Shami Adapt To The Arid Environment Of The Physiological And Ecological Mechanisms

Agriophyllum squarrosum was selected as experimental material for the research on the distribution pattern,photosynthesis,chlorophyll fluorescence,chlorophyll contents,seed vigour and germination percentage of the modify dune and semi-fixed dune in Naiman,Wushen and Alashan zuoqi county of Inner Mongolia.The photosynthesis rate (P_n),water potential and proline contents of A.squarrosum under drought stress were measured in the laboratory.The following conclusions in this study are made out through the experiments:ⅠThe adaptative strategies of Agriophyllum squarrosum to drought environment1.The distribution characteristics of Agriophyllum squarrosumIn three experimental sites,the coverage,density and height of A. squarrosum in the semi-fixed dune was higher than those in the dune, because soil moisture content in the semi-fixed dune was higher than that in the dune.The experimental results showed that the distribution status of A.squarrosum was related to soil moisture content.The growth of A.squarrosum was related to dune terrain.The coverage,density and height of A.squarrosum in dune lowland were highest.Dune lowland was the best place for growth of A.squarrosum.The patterns of A.squarrosum population in the three experimental sites were all in aggregation distribution.The intensity of aggregation distribution in the dune was higher than that in semi-fixed dune.This is because the distributions of soil moisture and soil nutrient in semi-fixed dune were more uniform than that in the dune.2.Seed vigour and reproductive strategy of Agriophyllum squarrosumSeed vigour and germination percentage of A.squarrosum collected in different years were obviously different.The seed vigour and germination percentage collected in 2008 were higher than that in 2007 and 2006.The results showed that the newborn seeds have higher vigour.It presented the characteristic of continual germination in A. squarrosum adapted to the uncertainty desert environment through the strategy of extend the germination time.It was able to avoid the uncertain disturbance of drought and reduce the risk of seed disposable germination, heighten the success rate of species to settle.3.Influence of sand burial depth and water supply on seed germination of Agriophyllum squarrosumSeed germination percentage of A.squarrosum was decreased with the increase in depth of sand-burying.The sand-burying depth of 0.5cm was suitable to the seed germination of A.squarrosum.Deeper sand-burying depth was seriously impacted the germination percentage of A.squarrosum seeds.The results showed that the seed of A.squarrosum was suitable for the precipitation of 10mm and the percentage was 6.67%. Germination percentage of seeds with continued water supply was 3.33%, less than that with only one supply of water.ⅡPhysiological mechanism of adaptation of Agriophyllum squarrosum to drought environment1.Photosynthesis characteristics of Agriophyllum squarrosumDurial changes of photosynthesis rate(P_n) of A.squarrosum in three experimental sites were bimodal curve.The average P_n of A.squarrosum in Naiman,Wushen and Alashan zuoqi county were respectively 5.66μmol·m^-2·s^-1,14.63μmol·m^-2·s^-1 and 15.37μmol·m^-2·s^-1.The P_n of mature leaves was higher than that of young leaves.The P_n of A.squarrosum was negatively correlated with air temperature,and positive correlated with photosynthetic active radiation (PAR) and air relative humidity(RH).The P_n of A.squarrosum and PAR were more correlated.There was self-regulatory mechanism in P_n of A.squarrosum.The P_n of A.squarrosum was declined in morning,intercellular CO₂ concentration(C_i) and stomatal conductance(G_s) were declined at the same time,and stomatal limitation value(L_s) was increased.It showed photosynthesis was limited by stomata factors.The P_n of A.squarrosum was declined in afternoon,Ls was declined at the same time,and G_s was increased.It showed photosynthesis was limited by non-stomata factors.2.The response of photosynthesis of Agriophyllum squarrosum to elevated CO₂ concentration and air temperatureWhen the increased temperature reached 5℃,the P_n of A. squarrosum was declined.The maximum of P_n was 7.52μmol·m^-2·s^-1,and the average was 3.36μmol·m^-2·s^-1.The photosynthesis of A.squarrosum was limited by the increased temperature.When the CO₂ concentration was doubled,P_n of A.squarrosum was increased one time.The maximum P_n was 18.07μmol·m^-2·s^-1,and the average P_n was 11.81μmol·m^-2·s^-1.CO₂ concentration enrichment improved the photosynthesis of A.squarrosum.3.The chlorophyll fluorescence characteristic of Agriophyllum squarrosumIn natural environment,maximum chlorophyll fluorescence(F_m'), PSⅡprimary chemical efficiency(F_v/F_m),quantum yields(Yield) and photochemical quenching factor(qP) of A.squarrosum were declined from morning,and reached minimum value at noon.Electronic transmission rate(ETR) and non-photochemical quenching factor(qN) of A.squarrosum were increased in the morning.Midday depression of P_n of A.squarrosum appeared.It was showed that the photosynthesis of A. squarrosum was impacted by light stress.Only few lights were used for photochemical electron transfer and CO₂ fixed.The unnecessary light was dissipated in the form of hot.It was beneficial to prevent the destruction of photosynthetic apparatus,and maintain a high photosynthetic capacity.4.The physiological response of Ariophyllum squarrosum to drought stressIn increased drought stress,P_n,water potential,G_s and C_i of A. squarrosum were tending to decline,proline contents and L_s were tending to raise.The proline content of A.squarrosum was three times of normal concentration under serious drought stress.The increase of proline content of A.squarrosum was enhanced water-retention capacity and improved the capacity of drought resisting.