Cold acclimation in white clover subjected to chilling and frost: changes in water and carbohydrates status

International audienceThe effect of cold acclimation on the water status and the fate of carbohydrates was studied in white clover (Trifolium repens L., cv Huia) subjected to chilling and/or freeze-thaw cycles. Treatments were applied in a controlled environment, with a constant photoperiod, for 6 weeks to plants either acclimated or non-acclimated to low temperature. Cold acclimated plants had a higher concentration of starch in the stolons at the end of the acclimation period than non-acclimated plants (54 vs. 15 mg g(-1) DW). During the experiment, the leaves of cold acclimated plants subjected to frosts maintained a higher relative water content (RWC) than did leaves of plants not acclimated for which we observed a strong dehydration of 80%. Under chilling, cold acclimated plants demonstrated an osmotic adjustment. We showed that only 30-40% of the variation of the osmotic potential was explained by variation in free sugar concentration, suggesting that compounds other than carbohydrates participated in the osmotic regulation. Chilling increased the carbohydrate content and frost decreased the starch concentration in non-acclimated plants only. We showed in white clover that the cold acclimation contributed to frost and chilling tolerance by the maintenance of the hydration of tissues. We demonstrated that osmotic adjustment was not completely explain by the accumulation of free sugars

Comportement hivernal et repousse printanière du trèfle blanc : importance du cultivar

La morphogenèse de la plante ainsi que la survie des bourgeons affectés par la période hivernale conditionnent la repousse printanière et la pérennité de l'association. On constate une évolution saisonnière des réserves glucidiques des stolons, avec une accumulation automnale et une hydrolyse hivernale. Les résultats montrent que les réserves en début d'hiver (liées à la surface foliaire par axe plus élevée en automne, et à des stolons plus épais) sont plus élevées pour AberHerald que pour Huia, les 2 variétés étudiées. Le potentiel de repousse au printemps (nombre de bourgeons actifs de feuilles et de racines, vitesse d'apparition des feuilles) de AberHerald est significativement supérieur à celui de Huia. D'où l'importance, pour le praticien, de choisir un cultivar adapté aux conditions pédoclimatiques locales

Overwintering and growing season dynamics of Trifolium repens L. in mixture with Lolium perenne L. : A model approach to plant-environment interactions

In attempting to increase the reliability of clover contribution in clover/ryegrass systems it is important to understand the roles of (1) specific traits of the clover genotype (2) climate and (3) their interactions in determining clover behaviour in swards. Overwintering and spring growth of white clover (cultivars AberHerald and Huia) grown in binary mixtures with perennial ryegrass were measured at 12 European sites ranging in latitude from Reykjavik, Iceland (64°30' N) to Pordenone, Italy (46°30' N). In the overwintering period, tiller density of the grass was assessed and detailed morphological and chemical measurements were made on the clover at each sampling time. During the growing season, the clover contribution to total available biomass was recorded. Detailed climatic data were available at all sites. The annual growth cycle of swards was divided into four functional periods (spring, summer, autumn and winter). Within each functional period community responses were modelled. The models incorporated independent biotic variables characterizing each community within each site at the start of the period and independent variables characterizing the climate at each site during the period. The models were linked dynamically by taking, as response variable(s) for a functional period, the independent biotic variable(s) of the succeeding period. In general, the modelling strategy was successful in producing a series of biologically meaningful linked models. Essential prerequisites for this were (a) the establishment of a well-devised common protocol prior to the experiment and (b) the extensive gradients of climatic and other variables obtained by using numerous sites. AberHerald generally performed as well as, or better than, Huia throughout the annual cycle across the range of climatic conditions encountered, and especially under low temperature conditions in winter and autumn. Clover leaf area index appeared to be a key variable in determining clover performance over winter and through the following growing season. Grass tiller density had a strong negative effect on clover content in spring but only at low temperatures. This emphasizes the importance of a high clover leaf area index in autumn as the main biotic factor related to spring clover content in milder conditions. The importance of climatic variables in the models is their use in explaining the reliability of the contribution of clover in clover/ryegrass systems. Temperature was the primary climatic determinant of clover response in all periods, having a direct effect on clover content and leaf area index or mediating the effect of the associate species. Radiation strongly influenced clover dynamics during winter and spring but not in the other periods, possibly because it was confounded with the effect of higher temperature. Precipitation was positively related to clover growth during spring and autumn and was related to tiller density in a complex manner during autumn and winte

Overwintering of Trifolium repens L. and succeeding growth : Results from a common protocol carried out at twelve European sites

A common experimental protocol was followed at 12 sites in Europe to study the development of two clover cultivars (AberHerald and Huia) grown in association with a ryegrass cultivar throughout their annual cycle. The duration of the experiment was between 1 and 3 years at each site. Detailed information about the morphogenesis and carbohydrate reserves of white clover during winter and the subsequent productivity of clover plants during the growing season was collected. Yield of the companion ryegrass was also measured at several harvests during the growing season and grass tiller density was recorded several times during winter. There was wide variation among sites and between years in climatic conditions, in the growth characteristics and chemical composition of the two cultivars, and in the tiller density of the ryegrass. The relative performance of the two cultivars varied among sites but AberHerald generally outperformed Huia. Major changes in plant characteristics (morphology, population size, chemical composition, etc.) occurred during overwintering. This paper presents a preliminary analysis of the effects of site, clover cultivar and sward age (years) on various plant characteristics. It is established that the data provide a unique basis for modelling the effects of a wide range of environmental conditions and plant properties on the performance of white clover in mixed swards. A modelling approach that seeks to replace site and year by climatic variables characterizing each site by year combination is developed in two companion papers

A model approach to white clover summer dynamics at twelve European sites

vokPA

Overwintering of Trifolium repens L. and Succeeding Growth: Results from a Common Protocol carried out at Twelve European Sites

vokEKO/Karil

Overwintering and Growing Season Dynamics of Trifolium repens L. in Mixture with Lolium perenne L.: A Model Approach to Plant-environment Interactions

vokEKO/Karil