Source: Alward, R.D., J.K. Detling, D.G. Milchunas. 1999. Grassland vegetation changes and nocturnal global warming. Science 283:229-231.

Plants influence the stability, structure, and function of a natural ecosystem. Temperature and precipitation are among the most prevalent of the factors that influence plant growth, development, and survival. Consequently, as global warming increases and the minimum annual temperature (TMIN) steadily increases at twice the rate of the maximum annual temperature, crop plants will be greatly affected. There are two possible outcomes to elevated TMIN levels. Either the growing season will become longer with increased productivity and carbon sequestration, or increased C4 plant respiration with no increase in photosynthesis will cause these plants to die. Because of these two possible scenarios, there is no reason to assume that future global warming will affect plants more so during the day than uniformly over a daily period. It could also affect the plants nocturnally by disrupting their photosynthesis cycle. Either way, these global climate changes will affect the aboveground net primary productivity (ANPP) of plants in an ecosystem. This article analyzes the correlation between temperature and ANNP of key plant species in the central plains of northeastern Colorado over the course of a 37-year study. It also illustrates strategies that C4 and C3 plants use in dealing with warming. Although there was no significant relation between the TMIN and the precipitation, there was a significant correlation between the temperature and ANNP. For each 1 degree Celsius increase in average spring TMIN, the ANNP of the dominant plant species, a C4 plant, decreased by nearly one third while C3 plants, in contrast, actually increased. It was found that C3 plants also increased in density. These data support the hypothesis of increased respiration in C4 plants with no reciprocity in photosynthesis, causing them to die. Although the observation may be a result of biotic interactions (more space and nutrients made available to C3 plants caused their sudden increase), it is also likely that C3 plants benefited directly from the global warming and elevated TMIN levels. The combination of a decreased dominant plant population and the potential for increased exotic C3 plant life threatens the natural structure and function of the ecosystem and could have consequences for livestock production.

Abstract author: Olubukola Gbadegesin, 13 November 1999.

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