『Abstract
We review measured rates of soil respiration from terrestrial
and wetland ecosystems to define the annual global CO2
flux from soils, to identify uncertainties in the global flux
estimate, and to investigate the influences of temperature, precipitation,
and vegetation on soil respiration rates. The annual global CO2 flux from soils is estimated to average (±S.D.)
68±4 PgC/yr, based on extrapolations from biome land areas.
Relatively few measurements of soil respiration exist from arid,
semi-arid, and tropical regions; these regions should be priorities
for additional research. On a global scale, soil respiration rates
are positively correlated with mean annual air temperatures and
mean annual precipitation. There is a close correlation between
mean annual net primary productivity (NPP) of different vegetation
biomes and their mean annual soil respiration rates, with soil
respiration averaging 24％ higher than mean annual NPP. This difference
represents a minimum estimate of the contribution of root respiration
to the total soil CO2 efflux. Estimates of
soil C turnover rates range from 500 years in tundra and peaty
wetlands to 10 years i tropical savannas. We also evaluate the
potential impacts of human activities on soil respiration rates,
with particular focus on land use changes, soil fertilization,
irrigation and drainage, and climate changes. The impacts of human
activities on soil respiration rates are poorly documented, and
vary among sites. Of particular importance are potential changes
in temperatures and precipitation. Based on a review of in
situ measurements, the Q10 value for
total soil respiration has a median value of 2.4. Increased soil
respiration with global warming is likely to provide a positive
feedback to the greenhouse effect.』
1. Introduction
2. Soil respiration as an ecosystem process
3. Global patterns of soil respiration
3.1. Selection of data
3.2. Soil respiration in major vegetation biomes
『
| Table 1. Mean rates of soil respiration in different types of vegetation, based on the data in the Appendix | |||
|
|
（土壌呼吸） (gC/m2/yr) (mean±S.E.) |
|
|
| Tundra（ツンドラ） | 60±6 | 11 | e |
| Boreal forests and woodlands（寒帯林） | 322±31 | 16 | cde |
| Temperate grasslands（温帯草原） | 442±78 | 9 | bcd |
| Temperate coniferous forests（温帯針葉樹林） | 681±95 | 23 | b |
| Temperate deciduous forests*（温帯落葉樹林） | 647±51 | 29 | b |
| Mediterranean woodlands and heath（地中海性潅木林） | 713±88 | 13 | b |
| Croplands, fields, etc.（農地） | 544±80 | 26 | bc |
| Desert scrub（砂漠） | 224±38 | 3 | de |
| Tropical savannas and grasslands（熱帯サバンナ） | 629±53 | 9 | bc |
| Tropical dry forests（熱帯季節林） | 673±134 | 4 | b |
| Tropical moist forests（熱帯多雨林） | 1260±57 | 10 | a |
| Northern bogs and mires（北方泥炭） | 94±16 | 12 | e |
| Marshes（湿地） | 413±76 | 6 | bcd |
|
Letters in the final column refer to the results of a Duncan's
multiple range test (SAS Institute 1985); vegetation types followed
by the same letter do not have significantly different respiration
rates. *Including mixed broad-leaved and needle-leaved forests. |
|||
3.3. Climatic controls over soil respiration
3.4. Global soil respiration
4. Soil carbon turnover
5. Human impacts on soil respiration rates
5.1. Land use changes
5.2. Fertilization
5.3. Irrigation ad drainage
5.4. Temperature changes
6. Summary and conclusions
7. Acknowledgments
Appendix. Annual soil respiration rates (gC・m-2・yr-1)
in the world's major terrestrial biomes
References