| Impacts of fencing of Agropyron mongolicum community in Yanchi county of Ningxia on the characteristic of soil,aboveground vegetation,soil seed bank(SSB)and the reproductive allocation strategy of its population were studied through laboratory experiments and field investigations.To reveal the influence of enclose on soil factors,aboveground vegetation and seed bank,and how does the plant adapt to the environment through the best resource allocation pattern,in order to provide a theoretical reference for the restoration and rehabilitation of desert steppe ecosystem.The results showed as following:1.Enclosure can make soil particles finee and have different influence on soil nutrients.The components of clay(<2 ?m)and silt(2?m-50 ?m)were dominant in the fence,but the components s of very fine sand(50 ?m-100 ?m)had a largest proportion,furthermore,the ratio of medium sand(>250 ?m)was almost zero outside the fence.Among 0 cm-10 cm,10 cm-20 cm and 20 cm-40 cm soil layers inside the fence,the clay content increase significantly,but the very fine sand significantly decreased(P<0.05),the silt sand and fine sand content changed insignificantly(P>0.05).The distribution of soil particle size is from 0 ?m to 250?m.Secondly,the soil organic carbon,total nitrogen(TN),total phosphorus(TP)content increased generally in 0 cm-10 cm soil layer inside fence,especially,TN and TP enhanced significantly;however,soil nutrient declined to some extent in 10 cm-40 cm layer inside fence,moreover,the content of alkaline nitrogen and available phosphorus decreased significantly(P<0.05).2.After enclosure,the coverage of the aboveground vegetation increased greatly;the number of total species increased,among them,the perennial herbage increased and annual decreased gradually.The total vegetation coverage of the enclosed and unenclosed plots was 75%and 40%,respectively,the total cover coverage of the enclosed vegetation was 35%higher than that in the unenclosed land.There were 32 species in the enclosure plots,but 28 species in outside enclosure,After enclosure,the proportion of ground species increased by 14%,among them,perennial herbage increased by 8.5%,and annual herbage decreased by 6.9%.3.Enclosure had a significant effect on the SSB.The density outside enclosure SSB were 1052 ±273 viable seeds m-2,but the inside enclosure 1885 ± 100 viable seeds m-2.The growth rate of SSB density was 79.0%,among them,the annual species decreased by 8.2%,while seed density increased by 44.0%.4.There was no significant influence on the diversity index of the vegetation and seed bank,but the diversity of different life type functional groups in the community could be changed by enclosure.After enclosure,Shannon-wiener index,the Margalef Richness index,Pielou Evenness index and Simpson Dominance index of SSB and aboveground vegetation showed increasing trend,but the difference were not significant(P>0.05).However,the diversity of life form functional groups changed to some degree.Among them,the perennial Shannon-Wiener index,Pielou evenness index and annual Margalef richness index and Simpson dominance index of ground vegetation increased significantly,while the Shannon-Wiener index of annual vegetation of aboveground vegetation and soil seed bank decreased significantly.5.The similarity coefficient of the SSB and the aboveground plant were moderately dissimilar,similarity coefficient of the outside enclosure(0.33)was slightly low than that the inside enclosure site(0.35).The similarity of SSB was 0.71,and the aboveground vegetation was 0.62 between and outside enclosure sites,which indicated that external disturbance had a greater influence on aboveground vegetation than on SSB.6.The enclosure had a significant effect on the biomass and distribution pattern of the modules of A.mongolicum population.Height,clump width,coverage and total biomass of A.mongolicum population were significantly increased after enclosure,their proportion were 78.96%(P = 0.040)?63.50%(P = 0.013)?50.89%(P=0.032)?205.38%(P = 0.022),respectively,while the density did not change significantly(P = 0.330).Enclosure had a significant effect on the biomass of the modules of A.mongolicum population.Compared with the outside fence,root,leaf and spike biomass increased significantly in enclosure sites,the proportion were 183.52%(P = 0.020),334.09%(P = 0.011),381.25%(P = 0.005),respectively.The root biomass both inside and outside fence were the largest(inside was 38.53 g,outside 13.59 g),and the biomass of the spike was the smallest(inside was 6.16 g,outside 1.28 g).After enclosure,the allocation proportion of the biomass of A.mongolicum changed in different degrees.The biomass allocation ratio of reproductive branches and leaves increased significantly,the proportion were 31.45%(P= 0.020)and 4.20%(P = 0.000),respectively.While the biomass allocation ratio of nutritional branches and root shoot ratio decreased significantly,the proportion were 281.62%(P = 0.002)and 13.33%(P = 0.023).Except the biomass of vegetative branches and clump width had significant negative correlation relationship(P = 0.039),there showed positive or significant positive correlation among the modular biomass of A.mongolicum,among between biomass and plant height,and between biomass and clump width.It was suggested that enclosure is one of the important measures for this population of A.mongolicum to maintain its regeneration ability.7.Enclosure could affect the distribution of nutrient elements and calorific values of various components of A.mongolicum.There were significant differences in the contents of C,N,P among different components of A.mongolicum.Among them,the contents of C,N and P of root were the lowest,but the highest in the ear.Fencing significantly decreased the content of TC,TN,TP in roots,content of TN?TP in spikes and the total TN content in leaves fencing significantly increased the TC content of spike by 9.78%.The calorific values of A.mongolicum components in both inside and outside of the fence showed spike>leaf>vegetative>reproductive branch>stem>root.After enclosure,the calorific value of spike and root increased significantly,but the leaf decreased significantly.The calorific value of each component of A.mongolicum was positive or significantly positive correlation with its carbon content(except leaves),while there was no consistent correlation with the content of nitrogen and phosphorus.These facts indicated that the tradeoff of caloric values between vegetative organs such as root,stem and leaf and reproductive organs such as fruit,flower was evolutionary adaptations of plant populations to specific environments. |
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