13C-Labeled Artificial Root Exudates Are Immediately Respired in a Peat Mesocosm Study

Abstract

Globally, peatlands have been recognized as important carbon sinks while only covering approximately 3% of the earth’s land surface. Root exudates are known key drivers of C cycling in soils and rhizosphere priming effects have been studied extensively in terrestrial ecosystems. Their role for decomposition of peat still remains unclear, as little research about their fate and potential priming effects in peat exists. In this study, we aimed to evaluate pathways of root exudates and their short-term priming effects by daily determination of stable carbon isotope fluxes of CO2 and CH4. As the drainage of peatlands strongly alters processes of decomposition, we included measurements after drainage as well. Results revealed the immediate respiration of root exudates in peat, mainly as CO2, while CH4 release was associated with a lag time of several days. However, the largest proportion of added root exudates remained in the solid and liquid phase of peat. In conclusion, our findings suggest that no priming occurred as added substrates remained immobile in peat.

Stronger negative priming effect and lower basal respiration rates in nutrient‐poor as compared to nutrient‐rich forestry‐drained peatland

“…Leiber‐Sauheitl et al 54 found no significant priming (no priming at all or insignificant negative priming) in organic soil used for grazing after an addition of isotopically labelled sheep excrements. More recently, Müller et al 33 found no noticeable priming in nutrient‐poor bog peat after addition of artificial root exudates, and Aaltonen et al 32 found no priming after glucose addition and water table manipulation in an incubation experiment with peat collected from clear‐cut and forested peatlands. These results are in accordance with results presented here as well as with previous results of the same peat soils utilizing a natural abundance ( 14 C) approach 36 …”

“…In this study we found a negative PE in peat soils from two different study sites with different nutrient status: the added 13 C-glucose simulating in a simplified manner fresh photosynthates and leachates into the soil did not increase the decomposition of the old SOM in these peat soils, but on the contrary, decreased it. Studies of PE in organic soils are still inadequate and contradictory; both positive (e.g., 12,30,34,37,52,53 ) and negative priming (e.g., 12,29,31,37 ), as well as observations without significant priming (e.g., 32,33,36,37,54 ) have been reported. These results suggest that the factors behind PE are complicated and depend on various variables, such as the humification rate, C and N content, substrate type and concentration, microbial communities, soil moisture or water table level.…”

“…There is also evidence that the direction and magnitude of the PE depends on the environmental conditions and the quality of fresh C (e.g., [28][29][30][31][32][33]. Most of the studies of PE have been conducted in mineral soils, but increasing number of experiments report about PEs in C-rich organic soils, such as peat soils (e.g., 12,29,[32][33][34][35][36][37][38] ). These studies report both positive and negative PE as well as no significant priming at all; thus no consensus has been found for peat soils.…”

“…Understanding of the PE, its magnitude and direction is still incomplete, particularly in peatlands. There is also evidence that the direction and magnitude of the PE depends on the environmental conditions and the quality of fresh C (e.g., [28][29][30][31][32][33]. Most of the studies of PE have been conducted in mineral soils, but increasing number of experiments report about PEs in C-rich organic soils, such as peat soils (e.g., 12,29,[32][33][34][35][36][37][38] ).…”