The compensation effect between safety and efficiency in xylem and its
role in photosynthesis of gymnosperms
Abstract
The safety-efficiency trade-off (SETO) hypothesis is a common theme in
plant sciences. Despite safety and efficiency are physiologically
compensated for each other, they are always mathematically described
into trade-off against one another. However, the compensation effect has
never been defined and quantified. What remains unclear is how
compensation effect has influenced the xylem water transport and
subsequently photosynthesis. Here, we proposed that the compensation
effect between safety and efficiency was actually a safety-efficiency
tie-up strategy (SETU; a positive relationship between safety and
efficiency) within xylem functions. Then we proposed a theoretical
framework that integrated the compensation effect into the xylem
hydraulic functional strategy to quantify SETU and SETO. Finally, we
tested SETO- and SETU-photosynthetic rate relationships across different
levels, based on a common garden experiment using nine conifers and
published data for gymnosperms. The results demonstrated that the
compensation effect in xylem functions was the dominant force in
facilitating photosynthetic rates at scales from the species to the
phylum. By integrating the compensation effect into the xylem hydraulic
functional strategy, our study clearly indicates that the compensation
effect is the evolutionary basis for the coordination of xylem hydraulic
and photosynthesis physiology.