| Tibet is rich in natural resources and has a wide range of vegetation species,including 20 species of Calanthe including three newly discovered species recently,which provide valuable resources for the study of Calanthe.The fragile ecological environment of the highlands has led to serious damage to the natural populations of wild Calanthe due to factors such as climate change,human excavation and engineering construction.At present,there is still a lack of comprehensive understanding of the mechanisms of adaptation to environmental changes in Tibetan two species of wild Calanthe plants.In this dissertation,we select two species of Tibetan Calanthe as research objects,and conduct experimental studies on the environmental adaptations of Calanthe reflexa and Calanthe mannii under different moisture conditions and the growth of Calanthe reflexa under different light conditions through control experiments,using morphological anatomy,photosynthesis and other means,starting from both moisture and light.By studying the environmental adaptation strategy and morphological structure of Calanthe,we elucidate its environmental adaptation mechanism and provided basic data for the conservation and sustainable use of the plant.The scientific and reliable results are obtained as follows:（1）The dissection of the nutritional organs of Tibetan Calanthe of Calanthe reflexa and Calanthe mannii reveal that the two types of terrestrial orchids in the same domain have the characteristics of shade plants,such as the roots are fibrous root system with more number,but the root system is shallow,the root hairs are sparse and the xylem ducts in the roots are less conducive to the plants to transport the absorb water into the above-ground parts in large quantities and at high speed.The leaf blade is large and thin,with closely spaced epidermal cells and loose interstitial flesh cells,and simple intra-leaf tissues,with only upper epidermal cells,lower epidermal cells and flesh cells,and no cuticle or other tissue differentiation.These characteristics are conducive to photosynthesis in the weaker light conditions for the survival of the two species of shrimp ridged orchids,but are not conducive to survival in the absence of water and strong light conditions.The large number of vascular bundles scatter in the pseudobulbs has a supportive effect on the plant,resisting water scouring and supporting the growth of leaves.（2）The differences in water use strategies between Calanthe reflexa and Calanthe mannii are investigated.It is find that water stress reduced parameters such as maximum photosynthetic rate,stomatal conductance,photoresponse center II activity and chlorophyll content in both Calanthe,and reduce stomatal conductance is the main cause of reduce photosynthetic capacity in both Calanthe under moderate water stress,while reduced photosynthesis in severe drought is caused by non-stomatal limiting values.The two also differed in a number of water-related functional traits.The pseudobulbs of Calanthe reflexa had higher saturated water content（SWC）,indicating that their pseudobulbs has higher water storage capacity.The leaf traits of the two species of terrestrial orchids also differ significantly.Compare with Calanthe reflexa,Calanthe mannii has lower SWC,weaker water storage capacity and lower stomatal density,and take less time to lose water to 70%（T70）,but had higher net photosynthetic rate under adequate water conditions.The photosynthetic rate,stomatal conductance,and instantaneous water use efficiency of Calanthe reflexa are higher than those of Calanthe mannii in the face of drought stress.After experiencing severe water stress,Calanthe reflexa for 1 day restore photosynthetic rate and stomatal conductance to pre-drought levels,while Calanthe mannii fail to recover.The differences in water-related functional traits explain the different water adaptation strategies chosen by these two terrestrial orchids when encountering hydropenia,with Calanthe reflexa being more hydropenia tolerant and Calanthe mannii being hydropenia intolerant,and the latter being more susceptible to climate change and habitat destruction.（3）The leaves of Calanthe reflexa.reversus are subjected to"high light（FG）"(about 75%of full light,1500μmol-2s-1),"medium light（FZ）"(about 30%of full light,600μmol-2s-1),and"low light（FD）"(about 30%of full light,600μmol-2s-1),"low light（FD）"(about 5%full light,100μmol-2s-1)and field control（FY）(about 45%full light,900μmol-2s-1),exhibit some physiological and morphological structural plasticity under four light intensity gradients,and in different months of the growing season"The photosynthetic pigment content is significantly higher in the"medium light"condition than in the other three conditions,while the chlorophyll a/b values are significantly lower than in the other three treatments,which indicate that the lower chlorophyll a/b values are beneficial to the absorption and utilization of low light such as scattered light.The lower chlorophyll a/b values facilitate the plant’s absorption and utilization of low light such as scattered light.The values of photochemical quantum efficiency（Fv/Fm）and PSII quantum efficiency（Fv/Fo）are the highest under"medium light"condition,which indicate that the PSII reaction center of the leaves has the highest potential for light energy conversion under this condition.The net photosynthetic rate（Pn）,stomatal conductance（Gs）and water use efficiency（WUE）of the"medium light"treatment were greater than those of the"high light","low light"and field controls,indicating that The plants under"medium light"conditions could effectively convert the absorb light energy into biochemical energy,and their photosynthetic physiological functions were stronger and their photochemical efficiency is higher.（4）Analysis of the differences in leaf morphology and anatomical structure of Calanthe reflexa under different light conditions show that the leaf length,leaf width,leaf area and leaf biomass of the"medium light"condition are significantly higher than those of the other three conditions,with the most biomass accumulation,the longest stomata,the greatest density and the greatest thickness of leaf flesh.The leaf leaf area and leaf biomass are significantly higher than the other three conditions.In general,water stress has a significant effect on the growth of the nutritional organs of Calanthe reflexa and Calanthe mannii,and the different light conditions were important for the phenotypic traits of the leaves of Calanthe reflexa,the accumulation of biomass,the accumulation of chlorophyll content and photosynthetic capacity,and the light intensity of the"medium light"condition is more suitable for the growth of the leaves of Calanthe reflexa.The results of the study provide basic data for understanding the environmental adaptation strategies of Calanthe and for the conservation and utilization of Calanthe reflexa and Calanthe mannii. |
