The canopy layer, a biogeochemical actor in the forest N-cycle

Bortolazzi, Anna; Ros, Luca Da; Rodeghiero, Mirco; Tognetti, Roberto; Tonon, Giustino; Ventura, Maurizio

doi:10.1016/j.scitotenv.2021.146024

Cited by 28 publications

(20 citation statements)

References 152 publications

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“…Canopies have an important role in the forest N cycle (Bortolazzi et al., 2021). We found that direct uptake of N was occurring at our study site, potentially enough to satisfy the entire leaf turnover.…”

Section: Discussionmentioning

confidence: 99%

“…There is also considerable evidence of canopy water uptake from many biomes (Schreel & Steppe, 2020) and foliar N treatments are common in agriculture (Fageria et al., 2009). Forest canopies also play an important general role in N cycling (Bortolazzi et al., 2021; Guerrieri et al., 2021), but actual rates, mechanisms and effects of canopy nitrogen uptake (CNU) in forest ecosystems are difficult to generalise or scale. A key question relates to differences between experimental approaches.…”

Section: Introductionmentioning

confidence: 99%

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Forest canopy nitrogen uptake can supply entire foliar demand

et al. 2022

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1. Plant canopies intercept, process and potentially assimilate atmospheric nitrogen (N) additions, but the forest-scale effects of canopy processes on N cycling and plant nutrition are not clear. Substantial method artefacts and scaling issues exist in previous experimental studies which measure relevant N fluxes either at (a) natural abundance, (b) via a 15 N tracer or (c) by incorporation of additional 15 N into measured biomass, meaning these processes are often overlooked or discounted.2. Here, working in a mature Sitka spruce plantation and under ambient conditions, we used all three of these methods independently at stand, tree and branch scale to assess the effects of canopy interception on capture, assimilation and incorporation of inorganic N deposition by canopy biomass.3. We consistently found that above 70% of N deposition was unaccounted for (i.e. assimilated, processed beyond detectability, volatilised or retained) when passing through the canopy, independent of the assessment method. Using shortterm 15 N tracers, we found that this unaccounted N was retained in canopy tissues. Apparent uptake from monitoring of ecohydrological fluxes was sustained and consistent, suggesting that the tree canopies were a sink for N deposition. Seasonal variation in NO − 3 recovery also suggested biological activities influenced fluxes and transformations of this ion within the canopy. 4. The total amount of this canopy N uptake was greater than the mean annual N in litterfall, implying that this flux was supporting the turnover of the canopy.When we used 15 N to directly assess uptake into branch biomass we also did not find evidence for immediate relocation to other parts of the tree. 5. Our findings suggest that at our N-limited site, canopy uptake of N deposition is likely to be as important as root uptake of N but may be limited to supplying N to the canopy rather than the whole tree. Further research in this area is crucial to better understand the interactions of future changes in N deposition on primary production and carbon storage in forests.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Forest canopy nitrogen uptake can supply entire foliar demand

et al. 2022

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“…2, Table S1). During the first twenty years of succession the forests show negative values of canopy exchange that is indicative of net canopy N uptake and conservation (Table S1; Bortolazzi et al 2021). The net canopy N uptake varied between 2.5% and 44.1% of total atmospheric N deposition.…”

Section: Nitrogen Input and Output Fluxesmentioning

confidence: 99%

“…First, the forest canopy structure acts as a trap for atmospheric particles, in a way that canopies that are more complex can lead to higher dry deposition inputs to the forest floor (Bauters et al 2021a). Second, canopy exchange adds (canopy leaching) or removes (canopy uptake) substantial nutrients to/from throughfall deposition that finally arrives on the forest floor (Parker 1983;Bortolazzi et al 2021). Additionally, central African forest ecosystems are subjected to substantial N loads through atmospheric N deposition as NO 3 − (14.3 kg ha −1 yr −1 ), NH 4 + (12.2 kg ha −1 yr −1 ) and dissolved organic N (DON, 26.6 kg ha −1 yr −1 ) species (Bauters et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Conservative N cycling despite high atmospheric deposition in early successional African tropical lowland forests

et al. 2022

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that forests of the Congo basin are subject to high inputs of atmospheric N deposition, potentially alleviating this N limitation in early succession. Methods To address this hypothesis, we assessed the N status along a successional gradient of secondary forests in the Congo basin. In a set-up of 18 plots implemented along six successional stages, we quantified year-round N deposition, N leaching, N 2 O emission and the N flux of litterfall and fine root assimilation. Additionally, we determined the N content and C:N stoichiometry for canopy leaves, fine roots, and litter, as well as δ 15 N of canopy leaves.

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“…Researchers have simulated atmospheric N deposition in forests by adding N to the understory [7,39,40]. In contrast to such artificially added N, much of the naturally deposited atmospheric N is intercepted and retained by the forest canopy [41,42]. It follows that understory N addition may overestimate the effects of N deposition on forest ecosystems and especially on the understory and soil-related ecological properties [43].…”

Section: Introductionmentioning

confidence: 99%

Influence of Simulated Nitrogen Deposition on the Soil Seed Bank of a Subtropical Evergreen Broadleaved Forest

Wang

Huang

Guo

et al. 2021

Forests

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Increased nitrogen (N) deposition may have profound effects on forest ecosystems. However, information on the impacts of elevated N deposition on belowground soil seed bank in forests is lacking. In a field experiment, we added N at 50 and 25 kg N ha−1 year−1 to the canopy (CAN50 and CAN25) and to the understory (UAN50 and UAN25), to determine the effects of N deposition on soil seed bank structure and composition in a subtropical evergreen broadleaved forest. A total of 1545 seedlings belonging to 37 species emerged from the 10 cm-depth soil samples. After 6 years of N addition, soil seed bank density significantly increased at the depth of 0–10 cm under CAN50 treatment relative to the control. N addition did not significantly affect species richness, the Simpson index, Shannon–Wiener index, or Pielou index of the soil seed banks. Seed bank density and species richness were positively correlated with soil organic matter content. For the whole 0–10 cm soil layer, the percentage of total seed abundance and total species richness represented by tree species among the N-addition treatments was ≤9.3% and ≤16.1%, respectively. Soil seed bank composition was similar among UAN25, UAN50, and the control, but canopy N addition and especially CAN50 altered the species composition of the seed bank. Overall, our results indicate that artificial canopy N deposition at 50 kg N ha−1 year−1 but not understory N addition tends to promote seed storage and to change species composition in the soil seed bank. Because of the dominance of shrubs and herbs in the soil seed bank, the potential to regenerate tree species from the soil seed bank is limited in the subtropical evergreen broadleaved forest.

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The canopy layer, a biogeochemical actor in the forest N-cycle

Cited by 28 publications

References 152 publications

Forest canopy nitrogen uptake can supply entire foliar demand

Forest canopy nitrogen uptake can supply entire foliar demand

Conservative N cycling despite high atmospheric deposition in early successional African tropical lowland forests

Influence of Simulated Nitrogen Deposition on the Soil Seed Bank of a Subtropical Evergreen Broadleaved Forest

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