Mechanisms of seed mass variation along resource gradients

Abstract

The enormous variation in seed mass along gradients of soil resources has fascinated plant ecologists for decades. However, so far, this research has focused on the description of such variation, rather than its underlying mechanisms. Here we experimentally test a recent model relating such variation to two fundamental properties of plant growth: allometry of biomass growth and size‐asymmetry of light competition. According to the model, mean seed mass should increase, and the variance of seed mass should show a unimodal response, to increasing soil resource availability (productivity). We test these predictions and their underlying assumptions using a combination of field observations, mesocosm experiments and greenhouse experiments focusing on Mediterranean annual plants. Our results support the predictions and assumptions of the model, and allow us to reject alternative models of seed mass variation. We conclude that growth‐allometry and size‐asymmetric light competition are key drivers of seed‐mass variation along soil resource gradients.

Plant functional trait response to environmental drivers across European temperate forest understorey communities

“…Communities in moister plots having on average lower seed mass is in accordance with other studies on the relationship between seed mass and Ellenberg soil moisture (Baker, ; Westoby et al ; Dubuis et al, ; Sonkoly et al, ). Larger seed mass has been linked with a higher resilience to various seedling disturbances, such as drought, likely due to the tendency of larger seeds to retain more metabolic reserves (Westoby et al, ; Westoby, ; DeMalach et al, ).…”

“…nitrogen deposition), given the demonstrated differences in resource acquisition between woody versus non‐woody as well as non‐mycorrhizal versus mycorrhizal plants (Ryser, ; Graves et al ; Kleyer et al, ; Hempel et al, ; Bardgett et al ; Valverde‐Barrantes et al ). Finally, higher community seed mass was expected to be associated with lower moisture or nutrient levels (Westoby et al ; DeMalach et al ), while the mean lateral spread of an understorey community could be higher in plots with a differing land‐use history, i.e . recent (RF) versus ancient forests (AF), because of potentially higher colonization capacities of plant species in RF (Verheyen et al, ; Flinn & Vellend, ; Baeten et al, ).…”

An experimental test of the area–heterogeneity tradeoff

“…The seeds required for the experiment were collected by sampling the seed bank of a Mediterranean annual grassland located in Beit Guvrin National Park (altitude is 420 m, mean annual rainfall is 420 mm, mean annual temperature is 19°C). This community was chosen because it is dominated by annual species, shows exceptional taxonomic and functional diversity, and was heavily investigated in previous studies (47,49,50,59,60). The seed bank samples were obtained by scraping the top 1-cm layer of the soil in randomly stratified patches scattered over the entire area.…”

The soil seed bank buffers long-term compositional changes in annual plant communities

“…This approach, which incorporates the dependence among replications of pairwise distance, was implemented using the 'Simba' R package (Jurasinski & Retzer, 2012) We investigated whether species' traits can explain differences in composition between the seed bank and the vegetation, as well as differences in temporal trajectories, focusing on seed mass, seed dormancy, and functional group (grasses vs. forbs). These traits were chosen because of their importance for community assembly in the region (DeMalach, Ron, & Kadmon, 2019;Harel et al, 2011). Seed mass data were taken from a previous study in the same sites (Harel, Holzapfel, & Sternberg, 2011) and were available for more than 90% of the individuals sampled.…”