Oecologia Supplementary Material for:
The role of isohydric and anisohydric species in determining ecosystem-scale response to severe drought - Roman, D.T.1, Novick, K.A.*1, Brzostek, E.R.2, Dragoni, D.3, Rahman, F.4, Phillips, R.P.5
1) School of Public and Environmental Affairs, Indiana University – Bloomington, 702 N Walnut Grove Ave. Bloomington, IN 47405
2) Department of Biology, West Virginia University, 53 Campus Dr. Morgantown, WV 26505
3) Department of Geography, Indiana University – Bloomington, 702 N Walnut Grove Ave. Bloomington, IN 47405
4) Department of Biology, The University of Texas Rio Grande Valley, 1201 W University Dr. Edinburg, TX 78539
5) Department of Biology, Indiana University – Bloomington, 1001 E Third St. Bloomington, IN 47405
* Author for Correspondence: (812) 855-3010
SI Figure 1. Relationships between soil water potential (ΨS) and leaf assimilation rate (A) for canopy and sub-canopy positions during the 2012 drought period (DOY 157-220). The slopes were significantly different from zero for sassafras (a) canopy (slope= 3.24, R2=0.57, p=0.012), sugar maple (b) canopy (slope= 3.79, R2=0.62, p=0.007) and sub-canopy (slope= 1.99, R2=0.41, p=0.047), tulip poplar (c) canopy (slope= 5.99, R2=0.69, p=0.003) and sub-canopy (slope= 2.21, R2=0.379, p=0.058) and for red oak (e) canopy (slope=2.07, R2=0.62, p=0.012), while no significant relationships were found for white oak (d). Regression slope parameters were significantly different between canopy and sub-canopy for sugar maple (df=8, t=-2.10, p=0.068) and tulip poplar (df=8, t=-2.176, and p=0.061).
SI Figure 2. The relationship between soil water potential (ΨS) and leaf assimilation rate (A) shown as a relative change by dividing A values by the intercept of their regressions in SI figure 1. The canopy and sub-canopy relationships were significantly different from zero, but not different from each other, for sugar maple (b, slope=0.371, R2=0.495, p=0.029) and tulip poplar (c, slope= 0.4116, R2=0.490, p=0.024, as indicated with dotted lines. For sassafras and red oak, the relationship was significantly different from zero for the canopy data only (sassafras: a, slope= 0.282, R2=0.57, p=0.012; red oak: e, slope=0.137, R2=0.62, p=0.012), as indicated with a solid line. No significant relationships were observed for white oak (d).
SI Figure 3. Relationships between soil water potential (ΨS) and stomatal conductance rate (gS) for canopy and sub-canopy positions during the 2012 drought period (DOY 150-220). Relationships were significantly different from zero for sassafras (a) canopy (slope= 0.082, R2=0.65, p= 0.005) and sub-canopy (slope=0.026, R2=0.55, p=0.014), sugar maple (b) canopy (slope= 0.035, R2=0.65, p=0.005) and sub-canopy (slope= 0.021, R2=0.499, p=0.022), tulip poplar (c) canopy (slope=0.117, R2=0.846, p=0.0002) and sub-canopy (slope=0.065, R2=0.81, p<0.001), while no significant relationships were found for white oak (d) and red oak (e). Regression slope parameters were significantly different between canopy and sub-canopy for sassafras (df=8, t=-8.02, p<0.001), sugar maple (df=8, t=-1.99, p= 0.08) and tulip poplar (df=8, t=-4.69, p=0.002).
SI Figure 4. Relationships between soil water potential (ΨS) and stomatal conductance rate (gS) shown as a relative change by dividing gs values by the intercept of their regressions in SI figure 3. The relationships were significantly different from zero, but not significantly different between canopy and sub-canopy positions (as indicated with a dotted line) for sassafras (a, slope= 0.456, R2=0.597, p< 0.069), sugar maple (b, slope= 0.359, R2=0.557, p=038), and tulip poplar (c, slope=0.561, R2=0.82, p=0.001), while no significant relationships were found for white oak (d) and red oak (e).
SI Figure 5. Relationships between soil water potential (ΨS) and leaf water potential (ΨL) for canopy and sub-canopy positions during all study years (2011-2013). ). The relationships were significantly different from zero, but not significantly different between canopy and sub-canopy positions (as indicated with a dotted line) for tulip poplar (c, slope=0.274, R2=0.104, p<0.001. Relationships were significantly different from zero for canopy and sub-canopy, but significantly different from each other (as indicated by solid and dashed lines) for white oak (d, canopy: slope=1.026, R2=0.50, p<0.001; sub-canopy: slope= 0.856, R2=0.60, p<0.001; df=66, t=-1.93, p=0.057) and red oak (e, canopy: slope=1.25, R2=0.47, p<0.001; sub-canopy: slope= 0.805, R2=0.523, p<0.001; df=56, t=-4.3, p=0.0001). No significant relationships were found for Sassafras (a) or sugar maple (b).
SI Figure 6. Relationships between soil water potential (ΨS) and leaf water potential (ΨL) shown as a relative change by dividing ΨL values by the intercept of their regressions in SI figure 7, where the intercept represents the well-watered mid-day leaf water potential (ψL(WW)) . The relationships were significantly different from zero, but not significantly different between canopy and sub-canopy positions (as indicated with a dotted line) for tulip poplar (c, slope=0.268, R2=0.13, p<0.001, white oak (d, slope=0.931, R2=0.54, p<0.001), and red oak (e, slope=1.15, R2=0.48, p<0.001), while no significant relationships were found for sassafras (a) or sugar maple(b).
SI Figure 7. Fine root biomass (a) and cumulative root biomass (b) with depth at MMSF. Data derived from 1 m2 soil pits dug in 15 plots during July and August of 2000. Roots were collected from various depths then dried, sorted by size and weighed. In this case fine roots are defined as those less than 5mm in diameter (although trends were similar among all root classes). Over 80% of fine root biomass can be found in the top 40 cm of soil indicating that soil moisture in these layers is representative of what is accessible to most trees.
SI Figure 8. The change in hydraulic conductance (k) from well watered conditions during the drought of 2012, which was only significant for white oak (d, slope=-0.016, R2=0.91, p=0.01). The relationships in Figure 6 were used to find gs from ambient D when mid-day ΨL was measured, which was then used to calculate transpiration based on equation 2 in Pataki & Oren 2003. Predawn ΨL was used as an estimate of ΨS for each tree, which was used along with transpiration and mid-day ΨL to estimate K. The difference in K was calculated as the difference from well watered conditions during early 2012 (DOY<150).
SI Table 1. The 20 most common tree species in North America, as identified by (Lines et al., 2010) from USDA Forest Service Forest Inventory Analysis (FIA) data, are shown in Table S1 together with associated literature-derived values for the stem water potential associated with a 50% loss in hydraulic conductance (ΨX,50), and the hydraulic safety margin. The latter represents the difference between the minimum mid-day stem water potential and ΨX,50. After Choat et al. (2012), the hydraulic safety margin is lower, and the ΨX,50 is higher, in anisohydric species. The summary shows that oak species (Quercus spp.), which have low safety margins and high ΨX,50, are the most anisohydric species. The southern pines (e.g. Pinus spp.) are among the most isohydric.
Safety Margin (Mpa) / ΨX,50 (Mpa) / SourceAcer rubrum / 0.67 / -1.97 / Choat et al. (2012)
Acer saccrum / -3.87 / Choat et al. (2012)
Betula papyrifera / -2.34 / Choat et al. (2012)
Carya spp. / -2.1 / Choat et al. (2012)
Fagus Grandifola / Choat et al. (2012)
Fraxinus americana / -1.92 / Choat et al. (2012)
Liquidambar styraciflua / -1.17 / -3.12 / Choat et al. (2012)
Liriodendron tulipifera / 2.32 / -3.0 / Johnson et al. (2010)
Nyssa sylvatica / 0.81 / -1.82 / Choat et al. (2012)
Populus tremuloides / 2.01 / -2.74 / Choat et al. (2012)
Quercus alba / 0.23 / -1.37 / Choat et al. (2012)
Quercus nigra / -0.23 / -1.31 / Choat et al. (2012)
Quercus prinus / -1.44 / Choat et al. (2012)
Quercus stellata / Choat et al. (2012)
Pinus echinata / -3.21 / Choat et al. (2012)
Pinus taeda / 1.53 / -3.13 / Choat et al. (2012)
Pinus virginiana / 3.8 / -4.2 / Johnson et al. (2010)
Thuja occidentalis / -3.57 / Choat et al. (2012)
Supporting information references:
Choat B, Jansen S, Brodribb TJ, Cochard H, Delzon S, Bhaskar R, Bucci SJ, Feild TS, Gleason SM, Hacke UG, et al. 2012. Global convergence in the vulnerability of forests to drought. Nature 491(7426): 752-+.
Johnson DM, McCulloh KA, Woodruff DR, Meinzer FC. 2012. Hydraulic safety margins and embolism reversal in stems and leaves: Why are conifers and angiosperms so different? Plant Science 195: 48-53.
Lines ER, Coomes DA, Purves DW. 2010. Influences of Forest Structure, Climate and Species Composition on Tree Mortality across the Eastern US. Plos One 5(10).
Pataki DE, Oren R. 2003. Species differences in stomatal control of water loss at the canopy scale in a mature bottomland deciduous forest. Advances in Water Resources (26): 1267-1278.