Morpho-functional classification of humus forms using the terrhum-app: Correlation of morphological indicators and standardized laboratory analysis parameters

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200212166

Centennial Celebration and Congress of the International Union of Soil Science. Book of Abstracts ; 135985 (2024) , 938

The humus form classification system TerrHum assigns morphological features to ecological soil functioning. We tested if soil organic matter (SOM) turnover diagnosed by this ecological indicator tool corresponds to standardized laboratory analysis parameters. By sampling 30 survey plots of a forest site classification project in Styria, Austria, we cover calcareous and felsic parent material, a steep elevation gradient and different vegetation communities. Humus profiles were classified and sampled (horizon-wise) in a nested design. Organic carbon (OC) and nitrogen (N) concentration, pH value, microbial biomass carbon (MBC) and nitrogen (MBN), basal respiration (R10), temperature response (Q10) and eco-physiological quotients differ significantly between diagnostic horizons. There was evidence for SOM turnover patterns following the ranking supposed in the classification system. Rapid SOM turnover in Mull systems is confirmed by large microbial biomass (MBC), no constraints regarding organic matter quality (C/N ratio and microbial quotient), and high respiration levels (R10, and predicted Rh). Mor systems with retarded decomposition show low MBC, high acidity, and low litter quality. In Amphi and Moder SOM turnover is constrained. Moder horizons show higher acidity, slightly lower litter quality, lower respiration, and higher fungal abundance than corresponding Amphi horizons. In Amphi, and even more pronounced in Tangel systems (very slow SOM turnover), climatic factors are the main constraints for turnover. Heterotrophic respiration (Rh) for individual humus systems can be predicted with multiple regression models with moisture, temperature and diagnosed horizon as independent predictors. A multinomial logistic regression model confirmed that environmental factors have a significant influence on the distribution of humus systems along catenas. We conclude that the morpho-functional classification is a useful tool in characterizing the main SOM turnover types.
Keywords: humus forms, SOM turnover, mircrobial biomass, chemical properties, respiration