Photosynthesis in co-occurring invasive Acacia spp. and native Bornean heath forest trees at the post-establishment invasion stage

ABSTRACT

Seedlings of invasive species often exhibit superior physiological traits that facilitate their spread at early stages of invasion, although it is unclear whether these traits persist at the post-establishment stage. To determine whether mature exotic Acacia spp. possess superior traits over mature native plants, we compared foliar gas exchange and chlorophyll a fluorescence of Acacia auriculiformis and Acacia mangium coexisting with tropical heath forest tree species Buchanania arborescens and Dillenia suffruticosa in Brunei Darussalam. The CO₂ assimilation rates of Acacia spp. were significantly higher than those of heath species at current prevailing conditions of ~400 ppm ambient CO₂, 1,500 µmol m⁻² s⁻¹ photosynthetically active radiation and 30°C leaf temperature. The photosystem II of Acacia spp. exhibited significantly higher maximum quantum yield of primary photochemistry at comparable temperatures, and was more sensitive to an elevated temperature (42°C for 1 h). Better photosynthetic performance of Acacia spp., due to larger stomatal openings, better light harvesting efficiency, and greater plasticity in photosystem II, may enable adult Acacia trees to sustain a competitive growth advantage and suppress native tropical heath forest species. The competitive advantage maintained by Acacia spp. in post-establishment stage likely facilitates the establishment of monospecific Acacia stands in invaded heath forests.

KEYWORDS:

• Competitive advantage
• heat stress
• kerangas
• OJIP test

Additional information

Funding

This work was funded by the Brunei Research Council (UBD/BRC/11) and partial postdoctoral funding awarded by Universiti Brunei Darussalam to LQV. We thank Mohammad Hilmi Ibrahim for assistance with fieldwork, and Salwana Md. Jaafar and Hazimah Hj Mohammad Din for assistance with logistics. We are grateful to the Forestry Department, Ministry of Primary Resources and Tourism, Brunei Darussalam for entry and collection permits ([99]/JPH/UND/17 PT1). We thank the Brunei Darussalam Meteorological Department for temperature and rainfall data from the Brunei International Airport. The authors have no conflicts of interest to declare.