Plant functional traits may be altered as plants adapt to various environmental constraints. Cold, low fertility growing conditions are often associated with root adjustments to increase acquisition of limiting nutrient resources, but they may also result in construction of roots with reduced uptake potential but higher tissue persistence. It is ultimately unclear whether plants produce fine roots of different structure in response to decreasing temperatures and whether these changes represent a trade-off between root function or potential root persistence. We assessed patterns of root construction based on various root morphological, biochemical and defense traits including root diameter, specific root length (SRL), root tissue density (RTD), C:N ratio, phenolic compounds, and number of phellem layers across up to 10 root orders in diverse populations of Scots pine along a 2000-km climatic gradient in Europe. Our results showed that different root traits are related to mean annual temperature (MAT) and expressed a pattern of higher root diameter and lower SRL and RTD in northern sites with lower MAT. Among absorptive roots, we observed a gradual decline in chemical defenses (phenolic compounds) with decreasing MAT. In contrast, decreasing MAT resulted in an increase of structural protection (number of phellem layers) in transport fine roots. This indicated that absorptive roots with high capacity for nutrient uptake, and transport roots with low uptake capacity, were characterized by distinct and contrasting trade-offs. Our observations suggest that diminishing structural and chemical investments into the more distal, absorptive roots in colder climates is consistent with building roots of higher absorptive capacity. At the same time, roots that play a more prominent role in transport of nutrients and water within the root system saw an increase in structural investment, which can increase persistence and reduce long-term costs associated with their frequent replacement.
Bibliographical noteFunding Information:
This research was supported by the National Science Center, Poland (2011/02/A/NZ9/00108), and the Institute of Dendrology of the Polish Academy of Sciences. Special credit is due to Bengt Nihlg?rd (Lunds Universitet) for valuable help given during field trip in Sweden. The authors are grateful to Dominik Tomaszewski for the preparation of Fig. We thank numerous students involved in root dissection into individual root orders and especially P. Sroka and A. Tala?ka who greatly contributed to root microtome sectioning. This manuscript was greatly improved by helpful suggestions from anonymous reviewers.
- Scots pine
- root order
- root structure
- temperature gradient