Controls of Plant and Siol Carbon in Semihumid Temperate Grassland

Seastedt, T.; Coxwell, C.; Ojima, D.; Parton, W.

A model study evaluated the importance of photosynthetic pathways (C3, C4, or both) and management strategies to the foliage productivity and soil carbon characteristics of a semi humid temperate grassland subjected to various combinations of climate change. Model values for plant and soil characteristics were obtained at sites near Manhattan, Kansas, and the Manhattan climate record provided the nominal climatic drivers. Model runs used both actual monthely temperature and precitpitation data for a 100-yr interval and average weather conditions generated from this record. Monthly temperatures were increased 2¦C, left unchanged, or decreased 2¦C; annual precipitaion was increased 6cm, left unchanged, or decreased 6cm. All possible combinations of temperature and precipitation were then used in 100-yr simulations. Regardless of the specific climate scenario, plant production was lowest for C3 grasses and highest for the mixed C3-C4 community. The nominal seasonal pattern of precipitation favored an active C3 plant community in early to late spring, prior to the emergence of the C4 vegetation during summer contributed to the maximization response of the grasslands containing both C3 and C4 grasses. An analysis of variance of annual average values observed from 100-yr simulations was used to evaluate the relative importance of climate, photosynthetic pathways, and management activities (annually burned, burned every 4 yr, unburned, or lightly grazed) to plant production and soil carbon values. Photosynthetic pathway and precipitation were identified as the most significan single variables affecting fliage production; the interaction between photosynthetic pathwa and temperature was the most significant interaction term. Management treatments were by far the most important variables affecting soil cabon values, but 2¦C warming did produce substantial soil carbon losses from the C3 grasslands. Enhanced carbon fixation by the C4 and the C3 - C4 plant communities negated the losses of soil carbon caused by enhanced soil respiration at warmer temperatures.

Controls of Plant and Siol Carbon in Semihumid Temperate Grassland

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