Fine-scale spatial distribution of soil organic carbon and its fractions after afforestation with Pinus sylvestris and Salix psammophila in a semiarid desert of China

半干旱沙漠中樟子松和沙柳造林后土壤有机碳及其组分的小尺度空间分布 半干旱沙漠造林有助于改善土壤功能以及增加土壤有机碳(SOC)固定,但人们对造林后SOC及其不稳定(LOC)组分的小尺度空间分布了解甚少。本研究以毛乌素沙地东南缘樟子松(Pinus sylvestris)和沙柳 (Salix psammophila)为研究对象,量化了距离树体20、80、150和240 cm处SOC、LOC组分及其相关变量的小尺度空间分布。研究结果表明,沙柳和樟子松造林显著提高了SOC、总氮(TN)、可溶性有机碳 (DOC)、微生物碳(MBC)和易氧化有机碳(ROOC)含量;在距离树体20 cm处,0–100 cm土层樟子松SOC 储量比沙柳高27.21%;在距离树体80和150 cm处,沙柳SOC储量分别比樟子松高5.50%和5.66%;与流 沙地相比,在距离树体20、80、150 和240 cm处,沙柳和樟子松SOC储量显著增加了94.90%、39.50%、 27.10%和18.50%;沙柳和樟子松ROOC分别占SOC的14.09%和18.93%。总之,造林促进了半干旱流沙地SOC的积累,樟子松比沙柳分配更多的有机质到距离树体<80 cm范围内的土体中。     

准噶尔荒漠大翅霸王的生殖物候及结实格局

大翅霸王是多年生早春开花草本植物,是准噶尔荒漠地区的建群种之一。对野生大翅霸王的生殖物候、果实形态、结实格局和种子萌发特性进行了研究。结果表明:(1)大翅霸王的营养期生长期为20—30d,占整个生活周期的1/4,生殖生长期长约90—100d,其中花期约占1/2,果熟期短;(2)大翅霸王种群能产生3种形态的果实,可将植株分为5翅型、4/5翅型和3/4/5翅型植株,它们分别占种群植株数的3.45%、83.15%和13.40%。(3)依据个体大小的变化,3种类型果实在植株上的比例发生了显著变化。随植株个体的增大,三翅果所占比例逐渐增多,由0增加到2.65%;四翅果所占比例也增多,但在二级个体上有最大比例17.01%;五翅果实所占比例最高(80%)且没有显著变化。(4)三翅果、四翅果和五翅果内种子形态无差异,萌发率均小于30%;划破种皮能不同程度的加速和促进种子的萌发。大翅霸王特有的生殖物候和果实的表型多样性是其对荒漠干旱地区恶劣多变环境长期适应的结果。     

The Oldowan site Aïn al Fil (El Kowm,Syria) and the first humans of the Syrian Desert

At present, the oldest traces of human cultures are found in Eastern Africa. New discoveries set anew the questions about human and animal dispersal into Eurasia. For over 1.8 million years, humans have been present in the Levant. An extensive program of surveys and excavations in the Syrian Desert showed that this part of the world was a very ancient land of settlement. In Central Syria, the oldest site, Aïn al Fil in the region of El Kowm, was excavated in 2008 and 2010. The lithic industry in the lowest layer can be characterized by numerous unretouched flakes, pebble-tools and core-like artefacts. This assemblage is typical in a broad sense of archaic Palaeolithic the debitage of which corresponds to mode 1. From a techno-typological point of view, this industry tallies quite well with the so-called Oldowan stage. It shows remarkable similarities with the oldest African assemblages. From a chronologic point of view, these levels occur before three positive events in the Matuyama paleomagnetic sequence. It seems consistent to place the Oldowan sequence around 1.8 Ma BP within the Olduvai subchron or just before Olduvai/Matuyama reversal limit. Together with those of the neighbouring site Hummal, these levels would be the oldest traces of human presence ever found in Syria. In the Levant, the first humans not only occupied favourable zones but regularly ventured deep into less welcoming environments suggesting an astonishing flexibility in their behavioural and survival skills.     

Not putting all their eggs in one basket: bet‐hedging despite extraordinary annual reproductive output of desert tortoises

Bet‐hedging theory makes the counter‐intuitive prediction that, if juvenile survival is low and unpredictable, organisms should consistently reduce short‐term reproductive output to minimize the risk of reproductive failure in the long‐term. We investigated the long‐term reproductive output of an Agassiz's desert tortoise (Gopherus agassizii) population and conformance to a bet‐hedging strategy of reproduction in an unpredictable but comparatively productive environment. Most females reproduced every year, even during periods of low precipitation and poor germination of food plants, and the mean percentage of reproducing females did not differ significantly on an annual basis. Although mean annual egg production (clutch size × clutch frequency) differed significantly among years, mean clutch size and mean clutch frequency remained relatively constant. During an El Niño year, mean annual egg production and mean annual clutch frequency were the highest ever reported for this species. Annual egg production was positively influenced by maternal body size but clutch size and clutch frequency were not. Our long‐term results confirm earlier conclusions based on short‐term research that desert tortoises have a bet‐hedging strategy of producing small clutches almost every year. The risk of long‐term reproductive failure is minimized in unpredictable environments, both through time by annually producing multiple small clutches over a long reproductive lifespan, even in years of low resource availability, and through space by depositing multiple annual clutches in different locations. The extraordinary annual reproductive output of this population appears to be the result of a typically high but unpredictable biomass of annual food plants at the site relative to tortoise habitat in dryer regions. Under the comparatively productive but unpredictable conditions, tortoises conform to predictions of a bet‐hedging strategy of reproduction with relatively small but consistent clutch sizes. Published 2015. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2015, 115 , 399–410.     

Germination response of Arabian desert species to gibberellic acid and potassium nitrate seed treatment

Abstract

Desert plant species commonly use seed dormancy to prevent germination during unfavorable environmental conditions and thus increase the probability of seedling survival. Seed dormancy presents a challenge for restoration ecology, particularly in desert species for which our knowledge of dormancy regulation is limited. In the present study the effect of gibberellic acid (GA₃) and potassium nitrate (KNO₃) on seed dormancy release was investigated on eight Arabian desert species. Both treatments significantly enhanced the germination of most species tested. GA₃ was more effective than KNO₃ in enhancing germination percentage, reducing mean germination time and synchronizing the germination in most of the studied species. Light requirement during germination was species-specific, but in general the presence of light promoted germination more effectively when combined with KNO₃ and GA₃. The wide variation in dormancy and germination requirements among the tested species is indicative of distinct germination niches, which might assist their co-existence in similar habitat/environmental conditions. Seed pre-treatments that optimize germination in this habitat must therefore be assessed for individual species to improve the outcomes of ecological restoration.     

Effect of ultraviolet radiation on chlorophyll,carotenoid, protein and proline contents of some annual desert plants

Investigation was carried out to find whether enhanced ultraviolet radiation influences the Malva parviflora L., Plantago major L., Rumex vesicarius L. and Sismbrium erysimoids Desf. of some annual desert plants. The seeds were grown in plastic pots equally filled with a pre-sieved normal sandy soil for 1 month. The planted pots from each species were randomly divided into equal groups (three groups). Plants of the first group exposed to white-light tubes (400–700 nm) 60 w and UV (365 nm) 8 w tubes. The second group was exposed to white-light tubes (400–700 nm) 60 w and UV (302 nm) 8 w tubes. The third group was exposed to white-light tubes (400–700 nm) 60 w and UV (254 nm) 8 w tubes, respectively, for six days. The results indicated that the chlorophyll contents were affected by enhanced UV radiation. The chlorophyll a, b, and total contents were decreased compared with the control values and reduced with the enhanced UV radiation, but the carotenoid was increased compared with the control and also reduced with the enhanced UV radiation. So, the contents of chlorophylls varied considerably. M. parviflora showed the highest constitutive levels of accumulated chlorophyll a, b, and total chlorophyll (0.463, 0.307 and 0.774 mg g⁻¹ f w) among the investigated plant species. P. major showed the lowest constitutive levels of the chloroplast pigments, 0.0036, 0.0038 and 0.0075 mg g⁻¹ f w for chlorophyll a, b, and total chlorophyll at UV-365 nm, respectively. The protein content was decreased significantly in both root and shoot systems compared with the control values but, it was increased with increasing wave lengths of UV-radiation of all tested plants. R. vesicarius showed the highest protein contents among the investigated plants; its content was 3.8 mg g⁻¹ f w at UV-365 nm in shoot system. On the other hand, decreasing ultraviolet wave length induced a highly significant increase in the level of proline in both root and shoot of all tested plants. From the results obtained, it is suggested that proline can protect cells against damage induced by ultraviolet radiation. Statistically, the variations of the studied metabolic activities were significant due to UV radiation treatment in shoot and root system of all investigated plant species.     

塔克拉玛干沙漠腹地胡杨林土壤细菌多样性分析

【目的】对塔克拉玛干沙漠腹地胡杨林土壤细菌多样性进行初步探索,为下一步从中筛选可用于生物饲料或生物肥料的微生物奠定基础。【方法】采用可培养方法,进行细菌的分离纯化。对各菌株进行革兰氏染色及淀粉酶、酯酶、纤维素酶和NaCl耐受浓度的测定,并提取各菌株基因组DNA,进行16SrRNA基因扩增、测序及系统进化树的绘制,分析其多样性。【结果】共分离得到27株菌,其中放线菌门(Actinobacteria)16株,变形菌门(Proteobacteria)4株,厚壁菌门(Firmicutes)6株,拟杆菌门(Bacteroidetes)1株。革兰氏染色结果表明,5株菌为革兰氏阴性,其余为革兰氏阳性;酶活测定结果表明,15株菌具有淀粉酶活性,9株菌具有酯酶活性,9株菌具有纤维素酶活性;NaCl耐受浓度测定结果显示,NaCl浓度为2%时所有菌株均能生长,5%时能生长的有22株,15%时能生长的有1株。【结论】塔克拉玛干沙漠腹地胡杨林土壤中存在较丰富的细菌类群,且具有一定的酶学活性和NaCl耐受性,具有进一步研究开发的价值。     

塔克拉玛干沙漠南缘3种果树幼苗光合及抗逆性研究

于2010年7~8月份,以塔克拉玛干沙漠南缘绿洲-荒漠过渡带人工种植的桑树(Morus albaL.)、沙枣(Elaeagnus angustifoliaL.)和杏树(Prunus armeniacaL.)幼苗为材料,研究了它们在相同生境条件下光合响应特征、水势、脯氨酸和可溶性糖含量等生理指标的变化,并用隶属函数值法对3种果树幼苗的抗旱性进行综合评价。结果表明:(1)3种果树幼苗光响应曲线具有相同的变化规律,当光合有效辐射(PAR)在0~200μmol.m-2.s-1之间变化时,净光合速率(A)随着PAR的增大呈直线增大,当PAR>200μmol.m-2.s-1时,A随PAR的变化呈二次曲线变化;(2)3种果树幼苗的光响应参数最大光合速率(Amax)、曲角(K)、表观量子效率(φ)、暗呼吸速率(Rday)、光饱和点(LSP)、光补偿点(LCP)以及光合色素的变化趋势并不完全一致,其中桑树具有最大的Amax、φ、Rday和叶绿素含量,而杏树的LSP最高,LCP最低,因此桑树具有最大的光能利用效率,而杏树能更有效地利用强光进行光合作用;(3)3种果树幼苗脯氨酸(Pro)、可溶性糖以及丙二醛(MDA)含量,除沙枣和杏树之间可溶性糖含量差异不显著外,其他指标含量差异在3种果树之间均达到显著水平(P<0.05);(4)在本研究期间3种果树的抗逆性表现为沙枣>桑树>杏树。研究发现,塔克拉玛干沙漠南缘绿洲-荒漠过渡带的3种果树幼苗光响应曲线变化趋势基本一致,体现了植物对环境条件适应的一致性,但是各个生理指标的变化趋势并不完全一致,这可能是由于植物种对环境条件的适应差异所导致。     

Unexpected side effects in biocrust after treating non‐native plants using carbon addition

Carbon addition has been proposed as an alternative to herbicide and manual removal methods to treat non‐native plants and reduce non‐target effects of treatments (e.g. impacts on native plants; surface disturbance). On Mojave Desert pavement and biocrust substrates after experimental soil disturbance and carbon addition (1,263 g C/m² as sucrose), we observed declines in lichens and moss cover in sucrose‐treated plots. To further explore this unforeseen potential side effect of using carbon addition as a non‐native plant treatment, we conducted biocrust surveys 5 and 7 years after treatments, sampled surface soils to observe if treatments additionally affected soil filamentous cyanobacteria, and conducted laboratory trials testing the effects of different levels of sucrose on cyanobacteria and desert mosses. Sucrose addition to biocrust plots reduced lichen and moss cover by 33–78% and species richness by 40–80%. Sucrose reduced biocrust cover in biocrust plots to levels similarly detected in pavement plots (<1%). While cyanobacteria in the field did not appear to be affected by sucrose, laboratory tests showed negative effects of sucrose on both cyanobacteria and mosses. Cyanobacteria declined by 41% 1 month after exposure to 5.4 g C/m² equivalent solutions. We detected injury to photosynthesis in mosses after 96 hour exposure to 79–316 g C/m² equivalent solutions. Caution is warranted when using carbon addition, at least in the form and concentration of sucrose, as a treatment for reducing non‐native plants on sites where conserving biocrust is a goal.