Warmer seed environments increase germination fractions in Australian winter annual plant species

Abstract

Citation: Dwyer, J. M., and T. E. Erickson. 2016. Warmer seed environments increase germination fractions in Australian winter annual plant species. Ecosphere 7(10):e01497. 10. 1002/ecs2.1497 Abstract. Climate can influence plant demographic processes and life stages in different ways, but such details are often ignored in analyses that focus on adult life stages and annual climate averages. In particular, the effects of climate on seeds may be hugely important under climate change. Climate is known to influence seed survival and germination, which in turn can strongly affect population persistence and community dynamics. We investigated climate and other environmental effects on seed viability and germination probabilities of six winter annual plant species persisting in small, isolated habitat fragments in the Mediterranean-climate region of southwestern Australia. Seeds were collected from southern (cool) and northern (warm) bushland remnants and factorially placed into each location to assess the effects of natural dormancy alleviation via after-ripening. Seeds were then exposed to cool and warm germination treatments (representing average germination conditions in the two remnants). For five of the six species, seeds from warm maternal populations had higher germination probabilities (or germinated more seeds sooner). Regardless of maternal population, germination probabilities were higher (or germination was more rapid) for seeds that were after-ripened in the warm remnant for almost all species. For all species, germination was higher (or more rapid) under the warmer germination temperatures. We also found strong microsite effects on seed viability for some species. In the absence of adaptation in dormancy regulation and germination physiology, our results indicate that most of the winter annual species studied will germinate higher fractions of seeds under future climate conditions due to the cumulative effects of warmer maternal, after-ripening, and germination environments. The fate of isolated populations under climate change may therefore depend strongly on postgermination survival and reproduction to prevent seed bank depletion.

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi‐arid annual plant communities

“…We believe that direct aridity effects on other unquantified vital rates (germination and seed survival), while likely to influence fitness differences (and thus interpretations of competitive superiority), would not change our conclusions about impacts of aridity on coexistence dynamics overall. Our two native focal species did have higher germination rates in xeric conditions, consistent with Dwyer and Erickson (), who found elevated germination rates and seed viability for these species at W. Perenjori. Though including germination and seed viability data from within our experimental plots would have been ideal, it would only have potentially changed coexistence outcomes for a few species pairs, as our model assumes these parameters act on fitness differences only (Figure , y‐axis).…”

“…Though including germination and seed viability data from within our experimental plots would have been ideal, it would only have potentially changed coexistence outcomes for a few species pairs, as our model assumes these parameters act on fitness differences only (Figure , y‐axis). In this system, increasing temperatures associated with climate change may confer a fitness advantage to native species via increased germination fractions (Dwyer & Erickson, ). However, these positive direct effects may be tempered by negative effects of shorter growing seasons (e.g., Matias et al, ) and increasing environmental stress.…”

“…However, these positive direct effects may be tempered by negative effects of shorter growing seasons (e.g., Matias et al, ) and increasing environmental stress. Combined, these factors may differentially alter plant growth rates (and thus interaction coefficients) and limit reproductive potential ( λ ) (Dwyer & Erickson, ; Lancaster, Morrison, & Fitt, ).…”

“…Native-Native Dwyer and Erickson (2016), who found elevated germination rates and seed viability for these species at W. Perenjori. Though including germination and seed viability data from within our experimental plots would have been ideal, it would only have potentially changed coexistence outcomes for a few species pairs, as our model assumes these parameters act on fitness differences only ( Figure 5, y-axis).…”

Constraints on trait combinations explain climatic drivers of biodiversity: the importance of trait covariance in community assembly

“…In our system, patchy woody plant cover creates local gradients of shade and temperature within all communities, but the temperature differences between open and shaded microsites are considerably greater in warmer, northern communities (Fig. in Dwyer & Erickson ). Thus, it is not only increasing regional temperatures but also steeper local temperature gradients that are likely increasing trait covariance within semi‐arid communities in our system.…”