Photosynthesis In Bryophytes Research Articles

Limitations to photosynthesis in bryophytes: certainties and uncertainties regarding methodology.

Bryophytes are the group of land plants with the lowest photosynthetic rates, which was considered to be a consequence of their higher anatomical CO2 diffusional limitation compared with tracheophytes. However, the most recent studies assessing limitations due to biochemistry and mesophyll conductance in bryophytes reveal discrepancies based on the methodology used. In this study, we compared data calculated from two different methodologies for estimating mesophyll conductance: variable J and the curve-fitting method. Although correlated, mesophyll conductance estimated by the curve-fitting method was on average 4-fold higher than the conductance obtained by the variable J method; a large enough difference to account for the scale of differences previously shown between the biochemical and diffusional limitations to photosynthesis. Biochemical limitations were predominant when the curve-fitting method was used. We also demonstrated that variations in bryophyte relative water content during measurements can also introduce errors in the estimation of mesophyll conductance, especially for samples which are overly desiccated. Furthermore, total chlorophyll concentration and soluble proteins were significantly lower in bryophytes than in tracheophytes, and the percentage of proteins quantified as Rubisco was also significantly lower in bryophytes (<6.3% in all studied species) than in angiosperms (>16% in all non-stressed cases). Photosynthetic rates normalized by Rubisco were not significantly different between bryophytes and angiosperms. Our data suggest that the biochemical limitation to photosynthesis in bryophytes is more relevant than so far assumed.

Anatomical constraints to nonstomatal diffusion conductance and photosynthesis in lycophytes and bryophytes

Photosynthesis in bryophytes and lycophytes has received less attention than terrestrial plant groups. In particular, few studies have addressed the nonstomatal diffusion conductance to CO2 gnsd of these plant groups. Their lower photosynthetic rate per leaf mass area at any given nitrogen concentration compared with vascular plants suggested a stronger limitation by CO2 diffusion. We hypothesized that bryophyte and lycophyte photosynthesis is largely limited by low gnsd . Here, we studied CO2 diffusion inside the photosynthetic tissues and its relationships with photosynthesis and anatomical parameters in bryophyte and lycophyte species in Antarctica, Australia, Estonia, Hawaii and Spain. On average, lycophytes and, specially, bryophytes had the lowest photosynthetic rates and nonstomatal diffusion conductance reported for terrestrial plants. These low values are related to their very thick cell walls and their low exposure of chloroplasts to cell perimeter. We conclude that the reason why bryophytes lie at the lower end of the leaf economics spectrum is their strong nonstomatal diffusion conductance limitation to photosynthesis, which is driven by their specific anatomical characteristics.

David T. Hanson and Steven K. Rice (eds): Photosynthesis in bryophytes and early land plants

David T. Hanson and Steven K. Rice (eds): Photosynthesis in bryophytes and early land plants

Bryophyte photosynthesis in sunflecks: greater relative induction rate than in tracheophytes

Photosynthetic kinetics in changing light intensity is considered pivotal for the survival of understorey tracheophytes; however, it is virtually unknown for bryophytes because bryophytes and tracheophytes have contrasting physio-ecological strategies. Anatomy suggests that relative rate of photosynthetic induction is faster in bryophyte gametophytes due to the absence of stomata, whose slow response may limit photosynthesis of tracheophyte leaves in changing light intensity. We measured steady-state and dynamic CO2 exchange in 10 bryophyte species. We performed an in-depth survey of the moss Hypnum cupressiforme sampled from sun and shade sites. Our key results are: (1) Bryophyte photosynthesis after dark acclimatisation induced much faster than in tracheophytes, reaching 50% of maximum gross photosynthesis (Agross) in about 90 s. Such rapid induction is comparable only to tracheophytes whose stomata do not limit CO2 uptake. Times to reach 90% of Agross were also substantially shorter in bryophytes (ca 220 s) than those reported for most tracheophytes (500–2000 s). (2) Shade-grown mosses did not reveal lower photosynthetic capacity than sun ones. (3) Shade-grown H. cupressiforme induced photosynthesis slightly faster than that from forest gaps. We conclude that bryophytes are efficient utilizers of temporal light heterogeneity, increasing carbon gain during short high-light events such as sunflecks in forest understorey.

Potential for fast chlorophyllafluorescence measurement in bryophyte ecophysiology

The aim of the study was to analyse if the measurement of fast fluorescence induction kinetics in bryophyte samples in field conditions could be used for characterizing the photochemistry of photosynthesis in bryophytes. Bryophyte samples were collected in five different habitats of the boreo-nemoral zone growing on various substrates. Twenty-four species were epigeic, six epilithic, ten epiphytic, three epixylic, and six semi-aquatic or aquatic. Extremely high variation was found for fluorescence parameters between bryophyte samples. Performance Index showed the highest variability, reaching 160% in the case of epiphytic bryophytes. There were statistically significant differences for mean values of Fv/Fm, RC/ABS, and Fv/F0 between epigeic and epiphytic bryophyte samples as well as between epiphytic and semi-aquatic & aquatic samples. For Performance Index, a significant difference was observed only between epiphytic and epigeic bryophytes. It was concluded that bryophytes display a low intensity of the photochemistry of photosynthesis even in relatively wet habitats. In general, measurement of fast fluorescence induction kinetics in field conditions could be a rapid and efficient tool to obtain quantitative data useful for ecophysiological studies.

Ecophysiology of photosynthesis in bryophytes: major roles for oxygen photoreduction and non‐photochemical quenching?

CO(2) fixation in mosses saturates at moderate irradiances. Relative electron transport rate (RETR) inferred from chlorophyll fluorescence saturates at similar irradiance in shade species (e.g. Plagiomnium undulatum, Trichocolea tomentella), but many species of unshaded habitats (e.g. Andreaea rothii, Schistidium apocarpum, Sphagnum spp. and Frullania dilatata) show non-saturating RETR at high irradiance, with high non-photochemical quenching (NPQ). In P. undulatum and S. apocarpum, experiments in different gas mixtures showed O(2) and CO(2) as interchangeable electron sinks. Nitrogen + saturating CO(2) gave high RETR and depressed NPQ. In S. apocarpum, glycolaldehyde (inhibiting photosynthesis and photorespiration) depressed RETR in air more at low than at high irradiance; in CO(2) -free air RETR was maintained at all irradiances. Non-saturating electron flow was not suppressed in ambient CO(2) with 1% O(2) . The results indicate high capacity for oxygen photoreduction when CO(2) assimilation is limited. Non-saturating light-dependent H(2) O(2) production, insensitive to glycolaldehyde, suggests that electron transport is supported by oxygen photoreduction, perhaps via the Mehler-peroxidase reaction. Consistent with this, mosses were highly tolerant to paraquat, which generates superoxide at photosystem I (PSI). Protection against excess excitation energy in mosses involves high capacity for photosynthetic electron transport to oxygen and high NPQ, activated at high irradiance, alongside high reactive oxygen species (ROS) tolerance.

Record of environmental change by α-cellulose δ 13C of sphagnum peat at Shennongjia, 4000–1000 aBP

The Dajiuhu Basin at Shennongjia, located within typical East Asian Monsoon region, preserves a sub-alpine sphagnum peat deposition in its central area. The topmost 120 cm of the peat covers the last 4000 years according to AMS 14C dating of pollen concentration. Carbon isotope of α-cellulose, extracted from sphagnum peat, provides a quantitative reconstruction of atmospheric relative humidity, based on transfer functions of C3 plants carbon isotopic fractionation equation and the bryophyte photosynthesis CO2 absorption rate equation. δ13C, TOC and C/N variations reveal that the Dajiuhu area has experienced a long-term tendency to dry during 4000–1000 aBP, with a major transition happening around 3000 aBP. Four relative dry events are identified at 3400–3200, 3000–2600, 2200–2000 and 1600–1400 aBP, respectively, corresponding to those climate events documented in many global records. Three periodicities, 664 a, 302 a and 277 a enclosed in the atmospheric humidity of Dajiuhu are correlated to the cycles of solar activities. The weakening of East Asia summer monsoon during this period registered in the Dajiuhu peat is consistent with the synchronous weakening of Indian Monsoon. This trend may be attributed to gradual decrease of Northern Hemispheric summer solar insolation and the consequently southward migration of Intertropical Convergent Zone (ITCZ).

The contribution of bryophytes to the carbon exchange for a temperate rainforest

AbstractBryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp‐broadleaved forest in New Zealand, dominated by 100–400‐year‐old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth &lt;30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light‐saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis – whole‐plant respiration) per unit ground area at saturating irradiance was 1.9 μmol m−2 s−1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air‐dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area.The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m−2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of −1010 g m−2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ∼11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate.

Stable carbon and oxygen isotope composition of calcites associated with modern freshwater cyanobacteria and algae

Abstract The composition of carbon and oxygen stable isotopes was determined for calcite associated with the freshwater cyanobacteria Homoeothrix Crustacea, Phormidium incrustatum, and Rivularia haematites and the green alga Gongrosira incrustans in a UK travertine‐depositing stream. The δ13C values of Rivularia calcites deposited in summer were significantly higher than those deposited during winter. This was interpreted as the result of photosynthetic activity within colonies. The δ13C values were similar for the three cyanobacterium species studied, and colonies of Homoeothrix sampled over a 531‐m length of stream showed progressive downstream enrichment of 13C (2.0‰). This resulted from CO2 degassing of the downstream water, augmented during summer by bryophyte photosynthesis. Subsequent deposition of calcite takes place irrespective of photosynthetic activity of the algae and may blur the isotopic characteristics in older colonies and fossil assemblages.

An Ecological Study of the Bryophytes of a Natural Prairie in Northwestern Iowa

An Ecological Study of the Bryophytes of a Natural Prairie in Northwestern Iowa