Edaphic factors and elevation gradient influence arbuscular mycorrhizal colonization and spore density in the rhizosphere of Shorea robusta Gaertn

Arbuscular mycorrhizal fungi (AMF) are important ecosystem engineers that improve nutrient uptake and help plants adapt to a variety of abiotic stresses. Few studies have examined the relationship between AMF and a specific host tree along an elevation gradient. Shorea robusta is the dominant tree species in Nepal's tropical forests, with very high timber value. The goal of this study was to ascertain how edaphic factors and elevation gradient influence AMF colonization and spore density within the rhizosphere of Shorea robusta. The present study was conducted in four S. robusta dominated forests ranging from 82 m to 950 m asl. Among the four forests, Tarai Sal forest (TSF); Bhabar Sal forest (BSF) belonged to lower elevation Sal forest and Plateau Sal forest (PSF); Hill Sal forest (HSF) belonged to high elevation Sal forest. The percentage of AMF colonization and soil spore density were assessed by magnified intersect method and wet sieving and decanting method respectively. The edaphic factors viz. organic matter, nitrogen, phosphorous, potassium, pH, soil temperature, bulk density, moisture content, and water holding capacity of soil were determined by standard methods. Total AMF colonization ranged from 33% to 57%. Spore density, on the other hand, ranged from 25 to 366 per 100 g of soil. The maximum AMF root colonization and spore density for lower elevation Sal forest was 52% and 39/100 g of soil respectively while that for higher elevation Sal forest was 57% and 366/100 g of soil respectively. Pearson's correlation test revealed that total AMF colonization as well as spore density in the rhizosphere of S. robusta were affected by phosphorus content, pH, moisture content, water-holding capacity, soil temperature, and elevation. Moreover, the spore density was also affected by nitrogen content. Total AMF colonization and spore density were found to be highly correlated. Overall, the intensity of AMF colonization and spore density were higher in higher elevation Sal forest compared to the lower elevation Sal forest. This study can be used to gain insights into the active involvement of AMF in the sustainable management of the forest ecosystem.