Soil depth detection by seeds and diurnally fluctuating temperatures: different dynamics in 10 annual plants

Abstract

International audienceBackground and Aims Seeds buried in the soil detect burial depth through light and diurnally fluctuating temperatures (DFT) and in this way limit losses due to germination too deep in the soil. DFTs and germination also increase in vegetation gaps. However, dry open environments with high DFTs can also increase seedling mortality, creating conflicting selection pressures for reaction to DFTs. Since this questions the general function of DFT detection, we therefore tested if interspecific differences in DFT detection are related to mortality in different soil depths. Methods We buried seeds of ten annual plants including species pairs of increasing and decreasing germination in response to DFTs. Seeds were buried in 5, 10 and 25cm soil depth and exhumed after two different burial times. Seed viability was tested using germination in growth chambers and tetrazolium. We also measured DFTs at these depths using temperature data loggers. Results DFT detection was not related to differences in mortality at three burial depths. Three species showed a clear pattern of depth dependent mortality, however inconsistently related to DFT detection. Conclusions Depth detection mechanisms are more species-specific than expected. Hence, interspecific differences in seed mortalities are difficult to predict by DFT detection alone and alternative soil depth sensing mechanisms should be explored in future

The ecophysiology of seed persistence: a mechanistic view of the journey to germination or demise

“…Higher temperatures can accelerate seed ageing (Ellis & Roberts, 1981) and alleviate physical (Baskin, 2003) and physiological dormancy (Iglesias-Fernández et al, 2011) in the laboratory. In the field, seeds in strongly seasonal climates can experience daily and seasonal fluctuations in temperature and moisture, particularly in the upper centimetres of soil (Benvenuti, MacChia & Miele, 2001;Merritt et al, 2007;Saatkamp et al, 2011a). Exposure to reduced rainfall and more stable temperatures affords longer persistence in desiccation-tolerant seeds (Burnside et al, 1996), whilst exposure to dry climates can kill desiccationsensitive seeds (Tweddle et al, 2003).…”

“…Seed persistence is further favoured at depth given that soil burial can protect seeds from predation (Hulme, 1998a) and the passage of fire (Weiss, 1984;Hodgkinson & Oxley, 1990). Whilst the ability to emerge successfully from depth may be favoured among larger seeds due to their larger storage reserves (Harper, Lovell & Moore, 1970;Grant et al, 1996), seeds of all sizes may germinate at depth and fail to emerge (a phenomenon known as suicidal germination), thus terminating their persistence in the soil seed bank (Benvenuti et al, 2001;Saatkamp et al, 2011a).…”

Temperature but not moisture response of germination shows phylogenetic constraints while both interact with seed mass and lifespan

“…Germination of seeds depends primarily on climatic variables such as temperature and moisture conditions in the seed bed (Kruk et al, 2006;Saatkamp et al, 2011a;Baskin and Baskin, 2014; growth (Poorter and Nagel, 2000;Rustad et al, 2001). Germination timing of non-dormant seeds with the environment can be modelled effectively as a function of time passed above threshold values such as base temperature (T b ) and base water potential (Ψ b ) (Steinmaus et al, 2000;Bradford, 2002;Trudgill et al, 2005).…”

Light and Temperature Requirements during Germination of Potential Perennial Grasses for Rehabilitation of Degraded Sandy Arabian Deserts

“…Absence of clonality necessitates the development of bigger persistent seed bank that help them to spread over time (Winkler & Fischer, 2002). Retention of a fraction of ungerminated seeds in the seed bank could be considered as a bet-hedging strategy to insure against reproduction failure, which could increase long-term fitness (Saatkamp et al, 2011). It also could be explained as a form of risk spreading in temporally variable, unpredictable desert environments (Venable & Brown, 1988;Gremer & Venable, 2014).…”