Comparison in fine root architectural patterns among six coexisting tree species in a broad-leaf temperate forest

Background/Question/Methods

Studies in temperate trees have demonstrated contrasting root morphological traits among tree species, which seem to be associated with different soil foraging strategies. However, few studies have attempted to describe root morphologies of coexisting species in forest ecosystems, and how the influence of other species or soil conditions determine root morphology among canopy tree species.  We addressed these questions by studying fine root (<2mm in diameter) morphological traits for six coexisting canopy tree species in a temperate forest in northeastern Ohio. Assuming a linkage between root traits and nutrient uptake strategies, we expected 1) a positive correlation between specific root length (SRL) and specific root tip abundance (SRTA), and a negative correlation between root mass density (RMD) and SRL. 2) That differences in root morphology among species will be more evident in the absorptive parts of the root system (distal roots) than in the structural parts (basal roots) due to inherent differences among species in acquisition strategies but similar adaptations for structural tissues. 3) That soil conditions will explain more morphological variation across species than will plant community composition, assuming a high plastic response of roots to surrounding soil conditions.

Results/Conclusions

Our results partially supported our hypotheses. Even though we found a positive correlation between SRL and SRTA at the whole-community level, we found a significant positive correlation between these traits in only three out of six species. On the other hand five out six species showed a negative correlation between SRL and RMD, suggesting that tree species may modify tissue composition rather than topology in order to increase root length. Comparisons among root orders across species confirmed our expected differences between distal roots. In fact, first order roots of the species with thicker roots (Prunus serotina) were on average 19% thicker and 54% longer than those of the species with the finest roots (Acer rubrum).  However, differences in diameter and length were still evident up to the fourth order, suggesting large variation in root morphology among species even within structural roots. In contrast to our third hypothesis, soil conditions did not significantly explain variation in root morphology at the species level, suggesting that either other biotic factors are more important explaining root plasticity or additional soil factors not included in this study are driving fine root morphology among the studied species.