| Reaumuria soongorica and Salsola passerine are the group species or dominant species in many arid and semi-arid desert plant communities,which are vital to the maintaining of desert ecological stability.The research on the adaptability of R.soongorica and S.passerine to rainfall and their interspecific and intraspecific relationships is crucial for such understanding as the distribution of plant communities in desert ecosystems,the dynamics of desert ecosystems due to climate change,the pattern of desert landscapes,and the protection of biodiversity.This paper reveals the mechanism of the response and adaptability of the seedlings of R.soongorica to rainfall by analyzing the influence of artificial regulation of rainfall(rainfallą30%and rainfall interval prolongs by 50%)on underground and aboveground morphological character.Based on the investigation and sampling with the natural rainfall gradient(S1 Lingwu,S2 Wuwei and S3 Jiuquan),the interaction between paired root system of R.soongorica and S.passerine was studied,and the distribution characteristics of their paired community with the environmental gradient were clarified,and the effects of paired growing on the growth and distribution of roots and their response mechanism to environmental gradient were revealed.Through planting R.soongorica and S.passerine in different individual relationships(single growing,intraspecific and interspecific competition)and with root separation methods(no separation,nylon separation and plastic film separation),the effects of individual growth and interspecific and intraspecific relationships on plant morphology were discussed,and the interspecific relationships under different root separation methods of R.soongorica and S.passerine were verified.The main results are as follows:1.The root morphology of R.soongorica responds to changes in rainfall pattern in the early growing season,with remarkable differences among different treatments(P<0.05).However,the aboveground parts show a significant response in the late growing season,with dramatic differences among different treatments(P<0.05).This suggests that root morphology responds to rainfall changes earlier than aboveground parts.The aboveground and underground biomass of R.soongorica will increase with more rainfall,and the rainfall will increase by 30%at the natural rainfall interval in the late growing season,with the total biomass up by 24.2%on average.However,the root-shoot ratio changes little during the whole growing season.In the late growing season,the prolonged rainfall interval leads to the early loss of the leaves of R.soongorica and the decreased biomass,which shows that plants enter the dormancy period ahead of time,with a shortened growth period of R.soongorica.When the rainfall increases or decreases by 30%in contrast to the normal year and the rainfall interval prolongs by 50%,R.soongorica can adapt to the environment and grow normally.2.R.soongorica,with obvious main roots,belongs to the taproot system.In natural environment,root biomass of different soil layers of paired growing R.soongorica is above that of single growing one,and paired-root biomass at point S1 is72.5%higher than that of single growing,with little difference;paired-root biomass at point S2 is 92.3%higher than that of single growing,with a significant difference(P<0.05).Paired-root biomass at point S3 is 86.2%higher than that of single growing,with a dramatic difference(P<0.05).It shows that the root system is more developed in paired growing R.soongorica.It may be that the water absorption of S.passerine causes R.soongorica to be at mild water stress,thereby making paired growing R.soongorica distribute more biomass to roots for a stronger water absorption capacity.The root system of S.passerine is closer to fibrous root system in single growing with an unobvious main root.The root biomass and root surface area are concentrated in the shallow layer of the soil(0-20cm),indicating that the rainfall is the main source of water required for single growing S.passerine.Under paired growing condition,the S.passerine root system moves downwardly to R.soongorica,slightly close to the taproot system;This shows that S.passerine has received the"conservation effect"of R.soongorica,that is,plants promote the growth and development of their neighboring plants through various ways.The interspecific relationship between R.soongorica and S.passerine can be summarized as commensalism.3.With the increase of environmental stress gradient,the plant height of R.soongorica decreases sharply,while that of S.passerine changes little.Under paired growing condition,the average plant height of the two plants is above that of them growing alone with the plant height of R.soongorica slightly higher than that of S.passerine.The height difference between paired growing R.soongorica and single growing one decreases with the increase of environmental stress gradient.The height difference between paired growing S.passerine and single growing one is about 3cm under different growing conditions.The density of single growing S.passerine and that of paired growing one decrease with the increase of environmental stress,and the plant density of single growing R.soongorica is at its lowest in S2 region with the most favorable environment.Corresponding to the plant density,S.passerine has an abnormally high paired growing rate in S3 region with less rainfall.The interspecific relationship between R.soongorica and S.passerine do not improve with the change of environmental gradient(water stress),which indicates that their interspecific relationship differs from the environmental stress gradient hypothesis.4.Under the artificial cultivation condition,the aboveground biomass of R.soongorica reaches the maximum value of 64.4g when being singly grown(OR.)and is significantly different from other treatments(P<0.05).In the presence of intraspecific competition,the aboveground biomass of the large plant(TS.L)of S.passerine reaches the maximum value of 145.4g,which varies greatly from all other conditions and is 258.9%above that of the small plant of S.passerine(40.5g).The change trend of aboveground space occupied by the two plants is identical to the aboveground biomass on the whole.The aboveground volume of R.soongorica also reaches the maximum value of(0.103 m~3)when being singly grown(OR.),with a significant difference with other treatments(P<0.05);In the presence of intraspecific competition,the aboveground volume of the large plant of S.passerine reaches the maximum value of 0.112m~3,with a significant difference with other treatments.The intraspecific competition intensity of R.soongorica and S.passerine is spectacularly greater than that of their interspecific competition.5.R.soongorica and S.passerine show different growth strategies in their growth process.Under single growing condition,the root biomass of R.soongorica first increases with the depth of soil layer,with the maximum value reaching 6.19g in the soil layer of 10-20cm,and then decreases with the increase of soil depth.Other treatments include interspecific competition and intraspecific competition,in which the root biomass of R.soongorica is evenly and vertically distributed in the soil layer.The root biomass of paired growing and paired growing with nylon treatments is smaller.The root biomass of S.passerine is also vertically and evenly distributed in the soil layer as a whole.However,the change of root surface area shows different trends,and the change trends of R.soongorica and S.passerine root surface all increase with the depth.In addition,under the interspecific interaction,the two plants share a similar root distribution pattern.6.In this study,the distribution of soil moisture is mainly affected by gravity.When there is no plants,the highest average soil moisture content is 17.35%,which vertically increases with the soil depth.Under such treatments as a single growing plant and two plants of the same species,the soil moisture is irregularly distributed with soil depth.For S.passerine,the average soil water content for a single growing S.passerine(OS.)is 16.11%,and that for two S.passerine growing together(TS.)is16.69%,and the two conditions share a similar distribution pattern of soil moisture.For R.soongorica,the soil water content during intraspecific interaction is low,with an average of 14.75%,while that of each layer in OR treatment(a single growing R.soongorica)is the lowest among all treatments,with an average of only 12.21%.In addition,the distribution pattern of soil moisture in paired growing(PG)and nylon separation(NP)treatments is identical to that in the blank control,with a low content.It can be seen that root system has greatly influenced the soil moisture. |
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