We investigated the effects of seasonal changes\ud in soil moisture on the morphological and growth traits\ud of fine roots (<2 mm in diameter) in a mature Turkeyoak\ud stand (Quercus cerris L.) in the Southern Apennines\ud of Italy. Root samples (diameter: <0.5, 0.5–1.0, 1.0–1.5,\ud and 1.5–2.0 mm) were collected with the Auger method.\ud Mean annual fine-root mass and length on site was\ud 443 g m!2 (oak fine roots 321 g m!2; other species\ud 122 g m!2) and 3.18 km m!2 (oak fine roots 1.14 km\ud m!2; other species 2.04 km m!2), respectively. Mean\ud specific root length was 8.3 m g!1. All fine-root traits\ud displayed a complex pattern that was significantly related\ud to season. In the four diameter classes, both fineroot\ud biomass and length peaked in summer when soil\ud water content was the lowest and air temperature the\ud highest of the season. Moreover, both fine-root biomass\ud and length were inversely related with soil moisture\ud (p < 0.001). The finest roots (<0.5 mm in diameter)\ud constituted an important fraction of total fine-root\ud length (79 %), but only 21 % of biomass. Only in this\ud root class, consequent to change in mean diameter,\ud specific root length peaked when soil water content was\ud lowest showing an inverse relationship (p < 0.001).\ud Furthermore, fine-root production and turnover decreased\ud with increasing root diameter. These results\ud suggest that changes in root length per unit mass, and\ud pulses in root growth to exploit transient periods of low\ud soil water content may enable trees to increase nutrient\ud and water uptake under seasonal drought conditions

Mechanical stress is a widespread condition caused by numerous environmental factors that severely affect plant stability. In response to mechanical stress, plants have evolved complex response pathways able to detect mechanical perturbations and inducing a suite of modifications in order to improve anchorage. The response of woody roots to mechanical stresses has been studied mainly at the morphological and biomechanical level, whereas investigations on the factors triggering these important alterations are still at the initial stage. Populus has been widely used to study the response of stem to different mechanical stresses and, since it has the first forest tree genome to be decoded, represents a model woody plant for addressing questions on the mechanisms controlling adaptation of woody roots to changing environments. In this study, a morphological and physiological analysis was used to investigate factors controlling modifications in Populus nigra woody taproots subjected to mechanical stress. An experimental model analyzing spatial and temporal mechanical force distribution along the woody taproot axis enabled us to compare the events occurring in its above-, centraland below-bending sectors. Different morphogenetic responses and local variations of lignin and plant hormones content have been observed, and a relation with the distribution of the mechanical forces along the stressed woody taproots is hypothesized. We investigated the differences of the response to mechanical stress induction during the time; in this regard, we present data referring to the effect of mechanical stress on plant transition from its condition of winter dormancy to that of full vegetative activity.

In tree species, fine-root growth is influenced by the interaction between environmental factors such as soil temperature (ST) and soil moisture. Evidences suggest that if soil moisture and nutrient availability are adequate, rates of root growth increase with increasing soil temperature up to an optimum and then decline at supraoptimal temperatures. These optimal conditions vary between different taxa, the native environment and the fine-root diameter sub-classes considered. We investigated the effects of seasonal changes of both ST and soil water content (SWC) on very fine (d < 0.5 mm) and fine-root (0.5 < d < 2 mm) mass (vFRM, FRM) and length (vFRL, FRL) in Italian Southern Alps beech forests (Fagus sylvatica L.). Root samples were collected by soil core method. Turnover rate was higher for the very fine (0.51) than for the fine (0.36) roots. vFRM, FRM, vFRL and FRL displayed a complex seasonal pattern peaking in summer when SWC was around 40 % and ST was around 14 °C. Above this temperature, under almost constant SWC, all above mentioned root traits decreased. vFRM, FRM, vFRL and FRL showed significant second-order polynomial relationship (p < 0.05) with SWC for both diameter classes, with the only exception of SRL. ST showed the same kind of relationship significant only with vFRM and vFRL, the latter within the 12-16 °C smaller range. Interpolation analysis between root mass and length for both diameter classes and investigated soil environmental characteristics (ST and SWC) showed a clear roundish delineation only for vFRM. In conclusion, these findings clarified the occurrence of a bimodal fine-root growth seasonal pattern for our beech forest. The optimal growth ST and SWC ranges were delineated only for very fine roots, giving further evidence on this root category as the more responsiveness to soil environmental changes. Furthermore, F. sylvatica seems to adopt an intensive strategy to cope with decreasing SWC. Finally, fine-root growth, mainly radial type, seems to be driven by SWC, whereas very fine-root growth, mainly longitudinal type, seems to be driven by ST

The aim of this study was to investigate the possible effects of coppice conversion to high forest on the beech fine-root systems. We compared the seasonal pattern of live and dead fine-root mass (d 5 2 mm), production and turnover in three beech stands that differed in management practices. Tree density was higher in the 40-year-old coppice stand than in the stands that were converted from coppice to high forest in 1994 and 2004, respectively. We found that a reduction in tree density reduced the total fine-root biomass (Coppice stand, 353.8 g m 72 ; Conversion 1994 stand, 203.6 g m 72 ; Conversion 2004 stand, 176.2 g m 72 ) which continued to be characterised by a bimodal pattern with two major peaks, one in spring and one in early fall. Conversion to high forest may also affect the fine-root soil depth distribution. Both fine-root production and turnover rate were sensitive to management practices. They were lower in the Coppice stand (production 131.5 g m 72 year 71 ; turnover rate 0.41 year 71 ) than in the converted stands (1994 Conversion stand: production 232 g m 72 year 71 , turnover rate 1.06 year 71 ; 2004 Conversion stand: production 164.2 g m 72 year 71 , turnover rate 0.79 year 71 ).

No abstract