Summer-drought constrains the phenology and growth of two coexisting Mediterranean oaks with contrasting leaf habit: implications for their persistence and reproduction

13 páginas, 9 figuras, 5 tablas.-- El PDF es la versión post-print.This study analyses how coexisting evergreen and deciduous oaks adjust their phenology to cope with the stressful Mediterranean summer conditions. We test the hypothesis that the vegetative and reproductive growth of the winter deciduous (Quercus faginea Lam.) is more affected by summer drought than that of the evergreen [Quercus ilex L. subsp. ballota (Desf.) Samp.]. First, we assessed the complete aboveground phenology of both species during two consecutive years. Shoot and litter production and bud, acorn and secondary growth were monitored monthly. Second, we identified several parameters affected by summer conditions: apical bud size, individual leaf area (LA), leaf mass per area (LMA) and acorn yield in both species, and leaf-fall in Q. faginea; and analysed their variation over 10 years. Q. ilex performed up to 25% of shoot growth and most leaf development during summer, whereas Q. faginea completed most of both phenophases during spring. Secondary growth was arrested in summer under drought conditions. Approximately, 30–40% of bud and 40–50% of acorn growth was undertaken during summer in both species. Summer drought related to differences in LA, LMA and leaf senescence, but not to acorn yield. Both species had similar year-to-year patterns of acorn production, though yields were always lower in Q. faginea. Bud size decreased severely in both species during extremely dry years. In Q. ilex, bud size tended to alternate between years of large and small buds, and these patterns were followed by opposite trends in stem length. In Q. faginea, bud size was more stable through time. Q. ilex was more phenologically active during summer than Q. faginea, indicating a higher tolerance to drought. Furthermore, bud and fruit growth (the only two phenophases that both species performed during summer) were more severely affected by summer drought in Q. faginea than in the evergreen. The differential effects of summer drought on key phenophases for the persistence (bud growth) and colonization ability (fruit production) of both species may have consequences for their coexistence.This study was possible thanks to the collaboration within the GLOBIMED network (Ministerio de Educación y Ciencia, Spain) and it was supported by the MEC-CICyT projects AGF96-0399, CGL2007-66066-C04/BOS and CGL2008- 04847-C02-01, DGA projects P-038/96 and GA-LC-011/2008, and INIA projects RTA2005-00100-C02-00 and SUM2006-00025-00-00. JJC acknowledges the support of the ‘‘Fundación Aragón I+D’’. SP and RM were funded by MEC by a postdoc (SEUI-FECYT) and a Juan de la Cierva contract, respectively. JA was funded by DGA.Peer reviewe

The role of phonological awareness in treatments of dyslexic primary school children

The present study investigated whether phonological awareness training is an effective intervention to significantly improve reading in German dyslexic third and fourth graders with a phonological awareness deficit, and whether these children can equally benefit from a phonology-based reading training or a visually-based reading training. German speaking dyslexic elementary school children (n=30; M=9.8 years) were matched by forming triplets based on IQ, reading quotient and phonological awareness and then randomly assigned to one out of three interventions (n=10): a phonological awareness training, a phonology-based reading training (phonics instruction), and a visually-based reading training (repeated reading of sight words). A total of 20 training sessions (30 minutes each) were distributed over four weeks. Typical readers (n=10; M=9.5 years) were assigned to the control group. Phonological awareness training directly improves reading comprehension in German dyslexic children with a phonological awareness deficit. However, these children can equally benefit from a visually-based reading training. In contrast, the phonology-based reading training has a direct selective effect on decoding but not on reading comprehension. Despite divergent short-term patterns, long-term improvement of reading comprehension and decoding is similar across all training groups, irrespective of the training method. Phonological awareness may but does not need to be part of reading remediation in dyslexic children with a phonological deficit when learning to read a consistent orthography. Rather, a visually-based reading strategy might compensate for the phonological deficit in dyslexic children after the initial stage of reading acquisition

Distinct neural signatures of cognitive subtypes of dyslexia with and without phonological deficits

AbstractDevelopmental dyslexia can be distinguished as different cognitive subtypes with and without phonological deficits. However, despite some general agreement on the neurobiological basis of dyslexia, the neurofunctional mechanisms underlying these cognitive subtypes remain to be identified. The present BOLD fMRI study thus aimed at investigating by which distinct and/or shared neural activation patterns dyslexia subtypes are characterized. German dyslexic fourth graders with and without deficits in phonological awareness and age-matched normal readers performed a phonological decision task: does the auditory word contain the phoneme/a/? Both dyslexic subtypes showed increased activation in the right cerebellum (Lobule IV) compared to controls. Subtype-specific increased activation was systematically found for the phonological dyslexics as compared to those without this deficit and controls in the left inferior frontal gyrus (area 44: phonological segmentation), the left SMA (area 6), the left precentral gyrus (area 6) and the right insula. Non-phonological dyslexics revealed subtype-specific increased activation in the left supramarginal gyrus (area PFcm; phonological storage) and angular gyrus (area PGp). The study thus provides the first direct evidence for the neurobiological grounding of dyslexia subtypes. Moreover, the data contribute to a better understanding of the frequently encountered heterogeneous neuroimaging results in the field of dyslexia

Shared vs. specific brain activation changes in dyslexia after training of phonology, attention, or reading

Whereas the neurobiological basis of developmental dyslexia has received substantial attention, only little is known about the processes in the brain during remediation. This holds in particular in light of recent findings on cognitive subtypes of dyslexia which suggest interactions between individual profiles, training methods, and also the task in the scanner. Therefore, we trained three groups of German dyslexic primary school children in the domains of phonology, attention, or visual word recognition. We compared neurofunctional changes after 4 weeks of training in these groups to those in untrained normal readers in a reading task and in a task of visual attention. The overall reading improvement in the dyslexic children was comparable over groups. It was accompanied by substantial increase of the activation level in the visual word form area (VWFA) during a reading task inside the scanner. Moreover, there were activation increases that were unique for each training group in the reading task. In contrast, when children performed the visual attention task, shared training effects were found in the left inferior frontal sulcus and gyrus, which varied in amplitude between the groups. Overall, the data reveal that different remediation programmes matched to individual profiles of dyslexia may improve reading ability and commonly affect the VWFA in dyslexia as a shared part of otherwise distinct networks

Subtypen-spezifisches Training bei Dyslexie

Kognitive Subtypen von Entwicklungsdyslexie können Defizite vor allem in der Phonologie oder der visuell-räumlichen Aufmerksamkeit haben, die mit hirnfunktionellen Unterschieden zu Normallesern einhergehen. Die subtypenspezifische Aktivierungsänderung durch ein visuelles Aufmerksamkeitstraining wurde bisher noch nicht untersucht.Die vorliegende fMRT-Studie untersucht den Einfluss von defizitspezifischen Trainings vs. Lesetrainings auf die neuronalen Korrelate dyslektischer Subtypen verglichen wiederum mit Normallesern. Dritt- und Viertklässler wurden psychometrischen Tests unterzogen, u. a. zu phonologischen und Aufmerksamkeitsfähigkeiten. Alle Dyslektiker erhielten ein vierwöchiges Training: Dyslektiker mit primär phonologischem Defizit ein rein phonologisches Training, Kinder mit primärem Aufmerksamkeitsdefizit ein Aufmerksamkeitstraining. Ein reines Lesetraining erhielt eine dritte Dyslexiegruppe: Dyslektiker unabhängig von ihrem kognitiven Defizit. Mittels fMRT wurde vor und nach dem Training das Posner Paradigma zur visuell-räumlichen Aufmerksamkeitsausrichtung mit den drei Trainingsgruppen und einer vierten Gruppe, den Normallesern, durchgeführt, um zu untersuchen, wie sich das Training auf die neurofunktionelle Verarbeitung der drei Dyslexiegruppen auswirkt. Die fMRT-Daten ergaben für alle Trainingsgruppen eine signifikante Veränderung im linken inferioren Frontalcortex. Das Maximum dieser Aktivierungsveränderung lag jedoch jeweils an verschiedenen Stellen innerhalb dieser Region: für die Trainingsgruppe Phonologie auf dem GFI in der Broca-Region, für die Trainingsgruppen Aufmerksamkeit und Lesen jeweils im Sulcus frontalis inferior. Die drei Gruppen verarbeiten möglicherweise verschiedene Funktionen in dieser sehr heterogenen Region. Das linkshemisphärische Aktivierungsmuster könnte somit auf unterschiedliche Kompensation nach den verschiedenen Dyslexie-Trainings hinweisen, die nicht in klassischen rechts-hemisphärischen Aufmerksamkeitsarealen, sondern im linkshemispärischen Sprachnetzwerk lokalisiert sind

Multi-parameter machine learning approach to the neuroanatomical basis of developmental dyslexia

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