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Prevalent interactions among marine phytoplankton triggered by long‐range climatic stressors are well‐known environmental disturbers of community structure. Dynamic response of phytoplankton physiology is likely to come from interspecies interactions rather than direct climatic effect on single species. However, studies on enigmatic interactions among interspecies, which are induced by bioactive extracellular compounds (BECs), especially between related harmful algae sharing similar shellfish toxins, are scarce. Here, we investigated how BECs provoke the interactions between two notorious algae, Alexandrium minutum and Gymnodinium catenatum, which have similar paralytic shellfish toxin (PST) profiles. Using techniques including electron microscopy and transcriptome analysis, marked disruptions in G. catenatum intracellular microenvironment were observed under BECs pressure, encompassing thylakoid membrane deformations, pyrenoid matrix shrinkage and starch sheaths disappearance. In addition, the upregulation of gene clusters responsible for photosystem‐I Lhca1/4 and Rubisco were determined, leading to weaken photon captures and CO2 assimilation. The redistribution of lipids and proteins occurred at the subcellular level based on in situ focal plane array FTIR imaging approved the damages. Our findings illuminated an intense but underestimated interspecies interaction triggered by BECs, which is responsible for dysregulating photosynthesis and organelle function in inferior algae and may potentially account for fitness alteration in phytoplankton community. Summary statement: The bioactive extracellular compounds of Alexandrium minutum can induce interspecies interaction by affecting the cell physiology of related harmful algae, mainly showing damage to photosynthetic organelles and redistribution of intracellular biomacromolecules. [ABSTRACT FROM AUTHOR]

Lichens are one of the most iconic and ubiquitous symbioses known, widely valued as indicators of environmental quality and, more recently, climate change. Our understanding of lichen responses to climate has greatly expanded in recent decades, but some biases and constraints have shaped our present knowledge. In this review we focus on lichen ecophysiology as a key to predicting responses to present and future climates, highlighting recent advances and remaining challenges. Lichen ecophysiology is best understood through complementary whole‐thallus and within‐thallus scales. Water content and form (vapor or liquid) are central to whole‐thallus perspectives, making vapor pressure differential (VPD) a particularly informative environmental driver. Responses to water content are further modulated by photobiont physiology and whole‐thallus phenotype, providing clear links to a functional trait framework. However, this thallus‐level perspective is incomplete without also considering within‐thallus dynamics, such as changing proportions or even identities of symbionts in response to climate, nutrients, and other stressors. These changes provide pathways for acclimation, but their understanding is currently limited by large gaps in our understanding of carbon allocation and symbiont turnover in lichens. Lastly, the study of lichen physiology has mainly prioritized larger lichens at high latitudes, producing valuable insights but underrepresenting the range of lichenized lineages and ecologies. Key areas for future work include improving geographic and phylogenetic coverage, greater emphasis on VPD as a climatic factor, advances in the study of carbon allocation and symbiont turnover, and the incorporation of physiological theory and functional traits in our predictive models. [ABSTRACT FROM AUTHOR]

The streptophyte algal class Zygnematophyceae is the closest algal sister lineage to land plants. In nature, Zygnematophyceae can grow in both terrestrial and freshwater habitats and how they do this is an important unanswered question. Here, we studied what happens to the zygnematophyceaen alga Mougeotia sp., which usually occurs in permanent and temporary freshwater bodies, when it is shifted to liquid growth conditions after growth on a solid substrate. Using global differential gene expression profiling, we identified changes in the core metabolism of the organism interlinked with photosynthesis; the latter went hand in hand with measurable impact on the photophysiology as assessed via pulse amplitude modulation (PAM) fluorometry. Our data reveal a pronounced change in the overall physiology of the alga after submergence and pinpoint candidate genes that play a role. These results provide insight into the importance of photophysiological readjustment when filamentous Zygnematophyceae transition between terrestrial and aquatic habitats. [ABSTRACT FROM AUTHOR]

In today’s oceans, diatoms are abundant and diverse primary producers distinguished by their silica shells. Although molecular clocks suggest that diatoms arose as much as 250 million years ago (Ma), the earliest known diatom fossils date from 190 Ma, leading to the suggestion that early diatoms were at best lightly silicified. By the Cretaceous Period, large circular (in cross section) diatoms with highly silicified frustules thrived in surface oceans, only later to be joined by species with elongated and thinner frustules, as well as lower SiO2 content. Decreased Si availability in surface oceans has been proposed as a principal driver of diatom evolution. Here, we investigate this through physiological experiments assessing the functional acclimation response of diatoms to reconstructed paleo-seawater. Four diatom species, differing in size and shape, were acclimated to reconstructed paleoenvironments mimicking Mesozoic/Cenozoic concentrations of nutrients in the presence of different Si regimes. When exposed to 500 µM Si, all populations, save for that of Conticribra weissflogii, became more highly silicified; the higher Si content per cell at 500 µM Si coincided with slower growth in small-sized cells. All species except C. weissflogii also showed lower photosynthetic efficiency as well as greater cell volume in comparison with diatoms acclimated to 205 or 25 µM Si. Average cell stoichiometry correlates with cell shape, but not size; pennates, in particular Phaeodactylum tricornutum, showed an acclimatory response to Si regimes, modulating Si use efficiency (the lower the external Si concentrations, the higher the C and N quotas per Si).Experimental data suggest that in the densely silicified and bigger C. weissflogii grown at higher Si, diffusion of silicic acid across membranes made a larger contribution to Si uptake, saving energy which could be reallocated into growth. In contrast, for less highly silicified and smaller species, high energy costs of Si homeostasis needed to prevent the overaccumulation of intracellular Si limited growth. While our experimental species reacted individualistically to changing silica availability, with distinct levels of plasticity, selective pressure associated with the temporal decline in Si availability may well have favored elongated shapes. Modern, less silicified species are unable to exploit high Si concentrations.

Diatoms are feedstock for the production of sustainable biocommodities, including biofuel. The biochemical characterization of newly isolated or genetically modified strains is seminal to identify the strains that display interesting features for both research and industrial applications. Biochemical quantification of organic macromolecules cellular quotas are time-consuming methodologies which often require large amount of biological sample. Vibrational spectroscopy is an essential tool applied in several fields of research. A Fourier transform infrared (FTIR) microscopy-based imaging protocol was developed for the simultaneous cellular quota quantification of lipids, carbohydrates, and proteins of the diatom Phaeodactylum tricornutum. The low amount of sample required for the quantification allows the high throughput quantification on small volume cultures. A proof of concept was performed (1) on nitrogen-starved experimental cultures and (2) on three different P. tricornutum wild-type strains. The results are supported by the observation in situ of lipid droplets by confocal and brightfield microscopy. The results show that major differences exist in the regulation of lipid metabolism between ecotypes of P. tricornutum.

Diatoms are feedstock for the production of sustainable biocommodities, including biofuel. The biochemical characterization of newly isolated or genetically modified strains is seminal to identify the strains that display interesting features for both research and industrial applications. Biochemical quantification of organic macromolecules cellular quotas are time-consuming methodologies which often require large amount of biological sample. Vibrational spectroscopy is an essential tool applied in several fields of research. A Fourier transform infrared (FTIR) microscopy-based imaging protocol was developed for the simultaneous cellular quota quantification of lipids, carbohydrates, and proteins of the diatom Phaeodactylum tricornutum. The low amount of sample required for the quantification allows the high throughput quantification on small volume cultures. A proof of concept was performed (1) on nitrogen-starved experimental cultures and (2) on three different P. tricornutum wild-type strains. The results are supported by the observation in situ of lipid droplets by confocal and brightfield microscopy. The results show that major differences exist in the regulation of lipid metabolism between ecotypes of P. tricornutum. [ABSTRACT FROM AUTHOR]

Digestate is a complex by-product of anaerobic digestion and its composition depends on the digestor inputs. It can be exploited as a sustainable source of nutrients for microalgae cultivation but its unbalanced composition and toxic elements make the use challenging. Screening algae in a simplified synthetic digestate which mimics the main nutrient constraints of a real digestate is proposed as a reproducible and effective method to select suitable species for real digestate valorisation and remediation. Growth performance, nutrient removal and biomass composition of eight microalgae exposed to high amounts of NH 4 +, PO 4 − and organic-C were assessed. Using a score matrix, A. protothecoides , T. obliquus , C. reinhardtii , and E. gracilis were identified as the most promising species. Thus, three strategies were applied to improve outcomes: i) establishment of an algal consortium to improve biomass production, ii) K+ addition to the medium to promote K+ uptake over NH 4 + and to reduce potential NH 4 + toxicity, iii) P starvation as pretreatment for enhanced P removal by luxury uptake. The consortium was able to implement a short-term response displaying higher biomass production than single species (3.77 and 1.03–1.89 mg mL−1 respectively) in synthetic digestate while maintaining similar nutrient remediation, furthermore, its growth rate was 1.6 times higher than in the control condition. However, the strategies aiming to reduce NH 4 + toxicity and higher P removal were not successful except for single cases. The proposed algal screening and the resulting designed consortium were respectively a reliable method and a powerful tool towards sustainable real digestate remediation. • Growth and remediation in synthetic digestate were scored to select suitable algae. • A new algal consortium was established by assembling the selected species. • Biomass production was higher in the consortium than in the single species. • Consortium growth rate was higher in synthetic digestate than in control condition. • Strategies of K+ enrichment and P starvation pretreatment were not successful. [ABSTRACT FROM AUTHOR]

This study is a first attempt to evaluate the toxic effects of prominent aquatic pollutants (nutrients and toxic metals) on the brown seaweed Bushy Rainbow Wrack (Cystoseira tamariscifolia) physiology along the Atlantic coast of Morocco. The physicochem(nutrients) of seawater, toxic metals (Chromium, Lead, Copper and Cadmium) and physiological parameters (Chlorophyll contents, Proline, Glycinebetaine and Total Phenolic Compounds) of the brown macroalgae Bushy Rainbow Wrack were studied in order to assess the pollution degree of 8 coastal areas. The results show that the toxic metal contents of Bushy Rainbow Wrack (especially Cadmium) and the concentration of phosphorus are correlated with stress physiological parameters, and inversely correlated with pigment contents. It shows that while these brown algae exist in the less polluted areas, their physiology is significantly affected. However, in the highly polluted areas, this brown seaweed disappears. Thus, this specie could be used for monitoring the pollution degree in coastal areas. [ABSTRACT FROM AUTHOR]

Raphidiopsis (Cylindrospermopsis) raciborskii is one of the most studied potentially harmful cyanobacteria. Single environmental factors such as increased temperature or light are reported to be promoters of R. raciborskii growth, but the interaction of two or more promoting factors is less understood. The performance of two strains of R. raciborskii (MVCC19, Uruguayan and LP1, Brazilian) were evaluated under acclimation and temperature shifts (25–32°C) in combination with two transitions from phosphorus (P) sufficiency to limiting growth conditions. When subjected to transition from high P sufficiency to a P-limiting state, strains were able to grow only at the warmer temperature if previously acclimated. The MVCC19 strain showed higher specific growth rates and a shorter growth phase than LP1. Morphological differences were also found: the MVCC19 strain produced shorter filaments, while the LP1 strain increased in length and the number of cells per filament. The results show the positive effect of high temperature on the ability of R. raciborskii to withstand P-limiting conditions, which may confer resilience of populations to periods of severe nutrient limitation in warm lakes. This finding contributes to the understanding of the success of this species in diverse environmental conditions. The effect of temperature on the tolerance of nutrient deficiency and the performance of strains under lake conditions suggests the need for a drastic reduction in nutrient loads to avoid R. raciborskii dominance in warmer lakes. [ABSTRACT FROM AUTHOR]

Crustose coralline algae (CCA) are key organisms in coral reef ecosystems, where they contribute to reef building and substrate stabilization. While ocean acidification due to increasing CO2 can affect the biology, physiology and ecology of fully developed CCA, the impacts of elevated CO2 on the early life stages of CCA are much less explored. We assessed the photosynthetic activity and growth of 10-day-old recruits of the reef-building crustose coralline alga Porolithon cf. onkodes exposed to ambient and enhanced CO2 seawater concentration causing a downward shift in pH of ∼0.3 units. Growth of the CCA was estimated using measurements of crust thickness and marginal expansion, while photosynthetic activity was studied with O2 microsensors. We found that elevated seawater CO2 enhanced gross photosynthesis and respiration, but significantly reduced vertical and marginal growth of the early life stages of P. cf. onkodes. Elevated CO2 stimulated photosynthesis, particularly at high irradiance, likely due to increased availability of CO2, but this increase did not translate into increased algal growth as expected, suggesting a decoupling of these two processes under ocean acidification scenarios. This study confirms the sensitivity of early stages of CCA to elevated CO2 and identifies complexities in the physiological processes underlying the decreased growth and abundance in these important coral reef builders upon ocean acidification.

The vegetative growth of Haematococcus pluvialis TMU1 was studied under batchwise cultivation in three common media, namely BBM, BG11, and 3NBBM. The BBM provided the best condition for the algal growth. It was further studied at different levels of nitrate and phosphate as macronutrients as well as iron and boron as trace elements. The dose-response of the algal growth to these macro/micronutrients was modeled with Monod/hormetic-type kinetics. Applying the modified BBM with 3-fold higher phosphate led to the highest cell density and up to 86% increase in the growth rate. At an inoculum size of 2 × 10 5 cells mL −1 , the algal growth rate in BBM containing either 0.185 mM boron or 0.046 mM iron was higher than the medium containing half or twice ion levels. These optimal concentrations depend on inoculum size, so that changes from the optima increased the level of peroxide signaling molecules and induced defense pathways. [ABSTRACT FROM AUTHOR]

Dinoflagellates are a major component of marine phytoplankton and many species are recognized for their ability to produce harmful algal blooms (HABs). Scrippsiella trochoidea is a non-toxic, marine dinoflagellate that can be found in both cold and tropic waters where it is known to produce red tide events. Little is known about the genomic makeup of S. trochoidea and a transcriptome study was conducted to shed light on the biochemical and physiological adaptations related to nutrient depletion. Cultures were grown under N and P limiting conditions and transcriptomes were generated via RNAseq technology. De novo assembly reconstructed 107,415 putative transcripts of which only 41% could be annotated. No significant transcriptomic response was observed in response to initial P depletion, however, a strong transcriptional response to N depletion was detected. Among the down-regulated pathways were those for glutamine/glutamate metabolism as well as urea and nitrate/nitrite transporters. Transcripts for ammonia transporters displayed both up- and down-regulation, perhaps related to a shift to higher affinity transporters. Genes for the utilization of DON compounds were up-regulated. These included transcripts for amino acids transporters, polyamine oxidase, and extracellular proteinase and peptidases. N depletion also triggered down regulation of transcripts related to the production of Photosystems I & II and related proteins. These data are consistent with a metabolic strategy that conserves N, while maximizing sustained metabolism by emphasizing the relative contribution of organic N sources. Surprisingly, the transcriptome also contained transcripts potentially related to secondary metabolite production, including a homolog to the Short Isoform Saxitoxin gene (sxtA) from Alexandrium fundyense, which was significantly up-regulated under N-depletion. A total of 113 unique hits to Sxt genes, covering 17 of the 34 genes found in C. raciborskii were detected, indicating that S. trochoidea has previously unrecognized potential for the production of secondary metabolites with potential toxicity.

Dinoflagellates are a major component of marine phytoplankton and many species are recognized for their ability to produce harmful algal blooms (HABs). Scrippsiella trochoidea is a non-toxic, marine dinoflagellate that can be found in both cold and tropic waters where it is known to produce "red tide" events. Little is known about the genomic makeup of S. trochoidea and a transcriptome study was conducted to shed light on the biochemical and physiological adaptations related to nutrient depletion. Cultures were grown under N and P limiting conditions and transcriptomes were generated via RNAseq technology. De novo assembly reconstructed 107,415 putative transcripts of which only 41% could be annotated. No significant transcriptomic response was observed in response to initial P depletion, however, a strong transcriptional response to N depletion was detected. Among the down-regulated pathways were those for glutamine/glutamate metabolism as well as urea and nitrate/nitrite transporters. Transcripts for ammonia transporters displayed both up- and down-regulation, perhaps related to a shift to higher affinity transporters. Genes for the utilization of DON compounds were up-regulated. These included transcripts for amino acids transporters, polyamine oxidase, and extracellular proteinase and peptidases. N depletion also triggered down regulation of transcripts related to the production of Photosystems I & II and related proteins. These data are consistent with a metabolic strategy that conserves N while maximizing sustained metabolism by emphasizing the relative contribution of organic N sources. Surprisingly, the transcriptome also contained transcripts potentially related to secondary metabolite production, including a homolog to the Short Isoform Saxitoxin gene (sxtA) from Alexandrium fundyense, which was significantly up-regulated under N-depletion. A total of 113 unique hits to Sxt genes, covering 17 of the 34 genes found in C. raciborskii were detected, indicating that S. trochoidea has previously unrecognized potential for the production of secondary metabolites with potential toxicity. [ABSTRACT FROM AUTHOR]

Diatoms are among the most diverse groups of phytoplankton in the ocean. Despite their widely recognized influence on ocean ecosystems and global biogeochemistry, little is known about the impact of this diversity on large-scale processes. Here, we examined the ramifications of between-species diversity by documenting the transcriptional response of three diatoms - Thalassiosira pseudonana, Fragilariopsis cylindrus, and Pseudo-nitzschia multiseries - to the onset of nitrate limitation of growth, a common limiting nutrient in the ocean. The three species shared 5,583 clusters of orthologous genes based on OrthoMCL clustering of publically available diatom genomes. These clusters represent 30-54% of the predicted genes in each diatom genome. Less than 5% of genes within these core clusters displayed the same transcriptional responses across species when growth was limited by nitrate availability. Orthologs, such as those involved in nitrogen uptake and assimilation, as well as carbon metabolism, were differently expressed across the three species. The two pennate diatoms, F. cylindrus and P. multiseries, shared 3,839 clusters without orthologs in the genome of the centric diatom T. pseudonana. A majority of these pennate-clustered genes, as well as the non-orthologous genes in each species, had minimal annotation information, but were often significantly differentially expressed under nitrate limitation, indicating their potential importance in the response to nitrogen availability. Despite these variations in the specific transcriptional response of each diatom, overall transcriptional patterns suggested that all three diatoms displayed a common physiological response to nitrate limitation that consisted of a general reduction in carbon fixation and carbohydrate and fatty acid metabolism and an increase in nitrogen recycling. Characterization of these finely tuned responses will help to better predict which types of diatoms will bloom under which sets of environmenta

Abstract: Harmful algal blooms (HABs) are often associated with eutrophication of coastal waters and estuaries. However, identifying quantitative relationships between nutrient input and proliferation of specific algal species is very challenging and complex. The complexity arises from the diversity of sources, forms and fluxes of nutrients both exported into and cycled within the system, the diversity of algal mechanisms for acquiring nutrients, and the interaction of the target harmful species with other members of the food web. Even more challenging is the development of forecasts and predictions, both on the short term and on the long term. Short term scales (days to weeks) are necessary for managers to prepare for, and respond to events; longer scales are needed to enable strategic planning to prevent HAB events, mitigate their impacts, or estimate the interactive effects of anthropogenic activities and climate change. To address these needs the HAB modeling community will need to engage with climate scientists (assess climate change scenarios), marine ecologists (describe organism ecophysiology), invasive species experts, watershed modelers and hydrologists (estimate future changes in the land derived inputs), and socio economists, managers and policy makers (define future land use scenarios and to interpret results in a policy context). [ABSTRACT FROM AUTHOR]

Abstract: A new non-destructive method to study the nutritional status of algal cells and their environments is demonstrated. This approach allows rapid examination of whole cells without any or little pre-treatment providing a large amount of information on the biochemical composition of cells and growth medium. The method is based on the analysis of a collection of infrared (IR) spectra for individual cells; each spectrum describes the biochemical composition of a portion of a cell; a complete set of spectra is used to reconstruct an image of the entire cell. To obtain spatially resolved information synchrotron radiation was used as a bright IR source. We tested this method on the green flagellate Euglena gracilis; a comparison was conducted between cells grown in nutrient replete conditions (Type 1) and on cells allowed to deplete their medium (Type 2). Complete sets of spectra for individual cells of both types were analyzed with agglomerative hierarchical clustering, leading to distinct clusters representative of the two types of cells. The average spectra for the clusters confirmed the similarities between the clusters and the types of cells. The clustering analysis, therefore, allows the distinction of cells of the same species, but with different nutritional histories. In order to facilitate the application of the method and reduce manipulation (washing), we analyzed the cells in the presence of residual medium. The results obtained showed that even with residual medium the outcome of the clustering analysis is reliable. Our results demonstrate the applicability FTIR microspectroscopy for ecological and ecophysiological studies. [Copyright &y& Elsevier]

Clones of the filamentous green alga Ctenocladus circinnatus Borzi were isolated from algae collected at Abert were Lake (Oregon) and Mono Lake (California). Stock cultures were exposed to varied salinities of natural lake water to examine the effects on growth rate, cell form, chlorophyll a, and were almost completely inhibited at 150g·L[sup-1] Chlorophyll a increased between salinities of 25and 100 g·L[sup-1] salinity . Shorter cell dimensions with increased salinity suggest that a lower surface-to -volume ratio may reduce the potential for passive loss of cell water. Prior acclimation of stock cultures to elevated salinity provided no enhancement of growth response al any salinity. The results indicate that environmental salinity can limit the productivity and distribution of Ctenocladus in nature. [ABSTRACT FROM AUTHOR]

Cultures pf Anabaena flos-aquae (Lyng.) Breb. Were used to determine changes in nitrogenase activity (acetylene reduction) after external concentration of phosphorus were lowered. Two days following immersion in phosphorus-free medium, nitrogenase activity (NA) had doubled and required 8 days to return to time zero levels. Subsequent long-term experiments showed that concentrations of soluble reactive phosphorus (SRP) released from the algae transferred into the - P medium reached maximum levels by day 3 and returned to initial low values by days 7-10. NA was always highest during the SRP release-reassimilation phase but steadily decreased after reassimilation was complete. Day 56 NA was 5-14% of initial activity. The data support the hypothesis that heterocyst and vegetative cell ATP pools are discrete and suggest that the short-term effects of phosphorus removal as an aquatic restoration technique need further study. [ABSTRACT FROM AUTHOR]

Periphytic communities in running waters were examined as they developed on granite rocks, concrete balls and glass slides. At equivalent cell densities, no differences in pigment concentrations, species diversity or production levels were found among the different substrata examined. Development of the assemblage appeared to result from the elongation of short algal filaments which had initially settled on the surface. As these communities matured, a distinct canopy and understory developed. Cellular metabolisms were comparable among the communities. In the understory of the communities, even though the cellular content of chl a and b did not differ, chl c and carotenoid pigment concentrations were higher than those in the overstory. Bicarbonate assimilation of Tabellaria fenestrata (Lyng.) Kütz and Eunotia pectinalis var. pectinalis (O. F. Müll?) Rabh. was higher than that of the more abundant Tabellaria flocculosa ( Roth. ) Kütz. var. flocculosa IV (sensu Koppen) at both high and low cell densities. This probably reflect a seasonal succession of colonizing species. Glucose assimilation appeared to be mainly attributable to bacterial activity, and algal cells of the upper layer were less active than those of the bottom. The small amount of glucose that was incorporated by the algal cells was probably absorbed passively since its amount was in direct proportion to cell volumes. [ABSTRACT FROM AUTHOR]

Continuous cultures of Merismopedia tenuissima Lemmerman, limited by phosphorus, nitrogen, sulfur, or carbon, were compared to non-limited batch cultures by two methods. The cellular content photosynthetic pigments (chlorophyll and phycocyanin) was found to decrease in all nutrient limited cultures, except for the carbon limited culture. The ratio of carbohydrate to protein was 4- to 7-fold higher in P, N or S limited cultures than in non-limited or C limited cultures. The macromolecular products of photosynthesis were determined in sample to which NaH[SUP14]CO[SUB3] was added. Relative incorporation into protein decreased in P or N limited cultures, increased accumulation of low molecular weight compounds was found in S and P limited cultures, and little change was noted in C limited cultures as compared to non-limited cultures. Although relative in-corporation into protein was significantly greater at 20 μEin·m[SUP-2]·s[SUP-1] light intensity than at 180 μEin·m[SUP-2]·s[SUP-1] in non-limited cultures. These results suggest that measurements of the cellular carbohydrate to protein ratio and the products of photosynthesis would be useful in the analysis of algal population dynamics in nature. [ABSTRACT FROM AUTHOR]

Previously reported transplantation experiments in the field showed that Gastroclonium coulteri (Harvey) Kylin could survive above its normal intertidal range (0.0-0.5 m above MLLW), except during periods of daytime low tides in spring. Net photosynthetic rate measurements in the laboratory were performed to determine which physical factors might determine the upper boundary for this species in the intertidal zone. Maximum net photosynthesis occurred between 15 and 20°C, but remained positive between 4 and 35°C. The air temperature extremes observed in the field were 2°C (only seen once) and 26°C, Net photosynthesis increased as expected with light intensity to the highest value obtainable in the laboratory, 1400 μEin m[sup-2] s[sup-1]. Plants collected from the filed under higher light intensity (up to 2000 μEin m[sup-2] s[sup-2]) also showed high rates of photosynthesis. Desiccation, however, resulted in a sharp decrease in both photosynthesis and respiration. G. coulteri fully recovered from successive daily treatments of about 35% desiccation, but not from successive treatments of 50% desiccation. One exposure to 70% desiccation allowed no recovery of photosynthetic capacity. [ABSTRACT FROM AUTHOR]