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Reliance on shallow soil water in a mixed-hardwood forest in central Pennsylvania.

Gaines KP, Stanley JW, Meinzer FC, McCulloh KA, Woodruff DR, Chen W, Adams TS, Lin H, Eissenstat DM - Tree Physiol. (2015)

Bottom Line: Based on multiple lines of evidence, including stable isotope natural abundance, sap flux and soil moisture depletion patterns with depth, the majority of water uptake during the dry part of the growing season occurred, on average, at less than ∼60 cm soil depth throughout the catchment.While there were some trends in depth of water uptake related to genus, tree size and soil depth, water uptake was more uniformly shallow than we expected.Our results suggest that these types of forests may rely considerably on water sources that are quite shallow, even in the drier parts of the growing season.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecosystem Science and Management, Pennsylvania State University, University Park, PA 16802, USA.

No MeSH data available.


(a) Boxplot of xylem water δ18O (top) and δ2H (bottom) compositions for genera sampled during dry sample dates. Upper and lower boundaries of box denote 75th and 25th percentile ranges, respectively, with median at center line. Error bars show maximum and minimum range of data with points for observations exceeding 1.5 times the interquartile range. Letters denote statistically significant differences (genus differences in δ18O, P < 0.0001; δ2H, P < 0.00001; Acer, n = 13; Carya, n = 5; Pinus, n = 3; Quercus, n = 17). (b) Scatter plot of tree DBH and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.00001, R2 = 0.35, y = −0.063x − 3.37; δ2H, P < 0.000001, R2 = 0.42, y = −0.46x − 28.45). (c) Scatter plot of soil depth at tree locations and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.05, R2 = 0.09, y = −0.020x − 4.57; δ2H, P < 0.05, R2 = 0.07, y = −0.12x − 38.1).
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TPV113F6: (a) Boxplot of xylem water δ18O (top) and δ2H (bottom) compositions for genera sampled during dry sample dates. Upper and lower boundaries of box denote 75th and 25th percentile ranges, respectively, with median at center line. Error bars show maximum and minimum range of data with points for observations exceeding 1.5 times the interquartile range. Letters denote statistically significant differences (genus differences in δ18O, P < 0.0001; δ2H, P < 0.00001; Acer, n = 13; Carya, n = 5; Pinus, n = 3; Quercus, n = 17). (b) Scatter plot of tree DBH and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.00001, R2 = 0.35, y = −0.063x − 3.37; δ2H, P < 0.000001, R2 = 0.42, y = −0.46x − 28.45). (c) Scatter plot of soil depth at tree locations and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.05, R2 = 0.09, y = −0.020x − 4.57; δ2H, P < 0.05, R2 = 0.07, y = −0.12x − 38.1).

Mentions: Univariate tests used in preparation for mixed effect model building showed that genus, tree size and soil depth were all significant predictors of both δ18O and δ2H (Figure 6). Quercus and Carya xylem water tended to be more depleted in heavy isotopes than that of Acer (overall genus effect, P < 0.0001 and R2 = 0.36 for δ18O; P < 0.00001 and R2 = 0.46 for δ2H) (Figure 6a). Tree size was a significant negative linear predictor of δ18O and δ2H, with larger trees tending to use water more depleted in heavy isotopes than smaller trees. Diameter at breast height was used in the model building process since DBH and tree height were positively correlated (r = 0.59), and DBH was a stronger predictor of xylem water δ18O than tree height (DBH, P < 0.00001, R2 = 0.35; tree height, P < 0.001, R2 = 0.22) and δ2H (DBH, P < 0.000001, R2 = 0.42; tree height, P < 0.01, R2 = 0.19) (Figure 6b). Soil depth was a significant linear predictor of δ18O (P < 0.05, R2 = 0.09) and δ2H (P < 0.05, R2 = 0.07) (Figure 6c), but with lower explanatory power compared with genus and DBH. Slope position and elevation were not significant predictors of δ18O or δ2H (δ18O, P = 0.19 for slope position and P = 0.91 for elevation; δ2H, P = 0.36 for slope position and P = 0.69 for elevation). A comparison of nested models with a random effect of individual tree and candidate fixed effects (Table 2) resulted in the selection of a final model with all possible fixed effects that we examined (genus, DBH and soil depth; Table 3). The final model explained ∼54% of the variation in tree xylem water δ18O and ∼63% of the variation in δ2H.Table 2.


Reliance on shallow soil water in a mixed-hardwood forest in central Pennsylvania.

Gaines KP, Stanley JW, Meinzer FC, McCulloh KA, Woodruff DR, Chen W, Adams TS, Lin H, Eissenstat DM - Tree Physiol. (2015)

(a) Boxplot of xylem water δ18O (top) and δ2H (bottom) compositions for genera sampled during dry sample dates. Upper and lower boundaries of box denote 75th and 25th percentile ranges, respectively, with median at center line. Error bars show maximum and minimum range of data with points for observations exceeding 1.5 times the interquartile range. Letters denote statistically significant differences (genus differences in δ18O, P < 0.0001; δ2H, P < 0.00001; Acer, n = 13; Carya, n = 5; Pinus, n = 3; Quercus, n = 17). (b) Scatter plot of tree DBH and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.00001, R2 = 0.35, y = −0.063x − 3.37; δ2H, P < 0.000001, R2 = 0.42, y = −0.46x − 28.45). (c) Scatter plot of soil depth at tree locations and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.05, R2 = 0.09, y = −0.020x − 4.57; δ2H, P < 0.05, R2 = 0.07, y = −0.12x − 38.1).
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TPV113F6: (a) Boxplot of xylem water δ18O (top) and δ2H (bottom) compositions for genera sampled during dry sample dates. Upper and lower boundaries of box denote 75th and 25th percentile ranges, respectively, with median at center line. Error bars show maximum and minimum range of data with points for observations exceeding 1.5 times the interquartile range. Letters denote statistically significant differences (genus differences in δ18O, P < 0.0001; δ2H, P < 0.00001; Acer, n = 13; Carya, n = 5; Pinus, n = 3; Quercus, n = 17). (b) Scatter plot of tree DBH and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.00001, R2 = 0.35, y = −0.063x − 3.37; δ2H, P < 0.000001, R2 = 0.42, y = −0.46x − 28.45). (c) Scatter plot of soil depth at tree locations and tree water δ18O (top) and δ2H (bottom) compositions for individuals sampled on dry dates (δ18O, P < 0.05, R2 = 0.09, y = −0.020x − 4.57; δ2H, P < 0.05, R2 = 0.07, y = −0.12x − 38.1).
Mentions: Univariate tests used in preparation for mixed effect model building showed that genus, tree size and soil depth were all significant predictors of both δ18O and δ2H (Figure 6). Quercus and Carya xylem water tended to be more depleted in heavy isotopes than that of Acer (overall genus effect, P < 0.0001 and R2 = 0.36 for δ18O; P < 0.00001 and R2 = 0.46 for δ2H) (Figure 6a). Tree size was a significant negative linear predictor of δ18O and δ2H, with larger trees tending to use water more depleted in heavy isotopes than smaller trees. Diameter at breast height was used in the model building process since DBH and tree height were positively correlated (r = 0.59), and DBH was a stronger predictor of xylem water δ18O than tree height (DBH, P < 0.00001, R2 = 0.35; tree height, P < 0.001, R2 = 0.22) and δ2H (DBH, P < 0.000001, R2 = 0.42; tree height, P < 0.01, R2 = 0.19) (Figure 6b). Soil depth was a significant linear predictor of δ18O (P < 0.05, R2 = 0.09) and δ2H (P < 0.05, R2 = 0.07) (Figure 6c), but with lower explanatory power compared with genus and DBH. Slope position and elevation were not significant predictors of δ18O or δ2H (δ18O, P = 0.19 for slope position and P = 0.91 for elevation; δ2H, P = 0.36 for slope position and P = 0.69 for elevation). A comparison of nested models with a random effect of individual tree and candidate fixed effects (Table 2) resulted in the selection of a final model with all possible fixed effects that we examined (genus, DBH and soil depth; Table 3). The final model explained ∼54% of the variation in tree xylem water δ18O and ∼63% of the variation in δ2H.Table 2.

Bottom Line: Based on multiple lines of evidence, including stable isotope natural abundance, sap flux and soil moisture depletion patterns with depth, the majority of water uptake during the dry part of the growing season occurred, on average, at less than ∼60 cm soil depth throughout the catchment.While there were some trends in depth of water uptake related to genus, tree size and soil depth, water uptake was more uniformly shallow than we expected.Our results suggest that these types of forests may rely considerably on water sources that are quite shallow, even in the drier parts of the growing season.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecosystem Science and Management, Pennsylvania State University, University Park, PA 16802, USA.

No MeSH data available.