Wrack burial limits germination and establishment of yellow flag iris (Iris pseudacorus L.)

Authors: CASTILLO, JESUS - University Of Seville; GALLEGO-TEVAR, BLANCA - University Of Seville; Grewell, Brenda

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2023
Publication Date: 3/30/2023
Citation: Castillo, J.M., Gallego-Tevar, B., Grewell, B.J. 2023. Wrack burial limits germination and establishment of yellow flag iris (Iris pseudacorus L.). Plants. 12(7). Article 1510. https://doi.org/10.3390/plants12071510.
DOI: https://doi.org/10.3390/plants12071510

Interpretive Summary: Yellow flag iris (Iris pseudacorus L.; Iridaceae) is a perennial macrophyte native to Europe, North Africa and western Asia, which is often used as an ornamental aquatic plant in garden and ponds worldwide and has escaped cultivation and invaded natural wetlands in nearly every global ecozone. Recent invasions have been spreading rapidly in Pacific west coast estuaries of the U.S. Germination and establishment are crucial stages in plant life cycles. Seed burial under wrack, stranded mats of water-transported plant debris, can limit germination and recruitment of seedlings in wetland ecosystems. Wrack mats can also introduce invasive plant propagules into wetlands. We studied the effects of five wrack burial depths (0, 1, 2, 4 and 8 cm) on germination and establishment of Iris pseudacorus in a complete randomized block experiment under controlled greenhouse conditions. We recorded percentages of germinating, senescent and quiescent seeds and evaluated seedling establishment and growth relative to substrate environmental factors (pH, electrical conductivity, redox potential and temperature). Seedling emergence of I. pseudacorus was reduced from more than 80% in control conditions without wrack burial to less than 40% at even the minimal wrack depths of 1 cm, which was primarily explained by reduction in daily temperature variation within the substrate. Few I. pseudacorus seedlings were able to emerge from wrack burial of up to 8 cm in depth. Along with reduced seedling emergence, we found greater numbers of quiescent seeds and seeds that had germinated but did not emerge from under wrack. Increased seed quiescence with wrack burial was mainly related to reduced variation in daily substrate temperature. No senescent seedlings were observed beneath wrack at any depth of wrack burial. Our results show that wrack burial limits germination and establishment of Iris pseudacorus. However, decomposition or removal of wrack can open habitat and stimulate emergence from the seed bank. In view of our results, management of I. pseudacorus invasion will be a long-term challenge where wrack is present, requiring continued control due to cycles of wrack deposition and decomposition that provide cycles of the invasive plant to emerge from wrack-buried seed banks. In sensitive zones impacted by wrack, removal of wrack mats should be considered in an integrated management scheme to deplete invasive plant seed banks.

Technical Abstract: Germination and establishment are crucial stages in plant life cycles. Seed burial under wrack, stranded mats of water-transported plant debris, can limit germination and recruitment of seedlings in wetland ecosystems. Wrack mats can also introduce invasive plant propagules into wetlands. We studied the effects of five wrack burial depths (0, 1, 2, 4 and 8 cm) on germination and establishment of Iris pseudacorus in a complete randomized block experiment under controlled greenhouse conditions. Iris pseudacorus is a macrophyte native to the Europe, the Mediterranean Basin and western Asia and that is invading wetlands in nearly every global ecozone. We recorded percentages of germinating, senescent and quiescent seeds and evaluated seedling establishment and growth relative to substrate environmental factors (pH, electrical conductivity, redox potential and temperature). Seedling emergence of I. pseudacorus was reduced from more than 80% in control conditions without wrack burial to less than 40% at even the minimal wrack depths of 1 cm, which was primarily explained by reduction in daily temperature variation within the substrate. Few I. pseudacorus seedlings were able to emerge from wrack burial of up to 8 cm in depth. Along with reduced seedling emergence, we found greater numbers of quiescent seeds and seeds that had germinated but did not emerge from under wrack. Increased seed quiescence with wrack burial was mainly related to reduced variation in daily substrate temperature. No senescent seedlings were observed beneath wrack at any depth of wrack burial. Our results show that wrack burial limits germination and establishment of Iris pseudacorus. However, decomposition or removal of wrack can open habitat and stimulate emergence from the seed bank. In view of our results, management of I. pseudacorus invasion will be a long-term challenge where wrack is present, requiring continued control due to cycles of wrack deposition and decomposition that provide cycles of the invasive plant to emerge from wrack-buried seed banks. In sensitive zones impacted by wrack, removal of wrack mats should be considered in an integrated management scheme to deplete invasive plant seed banks.