Mycorrhizal fungi determine salt‐marsh plant zonation depending on nutrient supply

Abstract

Summary1. Arbuscular mycorrhizal fungi (AMF) can affect nutrient uptake of associated plants and can vary in function from mutualism to parasitism as nutrient availability increases; thus they may interact with nutrient availability to influence plant community structure. 2. We experimentally investigated the hypotheses that AMF can affect the community structure of salt marshes by affecting plant competitive ability. We focused on: Spartina densiflora , that dominates physically benign high marsh habitats and S. alterniflora , which dominates more stressful low marsh habitats. 3. Colonization by AMF increased S. densiflora growth at low nutrient levels, but reduced growth at high nutrient levels. Spartina alterniflora was not colonized by AMF and showed increased growth only with nutrient amendment. Nutrient or fungicide additions resulted in S. alterniflora migrating to higher marsh elevations, displacing S. densiflora . When nutrient and fungicide additions were made together, however, dominance of S. densiflora was maintained in the high marsh. 4. Synthesis. These results show that AMF can affect the competitive ability of plants and can have a large impact on plant community structure. The community impacts of these symbioses may be especially sensitive to human-induced eutrophication, given that nutrient supply can modulate whether AMF positively or negatively affect associated plants.

Patterns of fungal diversity and composition along a salinity gradient

“…Generally, it is assumed that fungi are less active in anoxic sediments; however, studies document their presence in these habitats and indicate that they can account for up to 10% of the microbial biomass in surface sediments (Padgett and Celio, 1990;Cordova-Kreylos et al, 2006;Ipsilantis and Sylvia, 2007). In addition, mycorrhizal fungi have recently been shown to interact with Spartina patens roots in salt marshes (Burke et al, 2003) and to influence plant zonation (Daleo et al, 2008).…”

“…Alternatively, fungal diversity might be highest in the salt marsh with plants present, as the prominence of positive interactions, such as those between mychorrizal fungi and plants, typically increases with the severity of the abiotic environment (Bertness and Callaway, 1994). Indeed, arbuscular mychorrizae are abundant in salt marshes and can alter plant composition (Burke et al, 2003;Daleo et al, 2008). Finally, fungal diversity might peak at an environment of intermediate salinity, in the brackish marsh, because of the mixing of specialized freshwater and marine communities (Crump et al, 2004).…”

Efeitos da densidade de plantio e da adição de nutrientes na produção de mudas de gramas halófitas em recipientes

“…Em um experimento com parcelas monoespecíficas de marismas na Argentina, Daleo et al (2008) observaram após 16 meses de adubação com NPK (19:5:5) apenas um incremento de 60% da densidade de hastes de S. densiflora, em relação a parcelas-controles (de 1632 para 2604 hastes m -2 ), enquanto S. alterniflora respondeu com um aumento da altura média da copa de 65% (de 60 para 99 cm) e dobrou o número de hastes (de 133 para 277 hastes m -2 ). O denso perfilhamento é a principal estratégia utilizada por S. densiflora para ocupação espacial e exclusão de plantas competidoras, tendo sido observado em marismas populações com 900 a 5000 hastes m -2 (Nieva et al, 2001;Costa et al, 2003;Daleo et al, 2008;. Melhores eficiências nutricionais e capacidade de crescimento, em solos de marismas pobres em nutrientes, têm sido atribuídas às monocotiledôneas com pequena distância entre nós nos rizomas e que formam tufos de hastes, como S. densiflora.…”

“…Para otimização da produção de mudas em recipientes, é necessária a avaliação da resposta de crescimento ao adensamento de indivíduos. Nas marismas, gramas Spartina crescem em densidades de até 5000 hastes m -2 e suas raízes tendem a se concentrar no sedimento superficial, por causa da anoxia em camadas mais profundas (Nieva et al, 2001;Costa et al, 2003;Daleo et al, 2008). Logo, estas plantas apresentam um grande potencial de produção de mudas em recipientes, mas poucos estudos avaliaram esta possibilidade fitotécnica (Deng et al, 2008;Costa et al, 2011a;2011b) e faltam quantificações do efeito da densidade de plantio sobre a formação de perfilhos.…”

Invertebrate Community Composition Across Inundation Regimes and Its Potential to Reduce Plant Stress

“…Plant-animal facilitations have also been shown to lower the intertidal limits of marsh plants (Hacker and Bertness 1995, Bertness 1985, Daleo et al 2008. Several studies, focused on marshes on the Atlantic coasts, cited increased plant production through stress amelioration due to Uca spp.…”