Bryophyte spore germinability is inhibited by peatland substrates

Smoke promotes germination of peatland bryophyte spores

Northern peatlands are globally important carbon stores. With increasing fire frequency, the re-establishment of bryophytes becomes crucial for their carbon sequestration. Smoke-responsive germination is a common trait of seeds in fire-prone ecosystems but has not been demonstrated in bryophytes. To investigate the potential role of smoke in post-fire peatland recovery, we tested the germination of spores of 15 bryophyte species after treatment with smoke-water. The smoke responsiveness of spores with different laboratory storage times and burial depths/age (3-200 years) was subsequently tested. Smoke increased the germination percentage for 10 of the species and the germination speed for four of these. Smoke responsiveness increased along the fire frequency gradient from open expanse to forest margin, consistent with the theory that this selects for the maintenance of fire-adapted traits. Smoke enhanced the germinability of 1-year but not 4-year laboratory-stored spores, and considerably increased the germinability of spores naturally buried in peat for up to ~200 years. The effect of fire may be overlooked in non-fire-prone ecosystems, such as those in which wetland bryophytes dominate. Our study reveals a mechanism by which an increase in fire frequency may lead to shifts in species dominance, which may affect long-term carbon sequestration in peatlands.

Evidence of horizontal gene transfer between land plant plastids has surprising conservation implications

BACKGROUND AND AIMS

Horizontal gene transfer (HGT) is an important evolutionary mechanism because it transfers genetic material that may code for traits or functions between species or genomes. It is frequent in mitochondrial and nuclear genomes but has not been demonstrated between plastid genomes of different green land plant species.

METHODS

We Sanger-sequenced the nuclear internal transcribed spacers (ITS1 and 2) and the plastid rpl16 G2 intron (rpl16). In five individuals with foreign rpl16 we also sequenced atpB-rbcL and trnLUAA-trnFGAA.

KEY RESULTS

We discovered 14 individuals of a moss species with typical nuclear ITSs but foreign plastid rpl16 from a species of a distant lineage. None of the individuals with three plastid markers sequenced contained all foreign markers, demonstrating the transfer of plastid fragments rather than the entire plastid genome, i.e. entire plastids were not transferred. The two lineages diverged 165-185 Myr BP. The extended time interval since lineage divergence suggests that the foreign rpl16 is more likely explained by HGT than by hybridization or incomplete lineage sorting.

CONCLUSIONS

We provide the first conclusive evidence of interspecific plastid-to-plastid HGT among land plants. Two aspects are critical: it occurred at several localities during the massive colonization of recently disturbed open habitats that were created by large-scale liming as a freshwater biodiversity conservation measure; and it involved mosses whose unique life cycle includes spores that first develop a filamentous protonema phase. We hypothesize that gene transfer is facilitated when protonema filaments of different species intermix intimately when colonizing disturbed early succession habitats.

Induced defense and its cost in two bryophyte species

PREMISE

Current knowledge about defense strategies in plants under herbivore pressure is predominantly based on vascular plants. Bryophytes are rarely consumed by herbivores since they have ample secondary metabolites. However, it is unknown whether bryophytes have induced defenses against herbivory and whether there is a trade-off between growth and defense in bryophytes.

METHODS

In an experiment with two peatland bryophytes, Sphagnum magellanicum Brid. and S. fuscum (Schimp.) H. Klinggr., two kinds of herbivory, clipping with scissors and grazing by mealworms (Tenebrio molitor L.) were simulated. At the end of the experiment, we measured growth traits, carbon-based defense compounds (total phenolics and cellulose) and storage compounds (total nonstructural carbohydrates) of these two Sphagnum species.

RESULTS

Grazing but not clipping increased total phenolics and C:N ratio and reduced biomass production and height increment. A negative relationship between biomass production and total phenolics was found in S. magellanicum but not in S. fuscum, indicating a growth-defense trade-off that is species-specific. Grazing reduced the sugar starch content of S. magellanicum and the sugar of S. fuscum. Either clipping or grazing had no effect on chlorophyll fluorescence (including actual and maximum photochemical efficiency of photosystem II) except that a significant effect of clipping on actual photochemical efficiency in S. fuscum was observed.

CONCLUSIONS

Our results suggest that Sphagnum can have induced defense against herbivory and that this defense can come at a cost of growth. These findings advance our knowledge about induced defense in bryophytes, the earliest land plants.