Gm. Berntson et al., BELOW-GROUND ARCHITECTURAL AND MYCORRHIZAL RESPONSES TO ELEVATED CO2 IN BETULA-ALLEGHANIENSIS POPULATIONS, Functional ecology, 11(6), 1997, pp. 684-695
1. Replicate populations of crowded, regenerating stands of Betula all
eghaniensis were grown in ambient and elevated (700 p.p.m.) atmospheri
c CO2 concentrations in monoliths of forest soil. Early in the second
year the seedlings were harvested and detailed measurements of individ
ual plant root architectural parameters and ectomycorrhizal colonizati
on were made. 2. Comparing the average responses of individual plants
within the populations, elevated CO2 had no significant effects on arc
hitectural parameters that improve a plant's ability to forage for and
acquire soil resources. In contrast, the intensity and magnitude of m
ycorrhizal colonization, and whole plant C/N ratios were significantly
enhanced with elevated CO2. 3. The allometric scaling relationship be
tween total plant biomass and root biomass was not affected by CO2, su
ggesting that relative allocation between roots and shoots was not aff
ected. However, the allometric scaling relationships between root arch
itectural parameters and plant biomass, and between fine root biomass
and woody root biomass were significantly altered by elevated CO2. For
all of these relationships, elevated CO2 reduced the 'size bias' of a
rchitectural components in relation to plant size within the populatio
ns; in elevated CO2 root architectural size (e.g. root length) per uni
t biomass was more similar between the smallest and largest individual
s within the population than was the case for ambient CO2. 4. Overall,
the results of this study suggest that the average individual seedlin
g biomass and architectural growth responses within populations of pla
nts exposed to elevated atmospheric CO2 levels may be unresponsive, bu
t that mycorrhizal responses and interactions among plants within popu
lations may be altered significantly. These findings have important im
plications for how we make predictions about plant growth responses to
elevated CO2 in natural ecosystems. Significant increases in mycorrhi
zal infection rates and architecture-biomass allometries suggest that
below-ground competitive interactions within plant populations may be
reduced in elevated CO2. Alterations in competitive interactions may l
ead to shifts in productivity and plant population structure.