Plant Hydraulic-limitation In The Geographical Distribution And Growth Responses To Enhanced Temperature Of Picea Taxa In China

As a dominant component in many alpine and boreal evergreen forests, the distribution of the genus Picea (spruces) speices exhibits an obviously geographical substituted phenomenon in China. They are closely related species that genetically similar to one another, and massive gene flow and introgression occurs. Hence, these spruces present a rare opportunity to unravel the physiological underpinning of determining the modern geographical distribution and adapting to environmental conditions. Furthermore, due to the main treeline species and vegetation types in alpine and boreal forests, Picea are extremely sensitive to global warming, but little is known about the growth and carbon metabolism responses to enhanced temperature in Picea taxa from different geographical distributions. Therefore, this thesis included two aspects:first, the patterns of climatic factors in Picea taxa geographical distributions and differences in water ecophysioloical characteristics of Picea taxa in common garden were investigated to reveal the mechanisms of the geographical vicarism of Picea taxa in China from the aspects of plant hydraulic limitation; second, four year old Picea seedlings were grown at two different temperatures to know about the growth and leaf CO2 exchange characteristics responses to enhanced temperature in Picea taxa from different altitudes. The main results were as follows:(1) Climatic factors of geographical distribution sites from ten main members of Picea taxa were selected, and 13 water ecophysiological characteristics, including hydraulic traits of one year old branches and current year old twigs, cell dehydration resistance, and leaf photosynthetic rates were measured in a common garden.1) there were significant differences in five key climatic factors among the geographical distribution of Picea taxa. Compared with other climatic factors, precipitation of the warmest Quarter (PWQ) and min temperature of the coldest month (MTCM) exhibited larger variance among Picea taxa than within taxa, and coefficient of variation (CV) showed lower in PWQ and MTCM. Moreover, PWQ and MTCM had most highest loading of the first principal component in Principal Component Analysis. These results were suggested that PWQ and MTCM were the key driving factors of the geographical vicarism of Picea taxa in China. In addition, except for monthly mean diurnal temperature range (MDTR), all climate factors were significantly correlated with latitude and longitude, respectively.2) All measured traits showed significantly different among ten Picea taxa. Xylem cavitation resistance in branches and leaves, and cell dehydration resistance were mainly affected by PWQ in natural distributions, whereas bulk modulus of elasticity (s) and saturated water content per unit dry mass (SWC) were principally influenced by MTCM of their habitats. In other words, Picea taxa distributed in the regions with lower PWQ and MTCM had greater xylem cavitation resistance (more negative P50 branch and P50 leaf), cell dehydration resistance (more negative πtlp) and mechanical strength (ε), but had lower SWC. This pattern was reversed in Picea taxa occurred the higher PWQ and MTCM regions. Moreover, Picea taxa with higher xylem cavitation resistance and cell dehydration resistance was related with higher woody density (WD), leaf dry mass per unit area (LMA), and with lower water transport efficiency (Kmax leaf and Kmax branch) and leaf photosynthetic capacity (Pn). Therefore, the modern biogeography of the spruces conifers was shaped in large part by different xylem and cellular hydraulic characteristics limitations.(2) Growth characteristics and gas exchange parameters were recorded from four year old seedlings of two alpine(Picea likiangensis vars. rubescens and linzhiensis) and two lowland (P. koraiensis and P. meyeri) taxa which were grown at two different temperatures for four months.1) The approximated biomass increment (△D2H) for all taxa decreased under enhanced temperature treatment, associated with decreased photosynthetic rates in alpine Picea taxa and increased respiratory rates in lowland taxa. 2) Higher leaf nitrogen content per unit area (Narea), and a smaller change in LMA and the nitrogen use efficiency of photosynthesis (PNUE) for lowland taxa indicated that these maintained higher homeostasis of photosynthesis than alpine taxa. Moreover, the higher respiratory rates produced more energy for repair and maintenance biomass, especially for higher photosynthetic activity for lowland taxa, which causes lower respiratory acclimation. Thus, the changes of △D2H for alpine Picea taxa were larger than that for lowland taxa. These results indicate that long term enhanced temperature treatment negatively impact on the growth of Picea seedlings, and alpine taxa are more vulnerable than lowland ones by enhanced temperatures.In this thesis, we comprehensively analyzed the pattern of climatic factors and water physiological traits in different Picea taxa along geographical gradients, and found that the geographical vicarism of Picea taxa in China were driven by PWQ and MTCM; xylem cavitation resistance and cell dehydration resistance were the main ecophysiological constraints that prevented the geographical distribution of Picea taxa. In addition, alpine Picea taxa were more susceptible to enhanced temperature than lowland taxa. This study helped us to understand how ecophysiological mechanism limited the geographical distribution of Picea taxa and accurately predict how different altitudinal ranges of Picea taxa response to climate warming.