Soil Organic Matter Fractions in Relation to Root Characteristics of Different Tree Species in Altitude Gradient of Temperate Forest in Carpathian Mountains

Abstract

The roots are a key functional component of belowground systems and one of the main factors influencing the quality and quantity of soil organic matter. Our research aimed to determine the fractional composition of the soil organic matter (SOM) in soils under various tree species on an altitude gradient. In our research, we related the SOM fractions with the root characteristics. There is a lack of information on the relationship between the SOM fractions and the root properties. We assessed labile and heavy fractions of SOM content in forest mountain soils with a climosequence approach. The study plots were established at 600, 800, and 1000 m above sea level in a beech stand (Fagus sylvatica L.) and a fir stand (Abies alba Mill.). In this case, three research plots with beech and fir were designated in each altitude variant. Forest stands growing in the same soil conditions were selected for the study. The research used stands of similar age with the same tree canopy density. The basic physicochemical properties (pH, hydrolytic acidity, carbon and nitrogen content, base cations content) and the fractional composition of the SOM were determined from soil samples. In addition, we determined the basic characteristics of the roots (diameter, length, biomass, decomposition, production). The correlation between soil organic matter fractions and root characteristics was recorded. This study confirmed the importance of climatic conditions in shaping the fractional composition of forest soils. In the highest locations, characterized by lower temperatures, the light fraction of the SOM exhibited the highest C and N content, which is the effect of slower decomposition processes. Apart from climatic conditions, the stabilization of SOM is influenced by the tree species composition of a forest stand. Beech forest stands lead to a larger accumulation of a heavy fraction of SOM. This study indicates a positive correlation between the light fraction of SOM, root biomass, and decomposition rate of roots. Our research shows that avoiding single-species coniferous stands and introducing admixtures of deciduous species, which increase the heavy SOM fraction, is justified in forest management.