杉木不同冠层高度的水力结构和光合特性OA北大核心CSTPCD

Relevant indicators were determined at different canopy heights(lower,middle,and upper)to analyze the vertical gradient for variations in the hydraulic architecture and photosynthetic characteristics and the relationships between them in a 7-year old Chinese fir,in Baisha State-owned Forest Farm of Minhou,Fujian Province.Significant differences(P＜0.05)were found in the hydraulic architecture and photosynthetic characteristics at different canopy heights.Hydraulic conductivity,specific conductivity,leaf-specific conductivity,water potential,and sapwood area generally decreased with increasing canopy height,with upper canopy(9 m)showing reductions of 50.2%,35.5%,42.6%,23.7%,and 24.4%,respectively,compared to the lower canopy(4 m,P＜0.05).The Huber value initially decreased and then increased;however,the difference was not statistically significant.The net photosynthetic rate,stomatal conductance,transpiration rate,instantaneous water use efficiency,and stomatal limitation were significantly higher in the lower canopy than in the upper canopy,whereas the intercellular CO2 concentration was significantly higher in the upper canopy(P＜0.05).Compared with that in the lower canopy,the net photosynthetic rate in the middle and upper canopy leaves decreased by 24.4%and 32.9%,stomatal conductance decreased by 13.9%and 21.0%,transpiration rate decreased by 6.4%and 12.1%,instantaneous water-use efficiency decreased by 19.7%and 23.1%,and stomatal limitation decreased by 6.1%and 12.1%,respectively,whereas the intercellular CO2 concentration increased by 3.5%and 6.5%,respectively.Correlation analysis revealed significant positive relationships between hydraulic conductivity and both the net photosynthetic rate and stomatal conductance(P＜0.05).Specific conductivity was positively correlated with net photosynthetic rate,instantaneous water use efficiency,and stomatal limitation and negatively correlated with intercellular CO2 concentration(P＜0.01).Leaf-specific conductivity showed significant positive correlations with both stomatal conductance and the net photosynthetic rate(P＜0.01).Water potential was positively correlated with the net photosynthetic rate(P＜0.01),and sapwood area was positively correlated with stomatal conductance(P＜0.05).These findings suggest that increased tree height in Chinese fir leads to longer water transport paths,increased resistance and gravity,reduced hydraulic conductivity,closed stomata,and decreased photosynthetic efficiency to minimize water loss,indicating height-related hydraulic limitations.