Leaky nitrogen cycle in pristine African montane rainforest soil

Rütting, Tobias; Ntaboba, Landry Cizungu; Roobroeck, Dries; Bauters, Marijn; Huygens, Dries; Boeckx, Pascal

doi:10.1002/2015gb005144

Cited by 18 publications

(17 citation statements)

References 60 publications

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“…Gross N mineralization for the karst forest was only measured at one site (Zhu et al, ), which showed comparable rates with the current study. Compared with other subtropical/tropical regions of the world, gross N mineralization rates in the present study were higher than those (0.6–1.8 mg N kg −1 d −1 ) observed in forest soils of subtropical Australia (Burton et al, ) but were at the lower end of the range (2–14 mg N kg −1 d −1 ) reported for tropical forests (Rutting et al, ; Silver et al, , ; Sotta et al, ).…”

Section: Discussioncontrasting

confidence: 73%

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

Yang

Chen

et al. 2017

JGR Biogeosciences

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Soil gross nitrogen (N) transformations are crucial for assessing forest N status. Although there is evidence suggesting that the N cycle is open in the karst forest, southwest China, process‐based investigation of gross soil N transformations is limited. In the current study, gross soil N transformations were investigated using 15N isotope dilution and 15N tracer techniques in a typical karst forest with calcareous soil (Calcareous lithosols) in comparison with an adjacent nonkarst forest with red soil (Haplic acrisol).The gross rates of N mineralization, nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and nitrate immobilization were significantly greater in the karst forest. Ammonium immobilization was comparable to gross N mineralization, so that ammonium could be efficiently conserved in the nonkarst forest. Meanwhile, the produced nitrate was mostly retained via DNRA and nitrate immobilization. This resulted in a negligible net nitrate production in the nonkarst forest. In contrast, ammonium immobilization rate only accounted for half of gross N mineralization rate in the karst forest. The nitrate retention capacity is relatively low, with 41.6 ± 4.2% of the produced nitrate being retained via DNRA and nitrate immobilization. Due to relatively low nitrate retention capacity, nitrate was accumulated in the karst forest soil. Our results indicate that the nonkarst forest with red soil holds a very conservative N cycle, but the N cycle in the karst forest is leaky.

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Section: Discussioncontrasting

confidence: 73%

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

Yang

Chen

et al. 2017

JGR Biogeosciences

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“…The observations from lowland forest are in stark contrast to the high soil pore water and stream water NO 3 À concentrations observed in the montane forest with comparatively low DON losses. Previous reports have indeed also shown high NO 3 À losses from some Neotropical montane forests, which has led to the belief that many tropical montane forests are not N-limited (Mcdowell and Asbury 1994, Brookshire et al 2012b, R€ utting et al 2014. This is further supported by the lower soil C:N ratio in the montane compared to lowland forest, which is an indicator of higher soil available N (Appendix S1: Table S6).…”

Section: Comparing Lowland and Montane Mixed Forest (Lmf Vs Mmf)mentioning

confidence: 71%

“…, Rütting et al. ). This is further supported by the lower soil C:N ratio in the montane compared to lowland forest, which is an indicator of higher soil available N (Appendix : Table S6).…”

Section: Discussionmentioning

confidence: 99%

Contrasting nitrogen fluxes in African tropical forests of the Congo Basin

Bauters

Verbeeck

Rütting

et al. 2019

Ecological Monographs

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The observation of high losses of bioavailable nitrogen (N) and N richness in tropical forests is paradoxical with an apparent lack of N input. Hence, the current concept asserts that biological nitrogen fixation (BNF) must be a major N input for tropical forests. However, well‐characterized N cycles are rare and geographically biased; organic N compounds are often neglected and soil gross N cycling is not well quantified. We conducted comprehensive N input and output measurements in four tropical forest types of the Congo Basin with contrasting biotic (mycorrhizal association) and abiotic (lowland–highland) environments. In 12 standardized setups, we monitored N deposition, throughfall, litterfall, leaching, and export during one hydrological year and completed this empirical N budget with nitrous oxide (N2O) flux measurement campaigns in both wet and dry season and in situ gross soil N transformations using 15N‐tracing and numerical modeling. We found that all forests showed a very tight soil N cycle, with gross mineralization to immobilization ratios (M/I) close to 1 and relatively low gross nitrification to mineralization ratios (N/M). This was in line with the observation of dissolved organic nitrogen (DON) dominating N losses for the most abundant, arbuscular mycorrhizal associated, lowland forest type, but in contrast with high losses of dissolved inorganic nitrogen (DIN) in all other forest types. Altogether, our observations show that different forest types in central Africa exhibit N fluxes of contrasting magnitudes and N‐species composition. In contrast to many Neotropical forests, our estimated N budgets of central African forests are imbalanced by a higher N input than output, with organic N contributing significantly to the input‐output balance. This suggests that important other losses that are unaccounted for (e.g., NOx and N2 as well as particulate N) might play a major role in the N cycle of mature African tropical forests.

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“…This corroborates a recent finding of very high N losses at 1900 m a.s.l. at the Rwanda site (Rütting et al, 2014), and the observation of high retention potential of bio-available N in Chilean Andisols (Huygens et al, 2008). Further research is needed to explain the notable divergence in soil and foliage δ 15 N along the Ecuadorian transect, mainly driven by the highest elevational cluster.…”

Section: Discussionmentioning

confidence: 98%

Parallel functional and stoichiometric trait shifts in South American and African forest communities with elevation

et al. 2017

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Abstract. The Amazon and Congo basins are the two largest continuous blocks of tropical forest with a central role for global biogeochemical cycles and ecology. However, both biomes differ in structure and species richness and composition. Understanding future directions of the response of both biomes to environmental change is paramount. We used one elevational gradient on both continents to investigate functional and stoichiometric trait shifts of tropical forest in South America and Africa. We measured communityweighted functional canopy traits and canopy and topsoil δ 15 N signatures. We found that the functional forest composition response along both transects was parallel, with a shift towards more nitrogen-conservative species at higher elevations. Moreover, canopy and topsoil δ 15 N signals decreased with increasing altitude, suggesting a more conservative N cycle at higher elevations. This cross-continental study provides empirical indications that both South American and African tropical forest show a parallel response with altitude, driven by nitrogen availability along the elevational gradients, which in turn induces a shift in the functional forest composition. More standardized research, and more research on other elevational gradients is needed to confirm our observations.

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Leaky nitrogen cycle in pristine African montane rainforest soil

Abstract: ). This study provided new process understanding of soil N cycling in humid tropical forests and added geographically independent evidence that humid tropical forests are characterized by soil N dynamics and N inputs sustaining bioavailable N loss.

Cited by 18 publications

References 60 publications

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

Contrasting nitrogen fluxes in African tropical forests of the Congo Basin

Parallel functional and stoichiometric trait shifts in South American and African forest communities with elevation

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