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Unformatted text preview: Journal of Integrative Plant Biology 2008, 50 (2): 141146 Reproductive Allocation Patterns in Different Density Populations of Spring Wheat Jing Liu 1 , 3 , Gen-Xuan Wang 2 , Liang Wei 1 and Chun-Ming Wang 1 ( 1 Key Laboratory of Arid and Grassland Agroecology at Lanzhou University, Ministry of Education , Lanzhou 730000, China; 2 College of Life Sciences, Zhejiang University, Hangzhou 310027, China; 3 Institute of Modern Physics, the Chinese Academy of Sciences , Lanzhou 730000, China) Abstract The effects of increased intraspecific competition on size hierarchies (size inequality) and reproductive allocation were investigated in populations of the annual plant, spring wheat ( Triticum aestivum) . A series of densities (100, 300, 1 000, 3 000 and 10 000 plants/m 2 ) along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient ( R 2 = 0.927), which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition (100 plants/m 2 ), individual reproductive allocation was size independent but, in high density populations (300, 1 000, 3 000 and 10 000 plants/m 2 ), where competition occurred, individual reproductive allocation was size dependent: the small proportion of larger individuals were winners in competition and got higher reproductive allocation (lower marginal reproductive allocation; MRA), and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation (higher MRA). In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation (with a negative relationship between them). However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies. Key words: competition; density; reproductive allocation. Liu J, Wang GX, Wei L, Wang CM (2008). Reproductive allocation patterns in different density populations of spring wheat. J. Integr. Plant Biol. 50 (2), 141146. Available online at www.jipb.net In plant populations, increasing density can intensify plant plant competition directly (Pianka 1981). Competition among plants is an important factor in affecting size hierarchies (Weiner 1985; Bonan 1988; Pan et al. 2003a, b), growth rate (Ehleringer 1984; Weiner and Thomas 1992), survivorship (White 1981; Tanner 1997; van Kleunen et al. 2001), and reproductive output (Ehleringer 1984; Weiner and Thomas 1992; Soto-Pinto et al.(Ehleringer 1984; Weiner and Thomas 1992; Soto-Pinto et al....
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