With development of global warming and greenhouse effect, the global ecosystems are degrading. It is combustion of the fossil fuels, land use and land cover changes and human's activities that caused the increasing of atmospheric greenhouse gases, especially carbon dioxide (CO2) concentrations. The global mean temperature increased along with the greenhouse gases. Another important environmental problems is the nitrogen deposition which caused by combustion of fossil fuels, commonly using of fertilizers and human’s activities such as animal husbandry. In the present studies showed that plant growth and physiological reactions affected by elevated CO2, elevated temperature and nitrogen deposition. But little is known about different altitudinal population responses to climate changes and nitrogen deposition. In this experiment, Hippophae rhamnoides L. was used as model plant to study the responses to elevated CO2, elevated temperature and nitrogen deposition treatment respectively by using the ecological, physiological and biochemical methods, and to expose the population differences in growth, photosynthesis, water use efficiency and some biochemical material contents in the low and high altitudinal population of plant. In addition, we studied the effects of cadmium on Toxicodendron vernicifluum (Strokes) F. A. Barkley under different levels of nitrogen depositon. And to determine whether the different levels of N deposition can modify the detrimental effects of Cd. The results are as follows:
1 The responses of H. rhamnoides to elevated temperatures and nitrogen depositon
Compared with ambient temperature and nomal nitrogen content, under elevated temperatures, high altitudinal populationwere found to exhibit higher increasing extent of specific leaf area (SLA), total leaf area (TLA), total chlorophyll content (TC), light response curves, maximum net assimilation rate (Pmax), apparent quantum yield (Φ), carbon isotope composition (δ13C), peroxidase (POD), catalase (CAT), and lower decreasing extent of total solubal sugars and starch than low altitudinal population. In high altitudinal population, nitrogen deposition resulted in lower decreasing extent in root/shoot mass ratio (RS), SLA, leaf relative water content (RWC), TC, Pmax, light saturation point (LSP), light compensation point (LCP), δ13C, superoxide dismutase (SOD), POD, CAT and lower increasing extent of Proline, malondialdehyde (MDA), and higher decreasing extent of total solubal sugars and starch content than in low altitudinal population. Under the combination of elevated temperatures and nitrogen deposition, low altitudinal population exhibited significantly decrease in RWC, chlorophyll a/b (chl a/b) and carotenoids content (Caro). The decreasing extent of RS, Pmax, Φ, δ13C, SOD, POD in low altitudinal population was higher than in high altitudinal population.The results suggest that high altitudinal population will benefit from elevating temperature by possessing better ecophysiological processes than that of low altitudinal population, and suffer from lower negative effects than do low altitudinal population when grown under nitrogen deposition and the combination of elevated temperature and nitrogen deposition.
2 The responses of H. rhamnoides to elevated CO2 concentration and nitrogen deposition
Compared with controls, high altitudinal population exhibited higher increasing extent of RS, SLA, TLA, TC, Caro, net photosynthesis rate (A), intercellular CO2 concentration (Ci), transpiration (E), δ13C, CAT, carbon content in stem and root, carbon and nitrogen ratio and higher decreasing extent of proline, and lower increasing extent of total soluble sugars in leaf and root, starch in leaf, stem and root than low altitudinal population. Under the combination of elevated CO2 and nitrogen deposition, there were lower decreasing extent of RS, SLA, TLA, TC, Caro, chl a/b, A, Ci, E, δ13C, SOD, POD, CAT, carbon content in leaf and root in high altitudinal population than in low altitudinal population. In addition, high altitudinal population exhibited lower increasing extent of Proline, MDA, total soluble sugars in leaf and stem, starch in stem and root than low altitudinal population. The results suggest that high altitudinal population will benefit from elevated CO2 concentration and nitrogen deposition than low altitudinal population.
3 The responses of T. vernicifluum to different levels of nitrogen deposition and cadmium treatment
We exposed seedlings of T. vernicifluum to three cadmium (Cd) stress and three simulated nitrogen (N) deposition and their combinations.Cd stress caused significant decreases in the dry mass accumulation, RS, A, and chlorophyll content. Damage in the anatomical features of leaves was also visible as irregular shapes and disorganization of thylakoids, stroma and nuclear envelope, as well as leakage of nucleolus and disruption of mitochondria.Cd treatment caused the accumulation of superoxide radicals (O2.-), hydrogen peroxide (H2O2), MDA and Cd in plant tissues, while the antioxidation of guaiacol peroxidase (GPX) significantly decreased, as also did the activity of the nitrate reductase enzyme (NRA).
Under the combination of LN and Cd in general, the levels of free amino acids increased and higher values were found for total biomass, A, chl (a+b), free amino acids, GPX and NRA, while lower concentrations of Cd in leafs and stems and in MDA in general were observed, as compared to the effect of Cd stress alone. In contrast, a combination of HN and Cd caused a higher Cd accumulation in stems and roots, higher levels of MDA and H2O2, and a lower level of SOD activity, as compared to the effect of Cd alone.Our results showed that Cd had detrimental effects on T. vernicifluum seedlings. Under LN deposition, the tolerance of T. vernicifluum to Cd increased.
Key words: Hippophae rhamnoides, Toxicodendron vernicifluum, elevated temperature, elevated CO2 concentration, nitrogen deposition, cadmium treatment