Effects of Light, Temperature, and Soil Depth on the Germination and Emergence of Conyza canadensis (L.) Cronq.

Abstract

Understanding the dynamics of invasive species under global climate change requires knowledge about the effects of environmental factors on germination and emergence. We considered Conyza canadensis (L.) Cronq., an invasive species that is quickly invading Southern European agricultural systems, and performed germination assays in growth chambers at eight constant temperatures with alternating light (2.5, 5, 10, 15, 20, 25, 30, and 40 °C, with 12 h/12 h—light/dark), three alternating temperatures in alternating light (12/18, 17/23, and 22/28 °C, with 12 h/12 h—light/dark) and three fixed temperatures (15, 20, and 25 °C) in complete darkness. Furthermore, emergence assays were performed in pots considering four depths (0, 2.5, 5, and 10 mm), three temperatures with alternating light (15, 20, and 25 °C) and un-treated or pre-treated seeds (water imbibition and light for two days). C. canadensis was able to germinate in a wide range of temperatures (from 5–10 °C to 30 °C). The highest germination capacity was observed at 15 °C (light/dark); no differences were observed at 17/23 and 22/28 °C with respect to 20 and 25 °C (light/dark), while germinations were significantly reduced at 12/18 °C. The lowest germination time was observed at 25 °C (light/dark) and it was significantly increased at 12/18 °C and in darkness. The highest emergence was from 0 mm depth; pre-treatment significantly increased the emergence from 2.5 mm and 5 mm depth, but not from 10 mm depth. Modeling germination rates as a function of temperature allowed us to determine Tb = 6.8 °C (base temperature) and Tc = 35.8 °C (ceiling temperature). In light of these results, the potential for C. canadensis to spread into new environments and possible new management methods are discussed.

Seed germination ecology of Conyza sumatrensis populations stemming from different habitats and implications for management

“…These environmental cues include temperature, light/dark period, abiotic stresses, soil pH and seed burial depth [ 13 – 16 ]. Light has a positive impact on the seed germination of almost all Conyza species which require a definite light period for their successful seed germination [ 18 , 23 , 24 ]. Moreover, seeds of these species buried deep in the soil are unable to emerge due to unavailability of sufficient light for completing germination phase [ 13 , 15 , 25 – 27 ].…”

Germination ecology of hairy fleabane (Conyza bonariensis) and its implications for weed management

“…A previous study reported that seeds of C. bonariensis can germinate at different temperatures ranging from 10 to 25 C (Zinzolker et al 1985), while a similar study documented 5, 20, and 35 C as the minimum, optimum, and maximum temperatures, respectively (Wu et al 2007). In another study, highest germination of horseweed [Conyza canadensis (L.) Cronquist] was observed at 15 C (Ottavini et al 2019). We note that these studies were conducted using constant temperature conditions, and the likelihood of constant temperature in nature is very rare.…”

Changes in the germinability of seeds of dicotyledonous herbs from anthropogenic and wild habitats during two initial years in a seedbank

“…Gray] (Araki and Washitani 2000), silver cinquefoil ( Potentilla argentea L.) (Kolodziejek et al 2019), woodland figwort ( Scrophularia nodosa L.) (Vranckx and Vandelook 2012), and V. thapsus (Catara et al 2016), and in other weed species not included in our study, for example, Robert geranium ( Geranium robertianum L.) (Van Assche and Vandelook 2006) and addersmeat ( Stellaria holostea L.) (Vandelook et al 2008). In fact, the absence of a positive effect of alternating temperature on seed germinability is a rare phenomenon (Ottavini et al 2019). For the long-term survival of buried seeds, the dependence of germination on oscillating temperature conditions is a useful property.…”