Variation among traits of individual fine-roots determine belowground plant strategies for resource acquisition and mediate ecosystem-scale productivity, carbon and nitrogen fluxes. Therefore, to predict ecosystem processes under a changing climate it is important to first understand patterns and determine drivers of root trait variation. Further, research identifying factors controlling root trait variation may help in forecasting plant resilience to novel climates. For example, in Western North America, the range of the widely distributed Douglas-fir (Pseudotsuga menziesii) is predicted to move northwards in the next century. Responses of belowground traits to future environmental conditions may limit or enable successful establishment of new forest populations.
Here, we quantify the responses of fine-root traits in Douglas-fir to edaphic and climatic variations across a strong climate gradient in Western Canada. We expected that (i) root morphological and architectural traits respond independently to changes in the abiotic environment and that (ii) colder and drier climates favoring low soil resource availability relate to acquisitive root traits. To test these hypotheses, we measured morphological, architectural, and chemical traits for each of the first three root orders separately as well as patterns of mycorrhizal colonization. Relationships between traits and environmental factors were investigated using linear mixed effect modelling.
Results/Conclusions
We observed a higher degree of phenotypic variability for root morphology and chemistry. Root traits represented three axes for fine-root adjustments. Specific root length was independent from tissue density and all the morphological traits were weakly correlated with the chemical traits. Mean annual temperature (MAT) controlled morphological trait variations, although modulated by the effect of cation exchange capacity. Chemical traits were responsive to both MAT and mean annual precipitation whereas architectural traits were weakly associated to soil fertility but not related to a change in mycorrhizal colonization.
Root trait adjustments tended to increase fine-roots acquisitive potential in colder and/or drier environments, which may facilitate trees survival as climate warms. Our study brings support for a multidimensional root trait framework and will help developing a more realistic trait spectrum.