黄土高原土壤生物结皮对植物种子出苗和生长的影响

为了解生物土壤结皮对植物种子萌发出苗和植物生长的影响,于2009年7～8月在陕西省吴起县进行野外调查,对油松（Pinus tabulaeformis）、柠条（Caragana korshinskii）、沙棘（Hippophae rhamnoides）和杜梨（Pyrus betulae-folia）种子进行萌发实验,研究...     

Responses of microbial activities and soil physical-chemical properties to the successional process of biological soil crusts in the Gurbantunggut Desert,Xinjiang

Biological soil crusts(BSCs) are capable of modifying nutrient availability to favor the establishment of biogeochemical cycles. Microbial activities serve as critical roles for both carbon and nutrient transformation in BSCs. However, little is known about microbial activities and physical-chemical properties of BSCs in the Gurbantunggut Desert, Xinjiang, China. In the present research, a sampling line with 1-m wide and 20-m long was set up in each of five typical interdune areas selected randomly in the Gurbantunggut Desert. Within each sampling line, samples of bare sand sheet, algal crusts, lichen crusts and moss crusts were randomly collected at the depth of 0–2 cm. Variations of microalgal biomass, microbial biomass, enzyme activities and soil physical-chemical properties in different succession of BSCs were analyzed. The relationships between microalgal biomass, microbial biomass, enzymatic activities and soil physical-chemical properties were explored by stepwise regression. Our results indicate that microalgal biomass, microbial biomass and most of enzyme activities increased as the BSCs developed and their highest values occurred in lichen or moss crusts. Except for total K, the contents of most soil nutrients(organic C, total N, total P, available N, available P and available K) were the lowest in the bare sand sheet and significantly increased with the BSCs development, reaching their highest values in moss crusts. However, pH values significantly decreased as the BSCs developed. Significant and positive correlations were observed between chlorophyll a and microbial biomass C. Total P and N were positively associated with chlorophyll a and microbial biomass C, whereas there was a significant and negative correlation between microbial biomass and available P. The growth of cyanobacteria and microorganism contributed C and N in the soil, which offered substrates for enzyme activities thus increasing enzyme activities. Probably, improvement in enzyme activities increased soil fertility and promoted the growth of cyanobacteria, eukaryotic algae and heterotrophic microorganism, with the accelerating succession of BSCs. The present research found that microalgal-microbial biomass and enzyme activities played important roles on the contents of nutrients in the successional stages of BSCs and helped us to understand developmental mechanism in the succession of BSCs.     

古尔班通古特沙漠不同类型生物结皮对草本植物多样性影响

选择古尔班通古特沙漠的北部(一号点)、中部(二号点)、南部(三号点)3个不同样点的裸沙和藻结皮、地衣结皮与苔藓结皮3种生物结皮类型,对比研究了草本植物多样性的差异性及其主要环境影响因素。结果表明:(1)不同生物结皮类型的土壤理化性质有明显差异,土壤有机质、全氮、全磷、全钾含量以及黏粒、粉粒和细沙的含量随生物结皮演替显著上升,而中沙和粗沙的含量呈显著下降趋势,在沙漠不同区域呈现明显的空间异质性,二号样点中裸沙和藻结皮的养分含量和pH明显低于一号点和三号点。(2)草本植物的物种丰富度和Shannon-Wiener指数随生物结皮发育呈明显上升趋势,草本植物的物种组成、群落结构在不同类型生物结皮和沙漠不同区域均具有显著差异。(3)在土壤理化特征中,有机质、速效P和全K含量,以及pH和粉粒含量是影响草本植物分布的关键因子。(4)不同类型生物结皮之间的微地形和种类组成差异、种子生物学特性以及生物结皮在不同尺度下的土壤环境异质性共同影响草本植物在生物结皮中的物种组成和丰度,最终导致草本植物群落结构在生物结皮中的演替变化。     

化学覆盖与干湿变化对玉米生长及水分利用效率的影响

采用干旱防雨棚下盆栽的方法,研究不同土壤含水量下土壤表面化学覆盖对玉米抗旱成苗及水分利用效率(WUE)的影响。结果表明,利用保水剂和土壤改良剂PAM进行土壤表面覆盖能够提高玉米出苗率,有效降低土表蒸发,同时土壤干湿变化对玉米的生长更为有利,它可以引起强烈的生长补偿效应。     

Topographic differentiations of biological soil crusts and hydraulic properties in fixed sand dunes,Tengger Desert

Biological soil crusts(BSCs) play an important role in surface soil hydrology. Soils dominated with moss BSCs may have higher infiltration rates than those dominated with cyanobacteria or algal BSCs. However, it is unnown whether improved infiltration in moss BSCs is accompanied by an increase in soil hydraulic conductivity or water retention capacity. We investigated this question in the Tengger Desert, where a 43-year-old revegetation program has promoted the formation of two distinct types of BSCs along topographic positions, i.e. the moss-dominated BSCs on the interdune land and windward slopes of the fixed sand dunes, and the algal-dominated BSCs on the crest and leeward slopes. Soil water retention capacity and hydraulic conductivity were measured using an indoor evaporation method and a field infiltration method. And the results were fitted to the van Genuchten–Mualem model. Unsaturated hydraulic conductivities under greater water pressure(–0.01 MPa) and water retention capacities in the entire pressure head range were higher for both crust types than for bare sand. However, saturated and unsaturated hydraulic conductivities in the near-saturation range(–0.01 MPa) showed decreasing trends from bare sand to moss crusts and to algal crusts. Our data suggested that topographic differentiation of BSCs significantly affected not only soil water retention and hydraulic conductivities, but also the overall hydrology of the fixed sand dunes at a landscape scale, as seen in the reduction and spatial variability in deep soil water storage.     

生物土壤结皮结构、功能及人工恢复技术

生物土壤结皮作为典型的有机地被层,广泛分布在干旱半干旱地区。由于其具有良好的水土保持及土壤稳定等功能,可有效控制土地沙漠化,防治水土流失,因此,生物土壤结皮恢复被看作是荒漠生态系统修复和重建的关键。本文系统综述了国内外学者在生物结皮领域开展的研究工作,包括生物土壤结皮的生物组成、演替过程、生态功能、干扰响应、人工培育及生态恢复。以期深入认识生物土壤结皮的结构和功能及干旱半干旱地区的荒漠化治理提供参考。     

土壤微生物在生物结皮形成中的作用及生态学意义

在荒漠地区的固定、半固定沙地和流动沙地上,微生物、藻类植物及地衣、苔藓植物能参与并形成生物结皮,其在干旱和半干旱荒漠地区具有重要生态意义。其中土壤微生物因其极强的适应性和生存能力,在生物结皮形成各阶段都起着积极的作用。土壤微生物的生长和活性与土壤酶活性的变化具有良好的相关性,它的组成、分布和数量因沙丘类型和沙土层深度的不同而有所变化,也受到季节和植被的影响。土壤微生物的生理代谢活动及数量变化可以改变沙土表面理化性质,在土壤结皮的形成、植物营养的转化过程中发挥积极作用,为植物生长创造了良好的条件。     

古尔班通古特沙漠地衣结皮对放牧踩踏干扰的小尺度响应

古尔班通古特沙漠地衣结皮对放牧踩踏干扰及其所引起的生境异质性具有重要的指示作用。研究表明：① 放牧踩踏干扰主要集中于结皮层（0~5 cm）,随机调查的样方中,90%的样方干扰率均低于30%,生物土壤结皮(BSCs)破损尚处于较安全的范围;② 放牧踩踏干扰降低了BSCs总盖度,不同类型的结皮对践踏干扰的反应具差异性,其中,真菌-藻类共生形成的地衣结皮与干扰率呈极显著负相关（P<0.01）,干扰率>30%的样方中,抗风蚀能力较强的苔藓结皮、地衣结皮盖度均显著低于未受干扰样方,地衣共生体的破坏导致真菌数量显著增加（P<0.05）;③ 有机质、土壤容重等土壤理化指标均与干扰率呈负相关,干扰率>30%的样方中各指标均低于未受干扰样方。其中,土壤容重是对放牧干扰比较敏感的指标,与地衣结皮盖度亦呈极显著正相关（P<0.01）,与流沙盖度呈显著负相关（P<0.05）。     

黄土高原藓结皮覆盖土壤导水性能和水流特征

生物结皮具有特殊的水文物理性质,为探究其对土壤水分渗透性和水流特征的影响,以黄土高原风沙土和黄绵土上3种典型地表覆盖类型(裸地、藓结皮、藓结皮-草本植物混合)为对象,采用环刀法和染色示踪法对其导水性质与水流特征进行探究。结果表明:藓结皮对2种土壤类型0~5 cm土层土壤理化性质影响较大,与裸地相比土壤容重降低了9.85%~10.00%,土壤黏粒含量增加了1.01~1.29倍,表层有机质含量提高了2.73~3.02倍;藓结皮使0~5 cm土层土壤饱和导水率降低了61.32%~88.89%,而在5~10 cm土层饱和导水率则有明显上升。另外,由于草本植物的影响,藓结皮-草本植物0~5 cm土层与藓结皮土壤相比土壤饱和导水率提高了1.32~6.43倍;黄绵土藓结皮与藓结皮-草本植物的染色面积比均高于裸地,且水分下渗深度增加了10 cm,而风沙土藓结皮与风沙土裸地的染色面积比差异不明显。综上所述,藓结皮和藓结皮-草本植物的存在改变了表层土壤水分渗透性以及水流运动特征和水分下渗深度,影响着黄土高原土壤水分保持和生态恢复。     

Effects of artificially cultivated biological soil crusts on soil nutrients and biological activities in the Loess Plateau

Biological soil crusts （BSCs） play an important role in the early succession of vegetation restoration in the Loess Plateau, China. To evaluate the effects of artificially cultivated BSCs on the soil surface micro-envir- onment, we obtained natural moss crusts and moss-lichen crusts from the Loess Plateau of Shaanxi province, and subsequently inoculated and cultivated on horizontal and sloping surfaces of loess soil in a greenhouse. The chemical and biological properties of the subsoil under cultivated BSCs were determined after 10 weeks of cul- tivation. The results indicated that BSCs coverage was more than 65% after 10 weeks of cultivation. Moss crust coverage reached 40% after 5 weeks of cultivation. Compared with the control, soil organic matter and available nitrogen contents in moss crust with the horizontal treatments increased by 100.87% and 48.23%, respectively; increased by 67.56% and 52.17% with the sloping treatments, respectively; they also increased in moss-lichen crust with horizontal and sloping treatments, but there was no significant difference. Available phosphorus in cultivated BSCs was reduced, soil pH was lower and cationic exchange capacity was higher in cultivated BSCs than in the control. Alkaline phosphatase, urease and invertase activities were increased in artificially cultivated BSCs, and alkaline phosphatase activity in all cultivated BSCs was obviously higher than that in the control. Numbers of soil bacteria, fungi and actinomycetes were increased in the formation process of cultivated BSCs. These results indicate that BSCs could be formed rapidly in short-term cultivation and improve the mi- cro-environment of soil surface, which provides a scientific reference for vegetation restoration and ecological reconstruction in the Loess Plateau. China.     

Phalaris minor seedbank studies: longevity, seedling emergence and seed production as affected by tillage regime

Studies were conducted to investigate seed longevity, seedling emergence and seed production of the weed Phalaris minor in wheat in northern India. The longevity of P. minor seeds buried in bags in the field was often limited to less than 1 year, although many seeds buried at 30 cm depth in a rice–wheat rotation remained viable for longer. The application of direct seeding in wheat reduced the seedling emergence rate of P. minor , when compared with conventional ploughing and sowing. However, a larger P. minor seedbank in the upper soil layer in plots under direct seeding partly reversed this positive effect in one of the two studies. Besides differences in relative distribution of weed seeds through the soil profile, it was likely that other factors such as reduced soil disturbance and soil characteristics associated with the application of direct seeding were also involved in regulating the emergence rate. Mature P. minor plants in wheat were found to invest a stable part (27%) of their aboveground biomass in seed, so that total seed weight was strongly linearly correlated with the aboveground biomass of the mother plant. Individual seed weight, however, was little affected by the weight of the mother plant.     

沙漠生物结皮对维管植物养分吸收的影响

生物结皮是沙地表面被固定的重要特征,并能够富集养分,通过降水淋溶作用改善沙丘土壤的性质。研究表明,生物结皮层覆盖对植物体的养分元素吸收具有促进作用,但是,由于不同植物养分生理特性的差异及其根系分布深度的不同,不同植物吸收养分时对生物结皮层肥岛效应的敏感程度不同。     

黄土地与沙地生物结皮的发育特征及其生态功能异同

基于课题组已有研究成果,选取陕北水蚀风蚀交错区内气候条件相同但土壤质地迥异的试验区,探讨黄土地和沙地生物结皮发育特征及其生态效应的异同。结果表明:(1)苔藓结皮是2种土地生物结皮的重要类型,其中,黄土地的优势藓种为尖叶对齿藓[Didymodon constrictus(Mitt.)Saito.]、真藓(Bryum argenteum Hedw.)、狭网真藓(B.algovicum Sendt.);沙地的优势藓种为黄色真藓(B.pallescens Scheich.)、弯叶真藓(B.recurvulum Mitt.)、银叶真藓(B.argenteum Hedw.)。沙地乔灌植物下生物结皮盖度(77.5%)、厚度(11.8 mm)及容重(1.9 g·cm~(-3))均高于黄土地生物结皮,而黄土地多年生草本植物下生物结皮抗剪强度(26.5 k Pa)高于沙地生物结皮,总体上,沙地生物结皮发育的更好。(2)黄土地的入渗增幅和0~200 cm剖面的平均土壤含水率增幅均显著高于沙地(P0.05),且在旱季和雨季其0~200 cm剖面的平均土壤含水率增幅分别比沙地高1.4%和1.9%。(3)两地生物结皮均表现出了较好的减蚀作用,其减蚀效率分别为81.0%和90.6%。     

Cohort-dependent seedling recruitment, survival and reproductive capacity of Tribulus terrestris

Knowledge of the population biology of the summer annual Tribulus terrestris can provide valuable information for managing the risk of its colonising crop fields. Because of spring‐summer crop management practices, fields can exhibit bare ground in late April and early May. In this situation, four cohorts in 2000 and three cohorts in 2001 were censused and monitored throughout the vegetative and reproductive season, in order to evaluate the relationship between time of emergence, survival, vegetative growth and plant reproductive capacities. To a great extent, seedling survivorship depended on emergence timing; the earlier the emergence of the seedlings, the higher was the proportion of survivorship (64% and 4%, for early and late emergences). The time of emergence also influenced plant development; in both years, surviving individuals of the first cohorts presented significantly greater plant biomass and larger numbers of reproductive structures (60.5 fruits per plant) than those of later cohorts (0.8 fruits per plant). Reproductive meristem allocation was also highest in the earliest cohorts. Results showed that T. terrestris can increase its population size in fields if gaps of bare soil surface are available from mid spring to early summer.     

Precipitation amount and frequency affect seedling emergence and growth of Reaumuria soongarica in northwestern China

Climate change is shifting the amount and frequency of precipitation in many regions, which is expected to affect seedling recruitment across ecosystems. However, the combined effects of precipitation amount and frequency on seedling recruitment remain largely unknown. An understanding of the effects of precipitation amount and frequency and their interaction on seedling emergence and growth of typical desert plants is vital for managing populations of desert plants. We conducted two experiments to study the effects of variation in precipitation on Reaumuria soongarica(Pall.) Maxim. First, greenhouse experiments were conducted to examine the effects of three precipitation amount treatments(ambient, +30%, and-30%) and two precipitation frequency treatments(ambient and-50%) on seedling emergence. Second, the morphological responses of R. soongarica to changes in precipitation amount and frequency were tested in a controlled field experiment. Stage-specific changes in growth were monitored by sampling in different growth seasons. Our results showed that precipitation amount significantly affected germination, seedling emergence, and growth of R. soongarica, and there was a larger effect with decreased precipitation frequency compared with ambient. Germination and seedling emergence increased as precipitation increased under the same frequency of precipitation. The highest emergence percentage was obtained with a 30% increase in precipitation amount and a 50% reduction in precipitation frequency. Compared with ambient precipitation, a 30% increase in precipitation amount increased above-and below-ground biomass accumulation of R. soongarica during the growth season. A decrease of 30% in precipitation amount also resulted in an increase in below-ground biomass and root/shoot ratio in the early stages of the growth season, however, above-and below-ground biomass showed the opposite results at the end of the growth season, with larger effects on above-ground than below-ground biomass under decreased precipitation frequency. When precipitation frequency decreased by 50%, values of all growth traits increased for a given amount of precipitation. We concluded that precipitation frequency may be as important as precipitation amount to seedling emergence and growth of R. soongarica, and that understanding the effects of precipitation variability on seedling recruitment requires the integration of both precipitation amount and frequency. In particular, the combination of a 30% increase in precipitation amount and 50% reduction in precipitation frequency increased the emergence and growth of seedlings, suggesting that alteration of amount and frequency of precipitation caused by climate change may have significant effects on seedling recruitment of R. soongarica.     

The effect of maize residues and tillage on emergence of Setaria faberi, Abutilon theophrasti, Amaranthus retroflexus and Chenopodium album

Tillage and maize (Zea mays L.) residues at up to four times the base level had variable effects on the emergence of four annual weed species in the field. Environmental conditions varied during the three years of the research and interacted with residue and tillage to govern seedling emergence. When tillage affected Setaria faberi Herrm., emergence was greater in untillcd than tilled plots. The effect of residues varied among years. Abutilon theophrasti Medik, emergence from tilled soil was greater than from untilled soil in two of three years. Maize residue at two or four times the base levei reduced emergence. Amaranthus retroflexus L. emergence was often greater from untilled than tilled soil. The effect of maize residues on this species was dependent on tillage and precipitation. Chenopodium album L. emergence was affected by tillage and residues but differences over the three years were inconsistent. Results of this research indicate that tillage and residues interact with weed species, precipitation and other factors to regulate seedling emergence. The reduced soil disturbance and minimal weed seed burial associated with the elimination of tillage appear to have a greater impact on weed population dynamics than surface residues in non-tillage maize production systems.     

Factors affecting glyphosate activity in Imperata cylindrica (L) Beau, and Cyperus votundus L. I. Effect of soil moisture

Established Greenhouse grown plants of cogongrass Imperata cylindrica (L) Beauv.) and purple nutsedge (Cyperus rotundusL.) were given three different soil moisture regimes; field capacity, moderate stress and extreme stress, followed 6 weeks later by glyphosate [(N-phosphonomeihyl) glydne] applications to the shoots at 0.2,0.4 and 0.8 kg/ha for Imperata and 0.3,0.6 and 1.12 kg/ha for Cyperus. Field capacity watering stimulated most vegetative growth in hoth species. Glyphosate given at field capacity decreased shoot dry weight in both species, and rhizome length, rhizome dry weight and total carbohydrate in Imperata and total number of tuber-bulbs in Cyperus. In contrast. at extreme soil moisture stress, glyphosate showed reduced activity which appeared to be related to the physiological and morphological behaviour of the plants arising from the drought trealment. Application of waier to the roots of the plants grown at soil moisture stress. I week before and I week afler glypbosate spraying, enhanced glyphosate activity, probably because of the recovery of processes disturbed by ibe soil moisture deficit.     

植物疫苗鄂鲁冷特对番茄青枯病的田间防治效果

为了明确植物疫苗鄂鲁冷特对番茄育苗及其田间青枯病防治效果的影响,在番茄育苗基质中添加植物疫苗,测定处理后种苗株高、根系长度及出苗率;在田间种植共设疫苗袋装、沟施、浇灌及生防菌剂、化学农药和清水对照6个处理,对根系土壤的养分含量、植株的生物学性状及青枯病发病率进行研究。结果表明,植物疫苗处理分别能使番茄植株株高、根系长度和出苗率提高13.71%、68.20%和56.66%;疫苗袋装和沟施处理的番茄根系土壤有机质、全氮、全磷、全钾和交换性钙含量均显著高于其它处理;疫苗袋装、沟施和浇灌均能显著提高番茄植株的株高、花数和产量,其中疫苗袋装处理效果最好,番茄产量最高为99.55 t/hm~2,对不同生育期的平均防治效果最高为93.47%。表明植物疫苗鄂鲁冷特的应用能育出壮苗,降低青枯发病率,提高产量。     

Modelling the effect of weed-seed distribution in the soil profile on seedling emergence

Experiments to monitor weed seedling emergence from various soil depths were begun in 1989. Recently shed seeds were buried in either narrow bands at a range of depths in the soil or mixed evenly between the soil surface and each of these depths. Total emergence of Stellaria media (L.) Vill., Matricaria spp., Veronica persica Poiret, Veronica arvensis L. and Polygonum aviculare L., declined with increasing depth of burial. A similar pattern was observed for Chenopodium album L. with the exception of emergence from the surface layer. The reduction in emergence with increasing soil depth was greater for seeds in the narrow-banded treatments than for those in broad layers. A model was developed using the data from the narrow-banded treatments to predict emergence from distributions over broad layers. Predictions from the model closely agree with the data from the present broad-layer treatments and those from a similar experiment made in the 1960s. By including the effects of depth of seed burial on seedling emergence, this model could be combined with models that determine the effects of cultivation on seed distribution, and therefore improve precision of predictions of seedling emergence from the seedbank.     

Weed suppression by soil steaming in combination with activating compounds

The aim of this study was to determine the weed suppression potential of soil steaming plus activating compounds (KOH or CaO) to boost soil temperature. Different combinations between the compounds and rates were tested in experiments carried out in the field and in a controlled environment. Treatment effects were assessed on field weed vegetation and on seedbank and seedling emergence of three winter ( Alopecurus myosuroides , Matricaria chamomilla and Raphanus raphanistrum ) and four spring annuals ( Amaranthus retroflexus , Echinochloa crus-galli , Fallopia convolvulus and Setaria viridis ), were assessed on field weed vegetation. Neither maximum soil temperature (from 72 to 85°C) nor duration of high temperature in the 3 h following application consistently affected weed suppression. In the field, no significant effects on total weed density were recorded, but there were some significant effects on individual species. The weed seedbank was clearly suppressed by activated steaming: total seedling emergence was inversely related to increasing KOH rates both in the 0–10 and 10–20 cm soil layers, while for CaO the relationship was significant only in the 0–10 cm layer. Winter annuals were more sensitive to KOH than CaO and spring annuals had a more pronounced species-specific response to treatments. There was a strong negative relationship between compound rate and seedling emergence for all species. Alopecurus myosuroides was the most sensitive to the steam-alone treatment (77% reduction), whereas M. chamomilla and E. crus-galli were the least sensitive. Results from this study indicate that the type and rates of activating compounds for soil steaming must be adjusted to the weed community composition.