The second research line focuses on soil and vegetation interactions with atmospheric chemical compounds and pathogens in order to (1) quantify the impact of agricultural activities on radiative forcing, air pollution, and plant diseases spread, and (2) contribute to the development and evaluation of innovative management practices. Our objects are air contaminants, greenhouse gases, and pathogens. Nitrogen compounds were the most studied in the last period (ammonia - NH3, nitrous oxide – N2O, nitrogen oxides – NOx), together with pesticides, ozone (O3), and since 2 years VOC and very recently secondary organic aerosols (SOA).
Our work focuses on unravelling the environmental and biophysical drivers of reactive compounds, GHG, and pathogens exchange in the soil-vegetation-atmosphere system. It explicitly considers the spatial heterogeneity of the ecosystem, whether vertically (for trace gas and energy exchanges), or horizontally (for pathogens, ammonia and pesticides). We develop models and methods to quantify energy and mass transfers, adsorption-desorption-reactions of reactive compounds, pathogens washout and rain droplets impaction, and atmospheric transport at the field up to landscape scales. The drivers considered include environmental conditions as well as biological functioning: soil microbial activity, N and C fluxes; plant stomatal functioning, nitrogen metabolism and detoxification. The spatial scales range from soil aggregates or plant organs to multiple fields. Temporal scales range from infra-hour to several years. A specificity of our approach is to explicitly describe the canopy structure and microclimate as well as the thermodynamic interactions at leaf and soil surfaces. During the last term period, we contributed to gain insight into:
- Interactions of reactive trace gases with soils and plants. This component focused on processes that were largely unknown, in particular regarding ozone, nitrogenous gases and pesticides. Noticeably, we found that soil surface humidity was a strong driver of many of these processes. We indeed showed that O3 uptake on soil surface was the largest O3 sink in wheat-maize cropping system, was favored by dry soils (Stella et al., 2013), but also increased by reaction with emitted NO following slurry application (Vuolo et al., 2017); We also found that ammonia emission following slurry application was mainly driven by slurry and water transfer in the upper soil layer (Personne et al., 2015); Similarly pesticide volatilization from dry soils was found to be lower compared to wet soils, which was explained by gas adsorption onto soil (Garcia et al. 2014); Regarding processes at the plant surfaces, we showed that leaf penetration of systemic pesticides and their formulations was essential to account for leaf-volatilization modeling (Lichiheb et al., 2016); we further showed that O3 deposition was boosted on wet senescent wheat leaves, potentially due to interactions with leaking ascorbate (Potier et al., 2015; 2017); Tuzet et al. (2018) further demonstrated that plant water status was essential in driving the impact of reactive compounds deposition on plant functioning;
- Structure function interactions. In that component our researches mainly showed the essential role of the 3D structure of plants in controlling biotic particle and light transfers. We indeed showed that 3D dynamic representations of plant canopies (Abichou et al., 2016, 2018) was a useful tool to evaluate particle interception (Gigot et al., 2014b) or signal perceived by lidar or cameras (Liu et al., 2017); Incorporating this knowledge in transfer models, demonstrated that mixing of sensitive and resistant cultivars could moderate rain splash dispersal of pathogens (Gigot et al., 2014a; Vidal et al., 2018);
- Surface-atmosphere exchanges of reactive trace gases. In this component we developed state of the art methods for quantifying GHG and contaminant emissions in order to identify low emission management practices. In particular an inverse local-scale atmospheric dispersion method was developed for inferring ammonia emissions (Loubet et al., 2018). This method and other NH3 flux campaigns allowed improving NH3 surface exchange modeling for identifying best management practices (Hafner et al., 2018). On the GHG side, raw digestates was shown to emit large amounts of N2O compared to composted ones (Askri et al., 2016), while we showed that reducing N fertilization on wheat in Mediterranean context lowered N2O emissions while maintaining crop yield (Volpi et al., 2018); Regarding pesticides, volatilization was shown to be non-negligible source of atmospheric burden (Bedos et al., 2017), which could contribute to significant deposition to water streams (Bedos et al., 2017). Finally, in the current period we developed new methodology for characterizing VOC exchanges from soil and plants, which allowed showing that a large spectrum of VOC was emitted by soil microbes (Abis et al., 2018), while wheat and oilseed rape emissions were dominated by methanol (Gonzaga et al., 2017).