Study On Physiological And Ecological Characteristic Of Haloxylon Ammodendron To Global Climate Change Factors

In recent years,with the increase of greenhouse effect,global atmospheric temperature increases with the change of precipitation pattern and the amount of nitrogen deposition,so the relationship between global change and terrestrial ecosystem has become an important content and hotspot of research at home and abroad.Haloxylon ammodendron,a perennial shrub-like small tree,has strong drought resistance,high temperature resistance,salt resistance and windbreak and sand-fixation ability.In addition,because of its hard wood,strong firepower and rich nutrition of the current year's branches,it has become an important high quality carbon and feed tree species;However,its distribution area and species have been gradually reduced by the global change and human factors.In the context of future global change,it is not clear how the habitat environmental conditions of H.ammodendron and its photosynthetic physiological characteristics respond to the change;Therefore,we explore how H.ammodendron responds to global change from physical and chemical properties of its habitat soil,the assimilating shoots gas exchange parameters and resistance physiological characteristics by open top chamber?OTC?simulated warming,precipitation,nitrogen deposition and its effect on the coupling in this paper,in order to expound its adaptive strategy.The aim is to provide a scientif ic basis for the growth and distribution of H.ammodendron bes ides the protection and restoration of the desert ecosystem under the future global change.The main research results and conclusions are as follows:?1?Compared with the control,habitat soil moisture content,electrical c onductivity and p H of H.ammodendron were signif icantly decreased,but the soil organic matter,total nitrogen,total phosphorus and total potassium were signif icantly increased by warming,the results showed that warming was beneficial to habitat soil nutrient accumulation and reduce its salinization degree of H.ammodendron,and it can also lead to the increase of soil water stress.The effects of warming on the gas exchange parameters of H.ammodendron resulted the daily changes of its net photosynthetic rate,transpiration rate,water use efficiency,stomatal conductance,photosynthetic active radiation and relative humidity were decreased,the daily changes of its intercellular carbon dioxide concentration,leaf water pressure deficit,atmospheric temperature,leaf temperature and atmospheric carbon dioxide concentration were increased obviously;In addition,warming also caused the malondialdehyde content of H.ammodendron increased 6.03%,its peroxidase?POD?and superoxide dismutase?SOD?,catalase?CAT?activity and proline?Pro?,soluble sugar?SS?and soluble protein?Pr?content were increased 9.77%,33.31%,9.77%,112.07%,2.31%and0.99%respectively,the results showed that warming would inhibit the photosynthesis of H.ammodendron and would cause more severe stress injury.?2?Habitat soil moisture content,electrical conductivity,pH,total nitrogen and total phosphorus content of H.ammodendron were signif icantly increased,but the soil organic matter and total potassium were signif icantly decreased by increased of precipitation,the results showed that increased of precipitation can increase the moisture content of soil,promote the utilization of organic matter,potassium and accumulation of nitrogen and phosphorus,but also promote the salinization of soil.The effects of increased precipitation on the gas exchange parameters of H.ammodendron resulted the daily changes of its net photosynthetic rate,transpiration rate,stomatal conductance,photosynthetic active radiation,relative humidity,leaf water pressure and gas deficit were increased,its intercellular carbon dioxide concentration,water use efficiency and atmospheric carbon dioxide concentration were decreased;In addition,increased precipitation also caused the malondialdehyde content of H.ammodendron decreased 69.83%,its protective enzyme?POD,SOD and CAT?activity and osmotic regulation substances?Pro,SS and Pr?content were decreased 37.35%,61.98%,37.34%,77.62%,37.05%and 28.40%respectively,the results showed that the increase precipitation was beneficial to promote the photosynthesis of H.ammodendron,and thus to reduce its degree of stress injury.?3?Habitat soil moisture content,electrical conductivity,organic matter,total nitrogen and total phosphorus content of H.ammodendron were gradually increased with the increasing of nitrogen application,but soil pH and total potassium content showed a tendency to first increase and then decrease,the results show that the increase of nitrogen deposition was beneficial to regulate the soil moisture content and promote the accumulation of C,N and P nutrients,and a certain level of nitrogen content may also reduce the degree of salinity and soil potassium utilization.The influence of nitrogen deposition on the gas exchange parameters of H.ammodendron resulted the daily changes of its net photosynthetic rate,transpiration rate and stomatal conductance rate increase with the gradual increasing of nitrogen application,the variation of intercellular carbon dioxide concentration and water use efficiency were decreased gradually;In addition,the increase of nitrogen deposition also resulted in the decrease of malondialdehyde content,activity of protective enzyme?POD,SOD and CAT?and osmoregulation substance?Pro,SS and Pr?content of H.ammodendron,the results showed that the increase of moderate nitrogen deposition was beneficial to promote the photosynthesis of H.ammodendron,and thus to reduce its degree of stress injury.?4?When increasing 30%in precipitation on the basis of natural precipitation?W₁?,habitat soil moisture,electrical conductivity and total potassium content of H.ammodendron became first increased and then decreased with the increasing of nitrogen application,among them,the total potassium content was lower than that of the control group except for increasing 60 kg N ha^-1a^-1 on the basis of natural nitrogen deposition,the rest was higher than the control;But soil pH,organic matter,total nitrogen and total phosphorus content increased with the increasing of nitrogen application,the results showed that the proper precipitation-nitrogen coupling was beneficial to regulate habitat soil moisture content and nutrient content of accumulation and utilization of H.ammodendron.And the daily variation of net photosynthetic rate,transpiration rate and stomatal conductance of H.ammodendron increased gradually with the increasing of nitrogen application,the daily variation of intercellular carbon dioxide concentrations was overall reverse,while the daily variation of the water use efficiency of H.ammodendron decreased first and then increased with the increasing of nitrogen application,but all were lower than the control;In addition,the effects on malondialdehyde content,protective enzymes?POD,SOD and CAT?activity and osmoregulation substance?Pro,SS and Pr?content of H.ammodendron were studied,except for the increase of 44.74%in proline content at level of increasing 30 kg N ha^-1a^-1 on the basis of natural nitrogen deposition,the remaining indicators have been reduced,the results showed that the coupling of precipitation and nitrogen was also beneficial to promote the photosynthesis and to reduce the degree of the stress injury,but the effect depends on the ratio between them.?5?The coupling of precipitation-nitrogen-temperature resulted in a significant increase in habitat soil moisture,electrical conductivity,organic matter,total nitrogen,total phosphorus and total potassium content of H.ammodendron,but soil pH decreased,the results showed that the precipitation-nitrogen-temperature coupling effect was beneficial to improve the soil moisture and nutrient status and decrease the salinity of the soil.The effect of precipitation-nitrogen-temperature coupling on the gas exchange parameters of H.ammodendron resulted in a significant decrease in the daily changes of its net photosynthetic rate,transpiration rate,stomatal conductivity and water use efficiency,the daily variation of intercellular carbon dioxide conc entration and leaf water and gas deficit increased obviously;In addition,the content of malondialdehyde increased by 16.38%,The contents of POD,SOD,CAT and Pro,SS and Pr increased respectively by 21.14%,82.96%,21.15%,85.98%,12.13%and 5.17%,the results showed that the precipitation-nitrogen-temperature coupling improved habitat soil moisture and nutrient status of H.ammodendron,but there is still inhibition of the photosynthesis of H.ammodendron and thus to increase the degree of stress injury.?6?Under the conditions of simulated warming,precipitation,nitrogen deposition and their coupling,the daily var iation of the net photosynthetic rate of all H.ammodendron has obvious photosynthetic"lunch break",and according to the stomatal conductance,intercellular carbon dioxide concentration and stomatal restriction,it can be presumed that the photosynthetic"lunch break"of H.ammodendron was mainly affected by non-stomatal limitation factors.In summary,warming remains the most critic al factor in arid and semi-arid desert ecosystem in the context of future global change?warming,increased precipitation and nitrogen deposition?.The increase of precipitation,nitrogen deposition and its coupling effect can improve the photosynthetic capacity of H.ammodendron and promote its growth and distribution under the condition of keeping the temperature constant;but the photosynthesis of H.ammodendron could not be carried out under the condition of warming,increasing precipitation and nitrogen deposition,and it will pose a threat and challenge to the growth and distribution of H.ammodendron.