Mate limitation does not explain the lack of capsules in a Pseudocalliergon trifarium population

Abstract

(1) Net assimilation and respiration rates were measured at intervals after re-moistening, following various periods of desiccation, in Hookeria lucens, Hylocomium splendens, Neckera crispa, Plagiochila spinulosa, Plagiothecium undulatum, Rhacomitrium lanuginosum, Rhytidiadelphus loreus, Saccogyna viticulosa, Scorpiurium circinatum and Tortula ruraliformis.

(2) Rhacomitrium lanuginosum was extremely resistant, recovering apparently normally after 239 days' desiccation at 32% R.H.; Plagiochila spinulosa and Hookeria lucens were the most sensitive.

(3) Rhacomitrium lanuginosum and Tortula ruraliformis were most quickly damaged at the highest humidity (76%) and Plagiothecium undulatum at the lowest humidity tested (32%).

(4) Saccogyna viticulosa and Scorpiurium circinatum combined relatively rapid impairment and slow recovery of assimilation with the capacity to survive long dry periods.

(5) Dark respiration was relatively slow (commonly c. 5–20% of net assimilation). It usually showed a slight initial stimulation and a longer-term build-up following moderate or prolonged desiccation.

(6) Desiccation responses of bryophytes can be characterized in terms of parameters defining rate of loss of photosynthetic capacity with desiccationtime, rate of recovery after short periods of desiccation, and survival.     

The British Species of the Plagiothecium denticulatum–P. silvaticum Group

Abstract

Anomodon viticulosus was subjected to several different patterns of alternating wet and dry periods, and assimilation was measured at intervals over 49 days. Short periods of desiccation intercalated between 6-day moist periods had little effect on subsequent performance. Short moist periods breaking otherwise continuous desiccation had a very pronounced effect in mitigating desiccation damage. The results provide some evidence for a fairly slight, but probably cumulative, specific deleterious effect of drying and remoistening.     

Comparative desiccation tolerance of two Sphagnum mosses

Summary Sphagnum fallax (Klinggr.) Klinggr., a moss growing in hollows close to the water table, is more desiccation tolerant than S. nemoreum Scop., a hummock former distributed high above the hollows. Sphagnum fallax recovered to a greater proportion of its predesiccation photosynthetic rate after one and five days of tissue dryness. Further, a greater percentage of S. fallax plants survived five and ten day periods at low tissue water contents. Longer desiccated periods and lower water contents during these periods decreased both photosynthetic recovery and survival.Water contents measured in Bloomingdale Bog (Adirondack Mountains, NY, USA) showed that S. fallax probably dries more frequently and for longer periods than S. nemoreum. These results support previous findings that the greater ability of S. nemoreum to remain moist in the field is the most important character in its success as a hummock former. Greater tolerance of desiccation helps S. fallax to compensate for its greater tendency to become dry, and is a key physiological feature enabling it to dominate hollows.     

Effects of Desiccation on some Activated Oxygen Processing Enzymes and Anti-Oxidants in Mosses

The possibility that desiccation tolerance in mosses may bedependent on an ability to process species of activated oxygenwas investigated using the tolerant sand-dune moss Tortula ruraliformis(Besch.) Grout and the sensitive minerotrophic flush speciesDicranella palustris (Dicks.) ex. E. F. Warb (D. squarrosa (Starke)Schp.). Mosses were desiccated in low and high irradiance andresponses of these plants compared to those of dark-desiccatedand hydrated control plants. Both desiccated and undesiccatedplants of T. ruraliformis had a higher superoxide dismutase(SOD) activity than D. palustris, but had similar, or loweractivities of the chloroplastic H₂O₂-processing enzymes peroxidaseand ascorbate peroxidase. In T. ruraliformis, desiccation inboth light and dark led to a significant increase in SOD activity,but did not consistently stimulate the activities of peroxidaseand ascorbate peroxidase. In D. palustris, desiccation in combinationwith irradiance led to a decrease in peroxidase activity, buthad little affect on the activities of other activated oxygen-processingenzymes. Catalase, an extra-chloroplastic enzyme, was up to7-fold more active in hydrated T. ruraliformis than in D. palustris,but desiccation resulted in significant decreases in the activityof this enzyme in both species. Regardless of irradiance level,there was a depletion of the anti-oxidant ascorbic acid in bothspecies when desiccated. Only in T. ruraliformis was there asynthesis of     

Investigation on the Physiological Ecology of Tortula ruraliformis

Abstract

1. Tortula ruraliformis is a xerophyte whose structura1 and physiological features suit it to an environment subject to cosiderable desiccation and sand movement

2. Untwisting and expansion of the leaves depend on hygroscopic movements but turgor phenomena may also be concerned.

3. The moss is poikilobydrous, its water content quickly equilibrating with the environment. The leaves unfold at relative humidities pater than 90 %.

4. The tops of the shoots are physiologically the most active. Analyses of the chief constituents (carbohydrates, nitrogen compounds. ash) have been made.

5. Sucrose is the most important photosynthetic product, making up usually S % or more of the dry weight of the plant. Starch is absent from the leaves, and most of the hexose is glucose.

6. Photosynthesis virtually ceases when the leaves are tightly rolled inwards round the stem.

7. On re-hydration of moderately drougbted shoots, the respiration rate rises quickly from a very low value, and the tissues can photosynthesize immediately.

8. After very prolonged desiccetion, photosynthetic power is impaired, and the respiration rises to a peak rate some appreciable time after re-hydration and then declines.     

Sigfrid W. Arnell 1895–1970

Abstract

Six bryophyte species were investigated: Plagiochila spinulosa, Hylocomium splendens, Scorpiurium circinatum, Tortula ruraliformis, Rhacomitrium aquaticum and Andreaea rothii. Of these, all except A. rothii showed clear evidence of seasonal variation in desiccation tolerance, as measured by net assimilation following 24 h remoistening.

(2) In general these species showed low desiccation tolerance in autumn (October) and winter (January) and increased tolerance in spring and summer. Hylocomium splendens was a partial exception in showing relatively high tolerance in January and little change from then until July.

(3) On the whole, the seasonal pattern of desiccation response accords well with what might be expected from conditions in the habitats of the plants. The results are briefly discussed in relation to distribution of rainfall and some microenvironmental factors, and compared with some data from the literature.     

New national and regional bryophyte records, 46

Abstract

Bryophyte biomass and diversity vary strongly with altitude in the tropics. Low abundance and low species numbers in lowland rain forests are most likely due to reduced diurnal activity times combined with high nocturnal respiration rates at high temperatures. This may exclude many montane species from the warm lowlands. However, an alternative hypothesis explains the observed pattern, namely a limited desiccation tolerance of montane species, precipitation being more concentrated but less frequent in most lowland forests compared to montane cloud forests. To test this hypothesis, we studied the desiccation tolerance of four montane and four lowland bryophyte species. The effects of prolonged drought were quantified with chlorophyll fluorescence (F_v/F_m) and the extent of electrolyte leakage. Both montane and lowland species survived dry periods of ≧80 days, which far exceeds the duration of dry periods in the wet lowland tropics. We can thus exclude intolerance to long dry spells as an explaination for the absence of the tested montane species in the lowlands. We should continue to focus on other mechanisms to explain the altitudinal gradient of bryophyte abundance and diversity in the tropics, in order to understand this pattern, as well as to predict future trends under climatic warming.     

Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

There has been a strong research focus on optical properties in temperate estuaries but very much less in tropical estuaries. These properties comprise light and beam attenuation dominated by suspended particulate matter, Chl a, and CDOM. Spatially and temporally distributed data on optical properties in a tropical wet and dry estuary are compared and discussed in relation to those of temperate estuaries. Sampling in the Nha Phu estuary, Vietnam, consisted of five stations on a transect from head to mouth that was sampled four times during dry conditions and three times during wet conditions between May 2006 and April 2008. Methods comprised CTD, optical measurements, and water sampling for suspended matter, Chl a, and CDOM. Results showed high light attenuation—K _d(PAR)—in wet conditions and low in dry. K _d(PAR) was highest at the estuary head and lower in the outer part. Spatial and temporal variations in K _d(PAR) were in general dominated by variations in suspended particulate matter concentrations in both wet and dry conditions. Chl a concentrations were low and showed no strong variations between wet and dry conditions. CDOM absorption coefficients were higher in wet conditions with high values at the head and lower in the central part of the estuary. The depth of the photic zone was reduced by up to 50% during wet conditions. A residence time in the estuary of 5–6 days was derived from the rate of change of K _d(PAR) after a period of heavy rain and discharge of freshwater into the estuary. This complied with a residence time of four and a half days derived from a basic physical relation. Optical properties were in general comparable to temperate estuaries in dry conditions although Chl a concentrations were lower in Nha Phu. A second distinctive point, as compared to temperate estuaries, was the episodic character with days of strong rainfall followed by longer periods of dry weather. All sampling, both wet and dry, was carried out in the dry season which implies a less definitive perception of wet and dry seasons.     

Microclimate, light adaptation and desiccation tolerance of epiphytic bryophytes in two Venezuelan cloud forests

Aim Analysis of microclimate factors and physiological responses determining survival and growth of epiphytic bryophytes in the lower canopy and trunk space of north‐Andean cloud forests. Location Two cloud forests at 2000–2400 m in the northern Andes near Mérida, Venezuela. Methods Data‐logging of dry and wet‐season temperature, relative humidity (r.h.) and photosynthetically‐active radiation (PAR) for month‐long periods, and laboratory measurements of desiccation tolerance and light responses of selected epiphytic bryophytes. Results Rainfall averages 20 mm or less in January and February, and 200 mm or more from August to October, but is very variable at all seasons. The proportion of time ‘wet’ (continuous 100% r.h.) in the months sampled ranged from 8.5% to 52.2% or more; a dry/wet‐season range between 20% and 40% is probably commoner. The length of ‘wet’ and ‘dry’ periods approximated log‐normal distributions, with mid‐points for wet periods ranging from 2.8 to 10.7 h, and dry periods from 6.2 to 17.1 h. The longest recorded dry period was 143 h. Humidity typically rose during the night to > 90% r.h., reaching 100% for significant periods (implying cloudwater (fog) deposition) on about one night in two in all seasons. Of six bryophytes of pendulous growth form, all survived periods of at least a few days’ desiccation; most recovered better from high than low humidities. Measured 95% light‐saturation values ranged from 110 to 256 μmol m^?2 s^?1, somewhat but not greatly higher than ambient light levels Main conclusions Environmental conditions in the cloud forests are probably near‐optimal for epiphytic bryophytes, but in even the wettest forest these plants must tolerate at least short periods of drying at any time of year, and longer periods seasonally. Interception of cloudwater droplets from moving air is likely to be an important source of water for bryophytes of pendant and other diffuse life forms, especially in periods of low rainfall. Absorption of water from near‐saturated air is probably of little physiological significance. Bryophytes of these life‐forms are notably conspicuous in tropical‐montane cloud forests. They remain prominent into humid temperate regions such as southern Chile, New Zealand and Macaronesia, but progressively disappear at higher latitudes with the stresses of increasing seasonality.     

Comparative experiments on temperature responses of bryophytes: assimilation,respiration and freezing damage

Abstract

(1) Temperature-net assimilation and temperature-respiration curves based on manometric measurements at high carbon dioxide concentrations are presented for twenty-three mosses and five hepatics.

(2) In most of the species, the optimum temperature for net assimilation under the experimental conditions was about 25°–30°C and the temperature compensation point about 35°–40°C.

(3) Substantially lower optima and maxima were found in Orthothecium rufescens, Plagiopus oederi, Acrocladium trifarium, Fontinalis squamosa, Nardia compressa and Hookeria lucens.

(4) Several northern and montane species (e.g. Anthelia julacea, Andreaea nivalis, Rhacomitrium lanuginosum) did not differ substantially from the majority of lowland species in the response of net assimilation to temperature. Some substantial differences were found between species of differing habitats.

(5) Most of the mosses and leafy liverworts tested withstood rapid cooling to ?5°C for 6 hr. They are evidently protected from intracellular freezing at normal rates of cooling by the withdrawal of water to form extracellular ice.

(6) Conocephalum conicum, Targionia hypophylla and Pellia epiphylla were killed by rapid cooling to ?5°C.

(7) Plagiochila spinulosa and Myurium hebridarumwithstood periods of 1–2 weeks at ?5°C. Survival of bryophytes for long periods of low temperatures appears to be principally a matter of desiccation resistance.     

Effects of desiccation and rewetting on the release and decomposition of dissolved organic carbon from benthic macroalgae

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Ammonia volatilization after injection of anhydrous ammonia into arable soils of different moisture levels

Laboratory experiments have shown appreciable losses of ammonia after injection of anhydrous ammonia into dry and wet soils. In this study losses of ammonia injected into a moist (tension 10 kPa), dry (tension 160 kPa) and a wet (tension 1.6 kPa) sandy loam were measured under field conditions using wind tunnels. Losses were insignificant from a moist soil. However losses from a dry and a wet soil were 20% and 50% of injected ammonia, respectively. From the dry soil, losses of gaseous ammonia took place within the first hours after injection, which indicates a rapid transport through cracks and voids. From the wet soil, 20% of the injected ammonia was lost more gradually between 6 h and 6 d. This indicates that upward movement of water due to evaporation may be the cause of these ammonia losses which proceeded for longer periods.     

Survival ofalginate-ecapsulated Pseudomonas fluorescens cells in soil

Alginate-encapsulated and unencapsulated cells of Pseudomonas fluorescens Rsf were introduced into soil microcosms with and without wheat plants to evaluate bacterial survival and colonization of the rhizoplane and rhizosphere. Encapsualtion of cells in alginate amended with skim milk or with skim milk plus bentonite clay significantly enchanced long-term survival of the cells. There was a negligible effect on long-term bacterial survival when cells were encapsulated in alginate amended with TY medium or soil extract, as compared to water. Drying of beads resulted in a significant reduction in bacterial viability. After addition to soil, cells in dried beads increased in numbers and exhibited stable population densities, whereas cells added in moist beads showed stable dynamics at a higher level. Cells encapsulated in dried beads or fresh beads survived better than unencapsulated cells added to soil. Both cells in moist and dried alginate beads also survide a dry/wet cycle in soil, whereas unencapsulated cells were sensitive to these moisture fluctuations. Shortly after inoculation and 63 days after this, cells from moist beads colonized wheat roots at significantly higher levels than unencapsulated cells, whereas cells in dried beads did so at levels similat to unencapsulated cells. Cells in beads initially placed at different distance from developing root mat were able to move towards and colonize the rhizosphere, at levels of roughly 10⁴ to 10⁶ colony-forming units fo P. fluorescens R2f per gram of dry soil. Correspondence to: J. T. Trevors or J. D. van Elsas     

Synergy Between Low Temperature and Dessication in Breaking Gemmule Diapause of Eunapius fragilis (Leidy)

Summary

Gemmules of Eunapius fragilis collected during the fall and kept at 20° C for up to 6 months did not germinate. Freshly collected gemmules, which were dried at 20° C for 7 days and then rehydrated, also exhibited a very low capacity for germination. However, gemmules, stored at 20° C for several months and then dried, showed a much higher level of germination (but usually no more than 50%) after they were returned to pond water. Gemmules, stored at 4–5° C for 4 to 6 weeks, exhibited at most very little germination when they were tested at 20° C. On the other hand, gemmules, which were chilled at 4–5° C for 4 to 6 weeks and then dried for 7 days, underwent rapid and nearly complete germination upon rehydration. These results provide clear evidence for a synergistic effect between low temperature and desiccation in breaking gemmule diapause. It is suggested that in temporary habitats where E. fragilis often survives the dry summer as gemmules, drying may be the primary agent releasing the gemmules from diapause so that they germinate in the fall upon the return of water. A brief exposure of the gemmules to low temperatures before and/or during the dry period may enhance the effect of desiccation.     

Long-term droughts change the hatching patterns of zooplankton resting eggs from permanent and temporary lakes

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Growth rates of five pleurocarpous moss species under various climatic conditions

Abstract

Growth rates of the moss species Hylocomium splendens, Pleurozium schreberi, Hypnum cupressiforme, Ctenidium molluscum and Rhytidium rugosum were determined in terms of dry matter production and stem elongation. Sample sites were chosen to obtain a wide variety of altitudinal and climatic conditions in Austria. The annual increases were detected by using modified Petri dishes, external markers and morphological criteria. Individual shoots of H. splendens and P. schreberi showed a significant decrease of biomass increment with rising altitudes. Measurements of biomass and annual production per area of populations at various altitudes showed a reverse pattern. Central European individuals of H. splendens on average produced 15% more biomass than populations from Northern Europe. There is a strong correlation between stem elongation and temperature for all investigated mosses except R. rugosum. C. molluscum and R. rugosum showed maximum growth rates in shaded sites, with fairly high humidity, although their main occurrence in Austria is in open, mainly dry stands.     

The role of the persistent fruit wall in seed water regulation in Raphanus raphanistrum (Brassicaceae)

Background and Aims

Dry fruits remain around the seeds at dispersal in a number of species, especially the Brassicaceae. Explanations for this vary, but usually involve mechanisms of innate dormancy. We speculate that, instead, a persistent fruit may give additional protection through control of dehydration, to species growing in arid or Mediterranean environments where water is sporadic.

Methods

X-rays and weight measurements were used to determine the extent to which Raphanus raphanistrum seeds within mature fruits imbibe water, and germination tests determined the roles of the fruit and seed coat in seed dormancy. Rates of water uptake and desiccation, and seedling emergence were compared with and without the fruit. Finally, germinability of seeds extracted from fruits was determined after various periods of moist conditions followed by a range of dry conditions.

Key Results

Most seeds rapidly take up water within the fruit, but they do not fully imbibe when compared with naked seeds. The seed coat is more important than the dry fruit wall in maintaining seed dormancy. The presence of a dry fruit slows emergence from the soil by up to 6–8 weeks. The fruit slows the rate of desiccation of the seed to a limited extent. The presence of the fruit for a few days during imbibition somehow primes more seeds to germinate than if the fruit is absent; longer moist periods within the pod appear to induce dormancy.

Conclusions

The fruit certainly modifies the seed environment as external conditions change between wet and dry, but not to a great extent. The major role seems to be: (a) the physical restriction of imbibition and germination; and (b) the release and then re-imposition of dormancy within the seed. The ecological significance of the results requires more research under field conditions.     

Delayed fluorescence as a new screening method of plant species for urban greening: an experimental study using four bryophytes

Selecting suitable plant species is important in urban greening because urban environments often provide unfavorable conditions for plant growth. We focused on delayed fluorescence (DF), i.e., light emitted from plants immediately following light exposure as a result of back electron transfer in photosynthesis, as an indicator of photosynthetic activity. Moss greening, urban greening using bryophytes, has attracted attention as a new domain of greening that does not require soil. Therefore, tolerance to drying, which is a characteristic environmental factor in cities, of four bryophytes—Bryum argenteum Hedw., Racomitrium japonicum Dozy et Molk., Hypnum plumaeforme Wilson, and Polytrichum commune Hedw.—was evaluated in the laboratory using DF. Assuming an urban environment, experiments were performed to measure the transition of DF following the cessation of irrigation and re-watering. The recovery of accumulated DF values (0–200 s) by rehydration 8 days after irrigation cessation was increased in the order H. plumaeforme ≈ P. commune?<?R. japonicum?<?B. argenteum. B. argenteum presented an increase in the accumulated amount of DF 8 h after irrigation cessation, and presented a significantly higher DF when compared with the other three species at 16 h. Together with results of previous studies, these findings of desiccation tolerance in the studied species indicate that DF is a useful method for characterizing desiccation tolerance in plants and selecting potentially useful plants for urban greening.

     

Resurrection kinetics of photosynthesis in desiccation‐tolerant terrestrial green algae (Chlorophyta) on tree bark

The rough bark of orchard trees (Malus) around Darmstadt is predominantly covered in red to purple‐brown layers (biofilms) of epiphytic terrestrial alga of Trentepohlia umbrina. The smooth bark of forest trees (Fagus sylvatica L. and Acer sp.) in the same area is covered by bright green biofilms composed of the green algae Desmococcus, Apatococcus and Trebouxia, with a few cells of Coccomyxa and ‘Chlorella’ trebouxioides between them. These algae are desiccation tolerant. After samples of bark with the biofilms were kept in dry air in darkness for various periods of time, potential quantum yield of PSII, F_v/F_m, recovered during rehydration upon rewetting. The kinetics and degree of recovery depended on the length of time that the algae were kept in dry air in the desiccated state. Recovery was better for green biofilm samples, i.e. quite good even after 80 days of desiccation (F_v/F_m = ca. 50% of initial value), than the red samples, where recovery was only adequate up to ca. 30–40 days of desiccation (F_v/F_m = ca. 20–55% of initial value). It is concluded that the different bark types constitute different ecophysiological niches that can be occupied by the algae and that can be distinguished by their capacity to recover from desiccation after different times in the dry state.     

South American leaf blight of Hevea brasiliensis: spore dispersal of Microcyclus ulei

Trapping of ascospores and conidia of Microcyclus ulei among young trees of Hevea brasiliensis in Trinidad from May 1973 to May 1975 snowed that ascospores occurred throughout the year whilst conidia were present only during the wet season. Peak ascospore concentrations occurred in August and November during the wet season, the latter peak being more marked and the former coinciding with the period of maximum conidium liberation. In dry weather the number of ascospores increased during the night to a maximum at 06.00 h, and decreased to a low level during the day. On rainy days heavy ascospore discharge also occurred during the day. Ascospore concentration decreased significantly after dawn on sunny days whilst on overcast days the concentration remained high most of the day. Conidium production was highest around 10.00 h and decreased towards the evening to a low level during the night, reaching a minimum at 07.00 h.