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1. Plant- soil- microbe interactions in perennial bioenergy cropping systems
1.1 Tracking the transfer of photosynthesized carbon through the plant-microbe-soil continuum with 13CO2 pulse-chase

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We are using in situ 13C pulse chase methods to understand how the rhizosphere microbiome in perennial bioenergy cropping systems, switchgrass (Panicum virginitum var. Cave-In-Rock) in marginal lands acquires C resources from plants vs SOM to fuel N transformations and how newly photosynthesized C pass through the plant-soil-microbe continuum and contribute to SOM formation.

1.2  Root exudates shift how N mineralization and N fixation contribute to plant N supply in marginal lands soils 

  • ​Using laboratory incubation methods, we found that different root exudates regulate N transformations processes through different mechanisms: 

  • Carbohydrates addition increased soil N fixation relative to N mineralization.

  • Organic acids addition increased soil N mineralization relative to N fixation.

  • Organic acids addition significantly increased DON in Lake City soils.

  • Legacy of N addition had no effects on either N mineralization or N fixation.

  • Changes in soil pH and DON drive the change of N availability.

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2. Soil organic matter (SOM) formation and stabilization mechanisms

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  • Through an global synthesis, we generate, for the first time, global distribution maps of microbial necromass carbon (C) and nitrogen (N) and contributions to SOM in topsoil and subsoil.

  • Globally, necromass concentrations varied widely across ecosystems and by latitude, contributing 19-60% to SOC and 41-92% to soil N stocks, with particularly large accumulations in boreal and tropical ecosystems.

  • On average, fungal necromass contributions to SOM are 3x greater than bacterial, although this varied across ecosystems.

  • Microbial necromass contributions to SOC are strongly associated with soil C:N ratios and pH; necromass contributions are greater in soils with narrow C:N ratios and higher pH.

  • Microbial necromass is on average 23 and 77 times greater than living microbial biomass in topsoil and subsoil, respectively. link

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3. Temperature response of SOM decomposition

Research 1: A new incubation and measurement approach to estimate the temperature response of soil organic matter decomposition link

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  • We summarized two commonly used approaches for estimation of Q10.

  • We provide a new approach with rapid and automatic measurements for estimating Q10.

  • We compared the performance of three approaches using a laboratory experiment.

  • Traditional approaches underestimate Q10, especially in short time incubation.

  • The new approach performed better in estimating Q10 with high accuracy.

Research 2: The optimum temperature of soil microbial respiration: Patterns and controls link

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  • We investigated the optimum temperature (Topt) of SOM decomposition.

  • Topt ranged from 38.5 to 46.0 °C in 25 forest soils, with an average of 42.4 °C.

  • Topt increased significantly with increasing latitude.

  • Climate, substrate and soil microorganism regulate the regional variation in Topt.

  • The latitudinal variation of Topt should be considered in model optimization. 

Research 3: Regional variation in the temperature sensitivity of soil organic matter decomposition in China's forests and grasslands link

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  • We investigated the regional variation of Q10 in different forests and grasslands in China.

  • Q10 ranging from 1.16 to 3.19 (mean 1.63).

  • Q10 significantly increased with increasing altitude and decreased with increasing longitude.

  • pH and soil electrical conductivity primarily explained spatial variation in Q10. 

Research 4: A global synthesis of rate and temperature sensitivity of soil nitrogen mineralization: latitudinal patterns and mechanisms link

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  • Through an global synthesis, we investigated the variation in rate and Q10 of soil nitrogen mineralization (Nmin).

  • Nmin significantly increased with increasing latitude with an average of 2.41 mg N soil kg−1 day−1.

  • Q10 varied significantly among different ecosystems highest, with the highest found in forest soils (2.43) and the lowest found for grassland soils (1.67). 

  • Nmin was primarily affected by SOC, C:N ratio, and clay content.

  • Q10 was primarily influenced by the soil C:N ratio and soil pH. link

Research 5: Temperature sensitivity of soil microbial respiration in soils with lower substrate availability is enhanced more by labile carbon input link

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  • We examined the effects of glucose addition on Q10  of soil respiration.

  • Glucose addition increased Q10 , especially for mid-latitude soil samples.

  • Q10 in soils with lower substrate availability is enhanced more by glucose addition. 

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