Soil stabilization linked to plant diversity and environmental context in coastal wetlands

Abstract

BackgroundPlants play a pivotal role in soil stabilization, with above‐ground vegetation and roots combining to physically protect soil against erosion. It is possible that diverse plant communities boost root biomass, with knock‐on positive effects for soil stability, but these relationships are yet to be disentangled.QuestionWe hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity.MethodsWe tested this hypothesis in salt marsh grasslands, dynamic ecosystems with a key role in flood protection. Using step‐wise regression, the influences of biotic (e.g. plant diversity) and abiotic variables on root biomass and soil stability were determined for salt marshes with two contrasting soil types: erosion‐resistant clay (Essex, southeast UK) and erosion‐prone sand (Morecambe Bay, northwest UK). A total of 132 (30‐cm depth) cores of natural marsh were extracted and exposed to lateral erosion by water in a re‐circulating flume.ResultsSoil erosion rates fell with increased plant species richness (R 2 = 0.55), when richness was modelled as a single explanatory variable, but was more important in erosion‐prone (R 2 = 0.44) than erosion‐resistant (R 2 = 0.18) regions. As plant species richness increased from two to nine species·m−2, the coefficient of variation in soil erosion rate decreased significantly (R 2 = 0.92). Plant species richness was a significant predictor of root biomass (R 2 = 0.22). Step‐wise regression showed that five key variables accounted for 80% of variation in soil erosion rate across regions. Clay‐silt fraction and soil carbon stock were linked to lower rates, contributing 24% and 31%, respectively, to variation in erosion rate. In regional analysis, abiotic factors declined in importance, with root biomass explaining 25% of variation. Plant diversity explained 12% of variation in the erosion‐prone sandy region.ConclusionOur study indicates that soil stabilization and root biomass are positively associated with plant diversity. Diversity effects are more pronounced in biogeographical contexts where soils are erosion‐prone (sandy, low organic content), suggesting that the pervasive influence of biodiversity on environmental processes also applies to the ecosystem service of erosion protection.

Livestock grazing alters multiple ecosystem properties and services in salt marshes: a meta‐analysis

“…There is also evidence from salt marshes that increased plant richness improves sediment stability (Ford et al . ). Therefore grazers may directly and indirectly stabilise the marsh surface and protect against lateral and horizontal erosion.…”

“…This may be because grazer-driven compaction increases the strength of the soil, making it more resistant to erosion (Ghebreiyessus et al 1994). There is also evidence from salt marshes that increased plant richness improves sediment stability (Ford et al 2016). Therefore grazers may directly and indirectly stabilise the marsh surface and protect against lateral and horizontal erosion.…”

Large-scale predictions of salt-marsh carbon stock based on simple observations of plant community and soil type

“…Whilst surface SOC stock in UK salt marshes was broadly predicted by soil type, with non-sandy soils being more carbon rich, there remained a clear association between SOC stock and plant community type, with rush-dominated J. maritimus and J. gerardii communities associated with greater surface SOC stocks than either A. portulacoides or P. maritima communities. The deep-rooted salt-marsh shrub A. portulacoides (Decuyper et al, 2014) occurred predominantly as a near monoculture (Ford et al, 2016), with the shallow-rooted salt-marsh grass P. maritima community found alongside simple-rooted plants such as Plantago maritima. In contrast, the rushes J. gerardii and J. maritimus, characterised by extensive laterally creeping rhizomes with thick anchors and many shallow fine roots, commonly grew alongside the grasses Festuca rubra and Agrostis stolonifera and various other forbs.…”

“…The composition of the plant community, presence of dominant species, and plant diversity largely determine root properties (e.g. biomass, turnover, and exudates), which further influence SOM content and SOC stock (De Deyn et al, 2008;Ford et al, 2016). Species-rich plant communities are also often functionally diverse, with differing root strategies leading to enhanced root biomass (Loreau et al, 2001) and consequent impacts on SOC stock (Jones and Donnelly, 2004).…”

Elymus athericus encroachment in Wadden Sea salt marshes is driven by surface elevation change

“…Both Redelstein et al. () and Ford, Garbutt, Ladd, Malarkey, and Skov () found the fine‐root mass to increase with plant species richness, probably because the species in the more diverse low‐marsh community also represent diverse belowground space occupation strategies. Yet, the total fine‐root mass of a group of species does not rule out potential belowground competition and therefore these interactions should be further investigated in salt marshes.…”