Do aerial nitrogen depositions affect fungal and bacterial communities inhabiting phyllosphere of oak leaves?
The amount of nitrogen (N) deposition onto forest has globally increased and is expected to double by 2050 mostly because of the fertilizer production and fossil fuel burning. Several studies have already investigated the effects of N depositions in forest soils, highlighting negative effects on plant biodiversity and the associated biota. Nevertheless, the effects of N aerial depositions applied directly on the tree canopy are still unexplored. This study aimed to investigate the influence of increased N deposition on the fungal and bacterial communities associated with phyllosphere, in a temperate forest dominated by sessile oak (Quercus petraea Liebl.). The study area was located in Monticolo natural reserve (South Tyrol, Italy) where a long-term ecosystem experiment has been established simulating increased N deposition. The experimental design consisted in the analysis of triplicated samples taken from three control plots and three plots treated with canopy N fertilization. The fertilization consisted in the provision of NH4NO3 of 20 kg N ha-1 y-1 May 2015 May 2015 until and September 2015. Microbial analysis showed that bacterial alpha diversity increased within the nitrogen treated samples. On the contrary, fungal diversity remained stable. Fungal community structure resulted differentiated according with the treatment (Permanova: R2 = 0.13 p- value = 0.03; Cap scale under reduced analysis: F = 1.63 p-value < 0.01). A significant (p < 0.05) increase of fungi ecologically related to lichen symbiosis was seen, maybe due to a major proliferation of algal cells on leaf surface due to the increase of N availability. Differently, bacterial community showed an unclear pattern (Permanova: R2 = 0.1 p-value = 0.07; Cap scale under reduced analysis: F = 1.84 p-value = 0.04).Results highlight that N deposition affected clearly the fungal community structure, even in the short term, whereas the bacterial community structure did not show a clear pattern.