1,125 research outputs found
Stomatal Conductance Modeling to Estimate the Evapotranspiration of Natural and Agricultural Ecosystems
This chapter presents some of the available modelling techniques to predict stomatal conductance at leaf and canopy level, the key driver of the transpiration component in the evapotranspiration process of vegetated surfaces. The process-based models reported, are able to predict fast variations of stomatal conductance and the related transpiration and
evapotranspiration rates, e.g. at hourly scale. This high–time resolution is essential for applications which couple the transpiration process with carbon assimilation or air
pollutants uptake by plants.
In these cases, the big-leaf approach, together with the resistive analogy which simulates the gas-exchange between vegetation and atmosphere, is a simple but valid example of a process-based model which includes the stomatal conductance behaviour, as well as a basic representation of the canopy features
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
(Evapo)Transpiration Measurements Over Vegetated Surfaces as a Key Tool to Assess the Potential Damages of Air Gaseous Pollutant for Plants
Biological damages of a variety of plant organisms are evaluated according their evapotranspiration capacit
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
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
Interannual variability of ozone fluxes in a broadleaf deciduous forest in Italy
Multiannual measurements of ozone (O3) fluxes were performed from 2012 to 2020 in a broadleaf deciduous forest of the Po Valley, Italy. Fluxes were measured with the eddy covariance technique on a 41-m high tower, 15 m above the forest canopy. Different partition methodologies, based on concomitant water and carbon dioxide measurements, were compared for the calculation of the stomatal and non-stomatal components of the O3 fluxes. Total O3 fluxes revealed a marked interannual variability that was mainly driven by the stomatal activity in summer. Therefore, those factors that influence stomatal conductance were responsible for the flux variability, with soil water content being the main physiological driver. Despite the variability of the total O3 fluxes, the annual mean of the stomatal fraction was similar in the different years, around 42% on a 24-h basis, with an average summer value of 52% and a maximum around 60% during the summer daylight hours. The non-stomatal deposition was mainly driven by air humidity, surface wetness, and chemical sinks such as reaction of O3 with nitric oxide. Wind speed, turbulence intensity, and surface temperature showed a negative relationship with the non-stomatal fraction, but this was probably the result of a temporal misalignment between the daily cycles of non-stomatal conductance and those of temperature, turbulence, and wind speed. During the 7 years of measurements, the forest experienced a phytotoxic O3 dose of 10.55 mmolO3 m−2, as annual average, with an estimated reduction of the forest growth rate around 3% yr−1 according to the dose–effect relationships of the United Nations Economic Commission for Europe for broadleaf deciduous forests. Besides their implication for the O3 risk assessment for vegetation, these long-term measurements could be useful to test the deposition models used to correctly assess the O3 budget in troposphere on a multiannual time span
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
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
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
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