Abstract
In peatlands, decomposition of organic matter is limited by harsh environmental conditions and low decomposability of the plant material. Shifting vegetation composition from Sphagnum towards vascular plants is expected in response to climate change, which will lead to increased root exudate flux to the soil and stimulation of microbial growth and activity. We aimed to evaluate the effect of root exudates on the decomposition of recalcitrant dissolved organic carbon (DOC) and to identify microorganisms involved in this process. The exudation was mimicked by an addition of a mixture of 13C labelled compounds into the recalcitrant DOC in two realistic levels; 2% and 5% of total DOC and peatland porewater with added root exudates was incubated under controlled conditions in the lab. The early stage of incubation was characterized by a relative increase of r-strategic bacteria mainly from Gammaproteobacteria and Bacteriodetes phyla within the microbial community and their preferential use of the added compounds. At the later stage, Alphaproteobacteria and Acidobacteria members were the dominating phyla, which metabolized both the transformed 13C compounds and the recalcitrant DOC. Only higher exudate input (5% of total DOC) stimulated decomposition of recalcitrant DOC compared to non-amended control. The most important taxa with a potential to decompose complex DOC compounds were identified as: Mucilaginibacter (Bacteriodetes), Burkholderia and Pseudomonas (Gammaproteobacteria) among r-strategists and Bryocella and Candidatus Solibacter (Acidobacteria) among K-strategists. We conclude that increased root exudate inputs and their increasing C/N ratio stimulate growth and degradation potential of both r-strategic and K-strategic bacteria, which make the system more dynamic and may accelerate decomposition of peatland recalcitrant DOC.
Highlights
C addition can induce strong positive priming[12] and organic acids stimulate SOC decomposition more than carbohydrates[13]
The resulting priming effect on peatland dissolved organic carbon (DOC) decomposition was primarily affected by the exudate input: the low level of root exudates addition (2% of total DOC) to peatland water resulted in either a slightly negative or no priming effect on pre-existing peatland DOC (Fig. 1c), whereas the higher level of root exudates (5% of total DOC) induced a positive priming effect, which further increased with an increasing exudate C/N ratio from 7 to 50 (Fig. 1d)
Our results are in line with findings of Liu et al.[13] who found that low level of C addition led to a negative or no priming effect during a 7 week incubation, while the high level of C addition induced positive priming and of Wang et al.[29], who observed an increasing priming effect with an increasing C/N ratio of crop residues added to the soil
Summary
C addition can induce strong positive priming[12] and organic acids stimulate SOC decomposition more than carbohydrates[13]. It is likely that bacteria will play a dominant role in the decomposition of plant exudates, recalcitrant peatland DOC and in the priming effect, which may be induced by root exudate inputs. To determine the dynamics of exudate and peatland DOC decomposition and priming effect quantification, we needed to separate these two C sources and monitor the system for a longer period This would be impossible in the field due to heterogeneous conditions and DOC interaction with peat (sorption, chemical and microbial transformation) during porewater flow through the peat profile. (1) Addition of root exudates will stimulate decomposition of recalcitrant peatland DOC resulting in a positive priming effect. The positive priming effect will increase with increasing level of added exudates and their increasing C/N ratio
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
