The choice of genetic material for mechanistic studies of adaptation in forest trees

Introduction to the special issue: Tree invasions: towards a better understanding of their complex evolutionary dynamics

Many invasive plants show evidence of trait-based evolutionary change, but these remain largely unexplored for invasive trees. The increasing number of invasive trees and their tremendous impacts worldwide, however, illustrates the urgent need to bridge this knowledge gap to apply efficient management. Consequently, an interdisciplinary workshop, held in 2015 at Stellenbosch University in Stellenbosch, South Africa, brought together international researchers to discuss our understanding of evolutionary dynamics in invasive trees. The main outcome of this workshop is this Special Issue of AoB PLANTS. The collection of papers in this issue has helped to identify and assess the evolutionary mechanisms that are likely to influence tree invasions. It also facilitated expansion of the unified framework for biological invasions to incorporate key evolutionary processes. The papers cover a wide range of evolutionary mechanisms in tree genomes (adaptation), epigenomes (phenotypic plasticity) and their second genomes (mutualists), and show how such mechanisms can impact tree invasion processes and management. The special issue provides a comprehensive overview of the factors that promote and mitigate the invasive success of tree species in many parts of the world. It also shows that incorporating evolutionary concepts is crucial for understanding the complex drivers of tree invasions and has much potential to improve management. The contributions of the special issue also highlight many priorities for further work in the face of ever-increasing tree invasions; the complexity of this research needs calls for expanded interdisciplinary research collaborations.

Proteins responding to drought and high-temperature stress in Pinus armandii Franch

Proteomic analysis provides a powerful method for studying plant responses to stress at the protein level. To study stress-responsive molecular mechanisms for Pinus armandii Franch, one of the most important forest plantation tree species in subalpine regions of Asia, we analyzed the response of 2-year-old P. armandii seedlings to drought and high temperature using two-dimensional gel electrophoresis. More than 550 reproducible needle proteins were detected in the controls and treatments, and the abundance of 27 proteins were found to change noticeably. We identified five proteins affected by drought stress and eight proteins affected by high temperature. These proteins are functionally quite diverse and are involved in photosynthesis, cell division and elongation, antioxidant metabolism, ammonia assimilation, growth and development, and protein folding. Our results provide fundamental data for future research on responses to drought and high temperature. As drought and high temperature are two major factors limiting the growth of subalpine forests during summer under recent global warming, this research may contribute to an understanding of the development of stress tolerance in trees.

Molecular linkage maps of the Populus genome

We report molecular genetic linkage maps for an interspecific hybrid population of Populus, a model system in forest-tree biology. The hybrids were produced by crosses between P. deltoides (mother) and P. euramericana (father), which is a natural hybrid of P. deltoides (grandmother) and P. nigra (grandfather). Linkage analysis from 93 of the 450 backcross progeny grown in the field for 15 years was performed using random amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), and inter-simple sequence repeats (ISSRs). Of a total of 839 polymorphic markers identified, 560 (67%) were testcross markers heterozygous in one parent but null in the other (segregating 1:1), 206 (25%) were intercross dominant markers heterozygous in both parents (segregating 3:1), and the remaining 73 (9%) were 19 non-parental RAPD markers (segregating 1:1) and 54 codominant AFLP markers (segregating 1:1:1:1). A mixed set of the testcross markers, non-parental RAPD markers, and codominant AFLP markers was used to construct two linkage maps, one based on the P. deltoides (D) genome and the other based on P. euramericana (E). The two maps showed nearly complete coverage of the genome, spanning 3801 and 3452 cM, respectively. The availability of non-parental RAPD and codominant AFLP markers as orthologous genes allowed for a direct comparison of the rate of meiotic recombination between the two different parental species. Generally, the rate of meiotic recombination was greater for males than females in our interspecific poplar hybrids. The confounded effect of sexes and species causes the mean recombination distance of orthologous markers to be 11% longer for the father (P. euramericana; interspecific hybrid) than for the mother (P. deltoides; pure species). The linkage maps constructed and the interspecific poplar hybrid population in which clonal replicates for individual genotypes are available present a comprehensive foundation for future genomic studies and quantitative trait locus (QTL) identification.

Quantitative genetics and the persistence of environmental effects in clonally propagated organisms

Phenotype is often viewed as a product of genes and the environment in which these genes are expressed. However, numerous studies have shown that environment can cause lasting changes in phenotype that can be passed from one generation to the next, much as genes are transmitted. In clonally propagated organisms, persistence of environmental effects has been observed in a range of plant and animal species, but has rarely been the object of study. We measured the persistence and magnitude of environmental effects on phenotype over three clonal generations in the arctic sedge Eriophorum vaginatum. We found that the environment in which tillers developed had large effects on their later performance (parental effects) and that these effects were in part independent of the size of tillers. The magnitude and persistence of environmental effects did not differ between environmental treatments or among genotypes. However, after 52 weeks of growth and two rounds of clonal propagation, grandparental treatment effects were not significant. We describe methods that can be used in quantitative genetics studies of clonal organisms to reduce bias in estimates of genotypic and environmental variance and argue that the persistence of environmental effects in clonal plant material has ecological and evolutionary consequences similar to those described for maternal environmental effects in sexual organisms.

Suitability and use of poplars as bioindicators - A new concept

Practical considerations, characteristic physiological features, as well as the availability of hybrids with different resistances to air pollutants play an important role in the decision to use poplar cuttings as experimental plants for impact studies.This paper demonstrates the effect of the hybridization of two poplar clones on the resistance to different air pollutants and, additionally, presents a new concept of bioindication involving these two clones with different degrees of resistance to SO(2) and O(3).This concept, which is based on the results of fumigation experiments conducted in open-top chambers, uses six-week-old vital poplar cuttings as bioindicators. Both the anabolic defense reactions of younger leaves and the catabolic stress reactions of older leaves are examined. The measurement results obtained from cv. Loenen and cv. Rochester clones which differ in their sensitivities to individual pollutants, are examined to determine the specific relationships. The results can be verified by measuring the premature leaf losses of a third clone, cv. Unal, which reacts to both SO(2) and O(3) with highly pronounced leaf loss. To prevent false interpretations, it is necessary to standardize the plant material as far as possible by choosing clones of a defined age and number of leaves, and by selecting reproducible cultivation and exposure conditions. The impact criteria are methodologically simple and therefore suitable for routine examinations.