Abstract
Legume species promote productivity and increase the digestibility of herbage in grasslands. Considerable experimental data also indicate that communities with legumes produce more above-ground biomass than is expected from monocultures. While it has been attributed to N facilitation, evidence to identify the mechanisms involved is still lacking and the role of complementarity in soil water acquisition by vertical root differentiation remains unclear. We used a 20-months mesocosm experiment to investigate the effects of species richness (single species, two- and five-species mixtures) and functional diversity (presence of the legume Trifolium repens) on a set of traits related to light, N and water use and measured at community level. We found a positive effect of Trifolium presence and abundance on biomass production and complementarity effects in the two-species mixtures from the second year. In addition the community traits related to water and N acquisition and use (leaf area, N, water-use efficiency, and deep root growth) were higher in the presence of Trifolium. With a multiple regression approach, we showed that the traits related to water acquisition and use were with N the main determinants of biomass production and complementarity effects in diverse mixtures. At shallow soil layers, lower root mass of Trifolium and higher soil moisture should increase soil water availability for the associated grass species. Conversely at deep soil layer, higher root growth and lower soil moisture mirror soil resource use increase of mixtures. Altogether, these results highlight N facilitation but almost soil vertical differentiation and thus complementarity for water acquisition and use in mixtures with Trifolium. Contrary to grass-Trifolium mixtures, no significant over-yielding was measured for grass mixtures even those having complementary traits (short and shallow vs. tall and deep). Thus, vertical complementarity for soil resources uptake in mixtures was not only dependant on the inherent root system architecture but also on root plasticity. We also observed a time-dependence for positive complementarity effects due to the slow development of Trifolium in mixtures, possibly induced by competition with grasses. Overall, our data underlined that soil water resource was an important driver of over-yielding and complementarity effects in Trifolium-grass mixtures.
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Claims 11
Claim · model-written summary
Trifolium presence and abundance positively affected biomass production and complementarity in two-species mixtures from the second year.
- Treatment
- Trifolium presence and abundancee0
- Outcome
- biomass production and complementarity effectse0
- Direction
- positive effecte0
- Qualifier
- in the two-species mixtures from the second yeare0
TrifoliumNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found a positive effect of Trifolium presence and abundance on biomass production and complementarity effects in the two-species mixtures from the second year.”
Claim · model-written summary
Leaf area, N and water-use efficiency were higher in communities containing Trifolium.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In addition the community traits related to water and N acquisition and use (leaf area, N, water-use efficiency, and deep root growth) were higher in the presence of Trifolium.”
Claim · model-written summary
Deep root growth was higher in communities containing Trifolium.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In addition the community traits related to water and N acquisition and use (leaf area, N, water-use efficiency, and deep root growth) were higher in the presence of Trifolium.”
Claim · model-written summary
Regression identified water acquisition and use traits together with N as main determinants of biomass production and complementarity.
- Taxon
- Trifolium repens
Trifolium repenst0 - Compound
- Ne0
- Outcome
- biomass production and complementarity effectse0
- Qualifier
- traits related to water acquisition and usee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With a multiple regression approach, we showed that the traits related to water acquisition and use were with N the main determinants of biomass production and complementarity effects in diverse mixtures.”
t0“Trifolium repens”
Claim · model-written summary
Lower shallow root mass of Trifolium and higher soil moisture should increase water availability for associated grasses.
Verbatim
e0“At shallow soil layers, lower root mass of Trifolium and higher soil moisture should increase soil water availability for the associated grass species.”
Claim · model-written summary
Higher deep root growth and lower soil moisture indicate increased soil resource use in mixtures.
- Taxon
- Trifolium repensTrifolium repenst0
- Outcome
- soil resource usee0
- Direction
- increasee0
- Qualifier
- higher root growth and lower soil moisturee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Conversely at deep soil layer, higher root growth and lower soil moisture mirror soil resource use increase of mixtures.”
t0“Trifolium repens”
Claim · model-written summary
Results highlight nitrogen facilitation and vertical soil differentiation supporting water complementarity in Trifolium mixtures.
- Outcome
- complementarity for water acquisition and usee0
- Qualifier
- N facilitation but almost soil vertical differentiatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Altogether, these results highlight N facilitation but almost soil vertical differentiation and thus complementarity for water acquisition and use in mixtures with Trifolium.”
Claim · model-written summary
Grass mixtures showed no significant over-yielding even when their traits were complementary.
- Taxon
- grasse0
- Outcome
- over-yieldinge0
- Qualifier
- even those having complementary traits (short and shallow vs. tall and deep)e0
Not reportedDirection
Verbatim
e0“Contrary to grass-Trifolium mixtures, no significant over-yielding was measured for grass mixtures even those having complementary traits (short and shallow vs. tall and deep).”
Claim · model-written summary
Vertical complementarity depends on root plasticity as well as inherent root architecture.
- Taxon
- Trifolium repensTrifolium repenst0
- Outcome
- vertical complementarity for soil resources uptakee0
- Qualifier
- the inherent root system architecture but also on root plasticitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Thus, vertical complementarity for soil resources uptake in mixtures was not only dependant on the inherent root system architecture but also on root plasticity.”
t0“Trifolium repens”
Claim · model-written summary
Positive complementarity effects were time-dependent because Trifolium developed slowly, possibly due to grass competition.
- Interactor
- grassese0other
- Outcome
- time-dependence for positive complementarity effectse0
- Qualifier
- slow development of Trifolium in mixtures, possibly induced by competition with grassese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We also observed a time-dependence for positive complementarity effects due to the slow development of Trifolium in mixtures, possibly induced by competition with grasses.”
Claim · model-written summary
Soil water resources were an important driver of over-yielding and complementarity in Trifolium-grass mixtures.
- Interactor
- grasse0other
- Outcome
- over-yielding and complementarity effectse0
- Qualifier
- soil water resourcee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Overall, our data underlined that soil water resource was an important driver of over-yielding and complementarity effects in Trifolium-grass mixtures.”