Tree Water Use, Water Use Efficiency, and Carbon Isotope Discrimination in Relation to Growth Potential in Populus deltoides and Hybrids under Field Conditions

Maier Maier,Nichols Nichols,Burley Burley,Cook Cook,Ghezehei Ghezehei,Hazel Hazel

doi:10.3390/f10110993

Maier Maier, Nichols Nichols + Show 4 more

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https://doi.org/10.3390/f10110993

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Abstract

We explored the relationship between tree growth, water use, and related hydraulic traits in Populus deltoides Bartr. ex Marsh.and hybrid clones, to examine potential trade-offs between growth and water use efficiency. Nine genotypes, six P. deltoides and three hybrid clones, that represented genotypes with high (Group H), intermediate (Group I), and low (Group L) growth performance were selected for study, based on year-two standing stem biomass in a replicated field trial. In year four, tree growth, transpiration (Et), canopy stomatal conductance (Gs), whole-tree hydraulic conductance (Gp), and carbon isotope discrimination (Δ13C) were measured. Tree sap flux was measured continuously using thermal dissipation probes. We hypothesized that Group H genotypes would have increased growth efficiency (GE), increased water use efficiency of production (WUEp, woody biomass growth/Et), lower Δ13C, and greater Gp than slower growing genotypes. Tree GE increased with relative growth rate (RGR), and mean GE in Group H was significantly greater than L, but not I. Tree WUEp ranged between 1.7 and 3.9 kg biomass m3 H2O−1, which increased with RGR. At similar levels of Et, WUEp was significantly greater in Group H (2.45 ± 0.20 kg m−3), compared to I (2.03 ± 0.18 kg m−3) or L (1.72 ± 0.23 kg m−3). Leaf and wood Δ13C scaled positively with stem biomass growth but was not correlated with WUEp. However, at a similar biomass increment, clones in Group H and I had significantly lower leaf Δ13C than Group L. Similarly, Group H clones had a significantly lower wood Δ13C than Group L, supporting our hypothesis of increased WUE in larger trees. Tree physiological and hydraulic traits partially explain differences in WUEp and Δ13C, and suggest that clone selection and management activities that increase tree biomass production will likely increase tree and stand WUE. However, more research is needed to discern the underlying hydraulic mechanisms responsible for the higher WUE exhibited by large trees and distinct clones.

Highlights

Poplar (Populus spp.) and their hybrids, grown as short-rotation woody crops (SRWC), have multiple industrial applications, that provide solid wood products, veneer, pulp and paper, excelsior, chemicals, and feedstocks, for cellulosic energy and the biofuels industry [1,2]
We found that growth efficiency (GE) and water use efficiency of production (WUEp) were positively
We found that growth efficiency (GE) and water use efficiency of production (WUEp) were positively correlated with growth

Summary

Introduction

Poplar (Populus spp.) and their hybrids, grown as short-rotation woody crops (SRWC), have multiple industrial applications, that provide solid wood products, veneer, pulp and paper, excelsior, chemicals, and feedstocks, for cellulosic energy and the biofuels industry [1,2]. Forests 2019, 10, 993 tropical storms, and extended periods of heat or cold [3] These systems will likely be located on marginal lands, unsuitable for agriculture; low site quality, combined with high establishment and maintenance costs, may limit profitability on these sites [4]. Due to rapid growth and high transpiration rates, short rotation poplars have high water use [5,6,7,8], and seasonal water deficits can strongly limit poplar productivity and yield [9,10,11]. Potential tradeoffs between productivity and water use in short-rotation poplar are critical to understand, considering that management of these systems may need to account for multiple ecosystem services (e.g., biomass, water yield, waste management, carbon sequestration) [15,16]

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