Research On Stem CO₂ Release Rate And Water Use Efficiency In Pinus Elliottii Plation Of Degraded Red Soil Region

Water use efficiency is considered as the important index of plant water physiloogy,reflecting the relationship between carbon accumuation by photosynthesis and water consumption by transpiration.Trees are the main component of water transport in forest ecosystems.The transpiration and photosynthesis are two important processes linking water and carbon cycles in the ecosystem.This study was conducted to determine the dynamic characteristics of stem CO₂ release rate and water use efficiency and its influencing factors in Pinus elliottii plantation of degraded red soil region.We can not only understand the contribution of Pinus elliottii to the carbon budget of the region,predict its role in mitigating global warming,and reveal its inherent water consumption mechanism,but also reflect the water use strategies of dominant plants in ecological restoration process and their adaptation strategies.The main conclusions are as follows:?1?The diurnal variations of stem CO₂ release rate and stem temperature of Pinus elliottii showed similar typical single peak curve models.The stem CO₂ release rate in the growing season was significantly higher than that in the non-growth season.The stem CO₂release rate increased with the increasing DBH.?2?There are siginficant exponential relationships between stem CO₂ release rate and stem temperature in three DBH Pinus elliottii.Stem temperature can explain about 88.9%to 92.1%seasonal variation of stem CO₂ release rate.The correlation factor between stem CO₂ release rate and stem temperature was highest in the medium-diameter class,and lowest in the maximun-diameter class.?3?During the whole growing season,significant exponential relationship between stem CO₂ release rate and vapor pressure dificit.There was a significant linear correlation between stem CO₂ release rate photosynthetically active radiation,and there was no significant correlation with the relative humidity of the air.There was also a significant correlation between stem CO₂ release rate and soil moisture in the growing season,and vise versa.?4?The seasonal variation of WUE showed a double peak curve model,increasing first and then decreasing.The daily variations of WUE in different growing seasons showed a single peak or a double peak curve models.The WUE in the non-growing season was significantly greater than the growing season.?5?There were significant relationships between transpiration rate,air temperature,leaf temperature,stomatal conductance,intercellular CO₂ concentration and WUE.Among them,intercellular CO₂ concentration and transpiration rate were decided to have critical influence on leaf water use efficiency.?6?There existed significant linear negative correlation between stem CO₂ release rate and sap flow in the non-growing seasons but no significant correlation in the growing seasons.The measured stem CO₂ release rate in the growing season was 85%of the simulated value,but the stem CO₂ release rate in the non-growing season was 96%of simulated value.