Soil carbon storage under simulated climate change is mediated by plant functional type

Elise Pendall, Yui Osanai, Amity L. Williams, Mark J. Hovenden

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    Abstract

    The stability of soil organic matter (SOM) pools exposed to elevated CO 2 and warming has not been evaluated adequately in long-term experiments and represents a substantial source of uncertainty in predicting ecosystem feedbacks to climate change. We conducted a 6-year experiment combining free-air CO 2 enrichment (FACE, 550 ppm) and warming (+2 °C) to evaluate changes in SOM accumulation in native Australian grassland. In this system, competitive interactions appear to favor C 4 over C 3 species under FACE and warming. We therefore investigated the role of plant functional type (FT) on biomass and SOM responses to the long-term treatments by carefully sampling soil under patches of C 3- and C 4-dominated vegetation. We used physical fractionation to quantify particulate organic matter (POM) and long-term incubation to assess potential decomposition rates. Aboveground production of C 4 grasses increased in response to FACE, but total root biomass declined. Across treatments, C : N ratios were higher in leaves, roots and POM of C 4 vegetation. CO 2 and temperature treatments interacted with FT to influence SOM, and especially POM, such that soil carbon was increased by warming under C 4 vegetation, but not in combination with elevated CO 2. Potential decomposition rates increased in response to FACE and decreased with warming, possibly owing to treatment effects on soil moisture and microbial community composition. Decomposition was also inversely correlated with root N concentration, suggesting increased microbial demand for older, N-rich SOM in treatments with low root N inputs. This research suggests that C 3-C 4 vegetation responses to future climate conditions will strongly influence SOM storage in temperate grasslands.
    Original languageEnglish
    Pages (from-to)505-514
    Number of pages10
    JournalGlobal Change Biology
    Volume17
    Issue number1
    DOIs
    Publication statusPublished - 2011

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