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What explains long-term increases

in soil respiration?

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Surprise special topic: Root biomass

Tiantian Zhu

Graduate of

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At MELNHE sites, soil respiration is suppressed by N addition

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  • Decreased root biomass
  • Lower C:N ratio in soil
  • Decreased microbial activity

N addition

P addition

N+P

Control

Roter, 2021

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Soil temperature and litterfall fails to explain the increasing soil respiration.

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Mann, 2021

Median plot soil

temperature (°C)

Median plot respiration

(μmol CO2 m-2 s-1)

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Soil temperature and litterfall fails to explain the increasing soil respiration.

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Does soil moisture play a role? What about root biomass?

Mann, 2021

Litter mass

(g m-2)

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Fine Root Biomass

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Size < 1mm

Size = 1-5 mm

Depth = 1-10 cm

Depth > 10 cm

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Fine Root Biomass Analysis

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Mature

Size < 1mm

Size = 1-5 mm

Depth = 1-10 cm

Depth > 10 cm

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Soil respiration by stand age

Median soil

CO2 efflux

(μmol m-2 s-1)

2009-2010 (Pretreatment)

2011

2012-2014

2015-2017

2018-2020

Young

Mid

Mature

Mann, 2021

Young

Mid

Mature

Young

Mid

Mature

Young

Mid

Mature

Young

Mid

Mature

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Next steps

  • Two rounds of soil respiration measurements, along with soil temperature and moisture

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  • Moisture as a covariate in the full-factorial model. Explore moisture-respiration correlation among treatments, stand ages

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Acknowledgements

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Ruth Yanai

Tim Fahey

Thomas Mann

Brendan Leonardi

Scott Dai

Erin Cornell

Daniel Hong

Shiyi Li

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and the MELNHE crew!

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