7 research outputs found
Responses to water stress in two Eucalyptus globulus clones differing in drought tolerance
We evaluated drought resistance mechanisms in a
drought-tolerant clone (CN5) and a drought-sensitive clone
(ST51) of Eucalyptus globulus Labill. based on the responses
to drought of some physiological, biophysical and morphological
characteristics of container-grown plants, with particular
emphasis on root growth and hydraulic properties. Water loss
in excess of that supplied to the containers led to a general decrease
in growth and significant reductions in leaf area ratio,
specific leaf area and leaf-to-root area ratio. Root hydraulic
conductance and leaf-specific hydraulic conductance decreased
aswater stress became more severe. During the experiment,
the drought-resistant CN5 clone maintained higher leaf
water status (higher predawn and midday leaf water potentials),
sustained a higher growth rate (new leaf area expansion
and root growth) and displayed greater carbon allocation to the
root system and lower leaf-to-root area ratio than the droughtsensitive
ST51 clone. Clone CN5 possessed higher stomatal
conductances at moderate stress as well as higher hydraulic
conductances than Clone ST51. Differences in the response to
drought in root biomass, coupled with changes in hydraulic
properties, accounted for the clonal differences in drought tolerance,
allowing Clone CN5 to balance transpiration andwater
absorption during drought treatment and thereby prolong the
period of active carbon assimilation
Metabolic responses to water deficit in two Eucalyptus globulus clones with contrasting drought sensitivity
We compared the metabolic responses of leaves
and roots of two Eucalyptus globulus Labill. clones differing in
drought sensitivity to a slowly imposed water deficit. Responses
measured included changes in concentrations of soluble
and insoluble sugars, proline, total protein and several
antioxidant enzymes. In addition to the general decrease in
growth caused by water deficit, we observed a decrease in osmotic
potential when drought stress became severe. In both
clones, the decrease was greater in roots than in leaves, consistent
with the observed increases in concentrations of soluble
sugars and proline in these organs. In roots of both clones,
glutathione reductase activity increased significantly in response
towater deficit, suggesting that this enzyme plays a protective
role in roots during drought stress by catalyzing the
catabolism of reactive oxygen species. Clone CN5 has stress
avoidance mechanisms that account for its lower sensitivity to
drought compared with Clone ST51
Flavodoxin overexpression reduces cadmium-induced damage in alfalfa root nodules
13 pages and figuresFlavodoxins are electron carrier flavoproteins
that are involved in the response to oxidative stress in
bacteria and cyanobacteria. Recently, we obtained
Sinorhizobium meliloti bacteria that overexpressed
a flavodoxin from the cyanobacterium Anabaena
variabilis [Redondo et al. (2009) Plant Physiology
149:1166–1178]. In the present work, tolerance to
cadmium was evaluated in free-living transformed S.
meliloti and in alfalfa plants nodulated by the
flavodoxin-overexpressing rhizobia, in comparison
with plants nodulated by wild-type bacteria. Overexpression
of flavodoxin protected free-living S.
meliloti from cadmium toxicity and had a positive
effect on nitrogen fixation of alfalfa plants subjected to
cadmium stress. Flavodoxin notably reduced cadmiuminduced
structural and ultrastructural alterations in
alfalfa nodules. Putative protection mechanisms in
flavodoxin-overexpressing nodules are discussed. Flavodoxin
could have applications as a biotechnological
tool to improve the symbiotic performance of alfalfa
and other legumes in cadmium polluted soils.Peer reviewe
Responses to chilling of two Eucalyptus globulus clones with contrasting drought resistance
Réponses physiologiques et biochimiques à des températures froides positives de deux clones d’Eucalyptus globulus qui différent à travers leur résistance à la sécheresse
Activation of Rhizobium tibeticum With Flavonoids Enhances Nodulation, Nitrogen Fixation, and Growth of Fenugreek (Trigonella foenum-graecum L.) Grown in Cobalt-Polluted Soil
Comparison of methane, nitrous oxide fluxes and CO2 respiration rates from a Mediterranean cork oak ecosystem and improved pasture
Background and aims: During the recent decades, cork
oak (Q. suber) mortality has been increasing in Mediterranean
oak woodland endangering the economical and environmental
sustainability of the “montado” ecosystem.
This fact in combination with climate change and conversion
of forestland to pasture may significantly affect the
soil-atmosphere greenhouse gases (GHGs) exchange. Our
study evaluates the impact of oak trees as compared to
pasture on net ecosystem GHG (CH4, N2O, and CO2)
exchange as well as the main environmental factors
influencing this exchange.
Methods: We used field chamber measurements for the
collection of GHGs under three different conditions: 1)
open area (OA), 2) under tree canopy area (UC) and 3)
improved pasture (IP). Experiments were done under typical
Mediterranean climate at central Portugal in 2010 and
2011.
Results: The UC had higher nitrification potential, soil
C/N ratio, electrical conductivity, litter input and soil organic
matter (SOM) than OA and IP. SOM positively
correlated with soil CH4 and N2O fluxes but not with soil
CO2 respiration rates. Soil water content (SWC) drives
both CH4 and N2O fluxes. Under certain conditions, when
SWC reached a threshold (7 % for CH4 and 3 % for N2O)
the result was net uptake and that net uptake increased with
SWC. This was the case for the UC and OA. Conversely,
for the IP soil water content above 4 % promoted net CH4
release.
Conclusions: Our results show that cork oak influences
soil properties and consequently GHGs fluxes. In the UC
the input of litter for SOM together with soil moisture,
favoured microbiological activity and related GHGs
fluxes. Soil temperature is a secondary factor in the studied
conditions. Our results also emphasized the potential impact
posed by decreased cork oak tree density in the
functioning of the “montado” ecosystem.
Keywords Evergreen oak . Greenhouse gases