Decadal-scale litter manipulation alters the biochemical and physical character of tropical forest soil carbon

Cusack, Daniela; Halterman, Sarah; Tanner, Edmund V. J.; Wright, S. Joseph; Hockaday, William C.; Dietterich, Lee H.; Turner, Benjamín L.

doi:10.1016/j.soilbio.2018.06.005

Cited by 38 publications

(20 citation statements)

References 80 publications

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Section: Implications Of the Studysupporting

confidence: 91%

“…Previous work at our study site reported minor changes in C density fractions, which were largely equivalent to our results for accessible and mineral-associated SOM based on particle-size fractionation 45 . The seasonal increase in mineral-associated C stocks with litter addition at 0–5 cm depth 45 , indicates only minor changes in soil C storage close to the soil-litter interface. Hence, the rapid turnover of mineral-associated SOC at our study site and the lack of changes below 10-cm depth suggest that high biological activity at the soil surface is likely to be a key determinant of SOC storage over decadal time scales.…”

Section: Implications Of the Studysupporting

confidence: 91%

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Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Sayer

Lopez-Sangil

Crawford

et al. 2019

Sci Rep

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Soil organic carbon (SOC) dynamics represent a persisting uncertainty in our understanding of the global carbon cycle. SOC storage is strongly linked to plant inputs via the formation of soil organic matter, but soil geochemistry also plays a critical role. In tropical soils with rapid SOC turnover, the association of organic matter with soil minerals is particularly important for stabilising SOC but projected increases in tropical forest productivity could trigger feedbacks that stimulate the release of stored SOC. Here, we demonstrate limited additional SOC storage after 13–15 years of experimentally doubled aboveground litter inputs in a lowland tropical forest. We combined biological, physical, and chemical methods to characterise SOC along a gradient of bioavailability. After 13 years of monthly litter addition treatments, most of the additional SOC was readily bioavailable and we observed no increase in mineral-associated SOC. Importantly, SOC with weak association to soil minerals declined in response to long-term litter addition, suggesting that increased plant inputs could modify the formation of organo-mineral complexes in tropical soils. Hence, we demonstrate the limited capacity of tropical soils to sequester additional C inputs and provide insights into potential underlying mechanisms.

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Section: Implications Of the Studysupporting

confidence: 91%

Section: Implications Of the Studysupporting

confidence: 91%

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Sayer

Lopez-Sangil

Crawford

et al. 2019

Sci Rep

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“…Cross polarization spectra were applied with 5,000 scans, a 2 ms contact time, at 12 kHz MAS frequency, and 1.2 s recycle delay. More 13 C NMR analytical details can be found in Cusack et al (2018). Resulting spectra were divided into seven C functional groups, and the relative contributions were quantified by integrating the signal intensities of different chemical shift regions: 0–45 ppm assigned to alkyl C, 45–60 ppm to N ‐alkyl/methoxyl C ( N ‐alkyl), 60–95 ppm to O ‐alkyl C, 95–110 ppm to di‐ O ‐alkyl C, 110–145 ppm to aromatic C, 145–165 ppm to phenolic C, and 165–215 ppm to amide/carboxyl C. The percentages of six biomolecular SOM constituents, including carbohydrate, protein, lignin, lipid, carbonyl, and char, were estimated from the integrated spectra for each sample using a molecular mixing model constrained by C and N concentrations after the acid pretreatment (Table S4) measured by combustion on an elemental analyzer (Baldock, Masiello, Gélinas, & Hedges, 2004).…”

Section: Methodsmentioning

confidence: 99%

Trade‐offs in soil carbon protection mechanisms under aerobic and anaerobic conditions

Huang

Hockaday

et al. 2020

Global Change Biology

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Oxygen (O2) limitation is generally understood to suppress oil carbon (C) decomposition and is a key mechanism impacting terrestrial C stocks under global change. Yet, O2 limitation may differentially impact kinetic or thermodynamic versus physicochemical C protection mechanisms, challenging our understanding of how soil C may respond to climate‐mediated changes in O2 dynamics. Although O2 limitation may suppress decomposition of new litter C inputs, release of physicochemically protected C due to iron (Fe) reduction could potentially sustain soil C losses. To test this trade‐off, we incubated two disparate upland soils that experience periodic O2 limitation—a tropical rainforest Oxisol and a temperate cropland Mollisol—with added litter under either aerobic (control) or anaerobic conditions for 1 year. Anoxia suppressed total C loss by 27% in the Oxisol and by 41% in the Mollisol relative to the control, mainly due to the decrease in litter‐C decomposition. However, anoxia sustained or even increased decomposition of native soil‐C (11.0% vs. 12.4% in the control for the Oxisol and 12.5% vs. 5.3% in the control for the Mollisol, in terms of initial soil C mass), and it stimulated losses of metal‐ or mineral‐associated C. Solid‐state 13C nuclear magnetic resonance spectroscopy demonstrated that anaerobic conditions decreased protein‐derived C but increased lignin‐ and carbohydrate‐C relative to the control. Our results indicate a trade‐off between physicochemical and kinetic/thermodynamic C protection mechanisms under anaerobic conditions, whereby decreased decomposition of litter C was compensated by more extensive loss of mineral‐associated soil C in both soils. This challenges the common assumption that anoxia inherently protects soil C and illustrates the vulnerability of mineral‐associated C under anaerobic events characteristic of a warmer and wetter future climate.

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“…We quantified SOM associated with four soil particlesize fractions. While we acknowledge that particle size fractionation does not definitively distinguish POM and MAOM, previous studies in the experimental plots demonstrated that particle size fractionation yielded similar results to density fractions (Cusack et al 2018;Sayer et al 2019). Hence, we use the cutoff points for POM vs. MAOM recommended by Lavallee et al (2020) for ease of interpretation, whereby we refer to two size fractions representing POM (2000-200 lm and 200-50 lm) and two size fractions representing MAOM (50-20 lm and \ 20 lm).…”

Section: Particle-size Fractionationmentioning

confidence: 55%

Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

et al. 2020

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Soil organic matter (SOM) in tropical forests is an important store of carbon (C) and nutrients. Although SOM storage could be affected by global changes via altered plant productivity, we know relatively little about SOM stabilisation and turnover in tropical forests compared to temperate systems. Here, we investigated changes in soil C and N within particle size fractions representing particulate organic matter (POM) and mineral-associated organic matter (MAOM) after 13 years of experimental litter removal (L−) and litter addition (L+) treatments in a lowland tropical forest. We hypothesized that reduced nitrogen (N) availability in L− plots would result in N-mining of MAOM, whereas long-term litter addition would increase POM, without altering the C:N ratio of SOM fractions. Overall, SOM-N declined more than SOM-C with litter removal, providing evidence of N-mining in the L− plots, which increased the soil C:N ratio. However, contrary to expectations, the C:N ratio increased most in the largest POM fraction, whereas the C:N ratio of MAOM remained unchanged. We did not observe the expected increases in POM with litter addition, which we attribute to rapid turnover of unprotected SOM. Measurements of ion exchange rates to assess changes in N availability and soil chemistry revealed that litter removal increased the mobility of ammonium-N and aluminium, whereas litter addition increased the mobility of nitrate-N and iron, which could indicate SOM priming in both treatments. Our study suggests that altered litter inputs affect multiple processes contributing to SOM storage and we propose potential mechanisms to inform future work.

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Decadal-scale litter manipulation alters the biochemical and physical character of tropical forest soil carbon

Cited by 38 publications

References 80 publications

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Trade‐offs in soil carbon protection mechanisms under aerobic and anaerobic conditions

Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

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