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Visiting Scholar Research:
Estimating Above-ground Primary Productivity Through
Computer Modeling

by Jinzhi Wang, with Janet Patton


Highlights


Table of Contents

Introduction

Education and Experience

Research Interests

Current Project

Related Learning Experience

Summary


 

Introduction

There are many similarities between the Coteau of North Dakota and the typical grassland ecosystem in Inner Mongolia. Both sites lie at almost the same latitude and have a continental climate, where the winter is generally very cold and the summer is warm. Both locations show large annual variations in both precipitation and mean temperature. The average annual mean temperature and annual precipitation at the CGREC from 1989 to 2005 were 40º F and 19 inches, respectively, compared to 33º F and 14 inches for the typical grassland of Inner Mongolia. Also, both sites are mainly dominated by C3 (cool season) plants. After comparing these two sites, researchers have found that the net primary productivity in the mixed-grass prairie of the United States is much higher than that in Inner Mongolia, which may be due to higher precipitation and temperatures. This study will provide useful information for grassland management by comparing these two grasslands.


Education and Experience

Jinzhi Wang earned a bachelor’s degree from the Shenyang Agricultural University in 2003, where she majored in Soil and Water Conservation. After graduation, she engaged in grassland ecology research at the Inner Mongolia Grasslands Ecosystem Research Station in northern China (see Map), which is managed by the Institute of Botany of the Chinese Academy of Sciences. From September 2005 to January 2006, she was a Visiting Scholar at the University of New Hampshire. In April 2006, she came to the Central Grasslands Research Extension Center (CGREC), also as a Visiting Scholar.


Research Interests

Jinzhi’s research interest is in the role of the grassland ecosystem on the carbon cycle, and on the influence of climate and grazing intensity on biomass production in the grassland ecosystem. She has also been studying the responses of greenhouse gases (CO2, CH4, and N2O) of the typical grassland ecosystem to global climate change. This work involves predicting the influence of grazing management and climate on ecosystem function at a local site using the CENTURY and Denitrification-Decomposition (DNDC) computer models, and studying the influence of temperature on root respiration in the grassland ecosystem.


Current Project

Jinzhi’s research at CGREC involves grassland productivity and the carbon cycle. Researchers recognize the significant influence of the terrestrial biosphere (land plants and animals) on the global carbon balance. However, of the 5.5 billion metric tons of carbon produced per year from burning fossil fuels, 1 to 3 billion metric tons per year is taken up by a CO2 sink that has not yet been clearly identified. Without accounting for the fate of this “missing” carbon, predictions of future CO2 concentration and climate change will remain uncertain. To assess the future role of ecosystems in the global context, available local observations need to be put on a global scale, using physiological and physical parameters for the development of terrestrial ecosystem models.


When Jinzhi arrived at CGREC in April, she hoped to achieve the research goal of simulating plant biomass production in a Northern mixed-grass prairie using the CENTURY and the DNDC models. Both models have their own specific characteristics; by comparing the two models, one can tell which model best simulates the grassland ecosystem and provides more useful information for management of the grassland in the future. The CENTURY model simulates the long-term dynamics of carbon, nitrogen, phosphorus, and sulfur for different plant-soil systems. It has been successfully used to simulate carbon dynamics, especially in soil organic matter, across a variety of land-use, management, and climate types, and it is particularly good in describing grassland ecosystems. The model includes three soil organic matter pools (active, slow, and passive) with different potential decomposition rates. The DNDC model is a general model of carbon and nitrogen biogeochemistry in agricultural ecosystems, and soil organic matter is described for four major pools: plant residue (i.e., litter), microbial biomass, humads (i.e., active humus), and passive humus.


Above-ground biomass data collected in the field are used to test the models. During her stay, Jinzhi learned the field method for estimating above-ground biomass used at CGREC for the past 18 years. Sampling is conducted in July, when peak production occurs based on the phenological stage of development of the major plant species. Ten 0.25 m2 quadrats on each of two range sites per pasture are used: five within portable wire cages that exclude grazing, and five outside the cages where grazing has occurred. Above-ground biomass is measured with a harvest technique in which standing crop samples are clipped to ground level. All samples are oven-dried at 150º F for 48 hours before weighing.


Along with vegetation data, data on soil texture, weather, and grassland management from the CGREC database are used as parameters in the models. After both models are run, information is obtained about soil organic matter, above-ground and below-ground biomass, and the water-budget under different management practices, such as grazing intensity, fertilization, irrigation, harvest, and organic matter addition. To validate the models, the above-ground biomass data collected in the field are compared with the predictions. The models can then be compared to one another to determine which model is most suitable to simulate the mixed-grass prairie.


The dominant influence on the mixed-grass prairie can be determined and future trends predicted. This information on grasslands is essential for rangeland ecosystem management and to evaluate the global carbon cycle. Although the models’ simulated results do not match the field biomass data very well, Jinzhi is currently adjusting the parameters and formulation. She will also be able to compare these results with those from Inner Mongolia. A complete report will be posted on CGREC’s web site, www.ag.ndsu.nodak.edu/streeter/ when it becomes available.


Related Learning Experience

During her time at CGREC, Jinzhi not only learned new methods used to measure net primary production, plant frequency, and how to manage the prairie, but also had an introduction to different scientific instruments, such as the soil moisture probe used to measure soil water content at different levels, and the Li-Cor 6400 portable photosynthesis system to measure root/soil respiration and plant photosynthesis. In order to meet special requirements, the scientists at CGREC have improved the equipment, and now Jinzhi and other visiting students will be able to use these new ideas when they return to China.


Summary

Results from this study are currently being analyzed. When the research is completed, the results will improve our understanding of the carbon cycle and productivity of grassland ecosystems and will also provide useful information for grassland management in China and the U.S. For further information about this study, visit www.ag.ndsu.nodak.edu/streeter/.


NDSU Central Grasslands Research Extension Center
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