Grazing increases below-ground biomass and net primary production in a temperate grassland
Background and aims
Grazing can affect the stock and flow of C between above and below-ground vegetation layers. Components of below-ground stratum are one of the less studied. The goals of this research were: 1) to characterize and estimate the vertical distribution of below-ground biomass in grazed and ungrazed areas during a growing season, and 2) to evaluate grazing effects on below-ground net primary production (BNPP).
Below-ground biomass was cored four times to 100 cm depth during a growing season on three paired grazed-ungrazed areas in South-central Uruguayan grasslands. BNPP was estimated using both field data and CENTURY model.
On average, below-ground biomass was higher in grazed (1417 gm−2) than in ungrazed areas (945 gm−2) and showed a marked reduction in relation with soil depth. Turnover rates were 0.40 and 0.37 years−1 in grazed and ungrazed areas respectively. Field data and CENTURY simulation showed higher BNPP in grazed areas (1.86; 0.77 gm−2days−1 respectively) than in ungrazed areas (1.07; 0.67 gm−2days−1 respectively).
Grazed areas showed higher below-ground biomass, BNPP and turnover that ungrazed areas. Grazing has an important role in regulating both stock and dynamics of C in grassland ecosystems.
KeywordsC sequestration Grazed-ungrazed Root distribution Soil cores CENTURY model Uruguay
We particularly appreciate the assistance in the field work of G. Fernández, F. Gallego, S. Baeza, C. Bagnato, B. Costa, A. Guido, E. Leoni, F. Lezama, A.L. Mello, G. Parodi and F. Pezzani, and we thank Andrea Geymonat and Andrea Corona for technical assistance. We thank G. Piñeiro and two anonymous reviewers for useful comments on the manuscript. We thank the owners of “El Relincho”, who provided us with support and field facilities. Funding: Research was partially funded by Instituto Nacional de Investigación Agropecuaria (FPTA 175), and Agencia Nacional de Investigación e Innovación (BE-POS-2009-781). This work was carried out with the aid of a grant from the Inter-American Institute for Global Change Research (IAI) CRN3095 which is supported by the US National Science Foundation (Grant GEO-1128040).
Compliance with ethical standards
The authors declare that they have no conflict of interest.
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