The objective of this study was to determine the genetic parameters of methane (CH4) emissions and their genetic correlations with key production traits. The trial measured the CH4 emissions, at 5-min intervals, from 1225 sheep placed in respiration chambers for 2 days, with repeat measurements 2 weeks later for another 2 days. They were fed in the chambers, based on live weight, a pelleted lucerne ration at 2.0 times estimated maintenance requirements. Methane outputs were calculated for g CH4/day and g CH4/kg dry matter intake (DMI) for each of the 4 days. Single trait models were used to obtain estimates of heritability and repeatability. Heritability of g CH4/day was 0.29 ± 0.05, and for g CH4/kg DMI 0.13 ± 0.03. Repeatability between measurements 14 days apart were 0.55 ± 0.02 and 0.26 ± 0.02, for the two traits. The genetic and phenotypic correlations of CH4 outputs with various production traits (weaning weight, live weight at 8 months of age, dag score, muscle depth and fleece weight at 12 months of age) measured in the first year of life, were estimated using bivariate models. With the exception of fleece weight, correlations were weak and not significantly different from zero for the g CH4/kg DMI trait. For fleece weight the phenotypic and genetic correlation estimates were −0.08 ± 0.03 and −0.32 ± 0.11 suggesting a low economically favourable relationship. These results indicate that there is genetic variation between animals for CH4 emission traits even after adjustment for feed intake and that these traits are repeatable. Current work includes the establishment of selection lines from these animals to investigate the physiological, microbial and anatomical changes, coupled with investigations into shorter and alternative CH4 emission measurement and breeding value estimation techniques; including genomic selection.

Summary Three grassland communities in New Zealand with differing climates and proportions of C3 and C4 species were subjected to one‐off extreme heating (eight hours at 52.5°C) and rainfall (the equivalent of 100 mm) events. A novel experimental technique using portable computer‐controlled chambers simulated the extreme heating events. The productive, moist C3/C4 community was the most sensitive to the extreme events in terms of short‐term community composition compared with a dry C3/C4 community or an exclusively C3 community. An extreme heating event caused the greatest change to plant community species abundance by favouring the expansion of C4 species relative to C3 species, shifting C4 species abundance from 43% up to 84% at the productive, moist site. This was observed both in the presence and absence of added water. In the absence of C4 species, heating reduced community productivity by over 60%. The short‐term shifts in the abundance of C3 and C4 species in response to the single extreme climatic events did not have persistent effects on community structure or on soil nitrogen one year later. There was no consistent relationship between diversity and stability of biomass production of these plant communities, and species functional identity was the most effective explanation for the observed shifts in biomass production. The presence of C4 species resulted in an increased stability of productivity after extreme climatic events, but resulted in greater overall shifts in community composition. The presence of C4 species may buffer grassland community productivity against an increased frequency of extreme heating events associated with future global climate change.

Summary Phytometers of five C3 and five C4 species were transplanted into three different grasslands to study the effects of extreme climatic events on community invasibility and competition. Single extreme heating (eight hours at 52.5 °C) and rainfall (the equivalent of 100 mm) events in factorial combinations were superimposed on the grassland communities. A novel technique involving portable computer‐controlled chambers was used to create the heating events. In order to generate predictions of response to the extreme climatic events, the 10 phytometer species were categorized on the basis of 12 key plant functional traits. Using principal component analysis, two functional types (FTs) were identified as most likely to be advantaged (FT1, fast‐growing C4 annuals) and disadvantaged (FT2, slower‐growing C3 perennials) by an extreme climatic event. Competition between the resident vegetation and FT1 plus other C4 phytometers was consistently more intense within the exclusively C3 community compared to the dry C3/C4 community or moist C3/C4 community. The single extreme heating event had the greatest impact on competition, lowering the intensity of competition between the phytometers and resident vegetation. Our results indicate that competition is highly important in limiting the invasion of C3 grasslands by C4 species. The FT1 and FT2 responses confirmed predictions based on plant functional traits, whether growing as phytometers or as part of the resident vegetation. Future increases in climatic variability and the incidence of extreme climatic events are expected to suppress C3 competitive dominance and promote invasion of C4 species, in particular, the FT1 species.

White clover (Trifolium repens L.) is experiencing increased levels of ultraviolet-B (UV-B) radiation in temperate pastures due to the depletion of the stratospheric ozone layer. Based on 17 morphological, morphogenetic and physiological attributes, this study analysed the consequences of enhanced UV-B on 26 white clover populations using principal components analysis (PCA). After 18 d of exposure to 13·3 kJ m -2 d -1 UV-B in controlled environments, UV-B significantly decreased above-ground and below-ground plant growth attributes, epidermal cell surface area and maximum quantum efficiency of photosystem II photochemistry (F v /F m ). Aspects of cell division and cell expansion both were negatively affected by UV-B. Stomatal density, specific leaf mass, root-to-shoot ratio and levels of UV-B-absorbing compounds increased in response to UV-B. In the multivariate analysis, the main dimension of UV-B sensitivity was characterized by changes in plant growth attributes. Alterations in partitioning within and between plant organs constituted a secondary tier of UV-B responsiveness. Plant characteristics related to UV-B tolerance included lower growth rate, smaller epidermal cell surface area and higher UV-B-induced levels of UV-Babsorbing compounds. The results suggest overall UV-B tolerance for slower-growing populations from less productive habitats with higher natural UV-B irradiance.

A decline in the availability of nitrogen (N) for plant growth (progressive nitrogen limitation or PNL) is a feedback that could constrain terrestrial ecosystem responses to elevated atmospheric CO 2 . Several long-term CO 2 enrichment experiments have measured changes in plant and soil pools and fluxes consistent with PNL but evidence for PNL in grasslands is limited. In an 11 year Free Air CO 2 Enrichment (FACE) experiment on grazed grassland we found the amount of N harvested in aboveground plant biomass was greater at elevated CO 2 but declined over time to be indistinguishable from ambient after 5 years. Re-wetting after a major drought resulted in a large input of N from mineralisation and a return to a higher N harvested under elevated CO 2 followed by a further decline. Over these two periods the amount of N in soil significantly increased at elevated CO 2 . Data from mesocosms introduced into the rings at intervals, and therefore having different lengths of exposure to CO 2 , showed plant N availability declined at elevated CO 2 reaching a new equilibrium after 6 years of exposure. We conclude that the availability of N for plants in this grassland is dynamic but the underlying trend at elevated CO 2 is for PNL.