Using herbarium data to study impact of climate change on flowering phenology and hybridization potential of closely related plant species

Abstract

Considerable attention has been devoted to assessing the biological consequences of global warming during the past decades. Phenological events in plants, especially onset of flowering, has generally been observed to advance with rising temperature. However, phenology research is often restricted to short time periods because of limited data availability. Collection of flowering data from herbarium specimens provides one possible solution to this problem. This study uses specimens in two herbaria to explore patterns of phenology change over the past 160 years, with a special emphasis on the potential for hybridization. Flowering (collection) dates from ten pairs of species (each containing two well-collected, interfertile species from the same genus) were related to year of collection, temperature and latitude collection to identify and compare trends between closely related species. Flowering dates have advanced for most species, the largest change being 19.5 days per 100 years (Arabidopsis arenosa), with no strong evidence for either increasing or decreasing hybridization potential. Flowering time have been more strongly influenced by spring temperature than by summer and winter temperature. Interfertile species within Geum and Linaria differed in their phenological response to temperature, resulting in converging (Geum) and diverging (Linaria) flowering times with increasing temperature. Thus, one would expect an increasing potential for hybridization for Geum and decreasing potential for Linaria under a scenario of continued increase in temperature, even though no temporal trend was detected in the historical dataset.

Popular Abstract

Using herbarium data to assess the impact of global warming on flowering phenology and hybridization potential of closely related plant species

Global warming has become a major issue in the past decades. Our planet's average surface temperature has risen about 0.9 degrees Celsius since the late 19th century. The heat energy absorbed and emitted by the earth-atmosphere system is still out of balance; thus, the greenhouse effect continues to accumulate. Global warming has considerable potential to cause long-term changes in wild plant populations, especially with regard to flowering phenology. Such changes can present a major threat to the viability and survival of a plant population, by, for example, causing a mismatch between the flowering phenology of the plant and the activity period of its primary pollinators or by increasing the risk of hybridization with a closely related plant species through increasing overlap in flowering phenology.

In the present study, I obtained phenological data from 5448 herbarium specimens, collected in Sweden during 1860-2016, to assess the impact of global warming on flowering phenology and hybridization potential. The dataset represents 19 herbaceous species in eight genera (each from a separate family). Each genus was represented by two well-collected species known to form hybrids in Sweden and other areas. I recorded the year and date of collection as well as the geographical location of the collection site for each specimen and obtained relevant temperature data from the Swedish Meteorological and Hydrological Institute. I performed multiple regressions for each species to identify phenological trends and their main predictors, and used ANCOVA for each pair of interfertile species (genus) to test for significant differences between species in the overall flowering (collection) time and in the extent to which collection year or temperature influenced flowering time and hybridization potential.

Multiple regressions for individual species showed a general trend of advancing flowering time, as shown by negative regression coefficients for collection year in all but one case, although only four values reached significance at the 5 percent level. Stronger trends were found when using spring or summer temperature as a predictor, possibly because these analyses also captured temperature effects resulting from the extensive year-to-year fluctuations around the long-term trend in temperature.

Interfertile species usually responded similarly to increasing temperature or collection year, as shown by nonsignificant species-by-temperature interactions in ANCOVAs and quantitatively similar flowering advancements with increasing temperature in regression analyses. Significant interaction terms between flowering time and temperature were, however, detected for species of Geum (with G. urbanum showing a stronger response to both winter and spring temperature than G. rivale,) and Linaria (with L. repens showing a stronger influence of spring temperature than L. vulgaris). These interactions caused the trend lines to converge (Geum) or diverge (Linaria) with increasing temperature. Thus, under a scenario of continued increase in temperature (IPCC 2007), the hybridization potential can be expected to increase for Geum and decrease for Linaria, even though no temporal trend was detected in the historical dataset.

Master’s degree project in Biology 45 credits 2018
Department of Biology, Lund University
Supervisor: Stefan Andersson

• author: Kang, Luyi
• supervisor: Stefan Andersson
• organization: Degree Projects in Biology
• course: BION02 20172
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8958559
• date added to LUP: 2018-09-12 15:56:25
• date last changed: 2018-09-12 15:56:25