| In order to reveal the adaptation mechanism of desert plants to future rainfall pattern changes,we explored the variation of desert plant adaptability under the situation of increasing rainfall in arid regions of China.The study based on the long-term artificial simulated rainfall increasingexperiment in Dengkou,Inner Mongolia,selected the typical desert plant Nitraria tangutorum and Artemisia ordosica as research objects.On the basis of natural rainfall during the growing season,simulated rainfall increased by 0%,25%,50%,75%,100%,to analyze the response of Nitraria tangutorum and Artemisia ordosica seed germination,seedling growth,stoichiometry and spatial distribution pattern to different rainfall gradients,and combined with the leaf traits and photosynthesis of natural Nitraria tangutorum and Artemisia ordosicain growing period,final to reveal the adaptation strategies of desert plants to rainfall patterns change.The main conclusions of this study as follows:(1)Analysis of Nitraria tangutorum and Artemisia ordosica seeds with continuous 8-year simulated rainfall increasing experiment showed that the phenotypic traits such as length,width,volume,surface area,aspect ratio and 1000-grain weight of Nitraria tangutorum seed presented significant or extremely significant negative correlation with rainfall increasing(P<0.01),the coefficient of variation was 5.65%-20.39%.Nitraria tangutorum seeds evolved into small grains and circles with the increase of rainfall.The number and area of seed honeycomb cavity gradually decreased,the thickness of seed coats increased and the groove-like notches shortened.Variation of seed morphology of Nitraria tangutorum caused embryo swelled and increased the difficulty of radicle to break through seed coat,which significantly reduced the seed germination rate,germination start time,germination speed and seedling growth.The phenotypic traits of Artemisia ordosica seeds showed a tendency to promote and then inhibit as the rainfall increased.It reached the maximum at 50% rainfall treatment,and the adipose juice had the most dissolution.The seeds shape evolved from obovate to oval.Under moderate and low rainfall conditions(25% and 50% rainfall treatment),the germination rate of Artemisia ordosica seeds can be improved,accelerated seed germination speed and seedlings growth,which was most beneficial to sexual reproduction.(2)Studies on seedlings with different rainfall enhancement showed that the effect of increasing rainfall on the aboveground of the Nitraria tangutorum seedlings was significant,and the parameters of biomass and roots of the whole plant increased first and then decreased,it reached the maximum value at 50% and 75% treatment,and drops significantly at 100%treatment,and there existed a clear threshold for this promotion effect.Increase rainfall significantly reduced the root-shoot ratio of Nitraria tangutorum seedlings,and changing the biomass allocation pattern is an important strategy for adapting to water increase.The growth amount,component biomass and root parameters of Artemisia ordosica seedlings increased significantly with the increase of rainfall,reached the maximum under 100% treatment,and there was no significant difference in root-shoot ratio between each treatments,thencemainly embodied as synergistic growth effect.This indicated that the seed variability caused by rainfall has a greater impact on the germination stage of seedlings,while the seedling growth status mainly depended on the habitat factors.(3)The stoichiometric characteristics of seedlings with different rainfall enhancements showed that the N and P contents of Nitraria tangutorum roots were higher than that of stems and leaves,and the N and P contents of Artemisia ordosica leaves were higher than that of stems and roots.The content of C in Nitraria tangutorum and Artemisia ordosica were higher than that of leaves and roots,indicating that the distribution patterns of C,N and P in two desertplants were not the same.The N/P of Nitraria tangutorum stems,leaves and roots were relatively constant,and the ratio was greater than 16,indicating that the relative growth rate of Nitraria tangutorumwas low in rainfallincreasing environment,and it obviously restricted by P element.However,the N/P of Artemisia ordosica had significantly negative correlation with the amount of rainfall,and the relative growth rate was increasing.The N/P of stems and roots were less than 14,which obviously restricted by N elements;the N/P of leaveswere between 14 and 16,which showed that N and P elements were not lacking in plant.(4)The initial fluorescence of chlorophyll(F0)in Nitraria tangutorum showed a significant increase trend from July to September,indicating that the water stress formed by the decrease of rainfall caused damage or partial inactivation to the PSII reaction center,which caused the increase of F0.The F0 and the maximum photochemical quantum efficiency Fv/Fm of the Artemisia ordosica remained relatively stable during the growth period,indicating that the PSII of Artemisia ordosica leaves was not irreversibly damaged,and maintained reactivity well,and adapted to the environment through adaptive regulation.In addition,there was no significant difference in leaf area(SLA)between July and September,and the SLA of Artemisia ordosicawas higher in the July and August when rainfall relatively concentrated,and significantly lower in September.It indicated that Artemisia ordosica can regulate the absorption and utilization rate of nutrients by changing leaves phenotypic traits,thus showing strong environmental adaptability.(5)With the increase of rainfall,the aggregation intensity of Nitraria tangutorum shrub gradually decreased,the relative average spatial distance increased by 76%,the cluster effect gradually weakened,and the self-sparing phenomenon expanded outward.The random distribution scale of Artemisia ordosica population increased gradually.There was no distribution of Artemisia ordosica in the Nitraria tangutorum shrubs when there was no rainfall addition(CK),but 62 strains were distributed in the 100% rainfall treatment,which appeared to gradually invade the shrub with increasing rainfall and form a positive correlation.The relative average spatial distance is gradually decreased,and it lower than Nitraria tangutorumunder100% rainfall treatment,thus realizing the external expansion of Artemisia ordosica population.We have been verified by field that the experimental results of artificial simulated rain enhancement of Nitraria tangutorum and Artemisia ordosicawere consistent with the evolution of spatial pattern under natural rainfall gradient.This proved that the artificial simulation of precision rain enhancement for research spatial pattern of Nitraria tangutorum and Artemisia ordosica has scientific practical significance.This paper studies the effects of future rainfall patterns change on desert plants by artificial simulated rainfall addition,systematically explained the response process of Nitrariatangutorum and Artemisia ordosica to simulated rainfall addition,which provides important data support for the maintenance and evolution of desert ecosystems in the context of global climate change. |
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