Considera

Long-term differences in fertilisation type change the bacteria:archaea:fungi ratios and reveal a heterogeneous response of the soil microbial ionome in a Haplic Luvisol

Sanja A.Schwalb, Shiwei Li, Michael Hemkemeyer, Stefanie Heinze, Rainer Georg Joergensen, Jochen Mayer, Paul Mäder, Florian Wichern

Abstract
Organic farm management through farmyard manure application is associated with soil organic carbon sequestration facilitated by more balanced nutrient stoichiometry of macro- and micronutrients. Quantitative information on micronutrients within the soil microbial biomass is lacking. Using soils from a 40-year old long-term field trial (DOK), we investigated if fertilisation differences (farmyard manure equivalent to 0.7 or 1.4 livestock units per hectare and mineral fertilisation) and farm management (biodynamic, organic, conventional) changed the soil microbial ionome and stoichiometry and if this is related to microbial community shifts. Soil (15% sand, 70% silt and 15% clay) from the top 20 cm was analysed for microbial biomass carbon, nitrogen and phosphorus. Further elements were assessed via an adapted chloroform-fumigation extraction procedure. Abundances of bacteria, archaea, and fungi were determined (qPCR). Farmyard manure increased microbial biomass by approximately two-fold and the contribution of bacteria and archaea by up to approximately five-fold. Microbial biomass phosphorus and magnesium increased with mineral fertilisation (from 7 to 14 μg g−1 soil) and farmyard manure (from 0.5 to 2.7 μg g−1 soil), respectively. The microbial biomass carbon to potassium ratio remained similar, at around 47:1, revealing stoichiometric control. Microbial biomass manganese was reduced from 3.5 to 2.2 μg g−1 soil with lower availability due to raised pH in biodynamic management. The microbial stoichiometry and ionome were mainly affected by nutrient input and soil chemical properties; direct links between microbial (micronutrient-) stoichiometry and microbial community changes cannot be established with certainty due to potential confounding effects of pH changes.

Keywords
Chloroform-labile elementsSoil microbial ionomeSoil microbial elementomeStoichiometryChloroform-fumigation extractionMicronutrientsAgricultural management systems

Highlights
•Soil microbial biomass K, Mg, Zn, Mn, Cu measured in situ via chloroform-fumigation.
•Homeostatic (K, Cu) as well as plastic stoichiometry (Mg, Zn, Mn) was found.
•pH exerted control over available elements which influenced microbial stoichiometry.
•Farmyard manure increased bacterial and archaeal contribution to community.

Influence of long-term organic and conventional farming on soil microbial properties

Shiwei Li (2020)

In order to find out how different farming system influence microbial biomass and therefore influence the long-term soil fertility and soil quality, this study analyzed the impacts of conventional integrated and organic farming systems on soil microbiological parameters using soil samples from the DOK long-term field experiment (Switzerland). Farmyard manure fertilizer is applied to bio-dynamic (D), bio-organic (O) and conventional farming system (K) with two different intensities. Besides, there are a conventional mineral fertilizer received system (M) and an unfertilized control plot (U). The chloroform fumigation extraction (CFE) method and quantitative polymerase chain reaction (qPCR) test were applied for detection and quantification of soil microbial biomass along with some other tests in physical, chemical and biological aspects. Soil pH tends to increase by applying farmyard manure. Metabolic quotient (qCO 2 ) revealed a lower level in the manured system though there was no significant difference between conventional and organic system. On one hand, D treatment achieved the highest values regarding microbial biomass carbon, nitrogen and phosphorus, and the highest gene copies number of detected microbial domains. On the other hand, higher concentration of microbial biomass sodium, potassium, manganese, silicon, nickel and zinc were found in M and K system. Contrary to expectation, the soil organic matter content between different treatments had only a little difference. In general, each tested soil quality parameter was affected by the type and quantity of fertilizer used to a different extent, among which the soil microbiological parameters showed more pronounced difference compared with soil physical parameter, pH and soil organic matter content. In short, organic farming system had greater potential to maintain soil fertility and improve soil quality than conventional farming system in the long term; while the comparison between two organic systems emphasized the beneficial influence from applying compost manure and bio-dynamic additives.