Response of leaf day respiration in C4 plants to irradiance and vapour pressure deficit

Abstract

Leaf day respiration rate (R_L) plays a crucial role in the global carbon cycle. However, R_L of C₄ species has not been sufficiently studied and its response to environmental factors is largely unknown. This work studied the response of R_L of three C₄ species, Setaria viridis, Sorghum sudanense, and Zea mays, to alterations in the vapour pressure deficit (VPD) and irradiance of the growth environment. R_L was estimated using the Kok method (R_{L Kok}) and an improved method that combined gas exchange and chlorophyll fluorescence measurements (R_{L Yin}). On average, shade treatment led to a 24% reduction in R_{L Yin} and a 20% reduction in respiration in the dark (R_Dk), while a consistent VPD effect on R_L was not observed. R_L and R_Dk were positively correlated with nitrogen content per leaf area and net CO₂ assimilation rate but were not correlated with the capacity of carboxylation enzymes. We found a non-significant light inhibition of respiration (1 ​± ​2%), contradicting the assumption that respiration is inhibited by light and affected by light intensity. Our findings indicate that assuming R_L to be equal to R_Dk at the same temperature is a straightforward but reliable approach to model respiration of the examined C₄ species.