Effects of Temperature and Photoperiod on Stolon Characteristics, Dry Matter Partitioning, and Nonstructural Carbohydrate Concentration of Two White Clover Ecotypes1

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Abstract
Carbohydrate reserves are necessary for survival of perennial plants, but excess accumulation at the expense of harvestable new growth may interfere with the agronomic goal of maximizing herbage yields. The objective of this research was to examine the response of reserve carbohydrate storage and dry matter partitioning in white clover (Trifolium repens L.) to low temperature and short photoperiod. Spaced plants of two altitudinal ecotypes were grown in growth chambers at day/night temperatures and photoperiods of 18°/13°C, 16 h; 10°/7°C, 16 h; and 10°/7°C, 12 h. Plants grown under the lower temperature regime showed an increase in stolon diameter (+33% on average) and thus established a greater stolon volume (+53%) unit leaf area. Shortening the photoperiod resulted in a marked decrease in length of stolon internodes (−54%) and leaf size (−29%), but favored stolon branching (+ 23%). Low temperature depressed net assimilation rate (NAR) to a lesser extent (−38%) than rate of leaf appearance (−52%). Increased photosynthate availability under low temperature was expressed in higher total nonstructural carbohydrate (TNC) content of the leaves (+ 63%), and enabled a greater accumulation of TNC in stolons and roots (+48%). A shorter photoperiod caused a marked decrease TNC content of the leaves (−78%), but only slightly depressed reserve accumulation in stolons and roots (−14%). The alpine ecotype allocated a higher proportion of dry matter to the stolons (+ 35%) than did the valley type, which showed higher root weight proportions (+23%). It is concluded that ecotype and environment influence photosynthate partitioning by affecting plant morphology, by changing the ratio of photosynthate supply to demand, and by controlling carbohydrate use. Low temperature, short photoperiod, and alpine origin favor carbohydrate reserve storage, and thus improve prerequisites for winter survival in white clover.

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