| The Corydalis hhendersonii(papaveraceae), an alpine perennial herb, is an endemic species to the Tibetan Plateau, and is also a typical representative of the rare and endangered Tibetan medical plant. It grows at an altitude of 4700-5900 m in the alpine region of the Tibetan Plateau. Studies on the physio-ecological adaptability and population dynamics of an endangered these plants can provide scientific basis for protection and domestication of special plants, thus, this study investigated the C:N:P stoichiometry and environmental adaptation, physio-ecological adaptability, ecological adaptive strategy, population dynamics and the potential distribution of C. hendersonii by using ecological stoichiometry, physiological ecology, stable carbon isotope(δ13C), ecology niche model(ENM) and population dynamic assessment. The main results and conclusions as follows:(1) In order to adapt to the harsh environment through balancing growth and resource conservation, the strategy of nutrient reserve and accumulation were respectively enabled by C. hendersonii under limitation and sufficient nutrient condition. Results showed that the growth and distribution of C. hendersonii were limited by carbon(C), nitrogen(N), phosphorus(P) and other key nutrients, and the N limitation is greater than P. In addition, we found that the threshold value of the N and P limitation for C. hendersonii were STN 0.75 mg g-1 and STP 0.50 mg g-1(or SAP 5.00 mg kg-1), respectively.(2) C. hendersonii has a strong capability in C:N:P stoichiometric homeostasis, which was maintained by nutrient reserve capacity of root. This is one of the important mechanisms to adapt to the hardscrabble environment. Results showed that the trend of coefficient of variation of all N and P concentrations and C:N, C:P and N:P were soil>root>shoot>plant. Although N:P in environment has great change while it kept constant in C. hendersonii, the relationship of N and P in above- and belowground components was mainly decided by the state of soil nutrition, as growth was limited by N and P, the reserve of N and P in tissue can buffer the deficiency of N and P in environment. On the contrary, more nutrients allocated to the aboveground and enhanced the capacity of photosynthesis and biomass production. In addition, under nutrient and water abundant conditions, the aboveground nutrient concentrations increase but belowground components nutrient concentration decrease with the increase of the biomass, these results showed that C. hendersonii can adapt to nutrient-poor environment through the regulation and balance of nutrients in vivo.(3) The C:N≈17 and N:P≈1.75 in soil are the optimum soil C:N:P stoichiometry for growth of C. hendersonii.We found that the aboveground dry biomass and whole-plant dry biomass of C. hendersonii were quadratically correlated with soil C:N, the maximal value was seen when soil C:N≈17; the below- and aboveground dry biomass ratio were also quadratically correlated with soil C:N and N:P, but the minimum value was found when soil C:N≈17 and N:P≈1.75.(4) The trade-off between "growth-defence-resources conservation" strategy is an important ecological strategy for the adaptation of the C. hendersonii to cold, drought and barren environment. According to the relationships between functional traits and climatic factors, we found that the most suitable growth temperature for C. hendersonii was the mean annual temperature(MAT)-2.5℃, and under this temperature condition, the biomass reached its maximum while the N use efficiency and water use efficiency reached their respective minimum. The biomass significantly decrease while the concentrations of C、N、P in various tissue and the use efficiency of N and water markedly increase with the MAT decrease at the below of 2.5℃, implied that C. hendersonii implements resource conservation strategy through nutrient storage, at the same time, it can invest more photosynthetic products in the synthesis of cold resistant compounds including non-structural carbohydrates to tolerance to low temperature stress and enhance its survivability; but the aboveground dry biomass and nutrient(C, N, P) concentrations significantly decreased while the below- and aboveground dry biomass ratio, the use efficiency of N and water and the concentration of C in belowground components markedly increase with the MAT increase at upon of-2.5℃, implying that in order to adapt to the high temperature and drought, C. hendersonii allocated more photosynthetic products to the belowground and used to improve the ability of obtain resources. The threshold value of water limitation of C. hendersonii was mean annual precipitation(MAP)≈300 mm yr-1 and soil moisture content(SMC)≈20%. Under drought and nutrition limitation environment, C. hendersonii reduced biomass production and allocated more nutrients and biomass to the underground part, at the same time, it also enhanced the nitrogen use efficient(NUE) and water use efficient(WUE); however, in the moist and fertile soil, the opposite strategy was adopted.(5) C. hendersonii belongs to C3 plant and have a strong tolerance to barren envrionments. Its distribution is mainly restricted by water. As a C3 plant, the average value of δ13C in aboveground components, belowground components and whole-plant of C. hendersonii is-25.87‰,-25.71‰ and-25.79‰, respectively. A positive correlation relationship was found when δ13C>-20‰ in soil, and the soil δ13C negatively correlated with soil nutrition. These results showed that C. hendersonii have a strong tolerance to barren environment. The δ13C in various tissues of C. hendersonii have significant negative correlation with MAP, aridity index, SMC and specific leaf area, but have significant positive correlation with altitude, rainfall continentality index and leaf mass per area, indicating that the water is the key ecological factor to restrict C. hendersonii growth and distribution in Tibetan Plateau.(6) The result of ENM modelled showed that the spatial distributions of C. hendersonii was limited during last interglacial period, but a significant population expansion occurred in the last glacial maximum, and the potential distribution range of C. hendersonii have contraction in present compared to last glacial maximum, and its distribution will further shrink in the future. Results of neutral tests showed that the value of Fu’s Fs and Tajima’s D of the whole population and the western population of C. hendersonii were all negative while other region were positive, suggesting that the population of western region have experienced recent demographic expansion while the eastern population have experienced bottleneck events. The mismatch distribution for the population of the whole distribution region,south central and western Tibetan Plateau consisted of a single peak curve, which is indicative of a demographic expansion. However, the mismatch distribution for the north central and eastern population consisted of a double-peak curve, indicating that the populations of these regions have experienced bottleneck events. The results of Bayesian skyline plot analysis showed that the populations of the whole species were in a state of contraction before the last glacial period and then began to expand, the recent and most serious bottlenecks occurred at about 0.07 Ma; the population dynamic pattern of the population in the west of Tibetan Plateau is completely consistent with that of the whole region, but the bottleneck occurred about in 0.025 Ma; the populations of other regions have been shrinking, and recently experienced a serious bottleneck event. This is very consistent with the biological characteristics of C. hendersonii and the characteristic of the climatic changes during the historical time of the Tibetan Plateau, indicating that the endangered Tibetan medical plant, C. hendersonii, will further endangered in the future.(7) According to the optimum growth climate and soil nutrient conditions, we suggest that the range of latitude 30~31 N° and longitude 90~93 E° in the Tibetan Plateau is the ideal region to establish a natural reserve areas and wild tending base of C. hendersonii.In this paper, we revealed the physio-ecological adaptability and population dynamics of C. hendersonii through the study of nutrient reserves and accumulated strategy, stoichiometry homeostatic mechanism, the ecological strategy to adapt to low temperature, drought and barren environment, the change of the population trend of C. hendersonii, and provided technical support for the establishment of its nature reserve and artificial domestication cultivation. This study has important theoretical valueto solve the Tibetan medicine resources bottleneck issues and regional economic development. |
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