Rhizosphere effects on soil extracellular enzymatic activity and microbial abundance during the low-temperature dormant season in a northern hardwood forest

Abstract

Plant roots alter nutrient cycling, including nitrogen (N) and phosphorus (P) cycling, within the soil surrounding them (rhizosphere) by affecting microbes and enzyme activities. Recent studies have focused on nutrient uptake by plants in low-temperature seasons. This study aimed to reveal the nutrient dynamics in the rhizosphere during low-temperature seasons in a northern hardwood forest in Japan. For this purpose, the potential extracellular enzymatic activity, bacterial, fungal, and archaeal abundances, and soil chemical properties in the rhizosphere of canopy trees and understory vegetation and non-rhizosphere bulk soil were measured at the beginning of the dormant season (November), end of the dormant season (April and May), and middle of the growing season (August) in a northern hardwood forest in Japan. The abundance of fungi was 1.1–1.7 times higher in the rhizosphere than in non-rhizosphere bulk soil regardless of the season. The activity of enzymes involved in N- and P- cycles in the rhizospheres was also 1.4 to 4.0 and 1.3 to 1.9 times higher than that in bulk soil, respectively. The concentration of extractable organic N was 1.5–2.0 times higher in the rhizosphere than in the non-rhizosphere bulk soil at the beginning and end of the dormant season, respectively, but this trend was not observed in the middle of the growing season for organic N. Since the concentration of nutrients in the rhizosphere is determined by the balance between nutrient uptake by fine roots and root-induced acceleration of decomposition, our results suggest that plant roots would accelerate N and P cycles during the dormant season, even though the amount of nutrient uptake by plants was lower during the season.