Herbarium specimens can inform about long‐term effects on plants as a consequence of climate change. Since plants are sessile, they are particularly exposed to climate change and the period of their responses to this change are preserved in herbarium specimens. This provides a unique opportunity in space and time for studying climate change. Understanding plant and climate interactions is important because it informs our ability to describe, understand and predict the Earth system. Through physiological processes such as photosynthesis and transpiration, plants couple the carbon and water cycles and thereby play a pivotal role in Earth system and plant-climate feedbacks (Murray et al. 2020, 2019; Purcell et al. 2018).
Many theory and models predict that rising global carbon dioxide concentrations in our atmosphere will make the world’s trees grow in a more water-efficient way but few studies have tested these predictions. Using herbarium samples collected about 25 years ago by other botanists and then repeated these collections following their original species and sites at the present time (Fig. 1 and 2) (244 species, 21 sites, 8 biomes), our research shows that atmospheric carbon dioxide rise over the recent decades has already had a demonstrable impact on the water use of forests, making them more water wise. However, not all plant species behave in the same way. We find that with rising atmospheric carbon dioxide, evergreen trees and shrubs are more efficient in using water than deciduous plants in the cooler climate but there is no evidence for such pattern in the warmer climate (Soh et al. 2019).
Figure 1. Fieldwork in the seasonal dry forest, Puerto Rico.
The reason for the detected differences in evergreen and deciduous plants responses to climate change lies in their leaf texture. The leaves of evergreens are generally thicker and sturdier than deciduous plants in cooler climate while they are mostly similar in texture between the two groups in the warmer climate. Leaf texture affects plant sensitivity to rising atmospheric carbon dioxide. Because the evergreen and deciduous leaf habits are an important hallmark that define forest type, their differential behaviour to rising atmospheric carbon dioxide will have a profound impact on the land carbon and water cycles today and in the very near future (Soh et al. 2019).
Figure 2. Myristica chartacea collected in 1988 (left) and 2015 (right) at the same site in Seaqaqa, Fiji.
Details of funding and collaborator can be found in the listed publications. Future work will explore plant physiological responses to climate change in the Irish context utilising the herbarium collection in DBN.
Soh W.K., Yiotis C., Murray M., Parnell A., Wright I.J., Spicer R.A., Lawson T., Caballero R., McElwain J.C. Rising CO2 drives divergence in water use efficiency of evergreen and deciduous plants. 2019. Science Advances 5 (12), eaax7906. DOI: 10.1126/sciadv.aax7906
Murray M.*, Soh W.K.*, Yiotis C., Batke S., Parnell A., Spicer R.A., Lawson T., Caballero R., Wright I.J., Purcell C., McElwain J.C. 2019. Convergence in maximum stomatal conductance of C3 woody angiosperms in natural ecosystems across bioclimatic zones. Frontiers in Plant Science 10: 558 . DOI:10.3389/fpls.2019.00558
Murray A., Soh W.K., Yiotis C., Spicer R.A., Lawson T., McElwain J.C. 2020. Consistent relationship between field-measured stomatal conductance and theoretical maximum stomatal conductance in C3 woody angiosperms in four major biomes. International Journal of Plant Sciences 181 (1): 142-154. DOI: 10.1086/706260
Purcell C., Batke S.P., Yiotis C., Caballero R., Soh W.K., Murray M., McElwain J.C. 2018. Increasing stomatal conductance in response to rising atmospheric CO2. Annals of Botany 21: 1137-1149. DOI: 10.1093/aob/mcx208