Seedling size affects the strategy of dune seedlings responding to rainfall variation

Climate change poses a growing threat to population maintenance in harsh desert habitats with high precipitation variability. Desert seeds may germinate at different times as a bet-hedging strategy to cope with increased rainfall fluctuation. As a result, a population may consist of seedlings of various sizes. However, it remains unknown how the variation in seedling sizes affects their capacity to cope with different rainfall scenarios, thus impairing our capacity to manage populations under climate change.

To fill this gap in knowledge, we examined how seedling size (large seedlings with an average height of 14.30 cm vs. small seedlings with an average height of 5.85 cm) affects the strategy seedlings use to cope with a gradient of rainfall treatments (-75, -50, -25, 0, +25, +50, +75 % of the average monthly rainfall over the past 15 years) for Artemisia ordosica, a dominant shrub widely used for ecological restoration in the Mu Us Sandland, China.

We found that seedling performance was affected both by rainfall intensity and seedling size. Seedling survival and growth declined with a reduction in rainfall. Moreover, large seedlings allocated more biomass to roots, thus increasing their capacity for water absorption, resulting in relatively less reduction in their total biomass under water stress. In contrast, small seedlings invested more in above-ground growth, probably to compete for light.

Our study demonstrates that seedling size may strongly affect the responses of seedlings to rainfall variation. As a result, populations that recruit seedlings with different sizes may better spread mortality risk under variable rainfall conditions. Therefore, our results suggest that species with flexible germination time may be highly suitable for desert vegetation restoration under climate change.