Germination response of invasive plants to soil burial depth and litter accumulation is species-specific

By Judit Sonkoly, Orsolya Valkó, Nóra Balogh, Laura Godó, András Kelemen, Réka Kiss, Tamás Miglécz, Edina Tóth, Katalin Tóth, Béla Tóthmérész & Péter Török

As the worldwide spread of invasive species continues to be an ever-growing threat to biodiversity, having effective measures for controlling them is increasingly important. Old-fields are among the habitats most affected by plant invasions, where invasive plants can even disrupt natural vegetation succession and species assembly, so information on how plants that regularly invade them can be controlled is essential.

If a site is already infested with invasive plants’ seeds, limiting their chances of germination can be an effective method for suppression. Thus, to plan habitat management and restoration accordingly, information on their germination requirements is crucial. Numerous studies dealt with the effects of either soil burial depth or litter cover on the germination of different invasive plants, but their combined effects remained completely unexplored. To bridge this knowledge gap, we designed a greenhouse experiment in which we simultaneously manipulated soil burial depth and litter cover and studied their effects on the germination of 11 herbaceous species regularly invading old-fields.

The experiment showed that soil burial, litter cover and their interaction affect the studied species, as increasing burial depth and litter cover considerably hampered their germination and seedling growth. However, there were large differences between different species’ response to soil and litter cover. For some of them, there was no negative effect even at the largest burial depth and litter cover, while others were hampered even by shallow soil burial. As the size of a species’ seeds can affect its germination, we tested whether the observed differences could be explained by differences in seed size. We found that the effects of litter cover and the combined effects of soil burial and litter cover can be explained with differences in seed size quite well; large seeds were able to cope with being covered by soil and litter, while small seeds experienced adverse effects. On the other hand, the separate effects of soil burial could not be explained by seed size, as some species considerably deviate from the general trend. For example, the germination of Ambrosia artemisiifolia was largely inhibited by soil burial despite having quite large seeds, while the small seeds of Cynodon dactylon were practically not affected by soil burial, which might be attributed to their habitat preferences and strategy.

Based on our results, the germination of most invasive plants was negatively affected by soil burial and litter cover, which can help control them by planning habitat management and restoration accordingly. In the absence of species-specific information, the seed size of a species can be a good predictor of its response to soil burial and litter cover, but species-specific information is needed to effectively deal with the ever-increasing threat of invasive plants. A more general implication of our results is that although seed size is an important driver of plants’ response to several factors and it is associated with many plant attributes, other effects such as that of habitat preference or plant strategy can mask the influence of seed size.

This is a plain language summary for the paper of Sonkoly et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12891). The post was prepared by Judit Sonkoly and Péter Török.