Plant Responses to Extreme Climatic Events: A Field Test of Resilience Capacity at the Southern Range Edge

The expected and already observed increment in frequency of extreme climatic events may result in severe vegetation shifts. However, stabilizing mechanisms promoting community resilience can buffer the lasting impact of extreme events. The present work analyzes the resilience of a Mediterranean mountain ecosystem after an extreme drought in 2005, examining shoot-growth and needle-length resistance and resilience of dominant tree and shrub species (Pinus sylvestris vs Juniperus communis, and P. nigra vs J. oxycedrus) in two contrasting altitudinal ranges. Recorded high vegetative-resilience values indicate great tolerance to extreme droughts for the dominant species of pine-juniper woodlands. Observed tolerance could act as a stabilizing mechanism in rear range edges, such as the Mediterranean basin, where extreme events are predicted to be more detrimental and recurrent. However, resistance and resilience components vary across species, sites, and ontogenetic states: adult Pinus showed higher growth resistance than did adult Juniperus; saplings displayed higher recovery rates than did conspecific adults; and P. nigra saplings displayed higher resilience than did P. sylvestris saplings where the two species coexist. P. nigra and J. oxycedrus saplings at high and low elevations, respectively, were the most resilient at all the locations studied. Under recurrent extreme droughts, these species-specific differences in resistance and resilience could promote changes in vegetation structure and composition, even in areas with high tolerance to dry conditions.This study was supported by Ministerio de Ciencia e Innovación (Spanish Government) Projects CGL2008-04794 and CGL2011-29910 to R.Z., and by grant FPU-MEC (AP2005-1561) to A. H

Is variation in susceptibility to Phytophthora ramorum correlated with population genetic structure in coast live oak (Quercus agrifolia)?

* California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within- and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. * Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. * Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. * Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high

Evidence for the role of synchronicity between host phenology and pathogen activity in the distribution of sudden oak death canker disease

Variations in synchronicity between colonization rate by the pathogen and host phenology may account for unexplained spatial distribution of canker disease. The hypothesis that synchronous pathogenicity and host development are necessary for incidence of sudden oak death disease was tested by correlating seasonal variations in host cambial phenology and response to inoculation with Phytophthora ramorum. • Response to infection was estimated by inoculating branch cuttings from coast live oak (Quercus agrifolia) trees at nine dates through a full annual cycle in2003-2004 . Host phenology was estimated from measurements of bud burst and cambial activity in spring 2006. • Lesions were largest in the spring soon after the cambium resumed activity. A moderate genetic component to lesion size was detected. Variation among trees in date of largest lesions correlated with variation in timing of bud burst and cambial phenology. • The data support the hypothesis that active host cambial tissue is a necessary requisite for successful infection with the pathogen that causes sudden oak death canker disease. Genetic variation in host phenology will buffer coast live oak against epidemics of this diseas

Origin identification of Pinus nigra populations in southwestern Europe using terpene composition variations

The geographical variation of terpenes of Pinus nigra populations from southwestern Europe was studied. Terpenes from the foliage of 16 populations from Corsica, Herault (France) and the East Pyrenees (France and Spain) were analyzed. A total of 42 terpenes were detected, with alpha-pinene the dominant monoterpene and germacrene-d and caryophyllene the dominant sesquiterpenes. The differences in quantitative content of selected compounds clearly divide populations into two basic geographical groups: on one side the populations from Herault and the East Pyrenees and on the other the populations from Corsica. beta-Phellandrene and delta-cadinene have the greatest influence on this global discrimination. Some trees and populations show a similarity although they belong to different geographic locations. The similarity of some trees from Herault and the East Pyrenees and trees from Corsica points to their common origin (Corsica). Our results confirm the hypothesis that the afforestation of Herault and the East Pyrenees was also performed with black pine from Corsica.nul

Origin identification of Pinus nigra populations in southwestern Europe using terpene composition variations

The geographical variation of terpenes of Pinus nigra populations from southwestern Europe was studied. Terpenes from the foliage of 16 populations from Corsica, Herault (France) and the East Pyrenees (France and Spain) were analyzed. A total of 42 terpenes were detected, with alpha-pinene the dominant monoterpene and germacrene-d and caryophyllene the dominant sesquiterpenes. The differences in quantitative content of selected compounds clearly divide populations into two basic geographical groups: on one side the populations from Herault and the East Pyrenees and on the other the populations from Corsica. beta-Phellandrene and delta-cadinene have the greatest influence on this global discrimination. Some trees and populations show a similarity although they belong to different geographic locations. The similarity of some trees from Herault and the East Pyrenees and trees from Corsica points to their common origin (Corsica). Our results confirm the hypothesis that the afforestation of Herault and the East Pyrenees was also performed with black pine from Corsica.nul

Taxonomic study of subfamily Nepetoideae (Lamiaceae) by polynomorphological approach

The present study is insight into pollen morphology for characterizing species and their utility in the taxonomic separation of certain taxa of subfamily Nepetoideae (Lamiaceae) from Pakistan. The pollen micromorphology of 11 species of the Nepetoideae was analyzed and documented using light microscopy and scanning electron microscopy (SEM) for both qualitative and quantitative characteristics. Most species have hexazonocolpate pollen grains but trizonocolpate and tetrazonocolpate pollen with circular and oval amb were also rarely observed in Mentha spicata. The basic pollen shape in most of the studied species was subspheroidal but prolate grains were also observed in M. spicata, S. coccinea, and S. plebeia. The exine sculpturing of Nepetoideae pollen was taxonomically very informative particularly at subfamily level. Observations of exine sculpturing with SEM revealed various types of pollen grains: reticulate, bireticulate, microreticulate, perforate, aerolate, and gammate. The bireticulate type further subdivided into three subtypes based on the number of secondary lumina in each primary lumen and is characterized by varying characteristics of the secondary reticulum and primary muri. A significant variation was observed in colpus surface ornamentation. The maximum polar diameter was found in O. americanum (58 +/- 5.8 mu m) and the maximum equatorial diameter observed in O. basilicum (50.25 +/- 1.37 mu m). Pollen features of the studied species were discussed and compared based on the current taxonomical concepts. The results showed that pollen traits of the subfamily Nepetoideae was found significant to classify the taxa. Furthermore, pollen features provide additional evidence to distinguish macromorphologically similar taxa from each other