135 research outputs found
Leaf Eh and pH: A Novel Indicator of Plant Stress. Spatial, Temporal and Genotypic Variability in Rice (Oryza sativa L.)
A wealth of knowledge has been published in the last decade on redox regulations in plants. However, these works remained largely at cellular and organelle levels. Simple indicators of oxidative stress at the plant level are still missing. We developed a method for direct measurement of leaf Eh and pH, which revealed spatial, temporal, and genotypic variations in rice. Eh (redox potential) and Eh@pH7 (redox potential corrected to pH 7) of the last fully expanded leaf decreased after sunrise. Leaf Eh was high in the youngest leaf and in the oldest leaves, and minimum for the last fully expanded leaf. Leaf pH decreased from youngest to oldest leaves. The same gradients in Eh-pH were measured for various varieties, hydric conditions, and cropping seasons. Rice varieties differed in Eh, pH, and/or Eh@pH7. Leaf Eh increases and leaf pH decreases with plant age. These patterns and dynamics in leaf Eh-pH are in accordance with the pattern and dynamics of disease infections. Leaf Eh-pH can bring new insight on redox processes at plant level and is proposed as a novel indicator of plant stress/health. It could be used by agronomists, breeders, and pathologists to accelerate the development of crop cultivation methods leading to agroecological crop protection
Iron biogeochemistry across marine systems progress from the past decade
Based on an international workshop (Gothenburg, 14â16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas
Inherited biotic protection in a Neotropical pioneer plant
Chelonanthus alatus is a bat-pollinated, pioneer Gentianaceae that clusters in patches where still-standing, dried-out stems are interspersed among live individuals. Flowers bear circum-floral nectaries (CFNs) that are attractive to ants, and seed dispersal is both barochorous and anemochorous. Although, in this study, live individuals never sheltered ant colonies, dried-out hollow stems - that can remain standing for 2 years - did. Workers from species nesting in dried-out stems as well as from ground-nesting species exploited the CFNs of live C. alatus individuals in the same patches during the daytime, but were absent at night (when bat pollination occurs) on 60.5% of the plants. By visiting the CFNs, the ants indirectly protect the flowers - but not the plant foliage - from herbivorous insects. We show that this protection is provided mostly by species nesting in dried-out stems, predominantly Pseudomyrmex gracilis. That dried-out stems remain standing for years and are regularly replaced results in an opportunistic, but stable association where colonies are sheltered by one generation of dead C. alatus while the live individuals nearby, belonging to the next generation, provide them with nectar; in turn, the ants protect their flowers from herbivores. We suggest that the investment in wood by C. alatus individuals permitting stillstanding, dried-out stems to shelter ant colonies constitutes an extended phenotype because foraging workers protect the flowers of live individuals in the same patch. Also, through this process these dried-out stems indirectly favor the reproduction (and so the fitness) of the next generation including both their own offspring and that of their siblings, alladding up to a potential case of inclusive fitness in plants
Inputs and processes affecting the distribution of particulate iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) section
The aim of the GEOVIDE cruise (MayâJune 2014, R/V Pourquoi Pas?)
was to provide a better understanding of trace metal biogeochemical cycles in
the North Atlantic Ocean. As marine particles play a key role in the global
biogeochemical cycle of trace elements in the ocean, we discuss the
distribution of particulate iron (PFe), in relation to the distribution of
particulate aluminium (PAl), manganese (PMn), and phosphorus (PP). Overall,
32 full vertical profiles were collected for trace metal analyses,
representing more than 500 samples. This resolution provides a solid basis
for assessing concentration distributions, elemental ratios, size
fractionation, and adsorptive scavenging processes in key areas of the
thermohaline overturning circulation. Total particulate iron concentrations
ranged from as low as 9 pmol Lâ1 in surface waters of the Labrador Sea
to 304 nmol Lâ1 near the Iberian margin, while median PFe
concentrations of 1.15 nmol Lâ1 were measured over the sub-euphotic
ocean interior.
Within the Iberian Abyssal Plain, the ratio of PFe to PAl was identical to
the continental crust molar ratio (0.21 mol molâ1), indicating the
important influence of crustal particles in the water column. Overall, the
lithogenic component explained more than 87% of PFe variance along the
section. Within the Irminger and Labrador basins, the formation of biogenic
particles led to an increase in the PFeâPAl ratio (up to
0.64 mol molâ1) compared to the continental crust ratio. Continental
margins induce high concentrations of particulate trace elements within the
surrounding water masses (up to 10 nmol Lâ1 of PFe). For example,
horizontal advection of PFe was visible more than 250 km away from the
Iberian margin. Additionally, several benthic nepheloid layers were observed
more than 200 m above the seafloor along the transect, especially in the
Icelandic, Irminger, and Labrador basins, suspending particles with high PFe
content of up to 89 nmol Lâ1.</p
Iron, silicate, and light co-limitation of three Southern Ocean diatom species
The effect of combined iron, silicate, and light co-limitation was investigated in the three diatom species Actinocyclus sp. Ehrenberg, Chaetoceros dichaeta Ehrenberg, and Chaetoceros debilis Cleve, isolated from the Southern Ocean (SO). Growth of all species was co-limited by iron and silicate, reflected in a significant increase in the number of cell divisions compared to the control. Lowest relative Si uptake and drastic frustule malformation was found under iron and silicate co-limitation in C. dichaeta, while Si limitation in general caused cell elongation in both Chaetoceros species. Higher light intensities similar to SO surface conditions showed a negative impact on growth of C. dichaeta and Actinocyclus sp. and no effect on C. debilis. This is in contrast to the assumed light limitation of SO diatoms due to deep wind driven mixing. Our results suggest that growth and species composition of Southern Ocean diatoms is influenced by a sensitive interaction of the abiotic factors, iron, silicate, and light
Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution
During the 2014 GEOVIDE transect, seawater samples were collected for
dissolved Pb and Pb isotope analysis. These samples provide a high-resolution
snapshot of the source regions for the present Pb distribution in the
North Atlantic Ocean. Some of these stations were previously occupied for Pb
from as early as 1981, and we compare the 2014 data with these older data,
some of which are reported here for the first time. Lead concentrations were
highest in subsurface Mediterranean Water (MW) near the coast of Portugal,
which agrees well with other recent observations by the US GEOTRACES program
(Noble et al., 2015). The recently formed Labrador Sea Water (LSW) between
Greenland and Nova Scotia is much lower in Pb concentration than the older
LSW found in the West European Basin due to decreases in Pb
emissions into the atmosphere during the past 20Â years. Comparison of North
Atlantic data from 1989 to 2014 shows decreasing Pb concentrations consistent
with decreased anthropogenic inputs, active scavenging, and
advection/convection. Although the isotopic composition of northern North
Atlantic seawater appears more homogenous compared to previous decades, a
clear spatiotemporal trend in isotope ratios is evident over the past
15Â years and implies that small changes to atmospheric Pb emissions continue.
Emissions data indicate that the relative proportions of US and European Pb
sources to the ocean have been relatively uniform during the past 2 decades,
while aerosol data may suggest a greater relative proportion of natural
mineral Pb. Using our measurements in conjunction with emissions inventories,
we support the findings of previous atmospheric analyses that a significant
portion of the Pb deposited to the ocean in 2014 was natural, although it is
obscured by the much greater solubility of anthropogenic aerosols over
natural ones.</p
Atmospheric deposition fluxes over the Atlantic Ocean: a GEOTRACES case study
Atmospheric deposition is an important source of micronutrients to the
ocean, but atmospheric deposition fluxes remain poorly constrained in most
ocean regions due to the limited number of field observations of wet and dry
atmospheric inputs. Here we present the distribution of dissolved aluminium
(dAl), as a tracer of atmospheric inputs, in surface waters of the Atlantic
Ocean along GEOTRACES sections GA01, GA06, GA08, and GA10. We used the
surface mixed-layer concentrations of dAl to calculate atmospheric
deposition fluxes using a simple steady state model. We have optimized the
Al fractional aerosol solubility, the dAl residence time within the surface
mixed layer and the depth of the surface mixed layer for each separate cruise to
calculate the atmospheric deposition fluxes. We calculated the lowest
deposition fluxes of 0.15±0.1 and 0.27±0.13 g mâ2 yrâ1
for the South and North Atlantic Ocean (>40â S and >40â N) respectively, and the highest fluxes of 1.8
and 3.09 g mâ2 yrâ1 for the south-east Atlantic and tropical
Atlantic Ocean, respectively. Overall, our estimations are comparable to
atmospheric dust deposition model estimates and reported field-based
atmospheric deposition estimates. We note that our estimates diverge from
atmospheric dust deposition model flux estimates in regions influenced by
riverine Al inputs and in upwelling regions. As dAl is a key trace element
in the GEOTRACES programme, the approach presented in this study allows
calculations of atmospheric deposition fluxes at high spatial resolution for
remote ocean regions.</p
A call for refining the role of humic-like substances in the oceanic iron cycle
Primary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the iron-binding ligand pool throughout the water column. We demonstrate how maximum dissolved iron concentrations could be limited by the concentration and binding capacity of humic ligands, and provide a summary of the key processes that could influence these parameters. If this relationship is globally representative, humics could impose a concentration threshold that buffers the deep ocean iron inventory. This study highlights the dearth of humic data, and the immediate need to measure electroactive humics, dissolved iron and iron-binding ligands simultaneously from surface to depth, across different ocean basins
Mercury distribution and transport in the North Atlantic Ocean along the GEOTRACES-GA01 transect
We report here the results of total mercury (HgT) determinations along the 2014 Geotraces Geovide cruise (GA01 transect) in the North Atlantic Ocean (NA) from Lisbon (Portugal) to the coast of Labrador (Canada). HgT concentrations in unfiltered samples (HgTUNF) were log-normally distributed and ranged between 0.16 and 1.54âŻpmolâŻLâ1, with a geometric mean of 0.51âŻpmolâŻLâ1 for the 535 samples analysed. The dissolved fraction (<âŻ0.45âŻÂ”m) of HgT (HgTF), determined on 141 samples, averaged 78âŻ% of the HgTUNF for the entire data set, 84âŻ% for open seawaters (below 100âŻm) and 91âŻ% if the Labrador Sea data are excluded, where the primary production was high (with a winter convection down to 1400âŻm). HgTUNF concentrations increased eastwards and with depth from Greenland to Europe and from subsurface to bottom waters. The HgTUNF concentrations were similarly low in the subpolar gyre waters (ââŒââŻ0.45âŻpmolâŻLâ1), whereas they exceeded 0.60âŻpmolâŻLâ1 in the subtropical gyre waters. The HgTUNF distribution mirrored that of dissolved oxygen concentration, with highest concentration levels associated with oxygen-depleted zones. The relationship between HgTF and the apparent oxygen utilization confirms the nutrient-like behaviour of Hg in the NA. An extended optimum multiparameter analysis allowed us to characterize HgTUNF concentrations in the different source water types (SWTs) present along the transect. The distribution pattern of HgTUNF, modelled by the mixing of SWTs, show Hg enrichment in Mediterranean waters and North East Atlantic Deep Water and low concentrations in young waters formed in the subpolar gyre and Nordic seas. The change in anthropogenic Hg concentrations in the Labrador Sea Water during its eastward journey suggests a continuous decrease in Hg content in this water mass over the last decades. Calculation of the water transport driven by the Atlantic Meridional Overturning Circulation across the PortugalâGreenland transect indicates northward Hg transport within the upper limb and southward Hg transport within the lower limb, with resulting net northward transport of about 97.2âŻkmolâŻyrâ1
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