From cells to stems: the effects of primary vascular construction on drought‐induced embolism in fern rhizomes

Abstract

While a considerable amount of data exists on the link between xylem construction and hydraulic function, few studies have focused on resistance to drought-induced embolism of primary vasculature in herbaceous plants. Ferns rely entirely on primary xylem and display a remarkable diversity of vascular construction in their rhizomes, making them an ideal group in which to examine hydraulic structure-function relationships.New optical methods allowed us to measure vulnerability to embolism in rhizomes, which are notoriously difficult to work with. We investigated five fern species based on their diverse xylem traits at the cellular, histological, and architectural levels. To link below-and aboveground hydraulics, we then measured leaf-stem vulnerability segmentation.Overall, rhizome vulnerability to embolism was correlated most strongly with cellular but not histological or architectural traits. Interestingly, at P 6-12 , species with increased architectural dissection were actually more vulnerable to embolism, suggesting different hydraulic dynamics at low compared to high percent embolism. Importantly, leaves fully embolize before stems reach P 88 , suggesting strong vulnerability segmentation. This is the first study to explore the functional implications of primary vascular construction in fern rhizomes and leaf-stem vulnerability segmentation. Strong segmentation suggests that leaves protect perennial rhizomes against severe drought stress and hydraulically induced mortality.

Rapid diversification of vascular architecture underlies the Carboniferous fern radiation

“…More recently, physiological work on the hydraulics of fern leaves and seed plant stems has suggested that increased vascular dissection confers increased resistance to drought-induced embolism [71,72]. However, an explicit investigation of the physiological implications of vascular architecture in fern stems did not find evidence that increasing dissection leads to an increase in drought tolerance [73]. If increased vascular dissection is hypothesized to increase drought resistance, it may be expected that fern species with highly dissected vascular architecture should occur more frequently in ecosystems with a high potential for drought—a trend found in woody angiosperms [74].…”

A bump in the node: The hydraulic implications of rhizomatous growth

“…Stomatal conductance (g s ) was measured for 0.5-2 h for each treatment (rooted, uprooted, and cut) for a total of 3-6 h for 5-10 replicates per species. To ensure that the uprooted experiments were reflective of hydraulic integration and not rhizome capacitance, we left one replicate for each species uprooted for at least 24 h (longer than it takes for some of these species to fully desiccate; Suissa and Friedman, 2021), and stomatal conductance measurements were resumed. Stomatal conductance was binned every 5 min and plotted as a function of time.…”

Seeing is believing: what visualising bubbles in the xylem has revealed about plant hydraulic function

“…To date, VCs of a dozen economically important herbaceous species as well as early-diverging species (i.e. ferns, lycophytes, and Polytrichalean bryophytes) have been constructed using intact plants (Skelton et al 2017a;Cardoso et al 2018Cardoso et al , 2019Johnson et al 2018;Brodribb et al 2020a;Corso et al 2020;Suissa and Friedman 2021).…”

“…Even though debarking the stem to expose the xylem has been questioned, with Venturas et al (2019) claiming it might damage the xylem and alter the way this tissue will respond to dehydration, the amount of artificial embolism induced by careful bark removal and the application of hydrogel is negligible (Johnson et al 2020). For species where the periderm cannot be easily removed without damage to the xylem, or in species with a vascular stele such as lycophytes and ferns, thin paradermal sections can be made to expose the xylem before the hydrogel is applied (Cardoso et al 2020c;Suissa and Friedman 2021).…”