M. Luke McCormack1, Thomas S. Adams2, and David Eissenstat2. (1) Pennsylvania State University, (2) The Pennsylvania State University
Background/Question/Methods Fine roots represent a critical and poorly understood link in ecosystem cycling of carbon, water, and nutrients. Fine root lifespan is a key link in this process as it directly affects the flux of carbon into soil while also mediating the ability of a species to competitively acquire soil nutrients. However, few robust generalizations can be made relating fine root lifespan to more readily measurable fine root traits such as specific root length (SRL, m g-1) and root N:C ratios. Here we examine whether traits such as plant potential growth rate, root N concentration or SRL covary with fine root lifespan. This was done using non-destructive minirhizotron observations over two separate years in a common garden experiment located in central Pennsylvania. The planting consists of 12 indigenous temperate tree species covering a range of root morphologies, shade tolerance, mycorrhizal associations, and potential growth rates while also including 3 separate congeneric contrasts (Acer, Quercus, and Pinus). Due to a high proportion of censored roots in our study regression analysis was limited to first quartile survivorship rather than median survivorship.
Results/Conclusions Across all 12 species SRL ranged from 11 to 163 m g-1 and N:C ratios ranged from 0.043 to 0.104. First quartile root lifespan was negatively correlated with SRL (R2=0.48, p=0.01) with more coarsely rooted species tending to live longer than those with finer roots. Species with high root N:C ratios tended to have shorter lifespans than those with low N:C ratios (R2=0.40, p=.03). Kaplan Meier survivorship analysis also showed that roots receiving an aqueous N fertilizer treatment lived longer compared with those receiving a water control within the same tree species. This observation supports the hypothesis that plants may be able to extend the lifespan of their more efficient roots. Congeneric comparisons of fine root lifespan with plant potential growth rate were mixed. Overall, these findings provide support that roots have similar trait syndromes as those observed in leaves: roots of high N and high SRL tend to have shorter lifespans than roots of low N and low SRL. It remains to be seen whether plastic changes in root N and SRL to the environment affect root lifespan similarly as those observed across species.