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The Visiting Scholars Program at CGREC

The Visiting Scholars Program, started in 2004, continues to benefit both CGREC and the Chinese Academy of Science Institute of Botany. This educational and scientific program allows young scholars from China to come to the United States to conduct research that is useful to land managers and producers in both countries.


Research by a Visiting Scholar at CGREC:
The Effects of Grazing Intensity on the Eco-Physiology of Range Plants

By Xueyan Zhao, with Janet Patton


Introduction


The goal of this study is to identify the effects of different grazing intensities on the eco-physiology (the effect of the environment on the physiology) of individual plants. The preliminary experiment is being conducted on overflow range sites at CGREC under four different grazing intensities: ungrazed, lightly, moderately, and extremely heavily grazed. Each grazing intensity is replicated on three pastures (Grazing Intensity Study). The six plant species under study are dominant species found on the Missouri Coteau: western wheatgrass (Agropyron smithii), fringed sage (Artemisia frigida), stiff sunflower (Helianthus rigidus), Kentucky bluegrass (Poa pratensis), stiff goldenrod (Solidago rigida), and western snowberry (Symphoricarpos occidentalis).


Methods


Plant leaves were collected from the range sites in the middle of July 2007. To determine specific leaf area (SLA=leaf area/leaf dry mass), the fresh leaves of each species were sealed immediately in plastic bags and leaf area was measured. After that, the leaves were dried in an oven at 700C until their weight reached a constant mass. Total nitrogen was determined using the Kjeldahl method. Total carbon was estimated using an elemental analyzer and fiber content was estimated using a fiber analyzer. Chlorophyll content was determined by extraction using 95% alcohol. Photosynthetic rate was measured in the field using the Li-Cor-6400.

 

To study the effects of grazing on leaf anatomy, 15 leaves of each of the six species were collected from each pasture. Leaf segments were fixed in FAA [formalin (33%): acetic acid (100%): ethanol (50%), 5:5:90] and dehydrated through a gradient series of ethanol concentrations, followed by infiltration with xylene. The leaves were then embedded in paraffin and sliced in 9 µm thick sections with a microtome. These transverse sections were then mounted on slides, stained with safranin-fast green-contrast stain, and sealed by glass covers with a Canadian balsam fixative. This work is still in progress, and the following information on leaf anatomy will be collected from these sections: the thickness of the upper cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, lower cuticle, and total lamina. In order to measure these indices, photographs of the slides will be analyzed using ImageJ software.


Results


Results from this study will show whether grazing intensity has an effect on leaf anatomy, specific leaf area, nitrogen, carbon, and fiber content, and photosynthetic rate. No similar experiment has been conducted on the effect of different grazing intensities on leaf structure. We speculate that because productivity is highest on the pastures with a moderate grazing intensity, the leaf structure will reflect this difference in some way. This experiment will help confirm the level of grazing intensity that is most beneficial to the rangeland. Information from this study will be useful to land managers concerned with forage quality and rangeland productivity.


Researcher’s Background and Research Interests


Xueyan Zhao in the CGREC Lab in 2007.Xueyan Zhao is a graduate student participating in the Visiting Scholars Program at CGREC and began her work here in June 2007 (Figure 1). She graduated from The Henan Normal University in 2005, majoring in biology, and is now pursuing her master’s degree at the Institute of Botany of the Chinese Academy of Sciences, working with Dr. Shiping Wang. She is from Henan province, which is about the size of North Dakota and located in central China. Henan has subtropical temperatures with an average annual temperature of 54 to 61°F and 180 to 240 frost-free days a year. Monsoon rains occur there, with an average annual rainfall of 20 to 35 inches. The population of the province was more than a hundred million people in 2007.


Xueyan’s research in rangeland eco-physiology at CGREC is similar to studies she has conducted at the Inner Mongolia Grasslands Ecosystem Research Station in northern China. This region is much like North Dakota with regard to climate and vegetation. After she returns to China in November, she hopes to continue her studies and conduct similar research     in other parts of China.●


NDSU Central Grasslands Research Extension Center
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