On the phenology of soil organisms: current knowledge and future steps

Abstract

Phenology is the study of timing of periodic activities in biological life cycles. It describes an inherent component of ecosystem dynamics and shifts in biological activity have been increasingly recognized as an indicator of global change. Although phenology is mainly studied above the ground, major ecosystem processes, such as decomposition, mineralization, and nutrient cycling, are soil-dependent. Therefore, the phenology of soil organisms is a crucial, but understudied, aspect of terrestrial ecosystem functioning. We performed a systematic review of 96 studies, which reported 228 phenological observations, to evaluate the current knowledge of soil microbial and animal phenology. Despite the increasing number of soil phenology reports, most research is still concentrated in a few countries (centered in the Northern Hemisphere) and taxa (microbiota), with significant gaps in the most diverse regions of the globe (i.e., tropics) and important taxa (e.g., ants, termites, and earthworms). Moreover, biotic predictors (e.g., biodiversity and species interactions) have rarely been considered as possible drivers of soil organisms' phenology. We present recommendations for future soil phenology research based on an evaluation of the reported geographical, taxonomic, and methodologic trends that bias current soil phenology research.First, we highlight papers that depict good soil phenology practice, either regarding the research foci, methodological approaches, or results reporting. Then, we discuss the gaps, challenges, and opportunities for future research. Overall, we advocate that focusing both on highly diverse ecosystems and key soil organisms, while testing for the direct and indirect effects of biodiversity loss and climatic stressors, could increase our knowledge of soil functioning and enhance the accuracy of predictions depicting the effects of global change on terrestrial ecosystem functioning as a whole.

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“…It is undeniable that individual parameters specific to each species can play the role of markers of population status. However, for certain species, it may be preferable to use reasonable minimized integral indicators that can be used to assess the ecological status of the population (Yarwood et al, 2020;Gunstone et al, 2021;Asato et al, 2023). Based on monitoring data, it is possible to conduct an integrated ecological assessment of population indicators for rapid diagnosis of their condition.…”

Seasonal shifts in plant diversity effects on aboveground-belowground phenological synchrony

“…Evidence suggests that investments in shoot and root production are commonly not synchronous (e.g. Steinaker & Wilson 2008;Steinaker et al 2010;Sloan et al 2016;Blume-Werry et al 2016), as well as the dynamics of soil organisms (Bonato Asato et al, 2023;Eisenhauer et al, 2018). However, we lack experimental evidence demonstrating whether changes in biodiversity may influence the predictability and synchronization of the dynamics above and below the ground.…”

“…Most ecosystem processes are soil-related or even soil-dependent (Bardgett & van der Putten, 2014;Soliveres et al, 2016;Schuldt et al, 2018). However, phenology tends to be monitored on easily observed aboveground response variables, and evidence describing soil phenology is mostly lacking (Bonato Asato et al, 2023). This knowledge gap leads to uncertainty about how well soil properties and belowground processes (i.e.…”