物种和基物偏好对河北太行山区六种地衣的元素含量的影响

为了解物种和基物偏好对地衣元素水平的影响,测定了采集于河北太行山区6个地点的6种地衣体内的16种元素（Al、Ba、Cd、Cr、Cu、Fe、Mn、Mo、Na、P、S、Sc、Sr、Ti、V和Zn）的含量。这6种地衣包括3种石生地衣（鸡冠胶衣Collema cristatum、中国石黄衣Xanthoria mandschurica和淡腹黄梅Xanthoparmelia mexicana）,2种土生地衣（莲座石蕊Cladonia pocillum和石果衣Endocarpon pusillum）,及1种树生地衣（毛边黑蜈蚣衣Phaeophyscia hispidula）。主成分分析（PCA）和费里德曼双向秩方差分析（Friedman检验）结果显示,物种和基物偏好对地衣体内元素含量的影响显著,而地点的影响不显著。树生地衣累积的大气源元素（P、S和Zn）高于土生和石生地衣。土生地衣体内的地壳源元素（Al、Ba、Fe、Mn、Mo、Na、Sc、Sr、Ti和V）和大气源元素Cr的含量最高。石生地衣的大气源元素（P、S和Zn）含量近于土生地衣,但地壳源元素含量较低;3种石生地衣在这些元素的含量方面差异不大。这些结果表明以地衣化学组成监测大气元素沉降的研究需慎重考虑物种及基物偏好的影响。     

In vitro antiprotozoal activity of the lipophilic extracts of different parts of Turkish Pistacia vera L.

Thirteen lipophilic extracts prepared with n-hexane from various parts of Pistacia vera L. tree (Anacardiaceae) growing in Turkey were screened for their in vitro activity against four parasitic protozoa, Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum. Melarsoprol, benznidazole, miltefosine, artemisinin and chloroquine were used as reference drugs. The cytotoxic potentials of the extracts on rat skeletal myoblast (L6) cells were also assessed and compared to that of podophyllotoxin. The screening method employed was medium-throughput, where the extracts were tested at two concentrations, at 0.8 and 4.8 μg/ml (T. brucei rhodesiense, L. donovani and Plasmodium falciparum), or at 1.6 and 9.7 μg/ml (T. cruzi and L6 cells). At 4.8 μg/ml concentration, the branch extract of Pistacia vera (PV-BR) significantly inhibited (77.3%) the growth of L. donovani, whereas the dry leaf extract (PV-DL) was active against Plasmodium falciparum (60.6% inhibition). The IC₅₀ values of these extracts were determined as 2.3 μg/ml (PV-BR, L. donovani) and 3.65 μg/ml (PV-DL, Plasmodium falciparum). None of the extracts possessed cytotoxicity on mammalian cells.     

Pigment analysis of sun and shade populations of Cladonia verticillaris

The natural occurrence of the lichen Cladonia verticillaris as sunny and shaded populations implies changes in the pigment content. Shade specimens contain more chlorophyll a and b as well as more - and β-carotene than those found in unshaded lichens. However, lichens growing in sunny locations contain more methyl β-orcinol carboxylate, orcinol and fumarprotocetraric acid than those found in lichens growing under low light intensities. No structural differences in the chloroplasts of the two species bave been detected.     

Effects of tannic acid and its related compounds on food mutagens or hydrogen peroxide-induced DNA strands breaks in human lymphocytes

The effect of tannic acid (TA), gallic acid (GA), propyl gallate (PA) and ellagic acid (EA) on DNA damage in human lymphocytes induced by food mutagens [3-amino-1-methyl-5H-pyrido (4,3-b) indole (Trp-P-2) and 2-amino-1-methyl-6-phenylimadazo (4,5-b) pyridine (PhIP) or H₂O₂ was evaluated by using single-cell electrophoresis (comet assay). The toxicity of these tested compounds (0.1–100 μg/ml) on lymphocytes was not found. These compounds did not cause DNA strand breaks at lower concentrations of 0.1–10 μg/ml. At a concentration of 100 μg/ml, TA and GA exhibited slight DNA damage, whereas PA and EA showed no DNA strand breaks. TA and its related compounds decreased the DNA strand breaks induced by Trp-P-2, PhIP or H₂O₂ at concentrations of 0.1–10 μg/ml. DNA repair enzymes endonuclease III (Endo III) and formamidopyrimidine-DNA glycoslase (FPG)] were used to examine the levels of oxidised pyrimidines and purines in human lymphocytes induced by H₂O₂. All the compounds at 10 μg/ml can reduce the level of FPG sensitive sites. However, only EA inhibited the formation of EndoIII sensitive sites. The results indicated that these compounds can enhance lymphocytes resistance towards DNA strand breaks induced by food mutagens or H₂O₂ in vitro.     

Quantitative variation and the ecological role of vulpinic acid and atranorin in thallus of Letharia vulpina

High pressure liquid chromatography was used to determine concentrations of vulpinic acid and atranorin in the thaullus of Letharia vulpina. Vulpinic acid concentration is lowest in the old basal branches of the thallus and increases toward the young branch tips, whereas the reverse is true for atranorin. The suggested role of vulpinic acid as an anti-herbivore defense compound is supported by both this distribution of the compound and our observations that vulpinic acid acts as a feeding deterrent to certain invertebrates. No significant difference in the content of atranorin or vulpinic acid was found in lichens from microhabitats of different sunlight intensities.     

Development and validation of an in vitro Trichostrongylus colubriformis motility assay

Development and validation of an in vitro Trichostrongylus colubriformis motility assay. International Journal for Parasitology 17: 1441–1444. An in vitro Trichostrongylus colubriformis motility assay involving the use of a micromotility meter has been developed and validated. Four commercially available ruminant anthelmintics (albendazole, ivermectin, levamisole hydrochloride, and coumaphos) and an investigational hydrazone compound (p-toluoyl chloride phenylhydrazone) were evaluated in this assay at four concentrations each. At 100 μg ml^-1, all five treatments significantly (P 0.05) reduced the motility of ensheathed L-3 T. colubriformis larvae, thereby indicating anthelmintic activity. At this concentration, coumaphos was significantly less active than any of the other four treatments. At 10 μg ml^-1 albendazole, ivermectin, levamisole hydrochloride and the hydrazone compound were active, but coumaphos was not. At 1 μg ml^-1 albendazole, ivermectin and levamisole hydrochloride remained significantly active, but neither coumaphos nor the hydrazone compound showed significant activity. At all three of the higher concentrations (1,10 and 100 μg ml^-1), levamisole hydrochloride indicated greater activity than any of the other treatments. This difference was statistically significant at the 1 and 10 μg ml^-1 concentrations. None of the five treatments showed significant activity at the lowest concentration (0.1 μg ml^-1). The in vitro T. colubriformis motility assay proved to be sensitive, accurate, rapid, and repeatable. This assay system should be another valuable addition to the tests used to identify potential anthelmintics, monitor helminth resistance to drugs, and define the kinetics and mode of action of drugs.     

Chronic systemic treatment with epidermal growth factor in the rat increases the mucosal surface of the small intestine

We examined the effects of treatment with human recombinant epidermal growth factor (EGF) on the functioning small intestine in the rat. Male Wistar rats, 7–8 weeks old, were treated with EGF administered subcutaneously in doses of 0 (n = 7) or 150 μg/kg/day (n = 8) for 4 weeks. The histological composition and mucosal surface area of the perfusion-fixed small intestine was quantified with stereological principles. The length of the gut remained unchanged. The amount of tissue and surface area per length of gut (median (ranges)) were increased from 117 (101–131) mg/cm and 2.6 (2.1–3.5) cm²/cm in the controls to 146 (138–152) mg/cm and 3.5 (2.5–3.8) cm²/cm for the complete small intestine (both comparisons p < 0.02). The weight increase was due to mucosal growth in all parts of the intestine, whereas the surface area was only increased in proximal and middle parts. It is concluded that EGF treatment in rats increases the mucosal weight and surface area of the functioning small intestine.     

Lichen palatability depends on investments in herbivore defence

Lichens are well-suited organisms for experimental herbivory studies because their secondary compounds, assumed to deter grazing, can be non-destructively extracted. Thalli of 17 lichen species from various habitats were cut in two equal parts; compounds were extracted from one part by acetone, the other served as a control. These two pieces were offered as a paired choice to the generalist herbivore snail Cepaea hortensis. Control thalli of all lichens were consumed at a low rate regardless of their investments in acetone-extractable lichen compounds; naturally compound-deficient lichen species were not preferred compared to those with high contents. However, for extracted thalli, there was a highly significant positive correlation between rate of consumption and the extracted compound contents. These data imply that herbivore defence has evolved in different directions in different lichens. Studied members of Parmeliaceae, common in oligotrophic habitats, have high contents of carbon-rich acetone-soluble compounds; these lichens became highly palatable to snails subsequent to acetone rinsing. Extracted lichen compounds were applied to pieces of filter paper and fed to snails. Extracts from members of the Parmeliaceae significantly deterred feeding on paper. Such data suggest that generalist herbivores may have shaped evolution in the widespread and highly diverse Parmeliaceae towards high investments in lichen compounds. On the other hand, lichens belonging to the Physciaceae and Teloschistales, common in nutrient-enriched habitats, are deficient in, or have low concentrations of, lichen compounds. Such lichens did not become more palatable after acetone rinsing. The orange anthraquinone compound parietin, restricted to the Teloschistales, and which has previously been found to protect against excess light, did not deter grazing.     

Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets

Several lichen compounds, i.e. lobaric acid (1), a β-orcinol depsidone from Stereocaulon alpinum L., (+)-protolichesterinic acid (2), an aliphatic -methylene-γ-lactone from Cetraria islandica Laur. (Parmeliaceae), (+)-usnic acid (3), a dibenzofuran from Cladonia arbuscula (Wallr.) Rabenh. (Cladoniaceae), parietin (4), an anthraquinone from Xanthoria elegans (Link) Th. Fr. (Calaplacaceae) and baeomycesic acid (5), a β-orcinol depside isolated from Thamnolia vermicularis (Sw.) Schaer. var. subuliformis (Ehrh.) Schaer. were tested for inhibitory activity on platelet-type 12(S)-lipoxygenase using a cell-based in vitro system in human platelets. Lobaric acid (1) and (+)-protolichesterinic acid (2) proved to be pronounced inhibitors of platelet-type 12(S)-lipoxygenase, whereas baeomycesic acid (5) showed only weak activity (inhibitory activity at a concentration of 100 μg/ml: 1 93.4±6.62%, 2 98,5±1.19%, 5 14.7±2.76%). Usnic acid (3) and parietin (4) were not active at this concentration. 1 and 2 showed a clear dose–response relationship in the range of 3.33–100 μg/ml. According to the calculated IC₅₀ values the highest inhibitory activity was observed for the depsidone 1 (IC₅₀=28.5 μM) followed by 2 (IC₅₀=77.0 μM). The activity of 1 was comparable to that of the flavone baicalein, which is known as a selective 12(S)-lipoxygenase inhibitor (IC₅₀=24.6 μM).     

Effects of peptide YY and its analogues on chloride ion secretion in fed and fasted rat jejunum

The aim of our study was to determine whether a meal modifies the antisecretory response induced by PYY and the structural requirements to elicit antisecretory effects of analogue PYY(22–36) for potential antidiarrhea therapy. The variations in short-circuit current (Isc) due to the modification of ionic transport across the rat intestine were assessed in vitro, using Ussing chambers. In fasted rats, PYY induced a dose- and time-dependent reduction in Isc, with a sensitivity threshold at 5 × 10⁻¹¹ M (ΔIsc −2 ± 0.5 μA/cm²). The reduction was maximal at 10⁻⁷ M (Isc −23 ± 2 μA/cm²), and the concentration producing half-maximal inhibition was 10⁻⁹ M. At 10⁻⁷ M, reduction of Isc by PYY reached 90% of response to 5 × 10⁻⁵ M bumetanide. The PYY effect was partly reversed by 10⁻⁵ M forskolin (Isc +13.43 ± 2.91 μA/h·cm², p < 0.05) or 10⁻³ M dibutyryl adenosine 3′,5′ cyclic monophosphate (Isc +12 ± 1.69 μA/cm², p < 0.05). Naloxone and tetrodotoxin did not alter the effect of PYY. In addition, PYY and its analogue P915 reduced net chloride ion secretion to 2.85 and 2.29 μEq/cm² (p < 0.05), respectively. The antisecretory effect of PYY was accompanied by dose- and time-dependent desensitization when jejunum was prestimulated by a lower dose of peptide. The antisecretory potencies exhibited by PYY analogues required both a C-terminal fragment (22–36) and an aromatic amino acid residue (Trp or Phe) at position 27. At 10⁻⁷ M the biological activity of PYY was lower in fed than fasted rats (p < 0.001). Our results confirm the antisecretory effect of PYY, but show that the fed period is accompanied by desensitization, similar to the transient desensitization observed in the fasted period with cumulative doses. This suggests that PYY may act as a physiological mediator that reduces intestinal secretion.     

Wound-induced accumulations of condensed tannins in turtlegrass, Thalassia testudinum

Turtlegrass, Thalassia testudinum, produces high concentrations of proanthocyanidins (condensed tannins) which we hypothesized are induced by grazing, as a component of a general wound response. To test this we quantified condensed tannins in a variety of turtlegrass tissues following simulated fish grazing, grazing by the urchin Lytechinus variegatus, and treatment with the natural plant wound hormone jasmonic acid. We observed that simulated fish grazing triggered rapid induction of condensed tannins by an average of 10 mg tannin g⁻¹ dry mass (DM) after 5 days. Condensed tannin accumulations were correlated with a reduction of blade extension rates. Further, we observed that constitutive tannin levels in developing first-rank leaves were strongly correlated with the width of second-rank leaves on each shoot, with an increase of 7.7 mg tannin g⁻¹ tissue dry mass per millimeter blade width on average. We propose that wider source leaves provide additional resources for phenolic biosynthesis. There was no induction of tannins in leaves, meristematic or sheath tissues in response to grazing by the urchin L. variegatus, the presence of potential waterborne cues from nearby grazed plants, or to treatment with 5 mM jasmonic acid. However, urchin grazing did induce tannin production in root/rhizome tissues, where they accumulated to levels 3–4 times higher than in blades (up to 350 mg tannin g⁻¹ tissue dry mass). These results confirm the potential for rapid wound-induced condensed tannin accumulations in T. testudinum. The link between blade widths and the tannin content of new leaves indicates that leaf morphology may be a useful bioindicator for predicting herbivore and disease-resistance in the field.     

Effects of quantitative and qualitative variation in phenolic compounds on feeding in three species of marine invertebrate herbivores

The deterrent effects of brown algal phenolic compounds and the terrestrial polyphenolic tannic acid on feeding by three species of invertebrate herbivores from central California, including the gastropods Tegula funebralis (Adams) and Tegula brunnea (Phillipi) and the echinoid Strongylocentrotus purpuratus (Stimpson) were examined. Algal phenolics used were the monomeric phenolic phloroglucinol and polyphloroglucinols from Fucus vesiculosus (Linnaeus), Halidrys siliquosa (Linnaeus) Lyngbye and Eisenia arborea Areschoug. All of the polyphenolics deterred feeding by all three herbivores at concentrations of 5 mg · ml⁻¹ in agar disks. Concentrations of 2 mg · ml⁻¹ also generally deterred feeding by the gastropods (these levels were not tested against S. purpuratus). Relative amounts of deterrence by different compounds were similar, especially for the gastropods. Phloroglucinol deterred feeding by the echinoids, but not by T. funebralis. Responses of the echinoids were otherwise similar to the gastropods, but more variable. I also demonstrated deterrence of S. purpuratus by tannic acid using the “tanned” kelp technique of Steinberg (1985). Reactivity of the different phenolic compounds in the Folin-Denis procedure, a common colorimetric assay used to estimate levels of phenolics in plant tissue, was similar. This suggests that measuring phenolic levels in brown algae by this technique will not be greatly confounded by the occurrence of different kinds of phenolic molecules in different brown algae. This result, in combination with the similarity of the deterrent effects of the compounds used in this study, increases the validity of previous studies in the northeastern Pacific Ocean which correlate algal phenolic levels and diets or feeding preferences of invertebrate herbivores. For plants and herbivores in this region, this assay is a reasonable measure of a biologically meaningful phenomenon — levels of phenolic deterrents in the algae.     

Contrasting changes in palatability following senescence of the lichenized fungi Lobaria pulmonaria and L. scrobiculata

Epiphytic lichens can contribute significantly to ecosystem nutrient input because they efficiently accumulate atmospheric mineral nutrients and, in the case of cyanolichens, also fix nitrogen. The rate at which carbon and other nutrients gained by lichens enters the ecosystem is determined by lichen litter decomposability and by invertebrate consumption of lichen litter. In turn, these processes are driven by the secondary compounds present in senesced lichens. Therefore, we explored how lichen palatability and concentrations of secondary compounds change with tissue senescence for Lobaria pulmonaria, a green-algal lichen with cyanobacterial cephalodia, and Lobaria scrobiculata, a cyanobacterial lichen. During senescence both lichens lost 38–48 % of their stictic acid chemosyndrome, while m-scrobiculin and usnic acid in L. scrobiculata remained unchanged. Snails preferred senesced rather than fresh L. pulmonaria, while senesced L. scrobiculata were avoided. This provides evidence that species with labile secondary compounds will have higher turnover rates, through consumption and decomposition, than those producing more stable secondary compounds.     

Polyamine derivatives as inhibitors of trypanothione reductase and assessment of their trypanocidal activities

Trypanothione reductase (TR) occurs exclusively in trypanosomes and leishmania, which are the etiological agents of many diseases. TR plays a vital role in the antioxidant defenses of these parasites and inhibitors of TR have potential as antitrypanosomal agents. We describe the syntheses of several spermine and spermidine derivatives and the inhibiting effects of these compounds on T. cruzi TR. All of the inhibiting compounds displayed competitive inhibition of TR-mediated reduction of trypanothione disulfide. The three most effective compounds studied were N⁴,N⁸-bis(3-phenylpropyl)spermine (12), N⁴,N⁸-bis(2-naphthylmethyl)spermine (14), and N¹,N⁸-bis(2-naphthylmethyl)spermidine (21), with K_i values of 3.5, 5.5 and 9.5 μM, respectively. Compounds 12, 14, and 21 were found to be potent trypanocides in vitro with IC₅₀ values ranging from 0.19 to 0.83 μM against four T. brucei ssp. strains. However, these compounds did not prolong the lives of mice infected with trypanosomes. This work indicates that certain polyamine derivatives which target a unique pathway in Trypanosomatidae have potential as antitrypanosomal agents.     

Method for the determination of 5,5-diphenylbarbituric acid and its separation from 1,3-dimethoxymethyl-5,5-diphenylbarbituric acid in plasma by high-performance liquid chromatography

A method is described for the measurement of 5,5-diphenylbarbituric acid in plasma using high-performance liquid chromatography with UV detection. Briefly, the compounds are separated on a C₁₈ reversed-phase column using a mobile phase of 50 mM sodium acetate (pH 4.5) and methanol. The flow-rate is 1.0 ml/min and 25 μl are injected and detected at 215 nm. The method is specific and sensitive in the range of concentrations tested, with a limit of quantification of 0.25 μg/ml. The calibration curves are linear for concentrations between 0.25 and 10 μg/ml. Intra-day and inter-day coefficients of variation are less than 8.5 and 10.5%, respectively, over the linear range. Intra-day and inter-day bias are less than 7.0 and 8.0%, respectively. A pharmacokinetic study conducted in male Beagle dogs administered 10 mg/kg of 1,3-dimethoxymethyl-5,5-diphenylbarbituric acid or 8 mg/kg of 5,5-diphenylbarbituric acid intravenously demonstrates the utility of this method.     

Halophila ovalis (R. Br.) Hook. f. from a submarine hot spring in southern Japan

Colonies of the seagrass Halophila ovalis are found growing adjacent to coral Acropora sp. and Seriatopora hystrix in a submarine hot spring (at 15.7 m depth, 28.6°C) at the north coast of Taketomi Island, near the southern tip of Japan. Halophila plants grow in sea water containing sulphide 930 μg S ml⁻¹ and on the substratum with fine precipitates of the submarine hot spring which have sulphide content up to 5400 μg S g⁻¹ DW. The accumulated sulphide concentration reaches as high as 8400 μg S g⁻¹ DW in under ground tissues and 5700 μg S g⁻¹ DW in above-ground tissues, respectively. It is suggested that, not the sulphide concentration but light and possibly water temperature are the limiting factors for the Halophila colonization in the submarine hot spring.     

Evaluation of the trypanocidal and leishmanicidal in vitro activity of the crude hydroalcoholic extract of Pfaffia glomerata (Amarathanceae) roots

Three different concentrations (1, 10 and 50 μg/ml) of lyophilized hydroalcoholic crude extract of Pfaffia glomerata roots were assayed in vitro against strains of Trypanosoma cruzi (Y) and Leishmania braziliensis. It was observed that P. glomerata hydroalcoholic extract was relatively active within the tested concentrations for L. (V.) braziliensis, but inactive against T. cruzi. Despite the fact that both protozoans belong to the Trypanosomatidae family, we suggest that the difference observed for activity should be related to the biological differences between the two parasite species.     

Light might regulate divergently depside and depsidone accumulation in the lichen Parmotrema hypotropum by affecting thallus temperature and water potential

Depsides and depsidones are the most common secondary products uniquely produced in lichens by the fungal symbiont, and they accumulate on the outer surface of its hyphae. Their biological roles are subject to debate. Quantitatively the compounds typical of a given lichen can vary dramatically from thallus to thallus. Several studies have addressed whether this variability is correlated with the light reaching different thalli, but the conclusions are contradictory. We addressed the question with the lichen Parmotrema hypotropum growing on unshaded, vertical tree trunks, a controlled natural environment where the light absorbed by each thallus over its lifetime is the only major position-dependent variable. The exact north-east-south-west orientation of each thallus was used to calculate its yearly light exposure based on astronomical and meteorological considerations. The calculated irradiation around the trunk, distributed over a continuous 40-fold intensity range, then was compared with the amount of compound per unit thallus weight, determined by quantitative thin layer chromatography. P. hypotropum accumulates the depside atranorin in the cortex and the depsidone norstictic acid in the medulla and around the algae. A direct correlation was observed between the yearly amount of light reaching the lichen and the amount of atranorin. In contrast, the amount of norstictic acid decreased with increasing light. Although we did not measure thallus temperature and water potential, a unifying interpretation of these and other published data is that depside/depsidone accumulation in lichens is mediated by localized changes in temperature and water potential produced by light absorption within each thallus. This suggests water relations-based functions for depsides and depsidones.     

Highly selective inhibition of estrogen biosynthesis by CGS 20267, a new non-steroidal aromatase inhibitor

CGS 20267 is a new non-steroidal compound which potently inhibits aromatase in vitro (IC₅₀ of 11.5 nM) and in vivo (ED₅₀ of 1–3 μg/kg p.o.). CGS 20267 maximally inhibits estradiol production in vitro in LH-stimulated hamster ovarian tissue at 0.1 μM with an IC₅₀ of 0.02 μM and does not significantly affect progesterone production up to 350 μM. In ACTH-stimulated rat adrenal tissue in vitro, aldosterone production was inhibited with an IC₅₀ of 210 μM (10,000 times higher than the IC₅₀ for estradiol production); no significant effect on corticosterone production was seen at 350 μM. In vivo, in ACTH-treated rats, CGS 20267 does not affect plasma levels of corticosterone or aldosterone at a dose of 4 mg/kg p.o. (1000 times higher than the ED₅₀ for aromatase inhibition in vivo). In adult female rats, a 14-day treatment with 1 mg/kg p.o. daily, completely interrupts ovarian cyclicity and suppresses uterine weight to that seen 14 days after ovariectomy. In adult female rats bearing estrogen-dependent DMBA-induced mammary tumors, 0.1 mg/kg p.o. given daily for 42 days caused almost complete regression of tumors present at the start of treatment. Thus compared to each other, CGS 16949A and CGS 20267 are both highly potent in inhibiting estrogen biosynthesis in vitro and in vivo. The striking difference between them is that unlike CGS 16949A, CGS 20267 does not affect adrenal steroidogenesis in vitro or in vivo, at concentrations and doses several orders of magnitude higher than those required to inhibit estrogen biosynthesis.     

Dynamics of cover, UV-protective pigments, and quantum yield in biological soil crust communities of an undisturbed Mojave Desert shrubland

Biological soil crusts are an integral part of dryland ecosystems. We monitored the cover of lichens and mosses, cyanobacterial biomass, concentrations of UV-protective pigments in both free-living and lichenized cyanobacteria, and quantum yield in the soil lichen species Collema in an undisturbed Mojave Desert shrubland. During our sampling time, the site received historically high and low levels of precipitation, whereas temperatures were close to normal. Lichen cover, dominated by Collema tenax and C. coccophorum, and moss cover, dominated by Syntrichia caninervis, responded to both increases and decreases in precipitation. This finding for Collema spp. at a hot Mojave Desert site is in contrast to a similar study conducted at a cool desert site on the Colorado Plateau in SE Utah, USA, where Collema spp. cover dropped in response to elevated temperatures, but did not respond to changes in rainfall. The concentrations of UV-protective pigments in free-living cyanobacteria at the Mojave Desert site were also strongly and positively related to rainfall received between sampling times (R² values ranged from 0.78 to 0.99). However, pigment levels in the lichenized cyanobacteria showed little correlation with rainfall. Quantum yield in Collema spp. was closely correlated with rainfall. Climate models in this region predict a 3.5–4.0 °C rise in temperature and a 15–20% decline in winter precipitation by 2099. Based on our data, this rise in temperature is unlikely to have a strong effect on the dominant species of the soil crusts. However, the predicted drop in precipitation will likely lead to a decrease in soil lichen and moss cover, and high stress or mortality in soil cyanobacteria as levels of UV-protective pigments decline. In addition, surface-disturbing activities (e.g., recreation, military activities, fire) are rapidly increasing in the Mojave Desert, and these disturbances quickly remove soil lichens and mosses. These stresses combined are likely to lead to shifts in species composition and the local extirpation of some lichen or moss species. As these organisms are critical components of nutrient cycling, soil fertility, and soil stability, such changes are likely to reverberate throughout these ecosystems.