Satellite imagery, tsetse and trypanosomiasis in Africa

This paper describes the application of remote sensing to studies on the African trypanosomiases causing sleeping sickness in man and ‘nagana’ in domestic animals. After giving some biological background to the problem, an important relationship between the risk of infection of domestic animals, tsetse fly numbers and fly infection rates is presented. An understanding of the latter leads to a prediction of risk in cattle. The problems of analysing and interpreting the distribution and abundance patterns of flies are explored, and a mortality climogram approach is described in which the important meteorological variables appear to be temperature and saturation deficit. This approach, which can be applied to data collected at only very few sites, leads to extensive predictions of the distributional limits of the tsetse Glossina morsitans Westwood. These predictions are supported by the known distribution of this species throughout Africa.

A similarity noted between published whole-Africa normalised difference vegetation indices (NDVI) and tsetse distribution leads to an exploration of the usefulness of NDVI for such vector studies. The likely information content of the images is identified through principal component analysis, and correlations are shown between NDVI values and annual temperature, saturation deficit and rainfall figures for more than 300 sites throughout the sub-Saharan region of the continent. NDVI values are highly correlated with both saturation deficit and rainfall figures.

Significant correlations are shown between vector mortality rates and mean monthly NDVI values, and between the physical size of the vectors (known to reflect the mortality rates affecting the parental population) and NDVI along an approximately 700 km transect across a whole range of eco-climate conditions in West Africa. Reasons are suggested for the localisation of human sleeping sickness to just one of several regions sampled by the transect.

Finally, seasonal changes in case numbers of human sleeping sickness in both Uganda and Kenya are correlated with mean monthly NDVI from the areas concerned. The first of these correlations is negative, the second positive. Explanations for this difference are given in terms of the different vector species and epidemiological situations in these long-standing foci in East Africa.

It is concluded that the rather limited amount of information available in NDVI has already proved enormously useful, and a plea is made for a more complete exploration of National Oceanic and Atmospheric Administration (NOAA) data, especially at the highest available resolution, whilst not neglecting the vitally important ground-based studies that made possible the results presented in this paper.     

黑河中上游草地NDVI时空变化规律及其对气候因子的响应分析

植被动态监测以及与气候变化的耦合关系是陆地生态系统研究的热点,而草地NDVI时空动态以及影响其变化的关键气候因子分析,对于草地覆盖变化的动态机理研究具有重要意义。基于遥感和GIS技术,利用黑河流域1999-2007年SPOT-NDVI数据和气象站点数据,分析了黑河中上游草地植被NDVI的时空变化特征以及与气候因子的相关性。结果表明,黑河中上游草地植被NDVI在1999-2007年间呈明显增加趋势;草地植被NDVI增加和减少的面积分别占草地总面积的71.53%和19.43%;增加的区域主要分布在托来山、走廊南山、冷龙岭和河西走廊中段的典型草原和高寒草甸草地,减少的区域主要分布在托勒南山、走廊南山和冷龙岭的荒漠草地向非草地过渡区域;黑河中上游不同草地植被NDVI的年内变化均呈单峰型,7月份达最大值;草地NDVI与气温呈极显著正相关(r=0.942,P<0.01),与降水量呈显著正相关(r=0.922,P<0.05),NDVI与相对湿度呈不显著正相关,与日照时数呈负相关性,并且不同草地类型牧草生长的限制因子不同。近年来伴随西北地区气候向暖湿转型,黑河中上游草地植被覆盖明显增加,气温是影响研究区牧草生长的关键气候因子。     

The potential use of fractals in epidemiology

For diseases that are transmitted through parasitic vectors (e.g. tick-borne diseases), the potential distribution and impact of such diseases can be anticipated by studying the distribution of their vectors. Vector distribution is a matter of suitable habitat, which is the sum of a wide range of environmental factors. From remotely sensed data, it is possible to distinguish areas that will provide the most beneficial habitat(s) for a given tick species. The key point is that such data come in the form of patches. The stability of these patches, and therefore that of the tick vectors and the diseases that they transmit, can be mathematically measured using fractal dimensions (D). These fractal dimensions can then be directly related to a non-Markovian (i.e. history dependent) rate of asymptotic decay (H) by using the equation (D=2−H). It is this rate of decay (H) that measures the stability of a given patch(es) of tick habitat(s). If a time series of remotely sensed data is available, changes in the stability (H) can be checked over time. Ultimately, fluctuations of these patches of suitable habitats suggest changes in the tick, and therefore disease, populations. Such fluctuations could destabilize enzootically stable disease populations, or introduce the vectors and diseases into previously naive herds.

As an example of this fractal based measurement of habitat stability, this paper presents empirical evidence of the stability of grass patches in a communal land in Zimbabwe, using data from an aerial photograph. Beyond the practical aspects of measuring the patches, and obtaining their H values, the test data demonstrate that there are at least two distinctive, size based, dynamical systems within the whole set of patches. Generally, patches of a larger size are mathematical less stable than those of a smaller size. The next research objective for the use of such a mathematical tool is to take the concept and apply it on an even larger scale, with the first step undoubtedly being to define what environmental factors constitute suitable habitats for the important tick vector species.     

PCR-based detection of Theileria ovis in Rhipicephalus bursa adult ticks

Tick-borne diseases in ruminants are common in tropical and subtropical regions and lead to meat and milk production losses. In this study, polymerase chain reaction (PCR) was used to assess the presence of Theileria ovis in Rhipicephalus bursa ticks. We have demonstrated that the PCR enabled detection of T. ovis in field isolates of R. bursa collected from naturally infested sheep and goats in eastern Turkey. The sampling was done in spring season (between May and June 2004). A total of 420 R. bursa were collected and randomly selected 192 number of them (97 female and 95 male) were dissected. Primers specific for 520 bp fragments small subunit ribosomal RNA (ssu rRNA) gene of T. ovis amplified products from 37 of the 192 (19.27%) samples. The parasite was detected in 17 (17.52%) female and in 20 (21.05%) male ticks. Two T. ovis amplicons from the tick samples were purified and sequenced. The resulting sequences were identical to the nucleotide sequence of the Turkish sheep strain of T. ovis. These results showed that R. bursa might play an important role in the field as a natural vector of T. ovis.     

Retrospective observations on the geographical relationship between Rhipicephalus appendiculatus and East Coast fever in southern Africa

East Coast fever appeared in southern Africa in 1902, after the importation of cattle from East Africa, and spread throughout the range of Rhipicephalus appendiculatus until it reached the southern limit of distribution of this tick in 1916. It was progressively eradicated by quarantine, destocking, slaughter and frequent dipping in arsenic. The last case occurred in Swaziland in 1960. A computer based system for matching climates and ecology (CLIMEX) revealed a direct correlation between the climatic favorability of different areas for the tick and the time required to eradicate the disease.     

Influence of biotic and abiotic factors on the distribution and abundance of Culicoides imicola and the Obsoletus Complex in Italy

Culicoides imicola Kieffer (Culicoides, Diptera: Ceratopogonidae) is the principal vector of bluetongue virus (BTV) to ruminant livestock in southern Europe. The secondary potential vectors are Culicoides obsoletus (Meigen) and Culicoides scoticus Downes and Kettle of the Obsoletus Complex, Culicoides pulicaris (Linnaeus) of the Pulicaris Complex and Culicoides dewulfi Goetghebuer of the subgenus Avaritia Fox. Between 2000 and 2004 >38,000 light-trap collections were made for Culicoides across Italy including the islands of Sardinia and Sicily. Mapping of the 100 largest collections of C. imicola and of the Obsoletus Complex showed them to be disjunct overlapping in only 2% of the 200 municipalities selected. For each municipality the average values were calculated for minimum temperature, aridity index, altitude, terrain slope, normalised difference vegetation index (NDVI) and percentage forest cover. A factor analysis identified two principal factors (‘biotic’ and ‘abiotic’) and explained 84% of the total variability; a discriminant analysis classified correctly 87.5% of the observations. The results indicate adult populations of C. imicola to occur in more sparsely vegetated habitats that are exposed to full sunlight, whereas species of the Obsoletus Complex favour a more shaded habitat, with increased green leaf density. Heliophily and umbrophily, by shortening or lengthening the respective adult life cycles of these two vectors, will likely impact on the ability of each to transmit BTV and is discussed in the light of the current outbreak of BTV across the Mediterranean Basin.     

内蒙古乌拉特荒漠草原红砂灌丛林引入柠条后地面节肢动物群落结构分布特征

在内蒙古乌拉特荒漠草原退化红砂灌丛林地内,引入柠条灌丛已成为一种重要的生态恢复措施。关于人工种植柠条灌丛对天然红砂灌丛林地地面节肢动物群落结构及其多样性分布的影响研究,是该区域生物多样性保育和退化生态系统恢复过程研究的重要科学问题。本研究以红砂和柠条灌丛作为研究对象,以灌丛间裸露地为对照。于2018年春季（5月）、夏季（8月）和秋季（10月）,利用陷阱诱捕法,调查柠条和红砂灌丛微生境内地面节肢动物的群落结构分布及其与环境因子间的关系。结果显示：1）试验调查期间,共捕获地面节肢动物560只,隶属于10目23科。其中,优势类群有拟步甲科和蚁科,其个体数分别占总个体数的41.07%和22.14%;常见类群有10类,其个体数共占总个体数的32.68%;稀有类群有11类,其个体数共占总个体数的4.11%。2）地面节肢动物的群落组成在红砂灌丛、柠条灌丛和裸露地微生境内存在较大差异,狼蛛科和管巢蛛科仅在柠条灌丛微生境内存在,蜉金龟科和木伪蝎科仅在裸露地微生境内存在。3）地面节肢动物的个体数、类群数、Shannon-Wiener指数和Simpson指数在红砂灌丛、柠条灌丛和裸露地微生境间均无显著差异（P>0.05）。4）红砂灌丛、柠条灌丛和裸露地微生境间的Jaccard相似性指数均处于较高水平,为0.65~0.71,属于高度相似。5）冗余对应分析（RDA）和偏RDA结果表明,土壤pH是影响地面节肢动物个体数分布的主要环境因子。研究表明,在乌拉特荒漠草原红砂灌丛林地内种植柠条灌丛,虽然会对地面节肢动物的群落组成产生一定的影响,但对其个体数、类群数和多样性分布的影响较小,说明种植柠条灌丛对地面节肢动物多样性恢复乃至生物多样性恢复均存在局限性。     

A study on Theileria parva bovis carrier state

In two trials, Theileria parva bovis (which causes ‘January disease’ of cattle in Zimbabwe) produced a carrier state, over the 7–12 months after infection. Very severe clinical reactions were caused by infections from small numbers (29–43) of adult Rhipicephalus appendiculatus ticks, which had engorged on immunized cattle in the field. The transmission from healthy recovered cattle housed indoors was less efficient, even with high numbers of ticks (300). Two out of seven attempts were successful and disease reactions were rather severe. A non-pathogenic Theileria assumed to be Theileria taurotragi was transmitted in three out of seven attempts.     

Climate change decreases habitat suitability for some tick species (Acari: Ixodidae) in South Africa

Models predicting current habitat availability for four prominent tick species in Africa (Boophilus decoloratus, Amblyomma hebraeum, Rhipicephalus appendiculatus and Hyalomma truncatum) were constructed using remotely sensed information about abiotic variables and a point-to-point similarity metric. Year-to-year variations in the forecasted habitat suitability over the period 1983-2000 show a clear decrease in habitat availability, which is attributed primarily to increasing temperature in the region over this period. Climate variables were projected to the year 2015 using Fourier series analysis of the decadal abiotic data. The simulations show a trend toward the destruction of the habitats of the four tick species. In addition, a sensitivity analysis was developed to probe the changes in the habitat suitability in response to variations in temperature, vegetation availability and water vapour deficit. Four basic scenarios were studied: increasing or decreasing the temperature 1 or 2 degrees C together with correlated variations in the other abiotic variables. A decrease in temperature was predicted to promote habitat gain for every species except H. truncatum, while an increase of 1 degrees C was forecast to sustain a small but positive response in A. hebraeum and B. decoloratus. Increasing the temperature by 2 degrees C was forecast to have damaging effects on the habitat structure of all four species. The effect of climate warming on the habitat range of these ticks is considered in the light of economically sound control measures over an ecological background.     

外源脯氨酸对缓解红砂干旱胁迫的机理研究

红砂属于干旱半干旱荒漠区生态系统中重要的超抗旱树种,对维护荒漠区植物群落的稳定性具有重要的作用。近年来由于极端干旱气候的频发,导致以红砂为建群种的荒漠植物群落出现大面积死亡以及退化的趋势。因此,采用人工措施提高干旱荒漠区植物的抗旱能力显得尤为重要。通过对干旱胁迫中的红砂苗木喷施外源脯氨酸（Pro）以减缓干旱胁迫对其造成的伤害。研究设置5个Pro浓度,分别为50,100,150,200,250 mg·L^-1,对红砂植株进行喷施处理,于处理前第0天（CK）,处理后第1,3, 6和9天对叶片抗氧化酶系统、代谢调节系统、光合色素、光合性能进行测定,第9天对生长状况进行测定,以期揭示干旱胁迫下Pro的作用机理。结果表明,外源Pro处理红砂植株后,对其抗氧化酶系统、代谢调节系统、光合色素、光合性能以及生长状况均有显著影响。除叶绿素a/b（Chl a/b）在处理年份间差异不显著,可溶性糖含量在处理浓度间差异不显著外,其他指标在处理年份之间、处理浓度之间、处理后作用时间之间以及处理浓度与处理后作用时间交互作用之间均差异显著,其中以100 mg·L^-1 Pro处理效果最佳。100 mg·L^-1 Pro处理后第9天和CK相比,可溶性蛋白（SP）、脯氨酸（Pro）、过氧化氢酶（CAT）、过氧化物酶（POD）分别提高了4.48%、131.07%、30.66%、12.30%,可溶性糖（SS）、超氧化物歧化酶（SOD）分别下降了6.42%、1.95%;总叶绿素含量Chl（a+b）、叶绿素a含量（Chla）、叶绿素b含量（Chlb）分别较CK降低了5.81%、1.47%和22.22%;净光合速率（P_n）、气孔导度（G_S）、蒸腾速率（T_r）、胞间二氧化碳浓度（C_i）以及水分利用效率（WUE）分别比CK降低了16.07%、10.00%、6.44%、7.68%和9.92%;红砂苗木的生长特性在处理后第9天,株高净生长量为2.48 cm,侧芽萌发数量为3.67个,侧芽净生长量为1.87 cm,地径净生长量为0.27 mm,比处理效果最差的250 mg·L^-1处理分别高出0.68 cm,0.34个,0.32 cm,0.07 mm。因此,100 mg·L^-1 Pro处理干旱胁迫中的红砂植株,能显著提高其抗旱性。     

CO2浓度升高及降水变化对红砂植物碳氮特征的影响

本研究以荒漠优势植物红砂（Reaumuria soongorica） 1年生幼苗为研究对象,采用开顶式生长箱（Open top chambers,OTCs）模拟CO₂浓度变化（350和700 μmol·mol^-1）,研究了降水变化（-30%,-15%,0,+15%和+30%）及其协同作用对红砂地上和地下部分碳、氮含量与积累量的影响。结果发现：CO₂浓度倍增和降水对红砂地上和地下部分有机碳、全氮含量和有机碳积累量以及地上全氮积累量影响极显著,并且表现出极显著的交互作用。CO₂浓度倍增下,红砂地上和地下部分有机碳、C/N和有机碳积累量以及地下部分全氮显著增加。随着降水增加,红砂地上和地下部分有机碳含量和积累量以及地下部分全氮均呈增加趋势,地上和地下部分C/N呈先降后升趋势,而地上部分全氮先升后降。综上所述：未来CO₂升高时,降水增加协同高CO₂浓度有助于红砂植株有机碳积累,从而促进红砂植株对氮素的吸收,降水减少则有利于红砂调节自身碳氮平衡从而提高其抗旱性。     

PEG模拟干旱胁迫对四种荒漠植物种子萌发的影响

试验以内蒙古阿拉善荒漠4种优势植物:梭梭、红砂、驼绒藜和碱蓬种子为材料,在-3.0～0 MPa 的PEG渗透势下,研究了干旱胁迫对种子萌发的影响,探讨了经PEG浸种预处理后种子的萌发恢复能力。结果表明,随PEG渗透势的下降,梭梭、红砂、驼绒藜和碱蓬种子的萌发和初生根生长均受到不同程度的抑制,总体来看,PEG渗透势越低,抑制作用越明显。但是,轻度的干旱胁迫能促进红砂、驼绒藜和碱蓬种子的萌发,提高红砂和碱蓬种子的发芽指数,刺激了4种荒漠植物的初生根生长。4种荒漠植物种子萌发的最低渗透势阈值分别为-3.0,-2.1,-2.1和-1.5 MPa,说明梭梭种子萌发的抗旱性最强,而碱蓬的抗旱性最弱。经PEG浸种预处理的种子在适宜条件下可以恢复萌发,但浸种时间越长,种子受干旱胁迫的影响越大,甚至其萌发完全被抑制。短时间的PEG浸种预处理提高了红砂种子的发芽率,并显著提高了其发芽指数,刺激了梭梭、红砂、驼绒藜的初生根生长,而碱蓬的初生根生长则一直受到PEG浸种预处理的抑制。     

安南坝野骆驼国家级自然保护区鼠类群落结构的研究

为全面了解安南坝野骆驼国家级自然保护区鼠类群落结构和多样性,于2018-2019年采用铗日法对该区10种不同生境类型下的25个调查点进行鼠类调查,并对鼠类群落多样性进行分析。结果表明：捕获鼠类124只,分属3科6属9种;其中三趾跳鼠、子午沙鼠和柽柳沙鼠为保护区优势鼠种。聚类和PCA分析可知安南坝保护区鼠类主要分布于2个群落。荒漠耐旱群落广泛分布于保护区各生境,耐旱-喜湿混合群落主要分布在芦苇群系和水柏枝群系生境。在调查的10种生境中,芦苇群系生境丰富度指数和多样性指数均高于其他生境。除环境因素外,鼠类群落的多样性受群落内鼠种数目和物种分配的均匀程度2个因素影响。鼠类垂直分布表现出在1400~1800 m和2600~3000 m海拔分布的鼠种多,呈现出中间低两头高的趋势。由此可见,生境类型和海拔高度影响着安南坝保护区的鼠类群落结构。     

Prevalence and distribution of gastro-intestinal helminths and haemoparasites in young scavenging chickens in upper eastern region of Ghana, West Africa

We conducted a cross-sectional study to determine the prevalence and species of gastro-intestinal helminths and haemoparasites in 100 chickens kept under extensive management systems in Ghana, West Africa. All the examined chickens (100%) were infected with gastro-intestinal helminths; a total of 18 species were detected. The species and their prevalences were: Acuaria hamulosa (25%), Allodapa suctoria (20%), Ascaridia galli (24%), Capillaria spp. (60%), Choanotaenia infundibulum (13%), Gongylonema ingluvicola (62%), Heterakis gallinarum (31%), H. isolonche (16%), Hymenolepis spp. (66%), Raillietina cesticillus (12%), R. echinobothrida (81%), R. tetragona (59%), Strongyloides avium (2%), Subulura strongylina (10%), Tetrameres fissispina (58%), Trichostronygylus tenuis (2%), and finally one unidentified acanthocephalan (1%) and one unidentified trematode (1%). Thirty-five per cent of the chickens were infected with the haemoparasites Aegyptinella pullorum and Plasmodium juxtanucleare (prevalences 9% and 27%, respectively). Association between chicken sex and prevalences was not significant. An over-dispersed distribution was seen for most of the helminth species.     

High-resolution predictive mapping for Boophilus annulatus and B. microplus (Acari: Ixodidae) in Mexico and Southern Texas

In this study we use high-resolution satellite imagery to map habitat suitability for both Boophilus annulatus and B. microplus over an area covering parts of Texas and northeastern Mexico. The habitat for these tick species covers widely different regions. B. microplus finds satisfactory abiotic conditions in wet coastal habitats, whereas B. annulatus finds suitable habitat in the drier inner parts of southwestern Texas and northern Mexico; the two species have very different habitat requirements. We use habitat topology and data concerning abiotic habitat suitability to understand the effects of habitat configuration on tick abundance. This is achieved using traversability (habitat permeability) and recruitment (tick abundance at the patch level) to produce a model that computes the abundance of ticks at the patch level. Results from the computation are then compared with actual data on tick outbreaks at the Texas-Mexico border, as a test of the agreement between actual tick captures and abundance model predictions.     

陕北黄土丘陵区不同植被类型群落多样性与土壤有机质、全氮关系研究

为探讨陕北黄土丘陵区不同植被类型物种多样性与土壤有机质、全氮的关系,在野外调查和室内分析的基础上,采用相关性分析对5种不同植被群落特征、多样性、土壤碳氮之间的关系进行研究。结果表明：植物群落组成主要为菊科、禾本科和豆科,这3大科植物在该区具有较强的生态适应性;不同植被类型群落Gleason丰富度指数为30 a撂荒地最大,16 a撂荒地最小,Simpson指数、Shannon-wiener指数和Sheldon均匀度指数均为30 a刺槐林（Robinia pseudoacacia）最大,16 a撂荒地最小;土壤有机质、全氮含量均随土层深度增加而递减,其平均含量在0~30 cm和30~100 cm土层从大到小为30 a刺槐林>30 a撂荒地>16 a刺槐林>30 a柠条林（Caragana microphylla）>16 a撂荒地,30 a刺槐林表现出较好的土壤碳氮累积效果。相关性分析结果表明,不同植被类型群落物种多样性与土壤有机质、全氮之间显著相关（P<0.05）,表明土壤有机质和全氮是影响植物群落组成和多样性的关键生态因子。     

Geographical information systems for studying the epidemiology of cattle diseases caused by Theileria parva

Data on selected variables which influence the epidemiology of cattle diseases caused by Theileria parva were assembled and entered in a computerised geographical information system. Variables studied included the distributions of major hosts (cattle and buffalo), the vector ticks (Rhipicephalus appendiculatus and related species) and the reported presence of East Coast fever, corridor disease and January disease. In addition, the distribution of climatic suitability for R appendiculatus was assessed using the model CLIMEX run on an interpolated climate database developed for Africa. Distribution maps of each variable were produced. The potential value of geographical information systems in studies of disease epidemiology and control is discussed, with examples of how sensitivity may be enhanced by the inclusion of additional variables. In addition, subject areas in which poor data quality and inadequate data standardisation may limit the use of these systems are identified and discussed.     

不同降水量条件下C3植物红砂—C4植物珍珠混生光合特性研究

为探明种间关系和降水变化对混生植物群落光合特性的影响,以C₃植物红砂（Reaumuria soongarica）和C₄植物珍珠（Salsola passerina）为研究对象,沿自然降水梯度测定单生和混生红砂与珍珠光合参数。结果表明：混生可提高红砂的净光合速率、蒸腾速率、气孔导度,平均分别增加12.3%,13.7%,20.4%;而珍珠相反,平均分别减少5.5%,14.1%,28.9%。随降水的减少,混生红砂与珍珠的光合速率并没有显著提高,表明随干旱胁迫梯度增加其互惠作用并没有得到加强,并不支持胁迫梯度假说。西北干旱区和半干旱区红砂的净光合速率（Net Photosynthesis Rate,Pn）、蒸腾速率（Transpiration Rate,Tr）和气孔导度（Stomatal conductance,Gs）整体高于珍珠,平均分别增加6.6%,36.9%,27.8%,但其水分利用效率（Water Use Efficiency,WUE）低于珍珠,降低13.9%。研究表明,红砂可通过种间互惠更好地利用养分资源适应种间竞争及干旱胁迫环境,而混生珍珠竞争作用加强,在我国西北干旱和半干旱区红砂主要是通过提高光合速率来适应干旱环境,珍珠则通过提高水分利用效率来维持生长。     

东祁连山杜鹃灌丛草地灌木种群分布格局研究

对东祁连山杜鹃灌丛草地灌木种群分布格局的研究表明:在海拔高度相对较低的主样区(海拔3080m),陇蜀杜鹃在群落中的竞争能力和适应性受到限制,因而呈现出集聚程度较高的斑块状分布;柳属植物、鬼箭锦鸡儿、金露梅、烈香杜鹃、头花杜鹃和百里香杜鹃均为随机分布。随海拔高度上升,陇蜀杜鹃的分布格局由集聚型迅速转变为随机型,其余灌木则表现出一定程度的波动,但分布格局未发生根本性的变化。     

降水变化和生长方式对红砂和珍珠化学计量特征的影响

为揭示典型荒漠植物不同器官养分利用和调控策略对降水变化和生长方式的响应规律，本研究以红砂（Reaumuria soongorica）与珍珠（Salsola passerina）为材料，测定了不同降水梯度（年降水量50~300 mm，Δ=50）下单生和混生红砂和珍珠不同器官中的有机碳（C）、全氮（N）含量。结果表明：随降水量的减少（干旱胁迫增加），单生红砂叶C，C/N和茎N含量逐渐减小；单生珍珠茎和根C含量整体呈增大趋势，表明干旱胁迫加剧时，单生红砂茎受N限制作用增强，但红砂会通过降低叶片有机C含量和C/N以提高生长速率；单生珍珠会选择适当地增加地下部分根系的C分配比例，并将多余的C储藏在茎中。各降水量条件下，混生红砂叶C，C/N和根C，N含量均大于单生，茎C含量小于单生；混生珍珠茎C，C/N和根C，N含量均小于单生，叶C，C/N含量大于单生，表明混生后红砂倾向于向根系分配更多C，N，而珍珠主要通过降低茎的C/N来提高地上部分生长速率。