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1.
Seasonal relationships between leaf nitrogen content (photosynthetic capacity) and leaf canopy light exposure in peach (Prunus persica) 总被引:4,自引:3,他引:1
Abstract Field gas exchange measurements on intact peach (Prunus persica (L.) Batsch) leaves indicate that leaf nitrogen content (NL) and leaf weight per unit leaf area (Wa) are highly correlated with CO2 assimilation rate (A) and mesophyll conductance (gm). Therefore, NL and Wa were used to study seasonal relationships between leaf carboxylation capacity and natural light exposure in tree canopies. From mid-season onwards, NL and Wa were linearly correlated with light exposure expressed as the amount of time during a clear day that a leaf was exposed to a photosynthetic photon flux density (Q) of ≥ 100 μmol m?2 s?1. The data support the hypothesis that whole-tree photosynthesis is optimized by partitioning of photosynthetic capacity among leaves in deciduous tree canopies with respect to natural light exposure. 相似文献
2.
P. Meir B. Kruijt M. Broadmeadow E. Barbosa O. Kull F. Carswell A. Nobre P. G. Jarvis 《Plant, cell & environment》2002,25(3):343-357
The observation of acclimation in leaf photosynthetic capacity to differences in growth irradiance has been widely used as support for a hypothesis that enables a simplification of some soil‐vegetation‐atmosphere transfer (SVAT) photosynthesis models. The acclimation hypothesis requires that relative leaf nitrogen concentration declines with relative irradiance from the top of a canopy to the bottom, in 1 : 1 proportion. In combination with a light transmission model it enables a simple estimate of the vertical profile in leaf nitrogen concentration (which is assumed to determine maximum carboxylation capacity), and in combination with estimates of the fraction of absorbed radiation it also leads to simple ‘big‐leaf’ analytical solutions for canopy photosynthesis. We tested how forests deviate from this condition in five tree canopies, including four broadleaf stands, and one needle‐leaf stand: a mixed‐species tropical rain forest, oak (Quercus petraea (Matt.) Liebl), birch (Betula pendula Roth), beech (Fagus sylvatica L.) and Sitka spruce (Picea sitchensis (Bong.) Carr). Each canopy was studied when fully developed (mid‐to‐late summer for temperate stands). Irradiance (Q, µmol m?2 s?1) was measured for 20 d using quantum sensors placed throughout the vertical canopy profile. Measurements were made to obtain parameters from leaves adjacent to the radiation sensors: maximum carboxylation and electron transfer capacity (Va, Ja, µmol m?2 s?1), day respiration (Rda, µmol m?2 s?1), leaf nitrogen concentration (Nm, mg g?1) and leaf mass per unit area (La, g m?2). Relative to upper‐canopy values, Va declined linearly in 1 : 1 proportion with Na. Relative Va also declined linearly with relative Q, but with a significant intercept at zero irradiance (P < 0·01). This intercept was strongly related to La of the lowest leaves in each canopy (P < 0·01, r2 = 0·98, n= 5). For each canopy, daily lnQ was also linearly related with lnVa(P < 0·05), and the intercept was correlated with the value for photosynthetic capacity per unit nitrogen (PUN: Va/Na, µmol g?1 s?1) of the lowest leaves in each canopy (P < 0·05). Va was linearly related with La and Na(P < 0·01), but the slope of the Va : Na relationship varied widely among sites. Hence, whilst there was a unique Va : Na ratio in each stand, acclimation in Va to Q varied predictably with La of the lowest leaves in each canopy. The specific leaf area, Lm(cm2 g?1), of the canopy‐bottom foliage was also found to predict carboxylation capacity (expressed on a mass basis; Vm, µmol g?1 s?1) at all sites (P < 0·01). These results invalidate the hypothesis of full acclimation to irradiance, but suggest that La and Lm of the most light‐limited leaves in a canopy are widely applicable indicators of the distribution of photosynthetic capacity with height in forests. 相似文献
3.
Non-destructive and rapid method for assessment of leaf photosynthetic characteristics is needed to support photosynthesis
modelling and growth monitoring in crop plants. We determined the quantitative relationships between leaf photosynthetic characteristics
and canopy spectral reflectance under different water supply and nitrogen application rates. The responses of reflectance
at red radiation (wavelength 680 nm) to different water contents and nitrogen rates were parallel to those of leaf net photosynthetic
rate (P
N). The relationships of reflectance at 680 nm and ratio index of R(810,680) (near infrared/red, NIR/R) to P
N of different leaf positions and leaf layers in rice indicated that the top two full leaves were the best leaf positions for
quantitative monitoring of leaf P
N with remote sensing technique, and the ratio index R(810,680) was the best ratio index for evaluating leaf photosynthetic
characteristics in rice. Testing of the models with independent data sets indicated that R(810,680) could well estimate P
N of top two leaves and canopy leaf photosynthetic potential in rice, with the root mean square error of 0.25, 0.16, and 4.38,
respectively. Hence R(810,680) can be used to monitor leaf photosynthetic characteristics at different growth stages of rice
under diverse growing conditions. 相似文献
4.
The relationship between leaf photosynthetic capacity (p
n, max), net canopy CO2- and H2O-exchange rate (NCER and E
t, respectively) and canopy dry-matter production was examined in Lollium perenne L. cv. Vigor in ambient (363±30 l· l-1) and elevated (631±43 l·l-1) CO2 concentrations. An open system for continuous and simultaneous regulation of atmospheric CO2 concentration and NCER and E
t measurement was designed and used over an entire growth cycle to calculate a carbon and a water balance. While NCERmax of full-grown canopies was 49% higher at elevated CO2 level, stimulation of p
n, max was only 46% (in spite of a 50% rise in one-sided stomatal resistance for water-vapour diffusion), clearly indicating the effect of a higher leaf-area index under high CO2 (approx. 10% in one growing period examined). A larger amount of CO2-deficient leaves resulted in higher canopy dark-respiration rates and higher canopy light compensation points. The structural component of the high-CO2 effect was therefore a disadvantage at low irradiance, but a far greater benefit at high irradiance. Higher canopy darkrespiration rates under elevated CO2 level and low irradiance during the growing period are the primary causes for the increase in dry-matter production (19%) being much lower than expected merely based on the NCERmax difference. While total water use was the same under high and low CO2 levels, water-use efficiency increased 25% on the canopy level and 87% on a leaf basis. In the course of canopy development, allocation towards the root system became greater, while stimulation of shoot dry-matter accumulation was inversely affected. Over an entire growing season the root/shoot production ratio was 22% higher under high CO2 concentration.Abbreviations and symbols C350
ambient CO2, 363±30 l·l-1
- C600
high CO2, 631±43 l·l-1
-
c
a
atmospheric CO2 level
-
c
i
CO2 concentration in the intracellular spaces of the leaf
- Et
canopy evapotranspiration
-
I
o
canopy light compensation point
- NCER
canopy CO2-exchange rate
-
p
n
leaf photosynthetic rate
- PPFD
photosynthetic photon flux density
-
r
a
leaf boundary-layer resistance
- RD
canopy dark-respiration rate
-
r
s
stomatal resistance
- WUE
water use efficiency 相似文献
5.
Scaling CO2-photosynthesis relationships from the leaf to the canopy 总被引:11,自引:0,他引:11
Jeffrey S. Amthor 《Photosynthesis research》1994,39(3):321-350
Responses of individual leaves to short-term changes in CO2 partial pressure have been relatively well studied. Whole-plant and plant community responses to elevated CO2 are less well understood and scaling up from leaves to canopies will be complicated if feedbacks at the small scale differ from feedbacks at the large scale. Mathematical models of leaf, canopy, and ecosystem processes are important tools in the study of effects on plants and ecosystems of global environmental change, and in particular increasing atmospheric CO2, and might be used to scale from leaves to canopies. Models are also important in assessing effects of the biosphere on the atmosphere. Presently, multilayer and big leaf models of canopy photosynthesis and energy exchange exist. Big leaf models — which are advocated here as being applicable to the evaluation of impacts of global change on the biosphere — simplify much of the underlying leaf-level physics, physiology, and biochemistry, yet can retain the important features of plant-environment interactions with respect to leaf CO2 exchange processes and are able to make useful, quantitative predictions of canopy and community responses to environmental change. The basis of some big leaf models of photosynthesis, including a new model described herein, is that photosynthetic capacity and activity are scaled vertically within a canopy (by plants themselves) to match approximately the vertical profile of PPFD. The new big leaf model combines physically based models of leaf and canopy level transport processes with a biochemically based model of CO2 assimilation. Predictions made by the model are consistent with canopy CO2 exchange measurements, although a need exists for further testing of this and other canopy physiology models with independent measurements of canopy mass and energy exchange at the time scale of 1 h or less.Abbreviations LAI
leaf area index
- NIR
near infrared (700–3000 nm) radiation
- PAR
photosynthetically active (400–700 nm) radiation
- PI
photosynthetic irradiance (400–700 nm)
- PPFD
photosynthetic photon flux area density (400–700 nm)
- PS I
Photosystem I
- PS II
Photosystem II
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- RuP2
ribulose-1,5-bisphosphate 相似文献
6.
Genotypic variation in photosynthesis in cacao is correlated with stomatal conductance and leaf nitrogen 总被引:1,自引:0,他引:1
Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (PN) ranged from 3.4 to 5.7 μmol(CO2) m−2 s−1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency
ranging from 0.020 to 0.043 μmol(CO2) μmol−1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (gs) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (PN/gs) and instantaneous (PN/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found
for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed
on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen
content per unit mass. 相似文献
7.
JEAN-CHRISTOPHE DOMEC SARI PALMROTH ERIC WARD CHRIS A. MAIER M. THÉRÉZIEN & RAM OREN 《Plant, cell & environment》2009,32(11):1500-1512
We investigated how leaf hydraulic conductance (Kleaf) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO2 concentrations (CO2a and CO2e, respectively). We also examined how Kleaf varies with changes in reference leaf water potential (Ψleaf‐ref) and stomatal conductance (gs‐ref) calculated at vapour pressure deficit, D of 1 kPa. We detected significant reductions in Kleaf caused by N and CO2e, but neither treatment affected pre‐dawn or midday Ψleaf. We also detected a significant CO2e‐induced reduction in gs‐ref and Ψleaf‐ref. Among treatments, the sensitivity of Kleaf to Ψleaf was directly related to a reference Kleaf (Kleaf‐ref computed at Ψleaf‐ref). This liquid‐phase response was reflected in a similar gas‐phase response, with gs sensitivity to D proportional to gs‐ref. Because leaves represented a substantial component of the whole‐tree conductance, reduction in Kleaf under CO2e affected whole‐tree water use by inducing a decline in gs‐ref. The consequences of the acclimation of leaves to the treatments were: (1) trees growing under CO2e controlled morning leaf water status less than CO2a trees resulting in a higher diurnal loss of Kleaf; (2) the effect of CO2e on gs‐ref was manifested only during times of high soil moisture. 相似文献
8.
Elevated CO2 enhances photosynthesis and growth of plants, but the enhancement is strongly influenced by the availability of nitrogen. In this article, we summarise our studies on plant responses to elevated CO2. The photosynthetic capacity of leaves depends not only on leaf nitrogen content but also on nitrogen partitioning within a leaf. In Polygonum cuspidatum, nitrogen partitioning among the photosynthetic components was not influenced by elevated CO2 but changed between seasons. Since the alteration in nitrogen partitioning resulted in different CO2-dependence of photosynthetic rates, enhancement of photosynthesis by elevated CO2 was greater in autumn than in summer. Leaf mass per unit area (LMA) increases in plants grown at elevated CO2. This increase was considered to have resulted from the accumulation of carbohydrates not used for plant growth. With a sensitive analysis of a growth model, however, we suggested that the increase in LMA is advantageous for growth at elevated CO2 by compensating for the reduction in leaf nitrogen concentration per unit mass. Enhancement of reproductive yield by elevated CO2 is often smaller than that expected from vegetative growth. In Xanthium canadense, elevated CO2 did not increase seed production, though the vegetative growth increased by 53%. As nitrogen concentration of seeds remained constant at different CO2 levels, we suggest that the availability of nitrogen limited seed production at elevated CO2 levels. We found that leaf area development of plant canopy was strongly constrained by the availability of nitrogen rather than by CO2. In a rice field cultivated at free-air CO2 enrichment, the leaf area index (LAI) increased with an increase in nitrogen availability but did not change with CO2 elevation. We determined optimal LAI to maximise canopy photosynthesis and demonstrated that enhancement of canopy photosynthesis by elevated CO2 was larger at high than at low nitrogen availability. We also studied competitive asymmetry among individuals in an even-aged, monospecific stand at elevated CO2. Light acquisition (acquired light per unit aboveground mass) and utilisation (photosynthesis per unit acquired light) were calculated for each individual in the stand. Elevated CO2 enhanced photosynthesis and growth of tall dominants, which reduced the light availability for shorter subordinates and consequently increased size inequality in the stand. 相似文献
9.
Scaling carbon dioxide and water vapour exchange from leaf to canopy in a deciduous forest. I. Leaf model parametrization 总被引:1,自引:3,他引:1
In order to parametrize a leaf submodel of a canopy level gas-exchange model, a series of photosynthesis and stomatal conductance measurements were made on leaves of white oak (Quercus alba L.) and red maple (Acer rubrum L.) in a mature deciduous forest near Oak Ridge, TN. Gas-exchange characteristics of sun leaves growing at the top of a 30 m canopy and of shade leaves growing at a depth of 3–4 m from the top of the canopy were determined. Measured rates of net photosynthesis at a leaf temperature of 30°C and saturating photosynthetic photon flux density, expressed on a leaf area basis, were significantly lower (P = 0.01; n = 8) in shade leaves (7.9μmol m?2 s?1) than in sun leaves (11–5μmol m?2 s?1). Specific leaf area increased significantly with depth in the canopy, and when photosynthesis rates were expressed on a dry mass basis, they were not significantly different for shade and sun leaves. The percentage leaf nitrogen did not vary significantly with height in the canopy; thus, rates expressed on a per unit nitrogen basis were also not significantly different in shade and sun leaves. A widely used model integrating photosynthesis and stomatal conductance was parametrized independently for sun and shade leaves, enabling us to model successfully diurnal variations in photosynthesis and evapotranspiration of both classes of leaves. Key photosynthesis model parameters were found to scale with leaf nitrogen levels. The leaf model parametrizations were then incorporated into a canopy-scale gas-exchange model that is discussed and tested in a companion paper (Baldocchi & Harley 1995, Plant, Cell and Environment 18, 1157–1173). 相似文献
10.
Stable carbon isotope composition varies markedly between sun and shade leaves, with sun leaves being invariably more enriched (i.e., they contain more13C). Several hypotheses have emerged to explain this pattern, but controversy remains as to which mechanism is most general. We measured vertical gradients in stable carbon isotope composition (δ13C) in more than 200 trees of nine conifer species growing in mixed-species forests in the Northern Rocky Mountains, USA. For all species except western larch, δ13C decreased from top to bottom of the canopy. We found that δ13C was strongly correlated with nitrogen per unit leaf area (N
area), which is a measure of photosynthetic capacity. Usually weaker correlations were found between δ13C and leaf mass per area, nitrogen per unit leaf mass, height from the ground, or depth in the canopy, and these correlations were more variable between trees than for N
area. Gradients of δ13C (per meter canopy depth) were steeper in small trees than in tall trees, indicating that a recent explanation of δ13C gradients in terms of drought stress of upper canopy leaves is unlikely to apply in our study area. The strong relationship between N
area and δ13C here reported is consistent with the general finding that leaves or species with higher photosynthetic capacity tend to maintain lower CO2 concentrations inside leaves. We conclude that photosynthetic capacity is a strong determinant of δ13C in vertical canopy profiles, and must be accounted for when interpreting δ13C values in conifer forests. 相似文献
11.
The role of nitrogen in a simple scheme to scale up photosynthesis from leaf to canopy 总被引:10,自引:2,他引:10
A simple analytical scheme, involving the distribution of nitrogen, to scale up photosynthesis from leaf to canopy is proposed. The scheme is based on the assumption that there are two pools of nitrogen in leaves: nitrogen in photosynthetic, degradable structures (Np) and nitrogen in non-photosynthetic and non-degradable structures (Ns). The rate of photon-saturated photosynthesis, Fm, is assumed to be proportional to Np and is distributed inside the canopy similarly to photon flux density (PFD). Prior assumptions of an optimum distribution of nitrogen are not a prerequisite. Calculations made with the scheme lead to development of the hypothesis that the canopy can be treated as a ‘big leaf’ on the time scales involved in acclimation of photosynthesis to PFD. Simulations using parameters for tree species with different requirements for PFD show that shade-tolerant species may have denser canopies than sun-demanding species because of smaller amounts of non-photosynthetic structural nitrogen and/or supporting tissue in their leaves. 相似文献
12.
Photosynthetic capacity of field-grown durum wheat under different N availabilities: A comparative study from leaf to canopy 总被引:1,自引:0,他引:1
Llorenç Cabrera-Bosquet Rossella Albrizio José Luis Araus Salvador Nogués 《Environmental and Experimental Botany》2009,67(1):145-152
The effect of N availability on photosynthetic capacity, growth parameters and yield was studied in field-grown durum-wheat plants at both the leaf and canopy levels. Two contrasting nitrogen levels (120 and 0 kg ha?1) were assayed in a randomised block design with nine replicates each. Total biomass was measured at anthesis and yield and its agronomical components at maturity. Photosynthetic measurements were performed 2 weeks after anthesis in two plots of each N treatment. Flag leaves were measured, using a LI-COR 6400 combined with the chlorophyll fluorescence meter, and the whole canopy by measuring CO2 and H2O fluxes in an innovative canopy-chamber system. We showed a clear increase in photosynthetic gas exchange and chlorophyll contents with N fertilisation at both canopy and leaf levels. As a consequence the increase in yield as response to N fertilisation seems the result of a larger green leaf area combined with a higher photosynthetic capacity of the leaves attributable to an increase in the maximum carboxylation velocity of Rubisco. Moreover gas-exchange measurements of the flag leaf during grain filling seem to provide a realistic characterisation, not just of the photosynthetic performance of the crop, but also about the impact of N availability on yield. Thus, measurements performed on the flag leaf matched those at the canopy level, with proportional increases in terms of gas exchange and chlorophyll content, providing a fast, cheap and reliable estimation of canopy photosynthesis and the grain yield attained by the crop. 相似文献
13.
Partitioning of leaf nitrogen with respect to within canopy light exposure and nitrogen availability in peach (Prunus persica) 总被引:2,自引:0,他引:2
Summary Relationships between leaf nitrogen content and within canopy light exposure were studied in mature nectarine peach trees (Prunus persica cv. Fantasia) that had received 0, 112, 196, 280 or 364 kg of fertilizer nitrogen per hectare per year for the previous 3 years. The relationships between light saturated leaf CO2 assimilation rates and leaf nitrogen concentration were also determined on trees in the highest and lowest nitrogen fertilization treatments. The slope of the linear relationship between leaf N content per unit leaf area and light exposure was similar for all nitrogen treatments but the y-intercept of the relationship increased with increasing N status. The slope of the relationship between leaf N content per unit leaf area and light saturated CO2 assimilation rates was greater for the high N trees than the low N trees, but maximum measured leaf CO2 assimilation rates were similar for both the high and low N treatments. A diagrammatic model of the partitioning of leaf photosynthetic capacity with respect to leaf light exposure for high and low nitrogen trees suggests that the major influence of increased N availability is an increase in the photosynthetic capacity of partially shaded leaves but not of the maximum capacity of highly exposed leaves. 相似文献
14.
Andrew G. Peterson 《Oecologia》1999,118(2):144-150
The relationship between photosynthetic carbon assimilation (A
max) and leaf nitrogen content (N
leaf) can be expressed on either a leaf area basis (A
area vs N
area) or a leaf mass basis (A
mass vs N
mass). Dimensional analysis shows that the units for the slope of this relationship are the same for both expressions (μmol [CO2] g−1 [N] s−1). Thus the slope measures the change in CO2 assimilation per gram of nitrogen, independent of leaf mass or leaf area. Although they have the same units, large differences
between the area and mass-based slopes have been observed over a broad range of taxonomically diverse species. Some authors
have claimed that regardless of these differences, the fundamental nature of the A
max-N
leaf relationship is independent of the units of expression. In contrast, other authors have claimed that the area-based A
max-N
leaf relationship is fundamentally different from the mass-based relationship because of interactions between A
max, N
leaf, and leaf mass per area (LMA, g [leaf] m−2 [leaf]). In this study we consider the mathematical relationships involved in the transformation from mass- to area-based
expressions (and vice versa), and the implications this transformation has for the slope of the A
max-N
leaf relationship. We then show that the slope of the relationship is independent of the units of expression when the effect of
LMA is controlled statistically using a multiple regression. The validity of this hypothesis is demonstrated using 13 taxonomically
and functionally diverse C3 species. This analysis shows that the slope of the A
max-N
leaf relationship is similar for the mass- and area-based expressions and that significant errors in the estimate of the slope
can arise when the effect of LMA is not controlled.
Received: 7 May 1998 / Accepted: 19 October 1998 相似文献
15.
Specific leaf area and leaf nitrogen concentration in annual and perennial grass species growing in Mediterranean old-fields 总被引:1,自引:0,他引:1
We evaluated the hypothesis that photosynthetic traits differ between leaves produced at the beginning (May) and the end
(November–December) of the rainy season in the canopy of a seasonally dry forest in Panama. Leaves produced at the end of
the wet season were predicted to have higher photosynthetic capacities and higher water-use efficiencies than leaves produced
during the early rainy season. Such seasonal phenotypic differentiation may be adaptive, since leaves produced immediately
preceding the dry season are likely to experience greater light availability during their lifetime due to reduced cloud cover
during the dry season. We used a construction crane for access to the upper canopy and sampled 1- to 2-month-old leaves marked
in monthly censuses for six common tree species with various ecological habits and leaf phenologies. Photosynthetic capacity
was quantified as light- and CO2-saturated oxygen evolution rates with a leaf-disk oxygen electrode in the laboratory (O2max) and as light-saturated CO2 assimilation rates of intact leaves under ambient CO2 (Amax). In four species, pre-dry season leaves had significantly higher leaf mass per unit area. In these four species, O2max and Amax per unit area and maximum stomatal conductances were significantly greater in pre-dry season leaves than in early wet season
leaves. In two species, Amax for a given stomatal conductance was greater in pre-dry season leaves than in early wet season leaves, suggesting a higher
photosynthetic water-use efficiency in the former. Photosynthetic capacity per unit mass was not significantly different between
seasons of leaf production in any species. In both early wet season and pre-dry season leaves, mean photosynthetic capacity
per unit mass was positively correlated with nitrogen content per unit mass both within and among species. Seasonal phenotypic
differentiation observed in canopy tree species is achieved through changes in leaf mass per unit area and increased maximum
stomatal conductance rather than by changes in nitrogen allocation patterns.
Received: 7 March 1996 / Accepted: 1 August 1996 相似文献
16.
We investigated leaf physiological traits of dominant canopy trees in four lowland Panamanian forests with contrasting mean annual precipitation (1,800, 2,300, 3,100 and 3,500 mm). There was near complete turn-over of dominant canopy tree species among sites, resulting in greater dominance of evergreen species with long-lived leaves as precipitation increased. Mean structural and physiological traits changed along this gradient as predicted by cost–benefit theories of leaf life span. Nitrogen content per unit mass (Nmass) and light- and CO2-saturated photosynthetic rates per unit mass (Pmass) of upper canopy leaves decreased with annual precipitation, and these changes were partially explained by increasing leaf thickness and decreasing specific leaf area (SLA). Comparison of 1,800 mm and 3,100 mm sites, where canopy access was available through the use of construction cranes, revealed an association among extended leaf longevity, greater structural defense, higher midday leaf water potential, and lower Pmass, Nmass, and SLA at wetter sites. Shorter leaf life spans and more enriched foliar 15N values in drier sites suggest greater resorption and re-metabolism of leaf N in drier forest. Greater dominance of short-lived leaves with relatively high Pmass in drier sites reflects a strategy to maximize photosynthesis when water is available and to minimize water loss and respiration costs during rainless periods. Overall, our study links coordinated change in leaf functional traits that affect productivity and nutrient cycling to seasonality in lowland tropical forests. 相似文献
17.
P. Staffan Karlsson 《Ecography》1985,8(1):9-17
The seasonal course of photosynthetic rate, and light and temperature relations were studied in the dwarf shrubs Vaccinium uliginosum L., deciduous, and Vaccinium vitisidaea L., evergreen, at a subarctic site in northern Sweden, Using the photosynthetic characteristics and meteorological data from the site, the seasonal and life-span carbon dioxide gain was estimated. The photosynthetic capacity of V. uliginosum was at a maximum one month after the start of leaf expansion and declined rapidly in the beginning of September. The old V. vitis-idaea leaves needed about 2 wk to recover full photosynthetic capacity after snow-melt; the current-year V. vitis-idaea leaves needed the same time after bud-break to reach full capacity. The leaves of V. vitis-idaea showed no seasonal trend in photosynthetic capacity after the first two wk of recovery, but their capacity decreased by one third after the first winter and by approximately 10% yr?1 over the following two yr. The seasonal variation in the photosynthetic response to temperature was more marked in V. uliginosum than in V. vitis-idaea. Light saturation occurred at approximately 3000 μmol m?2 s?1 in V. uliginosum and at 60 μmol m?2 s?1 in one-year-old V. vitis-idaea leaves. The leaves of both species had a positive carbon balance at photon flux densities above 5 μmol m?2 s?1. The calculated seasonal CO2 gain was 21 g CO2 g?1 leaf in V. uliginosum and 6–8 g CO2 g?1 in V. vitis-idaea leaves. Life-span CO2 gain for leaves of V. vitis-idaea was the same as in V. uliginosum, viz. 21 g CO2 g?1. One fifth of the CO2 gain of V. vitis-idaea was assimilated during periods when V. uliginosum was leafless. 相似文献
18.
Z. -M. Ge X. Zhou S. Kellomäki K. -Y. Wang H. Peltola P. J. Martikainen 《Photosynthetica》2011,49(2):172-184
The effects of elevated growth temperature (ambient + 3.5°C) and CO2 (700 μmol mol−1) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted
on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development
stages, elevated temperature enhanced the maximum rate of photosynthesis (P
max) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass
at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (NL), and light response of effective photochemical efficiency (ΦPSII) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves
at both layers. CO2 enrichment enhanced the photosynthesis but led to a decline of NL and Chl content, as well as lower fluorescence parameters of ΦPSII and ETR in leaves at both layers. In addition, the down-regulation by CO2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly
negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low
canopy position. Elevated temperature exacerbated the impact of water shortage, while CO2 enrichment slightly alleviated the drought-induced adverse effects on P
max. We suggest that the light response of ΦPSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought
stress better than the fluorescence parameters under dark adaptation. 相似文献
19.
In a field rain-fed trial with 15 cassava cultivars, leaf gas exchanges and carbon isotope discrimination (Δ) of the same
leaves were determined to evaluate genotypic and within-canopy variations in these parameters. From 3 to 7 months after planting
leaf gas exchange was measured on attached leaves from upper, middle, and lower canopy layers. All gas exchange parameters
varied significantly among cultivars as well as canopy layers. Net photosynthetic rate (P
N) decreased from top canopy to bottom indicating both shade and leaf age effects. The same trend, but in reverse, was found
with respect to Δ, with the highest values in low canopy level and the lowest in upper canopy. There were very significant
correlations, with moderate and low values, among almost all these parameters, with P
N negatively associated with intercellular CO2 concentration (C
i), ratio of C
i to ambient CO2 concentration C
i/C
a, and Δ. Across all measured leaves, Δ correlated negatively with leaf water use efficiency (WUE = photosynthesis/stomatal
conductance, g
s) and with g
s, but positively with C
i and C
i/C
a. The later parameters negatively correlated with leaf WUE. Across cultivars, both P
N and correlated positively with storage root yield. These results are in agreement with trends predicted by the carbon isotope
discrimination model. 相似文献
20.
Clover seedlings were grown at different nitrogen concentrations (5, 10, 15, 20, 25 mM NO3
−, i.e. N5 to N25) and two irradiances, I (200 and 400 μmol m−2 s−1 of photon flux density, i.e. I
200 and I
400). Net photosynthetic rate (P
N), photosynthetic nitrogen use efficiency (PNUE), leaf chlorophyll (Chl) content, maximum photochemical efficiency (Fv/Fm), and actual photochemical efficiency of photosystem 2 (PS2) (ΦPS2) increased from N5 to N15 and decreased with N15 to N25. P
N, PNUE, and ΦPS2 were higher at I
400 than at I
200, but Fv/Fm and leaf Chl contents at I
400 were lower than at I
200. The effects of the N and I on specific leaf area (SLA) and N contents per unit dry mass (Nm) were similar, the SLA and Nm increased from N5 to N25 and they were higher at I
200 than at I
400. The nitrogen contents per unit area (Na) increased from N5 to N20, but decreased from N20 to N25. The Na was higher at I
200 than at I
400 when Trifolium repens grew at N5 and N10, but it was higher at I
400 than at I
200 at N15 to N25. 相似文献