Rosemary P. Collins

Ecosystem function enhanced by combining four functional types of plant species in intensively managed grassland mixtures: a 3‐year continental‐scale field experiment

1.A coordinated continental-scale field experiment across 31 sites was used to compare the biomass yield of monocultures and four species mixtures associated with intensively managed agricultural grassland systems. To increase complementarity in resource use, each of the four species in the experimental design represented a distinct functional type derived from two levels of each of two functional traits, nitrogen acquisition (N2-fixing legume or nonfixing grass) crossed with temporal development (fast-establishing or temporally persistent). Relative abundances of the four functional types in mixtures were systematically varied at sowing to vary the evenness of the same four species in mixture communities at each site and sown at two levels of seed density. 2.Across multiple years, the total yield (including weed biomass) of the mixtures exceeded that of the average monoculture in >97% of comparisons. It also exceeded that of the best monoculture (transgressive overyielding) in about 60% of sites, with a mean yield ratio of mixture to best-performing monoculture of 1·07 across all sites. Analyses based on yield of sown species only (excluding weed biomass) demonstrated considerably greater transgressive overyielding (significant at about 70% of sites, ratio of mixture to best-performing monoculture = 1·18). 3.Mixtures maintained a resistance to weed invasion over at least 3 years. In mixtures, median values indicate

Biodiversity effects on yield and unsown species invasion in a temperate forage ecosystem

BACKGROUND AND AIMS Current agricultural practices are based on growing monocultures or binary mixtures over large areas, with a resultant impoverishing effect on biodiversity at several trophic levels. The effects of increasing the biodiversity of a sward mixture on dry matter yield and unsown species invasion were studied. METHODS A field experiment involving four grassland species [two grasses--perennial ryegrass (Lolium perenne) and cocksfoot (Dactylis glomerata)--and two legumes--red clover (Trifolium pratense) and white clover (Trifolium repens)], grown in monocultures and mixtures in accordance with a simplex design, was carried out. The legumes were included either as single varieties or as one of two broad genetic-base composites. The experiment was harvested three times a year over three years; dry matter yield and yield of unsown species were determined at each harvest. Yields of individual species and interactions between all species present were estimated through a statistical modelling approach. KEY RESULTS Species diversity produced a strong positive yield effect that resulted in transgressive over-yielding in the second and third years. Using broad genetic-base composites of the legumes had a small impact on yield and species interactions. Invasion by unsown species was strongly reduced by species diversity, but species identity was also important. Cocksfoot and white clover (with the exception of one broad genetic-base composite) reduced invasion, while red clover was the most invaded species. CONCLUSIONS The results show that it is possible to increase, and stabilize, the yield of a grassland crop and reduce invasion by unsown species by increasing its species diversity.

Genetic Improvement of Forage Species to Reduce the Environmental Impact of Temperate Livestock Grazing Systems

Abberton, M. T., Marshall, A. H., Humphreys, M. W., Macduff, J. H., Collins, R. P., Marley, C. L. (2008). Genetic improvement of forage species to reduce the environmental impact of temperate livestock grazing systems. Advances in Agronomy, 98, 311-355.

Stolon characteristics related to winter survival in white clover

Changes in the stolon carbohydrate contents (water-soluble and total non-structural) of four white clover populations were measured at the beginning and end of winter. Three of the populations were of Swiss origin ― two of these were from high-altitude pastures, and the other from a valley location. Grasslands Huia was measured as a control variety. Levels of both types of carbohydrate declined during the winter in all populations. The Swiss populations from high altitudes contained the highest levels of both carbohydrate types. An artificial freezing test was carried out on stolon segments collected from a range of clover populations (including the two high-altitude Swiss clovers) growing in field plots in January, and values of «lethal dose 50» (LD 50 ) were calculated. The two Swiss populations had the lowest LD 50 values, indicating a greater intrinsic tolerance to freezing in those plants than in the other populations (of lowland temperate origin). One of the Swiss populations, Ac3785, was grown under two temperature regimes and short daylength to determine whether its tolerance to freezing increased with time. Significant increases in tolerance occurred after 8 days at 2°C, but plants grown at 8°C showed no change in tolerance even after 30 days. The results suggest that (i) stolon carbohydrate content is an important factor in the overwintering of white clover, (ii) there is a considerable amount of genetic variation in cold tolerance within white clover, (iii) artificial freezing tests can provide a method of predicting the survival of clover stolons during winter and (iv) the cold hardiness of white clover increases with time spent at temperatures near 0°C under short daylengths

Engineering a plant community to deliver multiple ecosystem services

The sustainable delivery of multiple ecosystem services requires the management of functionally diverse biological communities. In an agricultural context, an emphasis on food production has often led to a loss of biodiversity to the detriment of other ecosystem services such as the maintenance of soil health and pest regulation. In scenarios where multiple species can be grown together, it may be possible to better balance environmental and agronomic services through the targeted selection of companion species. We used the case study of legume-based cover crops to engineer a plant community that delivered the optimal balance of six ecosystem services: early productivity, regrowth following mowing, weed suppression, support of invertebrates, soil fertility building (measured as yield of following crop), and conservation of nutrients in the soil. An experimental species pool of 12 cultivated legume species was screened for a range of functional traits and ecosystem services at five sites across a geographical gradient in the United Kingdom. All possible species combinations were then analyzed, using a process-based model of plant competition, to identify the community that delivered the best balance of services at each site. In our system, low to intermediate levels of species richness (one to four species) that exploited functional contrasts in growth habit and phenology were identified as being optimal. The optimal solution was determined largely by the number of species and functional diversity represented by the starting species pool, emphasizing the importance of the initial selection of species for the screening experiments. The approach of using relationships between functional traits and ecosystem services to design multifunctional biological communities has the potential to inform the design of agricultural systems that better balance agronomic and environmental services and meet the current objective of European agricultural policy to maintain viable food production in the context of the sustainable management of natural resources.

Breeding white clover for tolerance to low temperature and grazing stress

SummaryLow temperature and grazing are the two major stresses limiting white clover yield in mixed swards grown in the marginal areas of the UK. White clover has traditionally been used to improve productivity in such areas but is increasingly being used to reduce input costs in more productive areas. Considerable genetic variation exists in characters associated with cold tolerance, low temperature growth and grazing tolerance. This paper describes recent progress in developing varieties tolerant to three major stresses and which give greater and more reliable production.

Variation in cold tolerance and spring growth among Italian white clover populations

Seven populations collected at different altitudes in northern Italy, two Ladino breeding populations and two control cultivars (AberHerald and Grasslands Huia) of white clover (Trifolium repens L.) were included in a series of experiments analysing: (i) levels of cold tolerance using artificial and field-based methods; (ii) relationships between these measures of cold tolerance; (iii) components of spring yield, various physiological traits, and their relationships with cold tolerance. Rates of seedling and growing point mortality in the populations over winter, assessed in separate field experiments, were closely related (r = 0.85). Grasslands Huia showed the highest death rates, and material originating from high altitudes the lowest. The LT50 value, i.e., the temperature at which 50% of the growing points would die, estimated by an artificial freezing test, was significantly correlated with field-based measures of seedling (r = 0.64) and growing point (r = 0.84) mortality. The existence of these correlations is of potential interest for the development of indirect selection criteria for complex and expensive-to-evaluate traits such as winter survival in field plots. Besides being reliable, in this study the artificial assessment was also sensitive, providing a greater degree of separation of the populations means than field-based measures. Of the several physiological traits (water content,concentrations of water soluble and total non-structural carbohydrate, and water soluble protein content of stolons) measured at a mid-winter sampling date under field conditions, the only character showing significant variation between populations was soluble protein content. There was a slight trend for material with a higher protein content to exhibit greater field-based values of cold tolerance. High altitude populations tended to have low spring yields. The highest spring yield was found in one of the Ladino populations. The study identified two populations which combined, to differing extents, cold tolerance and spring yield characteristics that would be of potential use in breeding for specified agronomic/climatic zones.

Benefits of sward diversity for agricultural grasslands

Abstract A pan-European experiment carried out at 28 sites across Europe showed strong benefits of sward diversity in agricultural grasslands. We systematically varied the relative abundance of four agronomic plant species (sown species evenness), and found that 4-species mixtures yielded more forage than could be expected on the basis of the monoculture yields. Mixtures generally yielded more than even the best performing monoculture (transgressive overyielding). Mixtures strongly reduced the incidence of unsown species in the sward. These diversity effects were consistent over the wide range of environmental conditions and persisted over three harvest years and in highly fertilized conditions. These results indicate a strong potential for agronomic mixtures to contribute to more sustainable agricultural systems. Agronomic diversity can improve forage yield and reduce weed invasion in intensively managed grasslands, and may also enhance the provision of other ecosystem services.

Response to divergent selection for stolon characters in white clover (Trifolium repens)

Stolon death, often caused by grazing or winter-kill, is a major factor determining the survival and persistence of white clover (Trifolium repens L.), the most important forage legume in UK agriculture. Since stolon morphology apparently affects stolon survival, this study was designed to assess the genetic variation for stolon characters within a white clover population from Switzerland and to assess the effects of two generations of selection for stolon characteristics on that population. Bidirectional selection was carried out simultaneously for stolon diameter (as the primary criterion of selection) and total stolon length i.e. the product of the length of the longest stolon and stolon number. Four selection lines were established: (a) plants with thick sparse stolons, (b) plants with thick profuse stolons, (c) plants with thin sparse stolons and (d) plants with thin profuse stolons. Realised heritabilities for stolon diameter, estimated in both directions and over both generations of selection, were found to lie within the range 0.28-0.44; significant shifts in population means for stolon diameter were demonstrated. Selection for thin profuse stolons and for thick sparse stolons was effective, but because of negative correlations between stolon diameter and both stolon length and number, selection for thin sparse stolons or thick profuse stolons was ineffective.

A new emphasis on root traits for perennial grass and legume varieties with environmental and ecological benefits

Abstract Grasslands cover a significant proportion of the agricultural land within the UK and across the EU, providing a relatively cheap source of feed for ruminants and supporting the production of meat, wool and milk from grazing animals. Delivering efficient animal production from grassland systems has traditionally been the primary focus of grassland‐based research. But there is increasing recognition of the ecological and environmental benefits of these grassland systems and the importance of the interaction between their component plants and a host of other biological organisms in the soil and in adjoining habitats. Many of the ecological and environmental benefits provided by grasslands emanate from the interactions between the roots of plant species and the soil in which they grow. We review current knowledge on the role of grassland ecosystems in delivering ecological and environmental benefits. We will consider how improved grassland can deliver these benefits, and the potential opportunities for plant breeding to improve specific traits that will enhance these benefits whilst maintaining forage production for livestock consumption. Opportunities for exploiting new plant breeding approaches, including high throughput phenotyping, and for introducing traits from closely related species are discussed.