Temporal changes in population genetic diversity and structure in red and white clover grown in three contrasting environments in northern Europe.

UNLABELLED: BACKGOUND AND AIMS: Extending the cultivation of forage legume species into regions where they are close to the margin of their natural distribution requires knowledge of population responses to environmental stresses. This study was conducted at three north European sites (Iceland, Sweden and the UK) using AFLP markers to analyse changes in genetic structure over time in two population types of red and white clover (Trifolium pratense and T. repens, respectively): (1) standard commercial varieties; (2) wide genetic base (WGB) composite populations constructed from many commercial varieties plus unselected material obtained from germplasm collections. METHODS: At each site populations were grown in field plots, then randomly sampled after 3-5 years to obtain survivor populations. AFLP markers were used to calculate genetic differentiation within and between original and survivor populations. KEY RESULTS: No consistent changes in average genetic diversity were observed between original and survivor populations. In both species the original varieties were always genetically distinct from each other. Significant genetic shift was observed in the white clover 'Ramona' grown in Sweden. The WGB original populations were more genetically similar. However, genetic differentiation occurred between original and survivor WGB germplasm in both species, particularly in Sweden. Regression of climatic data with genetic differentiation showed that low autumn temperature was the best predictor. Within the set of cold sites the highest level of genetic shift in populations was observed in Sweden. CONCLUSIONS: The results suggest that changes in population structure can occur within a short time span in forage legumes, resulting in the rapid formation of distinct survivor populations in environmentally challenging sites.

Grassland plant species diversity decreases invasion by increasing resource use.

Species richness of plant communities has been demonstrated to provide resistance to invasion by unsown species, though the relationship with resource availability varies between studies. The present work involved five grassland species grown in monocultures and in four-species mixtures sown in accordance with a simplex design. The species used represented different functional groups (i.e. grasses, legumes and non-N(2)-fixing species), each of which differed internally in terms of competitiveness. I hypothesized that sown diversity would negatively affect invader performance by decreasing the availability of light and soil nitrogen (N) for invading species, and that functional composition of the sown diversity would affect the functional composition of the invading flora. The experimental plots were harvested for two years, and were fertilized with 100 kg N ha(-1) each year. The number of unsown species (classified into four functional groups) invading each plot and their proportion of the biomass harvested were recorded. The penetration of incoming light through the canopy, the apparent N uptake by the sown species from the soil, and the mineral N content in the soil were measured. I found that diverse communities captured more resources both above- and belowground, and the number of invading species and their biomass production were smaller in mixed than in monoculture plots. However, the sampling effect of one grass was also strong. These results suggest that increased resource use in diverse communities can reduce invasion.

Feeding and performance of pigs in smallholder production systems in Northern Lao PDR.

A survey was carried out in the North of Lao PDR to study feeding systems and the performance of pigs in smallholder systems. A total of 341 farmers from five provinces were interviewed. To feed their pigs, farmers mainly rely on feedstuffs produced on the farm and collected from areas near the village. The feedstuffs used included by-products such as rice bran and distiller's waste, planted feeds, mainly maize and cassava, and various green plant materials. The feedstuffs used are usually high in energy and low in protein content, and the only readily available protein source is green plant material. This results in nutritionally imbalanced diets and as a result poor pig performance. The average growth rate of pigs in these systems was found to be only approximately 100 g/day. The reproductive performance of sows was found to be relatively low, as is the case of local breeds in the region, with an average litter size at birth of 6.8 piglets. The mortality of piglets was as high as 50% and was a main concern of farmers. In order to improve the productivity of pigs in smallholder systems, there is a need to find alternative feed resources to improve the nutritional feed quality, and to develop management systems which are suited to the needs and practices of smallholders.

Weed suppression greatly increased by plant diversity in intensively managed grasslands: A continental-scale experiment.

Grassland diversity can support sustainable intensification of grassland production through increased yields, reduced inputs and limited weed invasion. We report the effects of diversity on weed suppression from 3 years of a 31-site continental-scale field experiment.At each site, 15 grassland communities comprising four monocultures and 11 four-species mixtures based on a wide range of species' proportions were sown at two densities and managed by cutting. Forage species were selected according to two crossed functional traits, "method of nitrogen acquisition" and "pattern of temporal development".Across sites, years and sown densities, annual weed biomass in mixtures and monocultures was 0.5 and 2.0 t  DM ha-1 (7% and 33% of total biomass respectively). Over 95% of mixtures had weed biomass lower than the average of monocultures, and in two-thirds of cases, lower than in the most suppressive monoculture (transgressive suppression). Suppression was significantly transgressive for 58% of site-years. Transgressive suppression by mixtures was maintained across years, independent of site productivity.Based on models, average weed biomass in mixture over the whole experiment was 52% less (95% confidence interval: 30%-75%) than in the most suppressive monoculture. Transgressive suppression of weed biomass was significant at each year across all mixtures and for each mixture.Weed biomass was consistently low across all mixtures and years and was in some cases significantly but not largely different from that in the equiproportional mixture. The average variability (standard deviation) of annual weed biomass within a site was much lower for mixtures (0.42) than for monocultures (1.77). Synthesis and applications. Weed invasion can be diminished through a combination of forage species selected for complementarity and persistence traits in systems designed to reduce reliance on fertiliser nitrogen. In this study, effects of diversity on weed suppression were consistently strong across mixtures varying widely in species' proportions and over time. The level of weed biomass did not vary greatly across mixtures varying widely in proportions of sown species. These diversity benefits in intensively managed grasslands are relevant for the sustainable intensification of agriculture and, importantly, are achievable through practical farm-scale actions.