Background and Aims A comprehensive understanding of the rhizosphere priming effect (RPE) on the decomposition of soil organic carbon (SOC) requires an integration of many factors. It is unclear how N forminduced change in soil pH affects the RPE and SOC sequestration. Methods This study compared the change in the RPE under supply of NO3-N and NH4-N. The effect of the RPE on the mineralization of soil N and hence its availability to plant and microbes was also examined using a 15N-labelled N source. Key Results The supply of NH4-N decreased rhizosphere pH by 0.16-0.38 units, and resulted in a decreased or negative RPE. In contrast, NO3-N nutrition increased rhizosphere pH by 0.19-0.78 units, and led to a persistently positive RPE. The amounts of rhizosphere-primed C were positively correlated with rhizosphere pH. Rhizosphere pH affected the RPE mainly through influencing microbial biomass, activity and utilization of root exudates, and the availability of SOC to microbes. Furthermore, the amount of rhizosphere primed C correlated negatively with microbial biomass atom% 15N (R2 0.77-0.98, n = 12), suggesting that microbes in the rhizosphere acted as the immediate sink for N released from enhanced SOC decomposition via the RPE. Conclusion N form was an important factor affecting the magnitude and direction of the RPE via its effect on rhizosphere pH. Rhizosphere pH needs to be considered in SOC and RPE modelling.
History
Publication Date
2018-01-01
Journal
Annals of Botany
Volume
121
Issue
1
Pagination
9p. (p. 143-151)
Publisher
Oxford University Press
ISSN
0305-7364
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