Of the total 570 species, 194 species in 116 genera and 52 families were found with C3 photosynthesis, 24 species in 17 genera and 6 families with C4 photosynthesis, and 2 species in 1 genera and 1 family with CAM photosynthesis. 90 % of the total species can be found in Changbai Mountain flora, more a half (69 %) in North China flora, and about 1/3 in Mongolian flora and Xinan flora, respectively. The occurrence of C4 species was not as common as that in adjacent grasslands and deserts, but relatively more than in the adjacent forests. Of the total 24 C4 species, 63 % C4 species (15 of 24) was found in Gramineae. Nine life form types can be found, reflecting the moist climate in the region, especially the occurrence of epiphyte and liana forms. Relatively more geophyte life form plants suggested the winter in the region was much colder than in grasslands. These indicated that both ecological studies and land management decisions must take into account plant photosynthetic pathway and life form patterns, for both of them are closely related to climatic changes and land use.
Net CO2 uptake rates (PN) were measured for the vine cacti Hylocereus undatus and Selenicereus megalanthus under relatively extreme climatic conditions in Israel. Withholding water decreased rates and the daily amount of CO2 uptake by about 10 % per day. Compared with more moderate climates within environmental chambers, the higher temperatures and lower relative humidity in the field led to a more rapid response to drought. The upper envelopes of scatter diagrams for PN versus temperature for these Crassulacean acid metabolism species, which indicate the maximal rates at a particular temperature, were determined for both night time CO2 uptake in Phase I (mediated by phosphoenolpyruvate carboxylase, PEPC) and early morning uptake in Phase II (mediated by ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO). As stem temperature increased above 13 °C, the maximal PN increased exponentially, reaching maxima near 27 °C of 12 and 8 μmol m-2 s-1 for Phases I and II, respectively, for H. undatus and 6 and 4 μmol m-2 s-1, respectively, for S. megalanthus. Based on the Arrhenius equation, the apparent activation energies of PEPC and RuBPCO were 103 and 86 kJ mol-1, respectively, for H. undatus and 77 and 49 kJ mol-1, respectively, for S. megalanthus, within the range determined for a diverse group of species using different methodologies. Above 28 °C, PN decreased an average of 58 % per °C in Phase I and 30 % per °C in Phase II for the two species; such steep declines with temperature indicate that irrigation then may lead to only small enhancements in net CO2 uptake ability. and J. Ben-Asher ... [et al.].