The role of the understory in litter DOC and nutrient leaching in boreal forests

Hensgens, Geert; Laudon, Hjalmar; Peichl, Matthias; Gil, Itziar Aguinaga; Zhou, Quan; Berggren, Martin

doi:10.1007/s10533-020-00668-5

Cited by 30 publications

(26 citation statements)

References 64 publications

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“…O) layer as it grades into the A layer leads to increased leaching. This is in accordance with studies showing that leaching from pine litter, the main component of the O horizon in this study, increases as decomposition advances 52 , 53 . The Δ 14 C SOC signal of the O horizon indicates an average origin of roughly 20 years ago.…”

Section: Introductionsupporting

confidence: 93%

The undetected loss of aged carbon from boreal mineral soils

Hensgens

Laudon

Johnson

et al. 2021

Sci Rep

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The boreal forest is among the largest terrestrial biomes on earth, storing more carbon (C) than the atmosphere. Due to rapid climatic warming and enhanced human development, the boreal region may have begun transitioning from a net C sink to a net source. This raises serious concern that old biogenic soil C can be re-introduced into the modern C cycle in near future. Combining bio-decay experiments, mixing models and the Keeling plot method, we discovered a distinct old pre-bomb organic carbon fraction with high biodegradation rate. In total, 34 ± 12% of water-extractable organic carbon (WEOC) in podzols, one of the dominating boreal soil types, consisted of aged (~ 1000 year) labile C. The omission of this aged (i.e., Δ14C depleted) WEOC fraction in earlier studies is due to the co-occurrence with Δ14C enriched modern C formed following 1950s nuclear bomb testing masking its existence. High lability of aged soil WEOC and masking effects of modern Δ14C enriched C suggests that the risk for mobilization and re-introduction of this ancient C pool into the modern C cycle has gone undetected. Our findings have important implications for earth systems models in terms of climate-carbon feedbacks and the future C balance of the boreal forest.

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Section: Introductionsupporting

confidence: 93%

The undetected loss of aged carbon from boreal mineral soils

Hensgens

Laudon

Johnson

et al. 2021

Sci Rep

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“…Following collection, pure water extractions were carried out using a 48-h shaking (140 RPM) protocol at room temperature (Hensgens et al 2020). After filtration (0.7 lm; Whatman GF/F) and dilution to 5.9 mg C l -1 , samples were taken for FT-ICR MS analyses, acidified to pH * 2 using ultrapure HCl and immediately frozen (-24°C).…”

Section: Dom Extraction and Samplingmentioning

confidence: 99%

“…The characterization of litter-leached DOM has often not been detailed enough to provide a molecular understanding of the leaching dynamics and involved processes (Brock et al 2020). For example, while it is well-documented that there are large variations in microbial bioavailability of DOM (BDOM) between DOM leached from different litter sources (Cleveland et al 2004;Silveira 2011;Hensgens et al 2020) and at different litter decay stages (Don and Kalbitz 2005;Hensgens et al 2020), it is unknown if corresponding differences exist on a molecular composition level. This leaves the fundamental question of how BDOM relates to litter molecular DOM composition unanswered.…”

Section: Introductionmentioning

confidence: 99%

“…1 Conceptualizing high reactive (HR) and low reactive (LR) litter species based on litter mass loss rates and C solubility. Simplified data from (Hensgens et al 2020). Dashed lines show mass loss and DOM leaching potential (mg C g -1 ) at 10, 48 and 180 days of litter decay for HR (yellow) and LR (blue) species.…”

Section: Introductionmentioning

confidence: 99%

“…Dashed lines show mass loss and DOM leaching potential (mg C g -1 ) at 10, 48 and 180 days of litter decay for HR (yellow) and LR (blue) species. In reality, LR species could show either a slight decrease or a slight increase in leachable material depending on its source litter (Don and Kalbitz 2005;Hensgens et al 2020) decomposition progresses, leachate chemistry will show greater changes in HR as opposed to LR species, while (2.2) a higher degree of similarity is seen in leachate chemistry towards the later stages of litter decomposition. Finally, if the above hypotheses can be supported, we expect that fresh HR litter leachates contain unique chemical features that are linked to their higher overall reactivity.…”

Section: Introductionmentioning

confidence: 99%

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Impacts of litter decay on organic leachate composition and reactivity

et al. 2021

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Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.

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Seasonal patterns in nutrient bioavailability in boreal headwater streams

Rulli

Bergström

Sponseller

et al. 2022

Limnology & Oceanography

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Changes in nutrient bioavailability due to increased loading of dissolved organic matter (DOM) may impact boreal freshwaters. Yet, the relative bioavailability of carbon (C), nitrogen (N), and phosphorus (P) associated with terrestrial DOM remains poorly understood. We applied short-term bioassays with natural bacterial inocula to determine seasonal variation in bioavailable organic nutrient pools from four boreal headwater streams in northern Sweden. Experiments were designed to exhaust bioavailable nutrients associated with DOM by inducing limiting conditions when all required resources except for the targeted nutrient (C, N, or P) are provided in excess. We hypothesized that the supply of different bioavailable nutrients to streams would reflect seasonal variations in terrestrial demand, hydrology, and temperature. The delivery of bioavailable DOM-associated resources from the four streams were, on average, 2%, 11%, and 38% of the total dissolved organic C, N, and P, respectively, emphasizing the relatively low C bioavailability in these DOM-rich waters. Bioavailable N : P ratios peaked in autumn for all sites, with lower values in winter and spring. Both in terms of relative (% of total) and absolute bioavailable organic nutrient concentrations, the seasonal pattern was characterized by systematically high values for the autumn period. Furthermore, links between bioavailable resources and temperature and hydrology varied across sites, time periods, and the different elements. Thus, elevated concentrations of bioavailable organic resources in autumn suggest the potential for leaf fall, as well as late season storms that rewet dry soils, to serve as considerable sources of C, N, and P to boreal aquatic ecosystems.

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The role of the understory in litter DOC and nutrient leaching in boreal forests

Cited by 30 publications

References 64 publications

The undetected loss of aged carbon from boreal mineral soils

The undetected loss of aged carbon from boreal mineral soils

Impacts of litter decay on organic leachate composition and reactivity

Seasonal patterns in nutrient bioavailability in boreal headwater streams

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