Differences in vegetative growth of two invasive hawkweeds at temperatures simulating invaded habitats at two altitudes

Kris French,Eva Watts

doi:10.1038/s41598-020-58914-7

Abstract

Hieracium pilosella and H. aurantiacum are invading alpine regions in New South Wales, Australia. In a glasshouse experiment we investigated germination and growth rates of these two species at temperatures simulating the altitudes where invasions are occurring from autumn to spring. We measured germination rates, growth rates and the development of stolons and ramets using seedlings and plantlets from established plants. Germination was low in H. aurantiacum and unaffected by altitude or seed age. H. pilosella showed site to site variability in germination but had greater germination. No species produced flower spikes. Both species grew rapidly and put at least twice as much biomass into roots compared to shoots. H. aurantiacum could begin to produce stolons after 27 days and seedlings grew a little larger than for H. pilosella. Hieracium aurantiacum put significantly more resources into ramets, allocating between 4–15% of biomass. H. pilosella produced 2.6 stolons month−1, in contrast to 9.8 stolons month−1 for H. aurantiacum. Furthermore, plantlets from established plants had vastly different growth rates. Plantlets of H. aurantiacum produced 2.1 leaves day−1 from late summer to winter where H. pilosella was 3 times slower for the same period but faster following winter. Both species were able to maintain strong growth over cooler months suggesting hawkweeds have the capacity for fast growth in the invaded range under high nutrients and lower competition. H. aurantiacum is likely to be a more effective invader than H. pilosella spreading through stolons and the development of weed mats.

Highlights

Hieracium pilosella and H. aurantiacum are invading alpine regions in New South Wales, Australia
Three species have invaded Australia, but at present, in the alpine regions of NSW, two of the species are in early stages of establishment; orange hawkweed (Hieracium aurantiacum L.) and mouse-ear hawkweed (Hieracium pilosella L.)[6]
A greater proportion of seeds germinated for H. pilosella, with high levels of variation in the proportion of seed germinating from different sites, but with no obvious relationship with age of seeds (F3,27 = 13.100, P < 0.0001, Fig. 3)

Summary

Introduction

Hieracium pilosella and H. aurantiacum are invading alpine regions in New South Wales, Australia. Three species have invaded Australia, but at present, in the alpine regions of NSW, two of the species are in early stages of establishment; orange hawkweed (Hieracium aurantiacum L.) and mouse-ear hawkweed (Hieracium pilosella L.)[6] Both species are undergoing an eradication program in New South Wales, Australia, three aspects are of concern for the establishment of these invasive daisies if eradication fails. H. aurantiacum and H. pilosella can be apomictic[9,10,11] and can spread quickly with the establishment of single plants Both species are matt-forming, producing many stolons with ramets which allow genets to quickly take over available space in the landscape. The speed of germination, growth of individual plants and production of stolons and ramets all form important aspects in establishment, for species that rely so heavily on clonal reproduction. We sought some understanding of germination rates from different populations grown at temperatures reflective of establishment sites

Methods

Results

Conclusion