Carbohydrate transfer through root grafts to support shaded trees

Abstract

We investigated whether root grafts between lodgepole pine (Pinus contorta var. latifolia Dougl. ex. Loud.) trees can transfer sufficient carbohydrate reserves from a source tree to a grafted sink tree to affect the vigor of trees growing in a light-limited environment. Eleven plots were established in early spring and two grafted tree pairs and two independent non-grafted trees were selected at each plot. One tree in a grafted pair and one non-grafted tree were shaded at each plot, whereas the remaining trees were non-shaded during the experimental period. Shaded trees had significantly lower carbohydrate reserves and smaller crowns than non-shaded trees following one growing season. Grafted shaded trees had significantly higher root total nonstructural carbohydrate concentrations than non-grafted shaded trees, indicating that root grafts partially offset the effects of shading. Also, large root grafts transferred proportionately more carbohydrates to the shaded trees than small root grafts. Carbohydrates transferred through root grafts could allow grafted trees to persist under conditions where non-grafted trees would be removed by competition.

Natural root grafting in Picea mariana to cope with spruce budworm outbreaks

“…Moreover, as carbohydrates can be transferred through root grafts, larger and shared carbohydrate pools may contribute to the better performance of grafted trees to face outbreaks after carbon depletion that firstly occurs in non-grafted trees (see fig. 1 in Fraser et al (2006)). An attenuated effect of budworm outbreak in grafted trees supports the hypothesis that common functioning of genetically distinct individuals can overcome the death of weaker trees (Basnet et al 1993;DesRochers and Lieffers 2001;Fraser et al 2005Fraser et al , 2006) as a competitive strategy to impede recruitment of different species (Tarroux and DesRochers 2011).…”

“…1 in Fraser et al (2006)). An attenuated effect of budworm outbreak in grafted trees supports the hypothesis that common functioning of genetically distinct individuals can overcome the death of weaker trees (Basnet et al 1993;DesRochers and Lieffers 2001;Fraser et al 2005Fraser et al , 2006) as a competitive strategy to impede recruitment of different species (Tarroux and DesRochers 2011). Consistently, graft formation lagged behind the outbreak by up to 7 years, suggesting that defoliation might be the underpinning trigger of graft formation in black spruce (Loehle and Jones 1990).…”

“…nutrients (Stone and Stone 1975;Fraser et al 2006), and communal root systems allow maximum efficiency to capture and distribute resources among connected trees that may lead to increased stem growth . Moreover, as carbohydrates can be transferred through root grafts, larger and shared carbohydrate pools may contribute to the better performance of grafted trees to face outbreaks after carbon depletion that firstly occurs in non-grafted trees (see fig.…”

“…However, it might occur much more extensively given that it has received very little attention due to the difficulties to survey belowground tree attributes (Lev-Yadun 2011). Root connections could be beneficial under scenarios of limited carbon supply following outbreaks, as greater acquisition of resources and shared carbohydrate pools within physiologically integrated individuals (see Stone and Stone (1975) and Fraser et al (2005Fraser et al ( , 2006 and references therein) could attenuate the negative impact of defoliation in tree growth and mortality. Root grafting is gaining attention as an adaptive strategy to face disturbances and environmental hazards, as cooperative behaviour could limit tree mortality and hinder establishment of new species (Eis 1972;Tarroux and DesRochers 2011).…”

Xylem and soil CO2 fluxes in a Quercus pyrenaica Willd. coppice: root respiration increases with clonal size

“…In ecophysiological studies, trees have been traditionally considered as discrete individuals regenerating from seeds. Nevertheless, recent studies challenge this assumption as the processes of root grafting and resprouting can result in trees with multiple stems that share resources and function physiologically as a unit (Fraser et al 2006;Tarroux et al 2010;Baret and DesRochers 2011). Technical difficulties in the study of belowground structures have limited our understanding of root system dynamics, their relationships with aboveground structures, and their implications for ecosystem regeneration in clonal resprouting species.…”