Temporal Dynamics and Influencing Mechanism of Air Oxygen Content in Different Vegetation Types

Abstract

Air oxygen content, an essential index for measuring air quality, is affected by vegetation and the environment in the forest. However, the scientific understanding of the influential mechanism of air oxygen content in different vegetation types is still not clear. Focusing on four different vegetation types: broad-leaved forest, coniferous forest, coniferous and broad-leaved mixed forest, and non-forest land within Shimen National Forest Park, China, the temporal dynamics of air oxygen content and its relationship with four environmental factors (temperature, relative humidity, wind speed, and negative air ion concentration) in different vegetation types were explored based on path analysis and decision analysis. The results showed that there was a noteworthy impact of vegetation types on air oxygen content, with coniferous and broad-leaved mixed forest (21.33 ± 0.42%) presenting the highest levels. The air oxygen content indicated a fundamentally consistent temporal pattern across different vegetation types, with the highest diurnal variation occurring at noon. It reached its peak in August and hit its nadir in December, with summer > spring > autumn > winter. In broad-leaved forest, the air oxygen content was determined by temperature, wind speed, negative air ion concentration, and relative humidity; in both coniferous forest and coniferous and broad-leaved mixed forest, the air oxygen content was affected by temperature, wind speed, and relative humidity; in non-forest land, the air oxygen content was influenced by temperature and wind speed. Generally, temperature was the dominant factor affecting air oxygen content in different vegetation types, and its positive impact tremendously exceeded other environmental factors. Wind speed had a positive impact on air oxygen content in three forest communities but a negative effect on non-forest land. Relative humidity acted as a limiting factor for air oxygen content within three forest communities. Negative air ion concentration showed a significant positive correlation on air oxygen content in broad-leaved forest. Therefore, when planning urban forests to improve air quality and construct forest oxygen bars, it is recommended that the tree species composition should be given priority to the coniferous and broad-leaved mixed pattern. Meanwhile, make sure the understory space is properly laid out so that the forest microclimates are conducive to the release of oxygen by plants through photosynthesis.