Home-field advantage meets priming effect in root decomposition: Implications for belowground carbon dynamics

1. Home-field advantage (HFA) states that litter decomposes faster in ‘home’ than in ‘away’ soil, due to the specialization of decomposer organisms in decomposing litter derived from their local plant community. Demonstration of the HFA effect has been overwhelmingly based on aboveground leaf litter despite the fact that roots play a pivotal role in carbon (C) and nutrient cycling.

2. Labile C input in root exudates and newly shed root litters can enhance the activity of soil microorganisms, which in turn can favor the breakdown of older root litter, also referred to as the priming effect. It remains, however, unclear how the addition of fresh root-derived inputs affects HFA on the decomposition of absorptive roots (ARs) and transport roots (TRs), which have a different chemical composition.

3. Here, we conducted a two-stage (endogenous C consumption versus exogenous C priming) reciprocal transplant microcosm experiment to explore the effects of HFA on the decomposition of lower-quality ARs and higher-quality TRs of two subtropical tree species (Pinus elliottii and Cunninghamia lanceolata) and their responses to either labile (glucose) or recalcitrant (fresh ARs) C additions.

4. Decomposition of lower-quality ARs exhibited neutral HFA, while decomposition of higher-quality TRs exhibited positive HFA. The absence of HFA for short-lived ARs was possibly due to the legacy effect of their chemical defenses on decomposition. The neutral HFA for ARs became negative with glucose addition, which was linked to the dissimilarity of fungal community between the home and away soils. Neither glucose nor fresh ARs additions changed the HFA pattern of TRs, implying that these long-lived roots play a reinforced role in soil C accumulation when they decompose away from their origins.

5. These results indicate that the effect of HFA on decomposition differs between ARs and TRs, and could be modified by the priming effect induced by the root-derived C input. In general, our findings highlight that complex ‘HFA-priming’ interactions on root decomposition should be explicitly considered in the paradigm of belowground C dynamics.