Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting

Abstract. While radiocarbon (14C) abundances in standing stocks of soil carbon have been used to evaluate rates of soil carbon turnover on timescales of several years to centuries, soil-respired 14CO2 measurements are an important tool for identifying more immediate responses to disturbance and climate change. Soil Δ14CO2 data, however, are often temporally sparse and could be interpreted better with more context for typical seasonal ranges and trends. We report on a semi-high-frequency sampling campaign to distinguish physical and biological drivers of soil Δ14CO2 at a temperate forest site in northern Wisconsin, USA. We sampled 14CO2 profiles every three weeks during snow-free months through 2012 in three intact plots and one trenched plot that excluded roots. Respired Δ14CO2 declined through the summer in intact plots, shifting from an older C composition that contained more bomb 14C to a younger composition more closely resembling present 14C levels in the atmosphere. In the trenched plot, respired Δ14CO2 was variable but remained comparatively higher than in intact plots, reflecting older bomb-enriched 14C sources. Although respired Δ14CO2 from intact plots correlated with soil moisture, related analyses did not support a clear cause-and-effect relationship with moisture. The initial decrease in Δ14CO2 from spring to midsummer could be explained by increases in 14C-deplete root respiration; however, Δ14CO2 continued to decline in late summer after root activity decreased. We also investigated whether soil moisture impacted vertical partitioning of CO2 production, but found this had little effect on respired Δ14CO2 because CO2 contained modern bomb C at depth, even in the trenched plot. This surprising result contrasted with decades to centuries-old pre-bomb CO2 produced in lab incubations of the same soils. Our results suggest that root-derived C and other recent C sources had dominant impacts on respired Δ14CO2 in situ, even at depth. We propose that Δ14CO2 may have declined through late summer in intact plots because of continued microbial turnover of root-derived C, following declines in root respiration. Our results agree with other studies showing declines in the 14C content of soil respiration over the growing season, and suggest inputs of new photosynthates through roots are an important driver.

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Forage plant mixture type interacts with soil moisture to affect soil nutrient availability in the short term

Experimental Results ◽

10.1017/exp.2020.47 ◽

2020 ◽

Vol 1 ◽

Author(s):

S. Shepperd ◽

A. Thomson ◽

D. Beaumont ◽

T. Misselbrook ◽

H. Jones ◽

...

Keyword(s):

Soil Moisture ◽

Soil Carbon ◽

Soil Phosphorus ◽

Soil Nutrient ◽

Environmental Benefits ◽

Soil Function ◽

Floral Diversity ◽

Plant Mixture ◽

Soil Functionality ◽

Forage Mixtures

AbstractAgricultural intensification within forage systems has reduced grassland floral diversity by promoting ryegrass (Lolium spp.), damaging soil functionality which underpins critical ecosystem services. Diverse forage mixtures may enhance environmental benefits of pastures by decreasing nutrient leaching, increasing soil carbon storage, and with legume inclusion, reduce nitrogen fertilizer input. This UK study reports on how species-rich forage mixtures affect soil carbon, phosphorus, and nitrogen at dry, medium and wet soil moisture sites, compared to ryegrass monoculture. Increasing forage mixture diversity (from 1 to 17 species) affected soil carbon at the dry site. No effect of forage mixture on soil phosphorus was found, while forage mixture and site did interact to affect soil nitrate/nitrite availability. Results suggest that forage mixtures could be used to improve soil function, but longer-term studies are needed to conclusively demonstrate environmental and production benefits of high-diversity forages.

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Soil carbon release responses to long-term versus short-term climatic warming in an arid ecosystem

Biogeosciences ◽

10.5194/bg-17-781-2020 ◽

2020 ◽

Vol 17 (3) ◽

pp. 781-792 ◽

Cited By ~ 2

Author(s):

Hongying Yu ◽

Zhenzhu Xu ◽

Guangsheng Zhou ◽

Yaohui Shi

Keyword(s):

Soil Moisture ◽

Soil Carbon ◽

Field Experiments ◽

Sigmoid Function ◽

Desert Grassland ◽

Climatic Warming ◽

Short Term ◽

Exponential Relationship ◽

Carbon Release

Abstract. Climate change severely impacts the grassland carbon cycling by altering rates of litter decomposition and soil respiration (Rs), especially in arid areas. However, little is known about the Rs responses to different warming magnitudes and watering pulses in situ in desert steppes. To examine their effects on Rs, we conducted long-term moderate warming (4 years, ∼3 ∘C), short-term acute warming (1 year, ∼4 ∘C) and watering field experiments in a desert grassland of northern China. While experimental warming significantly reduced average Rs by 32.5 % and 40.8 % under long-term moderate and short-term acute warming regimes, respectively, watering pulses (fully irrigating the soil to field capacity) stimulated it substantially. This indicates that climatic warming constrains soil carbon release, which is controlled mainly by decreased soil moisture, consequently influencing soil carbon dynamics. Warming did not change the exponential relationship between Rs and soil temperature, whereas the relationship between Rs and soil moisture was better fitted to a sigmoid function. The belowground biomass, soil nutrition, and microbial biomass were not significantly affected by either long-term or short-term warming regimes, respectively. The results of this study highlight the great dependence of soil carbon emission on warming regimes of different durations and the important role of precipitation pulses during the growing season in assessing the terrestrial ecosystem carbon balance and cycle.

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Modelling carbon sink of urban street trees and soil in Helsinki, Finland

10.5194/egusphere-egu2020-13833 ◽

2020 ◽

Author(s):

Minttu Havu ◽

Liisa Kulmala ◽

Anu Riikonen ◽

Leena Järvi

Keyword(s):

Carbon Dioxide ◽

Soil Moisture ◽

Carbon Cycle ◽

Soil Carbon ◽

Urban Areas ◽

Carbon Dioxide Flux ◽

Specific Humidity ◽

Soil Conditions ◽

Surface Model ◽

Flow Measurements

A high proportion of anthropogenic carbon dioxide emissions originate from urban areas, which has led cities to become interested in reducing their own emissions and determining how much carbon could be sequestered by their own vegetation and soil. The challenge with the latter is that our current knowledge on carbon storage is based on data and models from natural and forest ecosystems, whereas the response of vegetation and soil to environmental factors most probably is altered in urban green space where the soil conditions, water availability and temperature are highly variable. Therefore, ecosystem models are required to correctly account for urban vegetation and soil to understand and quantify the biogenic carbon cycle in urban areas. In this study, urban land surface model SUEWS (the Surface Urban Energy and Water Balance Scheme) and the soil carbon decomposition model Yasso15 are used to simulate urban carbon cycle on two streets in Helsinki, Finland for years 2003-2016. Curbside trees (Alnus glutinosa and Tilia x Vulgaris) were planted while the two test streets were constructed in 2002. Thereafter, carbon and water fluxes and pools with detailed street tree soil compositions were monitored in 2002-2014. SUEWS creates a local spatially variable temperature and specific humidity environment which is used in the model runs. The modelled evaporation is evaluated against sap flow measurements and modelled soil moisture against soil moisture observations. The Yasso15 model is evaluated against loss-on-ignition based soil carbon measurements as it has not been previously evaluated in urban soils. The modelled carbon dioxide flux combined with the changes in the soil carbon stock is used to estimate the carbon cycle of urban street trees and soils.

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How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils

10.5194/egusphere-egu2020-13148 ◽

2020 ◽

Author(s):

Noah Sokol ◽

Steve Blazewicz ◽

Megan Foley ◽

Alex Greenlon ◽

Jennifer Pett-Ridge

Keyword(s):

Soil Moisture ◽

Soil Carbon ◽

Soil Microbial Communities ◽

Bulk Soil ◽

Carbon Pools ◽

Carbon Formation ◽

Soil Microbial ◽

Carbon Use Efficiency ◽

Use Efficiency ◽

Soil Carbon Formation

Carbon use efficiency (CUE) is theorized to be positively associated with the formation of microbially-derived, mineral-associated soil carbon.&#160; Yet few empirical studies have directly tested this relationship. Moreover, it is unclear: (1) how differences between distinct soil microbial communities (for example, differences in competitive interactions and/or growth rate among rhizosphere, detritusphere, and bulk soil communities) may yield different relationships between carbon-use efficiency and soil carbon formation, and (2) how microbial ecophysiology &#8211; such as physiological changes induced by drought &#8211; may modulate the strength and/or direction of the CUE-soil carbon relationship.To investigate these questions, we conducted a 12-week 13C tracer study to track the movement of two dominant sources of plant carbon &#8211;&#160;rhizodeposition and root detritus &#8211; into soil microbial communities and carbon pools under normal moisture vs drought conditions. Using a continuous 13CO2-labeling system, we grew the Mediterranean annual grass Avena barbata in controlled growth chambers and measured the formation of organic matter from 13C-enriched rhizodeposition. As the plants grew, we harvested rhizosphere and bulk soil at three time points (4, 8, and 12 weeks) to capture changes in soil carbon pools and microbial community dynamics. In parallel microcosms, we tracked the formation of soil carbon derived from 13C-enriched A. barbata root detritus during 12 weeks of decomposition; harvesting detritusphere and bulk soil at 4,8, and 12 weeks. In all microcosms, we manipulated soil moisture to generate drought (7.8 &#177; 2.1 % soil moisture) and &#8216;normal moisture&#8217; (15.1 &#177; 4.2 % soil moisture) treatments.In all samples (over 150 observations), we measured CUE via the 18O-H2O method, and quantified the formation of different 13C-soil organic carbon pools via density fractionation. Here we will present data on how soil moisture influences CUE in rhizosphere, detritusphere, and bulk soil communities, and whether differences in CUE are correlated with the formation of mineral-associated soil organic carbon. These results will help to illustrate whether CUE acts as a lynchpin variable with predictive power for stable soil carbon formation, or whether other microbial traits may require consideration.&#160;&#160;

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Climatic and landscape influences on soil moisture are primary determinants of soil carbon fluxes in seasonally snow-covered forest ecosystems

Biogeochemistry ◽

10.1007/s10533-015-0078-3 ◽

2015 ◽

Vol 123 (3) ◽

pp. 447-465 ◽

Cited By ~ 34

Author(s):

Clare M. Stielstra ◽

Kathleen A. Lohse ◽

Jon Chorover ◽

Jennifer C. McIntosh ◽

Greg A. Barron-Gafford ◽

...

Keyword(s):

Soil Moisture ◽

Soil Carbon ◽

Forest Ecosystems ◽

Carbon Fluxes ◽

Landscape Influences

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Carbon sequestration potential of street tree plantings in Helsinki

10.5194/bg-2021-242 ◽

2021 ◽

Author(s):

Minttu Havu ◽

Liisa Kulmala ◽

Pasi Kolari ◽

Timo Vesala ◽

Anu Riikonen ◽

...

Keyword(s):

Soil Moisture ◽

Carbon Sequestration ◽

Soil Respiration ◽

Carbon Cycle ◽

Soil Carbon ◽

Carbon Sequestration Potential ◽

Initial Carbon ◽

Street Tree ◽

Sequestration Potential ◽

Forested Ecosystems

Abstract. Cities have become increasingly interested in reducing their greenhouse gas emissions, and increasing carbon sequestration and storage in urban vegetation and soil as part of their climate mitigation actions. However, most of our knowledge on biogenic carbon cycle is based on data and models from forested ecosystems even though urban nature and microclimate are very different to those in natural or forested ecosystems. There is a need for modelling tools that can correctly consider temporal variations of urban carbon cycle and take the urban specific conditions into account. The main aims of this study are to examine the carbon sequestration potential of two commonly used street tree species (Tilia x vulgaris and Alnus glutinosa) and their soils by taking into account the complexity of urban conditions, and evaluate urban land surface model SUEWS and soil carbon model Yasso15 in simulating carbon sequestration of these street tree plantings at different temporal scales (diurnal, monthly and annual). SUEWS provides the urban microclimate, and photosynthesis and respiration of street trees whereas the soil carbon storage is estimated with Yasso. Both models were run for 2002–2016 and within this period the model performances were evaluated against transpiration estimated from sap flow, soil carbon content and soil moisture measurements from two street tree sites located in Helsinki, Finland. The models were able to capture the variability in urban carbon cycle due to changes in environmental conditions and tree species. SUEWS simulated the stomatal control and transpiration well (RMSE < 0.31 mm h−1) and was able to produce correct soil moisture in the street soil (nRMSE < 0.23). Yasso was able to simulate the strong decline in initial carbon content but later overestimated respiration and thus underestimated carbon stock slightly (MBE > −5.42 kg C m−2). Over the study period, soil respiration dominated the carbon exchange over carbon sequestration, due to the high initial carbon loss from the soil after the street construction. However, the street tree plantings turned into a modest sink of carbon from the atmosphere on annual scale as the tree and soil respiration approximately balanced photosynthesis. The compensation point when street trees plantings turned from annual source to sink was reached faster by Alnus trees after 12 years, while by Tilia trees after 14 years. Overall, the results indicate the importance of soil in urban carbon sequestration estimations.

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