Fine root morphological and functional traits in Fagus sylvatica and Fraxinus excelsior saplings as dependent on species, root order and competition

Aims

The mechanisms of belowground competition are not well understood. Addressing literature reports on competition-induced changes in tree fine root morphology, we conducted a growth experiment with tree saplings to investigate competition effects on important root morphological and functional traits in a root order-focused analysis.

Methods

European beech and European ash saplings were grown for 34 months in containers under greenhouse conditions in monoculture (2 conspecific plants), in mixture (1 beech and 1 ash) or as single plants. The root system was fractionated according to root orders and eight morphological and functional properties were determined.

Results

Root order was the most influential factor affecting the fine root traits (except for root diameter and δ¹³C); a significant species identity effect was found for root diameter, tissue density, N concentration and δ¹³C. Ash fine roots were thicker, but had lower tissue densities, contained more N and had systematically higher δ¹³C values than beech roots. The competition treatments had no significant effect on morphological root traits but altered δ¹³C in the 2nd root order.

Conclusion

Neither intra- nor interspecific root competition affected fine root morphology significantly suggesting that competition-induced root modification may not be a universal phenomenon in temperate trees.