Seminar: Quing-Fang Bi

Our understanding of soil organic carbon (SOC) sequestration has undergone a significant paradigm shift, highlighting soil microbes as key contributors, primarily through the accumulation of their necromass. One crucial aspect is the efficiency of microbial incorporation of plant carbon into microbial biomass, commonly referred to as microbial carbon use efficiency (CUE, defined as carbon allocation to growth over carbon uptake). Microbial CUE is believed to be a valuable parameter in predicting the soil carbon-climate and potential carbon sequestration in soils. However, due to the sensitivity to environmental changes and methodological restrictions, the response of CUE of soil microbial communities to global change drivers and its linkages to SOC stocks are not fully resolved.

Here, we synthesized 255 global and biome-level data points and 115 data pairs under global change conditions, of microbial CUE, respiration, and growth estimated by 18O-microbial DNA growth. We discussed the potential impacts of anthropogenic activities, such as land-use change and climate change, on CUE and its consequences for biomass build-up and SOC sequestration. Our findings reveal that the mean microbial CUE across all biomes was 0.31, with lower values observed in forests (0.27, n=100) compared to croplands (0.30, n=75) and grasslands (0.36, n=80). Moreover, microbial CUE was higher in temperate (0.38, n=71) and subarctic ecosystems (0.28, n=148) compared to subtropical ecosystems (0.27, n=36). We observed that lower soil C:N ratio and latitude, as well as increased mean annual temperature (MAT), were drivers of increased microbial CUE and growth. The effects of global change factors on microbial CUE were diverse. For instance, in topsoils, CUE increased under N addition (35%), NP addition (21%), and short-term warming (25%), but decreased under long-term warming (21%) and temporarily increased soil moisture content. In subsoils, NPKOM fertilization increased CUE, while short-term warming decreased it by 24%. Soil fertilization had positive effects on microbial CUE, growth, microbial biomass carbon (Cmic), and SOC contents. Conversely, long-term warming led to SOC loss, likely due to lower CUE and growth associated with increased respiration. Additionally, we found that microbial growth had a stronger positive impact on CUE, Cmic, and SOC contents compared to respiration.Consequently, there might be no simple linear relationship between CUE and C in microbial biomass and soil. We will also discuss how microbial CUE and growth can be integrated into soil carbon models and explore the inclusion of feedstock and SOC formation traits in these models. Our review highlights the importance of considering microbial CUE and growth, along with various microbial processes, to better project SOC fates.

Here, we synthesized 255 global and biome-level data points and 115 data pairs under global change conditions, of microbial CUE, respiration, and growth estimated by 18O-microbial DNA growth. We discussed the potential impacts of anthropogenic activities, such as land-use change and climate change, on CUE and its consequences for biomass build-up and SOC sequestration. Our findings reveal that the mean microbial CUE across all biomes was 0.31, with lower values observed in forests (0.27, n=100) compared to croplands (0.30, n=75) and grasslands (0.36, n=80). Moreover, microbial CUE was higher in temperate (0.38, n=71) and subarctic ecosystems (0.28, n=148) compared to subtropical ecosystems (0.27, n=36). We observed that lower soil C:N ratio and latitude, as well as increased mean annual temperature (MAT), were drivers of increased microbial CUE and growth. The effects of global change factors on microbial CUE were diverse. For instance, in topsoils, CUE increased under N addition (35%), NP addition (21%), and short-term warming (25%), but decreased under long-term warming (21%) and temporarily increased soil moisture content. In subsoils, NPKOM fertilization increased CUE, while short-term warming decreased it by 24%. Soil fertilization had positive effects on microbial CUE, growth, microbial biomass carbon (Cmic), and SOC contents. Conversely, long-term warming led to SOC loss, likely due to lower CUE and growth associated with increased respiration. Additionally, we found that microbial growth had a stronger positive impact on CUE, Cmic, and SOC contents compared to respiration.Consequently, there might be no simple linear relationship between CUE and C in microbial biomass and soil. We will also discuss how microbial CUE and growth can be integrated into soil carbon models and explore the inclusion of feedstock and SOC formation traits in these models. Our review highlights the importance of considering microbial CUE and growth, along with various microbial proce

sses, to better project SOC fates.

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