Indirect effects of bark beetle-generated dead wood on biogeochemical and decomposition processes in a pine forest
Bark beetle outbreaks are increasing in frequency and intensity, generating massive inventories of dead trees globally. During attacks, trees are pre-inoculated with ophiostomatoid fungi via bark beetles, which has been shown to increase termite presence and feeding. These events may, in turn, alter biogeochemical cycles during decomposition. We examined these relationships by experimentally inoculating dead wood with bluestain fungi in a temperate pine forest. Across ten replicate plots, eight 0.5 m-long logs were inoculated with Ophiostoma minus and eight with distilled water. Half of the logs from each inoculation treatment were covered from above with a mesh cage barrier to exclude aboveground beetles while permitting access by belowground decomposers. After 1 year, significant increases in mass (34%) and decreases in moisture content (− 17%) were observed across all treatments, but no consistent changes in density were evident. C concentrations were 12% greater in bark when barriers were present and 17% greater in sapwood when barriers and inoculation fungi were absent. N concentrations were 16% greater in bark for fungal-inoculated logs and 27% greater when barriers were present. C:N ratios in A horizon soils under fungal-inoculated logs were 12% greater. Furthermore, termites were present fourfold more in fungal-inoculated logs than controls and the presence of termites was associated with 6% less C in sapwood and 11% more N in both sapwood and heartwood. Together these results suggest dead wood generated via bark beetle attacks has different biogeochemical responses during initial decomposition phases, which could have implications for the C status in forests following bark beetle outbreaks.
KeywordsDead wood Termites Bark beetles Decomposition Biogeochemistry
This work is a contribution of the Forest and Wildlife Research Center and the Mississippi Agricultural and Forestry Experiment Station, Mississippi State University. This work was funded through the National Science Foundation (DEB # 1660346) and supported by the National Institution of Food and Agriculture, US Department of Agriculture, Mclntire Stennis capacity Grant # MISZ-069390 and Hatch project #069410. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the US Department of Agriculture. This project was made possible by the Mississippi State University Undergraduate Research Scholars Program, the Mississippi Agricultural and Forestry Experiment Station Small Research Initiative program, the Office of Research and Economic Development Cross-College Research Grant, the Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, the Institute for Genomics, Biocomputing and Biotechnology, and the field and laboratory assistance of Craig Bell, Sasith Karunarathna, Katy Limpert, Leana Rapp, Mercedes Siegle-Gaither, Jacob Landfield, John Formby, John Thomason, and Natalie Dearing. Special thanks to Misty Booth and the College of Forest Resources at Mississippi State University for site use in the John W. Starr Experimental Forest. Thank you to anonymous reviewers for their time and careful consideration.
Author contribution statement
CMS, NAC, JDT, and JJR conceived and designed the experiments. CMS, NAC, JDT, LGG, and JJR conducted fieldwork. CMS and LGG analyzed the hydrology and soil chemistry data. NAC analyzed the decomposition and invertebrate data. CMS, NAC, JDT, LGG, and JJR wrote the manuscript.
Compliance with ethical standards
Conflict of interest
J. J. Riggins is an inventor on a patent involving bluestain fungi in baiting methods for termites (US9924706B2). The author and his institution may financially benefit from this patent.
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