The relationship between flower size and leaf size and number reflects the plant adaptation strategies in external morphology during the long-term interaction of plants with different environments,and the variation of the relationship reflects plant adaptation to heterogeneous environments. In this study,an investigation was carried out to examine the relationship between flower size and leaf size and number of Stellera chamaejasme along four different altitude gradients in an alpine grassland in the northern slope of Qilian Mountains. The results showed that,with increasing elevation,the height,density,and aboveground biomass of the plant communities displayed a pattern of initial increase and then a decline. The aboveground biomass,plant height and leaf biomass of S. chamaejasme declined gradually,while reproductive allocation,flower size and leaf number both increased gradually. Flower size of S. chamaejasme was significantly positively correlated with leaf number( P 0. 05). Therefore,habitat had a significant influence on the dependency among size of flower and leaf size and number. The plant size would be decreased by the environmental stress at high altitude,and both flower size and leaf number are increased while the leaf size is declined to ensure the reproductive success of S. chamaejasme.

Reproduction has a very close relationship with species survival and development,and is the core in the study of plant life history.The environmental factors under the restriction by altitude have significant effects on the reproductive allocation of plants.In July 2010,a quadrat investigation was conducted to study the characteristics of the reproductive allocation of S.chamaejasme population at four altitudes with a gradient from 2700 m to 3000 m.With the increasing altitude,the aboveground biomass of S.chamaejasme presented a decreasing trend,but the total flower biomass and the plant height increased after an initial decrease,and the reproductive allocation had an increasing trend.Along the altitude gradient,the reproductive allocation had a significant negative correlation with the total aboveground biomass(except at altitude 2800 m),but less correlation with the plant height(except at altitude 3000 m).The reproductive allocation of S.chamaejasme population was limited by plant body size,and the limitation by total aboveground biomass was far larger than the limitation by plant height,indicating that with the increasing altitude,S.chamaejasme population could ensure its reproductive success via reducing the plant body size to decrease the resource consumption and increasing the allocation of the obtained limited resources to flower biomass.

The spatial pattern of aboveground biomass is an important content of species distribution pattern,whereas the environmental heterogeneity caused by the topographical differences in the scope of small scales is the environmental basis for the formation and evolution of this pattern.Based on the field survey in August 2011 and with the help of GIS and S-PLUS software,the generalized additive model(GAM) was applied to study the spatial distribution pattern of S.chamaejasme population in degraded alpine grassland,and to quantitatively analyze the response mechanisms of the spatial pattern of S.chamaejasme's aboveground biomass to topographical factors.Topographical factors had definite effects on the aboveground biomass of S.chamaejasme,with the sequence of aspect slope elevation plane curvature profile curvature.The contribution degree of aspect and slope to the spatial pattern of S.chamaejasme's aboveground biomass was 3.75 and 1.48,respectively,while the contribution of other topographic factors was relatively lower.The aboveground biomass of S.chamaejasme had a uniform distribution in the gradients of elevation,plane curvature,and profile curvature,but presented an open-down parabola tendency in aspect gradient and an open-up parabola tendency in slope gradient.The relationships between the spatial heterogeneity of S.chamaejasme's aboveground biomass and topographic factors reflected the response mechanisms and growth strategies of S.chamaejasme under the effects of the redistribution of water and heat conditions.

Aims The growth relationship between twig and leaf is a strategy that plant canopy structure employs to space resources and enhance photosynthetic efficiency and competitiveness through configuration adjustments.Our objective was to examine how Stellara chamaejasme exploited twig and leaf configuration to explore the effects of slope change.Methods In the upper reaches of Shiyang river,Gansu Province,China,80 plots were set up at intervals of 20 m from the foot of a mountain along eight aspects.GPS was used to record latitude,longitude and altitude of each plot.Community traits were investigated and five S.chamaejasme were cut randomly on each plot for measurement of twig length,twig number,leaf area and leaf number.ArcGIS was used to set up digital elevation model(DEM) and abstract slope data of the study site.The 80 plots were divided into 0°-10°,10°-20° and 20°-30° slope gradients.Values for twig and leaf traits were logarithmically converted,and then the standardized major axis(SMA) estimation method was used to examine the allometric relationship between twig number,twig length,leaf number and leaf length.Important findings Twig length,twig number and leaf area of S.chamaejasme gradually decreased along the slope gradient.Significant allometric relationships between leaf number and twig length and between twig number and twig length were found to be consistent in all three slope gradients.Growing speed of twig length was greater than the speed of leaf number,and the growing speed of twig number was greater than the speed of twig length.However,there were significant differences in SMA slope in the three slope gradients,suggesting that slope constrains the leaf number and twig number that can be supported by a given twig length.

The growth patterns of leaf and stem decide the light capture pattern of plants and the acreage of the material exchange between plants and external environment,whereas the biomass allocation is a main approach to study the plant life history strategies.Taking the degraded alpine grassland in the upper reaches of Shiyang River,Gansu Province of Northwest China as a case,the method of standardized major axis(SAM) estimation was adopted to study the effects of Stellera chamaejasme stem size on the biomass allocation in leaf and stem,and on the leaf area supporting efficiency.There existed an allometric relationship between the stem dry mass and the LMA,individual leaf area,and leaf dry mass,with a SMA slope of 0.781(95% confidence interval,CI=0.71-0.94),0.824(CI=0.77-0.95),and 0.856(CI=0.79-0.99),respectively.The S.chamaejasme with bigger stem had higher leaf biomass allocation percentage and leaf area supporting efficiency,and in the meantime,had higher LMA,indicating that the bigger S.chamaejasme mainly adopted an adaptive strategy of high resource-use efficiency,while the smaller one mainly employed an adaptive strategy of fast growth.