Leaf economics spectrum–productivity relationships in intensively grazed pastures depend on dominant species identity

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.

Combining field experiments and predictive models to assess potential for increased plant diversity to climate‐proof intensive agriculture

“…Instances where the more diverse mixture performs better could be due either to niche complementarity or positive selection effects. A previous study showed that adding the winter dormant forbs chicory and plantain to ryegrass–white clover mixtures enhances mean productivity due to their phenological (seasonal) complementarity with winter‐active ryegrass (Mason et al., ), suggesting there may be some potential for niche complementarity to enhance productivity even in intensively managed agricultural ecosystems. Other studies have emphasized the potential for increased diversity to enhance productivity through complementarity in nitrogen resource use between legumes and non‐N‐fixers (e.g., Nyfeler, Huguenin‐Elie, Suter, Frossard, & Lüscher, ).…”

“…Another consideration is the difficulty in maintaining diversity in pasture mixtures. A previous study of intensively managed grazed pastures showed that the abundance of chicory, plantain, and lucerne had declined markedly after 3 years (Mason et al, 2016). The requirements of intensive pastoral agriculture-the ability to produce large amounts of high-quality herbage while tolerating frequent defoliation and trampling-place severe constraints on the pool of viable species (Finn et al, 2013).…”

Season and dominant species effects on plant trait‐ecosystem function relationships in intensively grazed grassland

“…We measured traits related to plant growth strategies (leaf dry matter content [LDMC], leaf N, leaf thickness, specific root length [SRL], root tissue density [RTD] and root diameter) and water use efficiency or uptake (δ 13 C, root diameter) (Bardgett et al., ; Perez‐Harguindeguy et al., ; Reich, ), each of which may influence soil functioning through modifying the quality or quantity of inputs. Leaf traits were measured in spring only (Mason et al., ; Table ), using standard techniques (Perez‐Harguindeguy et al., ). Leaf δ 13 C was measured using a Europa Scientific 20‐20 Stable Isotope Analyzer.…”

“…Leaf trait diversity has also been shown to influence productivity, decomposition and N retention in these systems (Grigulis et al, 2013;Mouillot et al, 2011;Scherer-Lorenzen, 2008). Although there is some evidence that plant productivity may be influenced by leaf traits in intensively grazed systems (Mason et al, 2016), frequent grazing reduces the opportunities for leaf litter to enter the soil and therefore to influence soil C and nutrient cycling. Fertiliser and high-N grazer urine inputs may further reduce the ability of plants to influence nutrient cycling (Orwin et al, 2015;Soussana & Lemaire, 2014).…”

“…at peak biomass, Grigulis et al, 2013), or use measures that integrate processes over the entire year (e.g. annual net primary production, Mason et al, 2016). It is therefore largely unknown whether plant traits can predict ecosystem functions when temperatures or water availability limit activity (but see Chollet et al, 2014;Everwand et al, 2014;Eviner et al, 2006).…”