Relative Contribution of Biologic Soil Crusts to Ecosystem CO2

Project Number:

02R-06

Project Duration:

30 months

Dates:

May 1, 2002 to October 31, 2004

Institution of Principle Investigator while on this project:

Ben-Gurion University of the Negev

Investigators (most current known information)

Karnieli, Arnon (PI)

Head, Remote Sensing Laboratory, Remote Sensing Laboratory, Ben-Gurion University of the Negev, Sede J. Blaustein Institute for Desert Research, Sede Boker Campus 84990, ISRAEL

TEL: +972-8-659-6855, FAX: +972-8-659-6704, Email: karnieli@bgumail.bgu.ac.il

Huete, Alfredo

Professor, Soil, Water, & Environmental Sciences, The University of Arizona, Shantz 430, Tucson AZ 85721

TEL: +1-520-621-3228, FAX: +1-520-621-1647, Email: ahuete@ag.arizona.edu

Huxman, Travis

Assistant Professor, Department of Ecology and Evolutionary Biology, The University of Arizona, Bio Science West 310, Tucson AZ 85721

TEL: +1-520-621-8220, FAX: +1-520-621-9190, Email: huxman@ag.arizona.edu

Shachak, Moshe

Professor, Ben-Gurion University of the Negev, Mitrani Center for Desert Ecology, Institute for Desert Research, Sede Boqer 84990, ISRAEL

TEL: +972-8-659-6786, FAX: +972-8-659-6772, Email: shachak@bgumail.bgu.ac.il

Yakir, Dan

Weizmann Institute of Science, Environmental Sciences and Energy Research, Rehovot 76100, ISRAEL

TEL: +972-8-934-2549, FAX: +972-8-934-4124, Email: ciyakir@wisemail.weizmann.ac.il

Proposal Abstract

The project is dealing with assessing the relative contribution of biologic soil crusts to ecosystem CO₂ fluxes in semiarid environments, by conventional and remote sensing methods. Semiarid ecosystems with biological soil crusts (BSC) have been neglected in considerations of carbon exchange budgets and mostly laboratory or limited small-scale research had been conducted to address the role of this type of vegetation in trace gas cycling. Thus, the objective of the project was to investigate the contribution of CO₂ exchange between biological soil crusts (BSC) and the atmosphere to ecosystem carbon exchange in the semiarid region with respect to higher plants.

Three types of measurements were conducted: carbon exchange measurements; complementary soil and biological measurements; and remote sensing and spectral measurements. Ground-based measurements were consisted of enclosure studies (cuvette studies) for determination of CO₂ exchange rates between soil crust/atmosphere as well as higher plants/atmosphere in order to get an overview about the capability and share in total exchange of soil crusts, annual and perennial plants. Complementary measurements consisted of the determination of the soil moisture content, soil temperature, air temperature, light, soil inorganic, and organic carbon content, as well as biomass determination. All these data sets were related to spectral analysis and image processing.

From the ground measurements, fairly good correlations were found between the Normalized Difference Vegetation Index (NDVI) and the CO₂ fluxes on a seasonal scale. Hence, the NDVI successfully indicates the potential magnitude and capacity of the BSC's assimilation activity. The linear mixture successfully describes the phenological cycles of the BSC, annual, and perennial plants and corresponds well to the satellite data. Moreover, the model enables annual changes of the phenology cycle and the growing season length to be distinguished. Both the linear mixture model and the derived NDVI values recorded the recovery of the BSC at the beginning of the wet season before annuals had germinated. Finally, it is concluded that a combination of CO₂ exchange measurements, linear mixture model, and NDVI values is suitable for monitoring BSC's productivity in arid regions.

Study sites are located in the Negev Desert in Israel are representative of much larger arid areas in the Sahara, Sahel, Middle East, Central Asia, Gobi desert, Australia, and North America. Consequently, our results will provide information that can be extrapolated to other desert regions for first estimates of the regional/global scale importance of BSC to ecosystem functioning.

Thus, the results will help in reducing uncertainties in semiarid carbon budget through assessing the relative contribution of biological soil crusts to the ecosystem CO₂ fluxes. Combining direct CO₂ flux measurements with remote sensing techniques has the important advantages of providing the necessary calibration and validation of the remote sensing measurements, that can than be applied with more confidence in areas where direct measurements are not possible.