Herbaceous layer determines the relationship between soil respiration and photosynthesis in a shrub-dominated desert plant community

Although the linkages between aboveground photosynthates production and belowground respiration processes have been well studied, doubts remain as to the extent that photosynthate regulates soil respiration (Rsoil) and its generality throughout the growing season in a given ecosystem. This study aimed to test whether photosynthesis affected Rsoil at the diurnal scale and assess how the relation between them changed with changing vegetation composition. We measured Rsoil and gross primary productivity (GPP using eddy covariance) in two consecutive growing seasons (2013–2014) in a desert ecosystem, western China. We compared Rsoil on sunny days with that on adjacent cloudy days in two periods with different vegetation compositions [herbs-shrub coexistence period (HSP) and purely shrubs dominated period (SDP)] to identify how photosynthesis affect Rsoil. GPP regulated diurnal variations of Rsoil conspicuously in spite of the strong correlation between soil temperature (Tsoil) and Rsoil, but such regulation was limited in HSP. 48.3% of the changes in daytime Rsoil between sunny and cloudy days was explained by changes in Tsoil together with changes of GPP in HSP. When spring annuals died, no differences in daily amplitude and average of Rsoil between sunny and cloudy days were found. Our results suggested that effect of photosynthesis on Rsoil was not constant throughout the growing season. In the presence of herbaceous plants, Rsoil was directly related to photosynthesis. These findings highlighted the important role of photosynthesis played in Rsoil regulation and the importance of community composition in determining the extent that photosynthesis affects Rsoil.