Abstract
Plant functional traits are thought to drive variation in primary productivity. However, there is a lack of work examining how dominant species identity affects trait–productivity relationships. The productivity of 12 pasture mixtures was determined in a 3‐year field experiment. The mixtures were based on either the winter‐active ryegrass (Lolium perenne) or winter‐dormant tall fescue (Festuca arundinacea). Different mixtures were obtained by adding forb, legume, and grass species that differ in key leaf economics spectrum (LES) traits to the basic two‐species dominant grass–white clover (Trifolium repens) mixtures. We tested for correlations between community‐weighted mean (CWM) trait values, functional diversity, and productivity across all plots and within those based on either ryegrass or tall fescue. The winter‐dormant forb species (chicory and plantain) had leaf traits consistent with high relative growth rates both per unit leaf area (high leaf thickness) and per unit leaf dry weight (low leaf dry matter content). Together, the two forb species achieved reasonable abundance when grown with either base grass (means of 36% and 53% of total biomass, respectively, with ryegrass tall fescue), but they competed much more strongly with tall fescue than with ryegrass. Consequently, they had a net negative impact on productivity when grown with tall fescue, and a net positive effect when grown with ryegrass. Strongly significant relationships between productivity and CWM values for LES traits were observed across ryegrass‐based mixtures, but not across tall fescue‐based mixtures. Functional diversity did not have a significant positive effect on productivity for any of the traits. The results show dominant species identity can strongly modify trait–productivity relationships in intensively grazed pastures. This was due to differences in the intensity of competition between dominant species and additional species, suggesting that resource‐use complementarity is a necessary prerequisite for trait–productivity relationships.
Highlights
There is a growing literature linking plant functional traits to primary productivity (Garnier et al 2004; Mouillot et al 2011; Clark et al 2012; Roscher et al 2012)
Post hoc tests revealed that the ryegrass complex (RGCO) mixture had significantly higher productivity than the ryegrass standard (RGST), ryegrass standard with lucerne (RGLB), tall fescue standard with forbs (TFFB), and tall fescue complex (TFCO) mixtures
Multimodel comparisons showed that the model including main effects for Year, Base grass identity and Forbs, and the interaction between Base grass identity and Forbs had very strong Akaike’s information criterion (AIC) weight support (AIC weight = 0.958, giving a 95.8% chance of providing the most parsimonious fit to the data, Table S2b) among models including all possible combinations of the three predictors and their interactions
Summary
There is a growing literature linking plant functional traits to primary productivity (Garnier et al 2004; Mouillot et al 2011; Clark et al 2012; Roscher et al 2012). Much of this work has focussed on ecosystems, such as low-intensity semi-natural grasslands, where maximizing productivity is unlikely to be the primary aim of management (Leps 2004). Trait–productivity relationships may reveal processes behind variation in productivity between different pastoral mixtures and help design new mixtures for increased productivity (e.g., Storkey et al 2015). It is still not known if trait–productivity relationships emerging from the literature are truly general or highly dependent on species identity, environmental context, and management practices. This study tests whether relationships between leaf morphological traits and productivity in intensively managed pasture mixtures are influenced by dominant species identity
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