Location: Water Management and Systems ResearchTitle: Increasing axial parenchyma fraction allowed for the improvement of hydraulic efficiency during the evolution of Malagasy Magnoliids
|ARITSARA, AMY NY AINA - University Of Antananarivo|
|RAZAKANDRAINIBE, VONJISOA - University Of Antananarivo|
|RAMANANANTOANDRO, TAHIANA - University Of Antananarivo|
|CAO, KUN-FANG - Guangxi University|
Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2020
Publication Date: 9/27/2020
Citation: Aritsara, A., Razakandrainibe, V.M., Ramananantoandro, T., Gleason, S.M., Cao, K. 2020. Increasing axial parenchyma fraction allowed for the improvement of hydraulic efficiency during the evolution of Malagasy Magnoliids. New Phytologist. 229(3):1467-1480. https://doi.org/10.1111/nph.16969.
Interpretive Summary: One of the first physiological processes that fail during drought is the ability of vascular species to transport water (i.e., through xylem tissue). If we are to improve the drought tolerance of crop species, we must not only understand the xylem features that fail during drought stress, but also, the genetic underpinnings of these traits. One possible way forward towards the improvement of water transport in crop species is knowing whether or not xylem traits have evolved as a coordinated assemblage (simple genetic coding), or else have evolved in isolation of one another (more complex genetic coding). In this study, we examine the evolution of a basal angiosperm clade, and specifically the evolution of traits thought to be important in water transport during drought (hydraulic "safety"), and also to support fast growth (hydraulic "efficiency"). We found that the evolution of this basal clade led to the improvement of hydraulic efficiency with little adverse effect on hydraulic "safety". We also found that improvements in xylem tissue, specifically storage and hydraulic support cells (axial / ray parenchyma) led to these improvements in hydraulic efficiency with little impact on other xylem functions.
Technical Abstract: • The evolution of angiosperms was accompanied by the segregation and specialization of their xylem tissues. This study attempted to determine whether coordinated evolution of parenchyma tissue and water transport of basal angiosperms influenced the hydraulic efficiency-safety tradeoff. • We examined xylem anatomical structure and hydraulic functions of 28 woody species of Magnoliids in a tropical rainforest in Madagascar, and for the first time report the outcome of parenchyma evolution on the hydraulic efficiency-safety tradeoff. We also introduce a concept of distance to the tradeoff line to measure the optimization of the hydraulic system. • Although the basal angiosperms in this study had low hydraulic conductivity and safety, the increase in axial parenchyma fraction (APf) and decrease in ray parenchyma fraction (RPf) were associated with increasing hydraulic efficiency. Lower RPf species were more embolism resistant. Species closer to the tradeoff line had more APf and less RPf. Space competition between tissues existed. During the evolution of angiosperms, other adjustments to the xylem have occurred, such as the development of perforation plate structures and fiber/tracheid lumen fraction, improved xylem efficiency, improved safety, and improved mechanical support, but also reduced competition for space among xylem functions. • Our results revealed that axial parenchyma was more tightly coordinated with xylem functioning than ray parenchyma.