1- Semnan University
Abstract: (5 Views)
Background: Forests play a crucial role in mitigating atmospheric carbon dioxide, a greenhouse gas that is a significant contributor to the ongoing climate changes on Earth. Through the process of photosynthesis, forests absorb carbon dioxide and produce oxygen, thereby helping to reduce the concentration of greenhouse gases in the atmosphere. In this way, forests act as a natural buffer against climate change. Climate predictions indicate that atmospheric CO2 concentrations will reach 700 μmolmol-1 by the year 2100, which is expected to result in widespread and prolonged drought occurrences and temperature increases in Europe. The primary consequences of these climatic disruptions will disproportionately affect European forests, particularly European beech forests. Previous research has demonstrated that beech mortality is more significantly influenced by drought than by other factors. Consequently, recent studies have focused on the relationship between ecological factors such as temperature and light with photosynthesis rates, CO2 uptake, transpiration, and other physiological aspects of European beech. This tree species is recognized as an indicator of the sensitivity of European broadleaf forests to the impacts of climate change. This study investigates the effects of varying light intensities on leaf photosynthesis rates, transpiration, intercellular carbon dioxide concentration, and stomatal conductance.
Methods: To study the physiology of photosynthesis and gas exchange rates in European beech trees (Fagus sylvatica) at the Hainich National Park in Germany, five young trees, each approximately 2.5 meters in height, were selected under the canopy of mature trees. From each tree, five healthy, mature leaves that had developed naturally were selected for analysis. Measurements were conducted using the LC Pro+ device at ten different light intensities ranging from 0 to 696 micromoles of photons per square meter per second, with five replicates for each condition. The measurements were performed in a controlled temperature environment set to 21°C ± 1. An area of 6.25 cm² of live beech leaves was placed in the measuring chamber. After the initial measurements, CO2 and H2O concentrations were introduced to both leaf surfaces within the chamber. The concentration of CO2 in the air exiting the chamber, after being utilized in the photosynthesis process (which typically leads to a reduction), along with the concentration of H2O (released following leaf photosynthesis) were subsequently re-measured and analyzed. The net assimilation rate (photosynthesis) and transpiration were continuously calculated from the differences between the input concentration (reference values) and the final concentration (analyzed values) of CO2 and H2O gases. Thereafter, light response curves were constructed based on the average data for the European beech species.
Results: The light compensation point, defined as the light intensity at which the rate of CO2 assimilation equals the rate of CO2 consumption in the photosynthesis process in plant leaves, was determined for the European beech species at 7.5 µmol photons per square meter per second. The dark respiration rate was measured to be approximately -0.19 µmol of CO2 per square meter per second, based on the average of all tests conducted. The photosynthesis rate in European beech increased significantly with rising photosynthetically active radiation from 0 to 174 µmol photons per square meter per second, reaching its maximum at the radiation of 435 µmol photons per square meter per second, with an average rate of 2.94 µmol of CO2 per square meter per second. As PAR increased, the European beech exhibited a strong tendency to rapidly consume CO2, achieving the minimum light required on its leaf surfaces; specifically, with a slight increase in light intensity from 0 to 44 µmol per square meter per second, the CO2 concentration in the intercellular spaces of the mesophyll leaf significantly decreased to its minimum level. This reduction is attributed to the sudden influx of intercellular CO2 into the chloroplasts to initiate the photosynthesis process at very low light intensities, which also results in a considerable reduction in stomatal conductance. Beyond a light intensity of 44 µmol per square meter per second, both stomatal conductance and transpiration showed a continuous increase with a gradual slope, reaching their maximum at 696 µmol per square meter per second. Meanwhile, the intercellular CO2 concentration (Ci) exhibited a much slower relative increase from a light intensity of 44 µmol per square meter per second to 696 µmol per square meter per second and never reached the maximum level observed in darkness or at zero light intensity. Taking into account the maximum photosynthesis rate for European beech saplings of 2.94 µmol per square meter per second, the net CO2 uptake is approximately 4.66 kg per hectare per hour at a radiation level of 435 µmol photons per square meter per second, corresponding to a carbon (C) uptake of 1113 g per square meter per year (g C m-2 yr-1).
Conclusion: The present study indicates that the European beech is a highly shade-tolerant species with a significant response to environmental changes such as light, rendering it a very sensitive tree species to alterations in ecological conditions within European ecosystems. Given the close genetic relationship between the European beech and the Hyrcanian beech, the findings of this research could serve as a model for the management of beech forests in Iran.
Methods: To study the physiology of photosynthesis and gas exchange rates in European beech trees (Fagus sylvatica) at the Hainich National Park in Germany, five young trees, each approximately 2.5 meters in height, were selected under the canopy of mature trees. From each tree, five healthy, mature leaves that had developed naturally were selected for analysis. Measurements were conducted using the LC Pro+ device at ten different light intensities ranging from 0 to 696 micromoles of photons per square meter per second, with five replicates for each condition. The measurements were performed in a controlled temperature environment set to 21°C ± 1. An area of 6.25 cm² of live beech leaves was placed in the measuring chamber. After the initial measurements, CO2 and H2O concentrations were introduced to both leaf surfaces within the chamber. The concentration of CO2 in the air exiting the chamber, after being utilized in the photosynthesis process (which typically leads to a reduction), along with the concentration of H2O (released following leaf photosynthesis) were subsequently re-measured and analyzed. The net assimilation rate (photosynthesis) and transpiration were continuously calculated from the differences between the input concentration (reference values) and the final concentration (analyzed values) of CO2 and H2O gases. Thereafter, light response curves were constructed based on the average data for the European beech species.
Results: The light compensation point, defined as the light intensity at which the rate of CO2 assimilation equals the rate of CO2 consumption in the photosynthesis process in plant leaves, was determined for the European beech species at 7.5 µmol photons per square meter per second. The dark respiration rate was measured to be approximately -0.19 µmol of CO2 per square meter per second, based on the average of all tests conducted. The photosynthesis rate in European beech increased significantly with rising photosynthetically active radiation from 0 to 174 µmol photons per square meter per second, reaching its maximum at the radiation of 435 µmol photons per square meter per second, with an average rate of 2.94 µmol of CO2 per square meter per second. As PAR increased, the European beech exhibited a strong tendency to rapidly consume CO2, achieving the minimum light required on its leaf surfaces; specifically, with a slight increase in light intensity from 0 to 44 µmol per square meter per second, the CO2 concentration in the intercellular spaces of the mesophyll leaf significantly decreased to its minimum level. This reduction is attributed to the sudden influx of intercellular CO2 into the chloroplasts to initiate the photosynthesis process at very low light intensities, which also results in a considerable reduction in stomatal conductance. Beyond a light intensity of 44 µmol per square meter per second, both stomatal conductance and transpiration showed a continuous increase with a gradual slope, reaching their maximum at 696 µmol per square meter per second. Meanwhile, the intercellular CO2 concentration (Ci) exhibited a much slower relative increase from a light intensity of 44 µmol per square meter per second to 696 µmol per square meter per second and never reached the maximum level observed in darkness or at zero light intensity. Taking into account the maximum photosynthesis rate for European beech saplings of 2.94 µmol per square meter per second, the net CO2 uptake is approximately 4.66 kg per hectare per hour at a radiation level of 435 µmol photons per square meter per second, corresponding to a carbon (C) uptake of 1113 g per square meter per year (g C m-2 yr-1).
Conclusion: The present study indicates that the European beech is a highly shade-tolerant species with a significant response to environmental changes such as light, rendering it a very sensitive tree species to alterations in ecological conditions within European ecosystems. Given the close genetic relationship between the European beech and the Hyrcanian beech, the findings of this research could serve as a model for the management of beech forests in Iran.
Keywords: European beech, photosynthesis rate, transpiration, shade tolerance, photosynthetically active radiation, stomatal conductance
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