Carbon use efficiency and microbial functional diversity in a temperate Luvisol and a tropical Nitisol after millet litter and N addition

Julia Schroeder,Christine Wachendorf,Suvarna Chavannavar,Rainer Georg Joergensen,René Beuschel,Birgit Pfeiffer,Ramia Jannoura,Jens Dyckmans,Rajasekaran Murugan

doi:10.1007/s00374-020-01487-4

Abstract

Tropical soils often contain less soil organic C (SOC) and microbial biomass C (MBC) than temperate soils and, thus, exhibit lower soil fertility. The addition of plant residues and N fertilizers can improve soil fertility, which might be reflected by microbial C use efficiency (CUE) and functional diversity. A 42-day incubation study was carried out, adding leaf litter of the C4 plant finger millet (Eleusine coracana Gaertn.) and inorganic 15N fertilizer. The aim was to investigate amendment effects on CUE and functional diversity in a tropical Nitisol and a temperate Luvisol. At day 42, 28% of the millet litter-derived C (C4) added was mineralised to CO2C4 in the temperate Luvisol and only 18% in the tropical Nitisol, averaging all N treatments. In contrast, none of the different fractions used for calculating CUE values, i.e. CO2C4, MBC4, microbial residue C4, and particulate organic matter C4, differed between the soils in the N0 (no N addition) treatment. CUE values considering microbial residues varied around 0.63, regardless of soil type and sampling day, which needs further evaluation. Millet litter increased autochthonous SOC-derived CO2C3 production, but N addition did not. This priming effect was apparently not caused by N mining. The respiratory response to most substrates added by multi-substrate-induced respiration (MSIR) and, thus, functional diversity was higher in the Luvisol than in the Nitisol. Millet litter had positive and N addition negative effects on the functional diversity of Nitisol, indicating that MSIR is a useful tool for evaluating soil fertility.

Highlights

Soil organic matter (SOM) and soil microorganisms are central components for soil fertility (Joergensen 2010), i.e. the ability of soils to maintain key ecological functions, such as decomposition of plant residues and provision of nutrients for plant growth (Craswell and Lefroy 2001; Joergensen and Castillo 2001; Cerri et al 2006)
As these processes are controlled by temperature, the turnover rates of microbial biomass C (MBC) and soil organic C (SOC) are higher in tropical regions than in temperate climates (Jenkinson and Ayanaba 1977; Diels et al 2004; Sierra and Desfontaines 2018)
At the end of the incubation, 28% of the added millet litter C was mineralised to CO2 (ΣCO2C4) in the temperate Luvisol, but only 18% in the tropical Nitisol, averaging all N treatments (Table 1)

Summary

Introduction

Soil organic matter (SOM) and soil microorganisms are central components for soil fertility (Joergensen 2010), i.e. the ability of soils to maintain key ecological functions, such as decomposition of plant residues and provision of nutrients for plant growth (Craswell and Lefroy 2001; Joergensen and Castillo 2001; Cerri et al 2006). Soil microorganisms maintain the majority of enzymatic processes in soil and preserve energy and nutrients in their biomass (Jenkinson and Ladd 1981) As these processes are controlled by temperature, the turnover rates of microbial biomass C (MBC) and soil organic C (SOC) are higher in tropical regions than in temperate climates (Jenkinson and Ayanaba 1977; Diels et al 2004; Sierra and Desfontaines 2018). Dystric Nitisols are the dominating soil type of the old landscapes around tropical Bangalore in South India (Murugan et al 2019) These soils are characterised by high contents of Al and Fe oxides, which reduce P availability, as well as low contents of SOC, which intensify drought effects. SOC contents, and fertility, of tropical Nitisol soils can be improved by adding plant residues (Agegnehu et al 2016; Sierra and Desfontaines 2018), especially in combination with N fertilizers (Geisseler and Scow 2014)

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Discussion

Conclusion