Light intensity controls rhizosphere respiration rate and rhizosphere priming effect of soybean and sunflower

Abstract

Rhizosphere respiration (Rroot) and rhizosphere priming effect (RPE) are crucial for regulating soil carbon dynamics. However, their responses to light intensity are not fully resolved. We investigated Rroot and RPE of soybean and sunflower using a continuous isotope-labeling technique. The two species were subjected to five levels of light intensity in a growth chamber. Plants were maintained at full light from seeding for 45 or 59 days, and switched to shading treatments for four days. Soil respiration was partitioned into root- and soil-derived CO2 during the last five days (day0, full light; day1–4, shading). Both soybean and sunflower Rroot showed significant positive relationships with light intensity, particularly after one day of shading. Moreover, both plants showed positive RPE (44–98%) at full light, but with increasing duration and intensity of shading, the RPE declined and even became negative (up to –20%). Indeed, a positive relationship between light intensity and RPE was observed in both species. Overall, our results showed that shading, by influencing light intensity and presumably photosynthesis rate and belowground carbon allocation, exerts a significant control of rhizosphere respiration rate and priming effect of the two species.