Progress 07/01/02 to 06/30/08

Outputs
OUTPUTS: During the past year, worked focused on addressing carbon exchange between Great Basin plant communities and the atmosphere. Unfortunately, estimates of net ecosystem exchange of carbon (NEE) based on scaled-up measurements of chamber measures of soil and leaf CO2 exchange are most often greater than from eddy covariance. To assess problems associated with quantifying NEE, a large portion of this study focused on Bromus tectorum (cheatgrass), an important exotic annual grass in the Great Basin. Significant results from the past year were: a) Annual NEE measured for B. tectorum using a combination of methods was estimated at -26 +- 29 g C m-2, and NEE is likely near 0 for this community when averaged across years. It was concluded that average NEE under warmer temperatures regime (climate change) remain near 0 on average. b) Annual soil efflux was estimated at 406 +- 73 g C m-2. Nearly all of the variability in heterotrophic respiration during the non-growing season was explained by soil moisture and temperature differed in timing and magnitude from autotrophic respiration. PARTICIPANTS: Utah State University TARGET AUDIENCES: Rangeland managers (federal, state, private, NGO), policy makers (federal, state), scientists involved with carbon fluxes and/or climate change. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This project focused on basic research elements that may have important implications for management. These include assessing the carbon exchange in cheatgrass communities and implications of this invasive species on the global carbon budget and under climate change. Important evaluations of using eddy covariance as a monitoring tool were also conducted. Important new contributions were on understanding the functional importance of hydraulic redistribution. Significant findings from the project include: 1) Because heterotrophic respiration is primarily dependent on NPP from the previous year, we conclude Bromus tectorum stands tend to be approximately neutral for CO2 on a biennial time scale. In addition, since annual NEE of B. tectorum in this study was indistinguishable from that of native species assemblages that are being replaced by B. tectorum, we find no evidence of B. tectorum invasion altering land surface feedbacks to atmospheric CO2 and therefore, no evidence of invasion causing feedbacks to climate change. 2) Agreement was found among NEE measurements using different approaches in a wide range of conditions during canopy absence indicating that each measurement technique is fundamentally sound. However, disagreement among some measurements was found, indicating limitations with each method. Eddy covariance agreed with other measurements during the day but underestimated nocturnal respiration over a vegetated surface; the underestimation of NEE increased with LAI. We also saw evidence of apparent uptake with eddy covariance of 3 umol m-2 s-1 over a non-photosynthesizing surface in warm, conditions. The chamber method was incorrect in snow and the gradient method did not measure during summer rain. To estimate NEE in all conditions, a combination of methods is recommended. 3) High densities of Anabrus simplex (Mormon crickets) periodically afflict large areas of the western USA and could make them a significant source of CO2. Mean respiration from Mormon crickets was 0.96 g CO2 m-2 d-1. Since Mormon crickets are present when net carbon exchange (NCE) is otherwise near zero, they can potentially alter NCE between 20% (juniper woodland) and 60% (crested wheatgrass pasture). 4) Functional elements of hydraulic redistribution were assessed: Hydraulic redistribution is the movement of soil water by roots during the night between areas of high water potential and areas of low water potential. Important findings include: a) Artemisia tridentata (big sagebrush) was found to rapidly (within hours) redistribute significant quantities of rain water to depth. This movement of water was estimated to provide improved plant water status during late summer drought. b) Roots of B. tectorum individuals can continue to serve as conduits for water following senescence as long as those roots remain intact and hydrated in the soil. Soil water lifted by roots of senesced plants in the early summer may be used by the offspring of those individuals to enhance persistence following autumn germination.

Publications

• Leonard, E.D., Monaco, T.A., Stark, J.M., Ryel, R.J. 2008. Invasive forb, annual grass, and exotic shrub competition with three sagebrush-steppe growth forms: acquisition of a spring 15N tracer. Invasive Plant Science and Management :in press.
• Peek, M.S., Leffler, A.J., Hipps, L., Ivans, S., Ryel, R.J., Caldwell, M.M. 2006. Significant root turnover and relocation in the profile does not correspond with persistent foliage in Utah juniper (Juniperus osteosperma). Tree Physiology 26:1469-1476.
• Hibbard KA, Law BE, Reichstien M, Sulzman J, (contributors: Aubinet M, Baldocchi D, Bernhofer C, Bolstad P, Bosc A, Campbell JL, Cheng 2005. An Analysis of Soil Respiration Across Northern Hemisphere Temperate Ecosystems. Biogeochemistry 73 73:29-70.
• Leffler AJ, Peek MS, Ryel RJ, Ivans CY, Caldwell MM 2005. Hydraulic redistribution through the root systems of senesced plants. Ecology 86:633-642.
• Peek MS, Leffler AJ, Ivans CY, Ryel RJ Caldwell MM 2005. Fine root distribution and persistence under field conditions of three co-occurring Great Basin species of different life form. New Phytologist 165:171-180.
• Peek, M.S., Leffler, A.J., Ivans, C.Y., Ryel, R.J., Caldwell, M.M. 2004. Contrasting fine root properties in three co-occurring Great Basin species of different life form. Abstracts of Ecological Society of America 89th meeting, August.
• Leffler, A.J., Ivans, C.Y., Ryel, R.J., Caldwell, M.M. 2004. Gas exchange and growth responses of desert shrubs Artemisia tridentata and Chrysothamnus nauseosus to shallow-versus deep-soil water in a glasshouse experiment. Environmental and Experimental Botany 51:9-19.
• Ryel, R.J. 2004. Hydraulic redistribution. Progress in Botany 65:413-435.
• Ryel, R.J. 2004. Hydraulic redistribution: new perspectives on importance and function. Proceedings of the VII Simposio Luso-Espanhol: Relacoes Hidricas das Plantas, Faro, Portugal. September 27-29, pp. 23-26.
• Ryel, R.J., Leffler, A.J., Peek, M.S., Ivans, C.Y., Caldwell, M.M. 2004. Water conservation in Artemisia tridentata through redistribution of precipitation. Oecologia 141:335-345.
• Leffler, A.J., Peek, M.S., Ryel, R.J., Caldwell, M.M. 2003. Hydraulic redistribution: The role of shoots. Abstracts of Ecological Society of America 88th meeting.
• Ryel, R.J., Caldwell, M.M., Leffler, A.J. and Yoder, C.K. 2003. Rapid soil moisture recharge to depth by roots in a stand of Artemisia tridentata. Ecology 84:757-764.
• Peek, M.S., Leffler, A.J., Flint, S.D. and Ryel, R.J 2003. How Much Variance is Explained by Ecologists Additional perspectives. Oecologia 137:161-170.
• Yoder, C.K., Leffler, A.J., Spaulding, U., Stark, J.M., Ryel, R.J. and Caldwell, M.M. 2003. Nitrogen uptake and sensitivity of belowground responses of Artemisia tridentata and Agropyron desertorum to summer rainfall events of two intensities. Oecologia 134:317-324.
• Carvalho, L.M., Correia, P.M., Ryel, R.J. and Martins-Loucao, M.A. 2003. Spatial variability of arbuscular mycorrhizal fungal spores in two natural plant communities. Plant and Soil 251:227-236.
• Ryel, R.J., Caldwell, M.M., Yoder, C.K., Or, D., Leffler, A.J. 2002. Hydraulic redistribution in a stand of Artemisia tridentata: evaluation of benefits to transpiration assessed with a simulation model. Oecologia 173:184.
• Leffler, A.J., Ryel, R.J., Hipps, L., Ivans, S., Caldwell, M.M. 2002. Carbon acquisition and water use in northern Utah Juniperus osteosperma (Utah juniper) population. Tree Physiology 22:1221-1230.

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: The goal of this project was to address carbon fluxes in semi-arid plant communities in the Great Basin using eddy covariance and other approaches. Eddy covariance measures net ecosystem exchange of CO2 (NEE) at a scale between chambers and large-scale models, and is a link between small and large scale estimates of NEE. However, estimates of NEE based on scaled-up measurements of soil and leaf CO2 exchange are most often greater than from eddy covariance, and identifying the source of measurement discrepancy is difficult due to ecosystem complexity. To assess problems associated with quantifying NEE, a large portion of this study focused on Bromus tectorum (cheatgrass), an exotic annual grass in the Great Basin that has expanded to cover over 7% of the landscape. The simplicity of this community allowed for assessing the accuracy of measurement approaches. Three objectives were addressed: 1) quantify NEE and respiration in a B. tectorum stand; 2) evaluate CO2 flux estimates from common measurement techniques; and 3) partition root and microbial respiration to better understand the carbon cycle of B. tectorum. NEE was measured with 1) eddy covariance, 2) a combination of soil respiration and leaf gas exchange measurements, and 3) a combination of soil respiration measurements and plant gas exchange estimated from periodic harvest data. Both time series and annual sums were compared among methods. A combination of flux measurements from each method taken throughout the year 2005, indicated that the system was a weak sink with annual uptake of 80 to 84 g C m-2. Nearly all photosynthesis occurred between February and August but respiration continued in small amounts throughout the year except winter when it largely ceased. Annual NEE estimated for soil efflux was 406 +- 73 g C m-2. Agreement was found among NEE measurements using different approaches in a wide range of conditions during canopy absence indicating that each measurement technique is fundamentally sound. However, disagreement among some measurements was found, indicating specific limitations with each method. Eddy covariance agreed with other measurements during the day but underestimated nocturnal respiration over a vegetated surface; the underestimation of NEE increased with LAI. We also saw evidence of apparent uptake with eddy covariance of 3 u 925, Carbon dynamics of cool desert mol m-2 s-1 over a non-photosynthesizing surface in warm, conditions. The chamber method was incorrect in snow and the gradient method did not measure during summer rain. To measure NEE in all conditions, a combination of all three methods is recommended. This study also estimated autotrophic soil respiration with two approaches and found that nearly all of the variability in heterotrophic respiration during the non-growing season was explained by soil moisture and temperature. Results suggest B. tectorum and microbes respond differently to moisture and temperature. Nonetheless, with warmer temperatures, NEE may remain unchanged due to buffering effects of a minor species in the system. PARTICIPANTS: Utah State University TARGET AUDIENCES: Rangeland managers (federal, state, private, NGO), policy makers (federal, state), scientists involved with carbon fluxes and/or climate change.

Impacts
Eddy covariance is a technique that has been globally employed to assess carbon sequestration, but has not been effectively evaluated as a tool for such measurements. This research is assessing the effectiveness of the eddy covariance technique as a tool for measuring carbon sequestration by comparing eddy covariance estimates of carbon exchange with two independent estimates. Eddy covariance is also being used to estimate carbon sequestration in cheatgrass, crested wheatgrass, sagebrush and Utah juniper communities that will help in assessing the importance of the Intermountain West as a carbon sink (or source) related to increasing atmospheric carbon dioxide. Poster Presentations Myklebust M, Hipps L, Ryel R (2007) Eddy covariance measurement verification and partitioning of soil respiration in a semi-arid grass, Bromus tectorm. Workshop Marie Curie-iLEAPS - Models: Towards a process-based description of trace gas emissions in land surface models, Helsingborg, Sweden, 16- 19-Oct-2007.

Publications

• Ryel, R.J., Ivans, C.Y., Peek, M.S., Leffler, A.J. 2007. Functional differences in soil water pools: a new perspective on plant water use in water-limited ecosystems. Progress in Botany 69:397-422.
• Leonard, E.D., Monaco, T.A., Stark, J.M., Ryel, R.J. 2007. Invasive forb, annual grass, and exotic shrub competition with three sagebrush-steppe growth forms: acquisition of a spring 15N tracer. Invasive Plant Science and Management :in press.
• Beyschlag, W., Ryel, R.J. 2007. Plant physiological ecology: An essential link for integrating across disciplines and scales in plant ecology. Flora 202:608-623.
• Beyschlag, W., Ryel, R.J. 2007. Canopy modeling. Handbook of Functional Plant Ecology, 2nd Edition. Marcel Dekker Inc., New York, pp. 627-653.
• Leffler, A.J., Peek, M.S., Hipps, L., Ivans, S., Ryel, R.J., Caldwell, M.M. 2007. Potential contribution of respiration by Anabrus simplex (Mormon crickets) to net CO2 exchange in three Great Basin ecosystems. Western North American Naturalist 67:109-119.

Progress 01/01/06 to 12/31/06

Outputs
Work this past year has largely focused on validation of approaches to measuring soil efflux and partitioning of soil respiration for a cheatgrass (Bromus tectorum) stand. In general, clear agreement was found between the three approaches, but under certain conditions, estimates diverged. Conditions under which the methods disagreed usually related to periods during and immediately following precipitation events. This work helps confirm that eddy-covariance methods for measuring net ecosystem exchange and soil efflux seems to work in grasslands under most environmental conditions. Also, a model for heterotrophic soil efflux was developed and used to partition soil efflux into auto- and heterotrophic components. Although the method isn't directly transferable to most systems, it shows a unique solution to the problem of partitioning soil efflux that may be modified to suit other situations. This research was presented as a poster at both the Ecological Society of America meeting in Memphis, TN in August, 2006 and at the AmeriFlux meeting in Boulder, CO in October, 2006. In addition, carbon dioxide and water vapor exchange between the atmosphere and four plant communities (Utah juniper, big sagebrush, crested wheatgrass, and cheatgrass) were again collected at half hour intervals throughout 2006 using open-path eddy covariance instrumentation (LiCor 7500). Also measured at half hour intervals were soil CO2 fluxes using dual wavelength infrared sensors for CO2 that were installed at each site. Model development to simulate carbon dioxide and water vapor exchange between these plant communities and the atmosphere is essentially completed, and parameters for model have been collected. The model will soon be applied to the cheatgrass community to better understand the mechanisms affecting carbon exchange. A series of publications from this project is currently being developed and will be submitted during 2007.

Impacts
Eddy covariance is a technique that has been globally employed to assess carbon sequestration, but has not been effectively evaluated as a tool for such measurements. This research is assessing the effectiveness of the eddy covariance technique as a tool for measuring carbon sequestration by comparing eddy covariance estimates of carbon exchange with two independent estimates. Eddy covariance is also being used to estimate carbon sequestration in cheatgrass, crested wheatgrass, sagebrush and Utah juniper communities that will help in assessing the importance of the Intermountain West as a carbon sink (or source) related to increasing atmospheric carbon dioxide.

Publications

• (2007; 2 others in press)
• Peek MS, Leffler AJ, Hipps L, Ivans S, Ryel RJ, Caldwell MM (2006) Significant root turnover and relocation in the profile does not correspond with persistent foliage in Utah juniper (Juniperus osteosperma). Tree Physiology 26:1469-1476.

Progress 01/01/05 to 12/31/05

Outputs
Carbon dioxide and water vapor exchange between the atmosphere and four plant communities (Utah juniper, big sagebrush, crested wheatgrass, and cheatgrass) were collected at half hour intervals throughout 2005 using open-path eddy covariance instrumentation (LiCor 7500). Also measured at half hour intervals were soil CO2 fluxes using dual wavelength infrared sensors for CO2 that were installed at each site. This permitted continuous measurement of soil respiration to be compared with the eddy flux measurements. Synthesis of flux data and other types of data from previous years is continuing. In addition, plant structural data was collected regularly during the growing season. Synthesis of existing data resulted in several publications. A major research focus is to compare three methods of estimating net ecosystem exchange of CO2 a cheatgrass stand in Malta, ID. The methods are: 1. the eddy covariance technique, 2. a modeling approach based on direct instantaneous measurements of plant gas exchange and soil efflux, and 3. biweekly net primary production measurements combined with measurements of heterotrophic soil efflux with the recently acquired LI-8100. This research was presented as a poster in the AmeriFlux meeting in Boulder, CO in October, 2005 and was well received. This work is in line with the North American Carbon Program that states AmeriFlux stations must build process-based models of assimilation and respiration in order to enable net ecosystem exchange (NEE) predictions for similar vegetation stands across the landscape.

Impacts
Eddy covariance is a technique that has been globally employed to assess carbon sequestration, but has not been effectively evaluated as a tool for such measurements. This research is assessing the effectiveness of the eddy covariance technique as a tool for measuring carbon sequestration by comparing eddy covariance estimates of carbon exchange with two independent estimates. Eddy covariance is also being used to estimate carbon sequestration in cheatgrass, crested wheatgrass, sagebrush and Utah juniper communities that will help in assessing the importance of the Intermountain West as a carbon sink (for source) related to increasing atmospheric carbon dioxide.

Publications

• Peek, M.S., Leffler, A.J., Ivans, C.Y., Ryel, R.J., Caldwell, M.M. 2005. Fine root distribution and persistence under field conditions of three co-occurring Great Basin species of different life form. New Phytologist 165:171-180.
• Leffler, A.J., Peek, M.S., Ryel, R.J., Ivans, C.Y., Caldwell, M.M. 2005. Hydraulic redistribution through the root systems of senesced plants. Ecology 86:633-642.
• Hibbard, K.A., Law, B.E., Reichstien, M., Sulzman, J., (contributors: Ryel R, Turcu V, and 29 others) (2005) An Analysis of Soil Respiration Across Northern Hemisphere Temperate Ecosystems. Biogeochemistry 73:29-70.

Progress 01/01/04 to 12/31/04

Outputs
Carbon dioxide and water vapor exchange between the atmosphere and four plant communities (Utah juniper, big sagebrush, crested wheatgrass, and cheatgrass) were collected at half hour intervals throughout 2004 using open-path eddy covariance instrumentation (LiCor 7500). Also measured at half hour intervals were soil CO2 fluxes using dual wavelength infrared sensors for CO2 that were installed at each site. This permitted continuous measurement of soil respiration to be compared with the eddy flux measurements. Synthesis of flux data and other types of data from previous years is continuing. In addition, plant structural data was collected regularly during the growing season. Synthesis of existing data resulted in several publications. Data was collected from three Bowen ratio stations during the year in cheatgrass, mixed grass-shrubland, and big sagebrush communities located in Malta (cheatgrass, mixed grass-shrubland) and Dubois (big sagebrush), ID. They have been part of the Agriflux network and have at least three years of data available for analysis. In addition, structural data has been collected regularly at these sites. An important finding during this past year was the inadequacy of either flux measuring system to measure nighttime CO2 fluxes. Insufficient upward movement of air seems to be a problem when wind is minimal. We are presently working to construct a model for nighttime respiration based on plant and soil respiration activity. Synthesis with a simulation model for whole system carbon dioxide and water vapor exchange will be initiated this year. This model considers carbon dioxide and water vapor exchange of plants and the soil with the atmosphere.

Impacts
This project will provide a better understanding of the exchange of carbon dioxide between the atmosphere and important and widespread Great Basin plant communities. This information will help determine the potential for storing atmospheric carbon in these plant communities and will provide input to agencies managing rangelands.

Publications

• Ryel, R.J., Leffler, A.J., Peek, M.S., Ivans, C.Y., Caldwell, M.M., 2004. Water conservation in Artemisia tridentata through redistribution of precipitation. Oecologia 141:335-345.
• Ryel, R.J., 2004. Hydraulic redistribution: new perspectives on importance and function. Proceedings of VII Simposium Luso-Espanhol: Relacoes Hidricas das Plantas. Faro, Portugal, 27-29 September. ISBN: 972-9341-38-9. pp. 23-26.
• Ryel, R.J., 2004, Hydraulic redistribution. Progress in Botany 65:413-435.
• Leffler, A.J., Ivans, C.Y., Ryel, R.J., Caldwell, M.M. 2004. Gas exchange and growth responses of desert shrubs Artemisia tridentata and Chrysothamnus nauseosus to shallow- versus deep-soil water in a glasshouse experiment. Environmental and Experimental Botany 51:9-19.

Progress 01/01/03 to 12/31/03

Outputs
Carbon dioxide and water vapor exchange between the atmosphere and four plant communities (Utah juniper, big sagebrush, crested wheatgrass, and cheatgrass) were collected at half hour intervals throughout 2003 using open-path eddy covariance instrumentation. Synthesis of this data and data from the previous year is continuing. In addition, plant structural data was collected in 2-3 week intervals during the growing season and soil water potentials were collected at half hour intervals throughout the year. Synthesis of existing data resulted in several publications. Three Bowen ratio stations were added to the carbon flux network we are monitoring. The vegetation types include cheatgrass, mixed grass-shrubland, and big sagebrush. These are located in Malta (cheatgrass, mixed grass-shrubland) and Dubois (big sagebrush), ID. They have been part of the Agriflux network and have at least three years of data available for analysis. In addition, structural data has been collected regularly at these sites. Several parameters for the integrative simulation model for whole system carbon dioxide and water vapor exchange were collected. This model considers carbon dioxide and water vapor exchange of plants and the soil with the atmosphere. The soil component continues to be developed, with emphasis on production and movement of carbon dioxide within the soil column.

Impacts
This project will provide a better understanding of the exchange of carbon dioxide between the atmosphere and important and widespread Great Basin plant communities. This information will help determine the potential for storing atmospheric carbon in these plant communities and will provide input to agencies managing rangelands.

Publications

• Ryel, R.J., Caldwell, M.M., Leffler, A.J. and Yoder, C.K. 2003. Rapid soil moisture recharge to depth by roots in a stand of Artemisia tridentata. Ecology 84:757-764.
• Peek, M.S., Leffler, A.J., Flint, S.D. and Ryel, R.J. 2003. How much variance is explained by ecologists? Additional perspectives. Oecologia 137:161-170.
• Yoder, C.K., Leffler, A.J., Spaulding, U., Stark, J.M., Ryel, R.J. and Caldwell, M.M. 2003. Nitrogen uptake and sensitivity of belowground responses of Artemisia tridentata and Agropyron desertorum to summer rainfall events of two intensities. Oecologia 134:317-324.
• Carvalho, L.M., Correia, P.M., Ryel, R.J. and Martins-Loucao, M.A. 2003. Spatial variability of arbuscular mycorrhizal fungal spores in two natural plant communities. Plant and Soil 251:227-236.

Progress 01/01/02 to 12/31/02

Outputs
Carbon and water vapor exchange between the atmosphere and four plant communities (Utah juniper, big sagebrush, crested wheatgrass and cheatgrass) were collected throughout the year. Synthesis of this data is currently being conducted. A first version of a simulation model for whole system carbon dioxide and water vapor exchange has been developed. This model considers carbon dioxide and water vapor exchange of plants and the soil with the atmosphere. Several of the input parameters for this model were collected this year.

Impacts
This project will provide a better understanding of the exchange of carbon dioxide between the atmosphere and four widespread Great Basin plant communities. This information will help determine the potential for storing atmospheric carbon in these plant communities and will provide input to agencies managing rangelands.

Publications

• Leffler A.J., Ryel R.J., Hipps L., Ivans S., Caldwell M.M. (2002) Carbon acquisition and water use in northern Utah Juniperus osteosperma (Utah juniper) population. Tree Physiology 22:1221-1230.