Quantitative study on nitrogen deposition and canopy retention in Mediterranean evergreen forests

Abstract

To assess the impact of nitrogen (N) pollutants on forest ecosystems, the role of the interactions in the canopy needs to be understood. A great number of studies have addressed this issue in heavily N-polluted regions in north and central Europe. Much less information is available for the Iberian Peninsula, and yet this region is home to mountain forests and alpine grasslands that may be at risk due to excessive N deposition. To establish the basis for ecology-based policies, there is a need to better understand the forest response to this atmospheric impact. To fill this gap, in this study, we measured N deposition (as bulk, wet, and throughfall fluxes of dissolved inorganic nitrogen) and air N gas concentrations from 2011 to 2013 at four Spanish holm oak (Quercus ilex) forests located in different pollution environments. One site was in an area of intensive agriculture, two sites were influenced by big cities (Madrid and Barcelona, respectively), and one site was in a rural mountain environment 40 km north of Barcelona. Wet deposition ranged between 0.54 and 3.8 kg N ha year for ammonium (NH)-N and between 0.65 and 2.1 kg N ha year for nitrate (NO)-N, with the lowest deposition at the Madrid site for both components. Dry deposition was evaluated with three different approaches: (1) a canopy budget model based in throughfall measurements, (2) a branch washing method, and (3) inferential calculations. Taking the average dry deposition from these methods, dry deposition represented 51-67% (reduced N) and 72-75% (oxidized N) of total N deposition. Canopies retained both NH-N and NO-N, with a higher retention at the agricultural and rural sites (50-60%) than at sites located close to big cities (20-35%, though more uncertainty was found for the site near Madrid), thereby highlighting the role of the forest canopy in processing N pollutant emissions.

Partitioning between atmospheric deposition and canopy microbial nitrification into throughfall nitrate fluxes in a Mediterranean forest

“…Wet deposition as derived from N fluxes in RF was in the same range of values reported in previous studies at La Castanya (Aguillaume, Rodrigo, & Avila, ; Avila et al, ). The N fluxes in the form of were larger in TF than RF during the study period, suggesting that dry deposition may have contributed substantially to total deposition.…”

Twenty-five year record of chemicals in open field precipitation and throughfall from a medium-altitude forest catchment (Strengbach - NE France): An obvious response to atmospheric pollution trends

“…One possible explanation might be that with aging and stand decline (which was the case for the considered spruce forest), the nitrogen nutrient requirements and thus the uptake by the spruce needles decreased, explaining the increase of NO 3 − and NH 4 + in TF-S. However, in general NH 4 + was more efficiently retained in canopy than NO 3 − (Avila et al, 2017), which could explain why the increase in nitrate is higher than that in ammonia in TF-S ( Fig. 7b and d).…”

“…flux but with different percentage in agricultural, rural or urban site (58-80%; Avila et al, 2017), underlining the role played by the tree species, but also the site location (distance from urban or agricultural zone).…”

(E)merging directions on air pollution and climate change research in Mediterranean Basin ecosystems

“…A multidisciplinary approach that is patent in this special issue, which opens with two articles (Lo Cascio et al 2017;Ochoa-Hueso et al 2017b) that focus primarily on the response of Mediterranean soils and soil-inhabiting communities to N deposition, is followed by three articles that focus on the usefulness of cryptogams (mosses, lichens, and liverworts) as biomarkers of increasing aridity and toxic metal pollution (Basile et al 2017;Cogolludo et al 2017;Paoli et al 2017). The issue continues with two articles by Avila et al (2017) and Cabal et al (2017) about the patterns and effects of nitrogen deposition on woody plant-dominated ecosystems from Spain and finishes with three articles focused on the effects of tropospheric ozone on larch forests (Finco et al 2017), crops (Marzuoli et al, 2016), and pasture species (González-Fernández et al 2017). Soil is a crucial part of all the terrestrial ecosystems and a particularly complex one.…”

“…The role of the interactions between the canopy and N pollutants is one of them. In this issue, Avila et al (2017) measured N deposition (as bulk, wet, and throughfall fluxes of dissolved inorganic N) and air N gas concentrations from 2011 to 2013 at four Spanish holm-oak (Quercus ilex) sites characterized by different land use. The results showed that canopies retained both NH 4 -N and NO 3 -N, with a higher retention at the agricultural and rural sites than at sites located close to big cities, highlighting the role of the forest canopy in processing N pollutant emissions.…”