutrient-cumulative strategy, especially for P, across the fire-age gradient. Ulex rivasgodayanus maximized internal N concentrations due to its symbiotic activity with N₂-fixing bacteria. Cistus and Rosmarinus held high cation levels in their tissues. The nutritional characteristics of these shrub species are seen as advantageous adaptations to the specific soil properties and disturbance regime of the area.     

Invasive legume management strategies differentially impact mutualist abundance and benefit to native and invasive hosts

Determining the best management practices for plant invasions is a critical, but often elusive goal. Invasive removals frequently involve complex and poorly understood biotic interactions. For example, invasive species can leave potent legacies that influence the success of native species restoration efforts, and positive plant‐microbial feedbacks may promote continued reinvasion by an exotic species following restoration. Removal methods can vary in their effects on plant–soil feedbacks, with consequences for restoration of native species. We determined the effects of invasion by a leguminous shrub (French broom; Genista monspessulana) on the density and community composition of, and benefit conferred by, its microbial mutualists in its invading range. Densities of soil‐dwelling rhizobia were much higher in areas invaded by G. monspessulana relative to uninvaded areas, and this increased density of rhizobia fed back to increase seedling growth of both the invader and native legumes. We further compared how three techniques for removing G. monspessulana affected the densities of rhizobia relative to areas where G. monspessulana was still present. Removal by hand‐pulling reduced soil rhizobial densities, and reduced growth of one native legume, while having no effect on the growth of the invader. Overall, our results show that the consequences of restoration techniques, both above‐ and belowground, could be critical for the successful removal of an invasive legume and restoration of native species.     

Genetic structure in the Genista ephedroides complex (Fabaceae) and implications for its present distribution

The present investigation investigated the genetic structure of a monophyletic group of endemic species belonging to the Genista ephedroides species group: G. bocchierii, G. cilentina, G. demarcoi, G. dorycnifolia, G. ephedroides, G. gasparrinii, G. insularis, G. numidica, G. tyrrhena subsp. tyrrhena, G. tyrrhena subsp. pontiana and G. valsecchiae, all distributed in the western Mediterranean. Using seven plastid microsatellites, 16 populations (288 individuals) were screened. Haplotype fixation was observed in particular for most of the Tyrrhenian taxa (i.e. G. bocchierii, G. cilentina, G. demarcoi, G. ephedroides, G. gasparrinii, G. insularis, G. tyrrhena subsp. tyrrhena and G. valsecchiae). However, although genetic diversity within populations was low [(h_S = 0.132 (± 0.056)], a high level of total plastid DNA diversity [h_T = 0.866 (± 0.042)] was detected, and analysis of molecular variance indicated that variation is almost exclusively expressed among populations (95.25%). The plastid microsatellites identify two groups of taxa, one including Sardinian taxa and populations of G. tyrrhena subsp. pontiana and the other including two subgroups, one of which includes Sicilian/Aeolian elements and the other with G. numidica/G. cilentina and G. dorycnifolia. Results allow us to consider G. cilentina as originating by recent anthropogenic dispersal and G. tyrrhena subsp. pontiana as a possible stabilized hybrid between local plants and members of the Sardinian group contributing the maternal lineage. The evolutionary history of the group possibly results from the effects of ancient events fostering geodispersal and range contraction, followed by more recent long‐range dispersal or geodispersion over Pleistocenic land bridges. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 607–618.     

A new alpinumisoflavone derivative from Genista pichisermolliana

The aerial parts of Genista pichisermolliana Valsecchi (Fabaceae), an endemic plant of Sardinia, were extracted in Soxhlet apparatus and purified by several chromatographic methods. The new compound alpinumisoflavone 4′-O-glucopyranoside (6) was isolated together with nineteen flavonoids, p-coumaric methylester and d-pinitol, while no alkaloids were detected. All the chemical structures were elucidated by spectroscopic analysis. Since flavonoids represent the main constituents of this plant, the total flavonoid content was determined according to the Italian Pharmacopoeia IX Ed. method.     

A phytochemical study of the quinolizidine alkaloids from Genista tenera by gas chromatography-mass spectrometry

Gas chromatography coupled with mass spectrometry has been used to analyse the alkaloids present in the aerial parts of Genista tenera. Anagyrine, cytisine, N-formylcytisine, N-methylcytisine and lupanine were the major compounds, the last two alkaloids being known for their hypoglycaemic activity. Dehydrocytisine, 5,6-dehydrolupanine, rhombifoline, aphylline and thermopsine were the minor alkaloids. The characterisation of the constituents was based on comparison of their Kovats retention indexes and electron impact-mass spectrometric data recorded on-line with those of reference compounds and literature data.     

Sexual and geographical variation in life history parameters of the shorthorn sculpin

A total of 293 shorthorn sculpins Myoxocephalus scorpius from Tromsø, northern Norway, were sampled between November 1998 and April 1999 to determine sex, total length, age, growth, maturity and mortality. Females grew to larger sizes ( L _∞=26·9 v. 18·5 cm), matured later (2 v. 1 year of age) at larger size (maturation length=16 v. 14 cm L _T), and had lower instantaneous mortality rates (0·93 v. 1·20 year⁻¹) than males. The life history parameters of shorthorn sculpins in northern Norway were more similar to the parameters of short-lived central European populations than to the parameters of the long-lived population of Newfoundland. This study confirms that northern Norwegian shorthorn sculpins exhibit sexual dimorphism as in other shorthorn sculpin populations. The relationships between growth pattern, age at maturity and mortality rates observed in the Tromsø population and in other shorthorn sculpin populations, correspond well with the predictions from a published life history model.     

Effect of high temperatures on seed germination of two woody Leguminosae

Cytisus scoparius and Genista florida regenerate after fire by stump-sprouting but also by seed. Seeds of these species were heated to a range of temperatures similar to those registered on the surface soil during natural fires (from 50 to 150 °C) and a range of exposure times (from 1 to 15 min). No germination was observed at high temperatures, 130 °C, when the exposure time was 5 min or more. However, moderate heat treatments (at 70 and 100 °C) significantly increased the rate of germination relative to controls. Cytisus scoparius is more favoured by fire action than Genista florida, with germination rates slightly greater following 100 °C for 5 min and 130 °C for 1 min than after mechanical scarification.     

Changes in mediterranean shrub communities with Cytisus purgans and Genista scorpius

Summary Shrub communities are important in the mediterranean landscape and linked very much with human activities. The permaneney and the spreading of these communities are related to biological characteristics of the dominant species which control the patterns of changes in structure, richness, types of life forms, and ability of colonization by trees. In this paper, changes in communities are analysed and compared for Cytisus purgans and Genista scorpius (both Papilionaceae). For both communities the schemes of origin and spreading are rather the same: overgrazing and fire play a prominent role. Changes in structure show different stages emphasized by the types of distribution of the chlorophyll containing stratum. There is a direct relation between changes in structure and changes in species richness and life form spectrum: richness decreases generally from the second or third year after fire. According to the dryness of the stand therophytes may or may not be important in the youngest stands. The colonization of the shrub communities by trees is dependent on several conditions, either on the shrub community itself, or on the plant-matrix surrounding the shrub community patch and also on animals; man, too, plays an important role. In conclusion we think that the above-mentioned changes in shrub communities fit the inhibition model proposed by Connell & Slatyer (1977); but, more generally it seems that the plant successions observed in our regions follow both, this model and the facilitation and tolerance models of the same authors. Linked with this fact, it seems that the successions show generally fluctuating values of richness as is suggested by Whittaker (1975). We think that plant succession must be well analyzed at different levels of organization and include the study of the influences man and animals may have.Plant nomenclature follows Fournier (1961); for birds see Peterson et al. (1967).We are very much indebted to Ch. Rimbault for her contribution to the translation of this paper.     

Phylogeny of nodulation genes and symbiotic properties of Genista tinctoria bradyrhizobia

Pairwise comparisons of Genista tinctoria (dyer’s weed) rhizobium nodA, nodC, and nodZ gene sequences to those available in databanks revealed their highest sequence identities to nodulation loci of Bradyrhizobium sp. (Lupinus) strains and rhizobia from other genistoid legumes. On phylogenetic trees, genistoid microsymbionts were grouped together in monophyletic clusters, which suggested that their nodulation genes evolved from a common ancestor. G. tinctoria nodulators formed symbioses not only with the native host, but also with other plants of Genisteae tribe such as: Lupinus luteus, Sarothamnus scoparius, and Chamaecytisus ratisbonensis, and they were classified as the genistoid cross-inoculation group. The dyer’s weed root nodules were designated as indeterminate with apical meristem consisting of infected and uninfected cells.The GenBank accession numbers for the sequences reported in this paper are as follows: nodC, DQ139776–DQ139781; nodA, DQ135897, Q135898; nodZ, DQ135899–DQ135903.     

Seasonal Patterns of Photosystem 2 Photochemical Efficiency in Evergreen Sclerophylls and Drought Semi-Deciduous Shrubs under Mediterranean Field Conditions

Photochemical efficiency of photosystem 2 (PS2), assessed from in situ chlorophyll (Chl) fluorescence measurements, was seasonally monitored in five evergreen sclerophyll and five malacophyllous drought semi-deciduous species, co-occurring in the same Mediterranean field site. In evergreen sclerophylls, a considerable drop in the variable (F_v) to maximum (F_m) Chl fluorescence ratio coincided with the lowest winter temperatures, indicating low PS2 efficiency during this period. Summer drought caused a comparatively slight decrease in F_v/F_m and only in three of the five evergreen sclerophyll species tested. In drought semi-deciduous shrubs, the winter drop in F_v/F_m was much less conspicuous. During the summer, and in spite of the severe and prolonged desiccation of their malacophyllous leaves, F_v/F_m was maintained high and only in one species the PS2 efficiency was transiently suppressed, when the leaf relative water content became lower than 30 %. Thus evergreen sclerophylls are more prone to photoinhibition by low winter temperatures, while the sensitivity of drought semi-deciduals depends on the extent and duration of summer drought. This revised version was published online in September 2006 with corrections to the Cover Date.