略论延安市降水资源的潜力与高效利用模式

根据在甘肃子午岭 ,安塞墩滩和延安燕儿沟的试验观测资料 ,研究了梢林区植被对降水的拦蓄和消耗情况 ;分析了农区基本农田上和退耕还林 (草 )坡地上作物和植物对降水的拦蓄和土壤水分季节动态 ;计算了本区主要农作物和几种有代表性的乔、灌、草植物的全生育期内需水量和降水资源补给的盈亏状况 ;并提出了几种利用降水资源和河川径流的模式

黄土丘陵沟壑区乔灌木植物系数计算与适应性评价

利用长期定位试验资料,研究了黄土高原丘陵沟壑区乔木和灌木植物系数的计算方法,比较了两种代表性乔木(榆树和小叶杨)和两种代表性灌木(柠条和沙棘)的实际蒸散量和生育期土壤平均含水量的差异,分析了土壤含水量变化对植物根系吸水和土壤水分有效性的影响。结果发现:该地区灌木的实际蒸散量小于乔木,但同类植物的实际蒸散量没有显著差异;土壤含水量柠条最高,沙棘最低;榆树植物系数最小,柠条其次,沙棘最大,但榆树和小叶杨的土壤水分有效性高,耗水量大,所以灌木较适于该区生长。

黄土丘陵沟壑区沟沿线边缘植被特征初步研究

通过对黄土丘陵沟壑区安塞纸坊沟沟沿线边缘植被特征的调查,共发现隶属26科的66个物种,其中豆科、禾本科和菊科物种分别占19.70%1、5.15%和13.64%;物种中出现最多的是多年生草本,其次依次是1年生草本、灌木、小灌木、乔木、藤本和小乔木,其中灌乔物种多为主要物种且多为当地优势灌木虎榛子和酸枣等,指示着研究区植被恢复的方向;调查植物种基本包含了陕北黄土高原森林草原带次生演替各个阶段的主要植物种,是研究区次生演替的一个缩影;从沟沿线边缘植被的分布看,灌木远多于草本,其中以灌木为主的沟沿线区段植被的宽度、盖度均比以草本为主的沟沿线区段大,沟沿线防蚀效益较好。

生态恢复后的千烟洲植物群落种类组成及结构特征

Qianyanzhou(QYZ) Ecological Station established in 1983 with an area of 204 hm~2 is affiliated to the Chinese Ecosystem Research Network.Before 1982,herbs had been dominant,sparsely dotted with shrubs.After 20-year restoration of the vegetation,the vegetation showed significant changes in both forest coverage and species diversity.Forest coverage had increased to 93.3% in 1999 from 0.4% in 1982.The vegetation could be broadly classified into two groups: artificial forest,accounting for the most percent,and natural secondary forest.These two groups could be subdivided into 12 types.Based on the 2003 field work,The authors studied plant community composition and vertical structure.The results were as follows: 1) On the study plots were there about 150 species,of which 100,49,and 47 grew in arbor layer and shrub layer and herb layer,respectively.Of 12 community types,the amount of species in shrub layer was larger than that of other two layers.As to the species richness in the different community types,Liquidambar formosana community showed the highest and Imperata cylindrical var.major community the least.The amount of species in arbor layer of artificial forest was smaller than those of natural Pinus massoniana forest,but no difference in understory.2) Loropetalum chinense,Quercus fabric and Vaccinium bracteatum were dominant shrub species with a wide distribution.Three ferns Woodwardia japonica、Dryopteris atrata and Dicrannepteris dichotoma were dominant herb species.Lianas were sparse,but Milletlia reticulata were found in all forest types.3) Up to now some natural regeneration species,such as Eurya muricata、Quercus fabri、Vaccinium bracteatum、Rhus chinensis、Adinandra bockiana,had grown in the arbor layer of artificial forests.Some herb species,such as Arundinella setosa、Miscanthus floridulus、Isachne globosa、Scirpus triqueter,which were dominant ones in the herb layer before the restoration of vegetation,disappeared now.4) The vertical structure of natural Pinus massoniana community and Liquidambar formosana community showed more complex comparing with artificial forests.For the artificial forests,the conifer and broad-leaves mixed forest had a more complex structure.In both natural Pinus(massoniana) community and Liquidambar formosana community,it was dominated by individuals with height of 3～4 m,while 10～12 m in the artificial forests.

Nitrous oxide emissions from two alpine meadows in the Qinghai-Tibetan Plateau

Nitrous oxide (N2O) emission was measured in a Kobresia humilis meadow and a Potentilla fruticosa meadow in the Qinghai-Tibet Plateau from June 2003 to July 2006. Five treatments were setup in the two alpine meadows. Two bare soil treatments were setup in the K. humilis meadow (BSK) and in the P. fruticosa meadow (BSP) by removing the above- and belowground plant biomass. Three plant community treatments were setup with one in the K. humilis meadow (herbaceous community in the K. humilis meadow-HCK) and two in the P. fruticosa meadow (herbaceous community in the P. fruticosa meadow-HCP, and shrub community in the P. fruticosa meadow-SCP). Nitrous oxide emission from BSP was estimated to be 38.1 +/- 3.6 mu g m(-2) h(-1), significantly higher than from BSK (30.2 +/- 2.8 mu g m(-2) h(-1)) during the whole experiment period. Rates from the two herbaceous blocks (HCK and HCP) were close to 39.5 mu g m(-2) stop h(-1) during the whole experimental period whereas shrub community (SCP) showed significant high emission rates of N2O. Annual rate of N2O emission was estimated to be 356.7 +/- 8.3 and 295.0 +/- 11.6 mg m(-2) year(-1) from the alpine P. fruticosa meadow and from the alpine K. humilis meadow, respectively. These results suggest that alpine meadows in the Qinghai-Tibetan Plateau are an important source of N2O, contributing an average of 0.3 Tg N2O year(-1). We concluded that N2O emission will decrease, due to a predicted vegetation shift from shrubs to grasses imposed by overgrazing.

Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes

Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.

Experimental warming, not grazing, decreases rangeland quality on the Tibetan Plateau

We investigated experimental warming and simulated grazing ( clipping) effects on rangeland quality, as indicated by vegetation production and nutritive quality, in winter-grazed meadows and summer- grazed shrublands on the Tibetan Plateau, a rangeland system experiencing climatic and pastoral land use changes. Warming decreased total aboveground net primary productivity ( ANPP) by 40 g . m(-2) . yr(-1) at the meadow habitats and decreased palatable ANPP ( total ANPP minus non- palatable forb ANPP) by 10 g . m(-2) . yr(-1) at both habitats. The decreased production of the medicinal forb Gentiana straminea and the increased production of the non- palatable forb Stellera chamaejasme with warming also reduced rangeland quality. At the shrubland habitats, warming resulted in less digestible shrubs, whose foliage contains 25% digestible dry matter ( DDM), replacing more digestible graminoids, whose foliage contains 60% DDM. This shift from graminoids to shrubs not only results in lower- quality forage, but could also have important consequences for future domestic herd composition. Although warming extended the growing season in non- clipped plots, the reduced rangeland quality due to decreased vegetative production and nutritive quality will likely overwhelm the improved rangeland quality associated with an extended growing season.Grazing maintained or improved rangeland quality by increasing total ANPP by 20 - 40 g . m(-2) . yr(-1) with no effect on palatable ANPP. Grazing effects on forage nutritive quality, as measured by foliar nitrogen and carbon content and by shifts in plant group ANPP, resulted in improved forage quality. Grazing extended the growing season at both habitats, and it advanced the growing season at the meadows. Synergistic interactions between warming and grazing were present, such that grazing mediated the warming- induced declines in vegetation production and nutritive quality. Moreover, combined treatment effects were nonadditive, suggesting that we cannot predict the combined effect of global changes and human activities from single- factor studies.Our findings suggest that the rangelands on the Tibetan Plateau, and the pastoralists who depend on them, may be vulnerable to future climate changes. Grazing can mitigate the negative warming effects on rangeland quality. For example, grazing management may be an important tool to keep warming- induced shrub expansion in check. Moreover, flexible and opportunistic grazing management will be required in a warmer future.

重庆老龙洞二叠系-三叠系界线地层微生物岩研究

The largest mass extinction in the Phanerozoic happened at the end of the Permian. The microbialites formed in the extreme environments after the mass extinction has become a hotspot for geologists and paleontologists throughout the world. The dendroid microbialites that were described for the first time in 1999 from the Permian-Triassic boundary section at Laolongdong, Chongqing, have been studied by many geologists from China and overseas. Two important viewpoints about their origin have been proposed. Some researchers believed that they resemble Quaternary travertine shrubs in form, and may belong to microbialites. Some other researchers proposed that the dendroid structure is composed of clots formed by coccoidal cynaobacteria, and is microbialite. Our detailed survey on the section reveals that: (1) there is an interval of speckled “microbialite” in the section, and it underlies the dendroid “microbialite”, (2) the dendroid “microbialite” does not always have dendroid appearance; they are dendroid only in very local places; they are not dendroid in most places; for this reason, they are not comparable to recent tufa; (3) the volume of the dendroid structure greatly increases toward the top of the dendroid microbialite interval: accounting to 70% of the whole rock in the top part. This distribution pattern implies that the formation of this structure may be related to downward migration of the diagenetic fluid. Examination of thin sections reveals that the dendroid structure or point-like structure in the “microbialite” look as lighter areas in the thin sections and are composed of large blocky clear calcites containing scattered yellow dirty small calcite rhombi and irregular “points” of relict lime mudstone or wackestone or packstone. Their formation is by any one of the following two processes: (1) dissolution → filling of large blocky calcite; (2) dolomitization → dedolomitization → dissolution by meteoric fresh water → filling by large blocky calcites. It has been found that there are at least two sea-level falls during the P-T transition. As the sea level fall, the carbonate deposits came into supratidal environment, and suffered dolomitization caused by evaporative fluid or mixing water of sea water and meteoric water. Since the fluid migrated downward from the top of the deposits and in random pathway, the dolomitization formed dendroid or speckled dolomitic areas. As the deposits came into subaerial environments, the meteoric fresh water migrated along the dendroid or speckled dolomitic area with higher porosity, and dissolution happened, which caused the rock became spongy or alveolate. In later time, after the strata came into phreatic zone, large clear blocky calcites grew in and filled the pores in the spongy areas. The dendroid and speckled structure were formed in this way, rather than composed of clots formed by coccoid cyanobecteria. The microbial fossils in Laolongdong section include two types. The first is the tube-like cyanobecteria in middle Bed 3, which are generally less than 1 mm in length, taper toward one end, and are internally filled by microspars. They are straight or sinuous, with micritic wall 0.005~0.01 mm thick. Since this kind of microbial fossils are abundant in middle Bed 3, this rock belongs to microbialite. The second type occurs in Bed 5 and lower and middle Bed 6. They are irregular globular in shape, generally 0.2 ~ 0.5 mm in size, with several outward progresses, and internally filled by one layer of needle-like calcite cements on the wall and the large blocky calcite in the inner space. According to their shape and preservation way, it is inferred that this kind of fossils were formed from some kind of bacterial colony. The bacterial colony may be cuticle in composition, since it has some hardness as it is indicated by its resistance to deposit loading. These organisms discomposed during diagenetic time, and formed good porosity. In later diagenetic time, these pores were firstly cemented by needle-like calcites and later filled by large blocky calcites. So, the bacterial colony promoted the formation of dendroid and speckled structures. However, they did not always form such structures. On the other hand, even though no bacterial colony or other microbes or any kind of fossils were present, dendroid or speckled structures can form. Bed 4 of Laolongdong section contains abundant gastropods but no microbial fossils, and is not microbialite, even though it is speckled. The top of Bed 6 is dendroid, but contain no microbial fossils, and is not micrbialite.

北天山新生代构造演化与古环境演变

The Tianshan Mountains is located about 1000-2000 km north of the India-Asia suture and is the most outstanding topography in central Asia, with transmeridional length of nearly 2500 km, north-southern wideness of ~ 300-500 km, peaks exceeding 7000 m above sea level (asl.), and average altitude of over 4000 m asl. Much of the modern relief of the Tianshan Range is a result of contraction driven by the collision of the India subcontinent with the southern margin of Asia, which began in early Tertiary and continues today. Understanding where, when and how the deformation of the Tianshan Mountains occurred is essential to decipher the mechanism of intracontinental tectonics, the process of foreland basin evolution and mountain building, and the history of climate change in central Asia. In order to better constrain the Cenozoic building history of the Tianshan Mountains and the climate change in the southern margin of the Junggar Basin, we carried out multiple studies of magnetostratigraphy, sedimentology, and stable isotopes of paleosol carbonate at the Jingou River section, which is located at the Huoerguosi anticline, the westernest one of the second folds and thrust faults zone in the northern piedmont of the Tianshan Mountains. The Jingou River section with a thickness of about 4160 m is continuous in deposits according to the observed gradual change in sedimentary environments and can be divided into five formations: Anjihaihe, Shawan, Taxihe, Dushanzi and Xiyu in upward sequence. Characteristic remamences were isolated by progressive thermal demagnetization, generally between 300 and 680℃. A total of 1133 out of 1607 samples yielded well-defined ChRMs and were used to establish the magnetostratigraphic column of a 3270-m-thick section from the exposed base of the Anjihaihe Formation to the middle of the Xiyu Formation. Two vertebrate fossil sites and a good correlation with the CK95 geomagnetic polarity time scale suggest that the section was deposited from ~30.5 to ~4.6 Ma and the age of the top of the Xiyu formation is ~2.6 Ma based on an extrapolation of the sedimentation rates. A plot of magnetostratigraphic age vs. height at the Jingou River section shows that significant increases in sedimentation rates as well as notable changes in depositional environments occurred at ~26-22.5 Ma, ~13-11 Ma and ~7 Ma, which represent the initial uplift of the Tianshan Mountains and two subsequent rapid uplift events. In addition, changes in sedimentation rates display characteristic alternations between increases and decreases, which probably indicate that the uplift of the Tianshan Mountains was episodic. We discussed the history of C4 biomass and climatic conditions in the southern margin of the Junggur Basin using the stable carbon and oxygen isotope composition of paleosol carbonates from the Jingou River section during ~17.5-6.5 Ma. The δ13C values indicate that the proportion of C4 biomass was uniform and moderate (15-20 %) during the interval of ~17.5-6.5 Ma. We proposed three hypotheses for this pattern of C4 biomass: (1) counteraction of two opposed factors (global cooling since ~15 Ma and thereafter increased dry and seasonality in central Asia) controlling the growth of C4 grasses, (2) variability in abundance of C3 grasses relative to C3 trees and shrubs if vegetation had ever changed in ecosystems, and (3) the higher latitude of the studied region. The δ18O values show a stepwise negative trend since ~13 Ma which may be attributed to three factors: (1) the temperature decreasing gradually after the middle Miocene (~15 Ma), (2) the increasing contribution of the moistures carried by the polar air masses from the Arctic Ocean to precipitation, and (3) the gradual retreat westward and disappearance of the Paratethys Ocean. Among them, which one played a more important role will need further study of the paleoclimate in central Asia.

宁夏固原寺口子剖面磁性地层与孢粉植物群初步研究

In Asia continent, several significant environmental events happened during the Cenozoic era, such as uplift of the Tibet Plateau, formation of the Asian Monsoon system, aridification of the temperate inland region in Central Asia. To investigate the history of long-term palaeoclimate evolution during the late Cenozoic, a lacustrine sequence located at Sikouzi, Guyuan county, Ningxia-Hui Autonomous Region, was studied. The Sikouzi section is about 2880 m in thickness and has a general continuous nature according to field observation. Thus this thick lacustrine record is an important archive to further understand those environmental events. In this study, detailed field measurement, layer-after-layer description and sampling, and magnetostratigraphy and palynoflora investigations are conducted at the Sikouzi section and some preliminary results have been achieved as follows. Based on Hipparion fauna, pollen data and long distinctive patterns of the local magnetozones, the confident correlation of the Sikouzi magnetostratigraphic polarity to the GPTS (CK95) is best established, indicating that the top boundary of the Sikouzi formation is dated back to -19.8 Ma B.P. and consequently no Oligocene sediments deposited locally. On the other hand, both the field observation and the correlation to GPTS indicate a nearly continuous nature for the whole sequence. The palynological results show that the grassland has been a dominant vegetation in the Sikouzi area since ~19.8 Ma B.P, although some trees/shrubs were present sparsely during the intervals of relatively warm and wet climatic conditions. This implies that the onset of the aridification in northwestern China is dated back to at least 19.8 Ma B.P. ago. The Neogene Global Climatic Optimum (-16.0 Ma B.P.) occurring between the late Early Miocene and the early Middle Miocene is well documented in the Shanwang formation, Shandong Province. However, such event was not found in the Sikouzi record, and neither in the Guide and the Hualong basins, Qinghai province. This may lead us to the conclusion that the East-Asian Summer Monsoon system remained weak during the period of the Miocene Climatic Optimum although the onset of it was traced back to the Early Oligocene. In the Sikouzi area, it was warm between the latest Miocene and the early Pliocene and then became cool in the late Pliocene. This pattern is consistent with the palaeoclimate record of the Pliocene from other areas in the world.

中国北方典型生态区表土孢粉组合特征及其与现代植被和气候的关系

Surface pollen assemblages and their relationhips with the modern vegetation and climate provide a foundation for investigating palaeo-environment conditions by fossil pollen analysis. A promising trend of palynology is to link pollen data more closely with ecology. In this study, I summarized the characteristics of surface pollen assemblages and their quantitative relation with the vegetation and climate of the typical ecological regions in northern China, based on surface pollen analysis of 205 sites and investigating of modern vegetation and climate. The primary conclusions are as follows:The differences in surface pollen assemblages for different vegetation regions are obvious. In the forest communities, the arboreal pollen percentages are more than 30%, herbs less than 50% and shrubs less than 10%; total pollen concentrations are more than 106 grains/g. In the steppe communities, arboreal pollen percentages are generally less than 5%; herb pollen percentages are more than 90%, and Artemisia and Chenopodiaceae are dominant in the pollen assemblages; total pollen concentrations range from 103 to 106 grains/g. In the desert communities, arboreal pollen percentages are less than 5%. Although Chenopodiaceae and Artemisia still dominate the pollen assemblages, Ephedra, Tamaricaceae and Nitraria are also significant important in the pollen assemblages; total pollen concentrations are mostly less than 104grains/g. In the sub-alpine or high and cold meadow communities, arboreal pollen percentages are less than 30%. and Cyperaceae is one of the most significant-taxa in the pollen assemblages. In the shrub communities, the pollen assemblages are consistent with the zonal vegetation; shrub pollen percentages are mostly less than 20%, except for Artemisia and Hippophae rhamnoides communities.There are obvious trends for the pollen percentage ratios of Artemisia to Chenopodiaceae (A/C), Pinus to Artemisia (P/A) and arbor to non-arbor (AP/NAP) in the different ecological regions. In the temperate deciduous broad-leaved forest region, the P/A ratios are generally higher than 0.1, the A/C ratios higher than 2 and the AP/NAP ratios higher than 0.3. In the temperate steppe regions, the P/A ratios are generally less than 0.1, the A/C ratios higher than 1 and the AP/NAP ratios less than 0.1. In the temperate desert regions, the P/A ratios are generally less than 0.1, the A/C ratios less than 1, and the AP/NAP ratios less than 0.1.The study on the representation and indication of pollen to vegetation shows that Pinus, Artemisia, Betula, Chenopodiaceae, Ephedra, Selaginella sinensis etc. are over-representative in the pollen assemblages and can only indicate the regional vegetation. Some pollen types, such as Quercus, Carpinus, Picea, Abies, Elaeagus, Larix, Salix, Pterocelis, Juglans, Ulmus, Gleditsia, Cotinus, Oleaceae, Spiraea, Corylus, Ostryopsis, Vites, Tetraena, Caragana, Tamaricaceae, Zygophyllum, Nitraria, Cyperaceae, Sanguisorba etc. are under-representative in the pollen assemblages, and can indicate the plant communities well. Populus, Rosaceae, Saxifranaceae, Gramineae, Leguminosae, Compositae, Caprifoliaceae etc. can not be used as significant indicators to the plants.The study on the relation of pollen percentages with plant covers shows that Pinus pollen percentages are more than 30% where pine trees exist in the surrounding region. The Picea+Abies pollen percentages are higher than 20% where the Picea+Abies trees are dominant in the communities, but less than 5% where the parent plants are sparse or absent. Larix pollen percentages vary from 5% to 20% where the Larix trees are dominant in the communities, but less than 5% where the parent plants are sparse or absent. Betula pollen percentages are higher than 40% where the Betula trees are dominant in the communities" but less than 5% where the parent plants are sparse or absent. Quercus pollen percentages are higher than 10% where the Quercus trees are dominant in the communities, but less than 1% where the parent plants sparse or absent. Carpinus pollen percentages vary from 5% to 15% where the Carpinus trees are dominant in the communities, but less than 1% where the parent plants are sparse or absent. Populus pollen percentages are about 0-5% at pure Populus communities, but cannot be recorded easily where the Populus plants mixed with other trees in the communities. Juglans pollen accounts for 25% to 35% in the forest of Juglans mandshurica, but less than 1% where the parent plants are sparse or absent. Pterocelis pollen percentages are less than 15% where the Pterocelis trees are dominant in the communities, but cannot be recorded easily where the parent plants are sparse or absent. Ulmus pollen percentages are more than 8% at Ulmus communities, but less than 1% where the Ulmus plants mixed with other trees in the communities. Vitex pollen percentages increase along with increasing of parent plant covers, but the maximum values are less than 10 %. Caragana pollen percentages are less than 20 % where the Caragana plant are dominant in the communities, and cannot be recorded easily where the parent plants are sparse or absent. Spiraea pollen percentages are less than 16 % where the Spiraea plant are dominant in the communities, and cannot be recorded easily where the parent plants are sparse or absent.The study on the relation of surface pollen assemblages with the modern climate shows that, in the axis 1 of DCA, surface samples scores have significant correlation with the average annual precipitations, and the highest determination coefficient (R2) is 0.8 for the fitting result of the third degree polynomial functions. In the axis 2 of DCA, the samples scores have significant correlation with the average annual temperatures, average July temperatures and average January temperatures, and the determination coefficient falls in 0.13-0.29 for the fitting result of the third degree polynomial functions with the highest determination coefficient for the average July temperature.The sensitivity of the different pollen taxa to climate change shows that some pollen taxa such as Pinus, Quercus, Carpinus, Juglans, Spiraea, Oleaceae, Gramineae, Tamariaceae and Ephedra are only sensitive to the change in precipitation.