Effects of Temperature on Photosynthetic Rates in Korean Fir (Abies koreana) between Healthy and Dieback Population
Supported from the Restoration Project Fund provided by the Korea Forest Service (#S210606L0101104).
Abstract
The present study was carried out on natural Korean fir forests (Abies koreana) growing in Mount Halla in Jeju Island, Korea (33° 13–36′ N and 126° 12–57′ E). Mount Halla is the highest mountain (1 950 m a.s.l.) in South Korea. On the Korean fir forests near the top of Mount Halla in Korea, we established permanent plots between dieback and healthy population. Each permanent plot includes both dieback and relatively healthy Korean fir individuals. Three sites in this study showed similar altitude, topographic position, aspects, slope, diameter at breast height, average height and ages. Net photosynthetic rates (PN) on different temperature regimes were evaluated to explain the forest dieback phenomenon on Korean fir populations. Light response curves were determined on three different temperature regimes: 15 °C, 20 °C and 25 °C. The irradiance response curve showed higher values in lower air temperatures. Generally, irradiance response curves of healthy Korean fir populations were higher than the dieback population at all sites.
There is no doubt that global warming is now in process. Increased atmospheric temperature during this century due to global warming is not always a positive factor in plant growth environments. Sugar maple (Acer saccharum) decline has been observed in northern Pennsylvania since the early 1980s because declining stands often experience repeated drought stresses (Drohan et al. 2002). Alaskan white spruce underwent reduced growth in the twentieth century from temperature-induced drought stress (Barber et al. 2000). Single or combined effects of climatic extremes such as winter frost and summer drought have been attributed as causes of oak decline in Central Europe (Thomas et al. 2002). In these totally different regions, dieback phenomena have been shown in single trees or groups of trees within stands, parts of stands and whole stands.
Korean fir (Abies koreana) is a valuable tree species for ornamental purposes and is an endemic species in Korea (Lee 1986). It is known to grow at the upper parts of the high elevation of Mounts Halla, Chiri, Mudung, Kaji and Dukyu (Lee 1986) that are located at the southern part of the Korean peninsula. The Korean fir population in Mount Halla and links with global warming are focused on in this study because this area showed the widest distribution and the decline phenomenon was the most severe. This species was recorded as being in the lower risk/near threatened (LR/NT) category in the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Concern about Korean fir is in large part due to their severe and recent dieback.
Unfortunately, with the declining occurrence of this species, there has been little consensus on the reasons for the dieback. Many researchers have reported this dieback as probably being the result of complex interactions among multiple environmental factors caused by global warming (Drohan et al. 2002; Duchesne et al. 2005).
The objective of this study was to test the hypothesis that elevated temperature at high elevation can reduce net photosynthetic rates (PN) and affect growth during the growing season for Korean fir stands on Mount Halla. This physiological imbalance may be the reason for the visible dieback of Korean fir stands.
Results and Discussion
The result of PN generally indicated significant differences attributed to temperature (Table 1). In other words, CO2 assimilation of Korean fir at this high elevation is temperature-dependent. Korean fir demonstrated a general increase in PN with decreasing temperature in measurements taken during June (Figure 1). Needle PN results in lower temperatures (15 °C) were increased, but when they were measured in higher temperatures (25 °C), PN results were downregulated in both healthy and dieback populations. The regression line of PN against light intensities for the two sites falls below that for the warmer temperature. This population had the highest PN at 15 °C, but the lowest values at 25 °C (Table 1). Korean fir seems to be able to adapt development to low temperatures.
| Sample | Temperature (°C) | Site 1:YS-Youngsil (μmol [CO2]/g per s) | Site 2: WS-Witseoreum (μmol [CO2]/g per s) |
|---|---|---|---|
| Healthy population | 15 | 7.50* | 5.80* |
| 20 | 7.03** | 3.00** | |
| 25 | 6.60** | 1.33** | |
| Dieback population | 15 | 2.40** | 5.27** |
| 20 | 2.13** | 2.80** | |
| 25 | 1.97** | 1.13** |
- *P < 0.05; **P < 0.01.
Irradiance response curves in PN in June at the three different temperature regimes: 15 °C, 20 °C and 25 °C. Healthy (A) and dieback populations (B) of Youngsil (Site 1) were located in the southwest and healthy (C) and dieback populations (D) of Witseoreum (Site 2) were in the west. These curves were developed for each site at different temperatures by non linear regression using the PN measured at the 11 light levels. Solid line, 15 °C ( •); heavy dashed line, 20 °C (○); thin dotted line, 25 °C (▾). Bars indicate standard deviation. CO2 concentration was 360 μmol/mol. PPFD, photosynthetic photon flux density.
Evergreen conifers such as Korean fir are common in the northern temperature boreal regions. Although commencing PN measurements in the spring is a complex and gradual process, air temperature triggers the recovery of evergreen boreal forest PN results at this time of year (Tanja et al. 2003; Ben-Asher et al. 2006; Hassan 2006). In this study, lower temperatures showed higher PN results in Korean fir populations. This species has adapted to low temperatures, and the PN may have even been inhibited in elevated temperatures for a long time (Hjelm and Ögren 2003). Lee (1986) reported that the optimum altitudinal zone of Korean fir is about 1 200 m above see level (a.s.l.). No mountain areas have been identified with these tree lines below approximately 1 200 m a.s.l. in Korea. Cairns (2001) and Bertamini et al. (2006) reported that winter desiccation of Abies lasiocarpa and Picea abies due to global warming were strongly related to the elevation of the mountain. Injury to these species increased with elevation and on more southwesterly facing hillslopes. Generally, soil moisture of trees in mountain regions is strongly influenced by elevation (Boese et al. 1997; Manes et al. 2006). Global warming also may change and vertical zonation of Korean fir occurs. Elevated air temperature also affects the PN of this species at high elevations and contributes to the decline of the Korean fir. In central Europe, the optimum range of the Norway spruce in the mountain region in a zone that is approximately 600 m a.s.l. Growth of this species is strongly associated with temperature above this elevation (Modrzyński and Eriksson 2002; Bigras 2005). During the growing season, especially summer, the Korean fir population experiences warmer temperatures and has adapted to gradual temperature increases. Some Korean fir genotypes are very susceptible to high temperatures and this may contribute to the occurrence of dieback in the population in the current study.
In summary, the irradiance response curve showed higher values in lower air temperatures. In addition, the irradiance response curve of healthy Korean fir populations was higher than dieback populations. Warmer climates should have an affect on the PN of Korean fir populations.
Materials and Methods
Study site
The present study was carried out on natural Korean fir forests (Abies koreana Wilson) growing on Mount Halla in Jeju Island, Korea (33° 13–36′ N, 126° 12–57′ E). Mount Halla is the highest mountain (1 950 m a.s.l.) in South Korea. The mountain posseses diverse vegetation types by altitude, from evergreen broadleaved forests to sub-alpine forests (Koo et al. 2001). Most forests are secondary forests and the average Korean fir age ranges from 40 to 60 years (Table 2). On the Korean fir forests near the top of Mount Halla, we established permanent plots of 10 m × 20 m. The first, Site 1: YS was located near Youngsil in the southwest. The second, Site2: WS was located at Witseoreum in the west (Table 2). Each permanent plot includes both dieback and relatively healthy Korean fir individuals. Sites in this study showed similar physical environments to minimize variations.
| Site name | Altitude (m) | Topographical position | Aspect | Slope (°) | Diameter at breast height (cm) | Height (m) | Age (years) |
|---|---|---|---|---|---|---|---|
| Site 1:YS (Youngsil) | 1 633 | Near cliff | SWS | < 3 | 10.0 | 3.0 | 40–60 |
| (2.9–27.5) | (1.7–3.6) | ||||||
| Site 2: WS (Witseoreum) | 1 672 | Small ridge | SWS | < 3 | 9.8 | 4.0 | 40–60 |
| (3.1–22.1) | (1.7–5.6) |
Current annual mean temperatures of Korea have risen about 1.5 °C since 1912, and the Korean climate has warmed about 0.9 °C. In particular, below-average winter temperatures have been more frequent than above-average summer temperatures (Kwon 2003). These alpine forests are possibly vulnerable to global warming, and close attention should be paid to monitoring and conserving the communities. In 2005, an extreme weather event had been already recorded. More than 40 cities recorded the hottest air temperature in April since the beginning of meteorological measurement in Korea in 1904 (Kwon 2003). Currently, mean air temperatures of the Jeju islands have also increased, especially in winter and spring.
Photosynthetic rates
Needle PN was measured by portable, open circuit, infrared gas analyzer (Li-6400; Licor Inc., Lincoln, NE, USA) connected to a cuvette. The gas exchange system was calibrated each day before measurement, using a calibration gas with a known CO2 concentration. The rate of photosynthesis was measured in three replicates on each tree during the study. The measurements were made on the third branches from the bottom and a ribbon was tied to the branch to make sure the next measurements we taken from the same branches. Five trees were sampled for each plot for measurements.
Light response curves were determined on three different temperature regimes in June: 15 °C, 20 °C and 25 °C. At each of the different light intensities, the trees were acclimated for 3 min before the measurement was taken. Photon flux density was gradually increased to 2 000 μmol/m2 per s and back down to 0 photon flux density. Light intensity was divided into 11 levels: 0, 200, 400, 600, 800, 1 000, 1 200, 1 400, 1 600, 1 800 and 2 000 μmol/m2 per s. Artificial illumination was supplied to the leaf from a red-blue LED light source attached to the sensor head. Measurements were made at each temperature, with ambient CO2 concentration of 360 ± 10 μmol/mol and a photon flux density of 1 200 μmol/m2 per s. Environmental factors were reasonably stable during measurements. After the data between PN and light intensities at the different temperature regimes were obtained, a regression procedure was applied to fit the scattered measured values.
Statistical analysis
Photosynthetic rates of the measurements are expressed as the means ±SD of three replications. Differences between temperatures in the mean of net photosynthesis in the Korean fir were analyzed using one-way anova followed by Duncan's Multiple-Range Test. Statistical analyses were carried out using the statistical package SAS System for Windows, Version 9.01 (SAS Institute, USA).
(Handling editor: Congming Lu)
Acknowledgements
We especially thank Ms. Kwon Mi Jung and Je Sun Mi for their field assistance.
