Soil organic matter diagenetic state informs boreal forest ecosystem feedbacks to climate change
The fate of soil organic carbon (SOC) in boreal forests is dependent on the integrative ecosystem response to climate change. For example, boreal forest productivity is often nitrogen (N) limited, and climate warming can enhance N cycling and primary productivity. However, the net effect of this fee...
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Veröffentlicht in: | Biogeosciences 2023-02, Vol.20 (2), p.489-503 |
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Zusammenfassung: | The fate of soil organic carbon (SOC) in boreal forests
is dependent on the integrative ecosystem response to climate change. For
example, boreal forest productivity is often nitrogen (N) limited, and
climate warming can enhance N cycling and primary productivity. However, the
net effect of this feedback on the SOC reservoir and its longevity with
climate change remain unclear due to difficulty in detecting small
differences between large and variable carbon (C) fluxes needed to determine
net changes in soil reservoirs. The diagenetic state of SOC – resulting
from the physicochemical and biological transformations that alter the
original biomolecular composition of detrital inputs to soil over time – is
useful for tracing the net response of SOC at the timescales relevant to
climate change not usually discernible from fluxes and stocks alone. Here,
we test two hypotheses using a mesic boreal forest climate transect: (1) the SOC
diagenetic state is maintained across this climosequence, and (2) the
maintenance of the SOC diagenetic state is a consequence of coupled soil C and N
cycling, signifying the role of enhanced N cycling supporting SOC inputs
that maintain SOC stocks within the warmer-climate forests. Shifts in
nonvascular to vascular plant inputs with climate observed in these and
other boreal forests highlighted the need to carefully separate
biogeochemical indicators of SOC source from those signifying diagenetic
alteration. We thus evaluated and applied lignin biomarkers to assess the
diagenetic alteration of SOC in these boreal forest organic soils and
directly compared the lignin diagenetic state with that of soil organic
nitrogen (SON) assessed through amino acid composition. The lignin
diagenetic state remained constant across the climate transect, indicating a
balance between the input and removal of lignin in these mesic boreal
forests. When combined with previous knowledge of these forest ecosystems,
including the diagenetic state of SON and direct measures of C fluxes and
stocks, the results indicate a coupled increase in C and N cycling with
climate warming that supports forest productivity and maintains SOC stocks.
This balance could markedly shift as other factors begin to limit forest
productivity (e.g., trace nutrients, water) with further climate change or
affect forest nutrient allocation (e.g., forest age or compositional
change). Further application of the approach presented here could be used to
detect the limits of this and othe |
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ISSN: | 1726-4189 1726-4170 1726-4189 |
DOI: | 10.5194/bg-20-489-2023 |