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Photosynthetic and Growth Responses of Aspen Clones to Elevated Soil Temperature and Nutrient Availability
Reference
King, J.S., Pregitzer, K.S. and Zak, D.R. 1999. Clonal variation in above- and below-ground responses of Populus tremuloides Michaux: Influence of soil warming and nutrient availability. Plant and Soil 217: 119-130.

What was done
Four genotypically different aspen (Populus tremuloides) cuttings were grown for 98 days in pots exposed to ambient air in Michigan, USA, at low and high soil temperatures and low and high nutrient availability to study the effects of these parameters on the productivity and growth of the most widely distributed tree species in North America.

What was learned
High soil temperature (ranging between 10 and 29C) increased photosynthetic rates by about 35% across all clones, relative to photosynthetic rates exhibited by their respective controls grown at low soil temperature (average of 13C), while high soil nitrogen content (7.7-fold greater than the low nitrogen treatment) increased rates by approximately 69% relative to clones grown at low nitrogen concentration. The greatest absolute photosynthetic rates were produced by seedlings grown in the high soil temperature high nitrogen treatment; and they were about 30% greater than those displayed by the second most productive seedlings grown in the low soil temperature high nitrogen treatment.

High soil temperature also increased seedling biomass, regardless of clone, by an average of 47% relative to clones grown at low temperature, while high nitrogen increased biomass by 72%. The greatest absolute biomass was produced by seedlings grown in the high soil temperature high nitrogen treatment; and it was about 80% larger than that produced by the next most vigorously growing seedlings in the low soil temperature high nitrogen treatment.

High soil temperature caused significant increases in cumulative root production and mortality, while soil nitrogen had little influence on these parameters. At low soil temperature, however, root production and mortality were much greater when high, as opposed to low, soil nitrogen was present. Once again, there were no significant effects of genotype on these responses.

What it means
If air temperatures rise in the future, regardless of the cause, it is likely that trembling aspen genotypes will respond by enhancing their photosynthetic rates and biomass production, regardless of soil nitrogen availability. As a consequence of these phenomena, greater inputs of carbon and nutrients into forest soils will likely result. In addition, warmer temperatures should substantially increase rates of root production and turnover, which are major processes that also deliver significant quantities of carbon to forest soils. Furthermore, all of these carbon sequestering mechanisms should be enhanced by the rising atmospheric CO2 concentration, which will likely double within the next century. Thus, a tremendous potential for atmospheric carbon sequestration exists within the biomass and beneath the soils of the most widely distributed tree species in North America --the trembling aspen.


Reviewed 15 July 2000