Study On Carbon Budget Of Dominant Tree Ecosystem In Qilian Mountain Of Qinghai Province

Forest ecosystems play an important role in maintaining global carbon balance in the three major terrestrial ecosystems and it have the strongest function of carbon-fixing.The forest ecosystem includes three major carbon pools,namely,vegetation carbon stocks,soil carbon stocks and plant residue carbon stocks these three major carbon pools closely related to the carbon cycle of the global ecosystem.Qilian Mountain is not only an important ecological security barrier in northwest China,but also an important source of water resources in the Yellow River Basin.There are abundant animal and plant resources in Qilian Mountain and it also plays an extremely important role in maintaining ecological balance in the region.Plants photosynthesis absorbing atmospheric CO₂.However at the same time the soil respiration will emit CO₂ to the atmosphere,so in a certain extent expressed as a"carbon source"or"carbon sink",studies have shown that Small changes in soil respiration and the photosynthesis of forest ecosystems have a significant effect on atmospheric CO₂concentration changes.Therefore,the research on photosynthetic and soil respiration of dominant tree species in Qilian Mountains has certain guiding significance for further understanding and improving the capacity of forest carbon cycle.This paper focuses on the forest ecosystems of Qilian mountain dominant species including white birch,spruce,larch,poplar,and Qilian cypress.The alkali absorption method and LI-6400XT portable photosynthesis were adopted in September 2016 and August 2017.The determination system determined the soil respiration rate and photosynthesis rate of different dominant tree species and the related environmental factors that affected soil respiration and photosynthesis.The differences in soil respiration rates and the daily variation characteristics of photosynthesis rates among different tree species were analyzed,and the correlation analysis with path analysis were performed for analyizing the relationship between soil respiration rate and environmental factors,photosynthetic rate and environmental factors of dominant tree species in Qilian Mountain,What's more mechanisms affecting soil respiration rate,photosynthetic rate and environmental factors were established.An analysis of the carbon balance of the dominant tree species ecosystem in the Qilian Mountains on the daily scale was made.The system carbon balance provides a theoretical basis for the qualitative assessment of the ecological service value of Qilian Mountain and its response to global warming.The results are as follows:?1?There are some differences between dominant tree species with kinds of soil respiration rate.Daily respiration of soil between different species from high to low is:broad-leaved forest,coniferous forest.Daily respiration of soil between different ages from high to low is:middle-aged forest,young forest.Daily respiration of soil between pure and mixed forests from high to low is:pure forest,mixed forest.?2?The correlation analysis between soil respiration and environmental factors showed that the soil daily respiration intensity of broad-leaved forest was significantly positively correlated with forest age,soil temperature and organic matter content,and the daily respiration intensity of coniferous forest soil was significantly positively correlated with slope,slope direction,soil temperature and organic matter content.?3?Features of photosynthetic rate diurnal variation of Betula platyphylla community.In general,the net photosynthetic rate of arbors is greater than that of herbs and shrubs.The net photosynthetic rate between different ages from high to low is:twenty years old,forty years old,sixty years old.The change trend of photosynthetic rate of twenty years old,forty years old and Berberis showed a single Peak curve during the day.The peak of Betula platyphylla appeared at about 12:00,The peak of Berberis appeared at about 10:00.The change trend of photosynthetic rate of sixty years old and Polygonum viviparum showed a double Peak curve during the day and a phenomenon of midday depression appeared.?4?Correlation analysis about the changes of photosynthetic rate and eco-physiological factors in plants showed that,there are many environmental factors affected plant photosynthetic rate,such as the solar radiation,CO₂concentration,relative humidity,temperature,transpiration rate of plants and so on.There are some differences between all kinds of factor correlation respectively with photosynthetic rate of Betula platyphylla community.Stomatal conductance,intercellular CO₂ concentration,solar radiation,relative humidity has high correlation with photosynthetic rate of Betula platyphylla at twenty years old.Intercellular CO₂ concentration,Transpiration rate,solar radiation,relative humidity has high correlation with photosynthetic rate of Betula platyphylla at forty years old.Intercellular CO₂ concentration,stomatal conductance,solar radiation,atmospheric temperature has high correlation with photosynthetic rate of Betula platyphylla at sixty years old,and negatively correlated with stomatal limit value.Comprehensive ranking of all influence factors on photosynthetic rate of Berberis is:CE>PAR>Gs,and Polygonum viviparum is:CE>Gs.?5?The daily carbon flux of 20-year,40-year and 60-year Betula platyphylla community per unit land area is 38.3 kg CO₂·hm^-2·d^-1?72.3 kgCO₂·hm^-2·d^-1?94kgCO₂·hm^-2·d^-1.The greater the age of the forest,the stronger the carbon release and oxygen release capacity of the unit land area.