ABSTRACT
Mycorrhizas are a symbiotic association between fungi and the majority of terrestrial plants that assist with nutrient uptake and overall ecophysiological performance and may be particularly beneficial in poorly fertile tropical soils. An important minority of tropical trees form ectomycorrhizas (EcM), including the Dipterocarpaceae that dominates lowland forests of Southeast Asia. Controlling EcM colonisation can be challenging, but here I use nursery fungicide addition to determine how EcMs may influence seedling growth of two contrasting dipterocarp species. A six-month experiment was conducted with weekly additions of Mancozeb fungicide to seedlings of Hopea nervosa and Parashorea tomentella. Total percentage EcM colonisation decreased with fungicide addition from c. 60–70% to c. 10–20%. Growth rates of H. nervosa were reduced following fungicide addition (although only significantly for leaf production rate) mediated by a reduction in proportional root biomass (particularly fine root biomass), but these patterns were not clearly seen in P. tomentella. In contrast, P. tomentella showed clearer changes in foliar properties with a reduction in leaf mass per area, along with reductions in foliar phosphorus, calcium and δ15N. Notably, both species increased their foliar nitrogen with fungicide addition most likely due to increases in nitrification from soil fungal mortality. Bearing in mind the limitations imposed by fungicide addition, I show here contrasting responses of two dipterocarp species to reductions in EcM colonisation that may influence their regeneration under more natural conditions—this has implications for establishment of planted dipterocarp seedlings in reforestation efforts.
