Influence of Nepalese alder on soil physico-chemical properties and fine root dynamics in white oak forests in the central Himalaya, India

The main objective of the study was to investigate influence of Nepalese alder (Alnus nepalensis D. Don) on fine root biomass (diameter <= 2 mm) dynamics and the physical and chemical properties of the soil in white oak (Quercus leucotrichophora A. Camus) forests. Five representative stands of each oak mixed alder (OMA) and oak without alder (OWA) were selected along the stand development gradient in the Indian central Himalaya. Fine root and soil samples from of 0-10 cm, 10-20 cm, and 20-30 cm depths were collected using soil core method. Soil physical and chemical properties and monthly variations in fine root dynamics (biomass distribution and decomposition) were analyzed. Fine root decomposition was studied by using the litterbag technique. Redundancy and correlation analyses were performed to evaluate the relationship between fine root dynamics, stands, and tree total basal area and soil properties. Both the fine root biomass and production of Q. leucotrichophora were significantly (P < 0.05) higher for oak without alder stands than oak mixed alder stands. Fine mot biomass, production, and turnover rate of A. nepalensis were significantly (P < 0.05) higher than Q. leucotrichophora in oak mixed alder stands. Within the investigated soil profile, in all the sites, maximum fine root biomass and production were found in the upper (0-10 cm) soil depths. The analyses revealed clear differences in all the measured soil physical and chemical properties and fine root traits in oak mixed alder and oak without alder stands. The soil organic carbon (SOC), total nitrogen (TN) contents, and soil C and N stocks were significantly (P < 0.05) higher in oak mixed alder stands than oak without alder stands while opposite trends were found for soil pH and bulk density (BD). Present findings reveal that improvement of the soil properties under oak mixed alder stands was significantly higher than the oak without alder stands. Fine root decomposition for A. nepalensis was significantly faster than Q. leucotrichophora. Q. leucotrichophora fine roots in OMA stands decomposed at significantly faster rates compared to OWA stands. Additionally, the present study suggests that variation, in fine root dynamics across the forest stands was not only positively correlated to the soil physical and chemical properties but also highly dependent on the forest stand characteristics.

Automated summary

The study investigated the influence of Nepalese alder on fine root biomass dynamics and soil properties in white oak forests in the Indian central Himalaya. It found that the presence of alder significantly affected fine root production and turnover rates, with alder stands showing higher values compared to oak stands without alder. Soil organic carbon and total nitrogen contents were higher in alder mixed oak stands, while soil pH and bulk density were higher in oak stands without alder.