Abstract
Decaying roots contribute disproportionately to soil organic carbon (SOC) stocks in many ecosystems, yet few studies have examined the afterlife effects of root trait variability on the formation, stability and mineralization of SOC. In order to assess how root functional class (absorptive vs. transport) and mycorrhizal association (ectomycorrhizal vs. arbuscular mycorrhizal fungi) affect both formation and loss of SOC, we decayed lower-order absorptive (orders 1–2) and higher-order transport (orders 3–4) roots from six arbuscular mycorrhizal (AM) and six ectomycorrhizal (EcM) associated hardwood tree species in an isotopically distinct soil under laboratory conditions. We found that root litter effects on SOC differed significantly among root functional classes and mycorrhizal types. AM absorptive and transport roots (high in nitrogen and soluble compounds) contributed more to the formation of new mineral-associated organic carbon (MAOC), but also contributed to higher mineralization of native SOC (via priming effects). Moreover, absorptive AM roots formed MAOC gradually and rates saturated, whereas ECM roots formed MAOC more quickly, despite slower decay (via greater formation efficiency). Together, these findings demonstrate how different combinations of root traits might contribute to soil C balance, and that failure to account for the chemical and morphological heterogeneity of roots, as well their interactions with microbes over time, may lead to incorrect projections of SOC stocks and turnover.
| Original language | English |
|---|---|
| Article number | 109008 |
| Journal | Soil Biology and Biochemistry |
| Volume | 180 |
| DOIs | |
| State | Published - May 2023 |
Funding
4 Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (hxxp://energy.gov/downloads/doe-public-access-plan). We thank the following individuals for their assistance during root and soil processing: Elizabeth Huenupi Pena, Mary Huynh, Emma Hand and Brindin Parrot. This work was supported by the Smithsonian Forest Global Earth Observatory ( 2019 ForestGEO grant) and the Department of Energy ( DE-SC0016188 ). We are also grateful to the Oak Spring Garden Foundation’s 2021 Interdisciplinary Residency for providing support during the writing of this manuscript. KVB would like to thank Alexis Elton, Kaitlin Bryson, Brien Beidler, Yi Hsuan Sung and Lauren Winchester for their help with previous drafts of this manuscript. MEC would like to acknowledge that Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725. Lastly, we are grateful to the three anonymous reviewers for their close reading of our manuscript and their helpful comments which improved the quality of this manuscript. We found that absorptive roots had faster initial decay rates (k1), but the fraction of fast decomposing litter (s) was smaller compared with transport roots, resulting in more litter C remaining after 265 days (Table 2). Previous studies measuring root mass remaining in litterbags have found that lower order mycorrhizal roots had more mass remaining through time or decayed slower than non-mycorrhizal (Langley et al., 2006) and higher order transport roots (Fan and Guo 2010; Goebel et al., 2011). Slower mycorrhizal root decay is attributed to a larger acid unhydrolyzable fraction comprised of suberin, tannins, lignin and other polyphenolic compounds (Hendricks et al., 2006; Xia et al., 2015; Wei-Ping et al. 2018; Sun et al., 2018; Yin et al., 2021). In support of previous findings, we found that both AM and EcM absorptive roots had higher initial concentrations of AUR (Table 1). Fitting root C remaining to a two-stage decay model (Fig. 1) revealed that there was a small portion of absorptive root litter (<10%) that decays on the time scale of days to weeks, while the remaining litter may take decades to decompose (Table 2). Some species of roots went from decaying at a rate similar to fungi (Brabcová et al., 2016; Beidler et al., 2020) to decaying at rates similar to coarse woody debris (Kahl et al., 2017), all in a matter of weeks.We thank the following individuals for their assistance during root and soil processing: Elizabeth Huenupi Pena, Mary Huynh, Emma Hand and Brindin Parrot. This work was supported by the Smithsonian Forest Global Earth Observatory (2019 ForestGEO grant) and the Department of Energy (DE-SC0016188). We are also grateful to the Oak Spring Garden Foundation's 2021 Interdisciplinary Residency for providing support during the writing of this manuscript. KVB would like to thank Alexis Elton, Kaitlin Bryson, Brien Beidler, Yi Hsuan Sung and Lauren Winchester for their help with previous drafts of this manuscript. MEC would like to acknowledge that Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725. Lastly, we are grateful to the three anonymous reviewers for their close reading of our manuscript and their helpful comments which improved the quality of this manuscript.
Keywords
- Decomposition
- Mineral-associated organic matter
- Priming effects
- Root traits