Research On The Ratio Of Leaf Respiration To Photosynthesis And Its Response To Environmental Variation In East Subtropical China

Leaf net photosynthesis(P_n)and dark respiration(R)are the two most fundamental plant physiological processes,and they play a vital role in the carbon cycle at scales ranging from the leaf to the globe.The ratio of respiration to gross photosynthesis of whole plants(R:P)is a relevant parameter to describe the carbon balance of vegetation.Net photosynthesis(P_n)and dark respiration(R)were measured at constant 25℃in neither water nor nitrogen limited condition to assess whether the R/P was constant across different species and functional groups.We also changed four environmental factors as light,soil nitrogen,temperature and soil water to see the response of the plants.The main conclusions are as follows:(1)P_n and R were highly skewed among the 39 species,ranging from 5-25μmol m^-2 s^-1and 1-5μmol m^-2s^-1,respectively,while R/P was normally distributed at 0.1-0.3. Mean R/P was 0.19 for all 39 species,and 0.20 and 0.18 for woody and herb groups, respectively.R/P showed significant differences(P＜0.01)among the species within each functional group,although no significant difference was found between the two groups.Woody species held a similar carbon storage ability as herb species which showed that there is no sence to depart woody and herb with there carbon sequestration ability.(2)R/P of the 39 plants decreased as the light density(PPFD)increased.Plants increased the net carbon storage with the light increased.While the light increased, the woody species showed light inhibition,and the R/P went to 0.62.Five of the herbs which is Plantago virginica,Cirsium japonicum,Reineckia carnea showed similar inhibition.The carbon storage decreased for the photosynthesis inhibition under the light with PPFD surpass 1 200μmol m^-2s^-1.(3)Regardless of low water,saturated water,inundated water,Mosla hangchowensis showed no significant response to soil nitrogen(P＜0.05).Under drought condition, R/P of Mosla dianthera under low nitrogen was higher(0.75)than median nitrogen and saturated nitrogen(0.3).Under saturated water,R/P of M.dianthera under low nitrogen(0.38)was significantly higher than saturated nitrogen and high nitrogen (0.12)(P＜0.05).R/P of M.cavaleriei kept constant at 0.23 regardless of the soil nitrogen difference.The condition with inundated water was similar with the saturated water condition.(4)R/P of woody and herb species decreased significantly with the increase of soil water(P＜0.05).Woody and herb species had a higher R/P under drought condition than saturated water condition(P＜0.05).Low water condition is harmful for the net carbon storage ability of either woody species or herbs.(5)Woody and herb species held a similar R/P among different temperature treatment of 20℃,25℃and 30℃(P＜0.05).R/P of woody species was higher than herb species,while mean R/P was 0.4 of woody and 0.3 for herb under three temperature treatments.Plants respired the constant proportion of photosynthesis under this three temperature treatments.(6)From pooled data at global scale,and considering R/P performance under a combination of wet,warm conditions,the mean R/P of 0.19 fell between the R/P of 0.23 under dry,warm conditions and the R/P of 0.07 under cold regardless of the precipitation conditions.Plants storage less carbon into dry mass with the increase of temperature and drought degree.Woody plants showed higher R/P than herbs at global scale,but no difference was found when comparing under wet,warm conditions.