1,747 research outputs found
Seasonal variation of size-resolved aerosol fluxes in a Peri-urban deciduous broadleaved forest
Eddy covariance measurements of aerosol fluxes were performed above an oak-hornbeam forest in the Po Plain (Northern Italy), from February to May and from September to December 2019. Measurements aimed at assessing the influence of forest phenology and leaf presence/absence on the seasonal evolution of size-segregated aerosol fluxes. The size-resolved aerosol concentration in the range 0.006-10 μm was sampled with a 14-stage impactor (ELPI+, Dekati, FI), and the filters exposed in May were subjected to chemical analysis. Over the whole sampling period, the forest removed from the atmosphere an average of 3.12 mg of aerosol m−2 d−1. The direction and the intensity of the aerosol fluxes were not constant through the year, as a strong seasonal and size-dependent variability emerged. In particular, leaf-presence drove a net deposition of the accumulation mode aerosol (100 nm< particle diameter Dp<1000 nm) and an emission of the Aitken (10 nm< Dp<100 nm) and coarse mode (Dp>1000 nm) aerosols. On the contrary, in absence of leaves all the sub-micrometer aerosol size-classes showed net daily upward fluxes, while coarse mode aerosol fluxes were prevalently downward. Monthly averages of deposition velocities of Aitken and accumulation mode aerosols correlated with the Leaf Area Index (LAI) seasonal trend, thus indicating an important role of the amount of the leaf surface area on the deposition and emission of these size-classes. Furthermore, an influence of the stomatic activity was suggested for the Aitken mode aerosol, since its deposition velocity followed the same diel course of the stomatal conductance to water. The analysis of the influence of meteorological parameters on aerosol deposition velocities highlighted that dynamic and convective turbulence (described by friction velocity, u* and Deardorff velocity, w*) enhanced the vertical aerosol exchanges, both upward and downward, while the approaching of condensing conditions reduced the flux intensities
An integrated approach shows different use of water resources from Mediterranean maquis species in a coastal dune ecosystem
An integrated approach has been used to analyse the dependence of three Mediterranean species, A. unedo
L., Q. ilex L., and P. latifolia L. co-occurring in a coastal dune ecosystem on two different water resources: groundwater and rainfed upper soil layers. The approach included leaf level gas exchanges, sap flow measurements and structural
adaptations between 15 May and 31 July 2007. During this period it was possible to capture different species-specific response patterns to an environment characterized by a sandy
soil, with a low water retention capacity, and the presence of a water table. The latter did not completely prevent the development of a drought response and, combined with previous
studies in the same area, response differences between species have been partially attributed to different root distributions.
Sap flow of A. unedo decreased rapidly with the decline of soil water content, while that of Q. ilex decreased only moderately. Midday leaf water potential of P. latifolia and A. unedo ranged between 122.2 and 122.7MPa throughout
the measuring period, while in Q. ilex it decreased down to 123.4MPa at the end of the season. A. unedo was the only species that responded to drought with a decrease of its leaf area to sapwood area ratio from 23.9\ub11.2 (May) to
15.2\ub11.5 (July). While A. unedo also underwent an almost stepwise loss on hydraulic conductivity, such a loss did not occur for Q. ilex, whereas P. latifolia was able to slightly increase
its hydraulic conducitivity. These differences show how different plant compartments coordinate differently between species in their responses to drought. The different responses appear to be mediated by different root distributions of the species and their relative resistances to drought
are likely to depend on the duration of the periods in which water remains extractable in the upper soil layers
Assessing the Impact of Ozone on Forest Trees in An Integrative Perspective: Are Foliar Visible Symptoms Suitable Predictors for Growth Reduction? A Critical Review
Plant growth reduction (GR) is the most widely accepted damage parameter to assess the sensitivity of trees to tropospheric ozone (O3) pollution since it integrates different physiological processes leading to loss of photosynthetic activity and distraction of metabolic resources from growth to defense, repair, and recovery pathways. Because of the intrinsic difficulty to assess the actual O3 risk assessment for forests in field conditions, foliar visible symptoms (FVS) induced by O3 have been proposed as a proxy to estimate possible GR in forest trees. The rationale for this assumption is that the onset of FVS implies a reduction of the photosynthetic capacity of plants. In this review, we show that GR and FVS can be the consequences of independent physiological pathways involving different response mechanisms that can cause both FVS without GR and GR without FVS. The onset of FVS may not lead necessarily to significant GR at plant level for several reasons, including the rise of compensatory photosynthesis, the time lag between growth processes and the accumulation of critical O3 dose, and the negligible effect of a modest amount of injured leaves. Plant GR, on the other hand, may be induced by different physiological mechanisms not necessarily related to FVS, such as stomatal closure (i.e., carbon starvation) to avoid or reduce O3 uptake, and the increase of respiratory processes for the production of metabolic defense compounds. Growth reduction and FVS can be interpreted as different strategies for the acclimation of plants to a stressful environment, and do not mean necessarily damage. Growth reduction (without FVS) seems to prevail in species adapted to limiting environmental conditions, that avoid loss and replacement of injured leaves because of the high metabolic cost of their production; conversely, FVS manifestation (without GR) and the replacement of injured leaves is more common in species adapted to environments with low-stress levels, since they can benefit from a rapid foliar turnover to compensate for the decreased rate of photosynthesis of the whole plant
Case Study: Valle Camonica and the Adamello Park
Capitolo introdduttivo all'area di studio scelta nelle Alpi meridionali come focus per l'ozono e il rischio incendi. Presenta le propiezioni climatiche nell'arfea fino alla fine del secolo
Improved sapflow methodology reveals considerable night-time ozone uptake by Mediterranean species
Due to the evident tropospheric ozone impact on
plant productivity, an accurate ozone risk assessment for the
vegetation has become an issue. There is a growing evidence
that ozone stomatal uptake may also take place at night and
that the night-time uptake may be more damaging than diurnal
uptake. Estimation of night-time uptake in the field is
complicated because of instrumental difficulties. Eddy covariance
technology is not always reliable because of the
low turbulence at night. Leaf level porometry is defective
at relative humidity above 70% which often takes place at
night. Improved sap flow technology allows to estimate also
slow flows that usually take place at night and hence may
be, at present, the most trustworthy technology to measure
night-time transpiration and hence to derive canopy stomatal
conductance and ozone uptake at night. Based on micrometeorological
data and the sap flow of three Mediterranean
woody species, the night-time ozone uptake of these species
was evaluated during a summer season as drought increased.
Night-time ozone uptake was from 10% to 18% of the total
daily uptake when plants were exposed to a weak drought,
but increased up to 24% as the drought became more pronounced.
The percentage increase is due to a stronger reduction
of diurnal stomatal conductance than night-time stomatal
conductance
Turbulence in a Coastal Mediterranean Area: Surface Fluxes and Related Parameters at Castel Porziano, Italy
Measurement of turbulence above a Mediterranean maquis at Castelporziano, Rom
The ACCENT-VOCBAS field campaign on biosphere-atmosphere interactions in a Mediterranean ecosystem of Castelporziano (Rome): site characteristics, climatic and meteorological conditions, and eco-physiology of vegetation
Biosphere-atmosphere interactions were investigated
on a sandy dune Mediterranean ecosystem in a field
campaign held in 2007 within the frame of the European
Projects ACCENT and VOCBAS. The campaign was carried
out in the Presidential estate of Castelporziano, a periurban
park close to Rome. Former campaigns (e.g. BEMA)
performed in Castelporziano investigated the emission of
biogenic volatile organic compounds (BVOC). These campaigns
focused on pseudosteppe and evergreen oak groves
whereas the contribution of the largely biodiverse dune vegetation,
a prominent component of the Mediterranean ecosystem,
was overlooked. While specific aspects of the campaign
will be discussed in companion papers, the general climatic
and physiological aspects are presented here, together with
information regarding BVOC emission from the most common
plant species of the dune ecosystem. During the campaign
regular air movements were observed, dominated by
moderate nocturnal land breeze and diurnal sea breeze. A
regular daily increase of ozone concentration in the air was
also observed, but daily peaks of ozone were lower than those
measured in summer on the same site. The site was ideal as a natural photochemical reactor to observe reaction, transport
and deposition processes occurring in the Mediterranean
basin, since the sea-land breeze circulation allowed a strong
mixing between biogenic and anthropogenic emissions and
secondary pollutants. Measurements were run in May, when
plant physiological conditions were optimal, in absence of
severe drought and heat stress. Foliar rates of photosynthesis
and transpiration were as high as generally recorded
in unstressed Mediterranean sclerophyllous plants. Most of
the plant species emitted high level of monoterpenes, despite
measurements being made in a period in which emissions
of volatile isoprenoids could be restrained by developmental
and environmental factors, such as leaf age and relatively
low air temperature. Emission of isoprene was generally low.
Accounting for the high monoterpene spring emission of the
dune ecosystem may be important to correct algorithms at regional
and ecosystem levels, and to interpret measurements
of fluxes of volatile isoprenoids and secondary pollutants
Measurements of Soil Carbon Dioxide Emissions from Two Maize Agroecosystems at Harvest under Different Tillage Conditions
In this study a comparison of the soil CO2 fluxes emitted from two maize (Zea mays L.) fields with the same soil type was performed. Each field was treated with a different tillage technique: conventional tillage (30\u2009cm depth ploughing) and no-tillage. Measurements were performed in the Po Valley (Italy) from September to October 2012, covering both pre- and postharvesting conditions, by means of two identical systems based on automatic static soil chambers. Main results show that no-tillage technique caused higher CO2 emissions than conventional tillage (on average 2.78 and 0.79\u2009\u3bcmol CO2\u2009m 122\u2009s 121, resp.). This result is likely due to decomposition of the organic litter left on the ground of the no-tillage site and thus to an increased microbial and invertebrate respiration. On the other hand, fuel consumption of conventional tillage technique is greater than no-tillage consumptions. For these reasons this result cannot be taken as general. More investigations are needed to take into account all the emissions related to the field management cycle
Interactions among vegetation and ozone, water and nitrogen fluxes in a coastal Mediterranean maquis ecosystem
Ozone, water and energy fluxes were measured
over a Mediterranean maquis ecosystem from 5 May until 31
July 2007 by means of the eddy covariance technique. Additional
measurements of NOx fluxes were performed by the
aerodynamic gradient technique. Stomatal ozone fluxes were
obtained from water fluxes by a Dry Deposition Inferential
Method based on a big leaf concept.
The maquis ecosystem acted as a net sink for ozone. The
different water availability between late spring and summer
was the major cause of the changes observed in stomatal
fluxes, which decreased, together with evapotranspiration,
when the season became drier.
NOx concentrations were significantly dependent on the
local meteorology. NOx fluxes resulted less intense than the
ozone fluxes. However an average upward flux of both NO
and NO2 was measured.
The non-stomatal pathways of ozone deposition were investigated.
A correlation of non-stomatal deposition with air
humidity and, in a minor way, with NO2 fluxes was found.
Ozone risk assessment was performed by comparing the
exposure and the dose metrics: AOT40 (Accumulated dose
over a threshold of 40 ppb) and AFst 1.6 (Accumulated stomatal
flux of ozone over a threshold of 1.6 nmolm 122 s 121).
AOT40, both at the measurement height and at canopy height
was greater than the Critical Level for the protection of
forests and semi-natural vegetation (5000 ppb h) adopted by
UN-ECE. Also the AFst 1.6 value (12.6 mmolm 122 PLA, Projected
Leaf Area) was higher than the provisional critical
dose of 4 mmolm 122 PLA for forests. The cumulated dose
showed two different growth rates in the spring and in the
summer periods, while the exposure showed a more irregular
behavior in both periods
(Evapo)transpiration measurements over vegetated surfaces as a key tool to assess the potential damages of air gaseous pollutants for plants
Biological damages of a variety of plant organisms are evaluated according their evapotranspiration capacit
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