Response of Mid-Rotation Loblolly Pine (Pinus taeda L.) Physiology and Productivity to Sustained, Moderate Drought on the Western Edge of the Range
Adam Maggard | Rodney Will | Duncan Wilson | Cassandra Meek
The productivity of the approximately 11 million ha of loblolly pine plantations in the southeastern USA could be threatened by decreased water availability in a future climate. To determine the effects of sustained drought on leaf gas exchange, whole-tree water use, and individual tree growth, we examined the response of loblolly pine trees to 100% throughfall exclusion cumulatively spanning the sixth and seventh growing seasons of a plantation in southeastern Oklahoma. Throughfall exclusion reduced volumetric soil water content for 0–12 cm soil depth from 10.8% to 4.8% and for 12–45 cm soil depth from 24.2% to 15.6%. Compared to ambient throughfall trees, leaf water potential of the throughfall exclusion trees became more negative, −0.9 MPa vs. −1.3 MPa for predawn measurements and −1.5 MPa vs. −1.9 MPa for midday measurements. Throughfall exclusion did not significantly reduce leaf gas exchange or tree water use. However, throughfall exclusion significantly reduced leaf biomass by 21% and stem volume growth by 23%. These results indicate that sustained drought may cause downward shifts in leaf quantity to conserve water rather than reducing leaf-level water use.
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