NITRIPHYLL · A novel approach to determine canopy nitrification in the phyllosphere of European forests: combining multiple isotope tracers and proteogenomic techniques

A novel approach to determine canopy nitrification in the phyllosphere of European forests: combining multiple isotope tracers and proteogenomic techniques

Forest canopies play a significant role in regulating carbon and water exchanges with the atmosphere, with profound effects on our climate. However, their role in altering the chemical composition of precipitation and, consequently, the nutrient input to the soil has been less investigated. This is particular relevant for nitrogen (N)-limited forests in the Northern hemisphere, which have been exposed to a rapid human-induced increase in emissions of nitrogen compounds over the last century, due to increase in industrial activities, traffic and use of fertilizer in agriculture, to enhance food production and sustain the increase in growth population [1]. These reactive N compounds, however, do not remain in the atmosphere, but are deposited on terrestrial and aquatic ecosystems as N deposition, thus altering global N cycling. Significant differences for the nitrogen fluxes between precipitation in the open field (rainfall, RF) and below the forest canopies (throughfall, TF) have been observed at many forests [2]. This suggests that N deposition is substantially altered through its path into the canopy. How do these changes take place? By applying a multiple isotope approach in nitrate collected in RF and TF water we showed for the first time that biological nitrification (microbial conversion of ammonium/ammonia in nitrate) was responsible for the large changes in the amount of nitrate from RF to TF across two UK forests at high N deposition level [3]. Nevertheless, a number of studies have pointed out that tree canopies are habitat (i.e., phyllosphere) for incredible diverse microbial communities, with bacteria being the most abundant [4]. NITRIPHYLL aimed to prove that the microbial communities harbored in forest canopies carry out processes hitherto unrecognized for their significance, i.e., nitrification in the canopy, thereby helping cycling N before litter is returned to the soil. To achieve these objectives NITRIPHYLL for the first time merged two separate research avenues, i.e., the investigation of N transformation by forest canopies (through stable isotopes) with the study of abundance and diversity of microbes involved in nutrient cycling (through qPCR and NGS). [1] Galloway et al. (2004). Biogeochemistry 70: 153–226. [2] Ferretti et al. (2016). Global Change Biology 20: 3423–3438 [3] Guerrieri et al. (2015). Global Change Biology 21: 4613-4626 [4] Vacher et al. (2016). Annu. Rev. Ecol. Evol. Syst. 47:1-24

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