| 其他摘要 | Rises in ambient CO 2 are expected to cause global climate changes, including
increases in air temperature and shifts of regional scale rainfall patterns, which lead
to decreased soil water availability in some areas of the world. Elevated CO 2 affect
plant physiological and ecosystem processes and probably lead to the suppression of
plant N availability that limits the effect of CO 2 fertilization. Previous study have
shown that C 3 plants under elevated CO 2 often maintain growth during short term
drought due to improved water use efficiency, however, reduce long-term adaption
and result in down-regulation of photosynthesis. The maintenance of rapid growth
under conditions of CO 2 enrichment is directly related to the capacity of
photosynthesis and carbon and nitrogen transport in plants and its contribution to the
new foliar formation. Less is known about the phorosynthesis and carbon and
nitrogen transport in C 4 plants in response to drought, N limitation, precipitation
frequency and increasing CO 2 .
To test the effects of water and nitrogen limitation on plants under elevated CO 2 ,
maize (Zea mays), the world's most important C 4 crop, was planted to experience
combined elevated CO 2 (380 or 750 µmolmol -1
stomatal
, climate chamber), water stress (15%
PEG-6000) and nitrogen limitation (N deficiency treated since the 144th drought
hour) and rewatered at three intensities (300mL, 600mL, 900mL of distilled water).
During the growing period, the performance of PSII and electron transport,
limitation, non-stomatal limitation, photosynthetic potential parameters, leaf
nitrogen use efficiency, patterns of carbon and nitrogen delivery, and new leaf
productivities of the maize plants were investigated using chlorophyll-a fluorescence
OJIP induction curves, A/C i curves and 13 C and 15
(1). Compared to water-stressed maize under atmospheric CO 2 , the elevated CO 2 treatment interacted with water stress decreased number of active reaction
centers but increased antenna size and energy flux (absorb photon flux, trapping flux
and electron transport flux) of per reaction center in PSII. So the electron transport
rate (J) was increased, despite of the indistinctively changed quantum yield for
electron transport and energy dissipation. In carbon reaction, the combination of
elevated CO 2 and water stress treatment had the robust saturated photosynthetic rate
(A sat ). This study demonstrates that maize at doubled CO 2 was capable of
transporting more electron flow into carbon reaction.
(2). Elevated CO 2 could alleviate drought-induced photosynthetic limitation
through increasing capacity of PEPC carboxylation (V pmax ) and decreasing stomatal
limitations (SL). The N deficiency exacerbated drought-induced photosynthesis
limitations in ambient CO 2 . Elevated CO 2 partially alleviated the limitation induced
by drought and N deficiency through improving the capacity of Rubisco
carboxylation (V max ) and decreasing SL. Plants with N deficiency transported more
N to their leaves at elevated CO 2 , leading to a high photosynthetic nitrogen-use
efficiency but low whole-plant nitrogen-use efficiency. The stress mitigation by
elevated CO 2 under N deficiency conditions was not enough to improving plant N
use efficiency and biomass accumulation. The study demonstrated that elevated CO 2
could alleviate drought-induced photosynthesis limitation, but the alleviation varied
with N supplies.
(3). Compared to water-stressed maize under atmospheric CO 2 , the treatment
combining elevated CO 2 with water stress increased the accumulation of biomass
and partitioned more carbon and nitrogen to the formation of new leaves. Maize
seedlings enhanced the carbon resource in aging leaves and the carbon pool in new
leaves but decreased the carbon counterflow capability of roots. The seedlings also
had increased residence times of new nitrogen in roots and then delivered more
nitrogen to new leaves. Thus maize supported the development of new leaves at
elevated levels of CO 2 by altering the transport and remobilization of carbon and
nitrogen. In drought presence condition, increased activity of new leaves to store
carbon and nitrogen sustains enhanced growth under elevated CO 2 in maize.
(4). Elevated CO 2 significently increased the accumulation of nitrogen in
whole plant and new leaves. With nitrogen starvation, elevated CO 2 retard the new
nitrogen transport in functional leaves, accelerate the new nitrogen transport in ne leaves to sustains growth under drought.
(5). After they were rewatered, pre-drought stressed and N limited plants with
ambient CO 2 increased their water content higher than that of elevated CO 2 , while
the enhancement of growth rate were negatively proportional to the increasing plant
water content. Elevated CO 2 could help rewatered seedlings to have higher
photosynthetic capacity (F v /F m , Φ PSII , P n , P n /T r and P n /G s ) and new leaf recovery
ability under low water content, no matter the seedlings suffered nitrogen deficiency
or not. The study demonstrated that elevated CO 2 could help drought stressed
seedlings to have higher carbon assimilation rates under low water uptakes, as a
result to improve leaf water use efficiency, which allows the plants to have much
better performance under drought following being re-watered.
KEY WORDS: Elevated CO 2 ；Photosynthesis；N and C Allocation；Water Stress；
N Stress；Maize |
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