Saveyn An, Steppe Kathy, Lemeur Raoul
Laboratory of Plant Ecology, Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
Tree Physiol. 2007 Mar;27(3):365-74. doi: 10.1093/treephys/27.3.365.
A young potted oak (Quercus robur L.) tree was subjected to drought by interrupting the water supply for 9 days. The tree was placed in a growth chamber in which daily patterns of temperature and radiation were constant. The effects of drought on the water and carbon status of the stem were examined by measuring stem sap flow rate, stem water potential, stem diameter variations, stem CO(2) efflux rate (F(CO2)) and xylem CO(2) concentration ([CO(2)]). Before and after the drought treatment, diurnal fluctuations in F(CO2) and [CO(2)] corresponded well with variations in stem temperature (T(st)). Daytime depressions in F(CO2) did not occur. During the drought treatment, F(CO2) still responded to stepwise changes in temperature, but diurnal fluctuations in F(CO2) were no longer correlated with diurnal fluctuations in T(st). From the moment daily growth rate of the stem became zero, diurnal fluctuations in F(CO2) became closely correlated with diameter variations, exhibiting clear daytime depressions. The depressions in F(CO2) were likely the result of a reduction in metabolic activity caused by the lowered daytime stem water status. Xylem [CO(2)] showed clear daytime depressions in response to drought. When the tree was re-watered, F(CO2) and [CO(2)] exhibited sharp increases, coinciding with an increase in stem diameter. After resumption of the water supply, daytime depressions in F(CO2) and [CO(2)] disappeared and diurnal fluctuations in F(CO2) and [CO(2)] corresponded again with variations in T(st).
对一棵年轻的盆栽栎树（欧洲栓皮栎）进行干旱处理，中断供水9天。将该树置于生长室中，室内温度和辐射的日变化模式保持恒定。通过测量树干液流速率、树干水势、树干直径变化、树干CO₂ 排放速率（F(CO₂)）和木质部CO₂ 浓度（[CO₂*]），研究干旱对树干水分和碳状况的影响。在干旱处理前后，F(CO₂)和[CO₂*]的日波动与树干温度（T(st)）的变化密切相关。F(CO₂)在白天没有出现下降。在干旱处理期间，F(CO₂)仍对温度的逐步变化做出响应，但F(CO₂)的日波动不再与T(st)的日波动相关。从树干日生长速率变为零的那一刻起，F(CO₂)的日波动与直径变化密切相关，出现明显的白天下降。F(CO₂)的下降可能是由于白天树干水分状况降低导致代谢活动减少的结果。木质部[CO₂*]在干旱时出现明显的白天下降。当树木重新浇水时，F(CO₂)和[CO₂*]急剧增加，与树干直径的增加同时发生。恢复供水后，F(CO₂)和[CO₂*]的白天下降消失，F(CO₂)和[CO₂*]的日波动再次与T(st)的变化相对应。
