Young temperate tree species show different fine root acclimation capacity to growing season water availability

Background and aims Changes in water availability during the growing season are becoming more frequent due to climate change. Our study aimed to compare the fine-root acclimation capacity (plasticity) of six temperate tree species aged six years and exposed to high or low growing season soil water availability over five years. Methods Root samples were collected from the five upper strata of mineral soil to a total soil depth of 30 cm in monoculture plots of Acer saccharum Marsh., Betula papyrifera Marsh., Larix laricina K. Koch, Pinus strobus L., Picea glauca (Moench) Voss and Quercus rubra L. established at the International Diversity Experiment Network with Trees (IDENT) field experiment in Sault Ste. Marie, Ontario, Canada. Four replicates of each monoculture were subjected to high or low water availability treatments. Results Absorptive fine root density increased by 67% for Larix laricina, and 90% for Picea glauca, under the high-water availability treatment at 0–5 cm soil depth. The two late successional, slower growing tree species, Acer saccharum and Picea glauca, showed higher plasticity in absorptive fine root biomass in the upper 5 cm of soil (PIv = 0.36 & 0.54 respectively), and lower plasticity in fine root depth over the entire 30 cm soil profile compared to the early successional, faster growing tree species Betula papyrifera and Larix laricina. Conclusion Temperate tree species show contrasting acclimation responses in absorptive fine root biomass and rooting depth to differences in water availability. Some of these responses vary with tree species successional status and seem to benefit both early and late successional tree species. Supplementary Information The online version contains supplementary material available at 10.1007/s11104-023-06377-w.


Fig. S1
Variation in mean (± standard error of the mean) absorptive fine root density ratio of each soil depth related to total absorptive fine root density from 0-30 cm soil depth.Soil depths for six tree species in the high (blue) and low (orange) water treatments (H2O).No statistical analysis was performed on this ratio.From top to bottom, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S2
Variation in mean (± standard error of the mean) dead fine root density ratio of each soil depth related to total absorptive fine root density from 0-30 cm soil depth.Soil depths for six tree species in the high (blue) and low (orange) water treatments (H2O).No statistical analysis was performed on this ratio.From top to bottom, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S3
Variation in mean of root to aboveground biomass ratio (absorptive fine roots, transportive fine roots, and coarse roots), (R/S ratio, ± standard error of the mean) for six tree species in the high (blue) and low (orange) water treatments (H2O).Significant water treatment effects for a given soil depth are noted by an asterisk and marginal effects by a dot ('*', p< 0.05 -p<0.1 '.').From left to right, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S4
Variation in mean leaf biomass to absorptive fine root ratio (± standard error of the mean) for six tree species in the high (blue) and low (orange) water treatments (H2O).Significant water treatment effects for a given soil depth are noted by an asterisk and marginal effects by a dot ('*', p< 0.05 -p<0.1 '.').From left to right, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S5
Variation in mean aboveground woody biomass to root ratio (absorptive fine roots, transportive fine roots, and coarse roots) (± standard error of the mean) for six tree species in the high (blue) and low (orange) water treatments (H2O).Significant water treatment effects for a given soil depth are noted by an asterisk and marginal effects by a dot ('*', p< 0.05 -p<0.1 '.').From left to right, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S6
Variation in mean (± standard error of the mean) transportive fine root density with soil depth for six tree species in the high (blue) and low (orange) water treatments (H2O).From top to bottom, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Fig. S7
Variation in mean (± standard error of the mean) coarse root density with soil depth for six tree species in the high (blue) and low (orange) water treatments (H2O).From top to bottom, data for broadleaved and conifer species are presented separately in order of increasing shade tolerance.

Supplementary tables:
Table S1 Post-hoc Tukey-test results for the interaction between water availability (High vs. Low), species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina: Ll), and soil depth (cm) on absorptive fine root density (mg cm -3 ).Responses between high and low water availability are tested separately for each species and soil depth layer.

Table S3
Post-hoc test results of the interaction between water availability (High vs. Low) and species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina: Ll) on absorptive fine roots weighted mean rooting depth (cm).Contrasts between high and low water availability are tested separately for each species.

Table S6
Results of TypeⅢ analyses of variance testing for the tree species (Betula papyrifera, Quercus rubra, Acer saccharum, Larix laricina, Pinus strobus, and Picea glauca), and high and low water (H2O) treatment on root to shoot ratio (R/S ratio, g g -1 ).

Table S7
Ll) on root to shoot ratio (R/S ratio, g g -1 ).Contrasts between high and low water availability are tested separately for each species.
Post-hoc test results of the interaction between water availability (High vs. Low) and species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina:

Table S8
Results of TypeⅢ analyses of variance testing for the tree species (Betula papyrifera, Quercus rubra, Acer saccharum, Larix laricina, Pinus strobus, and Picea glauca), and high and low water (H2O) treatment on leaf biomass to absorptive fine root ratio (g g -1 ).

Table S9
Post-hoc test results of the interaction between water availability (High vs. Low) and species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina:Ll) on leaf biomass to absorptive fine root ratio (g g -1 ).Contrasts between high and low water availability are tested separately for each species.

Table S10
Results of TypeⅢ analyses of variance testing for the tree species (Betula papyrifera,

Table S11
Post-hoc test results of the interaction between water availability (High vs. Low) and species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina: Ll) on aboveground woody biomass to root ratio (g g -1 ) (absorptive fine roots, transportive fine roots, and coarse roots).Contrasts between high and low water availability are tested separately for each species.

Table S12
Results of TypeⅢ analyses of variance testing for the tree species (Betula papyrifera, Quercus rubra, Acer saccharum, Larix laricina, Pinus strobus, and Picea glauca), and high and low water (H2O) treatment on aboveground woody biomass (g).

Table S13
Post-hoc test results of the interaction between water availability (High vs. Low) and species (Acer saccharum: As, Betula papyrifera: Bp, Pinus strobus: Ps, Picea glauca: Pg, and Larix laricina: Ll) on aboveground woody biomass (g).Contrasts between high and low water availability are tested separately for each species.