Title: Soil Oxygen Limits Microbial Phosphorus Utilization in Humid Tropical Forest Soils

Abstract

Soil phosphorus (P) availability is of special interest in many humid tropical forests, especially those on highly weathered, iron (Fe)- and aluminum (Al)-rich soils where P often limits net primary productivity. Phosphorus cycling is partly dependent on the ability of microbes to compete for P with Fe and Al minerals, which strongly bind P. Soil P availability is also indirectly affected by soil redox conditions due to its effects on microbial activity and reductive dissolution of Fe oxides that may weaken Fe-O-P sorption strength. Here, we explored P sorption, soil Fe (II) concentrations, soil CO2 production, organic and inorganic P pools, and microbial biomass P in tropical soils that typically experience frequent low redox (valley soils), or fluctuating redox conditions (slope soils). Soils from both topographic positions were pre-incubated under oxic or anoxic headspaces and then amended with a mixture of P (as orthophosphate) and carbon (C, as acetate, to maintain microbial activity) and incubated in the dark for 24 h. Phosphorus sorption to the mineral phase occurred on a time scale of seconds to minutes in valley and slope soils, reflecting strong abiotic P sorption capacity. Valley soils were characterized by inherently higher Fe(II) concentrations and lower respiration rates.more » Under anoxic headspaces, Fe(II) concentrations increased 3-to 5-fold in the both soils. Soil respiration and microbial P utilization declined significantly in both soils under anoxic conditions, regardless of Fe(II) concentrations. Microbial P concentrations were highest when slope soils were incubated under an oxic headspace, despite the high P sorption under these conditions. Our results suggest that microbial P utilization is indirectly limited by low O2 availability and that microbes are able to effectively compete with minerals for P under Fe-oxidizing conditions. These results emphasize the central role of soil microorganisms in regulating P availability, even in the presence of strong abiotic sorption capacity.« less

Authors:

Gross, Avner ^[1]; Pett-Ridge, Jennifer ^[2]; Silver, Whendee  ^[3]

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+ Show Author Affiliations

1. Univ. of California, Berkeley, CA (United States). Dept. of Environmental Science, Policy, and Management; Ben Gurion Univ. of the Negev, Beer-Sheva (Israel). Dept. for Geography and Environmental Development
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Sciences Directorate
3. Univ. of California, Berkeley, CA (United States). Dept. of Environmental Science, Policy, and Management

Publication Date:

Thu Nov 29 00:00:00 EST 2018

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1513130

Report Number(s):

LLNL-JRNL-738829
Journal ID: ISSN 2571-8789; 892108

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Soil Systems

Additional Journal Information:

Journal Volume: 2; Journal Issue: 4; Journal ID: ISSN 2571-8789

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; phosphorus availability; microbial biomass; tropical soils; iron reduction; anoxic conditions