Progress 08/01/03 to 07/31/07
Outputs
The goal of the project was to search for general patterns that describe the interactions between rhizosphere processes and soil carbon and nitrogen cycles. One of the key phenomena of the interactions is called the rhizosphere priming effect in which the activities of roots and rhizosphere microbes substantially control the level of soil carbon and nitrogen mineralization. We hypothesized that soil conditions impose more controls on the level of rhizosphere priming effects of the roots than plant species, and that roots of different tree species produce significantly different rhizosphere priming effects when they are grown in different soils. Our results tend to support the hypothesis. Soil types have stronger control on the magnitude of the rhizosphere priming effects than plant species do. Results from our second experiment suggest that different tree species stimulate soil organic matter decomposition through rhizosphere priming at different magnitudes. Soil
moisture, in concert with other factors, significantly affects the level of the rhizosphere priming effect. Furthermore, the rhizosphere priming effect on decomposition is a long lasting process, not a short pulse-type of phenomenon as has been believed. Our results also indicate that the rhizosphere priming effect has the potential to obscure the measurement of temperature sensitivity of soil organic matter decomposition, and to significantly mobilize a suit of other nutrients in addition to nitrogen.
Impacts
Soil-root interactions play a major role in regulating soil organic matter dynamics and nutrient availability. Different plant-soil systems are more sensitive to the rhizosphere priming effect than others. Our knowledge about the rhizosphere priming effect on soil organic matter decomposition can be incorporated into models of carbon cycling and soil management regimes.
Publications
- Bader, N. E. and W. Cheng. 2007. Rhizosphere priming effect of Populus fremontii obscures the temperature sensitivity of soil organic carbon respiration. Soil Biology and Biochemistry, 39: 600 - 606.
- Cheng, W. and F. A. Dijkstra. 2007. Theoretical proof and empirical validation of a continuous labeling method using naturally 13C-depleted carbon dioxide. Journal of Integrative Plant Biology, 49(3): 401-407.
- Dijkstra, F.A. and W. Cheng. 2007. Interactions between soil and tree roots accelerate long-term soil carbon decomposition. Ecology Letters, Vol. 10, doi: 10.1111/j.1461-0248.2007.01095.x
- Dijkstra, F.A. and W. Cheng. 2007. Moisture modulates rhizosphere effects on C decomposition in two different soil types. Soil Biology and Biochemistry, 39: 2264-2274.
- Johnson, D.W., F.A. Dijkstra, and W. Cheng. 2007. The effects of Glycine max and Helianthus annuus on nutrient availability in two soils. Soil Biology and Biochemistry, 39: 2160 - 2163.
- Cheng, W. and A. Gershenson. 2007. Carbon fluxes in the rhizosphere. In: The Rhizosphere - An Ecological Perspective, Z.G. Cardon and J.L. Whitbeck, (Eds.), Academic Press, San Diego. Pages 31 - 56.
- Dijkstra, F.A., W. Cheng, and D. W. Johnson. 2006. Plant biomass influences rhizosphere priming effects on soil organic matter decomposition in two differently managed soils. Soil Biology and Biochemistry, 38: 2519- 2526.
- Cheng, W., S.L. Fu, R.B. Susfalk, and R.J. Mitchell. 2005. Measuring tree root respiration using 13C natural abundance: rooting medium matters. New Phytologist, 167: 297-307.
- Cheng, W. and Y. Kuzyakov. 2005. Root effects on soil organic matter decomposition. In R. Zobel and S. Wright (eds.) Roots and Soil Management: Interactions Between Roots and Soil, Agronomy Monograph, no.48, ASA-SSSA-CSSA, Madison, WI, USA. Page: 119 - 143.
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Progress 10/01/05 to 09/30/06
Outputs
The goal of the project was to search for general patterns that describe the interactions between rhizosphere processes and soil carbon and nitrogen cycles. We hypothesized that soil conditions impose more controls on the level of rhizosphere priming effects of the roots than plant species, and that roots of different tree species produce significantly different rhizosphere priming effects when they are grown in different soils. Our results obtained so far tend to support the first hypothesis. Soil types have stronger control on the magnitude of the rhizosphere priming effects than plant species do. Results from our second experiment suggest that different tree species stimulate soil organic matter decomposition through rhizosphere priming at different magnitudes. Furthermore, the rhizosphere priming effect on decomposition is a long lasting process, not a short pulse-type of phenomenon as has been believed. Our results also indicate that the rhizosphere priming
effect has the potential to obscure the measurement of temperature sensitivity of soil organic matter decomposition.
Impacts
Our results so far strongly suggest that the rhizosphere priming effect resulted from soil-root interactions plays a major role in regulating soil organic matter dynamics and different plant-soil systems are more sensitive to the priming effect than others. Our knowledge about the rhizosphere priming effect on soil organic matter decomposition should be incorporated into soil management regimes.
Publications
- Dijkstra, F. A., W. Cheng, and D. W. Johnson. 2006. Plant biomass influences rhizosphere priming effects on soil organic matter decomposition in two differently managed soils. Soil Biology and Biochemistry 38: 2519-2526.
- Cheng, W. and A. Gershenson. 2007. Carbon fluxes in the rhizosphere. In: The Rhizosphere - An Ecological Perspective, Z.G. Cardon and J.L. Whitbeck, (Eds.), Academic Press, San Diego. Pages 29-54.
- Cheng, W., and F. A. Dijkstra. 2007. Theoretical proof and empirical validation of a continuous labeling method using naturally 13C-depleted carbon dioxide. Journal of Integrative Plant Biology. In press.
- Bader, N. E. and W. Cheng. 2007. Rhizosphere priming effect of Populus fremontii obscures the temperature sensitivity of soil organic carbon respiration. Soil Biology & Biochemistry 39: 600-606.
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Progress 10/01/04 to 09/30/05
Outputs
The goal of this project is to search for general patterns that govern the interactions between rhizosphere activities and soil carbon and nitrogen cycles in two experiments. Continuous labeling facility is required to carry out these experiments. We have successfully established two continuous labeling facilities, a plant growth chamber and a greenhouse at University of California, Santa Cruz. We have finished the first experiment studying the control of root-associated processes on soil organic matter decomposition using two plant species (soybean and sunflower) and two soils under different managements, an organically farmed soil and a soil from an annual grassland near the organic farm. Results of the first experiment indicated that soil types have a stronger control on the magnitude of rhizosphere priming effects than plant species does, confirming our first hypothesis. The second experiment is ongoing. We are collecting samples and analyzing data. We aim to
finish the second experiment within the next year.
Impacts
Our results indicate that soil types and properties have stronger control on the rate of soil organic matter loss than plant species do. These results suggest that different management practices not only affect the total organic matter input to the soil system, but also influence the rate of organic matter loss through rhizosphere effects. Some soil types may particularly be susceptible to organic matter loss via rhizosphere priming than other soil types.
Publications
- Dijkstra, F.A., W. Cheng and D. W. Johnson. 2006. Soil types and plant biomass influence rhizosphere priming effects on soil organic matter decomposition. Soil Biology & Biochemistry. In press.
- Cheng, W. and A. Gershenson. 2006. Carbon fluxes in the rhizosphere. In Zoe. Cardon and Julie whitbeck (eds) The Rhizosphere; An Ecological Perspective, Z.G. Cardon and J.L. Whitbeck, editors, Academic Press, San Diego. USA. In press.
- Cheng W Fu S Susfalk RB Mitchell RJ. 2005. Measuring tree root respiration using 13C natural abundance: rooting medium matters. New Phytologist, 167: 297-307.
- Cheng, W. and Y. Kuzyakov. 2005. Root effects on soil organic matter decomposition. In R. Zobel and S. Wright (eds.) Roots and Soil Management: Interactions Between Roots and Soil, Agronomy Monograph, no.48, ASA-SSSA-CSSA, Madison, WI, USA. Page: 119-143.
- Fu S. & Cheng W. 2004. Defoliation affects rhizosphere respiration and rhizosphere priming effect on decomposition of soil organic matter under a sunflower species: Helianthus annuus. Plant Soil, 263: 345-352.
- Kuzyakov Y Cheng W 2004 Photosynthesis controls of CO2 efflux from maize rhizosphere. Plant Soil, 263: 85-99.
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Progress 10/01/03 to 09/30/04
Outputs
One of the objectives of the project was to investigate the influence of plant roots on the loss of soil organic matter through decomposition for soils under different management regimes. During this funding period, we instrumented novel continuous labeling facilities with naturally 13C-depleted CO2 located on the campus of the University of California-Santa Cruz. In these facilities, we tested the control of root-associated processes on soil organic matter decomposition using two plant species (soybean, Glycine max, and sunflower, Helianthus annus) and two differently managed soils, an organically farmed soil and a soil from an annual grassland. Based on data obtained, the natural 13C-labeling approach was successful. Soil organic matter decomposition in the organically farmed soil increased up to 61% compared to decomposition rates in the no-plant control, while the annual grassland soil showed much smaller rhizosphere effects on soil organic matter decomposition
(up to 5% increase). Our findings indicated that soils under different management regimes were susceptible to root-stimulated loss of soil organic matter at much different levels.
Impacts
The results obtained so far suggested that the interactions between plant roots and soils under different levels of disturbance and management regimes resulted in significantly different level of soil organic matter loss through decomposition. This information is useful for better management of soil resources.
Publications
- Fu, S. and W. Cheng. 2005. Defoliation affects rhizosphere respiration and rhizosphere priming effect on decomposition of soil organic matter under a sunflower species: Helianthus annuus. Plant and Soil, in press
- Kuzyakov, Y. and W. Cheng. 2004. Photosynthesis controls of CO2 efflux from maize rhizosphere. Plant and Soil, 263:85-99
- Cheng, W. and Y. Kuzyakov. 2004. Root effects on soil organic matter decomposition. IN: S. Wright et al (eds.) Interactions between Roots and Soil, Soil Science Society of America Monograph. In press.
- Cheng, W. and A. Gershenson. 2005. Carbon fluxes in the rhizosphere. In Zoe. Cardon and Julie whitbeck (eds) The Rhizosphere; An Ecological Perspective. Elsevier. In review.
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