Warm nights without respite accelerates the death of seedlings in a drought

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Seedlings have a better chance of surviving in a drought if they cool at night. The study by Ruiling Lu and colleagues, published in Tree Physiology, highlights the role of stomatal regulation revealing how higher night-time temperatures kill plants. This could help scientists predict how trees will react to global warming.

The botanists exposed seedlings of two wide-ranging subtropical tree species, Castanopsis sclerophylla and Schima superba, two common evergreen species found across subtropical eastern China, to night-time temperatures elevated by 2°C. They then observed the effects of the raised temperatures on photosynthesis, respiration, transpiration and water-use efficiency.

Tree don’t simply ‘breathe out’ oxygen. They make sugars in sunlight. When they use those sugars, they leave as carbon dioxide.

Nocturnal warming can affect plant survival during drought by enhancing the respiratory loss of carbon at night. The effect is striking. In this experiment, time-to-mortality increased by around a 7% per degree increase in temperature at night. In contrast, investigations of warming during the day increased time-to-mortality in a drought by 0 to 5% per degree rise in temperature.

Lu and colleagues conclude: “Predawn leaf water potential and leaf WUE of C. sclerophylla were significantly lower under night warming, which could explain the earlier drought mortality of C. sclerophylla under night warming. Although night warming showed no effect on nocturnal total NSC in leaves of both species, increasing nocturnal respiratory losses of S. superba and reducing photosynthetic rates of both species resulted in reduced leaf net carbon gain in both species under night warming. These negative effects were more pronounced in S. superba more than C. sclerophylla. Drought mortality in S. superba appears to be related to carbon metabolism changes under night warming.”

RESEARCH ARTICLE

Lu, R., Du, Y., Sun, H., Xu, X., Yan, L. and Xia, J. (2021) “Nocturnal warming accelerates drought-induced seedling mortality of two evergreen tree species,” Tree Physiology. Oxford University Press (OUP). doi:10.1093/treephys/tpab168.