Variation of stomatal traits from cold-temperate tropical to tropical cold-temperate forests and association with water use efficiency

Congcong Liu, Nianpeng He, Jiahui Zhang, Ying Li, Qiufeng Wang, Lawren Sack, Guirui Yu

 

Stomata, pores that are bounded by two guard cells and distributed over the leaf surface, control the uptake of CO₂ for photosynthesis and the concomitant loss of water vapor from leaves. Therefore, the morphology and behavior of stomata can reflect the adaptive strategy of plants to some extent. However, the relationships between stomatal morphology and water use efficiency across natural communities remain unclear, especially at the large scale.

We collected 737 plant species from nine plant communities, from tropical to cold-temperate forests along a 3700 km transect, and measured stomatal density (the number of stomata per unit leaf area), stomatal size (or area) and stomatal area fraction (the product of stomatal density and size). By weighting  the data by leaf biomass for every plant species in the community, stomatal morphology was scaled-up from species (or leaf) to community levels.

We used an aridity index to indicate water availability or drought stress (note that a lower index corresponds to greater climatic aridity). At the community level, we found that stomatal area fraction was negatively correlated with climatic aridity index, i.e. stomatal area fraction was greater in drier climates. This somewhat counter-intuitive result arises from the ‘opportunistic’ strategy by which species from dry areas can achieve high maximum rates of gas exchange when water is available. Furthermore, and again slightly surprisingly, stomatal area fraction was positively correlated with water use efficiency in natural forest communities. Thus, although maximum stomatal conductance may be determined by anatomy, a high maximum conductance is coupled with the ability to operate with lower stomatal opening for most of the growing season, conferring a higher water use efficiency.

These findings broaden our current knowledge of the adaptive strategies of stomatal morphology at the large scale, and provide direct evidence on how plant stomatal morphology (as a common plant trait) is linked to functioning in forest communities across biomes.

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Image provided by authors.