Abstract
Abstract. Propagule traits vary among biomes along geographical gradients such as longitude, but the mechanisms that underlie these variations remain unclear. This study aims to explore seed mass variation patterns of different biome types along a longitudinal gradient and their underlying variation mechanisms by involving an in-depth analysis on the variation of seed mass, fruit type spectra, growth forms and dispersal mode spectra in Inner Mongolia and northeastern China. Plant community characterization and seed collection were conducted in 26 sites spreading over five vegetation types and covering 622 species belonging to 66 families and 298 genera. We found there are significantly declining trends for mean seed mass, vertebrate-dispersed species richness and fleshy-fruited species richness along a longitudinal gradient from forests to desert grasslands. However, we also found the lowest average seed mass and the smallest proportion of species dispersed by vertebrates occurring at typical grasslands in the five biomes. The variations of average seed mass display high congruence with transition of growth form spectra. The selection for these propagule attributes is driven mainly by climatic factors such as precipitation, temperature, soil moisture and evaporation, as well as by internal biotic factors such as growth forms, canopy coverage and leaf area (Ackerly and Donoghue, 1998). A hypothesis was provided that environmental factors and botanical traits that favor greater water availability lead to emergence (or speciation) of species with large seeds or fleshy fruits with high water content. Due to greater water availability and increasing leaf area, much more photosynthate (photosynthesis production) and allometric growth then ultimately increase the biome average seed mass from west to east. Phylogenetic signal or diversity are not found to be significantly involved in the effect on the patterns. A novel mechanistic framework and mathematical model are provided to expound seed variation among species or biomes.
Highlights
Seed traits have great impact on plants’ competitive ability, fitness, fecundity and reproduction
The study area is located in the continental arid Inner Mongolian plateau, where vegetation types shift from broad-leaved deciduous forest to typical grassland and to desert, due to a gradual increase in sunshine duration and intensity and decrease in rainfall (Table 1)
The average seed mass of typical grasslands is significantly smaller than that of desert grasslands (F = 11.92, p = 0.0025), while there is no significant difference between average seed mass of typical grasslands and sparse grasslands (F = 0.019, p = 0.892)
Summary
Seed traits have great impact on plants’ competitive ability, fitness, fecundity and reproduction. An individual plant’s seed size is a combined result of its taxonomic group’s evolutionary history and immediate selective pressures of the local environment (Westoby et al, 2002; Moles et al, 2005a). As an important aspect in the reproductive biology of plants, seed mass is evolutionarily associated with and corresponds to other plant traits, relating to growth forms (for instance, trees, shrubs and herbs), life history Yu et al.: Shift of seed mass and fruit type spectra along longitudinal gradient nual plants or perennial plants) (Garnier, 1992; Moles et al, 2005a), stature and canopy sizes (Venable, 1992; Leishman and Westoby, 1994; Moles et al, 2005a), dispersal modes (Greene and Johnson, 1993; Hughes et al, 1994), leaf area (Díaz et al, 2016), and plant longevity (Telenius and Torstesson, 1991), as well as to anatomical traits of flowers and fruits (Primack, 1987)
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