Geothermally warmed soils reveal persistent increases in the respiratory costs of soil microbes contributing to substantial C losses

Increasing temperatures can accelerate soil organic matter decomposition and release large amounts of CO₂ to the atmosphere, potentially inducing positive warming feedbacks. Alterations to the temperature sensitivity and physiological functioning of soil microorganisms may play a key role in these carbon (C) losses. Geothermally active areas in Iceland provide stable and continuous soil temperature gradients to test this hypothesis, encompassing the full range of warming scenarios projected by the Intergovernmental Panel on Climate Change for the northern region. We took soils from these geothermal sites 7 years after the onset of warming and incubated them at varying temperatures and substrate availability conditions to detect persistent alterations of microbial physiology to long-term warming. Seven years of continuous warming ranging from 1.8 to 15.9 °C triggered a 8.6–58.0% decrease on the C concentrations in the topsoil (0–10 cm) of these sub-arctic silt-loam Andosols. The sensitivity of microbial respiration to temperature (Q₁₀) was not altered. However, soil microbes showed a persistent increase in their microbial metabolic quotients (microbial respiration per unit of microbial biomass) and a subsequent diminished C retention in biomass. After an initial depletion of labile soil C upon soil warming, increasing energy costs of metabolic maintenance and resource acquisition led to a weaker capacity of C stabilization in the microbial biomass of warmer soils. This mechanism contributes to our understanding of the acclimated response of soil respiration to in situ soil warming at the ecosystem level, despite a lack of acclimation at the physiological level. Persistent increases in the respiratory costs of soil microbes in response to warming constitute a fundamental process that should be incorporated into climate change-C cycling models.     

Socioecological Factors Affecting Range Defensibility Among Howler Monkeys

Range defensibility is defined as the ability of animals to efficiently move over an area to monitor and defend it. Therefore, range defensibility can help us understand the spatial structure of animal territoriality. We used howler monkeys (Alouatta spp.), a genus for which no agreement on the extent of their territoriality exists, to investigate the factors mediating range defensibility. We compared the defensibility index (D) across 63 groups of howler monkeys, representing 8 different species, based on a literature review. All species, except Alouatta palliata, were classified as potentially territorial according to D, although there was high variability within and among species. Group size had a positive effect on D, probably owing to the greater ability of groups to defend a territory as they become larger. Study area had a negative effect on D, perhaps suggesting that unlike small areas, large areas allow groups to have territories that do not require significant defense from neighbors. However, population density was the factor with the strongest effect on D, with greater monitoring of home ranges under high levels of competition. Our results suggest that howler monkeys are theoretically capable of maintaining a territory and suggest that animals can show a gradient in territoriality, which can be mediated by the competitive context in which it occurs.     

The effect of bioturbation by polychaetes (Opheliidae) on benthic foraminiferal assemblages and test preservation

Biological activity such as burrowing can alter benthic foraminiferal shell preservation and may also modify benthic foraminiferal assemblages by vertical mixing, inducing sediment homogenization. Here, we analyse benthic foraminiferal assemblages and taphonomy of upper Miocene marine deposits from Conil de la Frontera (Cádiz, south‐western Spain). The deposits consist of marls displaying a pervasive alternation of intensively bioturbated beds dominated by Macaronichnus segregatis traces (ichnofabric index 4–5) and non‐bioturbated beds. Benthic foraminiferal assemblages are dominated by Cibicidoides mundulus and Cibicides refulgens, indicating that the marls were deposited on an oligotrophic, well‐oxygenated upper slope. The impact of burrowing on the preservation of benthic foraminiferal tests was tested using Q‐mode cluster analysis, which found two well‐differentiated groups of samples, one including the non‐bioturbated beds and the other encompassing the bioturbated ones. Fragmentation and recrystallization account for the differentiation of these groups, both being higher in the bioturbated sediments. Aggressive chemical digestion by the Macaronichnus trace‐makers, assumed to be a polychaete worm of the family Opheliidae, etched the microfossil shells, making them more vulnerable to fragmentation. Intense bioturbation favoured the circulation of pore fluids, encouraging recrystallization. Pervasive burrowing resulted in significant vertical reworking of microfossils. As a consequence, benthic foraminiferal assemblages in the bioturbated beds were homogenized in the mixed layer; that is, the uppermost layer of the substrate totally burrowed. The alternation of bioturbated and non‐bioturbated beds reflects episodic transfer of food particles down slope from shallower parts of the shelf as well as from the continent due to storms under otherwise homogeneous oligotrophic marine conditions.     

Rainfall reduction impacts rhizosphere biogeochemistry in eucalypts grown in a deep Ferralsol in Brazil

Plant and Soil - Comparing root functioning under contrasting rainfall regimes can help assessing the capacity of plant species to cope with more intense and frequent drought predicted under...     

Effects of long-term experimental night-time warming and drought on photosynthesis, <Emphasis Type="Italic">F</Emphasis>v/<Emphasis Type="Italic">F</Emphasis>m and stomatal conductance in the dominant species of a Mediterranean shrubland

We conducted a night-time warming and drought field experiment for 7 years (1999–2005) in a Mediterranean shrubland. We focused on the two dominant shrub species, Erica multiflora L. and Globularia alypum L. and the tree Pinus halepensis L. and the final years to study the effects of the experimental night-time warming and drought on Fv/Fm, photosynthesis, and stomatal conductance. Warming treatment increased mean air temperature and mean soil temperature through the years by an average of 0.7 and 0.9°C respectively, and drought treatment reduced soil moisture through the years by an average of 19%. Warming tended to increase photosynthetic rates in E. multiflora, G. alypum and P. halepensis mostly in the cold seasons, when plants were more limited by temperature, as shown by the lowest values of Fv/Fm being detected in winter in the three studied species. A negative effect of warming was only detected for E. multiflora in summer 2003. Drought treatment generated different responses of net photosynthetic rates depending on the species, season and year. Stomatal conductance showed the same pattern as photosynthesis for the three studied species, displaying seasonal and inter-annual variability, although with an overall negative effect of drought for P. halepensis. Photosynthetic rates decreased significantly in the dry winter 2005 and spring 2005 in comparison to the same seasons of 2003 and 2004. There were positive correlations between the photosynthetic rates in different seasons for E. multiflora, G. alypum and P. halepensis and the soil moisture of the week prior to measurements. The great variation in the photosynthetic rates was thus explained in a significant part by soil moisture levels. The lowest Fv/Fm values usually corresponded with lowest stomatal conductances suggesting that drought stress could be associated to stress by low temperatures in winter.     

Mobilization of Neural Stem Cells and Generation of New Neurons in 6-OHDA�Clesioned Rats by Intracerebroventricular Infusion of Liver Growth Factor

Neural stem cells with self-renewal and multilineage potential persist in the subventricular zone of the adult mammalian forebrain. These cells remain relatively quiescent but, under certain conditions, can be stimulated, giving rise to new neurons. Liver growth factor (LGF) is a mitogen for liver cells that shows biological activity in extrahepatic sites and is useful for neuroregenerative therapies. The aim of this study was to investigate the potential neurogenic activity of LGF in the 6-hydroxydopamine rat model of Parkinson''s disease. Proliferation was significantly increased in the subventricular zone and denervated striatum of rats receiving ICV LGF infusions, and 25% of the proliferating cells were doublecortin-positive neurons. Doublecortin-positive cells with the morphology of migrating neuroblasts were also observed in the dorsal and ventral regions of the striatum of LGF-infused animals. Moreover, some newly generated cells were neuronal nuclei-positive mature neurons. LGF also stimulated microglia and induced astrogliosis, both phenomena associated with generation and migration of new neurons in the adult brain. In summary, our study shows that LGF stimulates neurogenesis when applied intraventricularly in 6-hydroxydopamine–lesioned rats. Considering that this factor also promotes neuronal migration into damaged tissue, we propose LGF as a novel factor useful for neuronal replacement in neurodegenerative diseases. (J Histochem Cytochem 57:491–502, 2009)     

The introduction of fluorine atoms or trifluoromethyl groups in short cationic peptides enhances their antimicrobial activity

The effect of introducing fluorine atoms or trifluoromethyl groups in either the peptidic chain or the C-terminal end of cationic pentapeptides is reported. Three series of amide and ester peptides were synthesised and their antimicrobial properties evaluated. An enhanced activity was found in those derivatives whose structure contained fluorine, suggesting an increase in their hydrophobicity.     

Chlorophyll fluorescence responses to temperature and water availability in two co-dominant Mediterranean shrub and tree species in a long-term field experiment simulating climate change

A rain exclusion experiment simulating drought conditions expected in Mediterranean areas for the following decades (15% decrease in soil moisture) is being conducted since 1999 in a Mediterranean holm oak forest to study its response to the forecasted climatic changes for the coming decades. The maximum PSII quantum yield of primary photochemistry (Fv/Fm) was measured in Quercus ilex, and Phillyrea latifolia, the co-dominant species of the studied forest, from 1999 to 2009 in four plots: two of them were control plots and the other two plots received the rain exclusion treatment. In both species, the Fv/Fm values were highly dependent on air temperatures, and in a second term, in water availability. P. latifolia was the species with the larger decrease in Fv/Fm values induced by low air temperatures, while in hot seasons, the Fv/Fm values in P. latifolia were even higher than in Q. ilex. Rainfall exclusion decrease Fv/Fm values significantly only in few monitoring dates. The most drought resistant species P. latifolia was more affected by the experimental rainfall exclusion than Q. ilex that instead lost number of leaves per tree. There was a synergic effect of drought stress and winter cold in P. latifolia not observed in Q. ilex, but a more conservative strategy in P. latifolia maintaining leaves with a down-regulation of the linear photosynthetic electron transport. These results indicate that, although other physiological and reproductive strategies at whole plant level must be also taken into account, the warmer and drier environment expected for the following decades could favour the species more sensitive to cold and more resistant to drought, the shrub P. latifolia, in detriment of the tree Q. ilex as already observed in the field after severe heat-drought episodes.