|Bolton, Harvey, Jr.|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2002
Publication Date: 2/10/2003
Citation: Link, S.O., Smith, J.L., Bolton Jr., H., Halvorson, J.J. 2003. A reciprocal transplant experiment within a climatic gradient in a semi-arid shrub-steppe ecosystem: effects on bunchgrass growth and reproduction, soil carbon, and soil nitrogen. Global Change Biology 9:1097-1105. Interpretive Summary: The climate in the Northern hemisphere is projected to become warmer and drier over the next 100 years.In many parts of North America this warmer climate will amount to 3 to 6oC difference from todays climate. What is of interest is how this warming of the climate will effect different ecosystems and their processes. We induced climate change on soils from a semi-arid ecosystem by transplanting soil cores from an upper slope (cooler and wetter) to a lower slope (hotter and drier) and also did the reverse transplant. After 5 years we found that the plants showed very little change to the climate difference. However, the soil organic matter, measured as total carbon and nitrogen, decreased significantly in the cores exposed to hotter and drier conditions. The cores exposed to a wetter and cooler climate had no change in soil organic matter after 5 years. Thus as the climate becomes warmer and drier we can expect large changes in soil organic matter and related functions of soils in the semi- arid regions.
Technical Abstract: The effect of climate change on Poa secunda and soils in a shrub-steppe ecosystem was investigated in the field. Intact soil cores containing P. secunda were transplanted between two elevations and examined in a six- month period, 4.5 to 5 years later. The lower elevation site represents a warmer (12.5 C average January maximum) and drier (187 mm yr-1) climate while the upper elevation site represents a cooler (8.0 C average January maximum) and wetter (270 mm yr-1) climate. There was no effect of climate change on plant density, shoot biomass, or carbon isotope discrimination in either plant population. Cooling significantly reduced percent cover and leaf length, while warming had no effect.Culm density was zero for the lower elevation plants transplanted to the upper site and was 10.3 culms m- 2 at the lower site. There was no significant effect of warming on the culm density of the upper elevation plants transplanted to the lower site. Culm density of the in situ lower elevation plants was significantly greater than that of the in situ upper elevation plants. Warming resulted in a reduction in total soil carbon of 32% and a reduction in total soil nitrogen of 40%. Cooling had no effect on total soil C or N. Of the C and N that was lost as a function of time, 64% came from the particulate organic matter fraction (POM, >53 ?m). With the hotter and drier conditions that may develop with climate change, the total C and N of semi-arid soils will decrease at the expense of the active fraction of soil C, which may alter ecosystem diversity and function.