Freeze-thaw cycles alter the growth sprouting strategy of wetland plants by promoting denitrification

Abstract Freeze-thaw cycles exert an important abiotic stress on plants at the beginning of winter and spring in mid-to-high latitudes. Here, we investigate whether the effects of freeze-thaw cycles are carried over into the growing season in wetlands. We conduct a temperature-controlled experiment under two freeze-thaw and two flooding conditions on a typical plant ( Scirpus planiculmis ) and soil from the Momoge wetland (China) and analyze the microbial nitrogen metabolism, based on metagenomic sequencing. We show that freeze-thaw cycles earlier in the year significantly inhibit plant sprouting and early growth. Specifically, they promote denitrification and thus reduce nitrogen levels, which in turn intensifies nitrogen limitation in the wetland soil. We find that plants tend to sprout later but faster after they are exposed to freeze-thaw cycles. Wetland flooding could alleviate these medium-term effects of freeze-thaw cycles. Our results suggest that wetland plants in mid-to-high latitudes have evolved sprouting and growth strategies to adapt to climatic conditions at the beginning of winter and spring.