BayCEER Workshop 2016

Phosphorus solubilization by microorganisms at different stages of soil development

P 2.1 in Cross-scale relations in ecology and environmental research

Introduction

Solubilization of phosphorus (P) from minerals is an important process for ecosystem nutrition. However, little is known about changes of P solubilization rates and mechanisms during soil formation. Therefore, we studied P solubilization along a sequence of soil development in the coastal range of Chile that runs along a climate gradient.

Hypotheses:

i) Higher developed soils in temperate ecosystems show higher rates of P solubilization than poorly developed soils in dry ecosystems.

ii) Topsoil horizons reveal higher rates of P solubilization than subsoil horizons due to higher amounts of available C for microorganisms.

iii) P solubilization is caused by microbial release of protons and OA.

Material and Methods

We studied soils in four different areas along a climate gradient in Chile and conducted incubation experiments with soil-extracted microorganisms and apatite. The incubation lasted for one month at 15° C. Treatment 1 was performed without additional nutrients and in treatment 2 we used a minimal growth medium (MGM). The concentrations of phosphate and different OA were measured as well as pH values.

Results

The soil at the semi-desert site had the highest increase and the soil at the desert site showed the lowest increase in the phosphate concentration. Only the addition of MGM lead to a significant pH decrease during the incubation. Oxalic and acetic acid showed the highest concentrations out of eight measured OA. Topsoil horizons exhibited higher rates of P solubilization than subsoil horizons in both treatments, except for one site.

Conclusions

i) The rates of P solubilization at the temperate sites were up to ten times higher than at the dry site, ii) Topsoil horizons generally exhibited higher rates of P solubilization than subsoil horizons and iii) P solubilization went along with decreases in pH when MGM was added and was associated with relatively high concentrations of OA.

Keywords: Phosphorus, solubilization, apatite, organic acids, incubation, climate gradient, soil