Influence of season and edaphic factors on endorhizal fungal associations in subtropical plantation forest trees of Northeastern India

• We assessed seasonal patterns of endorhizal fungal symbioses in four tree species.
• All tree species examined had dual association of AMF and DSE fungi.
• A total of 18 AMF spore morphotypes were isolated from the soils.
• Both AMF and DSE fungal colonization varied significantly with trees and seasons.

Investigations on arbuscular mycorrhizal (AM) and dark septate endophyte (DSE) fungi are limited in trees of subtropical forests compared to other terrestrial ecosystems. We assessed the seasonal dynamics of endorhizal fungal symbioses in four dominant tree species (Alnus nepalensis, Castanopsis hystrix, Emblica officinalis, Schima wallichii) in two plantation forest stands of Northeastern India, a biodiversity hotspot part of the Indo-Burma region. All tree species examined had a dual association of AM and DSE fungi and such fungal symbioses are reported for the first time in A. nepalensis, C. hystrix and S. wallichii. Intermediate-type AM morphology was common in three tree species, while Paris-type AM morphology was found in S. wallichii. Colonization of AM and DSE fungi varied significantly across tree species and seasons. A total of 18 AM fungal spore morphotypes were isolated from the air-dried natural rhizosphere soils and trap culture experiments. Spore density of AM fungi was highest in summer, whereas AM colonization in roots was highest during the rainy season. In contrast, root colonization with DSE fungi was highest during summer, except for E. officinalis. A significant negative correlation occurred between certain AM fungal and soil variables. In contrast, DSE fungal measures were not correlated to any of the soil properties examined. Correlation analysis indicated a certain degree of competition between AM and DSE fungi. Occurrence of AM and DSE fungal associations in economically important indigenous tree species indicates the possibility of utilizing them in future conservation programs.