Assessing the effects of a drought experiment on the reproductive phenology and ecophysiology of a wet tropical rainforest community

Nara Vogado; Susan G Laurance; Michael J Liddell; Jayden E Engert; Christopher M Wurster; Michele Schiffer; Andrew Thompson; Cassandra Nichols; Lucas A Cernusak

doi:10.1093/conphys/coad064

Assessing the effects of a drought experiment on the reproductive phenology and ecophysiology of a wet tropical rainforest community

Conserv Physiol. 2023 Sep 19;11(1):coad064. doi: 10.1093/conphys/coad064. eCollection 2023.

Authors

Nara Vogado¹, Susan G Laurance¹, Michael J Liddell¹, Jayden E Engert¹, Christopher M Wurster², Michele Schiffer³, Andrew Thompson³, Cassandra Nichols⁴, Lucas A Cernusak¹

Affiliations

¹ Centre for Tropical Environmental and Sustainability Science, College of Science and Engineering, James Cook University, 1/14-88 McGregor Rd Smithfield, Cairns, 4870, Australia.
² ARC Centre of Excellence for Australian Biodiversity and Heritage, James Cook University, 1/14-88 McGregor Rd Smithfield, Cairns, 4870, Australia.
³ Daintree Research Observatory, James Cook University, Cape Tribulation, 4873, Australia.
⁴ La Trobe University, Yarraville, Victoria, Australia.

Abstract

Climate change is expected to increase the intensity and occurrence of drought in tropical regions, potentially affecting the phenology and physiology of tree species. Phenological activity may respond to a drying and warming environment by advancing reproductive timing and/or diminishing the production of flowers and fruits. These changes have the potential to disrupt important ecological processes, with potentially wide-ranging effects on tropical forest function. Here, we analysed the monthly flowering and fruiting phenology of a tree community (337 individuals from 30 species) over 7 years in a lowland tropical rainforest in northeastern Australia and its response to a throughfall exclusion drought experiment (TFE) that was carried out from 2016 to 2018 (3 years), excluding approximately 30% of rainfall. We further examined the ecophysiological effects of the TFE on the elemental (C:N) and stable isotope (δ¹³C and δ¹⁵N) composition of leaves, and on the stable isotope composition (δ¹³C and δ¹⁸O) of stem wood of four tree species. At the community level, there was no detectable effect of the TFE on flowering activity overall, but there was a significant effect recorded on fruiting and varying responses from the selected species. The reproductive phenology and physiology of the four species examined in detail were largely resistant to impacts of the TFE treatment. One canopy species in the TFE significantly increased in fruiting and flowering activity, whereas one understory species decreased significantly in both. There was a significant interaction between the TFE treatment and season on leaf C:N for two species. Stable isotope responses were also variable among species, indicating species-specific responses to the TFE. Thus, we did not observe consistent patterns in physiological and phenological changes in the tree community within the 3 years of TFE treatment examined in this study.

Keywords: Climate change; Wet Tropics; drought; flowering; fruiting; stable isotopes; water use efficiency.