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Most epiphytes are found in low-nutrient environments with an intermittent water supply. To deal with water limitation, many bromeliads perform crassulacean acid metabolism (CAM), such as Guzmania monostachia, which shifts from C3 to CAM and can recycle CO2 from the respiration while stomata remain closed during daytime and nighttime (CAM-idling mode). Since the absorbing leaf trichomes can be in contact with organic (urea) and inorganic nutrients (NO3 -, NH4 +) and the urea hydrolysis releases NH4 + and CO2, we hypothesized that urea can integrate the N and C metabolism during periods of severe drought. Under this condition, NH4 + can be assimilated into amino acids through glutamine synthetase (GS), while the CO2 can be pre-fixated by phosphoenolpyruvate carboxylase (PEPC). In this context, we evaluated the foliar transcriptome of G. monostachia to compare the relative gene expression of some genes involved with CAM and the N metabolism when bromeliads were submitted to 7days of drought. We also conducted a controlled experiment with an extended water deficit period (21days) in which bromeliads were cultivated in different N sources (urea, NH4 +, and NO3 -). Our transcriptome results demonstrated an increment in the expression of genes related to CAM, particularly those involved in the carboxylation metabolism (PEPC1, PPCK, and NAD-MDH), the movement of malate through vacuolar membrane (ALMT9), and the decarboxylation process (PEPCK). Urea stimulated the expression of PEPC1 and ALMT9, while Urease transcripts increased under water deficit. Under this same condition, GS1 gene expression increased, indicating that the NH4 + from urea hydrolysis can be assimilated in the cytosol. We suggest that the link between C and N metabolism occurred through the supply of carbon skeleton (2-oxoglutarate, 2-OG) by the cytosolic isocitrate dehydrogenase since the number of NADP-ICDH transcripts was also higher under drought conditions. These findings indicate that while urea hydrolysis provides NH4 + that can be consumed by glutamine synthetase-cytosolic/glutamate synthase (GS1/GOGAT) cycle, the CO2 can be used by CAM, maintaining photosynthetic efficiency even when most stomata remain closed 24h (CAM-idling) as in the case of a severe water deficit condition. Thus, we suggest that urea could be used by G. monostachia as a strategy to increase its survival under drought, integrating N and C metabolism.

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Guzmania monostachia is an epiphytic tank bromeliad that displays the inducible CAM photosynthesis under stressful conditions and had the highest stomata density in the leaf apex, while the base portion has the highest density of trichomes, which are specialized structures used to acquire water and nutrients from the tank solution. In order to correlate the genetic factors behind these morpho-physiological characteristics along the leaf blade of G. monostachia, a comparative transcriptome analysis was performed to identify the functional enriched pathways and unigenes that could play a role in the apical, middle and basal leaf portions. A total of 653 million reads were used for de novo transcriptome assembly, resulting in 48,051 annotated unigenes. Analysis of differentially expressed genes (DEGs) among distinct leaf regions revealed that 806 DEGs were upregulated in the apex compared to the middle portion, while 9685 DEGs were upregulated in the apex and 9784 DEGs were upregulated in the middle portions compared to the base. Our outcomes correlated some DEGs and identified unigenes with their physiological functions, mainly suggesting that the leaf apex was related to the regulation of stomatal movement, production of chlorophyll, cellular response to stress, and H2O2 catabolic process. In contrast, the middle portion showed DEGs associated with the transport of amino acids. Furthermore, DEGs from the leaf base were mainly correlated with responses to nutrients and nitrogen compounds, regulation of potassium ion import, response to water deprivation, and trichome branching, indicating that, at least in part, this leaf portion can replace some of the root functions of terrestrial plants. Therefore, possibly candidate unigenes and enriched pathways presented here could be prospected in future experimental work, opening new possibilities to bioengineer non-inducible CAM plants and/or improve the fertilization use efficiency by increasing leaf nutrient acquisition of crop plants.

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Light energy is essential for carbon metabolism in plants, as well as controlling the transport of metabolites between the organs. While terrestrial plants have a distinct structural and functional separation between the light exposed aerial parts and the non-exposed roots, epiphytic plants, such as orchids, have shoots and roots simultaneously fully exposed to light. The roots of orchids differ mainly from non-orchidaceous plants in their ability to photosynthesize. Since the roots of Catasetum fimbriatum can synthesize auxin which is acropetally transported to the shoot region, we decided to investigate whether: (1) light treatment of C. fimbriatum roots raises the auxin levels in the plant; and (2) distinct auxin concentrations can change the source-sink relationships, altering the amounts of sugars and organic acids in leaves, pseudobulbs and roots. Among the organs studied, the roots accumulated the highest concentrations of indole-3-acetic-acid (IAA); and when roots were exposed to light, IAA accumulated in the leaves. However, when polar auxin transport (PAT) was blocked with N-(1-Naphthyl)phthalamic acid (NPA) treatment, a significant accumulation of sugars and organic acids occurred in the pseudobulbs and leaves, respectively, suggesting that auxin flux from roots to shoots was involved in carbon partitioning of the aerial organs. Considering that C. fimbriatum plants lose all their leaves seasonally, it is possible the roots are a substituting influence on the growth and development of this orchid during its leafless period.

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Tank bromeliads are important components of tropical forests and are capable of hosting many species of invertebrates in their tank water, such as insect larvae, ostracods and oligochaetes (Frank & Lounibos 2009; Jocque & Field 2014; Richardson 1999).

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BACKGROUND AND AIMS: Bromeliads are able to occupy some of the most nutrient-poor environments especially because they possess absorptive leaf trichomes, leaves organized in rosettes, distinct photosynthetic pathways [C3, Crassulacean acid metabolism (CAM) or facultative C3-CAM], and may present an epiphytic habit. The more derived features related to these traits are described for the Tillandsioideae subfamily. In this context, the aims of this study were to evaluate how terrestrial predators contribute to the nutrition and performance of bromeliad species, subfamilies and ecophysiological types, whether these species differ in their ecophysiological traits and whether the physiological outcomes are consistent among subfamilies and types (e.g. presence/absence of tank, soil/tank/atmosphere source of nutrients, trichomes/roots access to nutrients). METHODS: Isotopic (15N-enriched predator faeces) and physiological methods (analyses of plant protein, amino acids, growth, leaf mass per area and total N incorporated) in greenhouse experiments were used to investigate the ecophysiological contrasts between Tillandsioideae and Bromelioideae, and among ecophysiological types when a predatory anuran contributes to their nutrition. KEY RESULTS: It was observed that Bromelioideae had higher concentrations of soluble protein and only one species grew more (Ananas bracteatus), while Tillandsioideae showed higher concentrations of total amino acids, asparagine and did not grow. The ecophysiological types that showed similar protein contents also had similar growth. Additionally, an ordination analysis showed that the subfamilies and ecophysiological types were discrepant considering the results of the total nitrogen incorporated from predators, soluble protein and asparagine concentrations, relative growth rate and leaf mass per area. CONCLUSIONS: Bromeliad subfamilies showed a trade-off between two strategies: Tillandsioideae stored nitrogen into amino acids possibly for transamination reactions during nutritional stress and did not grow, whereas Bromelioideae used nitrogen for soluble protein production for immediate utilization, possibly for fast growth. These results highlight that Bromeliaceae evolution may be directly associated with the ability to stock nutrients.

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The rosette architecture of some bromeliad species traps water and organic matter from the canopy in leaf axils (forming phytotelmata) and harbors many species of invertebrate animals (Frank & Lounibos 2009). Some water mites are adapted to live in phytotelmata; typically recorded from water-filled tree holes, bromeliad tanks, and a range of plant axils. Karl Viets (1939) was the first acarologist who discovered Micruracaropsis phytotelmaticola (Viets, 1939) in the water contained in the leaf bases of epiphytic Bromeliaceae in Surinam. Later on, Orghidan et al. (1977) described Arrenurus bromeliacearum Orghidan, Gruia & Viña Bayés, 1977 from phytotelmata in Cuba. Orghidan & Gruia (1987) reported Arrenurus andrewfieldi Orghidan & Gruia, 1983 from phytotelmata of epiphytic bromeliad Vriesea platynema in Venezuela. Smith & Harvey (1989) described Arrenurus kitchingi Smith & Harvey, 1989 from water-filled tree holes in Queensland, Australia. The same authors (Smith & Harvey 1989) also reported that members of genus Thyopsis occur in water-filled tree holes in Ohio, USA. Rosso de Ferradás & Fernández (2001) reported two Arrenurus species from water accumulated in Guzmania mucronata (Bromeliaceae) in Venezuela, A. andrewfieldi Orghidan & Gruia, 1983 and A. caquetiorum Rosso de Ferradás & Fernández, 2001.

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BACKGROUND AND AIMS: Several animals that live on bromeliads can contribute to plant nutrition through nitrogen provisioning (digestive mutualism). The bromeliad-living spider Psecas chapoda (Salticidae) inhabits and breeds on Bromelia balansae in regions of South America, but in specific regions can also appear on Ananas comosus (pineapple) plantations and Aechmea distichantha. METHODS: Using isotopic and physiological methods in greenhouse experiments, the role of labelled ((15)N) spider faeces and Drosophila melanogaster flies in the nutrition and growth of each host plant was evaluated, as well as seasonal variation in the importance of this digestive mutualism. KEY RESULTS: Spiders contributed 0·6 ± 0·2 % (mean ± s.e.; dry season) to 2·7 ± 1 % (wet season) to the total nitrogen in B. balansae, 2·4 ± 0·4 % (dry) to 4·1 ± 0·3 % (wet) in An. comosus and 3·8 ± 0·4 % (dry) to 5 ± 1 % (wet) in Ae. distichantha. In contrast, flies did not contribute to the nutrition of these bromeliads. Chlorophylls and carotenoid concentrations did not differ among treatments. Plants that received faeces had higher soluble protein concentrations and leaf growth (RGR) only during the wet season. CONCLUSIONS: These results indicate that the mutualism between spiders and bromeliads is seasonally restricted, generating a conditional outcome. There was interspecific variation in nutrient uptake, probably related to each species' performance and photosynthetic pathways. Whereas B. balansae seems to use nitrogen for growth, Ae. distichantha apparently stores nitrogen for stressful nutritional conditions. Bromeliads absorbed more nitrogen coming from spider faeces than from flies, reinforcing the beneficial role played by predators in these digestive mutualisms.

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