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

LAURA YAHDJIAN; PABLO MONTES; CHANETON, ENRIQUE

Mar del Plata

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

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.