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Structure and function of marine angiosperms - Coggle Diagram
Structure and function of marine angiosperms
Seagrasses
anatomy:
seagrasses are modular in growth form, with units connected by horizontal stems, vertical shoots and roots coming off nodes.
Growth forms:
-rhizomes are underground stems
-they grow continuously out from their origin
-shoots and roots emerge from the rhizome periodically at nodes
-shoots tend to be short-lived but can leave behind fibrous leaf bases
-rhizome has asexual reproduction
Leaf sheaths:
no stomata
thin cuticles
protect from salt
-tube-like structure surrounding rhizome
-leaves inserted through leaf sheath
-encloses and protects meristem and newly formed leaves
-often lacks chlorophyll
-high lignin content
-very stiff that hold shape and pressure
-lignin helps prevent decomposition
-remains attached to rhizome for extended period
Structural adaptation:
-aerenchyma and spaces: tissues to conduct air through plant
-fibres for strength, flexibility
-much cellulose throughout shoots (provides strength and flexibility)
Pigments:
-chlorophyll a and b
Mangroves
habitat:
-waterlogged soil/mud (little oxygen, high respiratory rate)
-buttresses and aerial roots (pneumatophores, lenticels and aerenchyma)
-lateral roots: support
-hypertrophy
Xerophytes:
-leaves have waxy cuticle
-water storage tissues
-sunken stomata
Shade adaptation
-chloroplasts of seagrasses are found predominantly in epidermal cells
-epidermal chloroplasts capture light and exchange gases free from the barriers forced on chloroplasts in sub-epidermal tissues
Canopy behaviour:
-water flow has significant influence on leaves
-nature of flow can be significant in light climate
-tidal flows result in canopy compression for extended periods
-orbital flows produce more rapid flapping
Reduced density:
-as density declines, more light can penetrate
-more light gets through canopy during winter
-causes a reduction in shoot density
-early warning sign of stress
Epiphytes:
-natural part of seagrass ecosystems
-seagrasses provide a stable substrate for epiphyte growth
-excess epiphyte can be caused by: good growing conditions and eutrophication
-excess can block light
mechanisms of regulating salt:
-capacity of roots to exclude NaCl
-excretion of salt by leaves
-salt accumulation in bark, leaves
-loss of salt when shedding leaves
-osmoregulation
Salt uptake by roots:
-uptake of water nutrients is via fibrous roots
-shallow root system
Roots exclude salt:
-roots of higher plants generally selective in ion uptake/transport to xylem
-operates via Na+ pump at plasmalemma: salt excluded from cytoplasm
-species without glands exclude 95-98%
-species with salt-secreting glands in leaves exclude 80-85%
Salt accumulation:
-NaCl stored in mesophyll cells in leaves
-mostly stored within vacuoles