Principles of terrestrial ecosystem ecology.pdf

164 7. Terrestrial Decomposition
Mass remaining (% of original)
100
50
0
Pine branch
Pine needle
Pin-cherry leaf
0 12 24
Time (mo)
Figure 7.8. Time course of decomposition of a
deciduous leaf, a conifer needle, and wood in a
Canadian temperate forest (MacLean and Wein
1978).
Dry mass loss (% of original)
80
70
60
50
40
30
20
10
0
20
Vines
Herbs
Shrubs
Trees
Graminoids
present in litter. These compounds can be categorized
roughly as labile metabolic compounds,
such as sugars and amino acids; moderately
labile structural compounds, such as cellulose
and hemicellulose; and recalcitrant structural
material, such as lignin and cutin. Rapidly
decomposing litter generally has higher concentrations
of labile substrates and lower concentrations
of recalcitrant compounds than
does slowly decomposing litter.
Five interrelated chemical properties of
organic matter determine substrate quality (J.
Schimel, personal communication, 2001): the
size of molecules, the types of chemical bonds,
the regularity of structures, the toxicity, and the
nutrient concentrations. (1) Large molecules
cannot pass through microbial membranes
so they must be processed extracellularly by
exoenzymes. This limits the degree of control
that a given microbe can exert over the detection
of substrate availability, the delivery of
enzymes in response to substrate supply, and
the efficient use of breakdown products. Due to
differences in molecular size, sugars and amino
100
Temperate climate Semi-arid climate
Subshrubs
Trees
Shrubs
Subshrubs
Deciduous leaves Evergreen Deciduous leaves Other
leaves
Figure 7.9. A, Decomposition rate of leaves of
British deciduous and evergreen plant species.
(Redrawn with permission from Journal of Ecology;
80
60
40
20
0
Herbs
Trees &
shrubs
Graminoids
A B
Succulents
Bromeliads
Aphyllous
Cornelissen 1996). B, Decomposition rate of deciduous
plants and aridzone plants in Argentina.
(N. Perez; Perez-Harguindeguy et al. 2000.)