Comparison of physicochemical and microbial soil properties under Norway spruce (Picea abies (L.) H.Karst.) crowns and adjacent abandoned agricultural lands
The effect of secondary succession of abandoned agricultural lands on soil properties and soil microbial community is still poorly understood due to a complexity of interacting environmental factors. A significant area of agricultural lands has become abandoned in the central part of Latvia due to non-ideal agrotechnical conditions caused by soil and topography, resulting in natural colonization of trees. The aim of the study was to compare physicochemical parameters and microbial activity in soil adjacent to Norway spruce (Picea abies (L.) H.Karst.) trunks under the crown and on grassland outside the tree canopy, 15 years after the tree colonization. The redundancy analysis showed that bulk density, total nitrogen, total carbon, and exchangeable cations (Mg2+, K+, Ca2+, Mn2+) were positively related to substrate-induced respiration, fluorescein diacetate hydrolysis, and urease activity in sandy soil. However, positive correlations were found between urease activity and bulk density, exchangeable cations (Al3+, Fe2+, Mn2+) in loamy sand soil, while negative correlations were observed with pHBaCl2, total carbon, total nitrogen, CECe, bulk density, and exchangeable cations (K+, Ca2+). Significant differences were observed among the sampling sites (trunk and grassland), soil types (sandy Podzols and loamy sand Stagnosols), and depths (0–10 cm and 11–20 cm). Specifically, higher levels of potential ammonium oxidation and dehydrogenase activity, as well as concentrations of exchangeable cations (K+, Mn2+), were observed near the spruce trunk in sandy soil. In contrast, fluorescein diacetate hydrolysis activity, CECe, and exchangeable cations (Mg2+, Ca2+) showed higher levels in loamy sand soil. The observed spatial differences showed that secondary succession of agricultural lands with spruce affects physicochemical properties of soil and microbial activity, even in a relatively short period of time. Thus, we assume that these changes will be even more pronounced in the future, as the field transforms from grassland to forest. Keywords: Land abandonment · Picea abies · Natural afforestation · Podzols · Stagnosols · Topsoil · Soil microbial activity
