Abstract
Fall dormancy (FD) in alfalfa (Medicago sativa L.) can be described using 11 FD ratings, is widely used as an important indicator of stress resistance, productive performance and spring growth. However, the contrasting growth strategies in internode length and internode number in alfalfa cultivars with different FD rating are poorly understood. Here, a growth chamber study was conducted to investigate the effect of FD on plant height, aboveground biomass, internode length, and internode number in alfalfa individuals in the early growth stages. In order to simulate the alfalfa growth environment in the early stage, 11 alfalfa cultivars with FD ratings from one to 11 were chosen and seeded at the greenhouse, and then were transplanted into an artificial growth chamber. The experimental design was a randomized complete block in a split-plot arrangement with three replicates. Plant height, above-ground biomass, internode length, and internode number were measured in early growth stage in all individuals. Our findings showed that plant height and the aboveground biomass of alfalfa did not significantly differ among 11 different FD rated cultivars. Also, internode length and internode number positively affected plant height and the aboveground biomass of alfalfa individuals and the average internode length significantly increased with increasing FD rating. However, internode number tended to sharply decline when the FD rating increased. Moreover, there were no correlations, slightly negative correlations, and strongly negative correlations between internode length and internode number in alfalfa individuals among the three scales, including within-FD ratings, within-FD categories and inter-FD ratings, respectively. Therefore, our results highlighted that contrasting growth strategies in stem elongation were adopted by alfalfa with different FD ratings in the early growth stage. Alfalfa cultivars with a high FD rating have longer internodes, whereas more dormant alfalfa cultivars have a larger number of internodes. There were tradeoffs between internode length and internode number in response to FD in alfalfa, which reflected certain scale-dependence.
Highlights
Plant growth habit is a fundamental characteristic but one that is greatly modified by environmental factors [1]
We addressed the following three questions: (i) How does Fall dormancy (FD) rating affect the plant height and aboveground biomass in alfalfa in the early growth stages? (ii) How does FD rating affect the internode length and internode number? (iii) How do alfalfa cultivars with contrasting FD ratings react to the tradeoff between internode length and internode number? By scaling down our analysis to the internode, this study will provide novel information on the growth strategy of alfalfa
No significant differences existed among all alfalfa cultivars that belonged to different fall dormancy types doi:10.1371/journal.pone.0135934.g001 (Fig 1B)
Summary
Plant growth habit is a fundamental characteristic but one that is greatly modified by environmental factors [1]. Habit depends on a combination of different factors, such as internode patterns in the vegetative shoot, leaf traits, leaf to stem ratio, and growing canopy [2,3,4]. Varietal differences in internode number and internode length were statistically significant in ten common varieties of alfalfa [1]. That technique could be useful in varietal purity testing, genetic studies, and characterization of alfalfa varieties. The alfalfa stem is a major organ that affects plant height, above-ground biomass, and forage yield. Previous studies on alfalfa stem traits have revealed differences among cultivars in individual internodes, and suggested that the height of plants grown under standardized conditions might be of importance in cultivar purity testing [1]
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