Effects of Biochar and Maize Roots on CO2 Emissions and Microbial Biomass C in Loess Soils

Abstract

Background

Refractory substances such as biochar and labile substances such as dead fine and coarse roots play important roles in soil organic matter dynamics and have key ecological functions. However, interactions between these substances have only rarely been studied.

Aim

The objectives were to study the effects of biochar and maize roots on CO₂ emissions and microbial biomass C (MBC) in incubation experiments with loess soils from three arable sites.

Methods

Unaged and H₂O₂-artificially aged biochars were incubated with maize roots of different sizes and at different rates in field replicates of loess surface soils for approximately 6 months at 15°C and 60% of the water holding capacity. Total (∑CO₂–C) and maize-derived cumulative CO₂–C emissions and C₃- (autochthonous SOM-derived) and maize-derived microbial biomass contents (MBC_AS, MBC_MD) were determined, and mixed effects models were calculated.

Results

∑CO₂–C emissions and MBC_MD increased significantly with increasing root rates. H₂O₂-artificially aged biochar either significantly increased ∑CO₂–C (one site) and decreased MBC_AS (two sites) and MBC_MD (one site) or had no effect. Different root sizes did not significantly affect the response variables. Unaged biochar significantly increased ∑CO₂–C emissions and MBC_AS relative to control soils and soils with H₂O₂-artificially aged biochar, probably mainly due to increases in pH and water-extractable organic C.

Conclusions

Site variations in biochar effects on biological variables were considerable even for the controlled experiments with a defined sample of loess soils, indicating that a disentanglement of biochar effects according to soil types may not be feasible.