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Winter cover crops are capable of supplying multiple economic and environmental benefits in temperate environments of North America, but the lack of adapted populations for specific environmental and agricultural contexts has resulted in cover crops that are unreliable and perform ecosystem functions unevenly. To maximize the benefits provided by winter cover crops, we argue for trait selection by crop scientists that is cognizant of desired ecosystem functions, with the goal of providing commercially available populations that have variable functions. We illustrate this approach through a case study of a promising winter annual legume cover crop, hairy vetch (Vicia villosa). Six key traits and associated functions are considered within specific agroecological contexts. We discuss tradeoffs that may occur among desired plant traits and illustrate how over-selection for a particular trait could negatively affect performance and overall benefits from a cover crop. Intraspecific combinations of complementary cover crops are suggested as means to achieve multiple agroecosystem functions.  2008 Society of Chemical Industry Keywords: cover crops; hairy vetch; functional traits; agroecosystem; local adaptation INTRODUCTIONWinter cover crops in temperate environments can play important roles in soil protection and environmental amelioration. As cash crops are grown during the warm seasons but not cool seasons, the use of winter cover crops is an economically feasible alternative to bare fallow. Filling the winter niche with cover crops extends the presence of living roots and shoots, acting as sinks for nitrogen across the season,

PREMISE Nucleic acid integrity can be compromised under many abiotic stresses. To date, however, few studies have considered whether nucleic acid damage and damage repair play a role in cold‐stress adaptation. A further insufficiently explored question concerns how age affects cold stress adaptation among mature perennials. As a plant ages, the optimal trade‐off between growth and stress tolerance may shift. METHODS Oxidative damage to RNA and expression of genes involved in DNA repair were compared in multiple mature cohorts of Thinopyrum intermedium (an emerging perennial cereal) and in wheat and barley under intermittent freezing stress and under nonfreezing conditions. Activity of glutathione peroxidase (GPX) and four other antioxidative enzymes was also measured under these conditions. DNA repair genes included photolyases involved in repairing ultraviolet‐induced damage and two genes involved in repairing oxidatively induced damage (ERCC1, RAD23). RESULTS Freezing stress was accompanied by large increases in photolyase expression and ERCC1 expression (in wheat and Thinopyrum) and in GPX and GR activity (particularly in Thinopyrum). This is the first report of DNA photolyases being overexpressed under freezing stress. Older Thinopyrum had lower photolyase expression and less freezing‐induced overexpression of ERCC1. Younger Thinopyrum plants sustained more oxidative damage to RNA. CONCLUSIONS Overexpression of DNA repair genes is an important aspect of cold acclimation. When comparing adult cohorts, aging was associated with changes in the freezing stress response, but not with overall increases or decreases in stress tolerance.

The timing and abundance of flower production is important to the reproductive success of angiosperms as well as pollinators and floral and seed herbivores. Exotic plants often compete with native plants for space and limiting resources, potentially altering community floral dynamics. We used observations and a biomass-removal experiment to explore the effects of an invasive exotic flowering plant, Linaria vulgaris, on community and individual species flowering phenology and abundance in subalpine meadows in Colorado, USA. Invasion by L. vulgaris was associated with a shift in both the timing and abundance of community flowering. Invaded plant communities exhibited depressed flowering by 67% early in the season relative to uninvaded communities, but invaded sites produced 7.6 times more flowers than uninvaded sites once L. vulgaris began flowering. This increase in flowers at the end of the season was driven primarily by prolific flowering of L. vulgaris. We also found lower richness and evenness of resident flowering species in invaded plots during the period of L. vulgaris flowering. At the species level, a common native species (Potentilla pulcherrima) produced 71% fewer flowers in invaded relative to uninvaded plots, and the species had reduced duration of flowering in invaded relative to uninvaded sites. This result suggests that L. vulgaris does not simply alter the flowering of subordinate species but also the flowering of an individual common species in the plant community. We then used observational data to explore the relationship between L. vulgaris density and resident floral production but found only partial evidence that higher densities of L. vulgaris were associated with stronger effects on resident floral production. Taken together, results suggest that a dominant invasive plant can affect community and individual-species flowering.