The photosynthetic niche breadth of several desert shrubs and their potential ecological significance

The combination of niche theories and plant ecophysiology may show a link between macroscopic ecology and microscopic physiology. The experiment simulated three rainfall treatments representing the minimum, average and maximum annual precipitation found in the Shapotou area. The net photosynthesis rate (P_n) of four dominant desert shrubs (Reaumuria soongorica maximum, Salsola passerina Bge., Artemisia ordosica Krasch. and Caragana korshinskii Komar.) that grow in the arid zone in Northwest China was measured, together with the available environmental resources, photosynthetically active radiation (PAR), air temperature (CT) and volumetric soil moisture (SW). Based on these data and means derived from the Levins niche breadth index, this study calculated the photosynthesis – PAR niche breadth (PB_i), the photosynthesis – CT niche breadth (TB_i) and the photosynthesis – SW niche breadth (WBi) of the four shrubs. The results showed that PAR was not a directly limiting factor on growth and survival of the four shrubs and the values for PB_i were consistent either with the PAR response ranges (R. soongorica and S. passerina) or with the values for P_n (A. ordosica and C. korshinskii), although the values for PB_i between the four desert shrubs varied. In accordance with the calculated TB_i values, the CT tolerance ranges for photosynthesis also varied among the four desert shrubs. The lowest SWs that stopped photosynthesis varied amongst the four shrubs, and the lower the SW was: the wider the response range and the higher the WBi value. The photosynthetic niche breadth and the photosynthetic response ranges of the four shrubs were in agreement with their ecological breadth and geographic distributions. Thus, some micro-mechanisms can be explained using these relationships such as floral evolution, succession and the varietal development processes of the plant communities of R. soongorica – S. passerine and A. ordosica Krasch. – C. korshinskii Komar. It is also possible to account for the physiological changes that occur in each plant by calculating the photosynthetic niche breadth. These results show that this research methodology can be extended to niche theory and promote the practicality of plant physiological ecology as well as provide new ideas for the study of plant ecology.     

24种十字花科短命植物的扩散体特征与扩散对策

对准噶尔荒漠中24种十字花科短命植物的扩散体特征与扩散对策的观测结果表明:种间果实和种子的形态各异,角果开裂与否与其木质化程度有关。木质化程度较高的角果不开裂。其中长角果以果节为扩散单元自体扩散。而短角果有两种扩散单元,以果实为扩散单元的无辅助扩散结构或具翅或绵毛,分别进行自体或风媒扩散;以果序的一段为扩散单元的果实具坚硬呈勾状的喙,通过果序梗断裂或附在动物体表散布,兼具自体扩散和动物体外传播的二重性。木质化程度较低的角果开裂,以种子为单元扩散。其中微尘状种子无辅助扩散结构,在果皮开裂时产生的张力或风力的作用下散布;粘液种子以水媒为主,兼具风媒和动物传播的特点;粘液和翅并存的种子具有风媒和水媒扩散的二重性。果翅等辅助扩散结构有利于长距离散布,绵毛及种皮粘液使果实或种子与地表能更好地粘附,木质化结构及种皮粘液还具有保水和保护作用。从扩散的时空特征看,24种植物在扩散持续时间上有集中扩散和持续扩散两种方式,前者避免了种子干旱失水和被捕食,属逃逸对策;后者形成空气种子库逐批扩散,属保护对策。从空间上,异果芥(Diptychocarpus strictus)果序上、下部果实的开裂方式与时间、种子形态完全不同,导致其扩散时间与距离不同;离子芥(Chorispora tenella)等类群果实不同部位的果节非同步脱落以及爪花芥(Oreoloma sulfureum)果实上、下部木质化程度及开裂方式不同,导致其果节或种子的扩散时间不同。以上这些特征对于它们在荒漠环境中成功地扩散、定居,抵御干旱、逃避捕食,避免同胞种子间的竞争、保障物种延续并扩大种群等,具有重要的生态学意义。     

沙漠地区盐水灌溉对牧草产量及品质的影响

在以色列南部内盖夫沙漠农业实验站 ,采用较为先进的双管重叠水喷灌系统 ,研究了不同浓度盐水灌溉下狗牙根 (CynodondactylonL .) 6个品种的 (Suwannee、Coastcross、Tifton4 4、Tifton6 8、Tifton78、Tifton85 )牧草产量、粗蛋白、灰分、纤维素含量的变化 ,同时 ,采用较为先进的瘤胃胃液消化法分析了不同盐水灌溉的牧草干草在山羊体内的消化率 .结果表明 ,在Eci小于 10ds·m-1条件下 ,6个狗牙根品种维持较高产草量 ,尤其是Eci=4 .4ds·m-1,Coastcross、Suwannee、Tifton4 4、Tifton6 8、Tifton78和Tifton85的产量分别较淡水 (Eci=1.2 )灌溉的产量增加了 14 1%、6 1.1%、136 %、12 1.2 %、2 0 2 .3%和 10 9.7% ,干物质产量也随灌溉水盐浓度增加而提高 ,而牧草纤维素含量无明显增加 .饲养及消化实验表明 ,盐水灌溉的干草更为山羊喜食 ,干草消化率也随灌溉水盐浓度增加而增加 ,表明适当浓度的盐水灌溉不仅不会引起牧草产量下降 ,而且可提高牧草品质和喜食性 ,在农业和牧业上具有重要应用前景     

Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (<Emphasis Type="Italic">Ericameria nauseosa:</Emphasis> Asteraceae)

In heterogenous landscapes, seeds settle in some microsites more readily than others, independently of whether those microsites are suitable for germination and subsequent growth, and survival of seedlings. Wild seeds and seedlings of Ericameria nauseosa var. oreophila in the sand-dune ecosystem near Mono Lake, California show both concordance and conflict in where seeds are retained and where seedlings flourish. Using a field experiment, we followed performance of seeds and seedlings (i.e., the rate of germination and successful emergence, initial seedling size, seedling growth and survival over first growing season), by planting seeds of known sizes in pre-identified microsites (windward and lee aspects of interspaces between shrubs, under shrub canopies, and under snag canopies, respectively). Heavier seeds were more likely to germinate and emerge successfully and resulted in initially larger seedlings than lighter seeds. These initially larger seedlings subsequently remained larger over the growing season and lived longer than initially smaller seedlings. Independent of seed and initial seedling size, seedlings that germinated under the canopy of adult shrubs grew larger and survived longer than seedlings that germinated in interspaces (open space with little or no vegetation) or under snags (dead adult shrubs). Seedlings grown under the canopy of adult shrubs experienced significantly less solar radiation and wind-deposited sand than seedlings grown in interspace or snag microsites. Sand burial more than 1 cm was lethal for seedlings. The two variables of seed size and microsite type had by far greater impact on eventual growth and survival of seedlings than did aspect, and the effects of the former two variables were independent of each other. This study amplifies the body of work on E. nauseosa at this site demonstrating that the earliest events in the life history of this long-lived perennial shrub appear to persist through time despite the harsh and variable environment.     

内蒙古浑善达克沙地小毛足鼠的能量代谢和体温调节

为了解小毛足鼠对沙漠生境的适应特征,对其能量代谢和体温调节特征进行了测定。代谢率采用封闭式流体压力呼吸计测定,非颤抖性产热用皮下注射去甲肾上腺素诱导,能量摄入采用食物平衡法测定。结果显示:小毛足鼠的热中性区为25～33℃,平均体温为35 7±0 1℃,最小热传导率为0 21±0 01mlO2/g·h·℃,基础代谢率为2 61±0 04mlO2/g·h,最大非颤抖性产热为8 53±0 28mlO2/g·h,非颤抖性产热范围(最大非颤抖性产热与基础代谢率的比率)为3 3。基础代谢率和非颤抖性产热都高于以体重为基础的期望值,最小热传导接近期望值。小毛足鼠的摄入能为2 26±0 12kJ/g·d;消化能为2 18±0 13kJ/g·d;消化率为97±0 2%;可代谢能为2 13±0 12kJ/g·d;可代谢能效率为94±1 2%。这些结果表明小毛足鼠对沙地生境的适应特征是:基础代谢率较高,体温相对较低,最小热传导率与期望值相当,热中性区较宽,下临界温度较低;较高的最大非颤抖性产热和非颤抖性产热范围以及较高的食物消化效率。     

古尔班通古特沙漠南部短命植物群落物种多样性及空间分异

短命植物是早春多雨、夏季干热环境而形成的特殊植物类型,古尔班通古特沙漠南部是短命植物集中分布区,对保持沙漠稳定、防风固沙起到重要作用.目前对短命植物群落多样性、生态功能以及空间分布等研究较少.本研究采用分层抽样方法,调查分析了古尔班通古特沙漠南部35个样点3.86×104m2的短命植物多样性特征.共发现93个物种,分属...     

温带荒漠生物土壤结皮微生物群落结构与功能演替研究综述

生物土壤结皮(biological soil crusts,BSC)在荒漠植被的恢复及稳定性维持方面发挥了重要作用,被誉为“荒漠生态系统工程师”。BSC微生物群落是其发挥功能的主要成分,参与了BSC的形成、土壤性状的改善、土壤团聚体的稳定及植被的发育等过程。由于技术方法的限制,以往对BSC微生物群落发育如何调控荒漠植被稳定性的机理尚不清楚。近年来,随着土壤微生物组学技术的快速发展,BSC微生物群落组成及其功能的研究取得了较大进展,关于BSC微生物群落对荒漠生态系统贡献的认识日渐清晰。本文总结了温带荒漠BSC演替过程中微生物不同类群细菌、真菌、古菌群落的组成结构及参与碳氮循环的潜在功能变化,并对影响微生物群落结构和功能的土壤因素进行了剖析,阐释了BSC微生物群落与土壤功能性状相互作用及协同演替的模式,厘清了BSC促进荒漠土壤改善的机理,为温带荒漠植被恢复及荒漠生态系统对全球贡献的理解提供了依据。     

库姆塔格沙漠南缘植物物种丰富度格局及主要影响因素

通过对库姆塔格沙漠南缘植被进行实地调查,对该地区植物物种丰富度及其群落组成进行研究,并选取11个影响物种丰富度的气候因子和地形因子,利用PCA分析、方差分解等方法探讨气候、地形因子对物种丰富度的影响。结果显示：该区共有植物15科32属38种,植物群落种类匮乏,物种组成单一,植物生活型主要以灌木、多年生草本为主,占所有物种的80%以上;植物物种丰富度与植物群落组成明显受到水热条件的制约。回归分析结果表明,该区物种丰富度与能量因子呈显著负相关（P<0.05）,而与水分因子呈显著正相关（P<0.05）。方差分解结果表明,水分、能量共同制约了该地区的物种丰富度,二者的共同解释率为44.3%。此外,地形因子对研究区物种丰富度也存在一定影响,能进一步提高环境因子对物种丰富度的解释率。总之,库姆塔格南缘物种组成单一、物种丰富度格局受到水热条件的共同制约,同时地形的变化也有重要影响。     

The mycorrhizal status of Welwitschia mirabilis

This is the first report of the mycorrhizal status of Welwitschia mirabilis, a gymnosperm endemic to the Namib Desert. Like all other gymnosperms except the Pinaceae and Gnetaceae, W. mirabilis is associated with vesicular-arbuscular mycorrhizal (VAM) fungi. Mycorrhizal colonization of roots and the diversity and abundance of VAM species were determined at seven sites. Six sites received annual rainfall of 0–100 mm, varying widely from year to year. The seventh site experienced more predictable annual rainfall of 150–200 mm. Perennial vegetation was sparse at the six low-rainfall sites. Dry annual grasses from previous rain events were present at only three of these six sites and mean mycorrhizal colonization levels of W. mirabilis at these three sites were as high as 18%. W. mirabilis was not mycorrhizal at sites where grasses were absent. The seventh site, receiving higher rainfall, supported small trees and annual grasses in addition to W. mirabilis. Mycorrhizal colonization levels of W. mirabilis at this site were significantly higher than at the other six sites, closely paralleling those of the surrounding annual grasses. The mycorrhizal flora of W. mirabilis consisted of four Glomus species. These taxa were not unique to W. mirabilis, having been found with Stipagrostis and Cladoraphis grasses throughout the Namib and Kalahari deserts.     

Evidence for mutualism between a flower-piercing carpenter bee and ocotillo: use of pollen and nectar by nesting bees

Abstract.

• 1 Carpenter bees (Xylocopa californica arizonensis) in west Texas, U.S.A., gather pollen and ‘rob’ nectar from flowers of ocotillo (Fouquieria splendens). When common, carpenter bees are an effective pollen vector for ocotillo. We examined ocotillo's importance as a food source for carpenter bees.
• 2 The visitation rate of carpenter bees to ocotillo flowers in 1988 averaged 0.51 visits/flower/h and was 4 times greater than that of queen bumble bees (Bombus pennsylvanicus sonorus), the next most common visitor. Nectar was harvested thoroughly and pollen was removed from the majority of flowers. Hummingbird visits were rare.
• 3 Pollen grains from larval food provisions were identified from sixteen carpenter bee nests. On average, 53% of pollen grains sampled were ocotillo, 39% were mesquite (Prosopis glandulosa), and 8% were Zygophyllaceae (Larrea tridentata or Guaiacum angustifolium). Carpenter bee brood size averaged 5.8 per nest.
• 4 We measured the number of flowers, and production of pollen and nectar per flower by mature ocotillo plants, as well as the quantity of pollen and sugar in larval provisions. An average plant produced enough pollen and nectar sugar to support the growth of eight to thirteen bee larvae. Ocotillo thus has the potential to contribute significantly to population growth of one of its key pollinators.
• 5 Although this carpenter bee species, like others, is a nectar parasite of many plant species, it appears to be engaged in a strong mutualism with a plant that serves as both a pollen and as a nectar source during carpenter bee breeding periods.