Linkages between water transport, hydraulic architecture and carbon assimilation in woody species

Abstract

Water storage and transport play an important role in whole-plant water carbon balance. Different patterns of diurnal variation in sap flow, water content in stem tissues and changes in cross sectional area were observed. A typical diurnal pattern showed an increase in sapflow during the morning with the decrease in sapwood and bark tissue water content consistent with the shrinkage of the stems. This pattern strongly suggests that the internal water storages contribute to the leaf water consumption. However, other pattern also was observed in a species with an atypical extremely thick cortex. Water stem reservoirs were recharged during the daytime when the sap flow was substantially high. A third pattern was observed in species with very high wood density, where stem sectional area decreased when sap flow increased and sapwood water storages were recharged. The functional significance for these different patterns will be discussed. The coordination between capacitance and hydraulic efficiency across leaves and stems of tree species was also evaluated, including the linkages between these hydraulic traits and vulnerability to drought and the assimilation rates. Species with higher capacitance and hydraulic efficiency were more vulnerable to drought, had narrow safety margin and restricted transpiration and carbon assimilation earlier in the daytime. We will discuss also the consequences of these patterns under drought anomalies.