Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.

A Definitive Book on Seed Ecology@@@Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination

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Critical review of the impacts of grazing intensity on soil organic carbon storage and other soil quality indicators in extensively managed grasslands.

Summary 1. Ecosystem invasibility is determined by combinations of environmental variables, invader attributes, disturbance regimes, competitive abilities of resident species and evolutionary history between residents and disturbance regimes. Understanding the relative importance of each factor is critical to limiting future invasions and restoring ecosystems. 2. We investigated factors potentially controlling Bromus tectorum invasions into Artemisia tridentata ssp. wyomingensis communities across 75 sites in the Great Basin. We measured soil texture, cattle grazing intensity, gaps among perennial plants and plant cover including B. tectorum, biological soil crusts (BSCs) and bare soil. Using a priori knowledge, we developed a multivariate hypothesis of the susceptibility of Artemisia ecosystems to B. tectorum invasion and used the model to assess the relative importance of the factors driving the magnitude of such invasions. 3. Model results imply that bunchgrass community structure, abundance and composition, along with BSC cover, play important roles in controlling B. tectorum dominance. Evidence suggests abundant bunchgrasses limit invasions by limiting the size and connectivity of gaps between vegetation, and BSCs appear to limit invasions within gaps. Results also suggest that cattle grazing reduces invasion resistance by decreasing bunchgrass abundance, shifting bunchgrass composition, and thereby increasing connectivity of gaps between perennial plants while trampling further reduces resistance by reducing BSC. 4. Synthesis and applications. Grazing exacerbates Bromus tectorum dominance in one of North America’s most endangered ecosystems by adversely impacting key mechanisms mediating resistance to invasion. If the goal is to conserve and restore resistance of these systems, managers should consider maintaining or restoring: (i) high bunchgrass cover and structure characterized by spatially dispersed bunchgrasses and small gaps between them; (ii) a diverse assemblage of bunchgrass species to maximize competitive interactions with B. tectorum in time and space; and (iii) biological soil crusts to limit B. tectorum establishment. Passive restoration by reducing cumulative cattle grazing may be one of the most effective means of achieving these three goals.

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Conditions favouring Bromus tectorum dominance of endangered sagebrush steppe ecosystems

 Premise of the study : Atripliceae (Chenopodiaceae), including Atriplex (300 spp.) as the largest genus of the family, are an ecologically important group of steppes and semideserts worldwide. Relationships in Atripliceae are poorly understood due to obscure and potentially convergent morphological characters.  Methods : Using sequence variation of two chloroplast markers ( rbcL gene, atpB-rbcL spacer) and one nrDNA marker (ITS) analyzed with BEAST, we investigated the systematics and biogeography of Atripliceae. We surveyed fl ower morphology and fruit anatomy to study the evolution of fland fruits in the tribe.  Key results : Female fl owers with persistent foliar cover (the diagnostic character of traditional Atripliceae) evolved three times in Chenopodioideae, in Atripliceae s.s., Axyrideae, and Spinacia . Atripliceae s.s. started to diversify during the Early Miocene in Eurasia, separating into the Archiatriplex and the Atriplex clades. The former consists of eight species-poor, disjunct, and morphologically heterogeneous genera and is likely a relictual lineage. The Atriplex clade comprises the majority of species and evolved one C 4 lineage 14.1 – 10.5 Ma, which diversifi ed rapidly worldwide. The C 4 Atriplex entered North America during the Middle/Late Miocene and spread to South America subsequently. Australia was colonized by two C 4 lineages both arriving during the Late Miocene. One of them diversifi ed rapidly, giving rise to most Australian Atriplex species.  Conclusions : Atripliceae s.s. comprise Archiatriplex , Atriplex , Exomis, Extriplex , Grayia , Halimione , Holmbergia , Manochlamys , Proatriplex , and Stutzia . Microgynoecium is included based on morphology but only weak molecular support. Axyris , Krascheninnikovia , and Ceratocarpus (here described as Axyrideae) and Spinacia are excluded from Atripliceae.

Molecular phylogeny of Atripliceae (Chenopodioideae, Chenopodiaceae): Implications for systematics, biogeography, flower and fruit evolution, and the origin of C4 photosynthesis.

Soil seed bank in and between vegetation patches in arid Patagonia, Argentina

Wet meadows are important ecosystems for forage production and as carbon reservoirs in semi-arid areas. In Patagonia, Argentina, large areas of wet meadows have been classified as overgrazed by livestock. The objective of this study was to determine whether long-term overgrazing has affected carbon (C) storage in plant and soil pools in wet and mesic meadows. The study occurred in Northern Patagonia, in three study sites located along a precipitation gradient. Our results indicate that long-term overgrazing reduced, on average, 35 % of the total ecosystem C pool. There was significantly lower aboveground and belowground plant production in heavily grazed compared to lightly grazed sites, 419 ± 262 – 128 ± 110 g m2 year−1 and 3796 ± 2622 – 1702 ± 1012 g m2 year−1, respectively. Soil C concentrations were also less in heavily grazed sites (184 ± 98 – 105 ± 58 g kg−1 at 1 m depth, respectively). The response of meadows to long-term heavy grazing also appears to be influenced by different levels of precipitation, with sites in drier areas being apparently more susceptible to overgrazing. Our results indicate that new management and restoration practices are needed to stop and reverse meadow deterioration in degraded meadows of Northern Patagonia.

Grazing intensity levels influence C reservoirs of wet and mesic meadows along a precipitation gradient in Northern Patagonia

Vegetation of arid and semiarid environments has in general a patchy distribution. Our objective was to (a) determine several qualitative and quantitative analytical characteristics of vegetation patches in an arid zone of Patagonia, Argentina, and (b) investigate relationships between them. Annual precipitation in this area was 200 mm during 1999–2005. Eight transects involving ten patches each were studied within a 15 × 15 km area. Mean (±1 SE) values (n = 80) in the vegetation patches were 315 ± 25 and 207 ± 16 cm for the greatest and lowest patch diameter, respectively; 23 ± 2 cm for mound height; 113 ± 12 cm for maximum vegetation height; and 170 ± 18 cm and 58 ± 2% for distance to the next vegetation patch and vegetation patch cover within a transect, respectively. Correlations between greatest and lowest diameters, mound height, maximum plant height and distance to the closest vegetation patch were all significant (P 45%) was found for Stipa spp., Atriplex lampa and the shrubs Larrea divaricata Cav., Lycium chilense Miers ex Bertero and Junellia ligustrina (Lag.) Moldenke. Larrea divaricata and Atriplex lampa contributed more than 84% of the total patch standing crop (5,777 ± 435 g). Average patch size and specific diversity were 5.93 ± 0.33 m2 and 1.31 ± 0.11, respectively. Aboveground standing crop of the two dominant shrubs decreased as plant species diversity increased (P < 0.05). Conservation of vegetation patches is crucial to prevent increased soil erosion and desertification in the study ecological system.

Structure of vegetation patches in northwestern Patagonia, Argentina

Los humedales representan un componente importante de los ecosistemas andinos debido a su biodiversidad y endemismos, y a los numerosos servicios ambientales que ofrecen. A pesar de esto, el conocimiento basico acerca de los tipos de humedales y su funcionamiento ecohidrologico es escaso. El objetivo de este trabajo fue caracterizar los tipos y condiciones ecohidrologicas de humedales a lo largo de un gradiente de precipitacion en el norte de Patagonia. Aprovechamos el gradiente de precipitacion notable que existe como consecuencia de la barrera geografica de la Cordillera de los Andes en las cercanias de la ciudad de San Carlos de Bariloche. Seleccionamos cinco humedales representativos a una altitud semejante, pero bajo regimenes de precipitacion muy diferentes. En cada sitio realizamos analisis quimicos de agua y suelo, y registramos los niveles freaticos y la composicion floristica. Todos los parametros hidrologicos, quimicos y de vegetacion variaron con la precipitacion. En las zonas mas humedas se encontraron las turberas de Sphagnum que durante todo el ano presentaron el suelo saturado con un horizonte de turba. Los mallines se ubicaron en las zonas mas secas. Muestreamos tres comunidades diferentes: mallines humedos con Juncus balticus, mallines mesicos con Festuca pallescens y mallines salinos con Distichlis spicata, cada uno con un regimen hidrologico, quimica del agua y vegetacion diferente. Encontramos pantanos en las zonas intermedias del gradiente, con agua en superficie y suelos minerales, vegetados con Nothofagus antarctica y Scirpus spp. Estos resultados indican la importancia de la precipitacion en la estructura de los humedales y sugieren que cualquier modificacion de los regimenes pluviometricos podria causar cambios significativos en estos ecosistemas.

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Ecohydrological conditions of wetlands along a precipitation gradient in Patagonia, Argentina

The effects of various temperature combinations and water potentials were determined on the germination of Atriplex lampa Gill. ex Moquin, Larrea divaricata Cav., Leymus erianthus (Phil.) Dubcovsky, Stipa neaei Nees ex Steudel and Poa ligularis Nees ap. Steudel under controlled conditions. The tested hypothesis was that seed germination increases with increasing temperatures and water potentials in A. lampa, L. divaricata, L. erianthus, S. neaei and P. ligularis, and that time to reach 50% of total ger- mination is greater at lower than higher water potentials. PEG 2000 was used to impose water stress conditions. In general, obtained results conducted to accept the posted hyphotesis.

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Griselda Luz Bonvissuto

Papers

Soil seed bank in and between vegetation patches in arid Patagonia, Argentina

Grazing intensity levels influence C reservoirs of wet and mesic meadows along a precipitation gradient in Northern Patagonia

Structure of vegetation patches in northwestern Patagonia, Argentina

Ecohydrological conditions of wetlands along a precipitation gradient in Patagonia, Argentina

Germination of grasses and shrubs under various water stress and temperature conditions