Day and night respiration of three tree species in a temperate forest of northeastern China

Leaf day respiration is one of the most fundamental plant physiological processes and plays a vital role in the plant carbon cycle. However, day respiration is inherently complex and difficult to measure. In this study, the Kok method and the Laisk method were used to measure leaf day respiration on saplings of one evergreen conifer species (Pinus koraiensis) and two deciduous broadleaved species (Tilia amurensis and Fraxinus mandshurica) in a temperate forest of northeastern China. Results show that discrepancy between the corrected day respiration values estimated by the Kok and Laisk methods was only 4% for the three tree species. On average, day respiration was 55.9% and 52.6% lower compared to night respiration for the three tree species, as measured by the Kok and the Laisk method, respectively. Day respiration of the evergreen conifer species estimated by the Kok method was 31.7% lower, while that estimated by the Laisk method was 36.8% lower than that of the deciduous broadleaved species. Night respiration of the evergreen conifer trees was 40.7% lower than those obtained for the deciduous broadleaved trees. Day respiration rate was positively correlated with night respiration rate. Notably, day respiration rate decreased with increased photosynthetic photon flux density, and even a small amount of light significantly inhibited leaf day respiration in all the three species.