Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatum

Abstract

Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring-summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C4 grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species.

Variability in germination behaviour ofPaspalum dilatatumPoir. seeds is genotype dependent

“…(). This response is in agreement with evidence from field assays showing that flooding promotes germination and emergence in P. dilatatum (Cornaglia et al ., ). The comparable efficiency of alternating temperatures and warm pre‐conditioning followed by constant germination‐promoting temperatures suggests that pre‐conditioning at mild temperatures may be enough to break dormancy, and temperature alternation, as reported in other species (Benech‐Arnold et al ., ), is not strictly necessary for P. dilatatum .…”

Geographic variation in the flood‐induced fluctuating temperature requirement for germination in Setaria parviflora seeds

“…2007) as well as release from primary dormancy of seeds of other dominant species of the floodplain (Insausti et al. 1995; Cornaglia et al. 2009).…”

Unexpectedly, intense livestock grazing in arid rangelands strengthens the seedling vigor of consumed plants

“…Large herbivores directly damage plant tissues (Mc Naughton 1983;Tadey 2006) potentially reducing offspring production, germination, and/or seedling establishment (Edwards et al 2005). The effect of grazing on germination and seedling establishment has been frequently studied in grasslands from mesic environments (Cornaglia et al 2009) but is lacking for arid rangelands. In arid ecosystems, plant dynamics is different, and the impact of livestock on native vegetation offspring is less understood.…”

“…Other factors, such as life-form, nutrient availability, and moisture level, may influence germination and seedling growth under grazing conditions (Miller 1995;Rodríguez-Echeverría and Pérez-Fernández 2001). In habitats with no water deficit but with nutrient limitations, grazing may release competition, increasing plant isolation, generating open areas that facilitate the break of seed dormancy and increase germination (Jutila and Grace 2002;Cornaglia et al 2009). Conversely, in arid environments, water scarcity coupled with high temperatures strongly limit plant development (Andersen and Krzywinski 2007).…”