Effects of Phenology, Physiology, and Gradients in Community Composition
455
response to elevated CO2 that potentially lead to redistribution of nutrients
and modification of structure are beyond the present scope of this model,
the equations used to describe CO2 exchange are expected to be generally
applicable. Furthermore, as demonstrated, the aggregate GAS-FLUX model
is compatible with including aspects of vegetation change and can be developed to describe the response of a variety of community types under
elevated CO 2 environmental conditions, including the effects of long-term
temperature increase and precipitation effects on water table.
Although tundra ecosystems are unique in certain characteristics, such as
limited rooting volume and extremely cold soil temperatures due to permafrost, most aspects of the GAS-FLUX model are of a general nature,
making it a useful tool for analysis in other ecosystems. Similar types of data
are required to establish parameter values, to drive the model, and to
validate output. Present research efforts are directed toward model applications in temperate and mediterranean forests and shrublands. In these
situations, stress factors other than those found in tundra modify physiological response, i.e., stomatal closure in response to decreased water
availability or due to cold temperature in conifers. As a result of these
species-specific behaviors, it is possible that aggregate versions of the model
may become more complex and that other approaches are required. In
forest situations, small chambers provide important information on understory fluxes, while xylem sap flow methods and eddy correlation techniques
potentially provide validation for the overstory and at the stand level.
Potential to evaluate the impact of pollutants on mosses and to quantify
moss physiological response is an important new component of the model,
since mosses in terms of pollutant deposition provide the last buffer between
atmosphere and microbial and root responses in the soil. Models such as
GAS-FLUX will help us to describe physiological controls on exchange
rates, to understand the partitioning of total flux to the many sinks in the
ecosystem (both for carbon dioxide and gaseous pollutants), and to assess
potential impacts or response at different locations within the ecosystem
structure. GAS-FLUX will help us demonstrate a number of ways in which
ecophysiological information may be used to better understand relevant
responses of ecosystems important to us on a daily basis.
Acknowledgments. This research was supported by the US Department of Energy R4D
Program, the Bayreuth Institute for Terrestrial Ecosystem Research, and the German
Federal Ministry for Research and Technology (grant no. BEO-0339476A).
References
Ball JT, Woodrow IE, Berry JA (1987) A model predicting stomatal conductance and its
contribution to the control of photosynthesis under different environmental conditions.
In: Binggins I (ed) Progress in photosynthesis research, vol IV.5. Proc VII Int Photosynthesis Congr. Nijhoff, Dorrdrecht, pp 221-224
455
response to elevated CO2 that potentially lead to redistribution of nutrients
and modification of structure are beyond the present scope of this model,
the equations used to describe CO2 exchange are expected to be generally
applicable. Furthermore, as demonstrated, the aggregate GAS-FLUX model
is compatible with including aspects of vegetation change and can be developed to describe the response of a variety of community types under
elevated CO 2 environmental conditions, including the effects of long-term
temperature increase and precipitation effects on water table.
Although tundra ecosystems are unique in certain characteristics, such as
limited rooting volume and extremely cold soil temperatures due to permafrost, most aspects of the GAS-FLUX model are of a general nature,
making it a useful tool for analysis in other ecosystems. Similar types of data
are required to establish parameter values, to drive the model, and to
validate output. Present research efforts are directed toward model applications in temperate and mediterranean forests and shrublands. In these
situations, stress factors other than those found in tundra modify physiological response, i.e., stomatal closure in response to decreased water
availability or due to cold temperature in conifers. As a result of these
species-specific behaviors, it is possible that aggregate versions of the model
may become more complex and that other approaches are required. In
forest situations, small chambers provide important information on understory fluxes, while xylem sap flow methods and eddy correlation techniques
potentially provide validation for the overstory and at the stand level.
Potential to evaluate the impact of pollutants on mosses and to quantify
moss physiological response is an important new component of the model,
since mosses in terms of pollutant deposition provide the last buffer between
atmosphere and microbial and root responses in the soil. Models such as
GAS-FLUX will help us to describe physiological controls on exchange
rates, to understand the partitioning of total flux to the many sinks in the
ecosystem (both for carbon dioxide and gaseous pollutants), and to assess
potential impacts or response at different locations within the ecosystem
structure. GAS-FLUX will help us demonstrate a number of ways in which
ecophysiological information may be used to better understand relevant
responses of ecosystems important to us on a daily basis.
Acknowledgments. This research was supported by the US Department of Energy R4D
Program, the Bayreuth Institute for Terrestrial Ecosystem Research, and the German
Federal Ministry for Research and Technology (grant no. BEO-0339476A).
References
Ball JT, Woodrow IE, Berry JA (1987) A model predicting stomatal conductance and its
contribution to the control of photosynthesis under different environmental conditions.
In: Binggins I (ed) Progress in photosynthesis research, vol IV.5. Proc VII Int Photosynthesis Congr. Nijhoff, Dorrdrecht, pp 221-224