Variation in water potential, hydraulic characteristics and water source use in montane Douglas-fir and lodgepole pine trees in southwestern Alberta and consequences for seasonal changes in photosynthetic capacity.
ABSTRACT Tree species response to climate change-induced shifts in the hydrological cycle depends on many physiological traits, particularly variation in water relations characteristics. We evaluated differences in shoot water potential, vulnerability of branches to reductions in hydraulic conductivity, and water source use between Pinus contorta Dougl. ex Loud. var. latifolia Engelm. (lodgepole pine) and Pseudotsuga menziesii (Mirb.) Franco (interior Douglas-fir), and determined the consequences for seasonal changes in photosynthetic capacity. The Douglas-fir site had soil with greater depth, finer texture and higher organic matter content than soil at the lodgepole pine site, all factors that increased the storage of soil moisture. While the measured xylem vulnerability curves were quite similar for the two species, Douglas-fir had lower average midday shoot water potentials than did lodgepole pine. This implied that lodgepole pine exhibited stronger stomatal control of transpiration than Douglas-fir, which helped to reduce the magnitude of the water potential gradient required to access water from drying soil. Stable hydrogen isotope measurements indicated that Douglas-fir increased the use of groundwater during mid-summer when precipitation inputs were low, while lodgepole pine did not. There was a greater reduction of photosynthetic carbon gain in lodgepole pine compared with Douglas-fir when the two tree species were exposed to seasonal declines in soil water content. The contrasting patterns of seasonal variation in photosynthetic capacity observed for the two species were a combined result of differences in soil characteristics at the separate sites and the inherent physiological differences between the species.
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ABSTRACT: BACKGROUND: Douglas-fir (Pseudotsuga menziesii) extends over a wide range of contrasting environmentalconditions, reflecting substantial local adaptation. For this reason, it is an interesting model speciesto study plant adaptation and the effects of global climate change such as increased temperatures andsignificant periods of drought on individual trees and the forest landscape in general. However,genomic data and tools for studying genetic variation in natural populations to understand the geneticand physiological mechanisms of adaptation are currently missing for Douglas-fir. This studyrepresents a first step towards characterizing the Douglas-fir transcriptome based on 454 sequencingof twelve cDNA libraries. The libraries were constructed from needle and wood tissue of coastal andinterior provenances subjected to drought stress experiments. RESULTS: The 454 sequencing of twelve normalized cDNA libraries resulted in 3.6 million reads from which aset of 170,859 putative unique transcripts (PUTs) was assembled. Functional annotation by BLASTsearches and Gene Ontology mapping showed that the composition of functional classes is verysimilar to other plant transcriptomes and demonstrated that a large fraction of the Douglas-firtranscriptome is tagged by the PUTs. Based on evolutionary conservation, we identified about 1,000candidate genes related to drought stress. A total number of 187,653 single nucleotidepolymorphisms (SNPs) were detected by three SNP detection tools. However, only 27,688 SNPswere identified by all three methods, indicating that SNP detection depends on the particular methodused. The two alleles of about 60% of the 27,688 SNPs are segregating simultaneously in bothcoastal and interior provenances, which indicates a high proportion of ancestral sharedpolymorphisms or a high level of gene flow between these two ecologically and phenotypicallydifferent varieties. CONCLUSIONS: We established a catalogue of PUTs and large SNP database for Douglas-fir. Both will serve as auseful resource for the further characterization of the genome and transcriptome of Douglas-fir andfor the analysis of genetic variation using genotyping or resequencing methods.BMC Genomics 11/2012; 13(1):673. · 4.40 Impact Factor
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ABSTRACT: Conifers exhibit a number of constitutive and induced mechanisms to defend against attack by pests and pathogens such as mountain pine beetle (Dendroctonus ponderosae Hopkins) and their fungal associates. Ecological studies have demonstrated that stressed trees are more susceptible to attack by mountain pine beetle than their healthy counterparts. In this study, we tested the hypothesis that water deficit affects constitutive and induced responses of mature lodgepole pine × jack pine hybrids (Pinus contorta Dougl. ex Loud. var. latifolia Engelm. ex S. Wats. × Pinus banksiana Lamb.) to inoculation with the mountain pine beetle fungal associate Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield. The degree of stress induced by the imposed water-deficit treatment was sufficient to reduce photosynthesis. Grosmannia clavigera-induced lesions exhibited significantly reduced dimensions in water-deficit trees relative to well-watered trees at 5 weeks after inoculation. Treatment-associated cellular-level changes in secondary phloem were also observed. Quantitative RT-PCR was used to analyze transcript abundance profiles of 18 genes belonging to four families classically associated with biotic and abiotic stress responses: aquaporins (AQPs), dehydration-responsive element binding (DREB), terpene synthases (TPSs) and chitinases (CHIs). Transcript abundance profiles of a TIP2 AQP and a TINY-like DREB decreased significantly in fungus-inoculated trees, but not in response to water deficit. One TPS, Pcb(+)-3-carene synthase, and the Class II CHIs PcbCHI2.1 and PcbCHI2.2 showed increased expression under water-deficit conditions in the absence of fungal inoculation, while another TPS, Pcb(E)-β-farnesene synthase-like, and two CHIs, PcbCHI1.1 and PcbCHI4.1, showed attenuated expression under water-deficit conditions in the presence of fungal inoculation. The effects were observed both locally and systemically. These results demonstrate that both constitutive and induced carbon- and nitrogen-based defenses are affected by water deficit, suggesting potential consequences for mountain pine beetle dynamics, particularly in novel environments.Tree Physiology 12/2013; · 2.85 Impact Factor