Tore Skrøppa

Influence of the female flowering environment on autumn frost-hardiness of Picea abies progenies.

Two experiments were designed to test possible effects of photoperiod and temperature during microsporogensis to anthesis on early autumn frost-hardiness of Picea abies progenies. Pollen lots were produced in phytotron rooms and used in crosses in a seed orchard. No biologically important differences in progeny performance were evident either between high and low temperature or between long and short-day treatments, and no significant interaction between photoperiod and temperature was found. In a third experiment, however, an effect of the environment during female flowering was obtained. Crosses performed in early spring (March) inside a heated greenhouse (short day, high temperature) produced progenies which were less hardy than their full-sibs reproduced from crosses indoors (long day, high temperature) and outdoors (long day, low temperature) in May. The most hardy siblings originated from the late-spring outdoor crosses. These results indicate that some stages in reproduction during female flowering, such as female meiosis, pollen tube growth, syngamy, early embryogenesis and embryo competition, may be sensitive to temperature and/or photoperiodic signals which can be transmitted to the progeny. We suspect that the altered performance of the progenies could be due to an activation of a regulatory mechanism affecting the expression of genes controlling adaptive traits. Both the present and earlier results have implications for the genetic interpretation of provenance differences in Norway spruce.

Impacts of Climate Change on Cold Hardiness of Conifers

Due to increased anthropogenic emissions into the atmosphere, concentrations of CO2 and other greenhouse gases have been increasing globally during the past decades. Despite realized and planned control measures, this increase is predicted to continue in the future. Due to the accompanying changes in the physical properties of the atmosphere, the air temperature of the globe is predicted to rise dramatically in the future. According to most meteorological scenarios, the increase of the global mean temperature will be 1 to 4.5°C by the year 2100. However, it is also predicted that the level of warming will be more pronounced in the north than in the south and greater during winter than during summer months (IPCC 1996).

Adaptive properties of Picea abies progenies are influenced by environmental signals during sexual reproduction

SummarySeveral independent tests have shown that climate and weather during sexual reproduction influence the adaptive properties of the Picea abies progenies. This phenomenon is expressed in seed orchards established by moving parent trees, propagated as grafts, from north to south, from high to low elevation, or from outdoor to indoor greenhouse conditions. The progenies exhibit delayed flushing in the spring, later growth cessation of leader shoots in the summer, delayed bud-set, higher frequency of lammas shoots and delayed development of frost hardiness in the autumn compared to progenies reproduced in the colder native environment. The altered performance is persistent. We have found no effect on progenies of photoperiod and temperature treatments given to the males during meiosis and pollen production. However, when crosses were made in early spring (March), inside a heated greenhouse (short day, high temperature), the progenies are less frost hardy during cold acclimation than progenies from identical crosses performed in late spring (May; long day high temperature) in the greenhouse. The most hardy offspring were from crosses performed under outdoor conditions in May (long day, low temperature). These results indicate that some stages in reproduction, such as female meiosis, pollen tube growth, syngamy and early embryo development, are sensitive to temperature and/or photoperiod which then alter the phenotypic performance of the offspring. The most likely explanation is the existence of a regulatory mechanism affecting the expression of genes controlling adaptive traits. If this is true, it must have implications for the genetic interpretation of provenance differences in Norway spruce.

Diallel crosses in Picea abies

Complete diallel crosses were performed in three Norway spruce stands and in one seed orchard. Results are presented for seed yield and 1000 seed weights. Filled seed percentages were higher for open‐pollinated families than for outcrossed full‐sib families and were lowest for selfed families. A large variation was found between the maternal parent trees for this character and a smaller variation between the paternal parents. No distinction could be made between genetic and environmental variation in filled seed percentages. Two out of 34 parents produced no viable seeds after selfing. Seeds from controlled crosses were heavier than seeds from open pollination. The maternal parent accounted for more than 75% of the total variation in 1000 seed weight. In addition, a small, but statistically significant effect of the male parent was found.

Parents of Norway Spruce Adjust the Performance of Their Progeny According to Changes in Climate and Weather Conditions During Female Flowering

Several independent tests have shown that climate and weather conditions during sexual reproduction influence the adaptive properties of Picea abies progenies. This phenomenon is expressed in seed orchards established by moving parent trees, propagated as grafts, from north to south, from high to low elevation, or from outdoor to indoor greenhouse conditions. The progenies exhibit delayed dehardening and flushing in the spring, later growth cessation of leader shoots in the summer, delayed bud-set, higher frequency of lammas shoots and delayed development of frost hardiness in the autumn compared to their siblings reproduced in a colder native environment. The altered performance is persistent; data indicate that the changed phenology lasts for more than 17 years from seeds. The environmental signal is transmitted from parents to offspring during one or several reproductive stages in the female flowers. We suspect an existence of a regulatory mechanism which senses the changes in temperature and/or photoperiod, and then modifies the expression of genes controlling adaptive traits in the progeny. Regardless of type of mechanisms involved, these observations have affected our interpretation of provenance variation. The described phenomenon should be accounted for when predicting long term effects of global warming in both managed and natural boreal forests.

The Influence of the Environment during Sexual Reproduction on Adaptations of Conifers along Latitudinal and Altitudinal Gradients

Climatic adaptation seems to be the most important component in the evolutionary process of boreal forest tree species. Recent evidence has been accumulating that this process may be less clear-cut than earlier assumed. In Picea abies, several independent tests have shown that the climate and weather conditions during sexual reproduction influence the adaptive properties of the progenies. The phenomenon is expressed in Norway spruce seed orchards established by moving parent trees, propagated as grafts, from north to south, from high to low elevation, or from outdoor to indoor greenhouse conditions. The progenies exhibit a changed phenology and a delayed development of frost hardiness in the autumn compared to their siblings reproduced in a colder environment. Observations on seedlings from seeds harvested in northern stands of provenances transferred from the south to the north, show that they have tuned their photoperiodic responses towards that the of the local provenances. Results with other conifer species indicate that they express similar effects. A possible explanation for the phenomenon is the existence of a regulatory mechanism, sensing the changes in temperature and/or photoperiod at some stages during the reproductive process in the female flower, and then modifying the expression of genes controlling adaptive traits in the progeny. Regardless of the type of mechanisms involved, these observations have changed our understanding of ecotype formation in Norway spruce, and given us some ideas why this species express strong clinal variation in combination with a large within population variation for the same adaptive traits. The maternal influence will often alter the phenotypic performance of the progenies in the ssame direction as natural selection. It may be one of the reasons why some conifer species under conditions seem so highly adaptable.

The genetic response of plant populations to a changing environment: the case for non-Mendelian processes

Classical Mendelian inheritance assumes the existence of chromosomal genes which are transferred from the parents to the next generation in a random fashion. In a diploid plant species, the zygote is derived from the fusion of two haploid gametes, one contributed by its maternal and one by its paternal parent. These gametes were formed after a random segregation during meiosis in each parent. The fertilization of the female (egg) by the male gamete (pollen) is likewise thought to be random. Therefore, when no internal or external factors are operating, the genetic composition of the progeny population can be described with statistical precision by the laws of probability theory. Fundamental principles are regular segregation and independent assortment between different pairs of alleles (Grant 1975). Based on these assumptions a whole body of population and quantitative genetic theory has been developed for plant population changes under the evolutionary forces of natural selection, mutation, migration and drift (i.e. Falconer 1989; Hedrick 1985). The models have been verified in a large set of observational and experimental data.