Leaf respiration/photosynthesis relationship and variation: an investigation of 39 woody and herbaceous species in east subtropical China

Thirty-nine plant species including woody and herbaceous species grown in wet and warm subtropical regions were collected and classified into woody and herb functional groups. Net photosynthesis (Pn) and dark res- piration (R) were measured at constant 25C under neither water nor nitrogen limited condition to assess whether the R/Pn ratio was constant across different species and func- tional groups. Our results suggest that Pn and R were highly skewed among the 39 species, ranging from 5 to 25 and 1 to 5 lmol m -2 s -1 , respectively, while R/Pn ratio was normally distributed at 0.1-0.3. Mean R/Pn ratio was 0.19 for 39 species, and 0.20 and 0.18 for woody and herbs, respectively, showing no significant difference between the two groups. Leaf Pn, R, and R/Pn ratios exhibited large variations across 39 species while R/Pn ratio in our sub- tropical species was considerably higher than other studies. Our results also indicated that the difference within each group was even larger than between the two groups. Based on the pooled data set at global scale, and considering R/Pn ratios performance under a combination of wet and warm conditions, the mean R/Pn ratio of 0.19 fell between the R/Pn ratio of 0.23 under dry and warm conditions and the R/Pn ratio of 0.07 under cold regardless of the precipitation conditions. The comparison with published data sets indi- cated significant effects of long-term precipitation and temperature on leaf R/Pn ratios at global scale, and we found that the plants adapting to warm and wet climates including our thirty-nine species tend to have a lower R/Pn ratio.