Oxygen Isotopes Unravel the Role of Microorganisms in Phosphate Cycling in Soils

Abstract

Phosphorus (P) is considered the ultimate limiting nutrient for plants in most natural systems and changes in the distribution of inorganic and organic P forms during soil development have been well documented. In particular, microbial activity has been shown to be an important control on P cycling but its contribution in building up the pool of plant-available P during soil development is still poorly quantified. To determine the importance of different biological processes on P cycling, we analyzed the isotopic composition of oxygen in phosphate (δ(18)O-Pi) from the parent material, soil microorganisms, the available P pool, and from the vegetation along a 150-year soil chronosequence of a glacier forefield. Our results show that at all sites, δ(18)O-Pi of microbial Pi is within the range expected for the temperature-dependent equilibrium between phosphate and water. In addition, the isotopic signature of available Pi is close to the signature of microbial Pi, independently of the contribution of parent material Pi, vegetation Pi or Pi released from organic matter mineralization. Thus, we show that phosphate is cycled through soil microorganisms before being released to the available pool. This isotopic approach demonstrates for the first time in the field and over long time scales, and not only through controlled experiments, the role of the microbial activity in cycling of P in soils.

Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

“…O P values reflect a movement towards isotopic equilibrium with soil water, as was reported for the resin-P pool in a series of natural extra tropical soils (Zohar et al, 2010;Angert et al, 2011Angert et al, , 2012Tamburini et al, 2012;Gross et al, 2013;Gross and Angert, 2015).…”

“…18 O P values in isotopic equilibrium with soil water (Zohar et al, 2010;Angert et al, 2011Angert et al, , 2012Tamburini et al, 2012;Gross et al, 2013;Gross and Angert, 2015). The authors of these studies hypothesized that the close to equilibrium d We suggest the above equilibrium values we found in our study reflect a dynamic balance between two microbial processes: 1) the efflux of cell internal inorganic phosphate back to the soil surroundings and 2) the uptake of phosphate molecules by the microbial biomass.…”

“…The aim of this project was to derive information on the processes that control phosphate cycling in tropical forest soils, based on natural variation in the isotopic composition of oxygen in soil phosphate (d 18 O P ). This Technique has provided valuable information on soil P dynamics in different ecosystems worldwide (Zohar et al, 2010;Angert et al, 2011Angert et al, , 2012Tamburini et al, 2012;Gross et al, 2013;Gross and Angert, 2015), but has not so far been applied in tropical soils. We took advantage of two long-term and well-studied field experiments in lowland tropical forest in Panama: an experiment initiated in 1998 involving factorial P, nitrogen (N) and potassium (K) additions Yavitt et al, 2011;Sayer et al, 2012;Mirabello et al, 2013;Schreeg et al, 2013;Turner and Wright, 2014), and a second experiment initiated in 2003 at the same site involving litter manipulation (removal and addition) (Sayer and Tanner, 2010;Vincent et al, 2010;Sayer et al, 2012).…”

The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

“…In the terrestrial environment, the oxygen isotope composition (δ 18 O) of phosphate has been used as a tracer in the terrestrial environment to study the cycling of P in soils (Zohar et al, 2010a and b;Tamburini et al, 2010Tamburini et al, , 2012Angert et al, 2011Angert et al, , 2012Gross and Angert, 2015), in plants (Young et al, 2009;Pfahler et al, 2013) and in aerosols (Gross et al, 2013). Under ambient conditions and in the absence of biological activity, the δ 18 O of phosphate does not change (Kolodny et al, 1983;O'Neil et al, 2003).…”

Introduction to the special issue: Developments in soil organic phosphorus cycling in natural and agricultural ecosystems

“…This technique provides information on phosphorus cycling in freshwater and terrestrial ecosystems (Jaisi and Blake, 2014;McLaughlin et al, 2006;Tamburini et al, 2014) and was previously used to examine aspects of microbial phosphorus cycling along a short-term (150 year old) glacial foreland chronosequence in Switzerland (Tamburini et al, 2012). This is extended here to the 6500 year Haast chronosequence in New Zealand, revealing the importance of efficient organic phosphorus cycling in maintaining phosphorus availability during long-term ecosystem development (Roberts et al, 2015).…”