Fine-scale root community structure and below-ground responses to grazing show independence from above-ground patterns

AGUIAR, M. R.; REYES, M. F.; OÑATIBIA, G.R.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017 vol. 28 p. 1097 - 1106

1100-9233

Question: Root biomass distribution and below-ground processes are the maindrivers of community structure and dynamics in arid rangelands. However,despite their relevance, below-ground plant responses to disturbance regimesremain poorly understood. This knowledge is a pressing issue since most of ourideas derive from extrapolating above-ground ecological theory and data. Here,we asked how domestic grazing management changes (intensification and abandonment)impact on both below-ground species co-occurrence at microsite level(point-richness) in relation to above-ground patterns and below-ground biomassdistribution of dominant graminoid species across different soil layers.Location: Patagonian steppe, Argentina.Methods: We sampled and compared ungrazed, moderately grazed and intensivelygrazed steppes. We evaluated below- and above-ground point-richness(microsite level: 6-cm diameter), as well as total and specific root biomass in thetop 20 cm of soil along 50-m transects in commercial paddocks.Results: We found independence between fine-scale below- and above-groundresponses. Below-ground point-richness was at least three times higher thanabove-ground point-richness. Besides, below-ground point-richness decreasedfrom 4.2 species in ungrazed sites to 3.4 species in intensively grazed ones. Neithergrazing intensification nor abandonment changed total root biomass,although intensification changed the root biomass composition, reducing preferredand increasing non-preferred grass species. Strikingly, below-groundpoint-richness and total root biomass did not differ between microsites coveredor not covered in vegetation. This pattern was not affected by grazing.Conclusions: Our findings showed a higher degree of fine-scale below-groundspecies co-occurrence than above-ground in this Patagonian steppe. The intensi-fication of grazing slightly decreased below-ground species co-occurrence andchanged root composition (species abundance), although grazing managementdid not modify the high degree of independence between below- and abovegroundstructure. Even though intensive grazing markedly decreases abovegroundbiomass, total below-ground biomass does not vary along a wide rangeof grazing conditions. In general, most of our knowledge about vegetationresponses to grazing is based on above-ground information, assuming thatbelow-ground patterns and processes are analogous to those above-ground. Thisstudy suggests that below- and above-ground community structure at fine-scaleare not strongly correlated and they can be differentially affected by grazing.