Effects of Soil Warming and Substrate Complexity on Microbial Carbon Use Efficiency at Harvard Forest 2017

<para>Soil microbial carbon use efficiency (CUE) is a combination of growth and respiration, which may respond differently to climate change depending on physical protection of soil carbon (C) and its availability to microbes. In a mid-latitude hardwood forest in central Massachusetts, 27 years of soil warming (+5 ◦C) has resulted in C loss and altered soil organic matter (SOM) quality, yet the underlying mechanisms remain unclear. Here, we hypothesized that long-term warming reduces physical aggregate protection of SOM, microbial CUE, and its temperature sensitivity. Soil was separated into macroaggregate (250–2000 μm) and microaggregate (less than 250 μm) fractions, and CUE was measured with 18O-enriched water in samples incubated at 15 and 25 ◦C for 24 h. We found that long-term warming reduced soil C and nitrogen concentrations and extracellular enzyme activity in macroaggregates, but did not affect physical protection of SOM. Long-term warming showed little effect on CUE or microbial biomass turnover time because it reduced both growth and respiration. However, CUE was less temperature sensitive in macroaggregates from the warmed compared to the control plots. Our findings suggest that microbial thermal responses to long-term warming occur mostly in soil compartments where SOM is less physically protected and thus more vulnerable to microbial degradation.</para> </section> </abstract> <keywordSet> <keyword>carbohydrates</keyword> <keyword>carbon</keyword> <keyword>cellulose</keyword> <keyword>climate change</keyword> <keyword>decomposition</keyword> <keyword>microbes</keyword> <keyword>soil warming</keyword> <keywordThesaurus>LTER controlled vocabulary</keywordThesaurus> </keywordSet> <keywordSet> <keyword>organic matter</keyword> <keywordThesaurus>LTER core area</keywordThesaurus> </keywordSet> <keywordSet> <keyword>Harvard Forest</keyword> <keyword>HFR</keyword> <keyword>LTER</keyword> <keyword>USA</keyword> <keywordThesaurus>HFR default</keywordThesaurus> </keywordSet> <intellectualRights> <section> <para>This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.</para> </section> </intellectualRights> <licensed> <licenseName>Creative Commons Zero v1.0 Universal</licenseName> <url>https://spdx.org/licenses/CC0-1.0.html</url> <identifier>CC0-1.0</identifier> </licensed> <distribution> <online> <url function="information"> https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf372 </url> </online> </distribution> <coverage> <geographicCoverage> <geographicDescription>Harvard Forest. Coordinates based on WGS84 datum.</geographicDescription> <boundingCoordinates> <westBoundingCoordinate>-72.18</westBoundingCoordinate> <eastBoundingCoordinate>-72.18</eastBoundingCoordinate> <northBoundingCoordinate>+42.54</northBoundingCoordinate> <southBoundingCoordinate>+42.54</southBoundingCoordinate> <boundingAltitudes> <altitudeMinimum>365</altitudeMinimum> <altitudeMaximum>365</altitudeMaximum> <altitudeUnits>meter</altitudeUnits> </boundingAltitudes> </boundingCoordinates> </geographicCoverage> <temporalCoverage> <rangeOfDates> <beginDate> <calendarDate>2017</calendarDate> </beginDate> <endDate> <calendarDate>2017</calendarDate> </endDate> </rangeOfDates> </temporalCoverage> </coverage> <maintenance> <description> <para>complete</para> </description> </maintenance> <contact> <positionName>Information Manager</positionName> <organizationName>Harvard Forest</organizationName> <address> <deliveryPoint>324 North Main Street</deliveryPoint> <city>Petersham</city> <administrativeArea>MA</administrativeArea> <postalCode>01366</postalCode> <country>USA</country> </address> <phone phonetype="voice">(978) 724-3302</phone> <electronicMailAddress>hf-im@lists.fas.harvard.edu</electronicMailAddress> </contact> <publisher> <organizationName>Harvard Forest</organizationName> <address> <deliveryPoint>324 North Main Street</deliveryPoint> <city>Petersham</city> <administrativeArea>MA</administrativeArea> <postalCode>01366</postalCode> <country>USA</country> </address> <phone phonetype="voice">(978) 724-3302</phone> <phone phonetype="fax">(978) 724-3595</phone> <onlineUrl>https://harvardforest.fas.harvard.edu</onlineUrl> </publisher> <methods> <methodStep> <description> <section> <title/> <para>Soil samples were collected in October 2017 from the Soil Warming Study at the Harvard Forest. Soil was separated into macroaggregate (250–2000 μm) and microaggregate (less than 250 μm) fractions, and CUE was measured with 18O enriched water (H2 18O) in samples incubated at 15 and 25 ◦C for 24 h.</para> </section> </description> </methodStep> </methods> <project> <title>Harvard Forest Long-Term Ecological Research Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu https://ror.org/059cpzx98 pointOfContact The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210. hf372-01-bulk-soil-c-n.csv bulk soil carbon and nitrogen hf372-01-bulk-soil-c-n.csv 743 e6eff9abe33b33e060410a3838b59e14 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-01-bulk-soil-c-n.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value rep field replicate (plot) field replicate (plot) NA missing value mbc microbial biomass carbon (µg g-1), measured by CFE microgramsPerGram 0.1 real NA missing value doc dissolved organic carbon (µg g-1), extracted by 0.5 M K2SO4 microgramsPerGram 0.1 real NA missing value soc soil organic carbon (%), measured by elemental analyzer dimensionless 0.001 real NA missing value tsn soil nitrogen (%), measured by elemental analyzer dimensionless 0.001 real NA missing value mbcsoc ratio of mbc and soc dimensionless 0.001 real NA missing value mbcdoc ratio of mbc and doc dimensionless 0.001 real NA missing value docsoc ratio of doc and soc dimensionless 0.001 real NA missing value scn ratio of soc and tsn dimensionless 1 natural NA missing value 12 hf372-02-aggr-soil-c-n.csv aggregate soil carbon and nitrogen hf372-02-aggr-soil-c-n.csv 2116 f0e39eace325764753921e92047a4be6 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-02-aggr-soil-c-n.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value rep field replicate (plot) field replicate (plot) NA missing value mbc microbial biomass carbon (µg g-1), measured by CFE microgramsPerGram 0.1 real NA missing value doc dissolved organic carbon (µg g-1), extracted by 0.5 M K2SO4 microgramsPerGram 0.1 real NA missing value soc soil organic carbon (%), measured by elemental analyzer dimensionless 0.001 real NA missing value tsn soil nitrogen (%), measured by elemental analyzer dimensionless 0.001 real NA missing value mbcsoc ratio of mbc and soc dimensionless 0.001 real NA missing value mbcdoc ratio of mbc and doc dimensionless 0.001 real NA missing value docsoc ratio of doc and soc dimensionless 0.001 real NA missing value scn ratio of soc and tsn dimensionless 1 natural NA missing value soilmass soil mass of MA and MI gram 0.1 real NA missing value soil_pct percent of soil mass between MA and MI dimensionless 0.1 real NA missing value cstk_pct percent of soil carbon stock (by multiplying soc and soil mass) between MA and MI dimensionless 0.001 real NA missing value nstk_pct percent of tsn stock (by multiplying tsn and soil mass) between MA and MI dimensionless 0.001 real NA missing value 24 hf372-03-particle-fraction-soil-c-n.csv particle fraction of soil carbon and nitrogen hf372-03-particle-fraction-soil-c-n.csv 2011 c1a06f03c39a9cb5278defedf86bdd0f 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-03-particle-fraction-soil-c-n.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value size particle size 250-2000 250-2000 µm 53-250 53-250 µm Silt/clay silt/clay (less than 53 µm) NA missing value rep field replicate (plot) field replicate (plot) NA missing value soilmass soil mass of different particle sizes gram 0.001 real NA missing value totalmass total soil mass across particle sizes within one rep gram 0.001 real NA missing value soil_pct percent of soil mass of different particle sizes dimensionless 0.1 real NA missing value 48 hf372-04-density-fraction-soil-c-n.csv density fraction of soil carbon and nitrogen hf372-04-density-fraction-soil-c-n.csv 3268 1b7479a2036ee5d6a43a503fdf6b7b12 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-04-density-fraction-soil-c-n.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value size soil density fractions cPOM coarse particulate organic matter fPOM free particulate organic matter MAOM mineral associated organic matter oPOM occluded particulate organic matter NA missing value rep field replicate (plot) field replicate (plot) NA missing value soc soil organic carbon (%), measured by elemental analyzer dimensionless 0.1 real NA missing value tsn soil nitrogen (%), measured by elemental analyzer dimensionless 0.1 real NA missing value soilmass soil mass gram 0.001 real NA missing value soil_pct percent of soil mass among density fractions dimensionless 0.1 real NA missing value cstk_pct percent of soil carbon stock (by multiplying soc and soil mass) between MA and MI dimensionless 0.1 real NA missing value nstk_pct percent of tsn stock (by multiplying tsn and soil mass) between MA and MI dimensionless 0.1 real NA missing value 64 hf372-05-microbial-activity.csv microbial activity hf372-05-microbial-activity.csv 14387 f2ea741b84ae0862da8cc77fd9eb7732 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-05-microbial-activity.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value temp incubation temperature celsius 1 natural NA missing value sub substrate substrate NA missing value rep field replicate (plot) field replicate (plot) NA missing value resp microbial respiration (µg CO2-C g-1 soil) microgramsPerGram 0.001 real NA missing value growth microbial growth (µg C g-1 soil) microgramsPerGram 0.001 real NA missing value uptake microbial organic carbon uptake (µg C g-1 soil) microgramsPerGram 0.001 real NA missing value cue microbial carbon use efficiency (%) dimensionless 0.1 real NA missing value to1 microbial turnover rate (per day) number 0.001 real NA missing value to2 turnover time (days) number 0.1 real NA missing value mbc microbial biomass carbon microgramsPerGram 0.1 real NA missing value dna soil DNA content microgramsPerGram 0.1 real NA missing value mbcdna ratio of mbc and dna dimensionless 0.1 real NA missing value mresp mass-specific respiration (µg CO2-C g-1 mbc) microgramsPerGram 0.001 real NA missing value mgrowth mass-specific growth (µg C g-1 mbc) microgramsPerGram 0.001 real NA missing value muptake mass-specific uptake (µg C g-1 mbc) microgramsPerGram 0.001 real NA missing value dresp mass-specific respiration (µg CO2-C g-1 dna) microgramsPerGram 0.001 real NA missing value dgrowth mass-specific growth (µg C g-1 dna) microgramsPerGram 0.001 real NA missing value duptake mass-specific uptake (µg C g-1 dna) microgramsPerGram 0.001 real NA missing value 128 hf372-06-microbial-activity-temp-sens.csv temperature sensitivity of microbial activity hf372-06-microbial-activity-temp-sens.csv 6081 d2b59410aed086d69adeee73ff4a6e68 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-06-microbial-activity-temp-sens.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value sub substrate subtrate NA missing value rep field replicate (plot) field replicate (plot) NA missing value resp microbial respiration (µg CO2-C g-1 soil) microgramsPerGram 0.01 real NA missing value growth microbial growth (µg C g-1 soil) microgramsPerGram 0.01 real NA missing value uptake microbial organic carbon uptake (µg C g-1 soil) microgramsPerGram 0.01 real NA missing value cue microbial carbon use efficiency (%) dimensionless 0.01 real NA missing value turnover microbial turnover rate (per day) number 0.01 real NA missing value mbc microbial biomass carbon microgramsPerGram 0.01 real NA missing value dna soil DNA content microgramsPerGram 0.01 real NA missing value mbcdna ratio of mbc and dna dimensionless 0.01 real NA missing value mresp mass-specific respiration (µg CO2-C g-1 mbc) microgramsPerGram 0.01 real NA missing value mgrowth mass-specific growth (µg C g-1 mbc) microgramsPerGram 0.01 real NA missing value muptake mass-specific uptake (µg C g-1 mbc) microgramsPerGram 0.01 real NA missing value dresp mass-specific respiration (µg CO2-C g-1 dna) microgramsPerGram 0.01 real NA missing value dgrowth mass-specific growth (µg C g-1 dna) microgramsPerGram 0.01 real NA missing value duptake mass-specific uptake (µg C g-1 dna) microgramsPerGram 0.01 real NA missing value 64 hf372-07-soil-enzyme-activity.csv soil enzyme activity hf372-07-soil-enzyme-activity.csv 825 09dff6845c5503ca9ec2c005c937c364 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p37/hf372/hf372-07-soil-enzyme-activity.csv plot.id identification number of field plot identification number of field plot NA missing value trt warming treatment Control ambient Heated +5 °C NA missing value agg soil aggregate size MA 250-2000 µm MI less than 250 µm NA missing value rep field replicate (plot) field replicate (plot) NA missing value ap acid phosphatase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value bg β-glucosidase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value cbh cellobiohydrolase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value nag N-acetyl-glucosaminidase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value per polyphenol oxidase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value pox peroxidase (nmol g-1 soil h-1) nanomolePerGramPerHour 1 whole NA missing value apmbc acid phosphatase (nmol g-1 mbc h-1) nanomolePerGramPerHour 1.1 real NA missing value bgmbc β-glucosidase (nmol g-1 mbc h-1) nanomolePerGramPerHour 0.1 real NA missing value cbhmbc cellobiohydrolase (nmol g-1 mbc h-1) nanomolePerGramPerHour 0.1 real NA missing value nagmbc N-acetyl-glucosaminidase (nmol g-1 mbc h-1) nanomolePerGramPerHour 0.1 real NA missing value permbc polyphenol oxidase (nmol g-1 mbc h-1) nanomolePerGramPerHour 0.1 real NA missing value poxmbc peroxidase (nmol g-1 mbc h-1) nanomolePerGramPerHour 0.1 real NA missing value 12 plot soil long-term measurement