Differential responses of C3 and C4 grasses to shrub effects in a sub‐humid grassland of South America

Abstract

AbstractQuestionsPlant–plant interactions are key processes that strongly affect the survival, growth and reproduction of individuals in plant communities. In grasslands, the micro‐environment generated under the canopy of shrubs could differentially affect co‐occurring species with different abiotic requirements. In a C3/C4 grassland with scattered shrubs, we asked the following questions: (a) Does the aerial effect, the below‐ground effect, and the net effect of shrubs affect the vegetative and reproductive biomass, the number of tillers, the biomass allocation, and the leaf elongation rate of grasses? and (b) Do these effects differ between C3 and C4 grasses?LocationTemperate sub‐humid grassland of Uruguay.MethodsWe planted one C3 and two C4 grasses under a shrub canopy and in adjacent open sites. Half of the grasses were planted with a fabric bag to reduce root competition with the shrub. We measured leaf elongation rate, the number of tillers produced and the biomass of the grasses in every treatment. We also measured photosynthetic photon flux density (PPFD), air temperature and wind speed under shrub canopies and in adjacent open sites.ResultsRoot biomass, aerial biomass and reproductive biomass, the number of tillers and the leaf elongation rate of the C4 grasses were negatively affected by the reduction in radiation and probably by below‐ground competition with the shrub. On the other hand, the leaf elongation rate of the C3 grasses was positively affected by the shrub canopy. PPFD, air temperature and wind speed were lower under shrubs than in adjacent open sites.ConclusionsOur results show the interplay between plant interactions and photosynthetic metabolism on the vegetative and reproductive performance of grasses. The micro‐environmental conditions generated below shrub canopies create a more appropriate site for the growth of C3 than for C4 grasses. These results show that shrubs may differentially affect co‐occurring species with different abiotic requirements.