Legumes affect alpine tundra community composition via multiple biotic interactions

Abstract

Abstract. The soil engineering function of legumes in natural ecosystems is paramount but associated solely with soil nitrogen (N) subsidies, ignoring concomitant biotic interactions such as competitive or inhibitory effects and exchange between mycorrhizas and rhizobia. We aim to (1) disentangle legume effects on plant community composition, and plant and soil N and phosphorus (P) concentrations, separating the effects of N subsidies from other legume effects; (2) estimate effects of mycorrhizal-rhizobial interactions on nutrient acquisition modes of plants co-existing with legumes.We compared plant community structure and plant nutrition modes in micro-sites in a Caucasian alpine tundra ecosystem that were either: (1) dominated by legumes in symbiosis with N-fixing rhizobia ('Nfixing legumes'), (2) dominated by legumes without symbiosis with rhizobia ('not N-fixing legumes'), or dominated by non-legumes and either (3) unfertilized ('controls') or (4) experimentally fertilized.Fertilization and the presence of N-fixing legumes affected the ecosystem similarly: soil was enriched with plant-available N compared to controls and sites dominated by a not N-fixing legume. Also, N turnover pathways and plant nutrition modes were strongly affected by the latter site types, as indicated by 5-10% higher plant tissue N concentration, altered soil and plant d 15 N, more than 4-fold reduced lichen amounts, 2.5-fold increased litter accumulation and doubling of aboveground biomass of non-legume plants. Vascular plant community composition was affected by the presence of legumes in a similar way regardless of whether they fixed N, suggesting that other factors overrode the N subsidy effects. Shading and microclimate changes in sites dominated by both types of legumes are possible explanatory factors. Both tissue N and d 15 N of non-legume plants near legumes were affected by interactions of mycorrhizal type and site type (without legumes, dominated by N-fixing, or not N-fixing legume), suggesting an important role of plant mycorrhizal status for adjusting nutrition mode to the legume presence. We conclude that N-fixing legumes play an engineering role in natural plant communities, but their role goes much beyond N fixation. Plant mycorrhizal status defines the way plants adjust their nutrition mode to the presence of legumes.

Determinants of 15N Natural Abundance in Leaves of Co-Occurring Plant Species and Types within an Alpine Lichen Heath in the Northern Caucasus

“…This result confirms our visual observations of the absence of nodules in the root system of Trifolium polyphyllum. The nonnitrogen fixing status of Trifolium polyphyllum was also confirmed by its positive responses to N fertilization Soudzilovskaia et al, 2012) and by the acetylene reduction method (Makarov et al, 2011). Trifolium polyphyllum is therefore the first known temperate non-fixing legume besides previously reported tropical examples (Sprent, 2005).…”

Arbuscular Mycorrhizal Fungal Communities Are Influenced by Host Tree Species on the Loess Plateau, Northwest China

“…The five host tree species tested in this study belong to different genera. For example, R. pseudoacacia is a nitrogen-fixing leguminous tree of the Fabaceae plant family, and nitrogen fixation by such legumes is considered a key factor affecting the physiological processes of AM fungal colonization [47]. Although H. rhamnoides is a non-legume nitrogen-fixing tree of the family Elaeagnaceae, nodules and mycorrhizae coexist in the roots of this species [48].…”

The roles of stochasticity and biotic interactions in the spatial patterning of plant species in alpine communities

“…Facilitation has been suggested as the predominant biotic factor structuring alpine communities (Callaway et al., ), based on comparisons of species responses to neighbour removals in alpine and sub‐alpine communities. Facilitation has been described in association with specific plant growth forms, including cushion plants (Cavieres, Arroyo, Peñaloza, Molina‐Montenegro, & Torres, ; Fajardo, Quiroz, & Cavieres, ) and N‐fixing legumes (Jacot, Luscher, Suter, Nosberger, & Hartwig, ; Soudzilovskaia et al., ; Thomas & Bowman, ), which have important local influences on species composition.…”