Ramet population structure of Fargesia nitida in different canopy conditions of the subalpine dark coniferous forest in the Wolong Nature Reserve ,China

摘要

The bamboo Fargesia nitida,one of the giant panda's main food sources and the dominant shrub species of the forest understory,is mainly distributed in the dark coniferous belt in western Sichuan and southern Gansu in China.To study the impact of different forest canopy conditions on subalpine dwarf bamboo populations,ramet population structures of clonal Fargesia nitida were surveyed in:forest understory (FU),moderate gap (MG),large gap (LG) and marginal open space (MOS).In order to determine how the ramet structures could be affected and its effects on these four canopy conditions,a field survey of the age structure of Fargesia nitida population,its morphological traits and biomass was conducted in the Abies faxoniana forest situated in the Wolong Nature Reserve,western Sichuan,China.The main results were as follows.First,at the ramet level,the structures of the ramet populations in four canopy conditions were significantly different,and as the canopy density decreased,the mean height,basal diameter and biomass of the populations increased following the order:LG ＜ MG ＜ FU.Second,the biomass proportions of ramets modularly varied with different canopy conditions and leaf biomass proportion was positively related to the canopy density except for the MOS where the biomass proportions of rhizome and roots were both higher than those in the three other canopy conditions.Third,ramet specific leaf weight increased in parallel with the decrease in canopy density.In the MG,the values of the individual leaf biomass and leaf area were the largest,followed by those in the MOS.Both the individual leaf biomass and leaf area were significantly different from those in the FU and LG.Leaf number per ramet was significantly different among the four different canopy conditions and the biggest in the LG.Fourth,the ramet population mortality was the lowest in the FU (Chi-square test,p ＜0.01),while there was no significant difference in the average population age (Mann-Whitney test,p ＞ 0.05).All the results indicated that it was not ramet age,but the morphological changes and biomass distribution that exhibited the response of the ramet population of Fargesia nitida to the changed canopy conditions.