Development Towards a Chemotaxonomic Classification for New Zealand Plants - Implications for Using Biomarkers to Reconstruct Our Bioheritage

Aotearoa-New Zealand’s native plants are at risk, with factors such as land-use changes, introduced pests and climate change causing major changes in vegetation. To protect New Zealand’s biodiversity, we must first understand our bioheritage. Biomarkers offer a novel approach to vegetation reconstruction in New Zealand, using organic geochemical constituents of plants (i.e., lipid biomarkers) to reconstruct changes in vegetation. Biomarkers have been used internationally to investigate changes such as the presence of grasses versus woody plants and angiosperms versus gymnosperms. However, the use of biomarkers in vegetation reconstruction is location dependant and the study of native New Zealand plants geochemical properties is limited.

This study aims to classify New Zealand native plants based on their geochemical properties (chemotaxonomy) and use these properties to compare a biomarker record of Adelaide Tarn, Nelson, to the pollen and macrofossil record. The specific aims of this study are (I) to investigate the chemotaxonomic properties of native New Zealand plants (II) measure these chemotaxonomic properties to a downcore record of Adelaide Tarn, Nelson, New Zealand.

The lipid composition of 94 native plant was analysed, and distinct differences in the chemical characteristics of different plant types were identified in a number of cases. Firstly, the Paq, an aquatic plant indicator, is applicable in New Zealand, with high Paq values indicating aquatic plant input and low Paq values indicating terrestrial plant sources. Secondly, trees had lower n-alkane ACL (Average Chain Length), higher Paq values, and higher abundances of the terpenoids hexadecenoic acid, kaurenoic acid, and isopimaric acid than shrubs, tree-shrubs, herbs and grasses. Shrubs, tree-shrubs, herbs and grasses had higher n-alkane ACL values than trees and the terpenoids β- and α- amyrin and taraxerol are present in higher abundances than trees. Based on these properties, a forested land index was proposed to reflect input of trees to lake sediment relative to non-trees. Further chemotaxonomic classifications found include the presence of the terpenoid arundoin as a marker for the genus Chionochloa, beech trees being characterised by low n-alkane ACL and fatty acid CPI, and high cadalene abundances in members of the Myrtaceae family.

Comparison to the Adelaide Tarn vegetation record produced mixed results, with similar changes in Paq and ACL values in the biomarker record and aquatic macrophytes in the pollen. However, changes in the proposed forest index and arundoin concentration did not correspond to the changes observed in the pollen record. This may be due to the Adelaide Tarn biomarker record reflecting local changes in vegetation rather than regional changes.

The chemotaxonomic characteristics identified in New Zealand native plants and their application in the Adelaide Tarn Lake core provides a foundation for future work into using biomarkers to reconstruct vegetation changes and understanding New Zealand’s unique bioheritage.