Conceptualising carbon cycling pathways across different land-use types based on rates and ages of soil-respired CO₂

Soil carbon dioxide (CO₂) efflux constitutes a major carbon (C) transfer from terrestrial ecosystems to the atmosphere, driven by numerous metabolic and allocation processes in the plant-soil system. Land use affects key components of C cycling pathways through vegetation type, C allocation, abiotic conditions, and management impacts on soil organic matter (SOM). However, systematic comparisons of these pathways among land uses remain scarce. In two contrasting seasons, we measured respiration rates and C isotopic signatures (¹⁴C, ¹³C) of in situ soil-respired CO₂ and its autotrophic and heterotrophic sources derived from incubations at 16 sites across Switzerland, covering temperate and alpine grasslands, forests, croplands, and managed peatlands. Our findings revealed significant differences in the rates, ages, and sources of soil-respired CO₂ between land-use types, reflecting variations in C cycling dynamics. We propose that respiration rates and ages of soil-respired CO₂ serve as comprehensive indicators to categorize C cycling into: 1. High-throughput systems (temperate grasslands) where high respiration rates of young (