Dynamics and Biological Interactions of Phosphorus Cycling in Central Amazonian Forests

Soil nutrient availability is considered to constrain the productivity of terrestrial ecosystems, with phosphorus (P) considered to be the most limiting nutrient in tropical forests. Due the great importance of Amazon forests in carbon (C) cycling and the fact that the majority of Amazon forests grow in low-fertility soils, understanding how nutrient limitation may affect net primary productivity (NPP) in these ecosystems is crucial to predict C storage in response to future climate. The direct effects of nutrient limitation on above and belowground forest functioning can only be tested through experimentation and up to now, the few large scale fertilisation experiments installed in lowland tropical forests indicate that multiple nutrients may limit different aspects of tropical forests, with inconsistent evidence for P limitation. Since much less is known about the potential effects of nutrient limitation on belowground forest functioning, this research aimed to analyse the main belowground mechanisms involved in P cycling, and how roots and soil microorganisms adapt to different conditions of soil fertility in central Amazon forests. I investigated how root morphological traits, mycorrhizal colonisation as well as enzyme exudation both from roots and soil microbes were expressed in natural low-fertility soils and how these traits responded to the short-term addition of P, nitrogen (N) and cations, as part of the first large-scale soil nutrient manipulation experiment in a central Amazon lowland forest near Manaus, Brazil. I show that in natural low-fertility soils, roots display a range of adaptations to increase P-uptake efficiency and investments in root morphological and physiological adaptations as well as association with fungi symbionts are complementary towards maintaining forest productivity in a central Amazon forest. With nutrient addition, I found support for the hypothesis of P-limitation, since trees were able to rapidly adapt their root morphological traits, reduce investments in enzyme exudation and increase association with mycorrhizal fungi. Such responses were also affected by cation addition, reinforcing the idea that multiple nutrients may control the expression of root traits. The soil microbial community was also affected by the short-term addition of nutrients, with a reduction in enzyme production with the addition of phosphorus, indicating a rapid alleviation of phosphorus limitation, but this reduction was eliminated when cations were also added. My results suggest that plants and soil microorganisms can rapidly respond to changes in soil nutrient Abstract 4 availability by changing their investments in nutrient uptake mechanisms, ultimately impacting plant productivity. These responses are crucial if we are to better understand how these forests function and how they may respond to global change.Natural Environment Research Council (NERC

Stream ambient noise, spectrum and propagation of sounds in the goby Padogobius martensii: Sound pressure and particle velocity

The most sensitive hearing and peak frequencies of courtship calls of the stream goby, Padogobius martensii, fall within a quiet window at around 100Hz in the ambient noise spectrum. Acoustic pressure was previously measured although Padogobius likely responds to particle motion. In this study a combination pressure (p) and particle velocity (u) detector was utilized to describe ambient noise of the habitat, the characteristics of the goby’s sounds and their attenuation with distance. The ambient noise (AN) spectrum is generally similar for p and u (including the quiet window at noisy locations), although the energy distribution of uspectrum is shifted up by 50–100Hz. The energy distribution of the goby’s sounds is similar for p and uspectra of the Tonal sound, whereas the pulse-train sound exhibits larger p–u differences. Transmission loss was high for sound p and u: energy decays 6–10dB∕10cm, and sound p∕u ratio does not change with distance from the source in the nearfield. The measurement of particle velocity of stream AN and P. martensiisounds indicates that this species is well adapted to communicate acoustically in a complex noisy shallow-water environment

Acoustic communication in two freshwater gobies: Ambient noise and short-range propagation in shallow streams

Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra weremeasured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200–500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations

Sea Tide Influence on Ice Flow of David Drygalski’s Ice Tongue Inferred from Geodetic GNSS Observations and SAR Offset Tracking Analysis

David Glacier and Drygalski Ice Tongue are massive glaciers in Victoria Land, Antarctica. The ice from the East Antarctic Ice Sheet is drained through the former, and then discharged into the western Ross Sea through the latter. David Drygalski is the largest outlet glacier in Northern Victoria Land, floating kilometers out to sea. The floating and grounded part of the David Glacier are the main focus of this article. During the XXI Italian Antarctic Expedition (2005-2006), within the framework of the National Antarctic Research Programme (PNRA), two GNSS stations were installed at different points: the first close to the grounding line of David Glacier, and the second approximately 40 km downstream of the first one. Simultaneous data logging was performed by both GNSS stations for 24 days. In the latest data processing, the kinematic PPP technique was adopted to evaluate the dominant diurnal components and the very small semi-diurnal variations in ice motion induced by the ocean tide and the mean ice flow rates of both GNSS stations. Comparison of the GNSS time series with predicted ocean tide calculated from harmonic coefficients of the nearest tide gauge stations, installed at Cape Roberts and Mario Zucchelli Station, highlight different local response of the glacier to ocean tide, with a minor amplitude of vertical motion at a point partially anchored at the bedrock close to the grounding line. During low tide, the velocity of the ice flow reaches its daily maximum, in accordance with the direction of seawater outflow from the fjord into the ocean, while the greatest daily tidal excursion generates an increase in the horizontal ice flow velocity. With the aim to extend the analysis in spatial terms, five COSMO-SkyMED Stripmap scenes were processed. The comparison of the co-registered offset tracking rates, obtained from SAR images, with the GNSS estimation shows good agreement

Alice in wonderland: experimental jurisprudence on the internal point of view

Humans have this extraordinary cognitive ability: They imagine inexistent objects, they treat them as if they were real, and by doing so they make them real. They thus give rise to a shared institutional reality that enables them to cooperate in ways that would be impossible otherwise. In this paper, we would like to revisit the account that HLA Hart gives of the practice of collective acceptance that makes a legal system possible. We try to provide an explanation of what Hart calls the 'internal point of view', on the basis of experiments on institutional concepts, drawing on the paradigm known as 'embodied cognition'. Experts and non-experts in law rated the role of several cognitive dimensions for a list of words referring to two kinds of abstract concepts (institutional and theoretical/scientific) and two kinds of concrete ones (food and artifact). Institutional concepts were distinguished into pure-institutional (e.g., 'contract', 'state', 'property') and meta-institutional (e.g., 'norm', 'duty', 'justice'). The results provide an empirical account of how our way of thinking about institutions changes as we acquire expertise in the legal field, thus shading light on the cognitive underpinnings of the 'internal point of view'