Rubisco activity in Mediterranean species is regulated by the chloroplastic CO2 concentration under water stress

Water stress decreases the availability of the gaseous substrate for ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) by decreasing leaf conductance to CO2. In spite of limiting photosynthetic carbon assimilation, especially in those environments where drought is the predominant factor affecting plant growth and yield, the effects of water deprivation on the mechanisms that control Rubisco activity are unclear. In the present study, 11 Mediterranean species, representing different growth forms, were subject to increasing levels of drought stress, the most severe one followed by rewatering. The results confirmed species-specific patterns in the decrease in the initial activity and activation state of Rubisco as drought stress and leaf dehydration intensified. Nevertheless, all species followed roughly the same trend when Rubisco activity was related to stomatal conductance (gs) and chloroplastic CO2 concentration (Cc), suggesting that deactivation of Rubisco sites could be induced by low Cc, as a result of water stress. The threshold level of Cc that triggered Rubisco deactivation was dependent on leaf characteristics and was related to the maximum attained for each species under non-stressing conditions. Those species adapted to low Cc were more capable of maintaining active Rubisco as drought stress intensified

Drought effects on water flow, photosynthesis and growth of potted grapevines

In two consecutive years and under different environmental conditions, leaf gas exchange, sap flow and trunk diameter were measured to estimate transpiration of grapevine. Daily maxima of sap flow were lower than estimations obtained by gas exchange measurements. Sap flow was delayed with regard to variation of irradiance. For irrigated plants the correlation between transpiration rates of single leaves as determined by gas exchange and instantaneous sap flow was high (r2=0.84). However, the correlation of sap flow with the total daily water consumption was even higher (r2=0.98) and close to 1:1. At various water states, leaf photosynthetic rate was also correlated with sap flow (r2=0.78); the correlation coefficient increased to r2=0.91 when the daily balance was compared. Plant growth, estimated from linear variable displacement transducers was closely related to the daily sap flow.

Distribution of leaf photosynthesis and transpiration within grapevine canopies under different drought conditions

The effects of seasonal drought on the distribution of leaf area, photosynthesis and transpiration within the canopy were evaluated for two Spanish grapevine cultivars. Both varieties were cultivated according to their typical training system.At early stages of drought, reduction of photosynthesis and transpiration was only observed in sun-exposed leaves. As drought intensified, even less sun-exposed leaves were affected. Severe drought reduced photosynthesis and transpiration in all locations of the canopy except for most shaded leaves in the inner part. However, those leaves were almost unproductive, and seemed to be insensitive to variation of both light intensity and drought. Leaf area was also reduced by drought, but the distribution of these reductions within the canopy differed between cultivars, possibly reflecting differences in the training system.Leaves from all locations of the canopy except those in the central part showed a similar radiation use efficiency, suggesting that the observed variation in photosynthesis within the canopy was mostly related to different light interception, while other factors such as different leaf age should play only a minor role. Photosynthetic radiation use efficiency strongly depended on both, pre-dawn leaf water potential and light-saturated stomatal conductance. The interest of these results for modeling purposes is discussed.

CO2/O2 specificity factor of ribulose-1,5-bisphosphate carboxylase/oxygenase in grapevines (Vitis vinifera L.): First in vitro determination and comparison to in vivo estimations

The specificity factor (S) of ribulose-1,5-bisphosphate. carboxylase/oxygenase (Rubisco) defines the relative rates of carboxylation and oxygenation of Ribulose-1,5-bisphosphate (RuBP) catalysed by the enzyme. The determination of S for Rubisco purified from the Vitis vinifera L. cvs Tempranillo and Manto Negro is described here for the first time. Rubisco extraction was made in Bicine buffer with the inclusion of polyethylene glycol (PEG), beta-mereaptoethanol, diethyldithio-carbamic acid (DIECA) and several protease inhibitors. Furthermore, in the same cultivars, the apparent in vivo specificity factor for Rubisco (S*), was obtained from gas exchange and chlorophyll fluorescence measurements. For both cultivars the values of S were close to 100 at 25 degreesC. However, in mature leaves, S* was about 67 for Manto Negro and 55 or 77 for Tempranillo, depending on leaf age. Leaves of plants under drought showed even lower values. These discrepancies between S and S* are ascribed to equating CO2 in the sub-stomatal cavity with CO2 at the Rubisco catalytic site in the chloroplast. However, S* values from young developing leaves were very close to S for both cultivars. It is concluded that estimations of S* based on gas exchange and chlorophyll fluorescence data are reliable only in thin, young and non-stressed leaves.

Surface mesoscale pico–nanoplankton patterns at the main fronts of the Alboran Sea

© 2014 Elsevier B.V. The mesoscale (10-100. km, days-weeks) plays a key role in the Ocean's ecosystem structure and dynamics. This work compares the pico-nanoplankton patterns observed in the Alboran Sea (Western Mediterranean) during three oceanographic cruises. We analyse its response to different expressions of mesoscale circulation associated with the three major hydrodynamic features in the basin; namely the Northwestern Alboran Front (NWAF, surveyed in OMEGA-1 cruise), the Almeria-Oran Front (AOF, surveyed in OMEGA-2 cruise) and the Western Alboran Gyre (WAG, surveyed in BIOMEGA cruise). The first two surveys were carried out under the most typical quasi-stationary twin gyre conditions of the Alboran Sea, whereas the third cruise was performed after an eastward migration of the WAG. The analysis of pico and nanoplankton populations was carried out using flow cytometry. The patchiness observed in the three cruises indicates an association of phytoplankton peaks with the main frontal structures: abundances were higher in the NWAF/upwelling area in OMEGA-1, at the Mediterranean side of the AOF in OMEGA-2, and at a tongue of recent Atlantic Water west of the WAG in BIOMEGA. However, a more detailed analysis reveals that different factors explain the origin of the phytoplankton biomass in each front/cruise. Mixing processes at the Strait of Gibraltar and the subsequent advection of water properties into the Western Alboran Sea were the mechanisms responsible for the abundances observed in the NWAF. The highest concentrations observed in the AOF were related to the intrusion of Mediterranean Surface Waters to the north of the front. During the migrating WAG the phytoplankton distribution was influenced by the formation of a new gyre. The relation between phytoplankton and mesoscale dynamics is further explored in terms of vertical velocity diagnosis. In all cases, intense vertical motion is negatively correlated with the abundance of phytoplankton populations. This resulted from the intense geostrophic background flow associated with large vertical velocities, which drove low residence times of water mass properties and hence a weak biological response. Fast-repeated surveys made during the OMEGA-1 and OMEGA-2 cruises reveal that the surveyed hydrographic features are subjected to significant temporal variability. In this case, the impact on the biology is most evident at taxa level.This work was partially supported by the EU funded MAST project OMEGA (MAS3-CT95-0001) and by the BIOMEGA project, funded by the Spanish Marine Science and Technology Program (REN2002-04044-C02-02). P. Leon was financed by a FPI grant from the Spanish Ministry of Education and Science (BES-2003-1032)Peer Reviewe

Aesthetic appreciation: event-related field and time-frequency analyses

Improvements in neuroimaging methods have afforded significant advances in our knowledge of the cognitive and neural foundations of aesthetic appreciation. We used magnetoencephalography (MEG) to register brain activity while participants decided about the beauty of visual stimuli. The data were analyzed with event-related field (ERF) and Time-Frequency (TF) procedures. ERFs revealed no significant differences between brain activity related with stimuli rated as “beautiful” and “not beautiful.” TF analysis showed clear differences between both conditions 400 ms after stimulus onset. Oscillatory power was greater for stimuli rated as “beautiful” than those regarded as “not beautiful” in the four frequency bands (theta, alpha, beta, and gamma). These results are interpreted in the frame of synchronization studies

Weddell Sea Export Pathways from Surface Drifters

The complex export pathways that connect the surface waters of the Weddell Sea with the Antarctic Circumpolar Current influence water mass modification, nutrient fluxes, and ecosystem dynamics. To study this exchange, 40 surface drifters, equipped with temperature sensors, were released into the northwestern Weddell Sea’s continental shelf and slope frontal system in late January 2012. Comparison of the drifter trajectories with a similar deployment in early February 2007 provides insight into the interannual variability of the surface circulation in this region. Observed differences in the 2007 and 2012 drifter trajectories are related to a variable surface circulation responding to changes in wind stress curl over the Weddell Gyre. Differences between northwestern Weddell Sea properties in 2007 and 2012 include 1) an enhanced cyclonic wind stress forcing over the Weddell Gyre in 2012; 2) an acceleration of the Antarctic Slope Current (ASC) and an offshore shift of the primary drifter export pathway in 2012; and 3) a strengthening of the Coastal Current (CC) over the continental shelf in 2007. The relationship between wind stress forcing and surface circulation is reproduced over a longer time period in virtual drifter deployments advected by a remotely sensed surface velocity product. The mean offshore position and speed of the drifter trajectories are correlated with the wind stress curl over the Weddell Gyre, although with different temporal lags. The drifter observations are consistent with recent modeling studies suggesting that Weddell Sea boundary current variability can significantly impact the rate and source of exported surface waters to the Scotia Sea, a process that determines regional chlorophyll distributions

2014-2021, 8 years without bottom-reaching deep water formation in the Western Mediterranean. Probably, the longest known period

Deep Water Formation (DWF) appeared almost regularly every year, during central winter months, in an area located offshore the Gulf of Lions in the NW Mediterranean Sea. Since the early 1960s, the processes involved in the DWF have been monitored, more or less intensively by regular hydrographic surveys or by moored instruments. It is worth noting the international efforts carried out in late 60s-early 70s by the so-called MEDOC Group to obtain a quite precise description of the whole process. Although the intensity of the DWF, as well as the amount of the newly formed Western Mediterranean Deep Water (WMDW), have shown high interanual variability, those years when the DWF was absent were exceptional, e.g. 1990, and those not reaching the bottom were scarce, e.g. 1997. Typically, they were years with almost no cold northerly winds during winter. By contrast, in some years the amount of newly formed WMDW was exceptional, e.g. 1987, and in some cases, an extra amount of this water came from dense shelf cascading, e.g. 1999. Moreover, in some years, the so-called variable Bottom Water, a slightly warm and salty layer, appeared near the bottom. It was a layer not thicker than 300 m, attributed to a large area affected by DWF which caused an extra amount of Levantine Intermediate Water (LIW) involved in the process, e.g. 1973. Other concomitant conditions that contributed to the DWF variability across the years was the presence of a blocking anticyclone in the Balearic Sea, that would play a role in intensifying the exposure of surface water to the northerlies, e.g. 1999. In winter 2005, all the factors contributing to an intense DWF process acted simultaneously, resulting in a new structure within the WMDW. The amount of newly formed WMDW, with higher density, T and S, was so extraordinary that affected the entire western Mediterranean basin, and it was identified as the Western Mediterranean Transition (WMT). The remnants of the WMDW previous to the WMT have been uplifted as to being available for a relevant contribution to the Mediterranean Outlfow Water (MOW) through the Gibraltar sill. After the WMT, the MOW showed both lower T and S than previously recorded up to around 2015, indicating that the old WMDW has been almost completely lost by leakage and diffusion. After the 2005 episode, the WMDW has evolved, changing its TS shape and increasing both T and S at the bottom, but still maintaining a deep layer with higher stratification than before 2005. In a previous work, we attributed the long period (2014-2018) without DWF to a combination of mild winters, the absence of the old WMDW, and the deep stratification. Such a process would be similar to the recovery of the Eastern Mediterranean Transient. In the present communication we incorporate 3 new years of data to the series, discuss the current situation and try to identify the requirements for a successful bottom-reaching DWF

An observing system simulation experiment for the calibration and validation of the surface water ocean topography sea surface height measurement using in situ platforms

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 35 (2018): 281-297, doi:10.1175/JTECH-D-17-0076.1.The wavenumber spectrum of sea surface height (SSH) is an important indicator of the dynamics of the ocean interior. While the SSH wavenumber spectrum has been well studied at mesoscale wavelengths and longer, using both in situ oceanographic measurements and satellite altimetry, it remains largely unknown for wavelengths less than ~70 km. The Surface Water Ocean Topography (SWOT) satellite mission aims to resolve the SSH wavenumber spectrum at 15–150-km wavelengths, which is specified as one of the mission requirements. The mission calibration and validation (CalVal) requires the ground truth of a synoptic SSH field to resolve the targeted wavelengths, but no existing observational network is able to fulfill the task. A high-resolution global ocean simulation is used to conduct an observing system simulation experiment (OSSE) to identify the suitable oceanographic in situ measurements for SWOT SSH CalVal. After fixing 20 measuring locations (the minimum number for resolving 15–150-km wavelengths) along the SWOT swath, four instrument platforms were tested: pressure-sensor-equipped inverted echo sounders (PIES), underway conductivity–temperature–depth (UCTD) sensors, instrumented moorings, and underwater gliders. In the context of the OSSE, PIES was found to be an unsuitable tool for the target region and for SSH scales 15–70 km; the slowness of a single UCTD leads to significant aliasing by high-frequency motions at short wavelengths below ~30 km; an array of station-keeping gliders may meet the requirement; and an array of moorings is the most effective system among the four tested instruments for meeting the mission’s requirement. The results shown here warrant a prelaunch field campaign to further test the performance of station-keeping gliders.The authors would like to acknowledge the funding sources: the SWOT mission (JW, LF, DM); NASA Projects NNX13AE32G, NNX16AH76G, and NNX17AH54G (TF); and NNX16AH66G and NNX17AH33G (BQ). AF and MF were funded by the Keck Institute for Space Studies (which is generously supported by the W. M. Keck Foundation) through the project Science-driven Autonomous and Heterogeneous Robotic Networks: A Vision for Future Ocean Observations (http://kiss.caltech.edu/?techdev/seafloor/seafloor.html).2018-08-0