Leaf age-related and diurnal variation in gas exchange of kauri (Agathis australis)

Cate Macinnis-Ng*, Tristan Webb, Yan Shih Lin, Luitgard Schwendenmann, Belinda Medlyn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

New Zealand kauri (Agathis australis) (D.Don) Lindl. is a large and long-lived tree species endemic to the species-rich forests of the north of the North Island. Agathis australis are culturally and ecologically significant, but little is known about their ecophysiology. In particular, environmental drivers of fluxes of carbon and water for A. australis trees have not been quantified. We measured leaf gas exchange to explore the effect of leaf age, tree size, foliar nitrogen concentration, photosynthetically active radiation (PAR) and vapour pressure deficit (D) on assimilation rates (A) and stomatal conductance (gs). We also measured carbon isotope discrimination of leaves and applied an optimal stomatal behaviour model. Both gs and A were highest for year one leaves (130 mmol m−2 s−1 and 5 μmol m−2 s−1, respectively) then declined with leaf age to < 80 mmol m−2 s−1 and < 3 μmol m−2 s−1, respectively, in 4–5-year-old leaves. Instantaneous water use efficiency (A/gs) was highly variable, but there was no leaf age-related pattern. Our diurnal results indicate that A. australis gs peaks early in the day (before 0900 h at 250 mmol m−2 s−1) and A is comparatively low, remaining below 9 μmol m−2 s−1 throughout the day. Overall, water use efficiency is low based on intrinsic water use efficiency and the stomatal model. Isotopic analysis indicated moderate water use efficiency over the life of leaves compared to other temperate conifers. This information is valuable for modelling carbon and water fluxes of A. australis and for improving our understanding of the threat of summer droughts to these forest giants.

Original languageEnglish
Pages (from-to)80-99
Number of pages20
JournalNew Zealand Journal of Botany
Volume55
Issue number2
DOIs
Publication statusPublished - 3 Apr 2017
Externally publishedYes

Keywords

  • assimilation rates
  • carbon fluxes
  • New Zealand
  • photosynthesis
  • southern conifers
  • stomatal conductance
  • water fluxes
  • water use efficiency

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