Bryophyte physiology

groups of heavy metals

binding to ligands with oxygen

binding ligands with N and S

Borderline: binding affinity comparable for N, S and O ligands

heavy metal mass density

>5 g/cm3

metals that bind ligands with N and S (4)

Au

Ag

Hg

Pb

metals with binding affinity comparable for N, S and O ligands (8)

As

Cd

Co

Cr

Cu

Ni

Sn

Zn

sources of heavy metals (3)

combustion of fossil fuels

brake and tire wear

industry (transportation by fine dust)

chemical effect of heavy metals (4)

enzyme inhibition

binding on active centre, oxidative stress

free radicals

DNA and membrane destruction

heavy metal effect on protonema (2)

decline in ramification (development), thicker cell walls, bud formation

blocking bryophyte development

heavy metal effect on chlorophyll (2)

Cd or Cu binds instead of Mg in central part of chlorophyll

lost functionality

heavy metal accumulation locations in mosses (4)

particulate matter (on surface)

extracellular

intercellular

intracellular

heavy metal avoidance strategies

cell wall binding and cation exchange

heavy metal tolerance strategies (3)

intracellular chelation (forms nontoxic complexes)

Antioxidative system (Reactive Oxygen Species)

Vacuolar sequestration

bryophyte hydration status

poikilohydry

bryophyte water transport (2)

primarily ectohydric

lack of lignan

bryophyte water source (2)

atmospheric deposition

lack of true roots

bryophyte advantages of water system

high resilience and ability to colonise extreme habitats

bryophyte disadvantages of water system (2)

growth/activity restricted to periods of hydration

low productivity

bryophyte total water content

50–2000% of dry weight

Minimum water content for growth:

10–100% (species-specific)

scarcity in arid regions (3)

short hydration periods

metabolic cost of reactivating metabolism after rehydration

often insufficient to maintain positive C balance

Ectohydry

lack specialized internal water-conducting tissues and instead absorb water and nutrients across their entire surface

Surface absorption:

absorption: taking in water from the atmosphere (rain, fog, dew) through their entire body surface; water uptake from the substrate is minimal.

bryophyte leaf area index

larger than vascular plants

bryophyte water conduction

outside the thallus in specialised structures

eg: paraphyllia, tomentum, capillary spaces

bryophyte transport of assimilates

slower

The Gas Exchange Paradox:

The trade-off between the need for sufficient hydration and the necessity of unobstructed gas exchange.

strictly ectohydric groups (3)

leafy liverworts

hornworts

certain Pottiaceae

Ectohydry habitats (3)

saxicolous

epiphytic

extreme environments

Endohydry

internal water transport via differentiated conducting tissues (e.g., midribs of thalloid liverworts, sporophytes,

stems, leaf costae, protostele) →

protostele

larger mosses (such as Polytrichum commune) feature a central strand that functions structurally and anatomically like a protostele

Surface permeability endohydric spp (3)

thallus surface less permeable;

more developed cuticle,

sometimes underground rhizomes

Endohydry assimilates

rapid transport via leptoids

endohydric groups (3)

certain Polytrichaceae

Mniaceae

Marchantiales

endohydric species prefer

moister environments (forests, peat bogs, etc)

Endo and ectohydric continuum

spectrum btw. strictly ectohydric and endohydric species;

many bryophytes with both traits (e.g., easy surface absorption combined with internal distribution).

Mixohydry:

combination of ecto- and endohydric water transport.

adaptations against water loss (7)

pleurocarpy

life form

leaf arrangement

leaf morphology

specialised external structures

internal anatomy

cellular adaptations

water loss pleurocarps

pleurocarpous taxa retaining 20–35% more water than acrocarpous

water loss adaptations life form (4)

tufts/cushions/mats/wefts, etc

water adaptations leaf arrangement (3)

overlapping leaves (succubus/incubous)

leaf position spacing

multilayered thalli/leaves

leaf morphology water adaptations (3)

decurrent/concave/undulate/plicate/recurved margins/keeled/conduplicate/lamellae/limbidia (borders)

hyaline points

leaf twisting/contortion

specialised external structures water loss (5)

tomentum

paraphyllia

mucilage papillae

ventral scales

tuberculate rhizoids

cellular adaptations water loss/uptake (6)

alar cells

hyalocytes

pores

papillae

mammillae

secondary metabolites

internal anatomy adaptations water loss/uptake (3)

central strand

hydroids

stereids

external transport of water (capillary conduction) (4)

external capillary spaces

inter-organ capillary system

epi-organ capillary system

intra-organ system

external capillary spaces

general gaps between the plant and environment

inter-organ capillary system

between different parts of the thallus (eg. sheathing leaf bases, tomentum, paraphyllia)

epi-organ capillary system

on the surface of individual structures (eg: lamellae, papillose, mammillae, ridges)

intra-organ system

within dead cells (eg hyladermis)

internal water transport methods (4)

hydroids

hyalocytes

symplastic transport

apoplastic transport

hydroids

specialised elongated cells with oblique end walls, lacking lignan

hyalocytes

large, dead, water-storing cells

symplastic transport (2)

movement through the interor of living cells (cytoplasm)

main challenge is high hydraulic resistance of cell membranes (mitigated by cell elongation)

apoplastic transport (2)

movement through cell walls, outside cytoplasmic membranes

significantly faster than symplastic

desiccation tolerance

capacity to fully restore metabolism after full desiccation

bryophyte desiccation recovery time

within minutes to hours

interspecific differences in desiccation tolerance (3)

Sphagnum (minimal)

Tortular muralis (months)

Syntrichia ruralis (years)

speed of metabolism recovery and growth after desiccation tolerance depends on (5)

frequency of desiccation/rehydration (many short is worse than one long)

length of desiccation

length of rehydration

water loss quantity

speed of water loss

respiration recovery after desiccation

almost immediate

photosynthesis recovery after desiccation (2)

longer than respiration

depends on species/conditions, from minutes to hours

normal state after rehydration reached (2)

12-24 hours

xerophytes fast, hydrophytes slower

ecological differences in desiccation tolerance

epiphytic form of Hypnum cupressiforme faster recovery of photosynthesis than terricolous or saxicolous

Seasonal dependency for metabolism speed and growth recovery

Tortula muralis showed more variability in recovery throughout year than forest species

desiccation tolerance requires (2)

protective mechanisms during dry periods

repair mechanisms after rewetting

desiccation repair cellular/biochemical mechanisms promote

survival of water loss without major destruction of structure and function of organelles and membranes

protective mechanisms during desiccation

LEA proteins

accumulation of soluble sugars

protein transcription

LEA proteins (5)

Late Embryogenesis Abundant

hydrophyllic, intrinsically unstructured proteins

protect proteins and membranes from aggregation

ion sequestration (regulating concentration to prevent ion loss during rehydration)

stabilises cytoplasm components in dry state

accumulation of soluble sugars

protein of natural protein structures and phospholipids in membranes (substitute water in hydrogen bonds)

desiccation protein transcription

associated with periods of desiccation but function unknown

repair mechanisms during rehydration (3)

after each desiccation: repair damage to cell orangelles

fast rehydration to prevent breaking membrane

using dehydrins

dehydrins (2)

LEA proteins

stabilise cell environment after rehydration, membrane repair, metabolism restoration

desiccation tolerance differences with vascular plants (3)

both produce abscisic acid (ABA)

angiosperms slower, LEA proteins produced to late, fast desiccation is lethal

LEA proteins produced continuously in bryophytes, poikilohydry

temperature optimum compared to vascular (2)

lower

seasonal niche differentiation

max seasons of bryophyte growth

spring/autumn

temperature optimum for photosynthesis and growth

15-25 C

survival during low/high temperature depends on

water content

dry state temperature tolerance

under -30 C, above 40 C (up to 110 C)

water mosses temperature optimum (2)

lower

Fontinalis antipyretica 10-15 C

lower temperature limit for photosynthesis

4 to -20 C

low temperature survival depends on

speed of freezing and water content

slow freezing and high moisture content

-5 up to -10 C impossible to survive

frost tolerance (4)

similar to desiccation mechanisms:

red pigments, light protection, ABA

change fatty acids in membranes to those with lower frost points

increase in sucrose concentration

snow cover (2)

maintains acceptable temperature

water and nutrient source

high temperature limit hydrated

42-51 C

high temperature limit desiccated

85-110 C

hydrated bryophytes at high temperatures

significant increase in respiration at temperatures 30-35 C

high temperature species tolerance

mesophytic species max 80-90 C

xerophytic species reach 110 C limit

mesophytic

moderate moisture supply

cushions in high temperature (2)

tend to overheat

temperatures higher than surrounding air

adaptations to high temperatures (3)

hair points

hyaline leaf tips

curling leaves

water management correlation (2)

shady, moist habitats: photosynthesis even during cloudy weather

bryophytes often inactive during sunny, warm weather (due to desiccation)

light intensity response (2)

reaction to changes faster than vascular plants

eg: sunfleck utilisation

high light intensities and UV

can be lethal (free radicals, photosynthetic apparatus damage, degradation of chlorophyll)

optimal light intensity for photosynthesis

~ 400 lux

maximum light intensity photosynthesis

~40,000 lux (around ½ of light intensity at noon in summer)

minimum light intensity for photosynthesis

20 lux

light compensation point (2)

300-700 lux for most species

(temperature dependent, lower temperatures correspond to lower compensation point)

light pigment dynamics

changes in the quantity and ratios of pigments throughout the year

adaptation to highest light saturation points (3)

supported by assimilatory lamellae on leaf midribs

large area for CO2 absorption

eg peatland Polytrichaceae

photosynthetic efficiency within single species can depend on

moisture conditions of habitat

adaptations against high light intensity (4)

leaf curling

hairs or hair points (hyaline leaf tips)

layers of hyaline cells

pigmentation