A comparison of lodgepole and spruce needle chemistry impacts on terrestrial biogeochemical processes during isolated decomposition

Laura T Leonard; Kristin Mikkelson; Zhao Hao; Eoin L Brodie; Kenneth H Williams; Jonathan O Sharp

doi:10.7717/peerj.9538

A comparison of lodgepole and spruce needle chemistry impacts on terrestrial biogeochemical processes during isolated decomposition

PeerJ. 2020 Jul 16:8:e9538. doi: 10.7717/peerj.9538. eCollection 2020.

Authors

Laura T Leonard¹, Kristin Mikkelson¹, Zhao Hao², Eoin L Brodie², Kenneth H Williams^{2

3}, Jonathan O Sharp^{1

3}

Affiliations

¹ Colorado School of Mines, Golden, CO, USA.
² Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
³ Rocky Mountain Biological Laboratory, Crested Butte, CO, USA.

Abstract

This study investigates the isolated decomposition of spruce and lodgepole conifer needles to enhance our understanding of how needle litter impacts near-surface terrestrial biogeochemical processes. Harvested needles were exported to a subalpine meadow to enable a discrete analysis of the decomposition processes over 2 years. Initial chemistry revealed the lodgepole needles to be less recalcitrant with a lower carbon to nitrogen (C:N) ratio. Total C and N fundamentally shifted within needle species over time with decreased C:N ratios for spruce and increased ratios for lodgepole. Differences in chemistry correlated with CO₂ production and soil microbial communities. The most pronounced trends were associated with lodgepole needles in comparison to the spruce and needle-free controls. Increased organic carbon and nitrogen concentrations associated with needle presence in soil extractions further corroborate the results with clear biogeochemical signatures in association with needle chemistry. Interestingly, no clear differentiation was observed as a function of bark beetle impacted spruce needles vs those derived from healthy spruce trees despite initial differences in needle chemistry. These results reveal that the inherent chemistry associated with tree species has a greater impact on soil biogeochemical signatures during isolated needle decomposition. By extension, biogeochemical shifts associated with bark beetle infestation are likely driven more by changes such as the cessation of rhizospheric processes than by needle litter decomposition.

Keywords: Bark Beetle Disturbance; Lodgepole; Needle Decomposition; Nutrient Cycling; Soil Respiration; Soil biogeochemistry; Spruce.

Grants and funding

Financial support was provided by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research under exploratory university-led research: DE-SC0016451 with support through the Lawrence Berkley National Laboratory’s Watershed Function Scientific Focus Area under contract DE-AC02-05CH11231 (Lawrence Berkeley National Laboratory; operated by the University of California). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.