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Plants utilise various combinations of root morphological and architectural traits, root exudates and symbiosis with mycorrhizal fungi to acquire nutrients. These trait combinations and trade-offs have been well-documented in temperate and Neotropical forests but are understudied in major biodiversity hotspots in the Paleotropics. In Southeast (SE) Asia, dipterocarp forest communities are predominantly associated with ectomycorrhizal (EM), unlike the more common arbuscular mycorrhizal (AM) symbiosis in Neotropical systems. This EM association, coupled with root enzymatic activity, may provide dipterocarp trees with an enhanced capacity to access organic nutrient forms in the soil. However, it remains unclear if the organic nutrient economy underlying SE Asian dipterocarp forests translates into similar trade-offs in root traits as other forests globally. In this study, we test the hypothesis that SE Asian dipterocarp forest species experience similar trade-offs incurred during phosphorus acquisition and thus align with root trait trade-offs observed in other forest communities worldwide. We quantified root morphology, architecture, root enzymatic activity and mycorrhizal status of 35 species in an old-growth and secondary forest in Bukit Timah Nature Reserve, Singapore. Subsequently, we examined root trait coordination and trade-offs among species from both forest types and mycorrhizal associations. In agreement with previous studies, we found two primary axes of principal component analysis explained by traits pertaining to fungal collaboration (PC1 = 53.2% of total variance) and resource conservation (PC2 = 30.0% of total variance). Due to the highly contrasting nutrient uptake mechanisms between AM and EM fungi, AM and EM tree species exhibited significantly different trait syndromes, where EM trees exhibit greater root enzymatic activity (F1,40 = 7.85, P = 0.008), root tissue density (F1,41 = 4.25, P = 0.045) and lower root diameter (F1,41 = 4.78, P = 0.034). Overall, while we found similar root trait trade-offs among the collaboration and conservation axes as other forests worldwide, we also provide evidence for distinct nutrient acquisition strategies between AM and EM tropical species and how root enzymatic activity links to fungal collaboration and resource conservatism strategies. These findings suggest that the viable trait space for nutrient acquisition may be much larger than previously imagined in hyperdiverse tropical environments, warranting further investigation into how plants overcome nutrient limitation worldwide.

Keywords:

Root traits; phosphatase; mycorrhizal; phosphorus; nutrient acquisition

Ming Yang Lee, Qian Yi Ho, Kelly Andersen

Presentation within symposium:

S-22 Tropical forest restoration: Role of soil biota-root symbioses (mycorrhizae and N-fixing bacteria)

Do Southeast Asian dipterocarp forests follow global root trait trends and trade-offs?

-Review-