Lichen acclimation to changing environments: Photobiont switching vs. climate‐specific uniqueness in Psora decipiens

Unraveling the complex relationship between lichen fungal and algal partners has been crucial in understanding lichen dispersal capacity, evolutionary processes, and responses in the face of environmental change. However, lichen symbiosis remains enigmatic, including the ability of a single fungal partner to associate with various algal partners. Psora decipiens is a characteristic lichen of biological soil crusts (BSCs), across semi‐arid, temperate, and alpine biomes, which are particularly susceptible to habitat loss and climate change. The high levels of morphological variation found across the range of Psora decipiens may contribute to its ability to withstand environmental change. To investigate Psora decipiens acclimation potential, individuals were transplanted between four climatically distinct sites across a European latitudinal gradient for 2 years. The effect of treatment was investigated through a morphological examination using light and SEM microscopy; 26S rDNA and rbcL gene analysis assessed site‐specific relationships and lichen acclimation through photobiont switching. Initial analysis revealed that many samples had lost their algal layers. Although new growth was often determined, the algae were frequently found to have died without evidence of a new photobiont being incorporated into the thallus. Mycobiont analysis investigated diversity and determined that new growth was a part of the transplant, thus, revealing that four distinct fungal clades, closely linked to site, exist. Additionally, P. decipiens was found to associate with the green algal genus Myrmecia, with only two genetically distinct clades between the four sites. Our investigation has suggested that P. decipiens cannot acclimate to the substantial climatic variability across its environmental range. Additionally, the different geographical areas are home to genetically distinct and unique populations. The variation found within the genotypic and morpho‐physiological traits of P. decipiens appears to have a climatic determinant, but this is not always reflected by the algal partner. Although photobiont switching occurs on an evolutionary scale, there is little evidence to suggest an active environmentally induced response. These results suggest that this species, and therefore, other lichen species, and BSC ecosystems themselves may be significantly vulnerable to climate change and habitat loss.     

Global change and biological soil crusts: effects of ultraviolet augmentation under altered precipitation regimes and nitrogen additions

Biological soil crusts (BSCs), a consortium of cyanobacteria, lichens, and mosses, are essential in most dryland ecosystems. As these organisms are relatively immobile and occur on the soil surface, they are exposed to high levels of ultraviolet (UV) radiation and atmospheric nitrogen (N) deposition, rising temperatures, and alterations in precipitation patterns. In this study, we applied treatments to three types of BSCs (early, medium, and late successional) over three time periods (spring, summer, and spring–fall). In the first year, we augmented UV and altered precipitation patterns, and in the second year, we augmented UV and N. In the first year, with average air temperatures, we saw little response to our treatments except quantum yield, which was reduced in dark BSCs during one of three sample times and in Collema BSCs two of three sample times. There was more response to UV augmentation the second year when air temperatures were above average. Declines were seen in 21% of the measured variables, including quantum yield, chlorophyll a, UV‐protective pigments, nitrogenase activity, and extracellular polysaccharides. N additions had some negative effects on light and dark BSCs, including the reduction of quantum yield, β‐carotene, nitrogenase activity, scytonemin, and xanthophylls. N addition had no effects on the Collema BSCs. When N was added to samples that had received augmented UV, there were only limited effects relative to samples that received UV without N. These results indicate that the negative effect of UV and altered precipitation on BSCs will be heightened as global temperatures increase, and that as their ability to produce UV‐protective pigments is compromised, physiological functioning will be impaired. N deposition will only ameliorate UV impacts in a limited number of cases. Overall, increases in UV will likely lead to lowered productivity and increased mortality in BSCs through time, which, in turn, will reduce their ability to contribute to the stability and fertility of soils in dryland regions.     

黄土高原三种耐干藓营养繁殖的季节差异及机理

苔藓植物在园林绿化、水土保持等方面的应用日益增加,目前藓类植物营养繁殖的影响因素鲜见报道,限制了其应用研究。本研究以黄土高原常见的耐干藓(扭口藓、土生对齿藓、短叶对齿藓)为对象,研究了3种藓春、夏、秋、冬季营养繁殖能力(以活力指数表征)差异及其叶绿素、可溶性糖、可溶性蛋白质、丙二醛(MDA)含量等生理指标变化,探索了耐干藓营养繁殖的季节差异与其生理特征之间的关系。结果表明: 1)藓类繁殖具有明显的季节差异,3种藓夏季活力指数均低于其他3个季节,平均较秋、冬、春季分别下降56.1%、48.4%、10.1%;相同季节的活力指数具有明显的年际变化。2)3种藓繁殖能力具有明显的种间差异,以短叶对齿藓最高,扭口藓最低,且后者的繁殖能力季节和年际变化最大。3)3种藓不同季节生理特征差异显著,其中夏季MDA含量高于其他季节,可溶性糖和可溶性蛋白质含量低于其他季节。4)耐干藓的营养繁殖季节变化主要与可溶性糖含量有关。本研究明确了藓类营养繁殖能力随季节变化的规律,指出可溶性糖含量是影响藓类营养繁殖的关键因素,可为藓类植物保护和人工培养提供科学依据。     

Population dynamics of Echinops gmelinii Turcz. at different successional stages of biological soil crusts in a temperate desert in China

• The effects of biological soil crusts (BSC) on vascular plant growth can be positive, neutral or negative, and little information is available on the impacts of different BSC successional stages on vascular plant population dynamics.
• We analysed seedling emergence, survival, plant growth and reproduction in response to different BSC successional stages (i.e. habitats: bare soil, cyanobacteria, lichen and moss crusts) in natural populations of Echinops gmelinii Turcz. in the Tengger Desert of northwest China. The winter annual E. gmelinii is a dominant pioneer herb after sand stabilisation.
• During the early stages of BSC succession, the studied populations of E. gmelinii were characterised by high density, plant growth and fecundity. As the BSC succession proceeded beyond moss crusts, the fecundity decreased sharply, which limited seedling recruitment. Differences in seedling survival among the successional stages were not evident, indicating that BSC have little effect on survival in arid desert regions. Moreover, E. gmelinii biomass allocation exhibited low plasticity, and only reproductive allocation was sensitive to the various habitats. Our results further suggest that the negative effects of BSC succession on population dynamics are primarily driven by increasing topsoil water‐holding capacity and decreasing rain water infiltration into deeper soil.
• We conclude that BSC succession drives population dynamics of E. gmelinii, primarily via its effect on soil moisture. The primary cause for E. gmelinii population decline during the moss‐dominated stage of BSC succession is decreased fecundity of individual plants, with declining seed mass possibly reducing the success of seedling establishment.

     

Effects of chemical substances on the rapid cultivation of moss crusts in a phytotron from the Loess Plateau,China

In this study, typical moss crusts, which were dominated by the species Didymodon vinealis (Brid.) Zand., were collected from the Loess Plateau and a 65-day cultivation experiment was performed to study the effects of five kinds of nutrient solutions (Knop, Murashige-Skoog (MS), Benecke, Part and Hoagland), two kinds of carbohydrates (glucose and sucrose) and three kinds of plant growth regulators (thidiazuron (TDZ), 6-benzylaminopurine (6-BA) and naphthaleneacetic acid (NAA)) on the coverage, plant density, and plant height of moss crusts. The main conclusions are as follows. (1) All Knop, MS, Benecke, Part and Hoagland nutrient solutions improved the coverage and plant density of moss crusts to different degrees and the promotional effects of the Hoagland nutrient solution were most significant. (2) Glucose and sucrose could promote the formation of moss crusts, but they inhibited the development of moss crusts at concentrations greater than 10?g/L. (3) With an increase in concentration, the effects of TDZ on the development of moss crusts changed from “enhanced” to “inhibited”. Regardless of whether the concentration was high or low, 6BA had no significant effects on the growth of moss crusts, and NAA reduced the development of moss crusts. Results suggest that nutrient solutions (e.g. Hoagland), low concentration carbohydrates solutions, and some plant growth regulators (e.g. 1?mg/L TDZ) enhance the development of moss crusts in Loess Plateau under the appropriate environmental conditions.     

黄土高原水蚀风蚀交错区固氮微生物群落多样性在生物结皮中的演变规律

生物土壤结皮在黄土高原的水土保持、养分补给等方面发挥着重要生态功能。固氮微生物是固氮过程的关键功能群,影响着土壤氮素平衡,然而黄土高原水蚀风蚀交错区严重的水土流失导致土壤养分大量损失,尤其是氮素。该区域生物结皮广泛发育,它们在干旱半干旱区土壤氮素积累过程中起着重要作用。但是该区域生物结皮不同发育阶段中的固氮潜力、固氮微生物群落多样性及其关键环境控制因子尚不清楚。以黄土高原水蚀风蚀交错区为研究区,三种生物结皮类型和裸地对照为研究对象,采用Illumina HiSeq平台对nifH基因扩增产物进行生物信息学分析,揭示了固氮潜力及微生物群落多样性的分布规律。结果表明,生物结皮演替显著影响固氮酶活性、nifH基因丰度和固氮微生物α-多样性,各值均在苔藓结皮最高,显著高于其它演替阶段,且生物结皮层高于结皮下层土壤。在固氮微生物群落组成上,裸地以变形菌门的红螺菌目、酸硫杆菌目和根瘤菌目为主;而在藻结皮、地衣结皮和藓结皮阶段,均表现为蓝藻门的念珠藻目占绝对优势,是固氮微生物的关键类群,其中Trichormus、念珠藻属是优势固氮物种;与藻结皮、地衣结皮相比,藓结皮中念珠藻目的相对丰度显著降低,而变形菌门的红螺菌目、酸硫杆菌目和根瘤菌目的丰度明显上升。除此之外,蓝杆藻属、鱼腥藻属、斯克尔曼氏菌属、瘤胃梭菌属在藻结皮、地衣结皮、藓结皮也占明显优势。念珠藻目以及Trichormus的丰度与固氮酶活性、nifH基因丰度呈显著正相关关系,而与红螺菌目、酸硫杆菌目、梭菌目、根瘤菌目呈显著负相关;Trichormus相关的物种在黄土高原生物结皮氮输入过程中可能发挥着关键作用。生物结皮演替通过改变土壤pH值、有机质、全氮、含水量等理化特征而影响了微生境,通过环境筛选和物种重排作用对固氮微生物群落进行综合调控,其中pH与土壤全氮(TN)发挥着关键作用。     

不同微生境下齿肋赤藓(Syntrichia caninervis)生理生化特性对不同季节的响应

齿肋赤藓(Syntrichia caninervis)作为典型的耐旱藓类,在古尔班通古特沙漠的藓类结皮中占优势地位。该沙漠的季节气候差异较大,冬季低温湿润,春季干旱,夏季高温且干旱。荒漠藓类植物叶片仅具单层细胞,对外界环境的变化十分敏感。而有关荒漠藓类植物在生理上如何适应这种剧烈环境变化还不得而知。研究测定了生长于两种不同微生境下的齿肋赤藓,经由低温湿润的冬季到干旱的春季再到高温干旱的夏季过程中生理生化变化特征,以探究不同微生境下齿肋赤藓在水热变化剧烈的不同季节的适应机制。研究发现:季节、微生境及二者的交互作用能够显著影响齿肋赤藓的游离脯氨酸、可溶性糖、可溶性蛋白及丙二醛(MDA)含量、过氧化氢酶(CAT)、过氧化物酶(POD)、超氧化物歧化酶(SOD)活性。夏季的高温干旱使齿肋赤藓的脯氨酸、可溶性糖、MDA含量及3种抗氧化酶活性均显著高于冬季及春季,而可溶性蛋白含量却呈相反趋势。干旱的春季齿肋赤藓脯氨酸及可溶性糖显著高于冬季。而在低温湿润的冬季,齿肋赤藓丙二醛含量及过氧化氢酶活性均显著高于春季。表明夏季齿肋赤藓所受胁迫最大,脯氨酸、可溶性糖含量及抗氧化酶活性大幅度提高。同时,在具有积雪覆盖的冬季,两种微生境下的齿肋赤藓生理生化特性无显著差异;而在无积雪覆盖的春夏季节,灌丛的遮阴作用为齿肋赤藓提供了水含量相对较高的良好生活环境,其下齿肋赤藓的渗透调节物质含量和抗氧化酶活性均显著低于裸露地。表明生长在裸露地的齿肋赤藓较活灌丛拥有更强的胁迫耐受性。     

高寒沙区生物土壤结皮对吸湿凝结水的影响

高寒沙区,水资源匮乏,吸湿凝结水是维持当地生态环境的重要非生物影响因子。采用自制微渗仪(直径10 cm,高度分别为3、4、6、11 cm)观测3类生物土壤结皮(苔藓结皮、藻类结皮、物理结皮)和流沙的吸湿凝结水量变化规律。结果表明:观测期间,除去大风和降雨天气外,吸湿凝结水每天都会产生;不同地表类型产生的吸湿凝结水量存在差异,生物土壤结皮生成的吸湿凝结水量显著大于流沙上产生的吸湿凝结水(P0.05),即生物土壤结皮有利于吸湿凝结水的生成;随着结皮的发育,吸湿凝结水量呈增加趋势,主要表现为:流沙物理结皮藻类结皮苔藓结皮;凝结现象自19:00开始,次日7:00结束;日出后,吸湿凝结水量迅速下降,持续时间为5 h,其中苔藓结皮与流沙下降速率最快;吸湿凝结水主要集中在土壤表层5 cm内,达总凝结量的90%以上,且观测值变异系数小,可作为代表性土壤深度进行吸湿凝结水的相关研究;吸湿凝结水量与大气温湿度密切相关,与大气温度呈负相关关系,与大气湿度呈正相关关系;吸湿凝结水量受取样深度、地表类型、大气温湿度等多方面因素的影响。     

Further Readings in Geomicrobiology

Evaporite accumulations produced by artesian waters in the arid zones of southern Tunisia led to the formation of subrounded, gypsiferous mounds consisting of irregular alternations of mineral precipitates and aeolian sand. The joint occurrence of gypsum crusts and plant colonization determined the stabilization of their top surface. Careful examination of the pigmented (green-brown) crusts revealed endolithic microbial communities just below the surface. In previous optical and scanning electron microscope studies cyanobacteria were the dominant component of these communities. Molecular diversity studies based on small subunit ribosomal RNA (SSU rRNA) gene analysis revealed that Flavobacteria, Actinobacteria, Deinococcales, Alpha- and Gamma- Proteobacteria are also important components of the microbial assemblage. Their pigment analyses, determined by high performance liquid chromatography (HPLC), detected the presence of carotenoids and chlorophyll (chl) a and b. Microbial communities that produce pigmentation and display an endolithic lifestyle typify the extreme environments as those found in arid/semiarid and hot desert regions.     

黄土高原封禁林地藓结皮呼吸速率对放牧踩踏干扰强度的响应

放牧踩踏造成的土壤属性变化是引起土壤呼吸速率和碳固排波动的重要原因,但目前有关不同强度放牧踩踏对生物结皮呼吸的影响尚不明确。本研究针对黄土高原风沙土发育的藓结皮,以未干扰为对照,分别进行强度为10%、30%、50%和70%的模拟放牧踩踏干扰,连续测定了藓结皮呼吸速率的变化,分析了藓结皮呼吸速率对不同干扰强度的响应规律。结果表明: 1)适度干扰会激发藓结皮呼吸速率,而重度干扰则会抑制其呼吸速率。与未干扰相比,干扰10%和30%的藓结皮呼吸速率分别增加了41.1%和22.2%,而干扰50%和70%的藓结皮呼吸速率则分别降低了8.9%和15.3%。2)踩踏干扰显著改变了土壤温度,但对土壤含水量的影响不显著。与未干扰相比,干扰10%和30%的土壤温度分别显著降低了0.4和1.2 ℃,干扰50%和70%则分别显著增加了1.1和1.0 ℃。3)不同干扰强度下藓结皮呼吸速率与土壤温度和含水量分别呈显著指数和线性正相关关系,但与藓结皮基本特性无显著相关关系,土壤温度和水分可分别解释藓结皮呼吸速率动态变化的70.6%～96.3%和49.1%～70.0%。综上,放牧踩踏显著影响了藓结皮呼吸速率,短期适度放牧踩踏会激发藓结皮呼吸速率,而过度放牧踩踏则会抑制其呼吸速率。因此,在未来黄土高原地区土壤碳收支平衡研究中应考虑不同强度放牧踩踏对生物结皮呼吸的影响。