First field estimation of greenhouse gas release from European soil-dwelling Scarabaeidae larvae targeting the genus Melolontha

Abstract

Arthropods are a major soil fauna group, and have the potential to substantially influence the spatial and temporal variability of soil greenhouse gas (GHG) sinks and sources. The overall effect of soil-inhabiting arthropods on soil GHG fluxes still remains poorly quantified since the majority of the available data comes from laboratory experiments, is often controversial, and has been limited to a few species. The main objective of this study was to provide first insights into field-level carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) release of soil-inhabiting larvae of the Scarabaeidae family. Larvae of the genus Melolontha were excavated at various sites in west-central and southern Germany, covering a wide range of different larval developmental stages, larval activity levels, and vegetation types. Excavated larvae were immediately incubated in the field to measure their GHG production. Gaseous carbon release of individual larvae showed a large inter- and intra-site variability which was strongly correlated to larval biomass. This correlation persisted when upscaling individual CO2 and CH4 production to the plot scale. Field release estimates for Melolontha spp. were subsequently upscaled to the European level to derive the first regional GHG release estimates for members of the Scarabaeidae family. Estimates ranged between 10.42 and 409.53 kt CO2 yr-1, and 0.01 and 1.36 kt CH4 yr-1. Larval N2O release was only sporadically observed and not upscaled. For one site, a comparison of field- and laboratory-based GHG production measurements was conducted to assess potential biases introduced by transferring Scarabaeidae larvae to artificial environments. Release strength and variability of captive larvae decreased significantly within two weeks and the correlation between larval biomass and gaseous carbon production disappeared, highlighting the importance of field measurements. Overall, our data show that Scarabaeidae larvae can be significant soil GHG sources and should not be neglected in soil GHG flux research.

Fig 1. Direct CH₄ and CO₂ emissions, and larval biomass of individual Melolontha spp. larvae during field incubations.

The box midline shows the median, with the upper and lower limits of the box being the 75th and 25th percentile, respectively. The whiskers extend up to 1.5 times from the box edges to the furthest data point within that distance. Sampling sites are sorted by average larval biomass in ascending order. The colours of the boxplots indicate the species (white = Melolontha spp., green = M. melolontha, yellow = M. hippocastani).

Fig 2. Cumulated larval CO₂ and CH₄ emission estimates from field measurements for each individual sampling plot in relation to total cumulated larval biomass grouped by sampling site.

Error bars represent the propagated error of the individual larval emissions. Results of linear regression analysis using the complete dataset are given in the respective subfigure for CH₄ and CO₂.

Fig 3. Comparison of direct M. melolontha larval CO₂ and CH₄ emissions from field and laboratory measurements.

83 larvae were excavated at sampling Site 3 on 26.05.2017. Larval emissions of batch “Field” were sampled in the field directly after excavation. Batch “Lab1” and “Lab2” were kept 7 and 18 days in the laboratory, respectively, before emissions were measured. The boxplots for “Field” are identical to the boxplots for Site 3 in Fig 1. Numbers above the CO₂ and CH₄ emissions box plots are Spearman correlation coefficients between the respective gas emissions and the batch’s larval weight.