沙埋与供水对毛乌素沙地两种重要沙生植物幼苗生长的影响

沙埋与水分是影响毛乌素沙地植物存活、生长的关键因子。通过沙埋与供水的野外控制实验,研究了毛乌素沙地重要物种柠条(Caragana korshinskii)与羊柴(Hedysarum laeve)幼苗存活及生长对沙埋和供水的反应。结果表明:适量的沙埋(0.25H-0.50H沙埋,H为苗高)与供水(柠条50mm/月,羊柴75mm/月)可以促进幼苗生长,过量的沙埋与供水则会抑制生长甚至导致幼苗死亡。柠条幼苗在50mm/月供水,0.25H、0.50H沙埋,羊柴幼苗在75mm/月供水,0.25H、0.50H沙埋下具有较高的相对生长速率和净同化速率;幼苗在1.0H和1.25H沙埋下全部死亡。供水量较小、沙埋较浅时,两种植物根冠比均较高;当供水量最大时,柠条幼苗根冠比在沙埋最深和没有沙埋时较大,而羊柴幼苗根冠比仍在没有沙埋时最高。     

水分共享在毛乌素沙地4种灌木根系中的存在状况

为揭示水分共享在毛乌素沙化草地4种沙生灌木根系中的存在状况,选择酸性品红为示踪剂开展野外实验。结果表明,只有沙地柏（Sabina vulgaris)和油蒿（Artemisia ordosica）根系具有共享水分的潜力,而沙柳Salix psammophaila)和杨柴（Hedysarum mongolicum)根系不具有这种潜力。基于酸性品红在细根中的存在状况以及沙子与酸性品红发生中和反应,被步认为沙地柏和油蒿根系可能具有提水作用潜力。     

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Aims Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China.Methods Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated.Important findings PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.     

毛乌素沙地4种沙生植物种子萌发及出苗对沙埋及单次供水的响应

飞播固沙作为一项快速而有效的现代化治沙措施,已成为毛乌素沙地植被恢复与重建的重要手段。但此项技术仍存在一些问题,如飞播后成苗率较低等。以毛乌素沙地优势植物柠条（Caragana korshinskii）、羊柴（Hedysarum laeve）、油蒿（Artemisia ordosica）与籽蒿（Artemisia sphaerocephala）为研究对象,人工控制7个沙埋深度和9个水分梯度,研究4种植物种子萌发和幼苗出土对沙埋和单次供水的响应,阐明多大的单次降雨才能保证种子萌发与幼苗出土及出土幼苗的维持时间。结果表明,对于柠条和羊柴质量相对较大的种子而言．种子主要在供水量10．20mm,埋藏深度为0．5．2cm的条件下出苗,但在埋藏深度为5cm时这两个物种仍有少量种子能够出苗;而对于油蒿和籽蒿质量相对较小的种子而言,种子主要在供水量10．20mm,埋藏深度为0．5cm时出苗,当埋藏深度为1．5cm和2cm时不能顺利出苗。沙埋深度0．5cm条件下,4个物种具有最高的出苗率和出苗速率。在试验期内（30d）,柠条、羊柴和油蒿出土幼苗分别在单次供水量为5、7．5mm和7．5mm时全部死亡,在单次供水量高于15mm时4个种的出土幼苗死亡率大多低于50％,且随供水量的增加出土幼苗死亡率降低。结合毛乌素沙地降雨特点与本次实验结果,0．5cm的沙埋及7．5mm以上的单次降雨是上述4种植物自然条件下出苗较好的重要条件。     

Testing experimentally the effect of soil resource mobility on plant competition

Aims The volume of soil beyond a plant's roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil. For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility. We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition. In the first, the exchange of rhizosphere water and dissolved nutrients between two connected pots, each containing one plant, was manipulated by alternately raising and lowering the pots. In the second experiment, the roots systems of two competing plants were separated by partitions of differing porosity, thereby varying the plants' access to water and nutrients in the other plant′s rhizosphere. In this second experiment, we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided, and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments, lower mobility reduced competitive effects on plant biomass and on relative growth rate (RGR), as hypothesized. In the second experiment, however, competition was more intense under high nutrient input, suggesting that low nutrient supply rates reduced the strength of the superior competitor. Competitive effects on RGR were only evident under the low water level, suggesting that under lower nutrient concentrations, competitive effects might be less pronounced. Taken together, our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.     

EFFECTS OF AM FUNGI AND WATER STRESS ON DROUGHT RESISTANCE OF ARTEMISIA ORDOSICA IN DIFFERENT SOILS

 利用两种不同土壤研究了水分胁迫和接种AM真菌(摩西球囊霉(Glomus mosseae)和油蒿(Artemisia ordosica)根际土著AM真菌)对毛乌素沙地重要演替物种油蒿生长和抗旱性的影响。结果表明, 两种土壤中水分胁迫没有显著影响油蒿的植株形态和含水量, 但严重抑制了菌根侵染率。水分胁迫促使油蒿提高叶片保水能力, 抑制N、P在地上部的分配。在胁迫前期SOD活性较高, 而POD活性在后期较高。同一水分条件下接种AM真菌显著提高了AM真菌侵染率, 土壤中孢子数显著增多, 提高了植株分枝数并促进侧根发育, 显著提高根冠比和植株保水能力, 加强了根系对全磷、全氮的吸收。接种AM真菌的植株可溶性糖和丙二醛含量较低, 可溶性蛋白含量无显著变化, SOD和POD活性提高, 油蒿抗旱性加强。水分胁迫下在不同土壤中接种不同AM真菌对油蒿的促进效应差异较大, 接种土著AM真菌的效果优于摩西球囊霉单一接种。干旱导致菌根侵染率下降是宿主植物吸水能力下降的原因之一, 在植物生长前期接种AM真菌可以增强植物抵抗生长中后期环境干旱的能力。     

荒漠生境油蒿根围AM真菌多样性

为了阐明荒漠生境主要植被油蒿(Artemisia ordosica)根围AM真菌多样性, 2007年8月从毛乌素沙地和腾格里沙漠选取榆林、盐池、研究站和沙坡头4个样地, 按0–10、10–20、20–30、30–40、40–50 cm 5个土层采集油蒿根围土壤样品, 研究了油蒿根围AM真菌物种多样性和生态分布。在分离的4属28种AM真菌中, 球囊霉属(Glomus)16种, 无梗囊霉属(Acaulospora)7种, 盾巨孢囊霉属(Scutellospora)4种, 多孢囊霉属(Diversispora)1种。4个样地的共同优势种为摩西球囊霉(G. mosseae), 共同常见种为双网无梗囊霉(A. bireticulata)和网状球囊霉(G. reticulatum), 共同稀有种为缩球囊霉(G. constrictum)。地球囊霉(G. geosporum)仅出现在盐池, 蜜色无梗囊霉(A. mellea)、帚状球囊霉(G. coremioides)、浅窝无梗囊霉(A. lacunosa)和宽柄球囊霉(G. magnicaule)仅出现在研究站, 黑球囊霉(G. melanosporum)仅出现在榆林。盐池与研究站样地AM真菌种类最多, 榆林样地孢子密度最大, 沙坡头样地种类和孢子密度显著偏低。总体上, 孢子密度、分离频度、相对多度和重要值依Glomus >Acaulospora > Scutellospora> Diversispora呈现显著减小趋势。结果表明, 油蒿与AM真菌之间有良好共生性, 这对进一步利用菌根生物技术维护荒漠生态系统结构的完整性具有重要意义。     

毛乌素沙地飞播植被与生境演变的研究

飞播造林作为沙地大面积绿洲化的有效的手段，已在毛乌素沙地中运用并取得了显著的成效。本文根据伊金霍洛旗４个播区飞播后十余年的调查资料，分析了杨柴灌丛群落动态变化的特点以及演替的机制，并指出沙地土壤水分生境的改变是群落发生演替的主要原因。随着生境的变化，群落的演替可分为４个阶段：先锋植物群落、杨柴群落、油蒿群落和黑格兰、沙地柏、蒙古莸和柠条等中旱生灌丛群落阶段。为了防止杨柴群落的进一步演替或退化，确保这一人工草场的质量，对群落演替的合理人为干扰，是必要的。     

毛乌素沙地南缘沙柳灌丛土壤水分及水量平衡

以毛乌素沙地南缘沙柳人工固沙灌丛为研究对象,对不同栽植密度(0.2、0.6和0.8株·m-2)沙柳灌丛生长季土壤水分动态和蒸散量变化进行研究.结果表明:不同栽植密度沙柳灌丛区土壤水分动态和蒸散量存在明显差异,土壤含水量随着栽植密度增加呈单峰型曲线;生长季内沙柳灌丛土壤含水量变化呈“S”形曲线,并与降雨存在密切的关系.蒸散量以栽植密度0.8株·m-2的沙柳灌丛最高(114.5 mm),占同期降雨量的90.8％;以0.6株·m-2的沙柳灌丛最低(109.7 mm).根据生长季土壤水分动态和水分平衡特征,毛乌素沙地南缘沙柳灌丛适种密度为0.6株·m-2.     

Comparative study on spatial patterns of the Artemisia ordosica population in the Mu Us sandy land

Artemisia ordosica is an under-shrub species, which dominates the vegetation of the Mu Us sandy land in North China. The spatial patterns of the A. ordosica population in different sandy lands were compared with the methods of Spatial Auto-correlation Analysis, Semi-variance Analysis and Nine-Term Local Quadrat Variance (9TLQV). The results show that, by contrast with the A. ordosica population in fixed sandy land, the population in semi-fixed sandy land is of stronger auto-correlation and greater spatial heterogeneity, and meanwhile it presents more intense differentiation between patches and gaps. The spatial patterns of the A. ordosica population in semi-fixed sandy land are probably governed by drifting sand caused by strong winds. Drifting sand can easily put A. ordosica shrubs to death unless they live together in form of A. ordosica patches, where the distances between shrubs are short. In semi-fixed sandy land, patches are not only the form of the A. ordosica population to survive drifting sand, but also the foundation of the A. ordosica population to develop and broaden the area. The A. ordosica population is supposed to broaden the area through edge extending out from the patches scattering in semi-fixed sandy land. The spatial patterns of the A. ordosica population in fixed sandy land are possibly affected by intra-specific competition related to high plant coverage. This study is ecologically useful to improve the practice of vegetation restoration in sandy land. When transplanting A. ordosica shrubs to bare sandy land, one had better arrange them in form of patches separated by gaps, which can promote the survival of transplanted shrubs, and also help to take advantage of A. ordosica patches to revegetate bare gaps.     

Comparative study on spatial patterns of the Artemisia ordosica population in the Mu Us sandy land

Artemisia ordosica is an under-shrub species, which dominates the vegetation of the Mu Us sandy land in North China. The spatial patterns of the A. ordosica population in different sandy lands were compared with the methods of Spatial Auto-correlation Analysis, Semi-variance Analysis and Nine-Term Local Quadrat Variance (9TLQV). The results show that, by contrast with the A. ordosica population in fixed sandy land, the population in semi-fixed sandy land is of stronger auto-correlation and greater spatial heterogeneity, and meanwhile it presents more intense differentiation between patches and gaps. The spatial patterns of the A. ordosica population in semi-fixed sandy land are probably governed by drifting sand caused by strong winds. Drifting sand can easily put A. ordosica shrubs to death unless they live together in form of A. ordosica patches, where the distances between shrubs are short. In semi-fixed sandy land, patches are not only the form of the A. ordosica population to survive drifting sand, but also the foundation of the A. ordosica population to develop and broaden the area. The A. ordosica population is supposed to broaden the area through edge extending out from the patches scattering in semi-fixed sandy land. The spatial patterns of the A. ordosica population in fixed sandy land are possibly affected by intra-specific competition related to high plant coverage. This study is ecologically useful to improve the practice of vegetation restoration in sandy land. When transplanting A. ordosica shrubs to bare sandy land, one had better arrange them in form of patches separated by gaps, which can promote the survival of transplanted shrubs, and also help to take advantage of A. ordosica patches to revegetate bare gaps.     

Interactions of the indigenous evergreen shrub Sabina vulgaris with coexisting species in the Mu Us sandland

Aims Facilitation is widespread in plant communities and particularly common in highly stressful environments. In the semi-arid Mu Us sandland where soil water and nutrients are short and grazing is heavy, many species grow within the large patches formed by the dense individuals of the unpalatable clonal shrub Sabina vulgaris, the only natural evergreen shrub species in the Mu Us sandland. However, the interactions between S. vulgaris and these coexisting species remain unclear, and we hypothesize that S. vulgaris can facilitate at least some species because within the patches vegetation is not grazed and soil water and nutrients may also be higher.Methods We measured the maximum height, coverage and number of individuals of each vascular species, little cover and thickness of biological crust at the soil surface in 1 m × 1 m plots in three types of microsites associated with 40 patches of S. vulgaris : (i) at the center, (ii) at the inner edge and (iii) outside the patches. We also took soil samples and measured soil water content and content of total N, P, K and organic matter.Important findings Soil water, nitrogen, organic matter and litter cover were the highest at the patch center, lowest outside the patches and intermediate at the inner edge of the patches, whereas thickness of biological crust was greater outside than at the center or at the inner edge. Among the 32 species recorded, six species preferred to occur within the patches, suggesting that S. vulgaris can facilitate these species most likely by grazing exclusion, increasing water and/or nitrogen resources in soil. However, most (19) species did not show preference and seven preferred outside. Also, species richness, pooled cover and number of individuals of all species were greater outside than within the patches, and such effects did not vary with the size of the S. vulgaris patches. These results suggest that the dominant interactions between S. vulgaris and the coexisting species are competition. The findings add to our knowledge that facilitation can be shown even when the competitive effects from the potential nurse plants are very strong.     

沙地樟子松人工林土壤理化性质与微生物生物量的动态变化

为揭示不同林龄沙地樟子松人工林土壤理化性质和微生物生物量的动态和相互关系,以毛乌素沙地、科尔沁沙地和呼伦贝尔沙地不同林龄樟子松人工林为对象,分析土壤理化性质、土壤微生物生物量碳和微生物生物量氮变化规律。结果表明:樟子松人工林土壤理化性质随林龄增加在不同沙地中表现不同,毛乌素沙地土壤容重和养分含量明显降低,科尔沁沙地土壤孔隙度和养分含量明显升高,呼伦贝尔沙地土壤养分则呈现先增加后降低趋势。与土壤理化性质变化趋势类似,毛乌素沙地樟子松人工林土壤微生物生物量氮随着林龄的增加而降低,科尔沁沙地土壤微生物生物量氮随着林龄的增加而升高,呼伦贝尔沙地土壤微生物生物量氮随着林龄的增加呈先增加而后降低趋势。影响毛乌素沙地、科尔沁沙地和呼伦贝尔沙地土壤微生物生物量碳、氮的主要因子分别是硝态氮、铵态氮和有机质含量。毛乌素与科尔沁沙地樟子松人工林主要限制因子为土壤氮,而呼伦贝尔沙地樟子松受土壤有机碳限制较强。     

Determinants of pollen dispersal in the East Asian steppe at different spatial scales

Two sites from the East Asian steppe, the Mu Us Sandland as a regional case and the Anguli Nuur catchment as a local one, were chosen to detect roles of vegetation, climate, landform, and human disturbance on pollen dispersal. 1) Vegetation: The semi-arid steppe vegetation is characterized by Artemisia and Chenopodiaceae pollen under various vegetation conditions; however, no evident correlation between pollen percentages and corresponding plant species cover is found. 2) Climate: Samples under different Mean Annual Precipitations (MAPs) clearly distinguish themselves in the Mu Us Sandland, implying MAP-determined surface pollen spectra in regional scale. 3) Landform: Surface pollen assemblages in the azonal psammophytic vegetation and lowland meadow, show insignificant variance from the zonal steppe vegetation. The azonal halophilous vegetation, mostly distributed in the lowland or near the lake shore, leads to higher than average percentages of Chenopodiaceae pollen. Signal of exotic Pinus pollen is also strengthened in the lowland and lake sediment. 4) Human disturbance: The role of human disturbance on surface pollen assemblages is weak, as shown in the Mu Us Sandland.

This study also provides theoretical bases for quantitative reconstructions of palaeoclimate and palaeovegetation based on fossil pollen spectra from lake sediments and lowland soils in the semi-arid East Asian steppe. We suggest that calibration against locally dispersed pollen taxa is necessary to reliably reconstruct changes in vegetation pattern through time, for example, a factor of 1.75 for the widely used A/C (Artemisia/Chenopodiaceae) ratio is suggested according to the pollen assemblages in the surface layers of the lake sediment vs. slope soil in Anguli Nuur. However, uncertainties also exist for such calibration considering the dynamics of local-scale azonal vegetation.     

Effect of shade on the growth and mineral nutrition of a C4 perennial grass under field conditions

The effect of shading by a shrub legume on the growth and nutrient uptake of a C4 tropical grass was studied during four regrowth cycles. Regrowth periods were characterised by contrasting soil water availability. Dichanthium aristatum (Poir.) C. E. Hubbard swards were grown in full sun and under Gliricidia sepium (Jacq.) Walp. and Leucaena leucocephala (Lam.) de Wit with a light transmission level ranging from 80 to 30% of the incoming photosynthetically active radiation (PAR), depending on shrub regrowth. A treatment with high N and water supply was included in one of the cycles to quantify the effect of shade alone on potential growth.Aboveground biomass (DM) and leaf area index (LAI) of swards were not depressed by the reduction of incoming PAR. The reduction in transmitted PAR by shrubs was compensated by an increase in the radiation use efficiency (RUE) of shaded swards. Higher RUE of unfertilised, shaded stands may be explained by higher levels of N availability in the soil. This is supported by the analysis of curves relating sward N accumulation to sward DM accumulation. In fact, for similar measured biomass the accummulated N was higher in shaded stands, a consequence of their higher N concentrations. This allowed shaded leaves to improve their CO2 assimilation rates on a leaf area basis. Higher RUE reported on shaded stands may be the consequence of higher leaf CO2 assimilation rates and also possible changes in the shoot:root ratio. As with N, the amount of K taken up by the sward was higher under shade, whereas P data were higher under shade only during the driest cycle. A positive water balance, alone or in combination with high N fertilisation, eliminated the improvement of the N nutrition of shaded stands. Thus, the positive effects of shade may be only observed when N and water are limiting sward growth in the open.     

Responses of Hedysarum Laeve, a guerrilla clonal semi-shrub in the Mu Us sandland, to local sand burial

In arid and semi-arid inland deserts,one of the environmental stresses for plants is recurrent sand burial,which can influence the physical and biotic microenvironments of the plants and soil.Previous studies have shown that different levels of sand burial have different effects on plants.Slight sand burial could increase the height increment,leaf biomass and the number of new ramets of the plants while heavy sand burial could impair the growth of the plants and even decrease their chances of survival.In other words,below a certain threshold level of burial,the growth of plants is stimulated probably because of multiple factors.However,as the level of burial increases,the positive response starts to decline until it becomes a negative value.Arid and semi-arid inland deserts are frequently colonized and stabilized by many rhizomatous clonal plants.Clonal physiological integration often helps clonal plants buffer local environmental stress encountered by ramets.A rhizomatous clonal semishrub,Hedysarum laeve (H.laeve),is the dominant plant species and important for vegetation restoration in the Mu Us sandland.To investigate whether clonal integration can increase the threshold of sand burial and help rhizomatous H.laeve tolerate heavy sand burial,we conducted a field experiment.The results showed that slight sand burial could accelerate ramet growth and enhance leaf biomass,stem biomass and shoot biomass,while heavy sand burial reducesed the biomass of the plant and impairs survival and growth of the ramets.Clonal integration increased the threshold of sand burial.Under heavy sand burial,ramets connected to other ramets not buried in sand were more in terms of height increment,stem biomass,leaf biomass and shoot biomass compared to the ramets encountering sand burial but disconnected from other ramets.It suggested that clonal physiological integration could help H.laeve ramets tolerate relatively heavy sand burial.We also discussed that clonal integration plays a role in H.laeve presence in the Mu Us sandland.     

毛乌素沙地半固定沙丘油蒿种群对土壤湿度空间异质性的响应

将统计学和地统计学方法相结合,探讨了毛乌素沙地半固定沙丘土壤湿度空间异质性与油蒿种群空间异质性之间的关系. 结果表明,在块尺度（80 m×80 m）上,油蒿密度和生物量的空间异质性受制于土壤湿度的空间异质性,尤其油蒿生物量的空间异质性与土壤湿度的空间异质性呈显著正相关关系.表明在半固定沙丘阶段,土壤湿度的空间异质性决定油蒿种群的空间异质性. 由于沙丘地形对降水量的再分配在土壤湿度分布中的作用,土壤湿度和油蒿种群空间异质性相互作用的结果为地形的缀块性→土壤湿度分布的缀块性→油蒿种群分布的缀块性→油蒿生物量和密度的缀块性.     

Effects of biological soil crusts on profile distribution of soil water,organic carbon and total nitrogen in Mu Us Sandland,China

Aims Biological soil crusts (BSCs) can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems. Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer. Thus, little is known about effects of BSCs on properties throughout the soil profile. In the current study, we assessed the effects of BSCs on the distribution of soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) throughout the soil profile as well as the influence of water conditions on the effects of BSCs.Methods In a field investigation in Mu Us Sandland, North China, soil samples were taken from plots with and without BSCs on 13 and 28 September 2006, respectively. On the two sampling dates, average soil gravimetric water content was 3.83% (±1.29%) and 5.08% (±0.89%), respectively, which were regarded as low and high water conditions. Soil samples were collected every 5 cm to a depth of 60 cm, and SW, SOC and STN were measured in the laboratory.Important findings (i) BSCs affected profile distribution of SW, SOC and STN. In addition, water conditions within the plots significantly modified BSCs' effects on the profile distribution of SW, but marginally affected the effects on SOC and STN. (ii) Under high water conditions, SW in the surface soil layer (0–10 cm) was higher in soils with BSCs compared to those without BSCs, while the opposite was true in the deep soil layer (30–55 cm). (iii) Under low water conditions, SW was lower with BSCs compared with no BSCs in near-surface (5–20 cm) and deep (25–40 cm) soil layers. (iv) BSCs affected SOC and STN only in the surface soil layer (0–5 cm) and were modified by plot water conditions.     

Low rainfall-induced shift in leaf trait relationship within species along a semi-arid sandy land transect in northern China

It is unclear whether the shift in leaf traits between species of high- and low-rainfall sites is caused by low rainfall or by species replacement, because leaf traits vary substantially among species and sites. Our objective was to test if the within-species relationship between specific leaf area (SLA) and leaf N concentration (N(mass) ) shifts across a rainfall gradient in the semi-arid sandy lands of northern China. Data for SLA and N(mass) of dominant species and related canopy and soil variables were collected from 33 plots along a rainfall transect (270-390 mm) having similar temperatures in the Mu Us, Inner Mongolia. We further investigated the generality of Mu Us data using 12 additional plots in the southeastern Qaidam Basin, Qinghai. Artemisia ordosica is a widespread species in both regions. Across and within species, the positive SLA-N(mass) relationship shifted between two plant groups in the lowest rainfall plots (270 mm) and other higher rainfall plots (320-390 mm), which was confirmed by additional data from Qinghai. For A. ordosica populations, leaf area index (LAI) decreased and N(mass) increased with decreasing rainfall, while the foliage N pool and SLA varied little. Rainfall was the limiting factor that determined variations in N(mass) and LAI. Accordingly, N(mass) /SLA ratios continually increased with decreasing LAI along the rainfall gradient (r = -0.76, P < 0.001). Results indicate a low rainfall-induced shift in the SLA-N(mass) relationship associated with changes in LAI and foliage N pool, suggesting a link between leaf characteristics and ecosystem function.     

光和水分胁迫对臭柏实生幼苗光化学效率及色素组成的影响

为探明毛乌素沙地3年生臭柏(Sabina vulgaris)实生苗在不同光照和水分条件下的光抑制响应机制,研究了各处理臭柏实生苗的最大光化学效率(F_v/F_m)及叶绿素(Chla+Chlb)和叶黄素(A+V+Z)含量,分析了其叶绿素循环和叶黄素循环的变化规律。结果表明,77%透光区通过减少Chlb含量,升高Chla/Chlb,避免光能过剩;同时,增加A+V+Z及热散逸色素(A+Z)含量、提高(A+V+Z)/(Chla+Chlb)和(A+V)/(A+V+Z)值,耗散过剩光能,避免光破坏。25%透光区的叶绿素和叶黄素循环机制随着水分条件的变化迅速发生改变。10%透光区通过增加Chlb含量,降低Chla/Chlb,捕捉更多的光能,几乎不存在光抑制。毛乌素臭柏实生幼苗能够适应不同的光照和水分条件,在恶劣的沙漠中完成天然更新,形成独特的群落景观,与叶绿素循环和叶黄素循环有着密切的关系。