Monday, November 13, 2006 - 12:45 PM
42-1

Growth temperature and carbon dioxide concentration alters big bluestem (Andropogon gerardii Vitman) biomass, seed production and subsequent seed germination.

K.R. Reddy1, Satya Sai Kumar Matcha1, S. K. Singh1, Giridara Kumar Surabhi1, and Vijaya G. Kakani2. (1) Mississippi State University, Department of Plant and Soil Sciences, 117 Dorman Hall, Box 9555, Mississippi State, MS 39762, (2) University of Florida, "117 Dorman Hall, Box 9555, Dept. PS", "MSU, Mississippi Sta", MS 39762, United States of America

Big bluestem is an important C4 grass species of rangelands comprising up to 80% of biomass in favorable environments. Seed set and seed germination will play an important role in the survival and spread of rangelands. The objective of this study was to evaluate the effects of temperatures (20/12, 25/17, 30/22, 35/27 and 40/32 ºC) and carbon dioxide concentrations (360 and 720 ppm) on seed production, and subsequent seed germination response to temperature. Plants were grown in sunlit chambers until maturity, 125 days after sowing. At maturity, individual plants were harvested and weights of various organs were collected. Panicles were hand threshed and good seed was selected for germination tests. Biomass decreased either above or below the optimum temperature of 30/22 ºC. Panicle weight was 6-7% of biomass at 25/17 C and fell to 1.6% at 40/32. No seed set was observed at 40/32 C. Maximum seed germination of those developed under extreme temperatures was significantly lower than those from optimum temperature range (25/17 and 30/22 C) at both [CO2]. Time to 50% germination in response to temperature also followed similar trends. Growth temperature modified cardinal temperatures of seed germination. Seeds developed under elevated [CO2] had higher optimum temperature than those under ambient [CO2]. Decrease in seed germination at extreme temperatures can be attributed to reduced seed weight at these temperatures. Bigger seeds and more seed nitrogen would have contributed to higher optimum temperatures at elevated [CO2]. Seed protein qualitative analysis were performed by using gel electrophoretic technique to identify alterations in protein profiles  between seeds developed under different temperatures and [CO2] conditions. Our results demonstrate that growth temperature and [CO2] significantly affect big bluestem seed germination. Tolerance to high temperatures during seed set would play an important role in the survival of this species in the future climatic condition.

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