Carbon dioxide stimulation of photosynthesis in Liquidambar styraciflua is not sustained during a 12-year field experiment [electronic resource]

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Ngôn ngữ: eng

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Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2014

Mô tả vật lý: Size: Article No. plu074 : , digital, PDF file.

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ID: 261313

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We report that elevated atmospheric CO
2
(eCO
2
) often increases photosynthetic CO
2
assimilation (A) in field studies of temperate tree species. However, there is evidence that A may decline through time due to biochemical and morphological acclimation, and environmental constraints. Indeed, at the free-air CO
2
enrichment (FACE) study in Oak Ridge, Tennessee, A was increased in 12-year-old sweetgum trees following 2 years of ~ 40 % enhancement of CO
2
. A was re-assessed a decade later to determine if the initial enhancement of photosynthesis by eCO
2
was sustained through time. Measurements were conducted at prevailing CO
2
and temperature on detached, re-hydrated branches using a portable gas exchange system. Photosynthetic CO
2
response curves (A versus the CO
2
concentration in the intercellular air space (C
i
)
or A-C
i
curves) were contrasted with earlier measurements using leaf photosynthesis model equations. Relationships between light-saturated photosynthesis (Asat), maximum electron transport rate (J
max
), maximum Rubisco activity (V
cmax
), chlorophyll content and foliar nitrogen (N) were assessed. In 1999, A
sat
for eCO
2
treatments was 15.4� 0.8 ?mol m
-2
s
-1
, 22 % higher than aCO
2
treatments (P<
0.01). By 2009, A
sat
declined to <
50 % of 1999 values, and there was no longer a significant effect of eCO
2
(A
sat 
=6.9 or 5.7� 0.7 ?mol m
-2
s
-1
for eCO
2
or aCO
2
, respectively). In 1999, there was no treatment effect on area-based foliar N
however, by 2008, N content in eCO
2
foliage was 17% less than that in aCO
2
foliage. Photosynthetic N-use efficiency (A
sat 
: N) was greater in eCO
2
in 1999 resulting in greater A
sat
despite similar N content, but the enhanced efficiency in eCO
2
trees was lost as foliar N declined to sub-optimal levels. There was no treatment difference in the declining linear relationships between J
max
or V
cmax
with declining N, or in the ratio of J
max
: V
cmax
through time. Ultimately, results suggest that the initial enhancement of photosynthesis to elevated CO
2
will not be sustained through time if N becomes limited.

1. 54 environmental sciences
2. 60 applied life sciences
3. Acclimation
4. Down-regulation
5. Free-air co2 enrichment
6. Nitrogen limitation
7. Sweetgum
8. Sweetgum

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