Theme 1: Rangeland/Grassland Ecology--Oral Sessions

Description

We investigated species diversity effects and multifunctionality in an intensively managed grassland. A diversity experiment was set up with monocultures and mixtures comprising Lolium perenne, Dactylis glomerata, Trifolium pratense, and Trifolium repens, and was maintained for three years at 150 kg∙N∙ha-1∙ year-1. Ten functions were measured that represented i) forage production (aboveground biomass yield (μ), standard deviation of yield (σ), temporal stability (μ/σ), weed biomass), ii) N cycling (symbiotic-N2-fixation, N efficiency, NO3 in soil solution), and forage quality (crude protein content (CP), organic matter digestibility (OMD), metabolizable energy (ME)). We applied multivariate linear mixed-effects regression to estimate simultaneously species identity and diversity effects on the ten functions, and used the mean log response ratio (MLRR) across all functions to evaluate the diversity-multifunctionality relationship.

Across the three years, all functions regarding production and N cycling revealed significant beneficial effects in the four-species equi-proportional mixture (used as a reference) compared to averaged monocultures. The reference mixture had 61% more biomass yield, 8% less variation, 68% higher stability, 81% less weed biomass, 96% and 46% higher symbiotic-N2-fixation and N-efficiency, respectively, and 87% less NO3 (each P ≤ 0.05, except variation). The reference mixture and averaged monocultures did not significantly differ in CP, OMD (g∙kg-1∙yield), and ME (MJ∙kg-1∙yield). This, however, resulted in significant beneficial effects between 52% and 72% in all three forage quality functions on a hectare basis (kg or MJ∙ha-1∙year-1). On average across functions, the four-species reference mixture had 1.8 times the performance of averaged monocultures, indicating enhanced multifunctionality in mixtures.

The multivariate framework in combination with the MLRR as a measure of overall multifunctionality proved to be an effective tool for the evaluation of the diversity-multifunctionality relationship. We conclude that sown grass-legume mixtures at moderate N fertilization promote high multifunctionality and are a ‘ready-to-use’ option for sustainable intensification of agriculture.

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Multifunctionality of Sown Grassland Is Enhanced by Combining Four Complementary Species

We investigated species diversity effects and multifunctionality in an intensively managed grassland. A diversity experiment was set up with monocultures and mixtures comprising Lolium perenne, Dactylis glomerata, Trifolium pratense, and Trifolium repens, and was maintained for three years at 150 kg∙N∙ha-1∙ year-1. Ten functions were measured that represented i) forage production (aboveground biomass yield (μ), standard deviation of yield (σ), temporal stability (μ/σ), weed biomass), ii) N cycling (symbiotic-N2-fixation, N efficiency, NO3 in soil solution), and forage quality (crude protein content (CP), organic matter digestibility (OMD), metabolizable energy (ME)). We applied multivariate linear mixed-effects regression to estimate simultaneously species identity and diversity effects on the ten functions, and used the mean log response ratio (MLRR) across all functions to evaluate the diversity-multifunctionality relationship.

Across the three years, all functions regarding production and N cycling revealed significant beneficial effects in the four-species equi-proportional mixture (used as a reference) compared to averaged monocultures. The reference mixture had 61% more biomass yield, 8% less variation, 68% higher stability, 81% less weed biomass, 96% and 46% higher symbiotic-N2-fixation and N-efficiency, respectively, and 87% less NO3 (each P ≤ 0.05, except variation). The reference mixture and averaged monocultures did not significantly differ in CP, OMD (g∙kg-1∙yield), and ME (MJ∙kg-1∙yield). This, however, resulted in significant beneficial effects between 52% and 72% in all three forage quality functions on a hectare basis (kg or MJ∙ha-1∙year-1). On average across functions, the four-species reference mixture had 1.8 times the performance of averaged monocultures, indicating enhanced multifunctionality in mixtures.

The multivariate framework in combination with the MLRR as a measure of overall multifunctionality proved to be an effective tool for the evaluation of the diversity-multifunctionality relationship. We conclude that sown grass-legume mixtures at moderate N fertilization promote high multifunctionality and are a ‘ready-to-use’ option for sustainable intensification of agriculture.