Exploring mechanisms for the maintenance of alternative community states in old-field grasslands

LAURA YAHDJIAN; PABLO MONTES; CHANETON, ENRIQUE

Mar del Palta

Conferencia; 2nd World Conference on Biological Invasions and Ecosystem Functioning BIOLIEF 2011; 2011

BIOLIEF

The successional reassembly of plant communities in old fields with a strong legacy of cultivation frequently leads to the establishment of persistent communities dominated by exotic plant species. Such systems show little recovery towards the historical vegetation state, and may represent alternative stable states resistant to restoration. Here we report a study designed to assess potential shifts in ecosystem structure and functioning that may facilitate the persistence of a degraded vegetation state dominated by exotic species in post-agricultural grasslands. We measured several soil and vegetation structural parameters and ecosystem processes during one year in native grassland fragments and early-successional old fields in the Inland Pampa of Argentina (36° S, 61° W). We found that total soil carbon and nitrogen pools, and the cationic exchange capacity of the upper soil layer were higher in the invaded, old-field state than in nearby grassland remnants (P<0.05). Native and old-field grassland plots differed markedly in plant community composition and vegetation structure; whereas aboveground live biomass was similar (P>0.05), standing dead and litter biomass were significantly (P<0.05) higher in grassland remnants than in old field plots. Key soil functions including soil respiration and litter decomposition were significantly (P<0.05) higher in old field plots than in native remnants, suggesting increased soil biological activity under exotic plant dominance. These results illustrate how plant invasions may alter soil ecosystem attributes in ways that may reinforce the persistence of fast-growing, competitive exotic species in post agricultural grasslands.