The soil seed bank can buffer long‐term compositional changes in annual plant communities

Abstract

1. Ecological theory predicts that the soil seed bank stabilizes the composition of annual plant communities in the face of environmental variability. However, longterm data on the community dynamics in the seed bank and the standing vegetation are needed to test this prediction. 2. We tested the hypothesis that the composition of the seed bank undergoes lower temporal variability than the standing vegetation in a 9-year study in Mediterranean, semi-arid and arid ecosystems. The composition of the seed bank was estimated by collecting soil cores from the studied sites on an annual basis. Seedling emergence under optimal watering conditions was measured in each soil core for three consecutive years, to account for seed dormancy. 3. In all sites, the composition of the seed bank differed from the vegetation throughout the years. Small-seeded and dormant-seeded species had a higher frequency in the seed bank than in the standing vegetation. In contrast, functional group membership (grasses vs. forbs) did not explain differences in species frequency between the seed bank and the vegetation after controlling for differences between grasses and forbs in seed mass and seed dormancy. 4. Contrary to predictions, the magnitude of year-to-year variability (the mean compositional dissimilarity between consecutive years) was not lower in the seed bank than in the vegetation in all sites. However, long-term compositional trends in the seed bank were weaker than in the vegetation in the Mediterranean and semiarid sites. In the arid site where year-to-year variability was highest, no long-term trends were observed. 5. Synthesis. The effect of the seed bank on the temporal variability of the vegetation in annual communities depends on site conditions and timescale. While the yearto-year variability of the seed bank is similar to the vegetation, the soil seed bank can buffer long-term trends.

Temporal stability of biomass in annual plant communities is driven by species diversity and asynchrony, but not dominance

“…However, this concomitant increase in biomass and richness across the regional rainfall gradient does not necessarily imply a causality relationship, since increased water availability can simultaneously and independently enhance both biomass and richness in the plant community (Ma et al, 2010; Lewandowska et al, 2016). It can be argued that greater rainfall in the mediterranean site not only enhanced plant growth, but also allowed the establishment and co‐existence of a larger number of species emerging from the seed bank (Lebrija‐Trejos et al, 2011; De Malach et al, 2020). Differentiating between effects of rainfall on richness and productivity across rainfall gradients in natural grasslands requires further experimental work manipulating at the same time species diversity and rainfall (Xu et al, 2015; Hallett et al, 2017).…”

“…Thus, conditions in our study correspond to present and future scenarios resulting from both land‐use change (e.g., reduced grazing) and climate change in the region. We used data from two contrasting sites in mediterranean and semi‐arid ecosystems differing in precipitation amount, primary productivity, species richness and small‐scale spatial heterogeneity (Talmon et al, 2011; Tielbörger et al, 2014), characterized by fast temporal turnover in species composition of the vegetation and the seed bank (De Malach et al, 2020). The wide variation in temporal and spatial conditions offered a unique opportunity to test the relative importance of biomass‐stabilizing mechanisms in annual plant communities.…”

Vulnerability of grassland seed banks to resource‐enhancing global changes

“…Persistent life stages, such as dormant seeds in the soil, can play a critical role in buffering populations and biodiversity from changing in variable environments (Angert et al 2009, Venable and Kimball 2013, Baskin and Baskin 2014, DeMalach et al 2021. Depleted seed banks have been suggested to inhibit recovery from nutrient enrichment (Bakker and Berendse 1999, Stevens 2016, Payne et al 2017.…”

“…Seed-banking strategies are common especially among native annual forbs, while in contrast, exotic annual grasses that comprise most of the biomass in Californian grasslands often lack dormancy and persistent seed banks (Marshall and Jain 1970, Ewing and Menke 1983, Pavlik et al 1993, Levine and Rees 2004, Baskin and Baskin 2014. However, despite seed-banking strategies having the potential to buffer from interannual environmental variation (DeMalach et al 2021), these water-and nutrient-limited systems could be highly vulnerable to global changes that enhance essential limiting resources to plants (Harpole and Tilman 2007, Eskelinen and Harrison 2015, Harpole et al 2016. Thus, investigating how seed banks respond to global changes is critical for understanding plant community responses to global changes.…”

Linking spatial self-organization to community assembly and biodiversity

“…We assume that all functional groups are represented in the system, even if at diminishingly small biomass densities, which may represent long-lived seeds (DeMalach et al, 2021). Community assembly then proceeds on ecological time scales set by interspecific competition for water and ).…”