Studies On Water Physiological Ecology Characteristics Of 4 Native Herbs Communities In Loess Hill Region

1. Succession rule of arable old land after being abandoned in Loess hilly region was studied and mainly local herbs in this process were assessed, which provided evidence for research objects selection. Based on quantitative classification using system clustering and the field investigations, the rule of primary succession stage of arable old land after being abandoned in Loess hilly region was revealed, the result showed: from 1 to 6 years: annual weeds community ,annual weeds + tuft grass community ,annual weeds + perennial herbage community or rhizome grass ,from 7 to 16 years: perennial herbage community ? perennial grass+ undershrub community ,from 17 to 42 years, rhizome tuft grass + undershrub community or undershrub + perennial grass community ,undershrub community or perennial grass + tuft grass community. The representative communities were: Artemisia scoparia Waldstet kit community ,A.scoparia Waldstet kit + Stipa bungeana Trin ,A.scoparia Waldstet kit + Artemisia scarorum Ledeb. (or Agropyron cristatum(L.) community),A.scarorum Ledeb. ,A.scarorum Ledeb. + Lespedeza var.dahurica (Laxm.)Schindl ? Bothriochloa ischaemum(L.) + L.var.dahurica (Laxm.)Schindl or L.var.dahurica (Laxm.)Schindl + A.scarorum Ledeb. ,L.var.dahurica (Laxm.)Schindl or A.scarorum Ledeb. + Poa sphondylodes Trin. community. Based on the result of the investigation of succession, all 67 kinds of wild grasses arranged in order of important values, 1st～35th herbage were testified to have the ability for yielding more quantity production than from 36th to the last. This character was the most important not only for the ecological benefit but also for the economic effectiveness. According as the result of palatability experiment, 23 kinds of pastures was selected from the first 35 species, which were analyzed the chemical nutrient composition. Based on the score that gained by appraised chemical nutrient composition, they were classified 4 grades: excellent, fine, good and inferior. From the excellent 8 communities, 4 native herbs communities in Loess hilly region were screened out as research objects: Lespedeza davurica (Laxm.) Schindl. Community,Kengia songorica (Hook.f.) Rosh community,Agropyron cristatum (L.) Gaertn community,Bothriochioa ischaemum (L.) Keng community. 2. Characteristics of 4 native herbs communities in community ecology According to investigation scale and research purpose, the basic conditions for species-area curves has been analyzed. Four kinds of conducts has been selected from 7 typical models curves to study species-area curve on loess plateau, that is S = b+alnA,S = aln (b A+1),S = aAb,S = aA(1 +bA). With the aid of the SAS8.1, MATLAB6.5 system, fitting and diagram have been done respectively, and F result was chosen to assess the fitness of the first three models. Then S = aA(1 +bA) was regarded as the standard curve to get second derivative species-area of Lespedeza davurica (Laxm.) Schindl. Community,Kengia songorica (Hook.f.) Rosh community,Agropyron cristatum (L.) Gaertn community,Bothriochioa ischaemum (L.) Keng community, that is, 3.4 m2,4.1 m2,1.4 m2,4.8m2. Since each community fits this model, it can be considered as the best species-area curves model of herbage plant community on the Loess hilly region. Ecological characteristics of Lespedeza davurica (Laxm.) Schindl, Agropyron cristatum (L.) Gaertn, Bothriochioa ischaemum (L.) Keng, Kengia songorica (Hook f.) Rosh community were investigated in the least area, the indices of αdiversity were compare for different vegetation community. According to the result of 13 models, there is positive correlation between Margalef and Menhiniek index, PieLou and Heip index. The further study based on first analysis has been done by SAS 8.1 and MATLAB6.5, that indices were classified 2 kinds, one was that Menhiniek,PIE,Heip index decreased with the plant community succession, the order was Agropyron cristatum (L.) Gaertn>Kengia songorica (Hook.f.) Rosh>Lespedeza davurica (Laxm.) Schindl.>Bothriochioa ischaemum (L.) Keng; Another was Fisher and S index, the order changed as follows: Agropyron cristatum (L.) Gaertn>Kengia songorica (Hook.f.) Rosh>Bothriochioa ischaemum (L.) Keng>Lespedeza davurica (Laxm.) Schindl. By the means of taking entire root from soil, aground and underground biomasses of constructive species of 4 communities are studied. The order is Bothriochioa ischaemum (L.) Keng> Agropyron cristatum (L.) Gaertn>Lespedeza davurica (Laxm.) Schindl.>Kengia songorica (Hook.f.) Rosh Monthly growth varieties in a year of 4 communities were investigated by fix position observation means. Overall biomass of constructive species of each community's in whole year ordered as follow: Lespedeza davurica (Laxm.) Schindl>Bothriochioa ischaemum (L.) Keng >Kengia songorica (Hook.f.) Rosh>Agropyron cristatum (L.) Gaertn; comparing with the length of growth period, the order was: Agropyron cristatum (L.) Gaertn > Bothriochioa ischaemum (L.) Keng > Lespedeza davurica (Laxm.) Schindl> Kengia songorica (Hook.f.) Rosh; according to the height, the order was: Lespedeza davurica (Laxm.) Schindl>Agropyron cristatum (L.) Gaertn > Kengia songorica (Hook.f.) Rosh> Bothriochioa ischaemum (L.) Keng; in term of effective coverage, the order was: Lespedeza davurica (Laxm.) Schindl>Bothriochioa ischaemum (L.) Keng >Kengia songorica (Hook.f.) Rosh>Agropyron cristatum (L.) Gaertn. Relationship between ecological characteristics and soil water content was analyzed, the results showed: the phenomenon that biomass of Bothriochioa ischaemum (L.) Keng and Lespedeza davurica (Laxm.) Schindl communities were larger than others and the superiorities of constructive species were obvious was caused by considerable competitive abilities of each community which insured them to have priority in possessing niche. For this reason, companion species and rare species were restricted in development, thus limited resources could be fully utilized by Bothriochioa ischaemum (L.) Keng and Lespedeza davurica (Laxm.) Schindl communities. As the result, in the Loess plateau, pasture's extent of niche was determined by competitive power; total amount of productivity in overall year of communities was determined by plant's drought resistance; grass yield was determined by pastures'biological characteristics especially by plasticity of plant life history. That was the main reason why Bothriochioa ischaemum (L.) Keng and Lespedeza davurica (Laxm.) Schindl communities had stronger productivities than other 2 communities. 3. Biological characteristics of 4 native herbs communities The investigation of competition of intraspecfic and interspecfic in 4 native herbs communities showed that: Competition in Agropyron cristatum (L.)Gaertn communities can results in nonlinear allometry, and are mainly intraspecfic; in Kengia songorica (Hook.f.) Rosh community, competition mostly came from interspecfic with Artemisia sacrorum Leded. and Lespedeza davurica (Laxm.) Schindl communities, also from intraspecfic; competition in Bothriochioa ischaemum (L.) Keng community derived from interspecfic with Artemisia sacrorum Leded., Lespedeza davurica (Laxm.) Schindl and Artemisia scoparia Waldstet kit; in Lespedeza davurica (Laxm.) Schindl community, competition were mainly from interspecfic with Artemisia sacrorum Leded.and Stipa bungeana Trin. communities, as well as from intraspecfic. All above indicated the biological characteristics of constructive species in the middle and the late succession stage: considerable competitive abilities and in which resulted high adaptability and tolerance. At the same time, pasture collocations were provided in theory: Agropyron cristatum (L.) Gaertn + Lespedeza davurica (Laxm.) Schindl, Bothriochioa ischaemum (L.) Keng +Kengia songorica (Hook.f.) Rosh. The purpose of community management in Kengia songorica (Hook.f.) Rosh, Bothriochioa ischaemum (L.) Keng and Lespedeza davurica (Laxm.) Schindl was pointed out: preventing the growth of Artemisia sacrorum Leded. and releasing the niches.Studies of reproduction methods in 4 native herbs communities indicated:generativ propagation of each pastures had degenerated to a certain degree; yield, mature degree, and anti-ageing ability of seeds were fairly low. under a suitable condition: pH>7.0,27℃,fully sop-up 12h, the germination percentage of Bothriochioa ischaemum (L.) Keng seeds were 80%, Kengia songorica (Hook.f.) Rosh seeds were 60% and Agropyron cristatum (L.) Gaertn seeds were only 30%. Young seedlings of 4 species were sensitive in temperature. Through synthesize comparison of normal seedling percentage on all treatments, the average normal seedling percentage of Lespedeza davurica (Laxm.) Schindl was the lowest—78%, whereas, the other 3 herbs all reached 92%. Survival percent of tree seedling was fairly low under light radiance, however, Agropyron cristatum (L.) Gaertn was only 48%, the others were about 65%. All 4 communities had very strong vegetative propagation ability according to the field investigation results and advantages of clone growth—"share risk and benefit equally"was fully represented. 4. Characteristics of 4 native herbs communities in water physiological ecology Lespedeza davurica (Laxm.) Schindl has high adaptability in drought; its water consumption depends on soil water and it process fine plasticity. Pot experiment showed that its rapid growth period synchronized with peak time of water consumption; it depends on enhancing water-uptake ability to make up the excessive transpiration dehydration; its WUE declined along with the decrease of soil water; it belongs to drought-defensive herb which has the trait of high transpiration, photosynthesis and WUE. Water consumption peak of Agropyron cristatum (L.) Gaertn was from July to August. There was little relation between water consumption and soil water. Water deficit resulted in descent of water consumption, but the WUE were improved. It belongs to low transpiration and low water consumption grass. Compared with other herbs, Bothriochioa ischaemum (L.) Keng has the strongest drought-resistance, the water consumption peak and the heave growth period were in accordance with the rainy season of Loess hilly region, it could make fully use of precipitation for rapid growing. Its WUE kept high level under the water-stress condition. Water consumption of Kengia songorica (Hook.f.) Rosh was the least. The growth was slow; leaf area was small; amount of growth was small; rapid growth period was not obviously. Water consumption peak was from June to August. Heavy growth period lasted not very long time. It belongs to high transpiration, low WUE grass.