Effects of open-field artificial warming on photosynthetic responses of Fraxinus rhynchophylla, Zelkova serrata, Betula costata, and Quercus variabilis seedlings
Air temperature being increased due to climate change may affect the physiological traits of trees. Seedling stage is particularly important for tree survival and is easily influenced by warming. The objective of this study was to investigate the photosynthetic responses of seedlings to open-field artificial warming. Seedlings of four major Korean deciduous species (F. rhynchophylla, Z. serrata, B. costata, and Q. variabilis) were selected for the study. The seeds were sown in each 1 m x 1 m plot in April, 2014 and the newly germinated seedlings were warmed with infrared heaters. The air temperature difference between warmed plots and control plots was consistently maintained as 3.06℃. Monthly net photosynthetic rate was measured in July, September, and October using CIRAS-2 (PP-Systems, USA) and chlorophyll contents were measured by using DMSO extraction method.
In warmed plots, chlorophyll contents increased in every species and every month. Chlorophyll contents of F. rhynchophylla increased by 43.3% and nearly doubled for B. costata in October. The values were higher in warmed plots at every time of the measurements in Q. variabilis (10.2% in July; 24.3% in September; 31.2% in October) (p<0.05). In warmed plots, net photosynthetic rate of F. rhynchophylla increased by 356.2% compared to control plots in October, whereas net photosynthetic rate of B. costata decreased (35.2% in July; 22.2% in October) (p<0.05). Z. serrata and Q. variabilis did not show a certain tendency. Increased chlorophyll contents could result from the temperature increment which might provide optimal conditions for biosynthesis of photosynthetic pigments. It is generally known that chlorophyll contents are positively correlated with photosynthetic rate, however in these cases, net photosynthetic rate increased or decreased with increasing chlorophyll contents. Meanwhile, photosynthetic responses to artificial warming varied in each species. It could be conceived of as varying photosynthetic temperature sensitivity depending on the species. This study was supported by Korea Forest Service (Project No. S111114L030100).