Studies of a simple laboratory microecosystem: effects of stress

Inocula from an established microcosm were subjected to acute gamma radiation levels of 10 5 and 10 6 rads. Microcosms developed from these inocula were sampled through the 40—day successional period to determine effects of radiation stress. Chlorophyll "a" content, biomass, and community metabolism were measured. Significant reduction in chlorophyll "a" was found when each treatment level was compared to its control. Biomass was significantly reduced throughout succession for both treatment levels except for the last sample of 10 6 rad microcosms. Net productivity and nighttime respiration varied similarly and were significantly reduced during early succession at both treatment levels. Comparison of treatment effects revealed that the 10 5 rad level microcosms responded to the stress with a greater reduction in parameters measured than the 10 6 . Explanation of this phenomenon may lie in inhibitory interactions among microcosm components at 10 5 rads. Elimination of certain species at 10 6 rads may have limited this interaction. The action of radiation at the community level was similar to that of other forms of stress in that radiation can differentially affect the organisms comprising a community and subsequently change community structure. The present study illustrates the idea that stress changes species dominants and succession. In addition, it emphasizes the significance of changes in interactions among community components when a community is stressed.