Priming effects in different soil types induced by fructose, alanine, oxalic acid and catechol additions

It is well established that certain substrate additions to soils may accelerate or retard the mineralisation of soil organic matter. But up to now, research on these so called 'priming effects' was almost exclusively conducted with arable soils and with plant residues or glucose as additives. In this study. the effects of the uniformly C-14-labelled substrates fructose, alanine, oxalic acid and catechol on the mineralisation of soil organic carbon (SOC) from different horizons of two forest soils (Haplic Podzol and Dystric Cambisol) and one arable soil (Haplic Phaeozem) under maize and rye cultivation were investigated in incubation experiments for 26 days. Apart from the controls, all samples received substrate additions of 13.3 mug substrate-C mg(-1) C-org. During the incubation, CO2-evolution was measured hourly and the amount of (CO2)-C-14 was determined at various time intervals. In almost all soils, priming effects were induced by one or several of the added substrates. The strongest positive priming effects were induced by fructose and alanine and occur-red in the Bs horizon of the Haplic Podzol, where SOC mineralisation was nearly doubled. In the other soil samples, these substrates enhanced SOC mineralisation by + 10 to +63%. Catechol additions generally reduced SOC mineralisation by - 12 to -43% except in the EA horizon of the Haplic Podzol where SOC-borne CO2-evolution increased by + 46%. Oxalic acid also induced negative as well as positive priming effects ranging from - 24 to + 82%. The data indicate that priming effects are ubiquitously occurring in surface and subsoil horizons of forest soils as well as in arable soils. Although a broad variety of soils was used within this study, relationships between soil properties and priming effects could not be ascertained. Therefore, a prediction on occurrence and magnitude of priming effects based on relatively easily measurable chemical and physical soil properties was not possible. Nevertheless, the data suggest that positive priming effects are most pronounced in forest soils that contain SOC of low biodegradability, where the added substrates may act as an important energy source for microbial metabolism. (C) 2004 Elsevier Ltd. All rights reserved.