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Ecological Adaptation Of Some Dominant Plants In Otindag Sandland

Posted on:2005-03-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:X W ZhuFull Text:PDF
GTID:1100360152471697Subject:Plant ecology
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Otindag Sandland is one of the main sandlands and among the most seriously desertificated region in semiarid area of China. It is also one of the origins of the dust for dusty weather existing in Northeast China. It is helpful to study how the plants in Otindag Sandland adapt to the local environments for combating the desertification and accelerating ecological restoration of the ecosystems. In this thesis, the adaptive strategies of the psammophyte plants in Otindag Sandland to the sand moisture, sand burial and environmental heterogeneity are investigated using both field and greenhouse experiments.In semiarid sandland, like Otindag Sandland of China, the humid soil layer in which plant can get water moves down gradually after rain. In order to absorb water, the speed of root elongation in plants must surpass the speed of the humid soil layer moving down. Therefore, the root should have corresponding plasticity in morphology, growth and biomass investment patterns. Hedysarum laeve Maxim. (Leguminosae) is a dominant semishrub and major sand-binding species in Otindag Sandland. The response of the seedling growth to different sand water contents (SWCs) and different mimicked precipitations were studied. When SWC was lower than 3%, H. laeve seedling could not survive. From 3% to 12%, seedling biomass increased with SWC increasing. At the early stage, the roots of H. laeve developed quickly and thedownward extension of its root system surpassed the downward movement of humid soil layer at the top, the middle of leeward slope and the back of leeward slope in the sand dunes. The higher the precipitation, the greater the root depth, total root length and root diameter, the more lateral roots and the lower ratio of root to shoot.In arid or semiarid habitats such as sand dunes, the survival of plants mainly depends on the mechanisms ensuring germination and seedling development at the right time and in a suitable locality. Greenhouse experiments were conducted to study (1) response of seed germination and seedling emergence to depths of sand burial in Caragana microphylla Lam. and Hedysarum leave and (2) correlation of their responses with seed size. Freshly harvested seeds of both species germinated well in light and poorly in darkness. The optimal temperature for germination was 10℃ to 15℃ in both species. We investigated the influences of the depth of sand burial (1,2, 4, 6, 8, 10, 12, 14 cm) and seed size (small, medium, large) on seed germination and seedling emergence in these two species. Both plants had similar response to the sand burial. The seedlings of C. microphylla emerged from deeper in the sand than those of H. laeve. Within the species, the deeper the seeds in the sand, the lower were the germination and the emergence rates, and the slower the seed germination and seedling emergence. The depth of 2 cm was the optimal depth for seed germination and seedling emergence of both species.Agropyron cristatum (L.) Gaertn is a dominant perennial grass in Otindag Sandland, China. We investigated the SWC from April to October of 2002 in Otindag Sandland and the response of its seed germination, seedling emergence and seedling growth to SWC (1%, 2%, 3%, 4%, 6%, 8%, 12%, 16% and 20%). The SWC between April 20 and May 10 was critical to its seed germination, seedling emergence and seedling settlement. The optimal SWC for seed germination and seedling emergence in A. cristatum was from 12% to 20%. The optimal SWC for its establishment was 12% to 16%. When SWC was under 3%, the seed could not germinate and when SWC was lower than 6%, seedlings could neither emerge nor settle. When SWC was 16% and 20%, the biomass decreased slightly. At 6% to 8%, the seedlings allocatedmore biomass to roots.In Otindag Sandland, number of ramet and aboveground biomass of Leymus secalinus (Georgi) Tzvel. increased while the soil nutrient decreased from the lowland meadow, the ecotone of lowland meadow to the sand accretion area. The ramets of L. secalinus were significantly spatially autocorrelated in the lowland meadow, the ecotone an...
Keywords/Search Tags:Agropyron cristatum, Caragana microphylla, clonal plant, enforced dormancy, fractal analysis, Hedysarum laeve, heterogeneity, humid soil layer, Leymus secalinus, mimicked precipitation, Otindag Sandland, root character, sand burial
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