Photosynthetic organisms are able to sense energy imbalances brought about by the overexcitation of photosystem II (PSII) through the redox state of the photosynthetic electron transport chain, estimated as the chlorophyll fluorescence parameter 1-qL, also known as PSII excitation pressure. Plants employ a wide array of photoprotective processes that modulate photosynthesis to correct these energy imbalances. Low temperature and light are well established in their ability to modulate PSII excitation pressure. The acquisition of freezing tolerance requires growth and development a low temperature (cold acclimation) which predisposes the plant to photoinhibition. Thus, photosynthetic acclimation is essential for proper energy balancing during the cold acclimation process. Eutrema salsugineum (Thellungiella salsuginea) is an extremophile, a close relative of Arabidopsis thaliana, but possessing much higher constitutive levels of tolerance to abiotic stress. This comparative study aimed to characterize the photosynthetic properties of Arabidopsis (Columbia accession) and two accessions of Eutrema (Yukon and Shandong) isolated from contrasting geographical locations at cold acclimating and non-acclimating conditions. In addition, three different growth regimes were utilized that varied in temperature, photoperiod and irradiance which resulted in different levels of PSII excitation pressure. This study has shown that these accessions interact differentially to instantaneous (measuring) and long-term (acclimation) changes in PSII excitation pressure with regard to their photosynthetic behaviour. Eutrema accessions contained a higher amount of photosynthetic pigments, showed higher oxidation of P700 and possessed more resilient photoprotective mechanisms than that of Arabidopsis, perhaps through the prevention of PSI acceptor-limitation. Upon comparison of the two Eutrema accessions, Shandong demonstrated the greatest PSII operating efficiency (ΦPSII) and P700 oxidizing capacity, while Yukon showed greater growth plasticity to irradiance. Both of these Eutrema accessions are able to photosynthetically acclimate but do so by different mechanisms. The Shandong accessions demonstrate a stable response, favouring energy partitioning to photochemistry while the Yukon accession shows a more rapid response with partitioning to other (non-photochemical) strategies.

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Integrating Perennial Forage Seed Crops in RotationsCore Ideas  Integration of perennial forage seed crops in cropping sequences can be productive and profitable. Prevailing commodity prices have bearing on the relative profitability of the crops. Forage legumes can replace external nitrogen application for two succeeding crops. Complementary studies help to elucidate agro-ecosystem services of perennial seed crops.

White prairie clover [Dalea candida (Michx.) Willd.] is native to the dry prairies and hillsides of the Northern Great Plains. A study was initiated in 2012 with six white prairie clover populations collected from the Canadian Prairies. Plant growth characteristics, forage biomass, seed yield, and forage nutritive values were evaluated using a randomized complete block design in a field near Swift Current, SK. Three populations from Argyle, Carlowrie, and Big Grass Marsh (NCP588) in Manitoba displayed erect-type growth while those from Douglas Provincial Park and Stewart Valley in Saskatchewan and Writing on Stone Provincial Park in Alberta exhibited prostrate growth. The populations did not differ for mean biomass yield (79–104 g plant−1, p = 0.54) and mean seed yield (6.6–9.1 g plant−1, p = 0.69); however, they differed for bloom stage nutritional parameters such as acid detergent fibre (25%–30%, p = 0.04), neutral detergent fibre (34%–41%, p < 0.01), crude proteins (15%–18%, p < 0.01), phosphorus (0.24%–0.29%, p = 0.02), and iron content (144–360 ppm, p = 0.01). To our knowledge, this is the first report of comparative phenotypic, nutritional, and propagation study of native white prairie clover populations of Canada. The constraints and opportunities for successful domestication of white prairie clover as a forage crop are discussed.