Xuejun Dong, Paul Nyren, Bob Patton, Guojie Wang, Brian Kreft, Anne Nyren, NDSU, Central Grasslands Research Extension Center, Streeter, ND
Ryan Limb, Don Kirby, NDSU, Department of Animal and Range Science, Fargo, ND
Larry Cihacek, NDSU, Department of Soil Science, Fargo, ND
This year marked the second year of the three-year project entitled “Using an Ecosystem Model for Rangeland Management.” As indicated in the Central Grasslands Research Extension Center (CGREC) Annual Reports of 2003 and 2004, this project has a three-part working plan:
1. Use two physiological models (Thornley and Verberne, 1989; Thornley, 1996) as a framework to target a set of plant and soil parameters for site-specific determination.
2. Choose the appropriate field and laboratory measurements to estimate the model parameters and characterize ecosystem status; and
3. Test the parameterized model in the Missouri Coteau area of North Dakota.
By the end of the 2005 growing season, all scheduled field and laboratory measurements for the current phase of the project were completed. In this report, we highlight the following preliminary results.
(1) By measuring the functioning of the stomates (tiny openings) on plant leaf surfaces, we observed that the stomates of tall wheatgrass (Agropyron elongatum), an important forage grass, remained open even under adverse environmental conditions. This tendency of stomates to remain open would make this species a big user of soil moisture, which poses a problem in semi-arid areas where water resources are scarce.
(2) By analyzing soil samples collected from the field, we calculated that the microbial biomass nitrogen for the mollisols (grassland soils) at the CGREC averaged 71 μg/g dry soil and biomass carbon averaged 305 μg/g dry soil from June to September. These calculations are useful for modeling soil nitrogen flow.
(3) Using a CGREC-designed chamber for measuring photosynthesis and respiration of plant communities at the CGREC, we calculated the daily net flux of CO2 on selected clear days during the growing season. In June of 2004 and 2005, when plants were in an active growth stage, the grazed pastures (especially moderately grazed ones) had an increase in daily CO2 flux when compared with the protected (idled) exclosures. This increased net carbon gain was primarily the result of decreased ecosystem respiration in the grazed pastures, as compared with idled ones, which sometimes had a net loss in daily CO2 exchange.
This project has two interesting features that deserve mention. First, despite the fact that many new concepts and theories are arising in the field of ecology, this applied agricultural study is more appropriately based on a relatively mature paradigm so that research efforts over the years can be put into a consistent framework with an emphasis on practical uses. In this regard, the Hurley pasture model, which has successfully and transparently synthesized many advances in plant eco-physiology over the past decades, was our central interest when we started developing our research plan three years ago. Second, because the project fieldwork is demanding (involving several disciplines of the plant and soil sciences) but must be accomplished within a couple of years, we needed a single ecologically typical and socially important agricultural research site on which to concentrate our limited research efforts for field data collection. The CGREC and nearby pastures, representing the native grasslands and tame pastures of the Missouri Coteau area of North Dakota, served as an excellent research base.
Table of Contents
● Leaf physiology: Three forage species from the CRP (Conservation Reserve Program) study site
● Whole-plant physiology: Growing four grass species in a greenhouse
● Soil microbial biomass: an estimate for the Missouri Coteau mollisols
● Ecosystem carbon exchange: A diurnal budget