Out of the dark: Using energy flux to connect above‐ and belowground communities and ecosystem functioning

Abstract

Soil ecosystems are both particularly important to humans and vulnerable to human-made global change. Here, we identify some key aspects of soil community and ecosystem research that need to be more widely studied to understand soil responses to global change and enable us to efficiently protect them. This perspective integrates multiple taxa and trophic levels, combines structural community variables with ecosystem processes, and considers multiple energy channels rather than focusing on only bacterial, fungal, or plant-derived resources. Moreover, it enables implementing the claim that terrestrial ecosystem research should more widely adopt an integrative view of above-belowground processes. Having identified these key areas requiring higher attention, we suggest a wider application of the food-web energetics approach to calculating energy flux as a suitable and very powerful tool to simultaneously integrate these aspects. The approach combines food-web and metabolic theory to quantify energy flux through trophic networks as a universal currency of multitrophic ecosystem functioning. In addition to whole-community metrics, it allows for quantifying various important processes by summing up the flux out of autotrophs, detritus, or animals to their respective consumers. This includes the assessment of processes that are otherwise hard to quantify, such as belowground herbivory or predation. The calculation requires data on the focal community and its metabolic demand, trophic interactions, feeding preferences and assimilation efficiency, some of which can be measured, whereas other components can be inferred from readily available literature resources. We outline how novel, high-throughput methods, such as metabarcoding, can be combined with the energy-flux approach to improve our understanding of soil ecosystem structure and functioning. We hope that our article motivates fellow soil researchers to adopt energy-flux approaches for their community data and support the further development of this promising approach for soil community and ecosystem science.

Aboveground impacts of a belowground invader: how invasive earthworms alter aboveground arthropod communities in a northern North American forest

“…First, we need studies investigating the effects of earthworm invasion on vegetation structure, functional diversity and plant metabolites, as well as their impact on arthropod communities [ 45 , 48 , 52 ]. Furthermore, we need to assess the consequences of belowground invasions and the subsequent aboveground arthropod community changes for consumers of arthropods [ 12 ], above–belowground energy flux, ecosystem functions and services [ 8 , 53 , 54 ]. Future studies should also investigate if earthworm invasion facilitates secondary invasions in aboveground arthropod communities, potentially facilitated by non-native plants [ 23 ].…”

Global monitoring of soil animal communities using a common methodology

“…We have chosen these sampling methods as the most commonly used for the corresponding animal size groups and are straightforward enough to be used even by researchers with basic experience in soil animal ecology. These methods provide area-based estimations of biomass and density which is necessary for data comparability and calculations of energy fluxes and functional impacts of soil animals (Jochum & Eisenhauer 2022). For the latter reason, pitfall traps are not included in the main methods, but suggested as an auxiliary method (Supplementary protocol S1).…”

For flux's sake: General considerations for energy‐flux calculations in ecological communities

“…To calculate energy flux through a food chain or food web following the adapted food-web energetics approach (Figure 1), we need information on the focal community of organisms forming this trophic structure. This includes information on who comprises the community (trophic identity of organisms), the energetic demand of the organisms (metabolic rates), who eats whom (network topology) to which extent (preferences), and how much of the consumed energy TA B L E 1 Overview over the single steps involved in calculating energy flux with the adapted food-web energetics approach Jochum and Eisenhauer (2021) and Barnes et al (2018).…”

“…More generally, energy flux can be used as a universal currency of ecosystem functioning that can be compared across different ecosystem types (terrestrial, aquatic-freshwater or marine) providing several functions that would otherwise be hard, if not impossible, to compare (Barnes et al, 2018;Odum, 1968). Additionally, the approach allows the quantification of processes that are usually hard to measure, such as, for example, above-belowground interactions (Jochum & Eisenhauer, 2021). For example, many underground processes or the herbivory of sucking insect herbivores are hard to quantify with common methods.…”