Genetic effects on transpiration, canopy conductance, stomatal sensitivity to vapour pressure deficit, and cavitation resistance in loblolly pine

Abstract

Physiological uniformity and genetic effects on canopy-level gas-exchange and hydraulic function could impact loblolly pine (Pinus taeda L.) plantation sustainability and ecosystem dynamics under projected changes in climate. Over a 1-year period, we examined genetic effects on mean and maximum mid-day canopy conductance (G s , G smax ) and transpiration (E, max-E) within a juvenile loblolly pine plantation composed of 'genotypes' (e.g. different genetic entries) from each of the three different genetic groups (clones, full-sibs, open-pollinated). We also compared reference canopy conductance (G s ref or G s at a vapour pressure deficit D D 1 kPa), maximum E (E max ) in response to D, stomatal sensitivity to D, specific hydraulic conductivity (k s ), and cavitation resistance among genotypes. Based on genetic and physiological principles, we hypothesized that (1) within genotypes, physiological uniformity will increase as inherent genetic diversity decreases and (2) genotypes with greater k s and higher canopy-level gas-exchange rates will be more sensitive to increases in D, and more susceptible to loss of k s . In our results, high-and low-genetic diversity genotypes showed no differences in E and G s uniformity over time. However, E and max-E were significantly different among genotypes, and genotypes showed significant seasonal variability in G s and G smax . Additionally, there were significant differences in E max , G s ref , G s sensitivity to D, and the pressure at which 50% loss of k s occurs (P 50 ) among individual genotypes. We found no relationship between mean hydraulic conductivity parameters and overall G s ref or G s sensitivity. However, the genotype full embolism point (P 88 ) and loss of k s rate (LC rate ) both showed a significant positive relationship with genotype G s ref during the spring, indicating that genotypes with higher G s were less resistant to cavitation. Overall, genetic effects on canopy-level gas-exchange and cavitation resistance were significant, implying that physiological differences among genotypes might affect stand water use, carbon gain, drought tolerance, and hydrologic processes. Contrary to our expectations, uniformity in physiological process rates did not increase as inherent genetic diversity decreased, suggesting that clonal genotypes exhibit high physiological plasticity under plantation conditions. Lastly, our results imply that genotypes with higher spring-time gas-exchange rates may be more susceptible to catastrophic loss of k s . With changes in climate expected to continue, physiological differences among genotypes may affect loblolly pine plantation carbon and water cycling.

Loblolly Pine Productivity and Water Relations in Response to Throughfall Reduction and Fertilizer Application on a Poorly Drained Site in Northern Florida

“…This effect was even more pronounced in the throughfall reduction with fertilizer application treatment, which decreased G Cref from 171.9 to 119.0 mmol·m −2 ·s −1 . The contrast between the results of this study and those of Bartkowiak et al [50] may be due to differences in site conditions and/or differences in genetics, as the genetics of loblolly pine has been shown to affect G Cref and δ [19,20]. For example, Gonzalez-Benecke and Martin [19] found that irrigation increased G Cref and δ in a South Carolina loblolly pine seed source while a Florida seed source was unaffected.…”

Plant xylem hydraulics: What we understand, current research, and future challenges

“…Few of these molecular studies have focused on xylem cavitation, probably because of the time consuming phenotyping involved (but see Plavcova et al () for an example where it was performed). Some have evaluated the effect of ploidy levels on hydraulic traits including cavitation resistance (Maherali et al ; Hao et al ), others aquaporins expression and their effect on conductance or refilling (e.g., Hacke et al ; Secchi and Zwieniecki ), and several the relationships between population genetic diversity, cavitation resistance and the plasticity of this trait (Aspinwall et al ; Corcuera et al ; Lamy et al , ; Schreiber et al , ; Wortemann et al ; López et al , ). Most of the latter studies found limited genetic effect on hydraulic trait variations which were largely due to phenotypic plasticity, but in Pinus canariensis and Artemisia tridentata support for local adaptation of traits related to hydraulic safety and survival was also found (Kolb and Sperry , ; López et al , ).…”

Forest ecohydrological processes in a changing environment

“…Those examined variables in this special issue include genetic variants of tree species (e.g. loblolly pine by Aspinwall et al, 2011), structural and physiological control , elevated carbon dioxide (Warren et al, 2011) and extreme climate events (e.g. spring drought by Dong et al, 2011).…”