Canopy photosynthesis modulates soil respiration in a temperate semi-arid shrubland at multiple timescales

Abstract

Soil respiration (Rs) plays an important role in the terrestrial carbon cycle, but how canopy photosynthesis and abiotic drivers interact to affect Rs is poorly understood. This study aimed at examining the degree of control gross ecosystem productivity (GEP), photosynthetically active radiation (PAR), and soil temperature (Ts) and water content (SWC) may have on Rs in a semi-arid shrub ecosystem. We applied wavelet analysis and non-parametric spectral Granger-causality to a multi-year dataset. Wavelet coherence revealed synchronized diel cycles in photosynthesis proxies (GEP and PAR) and Rs. The spectral Granger-causality analysis suggested a possible causal linkage between GEP and Rs at the diel scale during the growing season. Significant wavelet coherence was also observed between GEP and Rs at seasonal to annual scales (200–365-day periods), with Rs lagging GEP by an average of two days. Fluctuations in SWC showed non-continuous temporal covariance with Rs over 4–64-day periods. Apart from direct moisture effects on decomposition processes, SWC also seemed to regulate Rs indirectly by affecting canopy carbon assimilation. Our findings indicate that photosynthesis may modulate Rs at multiple timescales in semi-arid shrub ecosystems. Future studies should combine field manipulations with spectral analysis for a mechanistic understanding of the coupling between photosynthesis and Rs.