Rhizosphere priming effect (RPE) is a key rhizosphere process in mediating soil organic matter decomposition and nutrient cycling. The RPE can affect nutrient supply to plants, but the RPE itself may also be affected by soil nutrient availability. These interactive effects may be of particular relevance in understanding the formation and maintenance of plant growth under the scenario of global climate change.  

"Compared to nitrogen (N) availability, fewer studies have focused on the effect of phosphorous (P) availability on the RPE. Furthermore, the mechanism responsible for P availability interacts with N availability in influencing RPE needs to be further examined," said assistant Professor LU Jiayu from the Institute of Applied Ecology of the Chinese Academy of Sciences.  

In a recent study, LU and other collaborators investigated the RPEs of ryegrass (Lolium perenne) and clover (Trifolium repens) with and without P fertilization at three sampling times after planting in a continuous depleted ¹³C-CO₂ labelling growth chamber.

They found that clover showed larger RPE than ryegrass at later stages, possibly due to the greater shoot regrowth rate, root activity, and rhizodeposition in clover treatment. P fertilization decreased the RPE of ryegrass at later stages, but did not significantly affect the RPE of clover during the entire experiment.  

"To explain the impact of P fertilization on the RPE, we put forward a new conceptual framework: P fertilization coupled with C supply from root exudates enhanced more microbial N immobilization, thus decreasing the RPE of ryegrass at later stages when soil N limitation negatively affect plant growth. However, P-induced N immobilization did not affect clover too much, because biological N fixation by clover alleviated soil N limitation," said LU Jiayu.  

"Our results demonstrate the importance of C-N-P interactions for understanding the RPE, and of equal significance is that the RPE is not only key to C and N but also to P cycling in plant-soil systems," said LU.  

This study was published in a paper entitled "Rhizosphere priming effects of Lolium perenne and Trifolium repens depend on phosphorus fertilization and biological nitrogen fixation" in Soil Biology & Biochemistry.  

This study was supported by grant from the Australian Research Council and the National Key Research and Development Program.