Ecophysiological Strategies Research Articles

Winter survival and cold hardiness in Stercutus niveus (Oligochaeta; Enchytraeidae)

Stercutus niveus Michaelsen, 1888 (Oligochaeta; Enchytraeidae) reaches densities of more than 1000 individuals per m 2 in the litter layer of deciduous forests in Central Europe during winter. As no vertical movement into deeper soil horizons and no cocoon production takes place during this period, the worms have eco-physiological strategies to survive the sub-zero temperatures that frequently occur in the absence of a protecting snow cover. The ability of S. niveus to supercool its body fluid to −15°C prevents the worms from freezing. The supercooling point (SCP) is significantly affected by the presence of gut contents and SCP data show a bimodal distribution throughout the winter. Glycerol, a potential antifreeze agent, was detected in the body fluid of the worms.

Strategies of nitrogen cycling of Phragmites australis at two sites differing in nutrient availability

AbstractBelow‐ground biomass and nitrogen content were determined at two genetically homogeneous Phragmites stands differing in morphology, in productivity, and in nutrient supply. Comparable ratios between above‐ground standing crop and rhizome biomass were found at both sites, whereas the root biomass/above standing crop ratio was significantly higher at the nutrient poor site. Investigations on the dynamics of nitrogen content revealed distinct differences in nitrogen translocation to the rhizomes between the investigated clones indicating two ecophysiological strategies in storage behaviour. These two strategies could be attached to the “assimilation type” and to the “translocation type”, respectively. A modified definition of both types is presented.

Microbial biomass reflects a nitrogen and phosphorous economy of halophytes grown in salty desert soil

Seasonal variations in soil salinity were recorded under the canopy of two halophyte shrubs typical of the hot, dry Negev desert, Zygophyllum dumosum and Reaumuria negevensis. The effects of the fluctuating soil salinity levels on total soluble N and on microbial biomass N and P were also monitored. The microhabitat of the shrubs showed differences in trend and magnitude of soil mineral N, the NOinf3sup-:NH4+ratio, and microbial N and P. The trends were assumed to be governed by the various mechanisms operating in the shrubs in order to survive salty environments. Data from the current study are discussed in terms of the assumption that the halophyte has developed ecophysiological strategies that force microbial communities coexisting in its microhabitat towards adaptation aimed at withstanding a fluctuating environment, and hence towards a beneficial plant-microorganism relationship.

Seed stratification and germination strategy in the Mediterranean pines Pinus brutia and P. halepensis

AbstractThe ecophysiology of germination in Pinus brutia and P. halepensis was studied in seeds collected from different areas of Greece. In regard to the temperature range of germination, both P. halepensis and the southern provenance (Lasithi, Crete) of the East Mediterranean pine, P. brutia, follow a typical Mediterranean pattern. In the latter species, dramatic differences in the degree of dormancy were noted among the three provenances investigated; in all seed lots however, 20°C was clearly the optimal temperature for germination. Stratification resulted in a considerable promotion of P. brutia seed germination. Nevertheless, the inductive effect of stratification was shown to differ among the three provenances used, escalating from a simple increase of germination rate (in the southern seed lot from Lasithi, Crete) through a broadening of the temperature range of germination (in the intermediate lot from Thasos Island) to, finally, a dramatic release from a particularly deep dormancy (in the northern lot from Soufli). These deeply dormant seeds of the latter provenance displayed an absolute stratification requirement; prolonged illumination or seed coat scarification could not substitute for the promotive effect of prechilling. A considerable interaction between far-red light and stratification was revealed in the dormant seeds of P. brutia (Soufli provenance); far-red pulses during stratification could either cancel or diminish the germination promotion induced by low temperatures. The differences observed in the germination behaviour among the various P. brutia provenances may be attributed to a variable ecophysiological strategy in regard to the temporal pattern of seedling emergence and establishment. According to the variants of this strategy, seed germination is timed to occur during either spring (in regions with relatively cold and moist climates), or autumn and early winter (in southern, mild and dry areas) or both (in intermediate conditions).

Microbial biomass response to seasonal fluctuation in soil salinity under the canopy of desert halophytes

The relationships between seasonal changes in soil salinity and the microbial biomass and activity (represented by the quotient for basal respiration—qCO2) were monitored year-round under the canopy of two halophytes; Zygophyllum dumosum and Reaumuria negevensis, typical of the hot, dry Negev Desert. Fluctuations in soil salinity were assumed to be the result of different ecophysiological strategies employed by the halophytes in order to survive in saline environments. The amount of the microbial biomass was not directly affected by the degree of soil salinity, especially in the R. negevensis microhabitat where the highest biomass (245 μg g−1) was observed in high salty soil (12.8 dS m−1) during the summer. A negative relationship was found between the microbial biomass and qCO2 values, indicating the possibility of channeling organic substrates to metabolic activity aimed at overcoming conditions of temporary stress.

Ecophysiological adaptations of coastal halophytes from foredunes and salt marshes

Ecophysiological strategies of coastal halophytes from foredunes and salt marshes are discussed. A comparison is made of the factors that limit growth in salt marshes and sand dunes. In salt marshes, zonation and succession are primarily governed by variation in soil salinity, which strongly depends on inundation with seawater. Results are described of experiments which aim at separating salinity and inundation effects on growth, osmotic and mineral relations in a comparison of salt-marsh halophytes. The growth response of plants cannot simply be correlated (and causally explained) with the concentration of Na, Cl, and K in the tissues. Also, the compatible osmotic solutes proline and methylated quaternary ammonium compounds may accumulate both in species with a positive response to increased salinity and in species with a growth reduction under seawater inundation. More likely inadequate adaptation of the plants water potential with these components is partly the cause of retarded growth. Disfunctioning of the plant in this respect may be at three levels: (a) total water potential of the plant, (b) (loss) of turgor pressure potential; (c) regulation at the cellular level. The ecological importance of some factors in seawater other than sodium chloride is considered. In coastal sand dunes airborne rather than soil salinity limits plant growth, together with the effects of abrasion, sand accretion, drought and the poor nutrient status of the dune sand. Adaptations of sand-dune species to these factors may consist of: large seeds with storage tissue germinating in the dark and seedling growth enough to emerge through the accreted sand. Aerial parts must be resistant to mechanical damage (high wind speed and abrasion), possibly by a sclerophyllous and tough structure. Efficient nutrient uptake, translocation and retranslocation seem to help survive sand-dune species in a nutrient-poor rooting medium.

The microfossil record of early land plants: advances in understanding of early terrestrialization, 1970-1984

The plant spore record indicates two major phases of adaptive radiation of land plants before the Devonian; these can be interpreted to correspond to different reproductive, vegetative, and ecophysiological strategies of these early terrestrial plants. The first major adaptive radiation by plants onto land occurred in the mid Ordovician. These early plants are represented by abundant obligate spore tetrads; this assemblage persists from the mid Ordovician to about the mid-late Early Silurian. The fossil spore records indicate that these primary producers were widespread by the end of the Ordovician and the beginning of the Silurian. The close similarity of the fossil tetrads with obligate spore tetrads produced by some hepatics and mosses suggests a non-vascular vegetative grade of organization for plants of this interval. The second major adaptive radiation begins with the replacement of the monotonous spore tetrad assemblage by single trilete spores in the mid-late Early Silurian. These trilete spores find morphological counterpart with spores produced by vascular cryptogams; they suggest a vegetative grade of organization at the vascular level for plants of this interval. The initially smooth-walled trilete spores of this radiation are followed by diverse assemblages of trilete spores with variously ornamented spore coat patterns and varied laesurae morphologies by the mid-Late Silurian. The interval from the mid Ordovician to the mid-late Early Silurian is hypothesized on the basis of the abundant and widespread spore records to be one of rapid colonization by founder populations with limited genetic diversity and with life-history strategies that included an ecophysiological tolerance to desiccation and a short vegetative life cycle. The interval from the mid-late Early Silurian to the Pridoli largely coincides with the appearance of vascular plant megafossils. It is hypothesized on the basis of the spore assemblages to be one of major establishment of large populations of genetically diverse plants exploiting a broad spectrum of ecological sites that have escaped representation in the meagre megafossil record.