Do seeds all behave in similar ways? In an article in Annals of Botany, Anne Visscher and colleagues argue that there is a bias towards temperate seeds and that this could mislead attempts to build ecological models. They conclude that the tendency to see mountain plants as Alpine plants loses some of the unique conditions that montane tropical plants face.
Visscher and colleagues examine the geographical bias in ecological studies and global reviews, focusing on tropical ecosystems. They argue that the tropics are significantly under-represented in research on plants and climate change studies. Plant seeds have numerous traits that play a role in ecological functions, and botanists have found that some of these traits show patterns correlating with geographical/climate zones.
To draw general/global conclusions or predict outcomes for the tropics, Visscher and colleagues introduce three additional seed traits/syndromes:
- Desiccation sensitivity
- Relative embryo size and post-dispersal embryo growth
- Germination requirements in high-mountain environments
The authors argue that bias towards temperate zones in analyzing these traits could negatively affect macroecological studies, predictive models, and plant conservation.
Visscher and colleagues’ first case study discusses research on seed desiccation tolerance, which is an essential factor to consider in plant conservation and ex-situ conservation. Global estimates have suggested that 8% of plant species worldwide are likely to produce desiccation-sensitive seeds, but this is based on data biased towards desiccation-tolerant species.
To evaluate seed storage behavior, protocols, such as the ‘100-seed test’, have been developed to reduce the number of seeds needed for experimentation. However, there is still a lack of data on seed desiccation responses for many tropical trees.
One example they give is a study by Mattana and colleagues to compare the results of gathering experimental data and global predictions of species seed desiccation likelihood in the Dominican Republic. The results showed that predictions were not always accurate, and new data is needed to improve the predictive models in the future.
As such, Visscher and colleagues say that it is essential to generate more data on seed desiccation sensitivity, particularly for species from tropical and subtropical regions, as this can support plant conservation and development programmes and improve predictive models.
Relative embryo size
For their next case study, the authors looked at the bias of relative embryo size and post-dispersal embryo growth data in tropical and non-tropical species. Botanists find clear differences in relative embryo size between tropical and non-tropical species. Tropical species have a larger embryo-to-seed length and embryo-to-seed surface ratio than non-tropical species.
There was also a bias towards studying the seed internal morphology of many species from a limited number of families and orders known to have small embryos. Regarding post-dispersal embryo growth, data were available for 171 non-tropical species from 32 plant families and 38 tropical species from 18 plant families.
This disparity in data, Visscher and colleagues argue, shows a lack of knowledge on tropical species and that more research needs to be done in this area to address the observed biases.
Germination requirements in high-mountain environments
Visscher and colleagues produce two case studies for germination requirements in high-mountain environments. The first discusses the differences between temperate and tropical high-mountain environments and how they affect seed germination.
Most research on seed germination has focused on temperate areas, but tropical high-mountain ecosystems are relatively aseasonal, and records indicate that tropical high-mountain plant species flower throughout the year. Tropical high-mountain plants face year-round stress from night-time frost instead of facing yearly cycles of snow in winter and high temperatures in summer.
The meta-analysis of the research on temperate high-mountain species found that the germination of strict high-mountain species is characterized by physiological seed dormancy and a strong need for cold stratification or GA3 (gibberellic acid) to break dormancy, as well as warm-cued germination and a positive response to alternating temperatures and light. However, the same study highlighted the general need for seed germination studies for tropical high-mountain species.
Research on perennial Asteraceae from the páramos of the Venezuelan Andes showed that their seeds reach high germination percentages over a range of temperatures and may lack seed dormancy.
The following case study specifically tackles the páramos, tropical high-mountain ecosystems found mainly in Colombia, Venezuela and Ecuador. These regions are known for their peculiar and harsh environmental and ecological conditions and are listed as part of the Andes Biodiversity Hotspot. They provide several ecosystem services such as carbon storage and water supply for cities, agriculture and hydropower. However, they are vulnerable to global climate changes, anthropogenic disturbances and the introduction of invasive species.
Despite the evolutionary and ecological importance of and threats facing these tropical high-mountain ecosystems, research into the seed traits of species found in the Colombian páramo has been less studied than those of more widely distributed species.
Analysis of the documents reporting on seed traits of species in the Colombian páramo found that peer-reviewed scientific articles were much less frequent than documents from other sources. The number of publications varied greatly among target species, with a maximum of over 500 documents for the cosmopolitan Juncus effusus and none for certain species.
When filtering by language, 36.6% of the documents retrieved were written in Spanish and other languages, such as Portuguese. This highlights the need for further studies on morphological and functional seed traits of the native páramo flora and for searches in multiple languages of both the grey and peer-reviewed literature to cover all currently available information.
Visscher and colleagues conclude:
To prevent the negative consequences of geographical bias on research and predictive models based on global datasets, we suggest: (1) improving inclusion of all existing data by performing multi-lingual searches of both the grey and peer-reviewed literature; (2) generating additional data from the tropics and a wider range of families in both temperate and tropical regions, accounting for intraspecific variability; and (3) improving the availability and accessibility of newly gathered data through their inclusion in seed trait datasets (e.g. Ordóñez-Parra et al., 2022), which could populate comprehensive global databases of seed traits (e.g. SeedArc: http://unioviedo.es/seedarc/). In addition, the availability of seed trait data generated by conservation seed banks could help overcome this geographical bias, as shown for example by the germination data downloaded from the Millennium Seed Bank Partnership Data Warehouse (http://brahmsonline.kew.org/msbp) in Sentinella et al. (2020) (see also the methodological approach in Carta et al., 2022). Because reasons for geographical bias include availability of funding and geographical distribution of researchers (Culumber et al., 2019), our suggested strategies could be enabled and supported through additional funding opportunities for tropical plant research, as well as international collaborations.Visscher et al. 2022
READ THE ARTICLE
Visscher, A.M., Vandelook, F., Fernández-Pascual, E., Pérez-Martínez, L.V., Ulian, T., Diazgranados, M. and Mattana, E. (2022) “Low availability of functional seed trait data from the tropics could negatively affect global macroecological studies, predictive models and plant conservation,” Annals of Botany, 130(6), pp. 773–784. Available at: https://doi.org/10.1093/aob/mcac130.
Summary edited from output from the GPT-3 model.