Tradeoff between physical and chemical defense in plant seeds is mediated by seed mass

Intraspecific variation in seed size is mediated by seed dispersal modes and animal dispersers - evidence from a global-scale dataset

Seed dispersal mechanisms play a crucial role in driving evolutionary changes in seed and fruit traits. While previous studies have primarily focussed on the mean or maximum values of these traits, there is also significant intraspecific variation in them. Therefore, it is pertinent to investigate whether dispersal mechanisms can explain intraspecific variations in these traits. Taking seed size as a case study, we compiled a global dataset comprising 3424 records of intraspecific variation in seed size (IVSS), belonging to 691 plant species and 131 families. We provided the first comprehensive quantification of dispersal mechanism effects on IVSS. Biotic-dispersed species exhibited a larger IVSS than abiotic-dispersed species. Synzoochory species had a larger IVSS than endozoochory, epizoochory, and myrmecochory species. Vertebrate-dispersed species exhibited a larger IVSS than invertebrate-dispersed species, and species dispersed by birds exhibited a larger IVSS than mammal-dispersed species. Additionally, a clear negative correlation was detected between IVSS and disperser body mass. Our results prove that the IVSS is associated with the seed dispersal mechanism. This study advances our understanding of the dispersal mechanisms' crucial role in seed size evolution, encompassing not only the mean value but also the variation.

Contrasting seed traits of co-existing seeds lead to a complex neighbor effect in a seed-rodent interaction

Scatter-hoarding rodents play important roles in seed dispersal and predation in many forest ecosystems. Existing studies have shown that the seed foraging preference of rodents is directly affected by seed traits and indirectly affected by the traits of other co-existing seeds nearby (i.e., neighbor effect). Plant seeds exhibit a combination of diverse seed traits, including seed size, chemical defense, and nutrient content. Therefore, it is difficult to evaluate the influence of each single seed trait on such neighbor effects. Here, by using artificial seeds, we investigated the impacts of contrasts in seed size, tannin content, and nutrient content on neighbor effects. We tracked 9000 tagged artificial seeds from 30 seed-seed paired treatments in a subtropical forest in southwest China. The contrast in seed size between paired seeds created obvious neighbor effects measured through three seed dispersal related indicators: the proportion of seeds being removed, the proportion of seeds cached, and the distance transported by rodents. However, the magnitudes and the signs of the neighbor effects differed among pairs, including both apparent mutualism and apparent competition, depending on the contrast in seed size between paired seeds. The contrasts of tannin and nutrient content between paired seeds showed relatively few neighbor effects. Our results suggest that the contrast in seed traits between the target seed and its neighboring seeds should be considered when studying rodent-seed interactions. Furthermore, we expect that similar complex neighbor effects may also exist in other plant-animal interactions, such as pollination and herbivory.

A metacommunity ecology approach to understanding microbial community assembly in developing plant seeds

Microorganisms have the potential to affect plant seed germination and seedling fitness, ultimately impacting plant health and community dynamics. Because seed-associated microbiota are highly variable across individual plants, plant species, and environments, it is challenging to identify the dominant processes that underlie the assembly, composition, and influence of these communities. We propose here that metacommunity ecology provides a conceptually useful framework for studying the microbiota of developing seeds, by the application of metacommunity principles of filtering, species interactions, and dispersal at multiple scales. Many studies in seed microbial ecology already describe individual assembly processes in a pattern-based manner, such as correlating seed microbiome composition with genotype or tracking diversity metrics across treatments in dispersal limitation experiments. But we see a lot of opportunities to examine understudied aspects of seed microbiology, including trait-based research on mechanisms of filtering and dispersal at the micro-scale, the use of pollination exclusion experiments in macro-scale seed studies, and an in-depth evaluation of how these processes interact via priority effect experiments and joint species distribution modeling.

Seed size affects rodent-seed interaction consistently across plant species but not within species: evidence from a seed tracking experiment of 41 tree species

Scatter-hoarding rodents play a crucial role in seed survival and seed dispersal. As one of the most important seed traits, seed size and its effect on rodent-seed interaction attract lots of attention. Current studies usually target one or a few species and show inconsistent patterns; however, few experiments include a large number of species although many plant species usually coexist in natural forest and overlap in fruiting time. Here, we tracked the dispersal and predation of 26,100 seeds belonging to 41 tree species in a subtropical forest for two years. Most species showed no relationships between seed size and rodent foraging preference, while the remaining species displayed diverse of patterns: monotonic decrease and increase trends, and hump-shaped and U-shaped patterns, indicating that a one-off study with a few species might give misleading information. However, the seed size effect across species was consistent in both years, indicating that including a large number of species that hold a sufficient range of seed size may avoid the aforementioned bias. Interestingly, seed size effect differed among rodent foraging processes: a negative effect on seed harvest, a hump-shaped effect on seed removal and removal distance, while a positive effect on overwinter survival of cached seeds, indicating that rodents may make trade-offs between large and small seeds both among foraging processes and within a single process, thus lead to a parabolic relationship between seed size and seed dispersal success, i.e., medium-sized seeds were more likely to be removed and cached, and transported with a further distance. This article is protected by copyright. All rights reserved.

Exposure time is an important variable in quantifying post-dispersal seed removal

A literature synthesis concluded that small mammals have the greatest impact on post-dispersal removal of intermediate-sized seeds (Dylewski et al. 2020). However, this study failed to consider the duration of seed exposure to predators. Re-analyses of the corrected dataset revealed only a weak effect of seed mass on seed removal.

Extending Plant Defense Theory to Seeds

Plant defense theory explores how plants invest in defenses against natural enemies but has focused primarily on the traits expressed by juvenile and mature plants. Here we describe the diverse ways in which seeds are chemically and physically defended. We suggest that through associations with other traits, seeds are likely to exhibit defense syndromes that reflect constraints or trade-offs imposed by selection to attract dispersers, enable effective dispersal, ensure appropriate timing of seed germination, and enhance seedling performance. We draw attention to seed and reproductive traits that are analogous to defense traits in mature plants and describe how the effectiveness of defenses is likely to differ at pre- and postdispersal stages. We also highlight recent insights into the mutualistic and antagonistic interactions between seeds and microbial communities, including fungi and endohyphal bacteria, that can influence seed survival in the soil and subsequent seedling vigor.

An allometry between seed kernel and seed coat shows greater investment in physical defense in small seeds

PREMISE OF THE STUDY

Numerous studies have treated the mass of a whole seed as an integrated unit, although the components seed kernel and seed coat play different roles and are subject to different evolutionary selection pressures. In this study, we provided the first global-scale quantification of the relative biomass investments in seed coats and seed kernels. We tested the following hypotheses: there is a negative allometry between seed kernel mass and seed coat mass, and therefore, seed coat ratio (SCR) is negatively correlated with seed mass.

METHODS

We compiled a global-scale data set from the published literature, including 680 plant species from 420 genera and 108 families. The relationships between seed components were quantified using standardized major axis regression, ordinary least squares regression, and phylogenetic independent analyses.

KEY RESULTS

We found a weak but significantly negative allometry between seed kernel mass and seed coat mass, which resulted in a negative relationship between seed mass and SCR. Similar results were found after accounting for the phylogeny.

CONCLUSIONS

The finding that smaller seeds invest more in protective tissues but less in stored reserves may explain the general prediction that larger seeds suffer greater predation than smaller seeds. Furthermore, this weak allometry may also explain, at least in part, why so many studies failed to identify a clear pattern of the effect of seed mass on many ecological processes. Our study suggests that the allometry between the two seed components must be considered when evaluating the ecological significance and evolutionary history of seed mass.

The role of botanical gardens in scientific research, conservation, and citizen science

Plant diversity is currently being lost at an unprecedented rate, resulting in an associated decrease in ecosystem services. About a third of the world's vascular plant species face the threat of extinction due to a variety of devastating activities, including, over-harvesting and over exploitation, destructive agricultural and forestry practices, urbanization, environmental pollution, land-use changes, exotic invasive species, global climate change, and more. We therefore need to increase our efforts to develop integrative conservation approaches for plant species conservation. Botanical gardens devote their resources to the study and conservation of plants, as well as making the world's plant species diversity known to the public. These gardens also play a central role in meeting human needs and providing well-being. In this minireview, a framework for the integrated missions of botanical gardens, including scientific research, in/ex situ conservation, plant resource utilization, and citizen science are cataloged. By reviewing the history of the development of Kunming Botanical Garden, we illustrate successful species conservation approaches (among others, projects involving Camellia, Rhododendron, Magnolia, Begonia, Allium, Nepenthes, medicinal plants, ornamental plants, and Plant Species with Extreme Small Populations), as well as citizen science, and scientific research at Kunming Botanical Garden over the past 80 years. We emphasize that Kunming Botanical Garden focuses largely on the ex situ conservation of plants from Southwest China, especially those endangered, endemic, and economically important plant species native to the Yunnan Plateau and the southern Hengduan Mountains. We also discuss the future challenges and responsibilities of botanical gardens in a changing world, including: the negative effects of outbreeding and/or inbreeding depression; promoting awareness, study, and conservation of plant species diversity; accelerating global access to information about plant diversity; increasing capacity building and training activities. We hope this minireview can promote understanding of the role of botanical gardens.