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The role of soil redox conditions in microbial phosphorus cycling in humid tropical forests

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Data Package:
Local Identifier:knb-lter-luq.204.13
Title:The role of soil redox conditions in microbial phosphorus cycling in humid tropical forests
Alternate Identifier:DOI PLACE HOLDER
Abstract:

Humid tropical forests are among the most productive ecosystems globally, yet they often occur on soils with high phosphorus (P) sorption capacity, lowering P availability to biota. Short-term anoxic events are thought to release sorbed P and enhance its acquisition by soil microbes. However, the actual effects of anoxic conditions on microbial P acquisition in humid tropical forest soils are surprisingly poorly studied. We used laboratory incubations of bulk soils, NanoSIMS analysis of single microbial cells, and landscape scale measurements in the Luquillo Experimental Forest (LEF), Puerto Rico to test the hypothesis that anoxic conditions increase microbial P acquisition in humid tropical forests. In laboratory and field experiments we found that microbial P uptake generally decreased under anoxic conditions, leading to high microbial carbon (C) to P ratios in anoxic soils. The decreased P acquisition under anoxic conditions was correlated with lower microbial C use efficiency (CUE), an index of microbial energy transfer in ecosystems. Phosphorus amendments to anoxic soils led to increased microbial P uptake and higher CUE suggesting that microbes were less able to access and utilize P under natural low redox conditions. Under oxic conditions, microbial C:P ratios and CUE did not respond to changes in substrate stoichiometry. These results challenge the existing paradigm by showing that anoxic conditions can decrease microbial P uptake and ultimately constrain microbial CUE. Our findings indicate that soil redox conditions tightly couple soil P and C cycles and advance our understanding of controls on P cycling in humid tropical forest ecosystems.

Publication Date:2019-10-03
Language:English

People and Organizations
Contact:Gross, Avner  [  email ]
Creator:Gross, Avner (University of California-Berkeley)
Creator:Lin, Yang (University of California-Berkeley)
Creator:Weber, Peter (University of California-Berkeley)
Creator:Pett-Ridge, Jennifer (University of California-Berkeley)
Creator:Silver, Whendee 

Data Entities
Data Table Name:
The role of soil redox conditions in microbial phosphorus cycling in humid tropical forests
Description:
Humid tropical forests are among the most productive ecosystems globally, yet they often occur on soils with high phosphorus (P) sorption capacity, lowering P availability to biota. Short-term anoxic events are thought to release sorbed P and enhance its acquisition by soil microbes. However, the actual effects of anoxic conditions on microbial P acquisition in humid tropical forest soils are surprisingly poorly studied. We used laboratory incubations of bulk soils, NanoSIMS analysis of single microbial cells, and landscape scale measurements in the Luquillo Experimental Forest (LEF), Puerto Rico to test the hypothesis that anoxic conditions increase microbial P acquisition in humid tropical forests. In laboratory and field experiments we found that microbial P uptake generally decreased under anoxic conditions, leading to high microbial carbon (C) to P ratios in anoxic soils. The decreased P acquisition under anoxic conditions was correlated with lower microbial C use efficiency (CUE), an index of microbial energy transfer in ecosystems. Phosphorus amendments to anoxic soils led to increased microbial P uptake and higher CUE suggesting that microbes were less able to access and utilize P under natural low redox conditions. Under oxic conditions, microbial C:P ratios and CUE did not respond to changes in substrate stoichiometry. These results challenge the existing paradigm by showing that anoxic conditions can decrease microbial P uptake and ultimately constrain microbial CUE. Our findings indicate that soil redox conditions tightly couple soil P and C cycles and advance our understanding of controls on P cycling in humid tropical forest ecosystems. test
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Data Table

Data:https://pasta-s.lternet.edu/package/data/eml/knb-lter-luq/204/13/cf7b7d555b3b892582bfa2aa2e1da7c1
Name:The role of soil redox conditions in microbial phosphorus cycling in humid tropical forests
Description:Humid tropical forests are among the most productive ecosystems globally, yet they often occur on soils with high phosphorus (P) sorption capacity, lowering P availability to biota. Short-term anoxic events are thought to release sorbed P and enhance its acquisition by soil microbes. However, the actual effects of anoxic conditions on microbial P acquisition in humid tropical forest soils are surprisingly poorly studied. We used laboratory incubations of bulk soils, NanoSIMS analysis of single microbial cells, and landscape scale measurements in the Luquillo Experimental Forest (LEF), Puerto Rico to test the hypothesis that anoxic conditions increase microbial P acquisition in humid tropical forests. In laboratory and field experiments we found that microbial P uptake generally decreased under anoxic conditions, leading to high microbial carbon (C) to P ratios in anoxic soils. The decreased P acquisition under anoxic conditions was correlated with lower microbial C use efficiency (CUE), an index of microbial energy transfer in ecosystems. Phosphorus amendments to anoxic soils led to increased microbial P uptake and higher CUE suggesting that microbes were less able to access and utilize P under natural low redox conditions. Under oxic conditions, microbial C:P ratios and CUE did not respond to changes in substrate stoichiometry. These results challenge the existing paradigm by showing that anoxic conditions can decrease microbial P uptake and ultimately constrain microbial CUE. Our findings indicate that soil redox conditions tightly couple soil P and C cycles and advance our understanding of controls on P cycling in humid tropical forest ecosystems. test
Number of Records:56
Number of Columns:15

Table Structure
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Record Delimiter:\r\n
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Simple Delimited:
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Table Column Descriptions
 TreatmentTreatment C:P ratio (molar)Treatment stdev of C:PSampleDOC+ (ppm)stdev of DOC+ (ppm)DOC+ (ug C g soil-1)stdev of DOC+ (ug C g soil-1)DOC- (ppm)stdev DOC- (ppm)DOC- (ug C g soil-1)stdev DOC- (ug C g soil-1)Microbial C (ug C g soil-1)Microbial P (ug P g soil-1)C:P ratio (molar)
Column Name:Treatment  
Treatment C:P ratio (molar)  
Treatment stdev of C:P  
Sample  
DOC+ (ppm)  
stdev of DOC+ (ppm)  
DOC+ (ug C g soil-1)  
stdev of DOC+ (ug C g soil-1)  
DOC- (ppm)  
stdev DOC- (ppm)  
DOC- (ug C g soil-1)  
stdev DOC- (ug C g soil-1)  
Microbial Carbon  
Microbial Phosphorus  
C:P ratio (molar)  
Definition:Approximately 250 g of soil (oven dry weight equivalent (ODW)) was placed in 487-ml gas-tight vessels and pre-incubated under either oxic or anoxic conditions for 10 days (n = 4 per treatment; total n = 64). Bulk oxic and anoxic conditions were created by flushing the jar headspace with either CO2-free air (oxic treatment) or N2 gas (anoxic treatment) (Pett-Ridge and Firestone 2005, Hall et al. 2015); jars were sealed and maintained under these headspace conditions for 10 days either in ambient air (oxic) or inside a glove box (anoxic) in order to reach oxic or anoxic conditions before the addition of P and C substrates. Following the pre-incubation period, the soils were amended with one of 3 different solutions, varying in their C:P ratios on a molar basis (7:1, 60:1 and 200:1) (Cleveland and Liptzin 2007, Wright et al. 2011). The C was added in the form of glucose in a concentration of 100 µg C g soil-1 (ODW), and P was added as potassium phosphate (KH2PO4) to achieve the desired C:P ratios. The substrate solutions were supplemented with N in the form of ammonium nitrate to keep the soil C:N ratio close to value of the untreated soil (13:1, Table S1, similar to the mean value in tropical forest soils (Cleveland and Liptzin 2007, Xu et al. 2013)). One set of samples received deionized water only and served as a control. The C:P ratio of soil organic matter (SOM) in the control samples was 240:1 (see supplementary method), within the range of the C:P ratio of SOM in humid tropical forests (Cleveland and Liptzin 2007, Xu et al. 2013). The glucose was labeled with 13C (99% 13C6-glucose, Sigma Aldrich ltd) and used to assess microbial cell uptake and microbial CUE. The total volume of the substrate or control solutions added to the soil was 10 mL; this had a negligible effect on the natural water content of the 250 g soil in each vessel.Microbial biomass C:P ratios are expressed on a molar basis.Standard deviation of the carbon to phosphorus ratio for the treatment.The Sample numberDissolved organic carbon (DOC) is the fraction of total organic carbon operationally defined as that which can pass through a filter size that typically ranges in size from 0.22 and 0.7 micrometers.[1] The fraction remaining on the filter is called particulate organic carbon (POC).standard deviation of DOC PPMDOC+ (ug C g soil-1)stdev of DOC+ (ug C g soil-1)DOC- (ppm)stdev DOC- (ppm)DOC- (ug C g soil-1)stdev DOC- (ug C g soil-1)For microbial biomass C determinations, 10 g of soil (ODW) was fumigated with chloroform for 72 h and extracted with 0.5 M of potassium sulfate (K2SO4) for 1 h. Microbial C was determined as the difference between fumigated and unfumigated samples, and corrected for unrecovered biomass using a conversion factor of 0.45 (Vance et al. 1987).Because the high contents of amorphous Fe and Al minerals likely contributed to strong P sorption, we adopted the method outlined by Kouno et al (1995) to measure microbial biomass P. Approximately 5 g of soil (ODW) were shaken for 24 h with 80 mL deionized water in the presence of 5 strips of anion exchange resin membrane (BDH-55164, VWR International, Lutterworth, UK) and fumigated with 1 mL hexanol. The P was eluted from the resin membranes by shaking for 24 h with 0.25 M HNO3, and the recovered P was determined by molybdate colorimetry in duplicate with an average difference between duplicates of 1.3%. We estimated the proportion of P sorbed to soil minerals by spiking the extraction system (i.e., soil + anion exchange membrane + water) with 50 µg P g-1 soil and found that an average of 35% of the added P was recovered by anion exchange membrane. Microbial biomass P was calculated as the difference between fumigated and unfumigated samples using a Kp factor of 0.4 to correct for fumigation efficiency in releasing P (Brookes et al. 1982) and the recovery rate against sorption we measured here.Microbial biomass C:P ratios are expressed on a molar basis.
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Measurement Values Domain:
DefinitionApproximately 250 g of soil (oven dry weight equivalent (ODW)) was placed in 487-ml gas-tight vessels and pre-incubated under either oxic or anoxic conditions for 10 days (n = 4 per treatment; total n = 64). Bulk oxic and anoxic conditions were created by flushing the jar headspace with either CO2-free air (oxic treatment) or N2 gas (anoxic treatment) (Pett-Ridge and Firestone 2005, Hall et al. 2015); jars were sealed and maintained under these headspace conditions for 10 days either in ambient air (oxic) or inside a glove box (anoxic) in order to reach oxic or anoxic conditions before the addition of P and C substrates. Following the pre-incubation period, the soils were amended with one of 3 different solutions, varying in their C:P ratios on a molar basis (7:1, 60:1 and 200:1) (Cleveland and Liptzin 2007, Wright et al. 2011). The C was added in the form of glucose in a concentration of 100 µg C g soil-1 (ODW), and P was added as potassium phosphate (KH2PO4) to achieve the desired C:P ratios. The substrate solutions were supplemented with N in the form of ammonium nitrate to keep the soil C:N ratio close to value of the untreated soil (13:1, Table S1, similar to the mean value in tropical forest soils (Cleveland and Liptzin 2007, Xu et al. 2013)). One set of samples received deionized water only and served as a control. The C:P ratio of soil organic matter (SOM) in the control samples was 240:1 (see supplementary method), within the range of the C:P ratio of SOM in humid tropical forests (Cleveland and Liptzin 2007, Xu et al. 2013). The glucose was labeled with 13C (99% 13C6-glucose, Sigma Aldrich ltd) and used to assess microbial cell uptake and microbial CUE. The total volume of the substrate or control solutions added to the soil was 10 mL; this had a negligible effect on the natural water content of the 250 g soil in each vessel.
DefinitionMicrobial biomass C:P ratios are expressed on a molar basis.
DefinitionStandard deviation of the carbon to phosphorus ratio for the treatment.
DefinitionThe Sample number
DefinitionDissolved organic carbon (DOC) is the fraction of total organic carbon operationally defined as that which can pass through a filter size that typically ranges in size from 0.22 and 0.7 micrometers.[1] The fraction remaining on the filter is called particulate organic carbon (POC).
Definitionstandard deviation of DOC PPM
DefinitionDOC+ (ug C g soil-1)
Definitionstdev of DOC+ (ug C g soil-1)
DefinitionDOC- (ppm)
Definitionstdev DOC- (ppm)
DefinitionDOC- (ug C g soil-1)
Definitionstdev DOC- (ug C g soil-1)
DefinitionFor microbial biomass C determinations, 10 g of soil (ODW) was fumigated with chloroform for 72 h and extracted with 0.5 M of potassium sulfate (K2SO4) for 1 h. Microbial C was determined as the difference between fumigated and unfumigated samples, and corrected for unrecovered biomass using a conversion factor of 0.45 (Vance et al. 1987).
DefinitionBecause the high contents of amorphous Fe and Al minerals likely contributed to strong P sorption, we adopted the method outlined by Kouno et al (1995) to measure microbial biomass P. Approximately 5 g of soil (ODW) were shaken for 24 h with 80 mL deionized water in the presence of 5 strips of anion exchange resin membrane (BDH-55164, VWR International, Lutterworth, UK) and fumigated with 1 mL hexanol. The P was eluted from the resin membranes by shaking for 24 h with 0.25 M HNO3, and the recovered P was determined by molybdate colorimetry in duplicate with an average difference between duplicates of 1.3%. We estimated the proportion of P sorbed to soil minerals by spiking the extraction system (i.e., soil + anion exchange membrane + water) with 50 µg P g-1 soil and found that an average of 35% of the added P was recovered by anion exchange membrane. Microbial biomass P was calculated as the difference between fumigated and unfumigated samples using a Kp factor of 0.4 to correct for fumigation efficiency in releasing P (Brookes et al. 1982) and the recovery rate against sorption we measured here.
DefinitionMicrobial biomass C:P ratios are expressed on a molar basis.
Missing Value Code:                              
Accuracy Report:                              
Accuracy Assessment:                              
Coverage:                              
Methods:                              

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LTER Network Data Access Policy, Data Access Requirements, and General Data Use Agreement
approved by the LTER Coordinating Committee April 6, 2005

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Keywords

By Thesaurus:
LTER Controlled Vocabularybiogeochemistry, phosphorus

Methods and Protocols

These methods, instrumentation and/or protocols apply to all data in this dataset:

Methods and protocols used in the collection of this data package
Description:

Surface soils (0-15 cm) for the incubation experiment were collected from a north facing mid-slope topographic zone (approximate slope angle of 25o) near the El Verde field station (elevation of approximately 350 m)

People and Organizations

Creators:
Individual: Avner Gross
Organization:University of California-Berkeley
Email Address:
Avner.Gross@gmail.com
Individual: Yang Lin
Organization:University of California-Berkeley
Individual: Peter Weber
Organization:University of California-Berkeley
Individual: Jennifer Pett-Ridge
Organization:University of California-Berkeley
Individual: Whendee Silver
Address:
University of California, Ecosystem Sciences Division Dept. of Environmental Science, Policy & Management Mulford Hall #3114,
Berkeley, CA 94720 US
Phone:
(510) 643-3074 (voice)
Phone:
(510) 643-5098 (facsimile)
Email Address:
wsilver@berkeley.edu
Contacts:
Individual: Avner Gross
Email Address:
Avner.Gross@gmail.com

Temporal, Geographic and Taxonomic Coverage

No coverage information available

Project

Other Metadata

EDI is a collaboration between the University of New Mexico and the University of Wisconsin – Madison, Center for Limnology:

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