Variability in flooding tolerance, growth and leaf traits in a Populus deltoides intraspecific progeny

Provenance, genotype, and flooding influence growth and resource acquisition characteristics in a clonal, riparian shrub

PREMISE

Riparian plants can exhibit intraspecific phenotypic variability across the landscape related to temperature and flooding gradients. Phenotypes that vary across a climate gradient are often partly genetically determined and may differ in their response to inundation. Changes to inundation patterns across a climate gradient could thus result in site-specific inundation responses. Phenotypic variability is more often studied in riparian trees, yet riparian shrubs are key elements of riparian systems and may differ from trees in phenotypic variability and environmental responses.

METHODS

We tested whether individuals of a clonal, riparian shrub, Pluchea sericea, collected from provenances spanning a temperature gradient differed in their phenotypes and responses to inundation and to what degree any differences were related to genotype. Plants were subjected to different inundation depths and a subset genotyped. Variables related to growth and resource acquisition were measured and analyzed using hierarchical, multivariate Bayesian linear regressions.

RESULTS

Individuals from different provenances differed in their phenotypes, but not in their response to inundation. Phenotypes were not related to provenance temperature but were partially governed by genotype. Growth was more strongly influenced by inundation, while resource acquisition was more strongly controlled by genotype.

CONCLUSIONS

Growth and resource acquisition responses in a clonal, riparian shrub are affected by changes to inundation and plant demographics in unique ways. Shrubs appear to differ from trees in their responses to environmental change. Understanding environmental effects on shrubs separately from those of trees will be a key part of evaluating impacts of environmental change on riparian ecosystems.

Floodwater Depth Causes Different Physiological Responses During Post-flooding in Willows

Willows are widely planted in areas under risk of flooding. The physiological responses of willows to flooding have been characterized, but little is known about their responses during the post-flooding period. After the end of the stress episode, plants may modify some traits to compensate for the biomass loss during flooding. The aim of this work was to analyze the post-flooding physiological responses of willow under two different depths of stagnant floodwater. Cuttings of Salix matsudana NZ692 clone were planted in pots in a greenhouse. The experiment started when the plants were 2 months old with the following treatments: Control plants (watered to field capacity); plants partially flooded 10 cm above soil level (F10) and plants partially flooded 40 cm above soil level (F40). The flooding episode lasted 35 days and was followed by a recovery period of 28 days (post-flooding period). After the flooding period, height, diameter and total biomass were higher in F10, while F40 plants showed an increase in plant adventitious root production and leaf nitrogen content. During the post-flooding period, the photosynthetic rate, nitrogen, chlorophyll and soluble sugar contents were significantly higher in leaves of F40 than in Control and F10 treatments. Stomatal conductance and specific leaf area were higher in the previously flooded plants compared to Control treatment. Plants from F10 treatments showed a higher growth in height, root-to-shoot ratio, and carbon isotope discrimination than F40, while the opposite occurred for growth in diameter, vessel size and leaf area. We conclude that depth of floodwater not only causes different responses during flooding, but that its effects are also present in the post-flooding recovery period, affecting the growth and physiology of willows once the stress episode has ended. Even when flooding impacted growth negatively in F40, in the post-flooding period these plants compensated by increasing the photosynthetic rate, plant leaf area and xylem vessel size. Willows endurance to flooding is the result of both responses during flooding, and plastic responses during post-flooding.

Variation and Genetic Parameters of Leaf Morphological Traits of Eight Families from Populus simonii × P. nigra

Leaf morphology in Populus L. varies extensively among sections, species and clones under strong genetic control. P. nigra L. (section Aigeiros), with large and triangular leaves, is a commercial forest tree of economic importance for fast growth and high yield in Europe. P. simonii Carr. (section Tacamahaca) with small land rhomboid ovate leaves performs cold and dry resistance/tolerance in the semi-arid region of Northern China. Leaf morphological traits could be used as early indicators to improve the efficiency of selection. In order to investigate the genetic variation pattern of leaf morphology traits, estimate breeding values (combining ability), as well as evaluate crossing combinations of parents, 1872 intersectional progenies from eight families (P. simonii × P. nigra) and their parents were planted with cuttings for the clonal replicate field trial in Northern China. Four leaf size traits (area, perimeter, length, width) and roundness were measured with leaf samples from the 1-year-old clonal plantation. Significant differences regarding leaf traits were found between and among three female clones of P. simonii from Inner Mongolia, China and six male clones of P. nigra from Casale Monferrato, Italy. The genetic variation coefficient, heritability and genetic variance component of most traits in male parents were greater than these of female parents. Heritability estimates of male and female parents were above 0.56 and 0.17, respectively. Plentiful leaf variations with normal and continuous distributions exited in the hybrid progenies among and within families with the genetic variation coefficient and heritability above 28.49 and 0.24, respectively. Heritability estimates showed that leaf area was the most heritable trait, followed by leaf width. The breeding value ranking of parents allowed us to select the parental clones for new crosses and extend the mating design. Two male parental clones (N430 and N429) had greater breeding values (general combining ability, GCA) of leaf size traits than other clones. The special combining ability (SCA) of the crossing combination between P. simonii cl. ZL-3 and P. nigra cl. N430 was greater than that of others. Eight putatively superior genotypes, most combined with the female parental clone ZL-3, can be selected for future testing under near-commercial conditions. Significant genetic and phenotypic correlations were found between five leaf morphology traits with the coefficients above 0.9, except for leaf roundness. The results showed that leaf morphology traits were under strong genetic control and the parental clones with high GCA and SCA effects could be utilized in heterosis breeding, which will provide a starting point for devising a new selection strategy of parents and progenies.