Download 绵羊口液对羊草（Leymus chinensis）再生生长的作用 及其生理机制

Ecological functions of litter in ecosystem
Jushan Liu
Institute of Grassland Science
2013.4.23
Instruction
Litter dynamics
Effects of litter on environment
Effects of litter on plant community
DIRT project
Introduction
Plant litter: the dead plant material of small size
lying loose on the ground
Introduction
Litter may affect environment and plant community
structure and dynamics, linked to climatic
conditions and environmental management
Substrate for the detritus food web, nutrient
reservoir, and contributor to mineral-nutrient
cycling and energy flow
Alter microenvironment
and plant community
Introduction
Production and decomposition have been widely
studied, carbon balance and cycling of nutrients
Effects on particular populations, but only recently
on community structure and dynamics. Few
attempts have been made to understand the
mechanisms underlying the effects of litter on
plant populations and communities
Litter dynamics
Litter accumulation is a complex process and
change in time and space, and affect the physical
and chemical environment
Balance among liter production, litter deposition
from outside system, litter destruction by physical
and biotic agents, and removal of litter
Litter dynamics
Litter production
Productivity of the plant community
Climate, rainfall and the length of growing season
Soil fertility, soil water retention, and species
composition is important
Herbivores may increase or decrease the
production of litter, though consumption usually
reduces the standing biomass
(Xiong and Nilsson 1914-2002)
Litter dynamics
Litter disappearance
Litter accumulated may be reduced by physical
and chemical degradation, heterotrophic
consumption and decomposition
Decomposition rates vary among ecosystems,
regulated mainly by temperature and water
regimes and soil fertility is secondarily important
Litter dynamics
Litter decomposition
Microenvironment surrounding the litter affects
decomposition rate
Decomposition is faster when trampling by cattle
or snow packing
Litter exposed to air is decomposed mostly by
fungi
Litter dynamics
Litter decomposition
Chemical composition of litter is another important
variable, lignin, nitrogen, cellulose and second
compounds
Short-lived organs have less lignin and secondary
chemicals
Adverse growth condition and herbivory may also
increase the concentration of tannin and phenolic
Effects on environment
Chemical environment
During life and senescence of organs, organic and
inorganic substances are accumulated, released
by leaching, or attacked by decomposers and their
products released into the soil
Chemical properties of the leachates depend on
the nature of the substances and on the
biochemical transformations
Effects on environment
Chemical environment
Mineral nutrients: retranslocated to other organs,
consumed by herbivores or pathogens, or lost by
plants with litter
Environmental conditions and physicochemical
characters of litter regulate the rate of nutrient
release from the organic matter
Effects on environment
Chemical environment
Litter indirect effects on nutrient availability
through changes in environmental variables that
regulate mineralization
Litter accumulation can create patchy distribution
of nutrient and produce high concentrations of
toxic minerals, heavy metals or salt
Effects on environment
Physical environment
Litter intercepts incident light and the rain, and
changes surface structure, affecting transfer of
heat and water between soil and the atmosphere
Direct effects on germination and establishment
and indirect effects on resource availability and
other biotic components
Effects on environment
Physical environment
Light environment
Light interception by litter is important and may
exert an important effect on the plant community
Changes in the light spectrum may have important
ecological significance, since light quality affects
germination, seedling development and tillering
Effects on environment
Physical environment
Light environment
Litter may prevent the germination of plants and
establishment is negatively affected by litter
Higher mortality of seedlings under a thick layer of
litter and establishment of species with very large
seeds may be hindered by litter
Effects on environment
Physical environment
Light environment
Sprouting of perennial herbs may also be
negatively affected as a result of light deprivation
Grass shoots growing under dense litter must
spend energy to reach the light, and tillers lessen
their capacity to fix carbon and reduce plant
productivity
Effects on environment
Physical environment
Soil temperature
Litter modifies soil temperature by intercepting
solar radiation, and by insulating the soil from air
temperature
Temperature of soil surface under litter is lower
than air temperature, and burning or hand litter
removal can increase soil temperature
Effects on environment
Physical environment
Soil temperature
Changes in soil temperature produced by litter
may directly affect plant growth, but may also
enhance the rate of mineralization, and therefore
nutrient availability
Early sprouting may be a result of increased soil
temperature and in bare areas higher temperature
early in the spring promotes early emergence
Effects on environment
Physical environment
Water dynamics
Litter affects exchange of water between soil and
atmosphere and increases water availability
Litter accumulation can increases infiltration,
reduce evaporation from the soil and decreases
run-off, indirectly by reducing the soil temperature
Effects on environment
Physical environment
Water dynamics
Changes in water availability mediated by litter
may have obvious effects on different plant
population, increase establishment of grass
seedlings and seedling survivorship. Litter
removal can decrease productivity where water
may be the main limiting factor
Effects on plant community
Germination and establishment
Sensitive to litter, and there exist both positive and
negative responses
Improving water conditions in dry habitats,
protecting seeds from or by reducing competition
Shading or obstructing plants, reducing
temperature, attracting predators, and probably
fostering pathogens
Effects on plant community
Community productivity
Production is enhanced, unchanged or inhibited,
attributable to different substrate conditions,
species compositions, and litter amounts, as well
as litter types and qualities
Substrate is one of most important factors, affect
the rates of both litter production and litter
disappearance and thus community responses
Effects on plant community
Species richness
Positive and negative effects have been found
Moderate input of litter may reduce dominance
and increase diversity
Thick mat of tree litter may reduce diversity of
ground vegetation and quadratic relationship with
the highest numbers of species at low to
intermediate accumulations of litter
Effects on plant community
Community dynamics
Litter-induced changes in soil nutrients, light, and
soil temperature and moisture initiate community
successions in different systems
Associated with a change of interspecific relations
induced by litter
Litter alters species interactions in a deciduous
forest (Sydes and Grime 1981)
Effects on plant community
Community dynamics
Litter changed the relative importance of different
species categories (Monk and Gabrielson 1985)
Succession of oldfield communities was indirectly
controlled by changing interspecific interactions
because of litter (Facelli and Pickett 1994)
Berendse (1994) developed a model suggesting
that species replacements were triggered by the
decomposability of litter
Effects on plant community
Community dynamics
Litter accumulation may affect seasonal changes
of a community
Litter addition suppresses and removal increases
density and richness (Carson and Peterson 1990)
Litter layer may prevent seeds from reaching the
soil and germinating in early spring
Redistribution of litter have different outcomes for
a specific vegetation
Conclusions
Litter is an important factor affecting community
organization and dynamics far beyond a transitory
bank of nutrients. Litter can alter the physical and
chemical environment, and therefore the
demography of various populations. The response
of different populations, with effect of the changes
in the performance of other populations, may play
an important role in shaping community structure
(Sayer 2006)
(Richard and Cotrufo 1998)
DIRT project
Detritus Input and Removal Treatments is an
international network of fieldbased organic matter
manipulations (Nadelhoffer et al 2004)
 How rates and sources of plant litter inputs control
the accumulation and dynamics of organic matter
and nutrients in soils?
 To determine contributions of live roots, aboveground litter, and belowground detritus to SOM and
nutrient dynamics
DIRT project
Site Location
University of Wisconsin Arboretum
Initiated
1956
Ecosystem Type
sugar maple forest, oak
forest, and prairie
Harvard Forest, Massachusetts
1990
Bousson Experimental Forest, Pennsylvania 1991
oak forest
black cherry-sugar maple
forest
HJ Andrews Experimental Forest, Oregon
1997
old-growth coniferous
Michigan Biological Laboratory at Pellston
2004
oak forest
Síkfökút Forest, Eger, Hungary
2000
oak forest
Francis D. Hole
(1914-2002)
DIRT project
Treatments
Method
Control (CK)
Normal litter inputs are allowed
No litter (NL)
Aboveground inputs are prevented by seasonal removals
Double litter (DL)
Aboveground inputs are doubled by adding litter from NO LITTER plots
No root (NR)
Roots are excluded by inserting barriers around plots in backfilled trenches
No input (NI)
Combined treatments from NO LITTER and NO ROOTS (above)
Double wood (DW)
Adding shredded course woody debris (HJA, SIK &UMBS, only)
DIRT project
 Live root respiration, aboveground litter and root
detritus constitute one-third of C inputs
 Doubling or excluding litter proportionally increased
or decreased respiration
 C and N stocks respectively increased or
decreased in response to doubling or excluding
aboveground litter inputs to root-intact soil
 Aboveground inputs strongly influence SOM, root
inputs on SOM quality
The function of litter on grassland under
the background of nitrogen deposition
 To determine how nitrogen and carbon inputs
interact in controlling nutrient cycling and stock
 How does different quantity and quality of litter input
influence ecosystem structure and functions?
Split–plot
Nitrogen
No nitrogen addition (0N)
Adding nitrogen (+N)
Plant
29 May
No plants (0P)
Experiment
With plants (+P)
design
Litter
No litter (0L)
One litter (1L)
Double litter (2L)
Replicates 6
Plot amount 72
Plot size
3×4m
Cycling
Photosynthesis
Every month
Respiration
Gas exchange
Plant
Productivity
Aboveground biomass
August
Belowground biomass
October
Litter biomass
October
Nutrient
Carbon
Nitrogen
Variables
Phosphorus
Litter
Decompositon
Every two
Biomass
months
Nutrient
Soil
Carbon
Total, Active, Solutive
Microbial, Heavy
Light, δ13
Nitrogen
Phosphorus
Design
Factors
R2= 0.52
R2= 0.90
R2= 0.84
L. chinensis
density
Shannon-Weiner
index
L. chinensis
density
1.15
-0.73
1.34
0.83
Grass
density
Nitrogen
R2= 0.66
-0.84
Litter
0.52
-0.22
-0.52
0.25
-1.07
R2= 0.98
Shoot
biomass
Nitrogen
0.58
0.82
Legume
density
Root
biomass
R2= 0.50
R2= 0.89
1.17
0.87
-0.33
Forb
density
Litter
biomass
R2= 0.42
R2= 0.75
Litter