The secretive underground trade(-off) : mycorrhizal associations of coexisting tree species in primary and secondary forests of Bukit Timah Nature Reserve, Singapore

Abstract

Being one of the most biodiverse ecosystems, the tropical forests grow on soils with limited phosphorous. Thus, plants have adopted various nutrient acquisition strategies by varying their root traits, phosphatase activities or work with fungi (mycorrhiza) to meet their needs. Recent studies have further suggested a collaboration gradient where roots may increase diameter to accommodate more mycorrhiza or increase the root network to explore the nutrients underground. However, studies relating to this underground trade-off in the Southeast Asian tropical forests remain understudied and whether the plants here follow this global trend remains an unknown.

In this study, I explored the root traits, PME (phosphatase) activity and mycorrhiza colonization rates of four key species (two EM and two AM) found within the primary and secondary forests of BTNR, Singapore. I found that the AM species followed the proposed collaboration gradient as the diameter of the roots were crucial for the colonization of mycorrhiza. However, the EM species do not follow the proposed gradient but instead showed unique correlations which suggest the absence of the gradient or a different gradient altogether. EM colonization rates were significantly higher in primary forests while AM colonization rates were significantly higher in secondary forests possibly due to their relative abundance in the respective forests.

PME activity and colonization rates also showed different trends between AM and EM. This suggests that different nutrient acquisition strategies could be adopted by the AM and EM species. Thus, including more species, soil nutrient content and other phosphatase activities may help uncover the various nutrient acquisition strategies, as well as the collaboration gradient for the EM species.