Comparative venation costs of monocotyledon and dicotyledon species in the Eastern Colorado steppe

Authors: DROBNITCH, SARAH - Colorado State University; Kray, Julie; Gleason, Sean; OCHELTREE, TROY - Colorado State University

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2024
Publication Date: 5/18/2024
Citation: Drobnitch, S., Kray, J.A., Gleason, S.M., Ocheltree, T. 2024. Comparative venation costs of monocotyledon and dicotyledon species in the Eastern Colorado steppe. Planta. 260. Article e2. https://doi.org/10.1007/s00425-024-04434-x.
DOI: https://doi.org/10.1007/s00425-024-04434-x

Interpretive Summary: Much like the circulatory system in animals, plants have complex vascular systems composed of tiny tubes that transport water and nutrients throughout their bodies. Most plants have systems which resemble the shape of branches on a tree, while other plants, like grasses and palms, have systems which are rather straight-lined, much like multiple side-by-side railroad tracks. In this study, we investigated if grassy plants, with their seemingly inefficient, straight-lined vascular systems, spend more energy than plants with branched systems. Surprisingly, our findings suggest that both types of vascular system are equally efficient. To test this further, we inflicted mild injuries on the plants to see how well their vascular systems recover. Remarkably, both plant types showed similar ability to route water around the injury. This study raises more questions. For example, what might be the functional reason these two vascular systems have arisen during the evolution of plant species? Has this evolutionary divergence occurred only once, or has it occurred multiple times? Overall, despite there being large differences between grasses and other plants, they all have evolved cost-effective and efficient mechanisms for transporting water and nutrients throughout their bodies.

Technical Abstract: Dendritic vascular networks optimize resource delivery while minimizing infrastructure costs, typically following Murray's law or the WBE framework. Monocots, such as grasses and palms, defy this norm with parallel venation systems. We explore whether monocots incur higher carbon/construction costs than dicots, and if they possess compensatory advantages. We measure venation networks at macroscopic vein, vascular bundle, and xylem vessel levels to differentiate mechanical support, total transport, and water transport investments. Our findings challenge assumptions of monocots having sub-optimal network designs, as major vein networks show no significant cost differences compared to dicots. However, dicots invest more in minor vein networks, highlighting divergent strategies in minor vein density and major vein network dimensions. Surprisingly, we find no significant relationships between vascular network size and gas exchange parameters, contradicting our hypothesis that minor vein density correlates with photosynthesis and leaf conductance. Ecologically, both monocots and dicots exhibit resilience to leaf injury, with no substantial leaf loss. This contradicts expectations of potential disadvantages in parallel venation systems. These results prompt further investigation into the evolutionary constraints limiting the prevalence of parallel venation. While monocots do not seem to exhibit hydraulic disadvantages compared to dicots, the underlying genetic events driving their unique venation systems remain an intriguing research avenue. This study challenges conventional wisdom regarding vascular network optimization and underscores the need for a deeper understanding of alternative resource distribution systems in plant evolution.