25 Are C 4 Pathway Plants
Threatened by Global Climatic Change?
S. Henderson, P. Hattersley, S. von Caemmerer, and
C.B. Osmond
25.1 Introduction
During his decades of leadership in plant photosynthetic ecophysiology Otto
Lange has seen many major developments in the field, and participated in
most of them. Perhaps none of these fields has been more exciting than the
recognition of the ecophysiological implications of the C4 pathway of photosynthetic carbon metabolism. Perhaps none will be so profound as the
response of vegetation to the now well established, inexorable increase in
atmospheric CO2 concentration, the major greenhouse gas and the principal
driver of impending global climatic change. Man, the dominant mammal,
has effectively accelerated global respiration about 10 6 fold, by the combustion of several billion years' worth of accumulated photosynthate and
other organic carbon in the course of a few hundred years. Here we ask if
this activity which is leading to a rapid increase in atmospheric CO 2 concentration will directly affect the relative fitness of C4-pathway plants, which
may have evolved in response to low atmospheric CO2 concentration.
The potential threat posed to C4 pathway plants by these changes has
been raised frequently. The concern arises because the advantages in productivity, water-use efficiency, and temperature tolerance that the CO2
concentrating mechanism confers on C4 plants over C 3 plants, may be
diminished at elevated CO2 , In this chapter we will retrace, briefly, our
understanding of photosynthetic ecophysiology that leads us to pose the title
question and explore some of its dimensions. We will conclude that plants
which evidently evolved an internal COTconcentrating mechanism to insulate
themselves against low external CO2 concentrations may be well equipped
to handle rising atmospheric CO2 concentrations. Indeed, the magnitude of
the threat is not likely to be determined by effects on fitness of C 4 plants at
all, but upon whether C3 plants can take advantage of elevated CO 2 and
thereby improve their fitness and competitive abilities.
Threatened by Global Climatic Change?
S. Henderson, P. Hattersley, S. von Caemmerer, and
C.B. Osmond
25.1 Introduction
During his decades of leadership in plant photosynthetic ecophysiology Otto
Lange has seen many major developments in the field, and participated in
most of them. Perhaps none of these fields has been more exciting than the
recognition of the ecophysiological implications of the C4 pathway of photosynthetic carbon metabolism. Perhaps none will be so profound as the
response of vegetation to the now well established, inexorable increase in
atmospheric CO2 concentration, the major greenhouse gas and the principal
driver of impending global climatic change. Man, the dominant mammal,
has effectively accelerated global respiration about 10 6 fold, by the combustion of several billion years' worth of accumulated photosynthate and
other organic carbon in the course of a few hundred years. Here we ask if
this activity which is leading to a rapid increase in atmospheric CO 2 concentration will directly affect the relative fitness of C4-pathway plants, which
may have evolved in response to low atmospheric CO2 concentration.
The potential threat posed to C4 pathway plants by these changes has
been raised frequently. The concern arises because the advantages in productivity, water-use efficiency, and temperature tolerance that the CO2
concentrating mechanism confers on C4 plants over C 3 plants, may be
diminished at elevated CO2 , In this chapter we will retrace, briefly, our
understanding of photosynthetic ecophysiology that leads us to pose the title
question and explore some of its dimensions. We will conclude that plants
which evidently evolved an internal COTconcentrating mechanism to insulate
themselves against low external CO2 concentrations may be well equipped
to handle rising atmospheric CO2 concentrations. Indeed, the magnitude of
the threat is not likely to be determined by effects on fitness of C 4 plants at
all, but upon whether C3 plants can take advantage of elevated CO 2 and
thereby improve their fitness and competitive abilities.