Initial decomposition of floating leaf blades of waterlilies: causes, damage types and impacts

Abstract

The initial decomposition of large floating-leaved macrophytes, such as waterlilies, can be studied by following changes in leaf damage and area loss of leaf blades tagged in their natural environment. This approach was taken in the present study to examine the initial decomposition patterns of floating leaf blades of Nuphar lutea (L.) Sm., Nymphaea alba L. and Nymphaea candida C. Presl at three freshwater sites differing in nutrient status, alkalinity and pH. Floating leaf blades of the three plant species were tagged and numbered within established replicate plots and the leaf length, percentages and types of damage and decay of all tagged leaves were recorded weekly during the growing season. Microbial decay, infection by phytopathogenic fungi (Colletotrichum nymphaeae) and oomycetes (Pythium sp.), consumption by pond snails, and mechanical factors were the most important causes of leaf damage. Several types of succession comprising different causes of damage were distinguished during the season. For example, young floating leaves are affected by more or less specialized invertebrate species consuming leaf tissue, followed by non-specialized invertebrate species feeding on the damaged floating leaves. In the two investigated hardwater lakes the seasonal patterns of initial decomposition differed between Nymphaea and Nuphar.

Initial decomposition of floating leaf blades of Nymphoides peltata (S.G. Gmel.) O. Kuntze (Menyanthaceae): causes, impact and succession

“…From similar research on plots with Nuphar lutea , Nymphaea alba and N. candida ( Klok & Van der Velde, 2017 , 2019 ), the growth period lasted 71 to 134 days, or 53% to 73% of the vegetation period of 135 to 199 days. Percentages of loss of photosynthetic area ranged from 38% to 50% for Nuphar and 44% to 54% for Nymphaea .…”

“…Decomposition of young leaf blades of N. peltata already starts under water before they unroll with consumption and/or damage. This is visible when they enroll at the water surface often as a row of similar damage patterns on the same leaf blade ( Klok & Van der Velde, 2019 ). During initial decomposition, when leaves are still floating, macrophyte tissue is used by herbivores and by phytopathogenic and saprotrophic microorganisms ( Kok, 1993 ).…”

“…Furthermore, leaves are colonized by microorganisms, causing microbial enrichment which makes the tissue more attractive for detritivorous macroinvertebrates ( Kok, 1993 ). Decayed floating leaves sink underwater to the bottom, where they provide a resource for detritus-based benthic food webs during further decomposition ( Klok & Van der Velde, 2019 ). To study the latter decomposition process, the litterbag method is commonly used ( Brock et al, 1982 ; Brock, 1985 ; Wieder & Lang, 1982 ).…”

Relationships between key functional traits of the waterlily Nuphar lutea and wetland nutrient content

“…For reproduction, we documented the number of flowers produced per apex per year (counting the flower peduncle scars in rhizomes, as described later in the ‘Rhizome traits’ section), the number of seeds produced per fruit, the fruit water content and the seed:fruit mass ratio. For defence, we focused on floating leaf blades (which face high grazing pressure, Stenberg & Stenberg, 2012; Klok & Van Der Velde, 2019), because submerged leaves were absent of many sites, particularly the eutrophic ones (despite the fact that submersed leaves may be more consumed by herbivores as ducks and swans, Cronin, Wissing & Lodge, 1998). For this purpose, the leaf water content (i.e.…”