Germination of the invasive legume Lupinus polyphyllus depends on cutting date and seed morphology

Abstract

In semi-natural grasslands, mowing leads to the dispersal of species that have viable seeds at the right time. For invasive plant species in grasslands, dispersal by mowing should be avoided, and information on the effect of cutting date on the germination of invasive species is needed. We investigated the germination of seeds of the invasive legume Lupinus polyphyllus Lindl. depending on the cutting date. We measured seed traits associated with successful germination that can be assessed by managers for an improved timing of control measures. To this end, we sampled seeds of L. polyphyllus on six cutting dates and analyzed the germination of these seeds in climate chambers and under ambient weather conditions. We collected information on seed morphology (color/size/hardseededness) for each cutting date to identify seed traits associated with successful germination. Observed germination patterns were highly asynchronous and differed between seeds cut at different dates. Seeds cut early, being green and soft, tended to germinate in autumn. Seeds cut late, being dark and hard, were more prone to germinate the following spring, after winter stratification. This allows the species to utilize germination niches throughout the year, thus indicating a bet-hedging strategy. Seed color and the percentage of hard seeds were good predictors of germination percentage, but not of mean germination time and synchrony. Managers should prevent the species producing black and hard seeds, while cutting plants carrying green and soft seeds is less problematic. Furthermore, germination patterns differed between climate chambers and the common garden, mainly because germination of dormant seeds was lower in climate chambers. More germination experiments under ambient weather conditions should be carried out, as they can give information on the germination dynamics of invasive species.

Constraints in the restoration of mountain meadows invaded by the legume Lupinus polyphyllus

“…Larger stands that need to be mown with mowing machinery can also be mown after full bloom of L. polyphyllus as long as the seeds are green and soft. What should be avoided in any case is the dispersal of ripe L. polyphyllus seeds (characterized by brown to black color and hardseededness; Klinger et al 2020) by mowing machinery or zoochory. Although another study found that mowing once annually reduced vital rates and biomass of L. polyphyllus (Ramula 2020), this could not be confirmed for the present study area (Klinger et al 2019).…”

Risk of Invasive Lupinus polyphyllus Seed Survival in Biomass Treatment Processes

“…The species is very modest with habitat requirements and produces a large amount of durable hard-coated [45] and small (average 4 mm length) seeds. The coloration of seeds is highly variable [46], and the coloration is connected to viability and timing of germination [47]. One inflorescence produces usually a few hundred seeds but can reach up to thousand seeds per plant [44][45][46].…”

“…The germination potential of common, nationally invasive and highly harmful garden lupin (Large-leaved lupin) Lupinus polyphyllus seed was studied to see if seed viability was affected in municipal tunnel or windrow composting processes or in farm-scale or laboratory-scale AD process in mesophilic conditions. Seeds of L. polyphyllus are capable of after-ripening and germinating even if vegetation is mowed in the early phase of seed ripening [47]. Germination potential increases with time, and therefore desiccated and hard seeds may prove to be resistant even in extreme conditions.…”

Seed bank offers potential for active restoration of mountain meadows

“…If seed viability would decrease significantly within the first 5 years after burial, as suggested by the classification as short‐term persistent, preventing seed shedding could rapidly reduce new germination and establishment events of L. polyphyllus in our study region. Also, the right timing of management actions plays an important role in preventing the incorporation of the seeds into the seed bank, as seeds of L. polyphyllus from meadows being cut early tend to germinate in autumn, seeds from meadows being cut late express higher levels of dormancy, and could potentially accumulate in the soil seed bank (Klinger et al 2020). To this end, early and, if necessary, repeated mowing of the mountain meadows would be crucial.…”

“…The management of large parts of the grasslands was optimized for the conservation of T. tetrix , that is meadows were mown later in summer since the early 1990s. This was beneficial for seed ripening of Lupinus polyphyllus (Klinger et al 2020) and may be a reason for the invasion success of this species.…”