We assessed the effects of red:far-red (R:FR) ratio on net CO2 assimilation, photosynthetic activity, and morphology of young white clover leaves developed under a simulated canopy light environment. Isolated cuttings of Trifolium repens L. were grown in controlled conditions under two irradiances in combination with two R:FR ratios. We used far-red light emitting diodes to reduce the R:FR ratio on leaves that were successively developing on the main stolon and were subject to strong competition for light within a sward. A leaf that developed under a low R:FR ratio had a lower chlorophyll content than the controls. However, this change had no consequences on the net CO2 assimilation rate and on the biomass allocated to shoots. The low R:FR ratio modified the leaf morphology by increasing the leaf area. A leaf that developed in lower irradiance had a lower net CO2 assimilation rate and a greater leaf area and petiole length than leaves that developed in higher irradiance. Therefore, irradiance was the main factor limiting the leaf CO2 assimilation under a canopy. Capture of light by clover leaves was improved by FR light only via modifications of leaf morphology, because there were no significant effects of FR light on photosynthesis.
Under temperate climates, grassland species are subjected to overwintering which may significantly influence their early spring growth capacity. In white clover (Trifolium repens L.), it is known that overwintering capacity can differ among cultivars. Ability of this forage legume to recover from winter damage will, therefore, have a great influence on its persistence in grass–clover associations. Experiments were undertaken with two different white clover cultivars (Huia and AberHerald). Leaf appearance rate, dry matter distribution, 14C assimilate partitioning, and vegetative storage protein accumulation were determined in plants subjected to a 4‐wk chilling period (5/0°C, day/night) and subsequent warmer temperatures (15/10°C), and compared with control plants (20/15°C). Chilling treatment decreased leaf appearance rate, with AberHerald producing more leaves than Huia. This can be considered as a major aspect of cold adaptation strategy because leaf appearance rate controlled carbon acquisition. Low temperature increased dry matter partitioning to below‐ground tissues. AberHerald allocated more assimilates to stolons than Huia. Accumulation of a 17.3‐kDa protein, believed to act as a vegetative storage protein, also increased after the chilling treatment. Regrowth was characterized by rapid mobilization of the 17.3‐kDa protein in stolons and by preferential carbon allocation to stolon apices. AberHerald showed a higher regrowth potential than Huia in view of its morphological and physiological characters which include carbon acquisition and assimilate partitioning patterns, favoring shoot regrowth and acquisition of stolon reserves.
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