Photosynthetic characteristics and ecological service capacity of five Quercus species in Beijing region

The investigation of photosynthetic traits and ecological service capabilities of Quercus species is crucial for their cultivation management and carbon sequestration assessment. In this study, five major Quercus plants in Beijing, including Quercus dentata Thunb., Quercus variabilis Blume, Quercus acutissima Carruth., Quercus mongolica Fisch. ex Ledeb. and Quercus aliena Blume were investigated. The diurnal variation of photosynthetic characteristics was measured using LI-6400XT portable photosynthmeter, and the ecological benefits of different Quercus pecies were estimated by combining their green quantity calculation model, carbon fixation, oxygen release and transpiration evaluation model. Our results showed that: 1）The diurnal variation of net photosynthetic rate and transpiration rate of the five Quercus species exhibited a a distinct bimodal curve pattern, characterized by peaks and troughs. 2）The daily variation range of net photosynthetic rate was 1.05~12.20 μmol·m⁻²·s⁻¹, and the daily variation range of transpiration rate was 0.48~5.46 mmol·m⁻²·s⁻¹. The average daily rates of both were as follows: Q. dentata, Q. variabilis, Q. mongolica, Q. acutissima, Q. aliena. 3）According to the green mass of an individual plant with a diameter of 20 cm, the daily carbon sequestration and oxygen release were as follows: Q. mongolica, Q. variabilis, Q. dentata, Q. acutissima, Q. aliena. Regarding cooling and humidification benefits, the daily water release was ranked as follows: Q. dentata, Q. variabilis, Q. mongolica, Q. acutissima, Q. aliena. The order of daily heat absorption is: Q. mongolica, Q. dentata, Q. variabilis, Q. acutissima, Q. aliena. 4）Based on the current total area of 122700 m² of the five major Quercus forest types in the Beijing region, the total ecological service capacity was estimated. The annual carbon sequestration amounts were 3.55 million tons, with annual oxygen release of 2.58 million tons. Annual water transpiration reaches 6.54 billion tons, while annual heat absorption totaled 1.756 × 10¹⁶ kJ. These findings provide a scientific basis for the selection and application of Quercus species in afforestation and greening initiatives in the Beijing region.