@article{kalu_seppanen_mganga_sietio_glaser_karhu_2024, title={Biochar reduced the mineralization of native and added soil organic carbon: evidence of negative priming and enhanced microbial carbon use efficiency}, volume={6}, ISSN={["2524-7867"]}, DOI={10.1007/s42773-023-00294-y}, abstractNote={AbstractBiochar has been widely recognized for its potential to increase carbon (C) sequestration and mitigate climate change. This potential is affected by how biochar interacts with native soil organic carbon (SOC) and fresh organic substrates added to soil. However, only a few studies have been conducted to understand this interaction. To fill this knowledge gap, we conducted a 13C-glucose labelling soil incubation for 6 months using fine-textured agricultural soil (Stagnosol) with two different biochar amounts. Biochar addition reduced the mineralization of SOC and 13C-glucose and increased soil microbial biomass carbon (MBC) and microbial carbon use efficiency (CUE). The effects were found to be additive i.e., higher biochar application rate resulted in lower mineralization of SOC and 13C-glucose. Additionally, soil density fractionation after 6 months revealed that most of the added biochar particles were recovered in free particulate organic matter (POM) fraction. Biochar also increased the retention of 13C in free POM fraction, indicating that added 13C-glucose was preserved within the biochar particles. The measurement of 13C from the total amino sugar fraction extracted from the biochar particles suggested that biochar increased the microbial uptake of added 13C-glucose and after they died, the dead microbial residues (necromass) accumulated inside biochar pores. Biochar also increased the proportion of occluded POM, demonstrating that increased soil occlusion following biochar addition reduced SOC mineralization. Overall, the study demonstrates the additional C sequestering potential of biochar by inducing negative priming of native SOC as well as increasing CUE, resulting in the formation and stabilization of microbial necromass.
                Graphical Abstract}, number={1}, journal={BIOCHAR}, author={Kalu, Subin and Seppanen, Aino and Mganga, Kevin Z. and Sietio, Outi-Maaria and Glaser, Bruno and Karhu, Kristiina}, year={2024}, month={Jan} }
 @article{mganga_rolando_kalu_karhu_2024, title={Microbial soil quality indicators depending on land use and soil type in a semi-arid dryland in Kenya}, volume={121}, ISSN={["1778-3615"]}, DOI={10.1016/j.ejsobi.2024.103626}, abstractNote={Soil microbial indicators help monitor soil quality. Limited studies have determined how land use in drylands affects soil microbial indices. Top soil (0–10 cm) from four land use systems in African drylands: (1) shrubland (natural), (2) grassland (natural), (3) pasture (agricultural) and (4) cropland (agricultural) occurring on two soil types: (1) Vertisol and (2) Acrisol, was used in laboratory incubations (6 days) to assess the effects of land use changes on organic carbon (Corg) mineralization, microbial biomass C (Cmic), mineralization quotient (qM), metabolic quotient (qCO2), Cmic:Corg ratio and sensitivity indices of these microbial indicators. Experimental plots were organized into a completely randomized design (n = 3) for every combination of land use and soil type. Cumulative CO2 produced from native Corg mineralization was the highest in Acrisol (108 ± 2.7 μg CO2–C g−1 soil) and the lowest in Vertisol (53 ± 2.5 μg CO2–C g−1 soil) croplands. Vertisol shrubland (1.34 ± 0.09 mg C g−1 soil) and Acrisol cropland (0.28 ± 0.07 mg C g−1 soil) had the highest and the lowest Cmic, respectively. Acrisol cropland (1.29 μg CO2–C g−1 h−1) had the highest qM, approximately five times higher than the lowest qM (0.26 μg CO2–C g−1 h−1) in a Vertisol cropland. Highest qCO2 was observed in an Acrisol pasture (12.04 μg CO2–C g−1 Cmic h−1), which was approximately 30 times higher compared to the lowest qCO2 observed in a Vertisol shrubland (0.41 μg CO2–C g−1 Cmic h−1). The Cmic:Corg ratio was the highest in a Vertisol shrubland (0.097), approximately five times higher than the lowest observed in an Acrisol pastureland (0.019). Our study demonstrated that the measured soil quality indicators' magnitude, direction, and sensitivity varied depending on land use and soil type. Higher N availability in Vertisols increased the biological stability of soil organic carbon (SOC) resulting to decreased SOC mineralization than Acrisols. In conclusion, the measured microbial soil quality indicators showed that Acrisols are prone to accelerated SOC mineralization after disturbance than Vertisols in the studied semi-arid dryland ecosystems. Thus, there is a need to manage natural ecosystem conversions to support sustainable crop and pasture production in African drylands.}, journal={EUROPEAN JOURNAL OF SOIL BIOLOGY}, author={Mganga, Kevin Z. and Rolando, Jose and Kalu, Subin and Karhu, Kristiina}, year={2024}, month={Jun} }