青藏高原不同生境下湿生扁蕾(Gentianopsis paludosa)个体大小依赖的繁殖分配

植物对资源的投资和分配是生态学中的重要问题,它反映了植物应对环境变化时的生活史策略。选择青藏高原东缘同一海拔下的嵩草草甸(Kobresia sp.meadow)、金露梅灌丛(Potentilla fruticosa shrub meadow)以及草甸-灌丛交错带3种生境类型,并以3种生境下的湿生扁蕾(Gentianopsis paludosa)为对象,研究了其繁殖分配特征。结果发现:(1)在种群水平上,在生境从草甸经交错带到灌丛的变化中,湿生扁蕾个体大小和繁殖分配比例逐渐增加;3个种群湿生扁蕾的总花数目没有显著差异,但草甸生境湿生扁蕾的蕾期花数目显著高于灌丛生境,而果期花数目则显著低于灌丛生境;(2)在个体水平上,湿生扁蕾的繁殖绝对投入与个体大小显著正相关,且各种群植株都存在繁殖所需的个体大小阈值,而繁殖阈值在生境从草甸经交错带到灌丛的过渡中逐渐减小;湿生扁蕾的繁殖相对投入与个体大小负相关,但相关系数随着生境从草甸经交错带到灌丛的过渡中逐渐减小;各种群花数目与湿生扁蕾植株个体大小显著正相关。研究表明,湿生扁蕾的繁殖投资存在大小依赖效应,但生境差异会对其繁殖投资和生活史策略造成显著影响,而这种影响主要是由不同生境下自然条件的不同造成的。同时,资源分配也与湿生扁蕾的遗传特性和延迟自交的繁育系统特征有关。湿生扁蕾这种不同生境下个体大小依赖的繁殖投资差异是湿生扁蕾与其生境长期适应和进化(生境选择)的结果。

Size-dependent reproductive allocation of Gentianopsis paludosa in different habitats of the Qinghai-Tibetan Plateau

Understanding plant resource investment and allocation is an important issue in ecology, since this can reflect the plant life-history strategies as a response to the changing environment. Many studies in the last decades have focused on plant resource allocation at different elevations, and most of them have determined that the plant resource allocation is strongly correlated with the plant size, representing a positive correlation between reproductive investment and plant size but a negative correlation between reproductive allocation and plant size. However, research has also shown that the reproductive allocation had no correlation with plant size. Significant elevation variation in the Qinghai-Tibetan Plateau provides the ecologists an ideal platform to reveal the plant resource allocations, since elevation variation can bring strong environment variances. However, previous studies did not address the variation in plant habitats, which could have directly affected the plant''s resource allocation. In this study, we tested the reproductive allocation characters of Gentianopsis paludosa at three habitats located on the same elevation, on the east Qinghai-Tibetan Plateau: Kobresia sp. meadow (CD), Potentilla fruticosa shrub meadow (GC), and their junction area (JC). Centering the study on two levels, population and individual, we aimed to test the resource allocation characters of G. paludosa and reveal the relationship between the plant resource allocation and the plant habitats. Our results revealed the following: (1) The abiotic conditions were different among the three habitats, among which habitat CD displayed relatively better abiotic conditions compared with the others since the soil temperature and humidity, air temperature, and the net carbon absorptions were higher and optimal for plant growth. (2) At the population level, the individual size and reproductive allocation increased following the habitat variation of CD-JC-GC; the total flower numbers of G.paludosa did not differ significantly among the three habitats, whereas the bud numbers in the meadow were greater than those in the shrub meadow, and fruiting flower numbers in the meadow habitat were lower than those in the shrub meadow. (3) At the individual level, the reproductive biomass was positively correlated with individual size; a size threshold existed in G.paludosa and it declined with the habitat variation of CD-JC-GC; the reproductive allocation of G.paludosa had a negative correlation with the individual size, whereas the correlation coefficient declined following the habitat variation of CD-JC-GC; the flower number was positively correlated with individual size in all three habitats. These results suggest that reproductive allocation of G. paludosa is size-dependent, and that habitat variation can influence reproductive allocation and life-history strategies. The plant size and reproductive allocation characters were strongly related with their habitats, and reproductive allocation varied at both the population level and individual level. These variations were caused, primarily, in two ways: (1) the different natural conditions of the three habits could play an important role in determining the reproductive allocation characters; and (2) the genetic characters and the delayed-selfing breeding system were also correlated with the reproductive allocation. Although it was difficult to determine which of the two was dominant, the size-dependent reproductive allocation of G. paludosa in different habitats was undoubtedly a result of co-evolution between a plant and its habitat.