Spatio‐temporal variability and intra‐event variation of throughfall ammonium and nitrate in a pine plantation

• Published in: Hydrological processes Vol. 37; no. 4
• Main Authors: Wang, Chunyu, Sun, Xinchao, Fan, Chunbin, Wei, Yixin, Jia, Guangkai, Cao, Yanhong
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.04.2023; Wiley Subscription Services, Inc
• Subjects: Agriculture; Ammonium; Ammonium compounds; biological nitrification; Canopies; Canopy; canopy exchange; Deposition; Dry deposition; Fluxes; Forest ecosystems; Growing season; intra‐event variation; N deposition; Nitrates; Nitrification; Nitrogen; Plant cover; Plantations; Precipitation; Rainfall; rainfall characteristics; Rainfall intensity; Spatial distribution; Spatial variability; Spatial variations; spatio‐temporal variability; Temporal variability; Temporal variations; Terrestrial ecosystems; Throughfall; Uptake; Variability
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.14872

Forest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems. Canopy modification of atmospheric inorganic nitrogen deposition in a pine plantation.