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1.
Elevated CO2 enhances carbon uptake of a plant stand, but the magnitude of the increase varies among growth stages. We studied the relative
contribution of structural and physiological factors to the CO2 effect on the carbon balance during stand development. Stands of an annual herb Chenopodium album were established in open-top chambers at ambient and elevated CO2 concentrations (370 and 700 μmol mol−1). Plant biomass growth, canopy structural traits (leaf area, leaf nitrogen distribution, and light gradient in the canopy),
and physiological characteristics (leaf photosynthesis and respiration of organs) were studied through the growing season.
CO2 exchange of the stand was estimated with a canopy photosynthesis model. Rates of light-saturated photosynthesis and dark
respiration of leaves as related with nitrogen content per unit leaf area and time-dependent reduction in specific respiration
rates of stems and roots were incorporated into the model. Daily canopy carbon balance, calculated as an integration of leaf
photosynthesis minus stem and root respiration, well explained biomass growth determined by harvests (r
2 = 0.98). The increase of canopy photosynthesis with elevated CO2 was 80% at an early stage and decreased to 55% at flowering. Sensitivity analyses suggested that an alteration in leaf photosynthetic
traits enhanced canopy photosynthesis by 40–60% throughout the experiment period, whereas altered canopy structure contributed
to the increase at the early stage only. Thus, both physiological and structural factors are involved in the increase of carbon
balance and growth rate of C. album stands at elevated CO2. However, their contributions were not constant, but changed with stand development. 相似文献
2.
Gross photosynthesis and respiration rates of leaves at different canopy heights in a Rhizophora stylosa Griff. stand were measured monthly over 1 year at Manko Wetland, Okinawa Island, Japan, which is the northern limit of its
distribution. The light-saturated net photosynthesis rate for the leaves at the top of the canopy showed a maximum value of
17 μmol CO2 m−2 s−1 in warm season and a minimum value of 6 μmol CO2 m−2 s−1 in cold season. The light-saturated gross photosynthesis and dark respiration rates of the leaves existing at the top of the
canopy were 2−7 times and 3–16 times, respectively, those of leaves at the bottom of the canopy throughout the year. The light
compensation point of leaves showed maximum and minimum peaks in warm season and cold season, respectively. The annual canopy
gross photosynthesis, foliage respiration, and surplus production were estimated as 117, 49, and 68 t CO2 ha−1 year−1, respectively. The energy efficiency of the annual canopy gross photosynthesis was 2.5%. The gross primary production GPP fell near the regression curve of GPP on the product of leaf area index and warmth index, the regression curve which was established for forests in the Western
Pacific with humid climates. 相似文献
3.
Lore T. Verryckt David S. Ellsworth Sara Vicca Leandro Van Langenhove Josep Peñuelas Philippe Ciais Juan M. Posada Clément Stahl Sabrina Coste Elodie A. Courtois Michael Obersteiner Jérôme Chave Ivan A. Janssens 《Biotropica》2020,52(6):1183-1193
Leaf-level net photosynthesis (An) estimates and associated photosynthetic parameters are crucial for accurately parameterizing photosynthesis models. For tropical forests, such data are poorly available and collected at variable light conditions. To avoid over- or underestimation of modeled photosynthesis, it is critical to know at which photosynthetic photon flux density (PPFD) photosynthesis becomes light-saturated. We studied the dependence of An on PPFD in two tropical forests in French Guiana. We estimated the light saturation range, including the lowest PPFD level at which Asat (An at light saturation) is reached, as well as the PPFD range at which Asat remained unaltered. The light saturation range was derived from photosynthetic light-response curves, and within-canopy and interspecific differences were studied. We observed wide light saturation ranges of An. Light saturation ranges differed among canopy heights, but a PPFD level of 1,000 µmol m−2 s−1 was common across all heights, except for pioneer trees species that did not reach light saturation below 2,000 µmol m−2 s−1. A light intensity of 1,000 µmol m−2 s−1 sufficed for measuring Asat of climax species at our study sites, independent of the species or the canopy height. Because of the wide light saturation ranges, results from studies measuring Asat at higher PPFD levels (for upper canopy leaves up to 1,600 µmol m−2 s−1) are comparable with studies measuring at 1,000 µmol m−2 s−1. 相似文献
4.
Intra- and inter-specific variation in canopy photosynthesis in a mixed deciduous forest 总被引:6,自引:0,他引:6
Within the same forest, photosynthesis can vary greatly among species and within an individual tree. Quantifying the magnitude
of variation in leaf-level photosynthesis in a forest canopy will improve our understanding of and ability to model forest
carbon cycling. This information requires extensive sampling of photosynthesis in the canopy. We used a 22-m-tall, four-wheel-drive
aerial lift to reach five to ten leaves from the tops of numerous individuals of several species of temperate deciduous trees
in central Massachusetts. The goals of this study were to measure light-saturated photosynthesis in co-occurring canopy tree
species under field conditions, and to identify sampling schemes appropriate for canopy tree studies with challenging logistics.
Photosynthesis differed significantly among species. Even though all leaves measured were canopy-top, sun-acclimated foliage,
the more shade-tolerant species tended to have lower light-saturated photosynthetic rates (P
max) than the shade-intolerant species. Likewise, leaf mass per area (LMA) and nitrogen content (N) varied significantly between species. With only one exception, the shade-tolerant species tended to have lower nitrogen
content on an area basis than the intolerant species, although the LMA did not differ systematically between these ecological
types. Light-saturated P
max rates and nitrogen content, both calculated on either an area or a mass basis, and the leaf mass to area ratio, significantly
differed not only among species, but also among individuals within species (P<0.0001 for both). Differences among species accounted for a greater proportion of variance in the P
max rates and the nitrogen content than the differences among individuals within a species (58.5–78.8% of the total variance for
the measured parameters was attributed to species-level differences versus 5.5–17.4% of the variance was attributed to differences
between individual trees of a given species). Furthermore, more variation is accounted for by differences among leaves in
a single individual tree, than by differences among individual trees of a given species (10.7–30.4% versus 5.5–17.4%). This
result allows us to compare species-level photosynthesis, even if the sample size of the number of trees is low. This is important
because studies of canopy-level photosynthesis are often limited by the difficulty of canopy access. As an alternative to
direct canopy access measurements of photosynthesis, it would be useful to find an ”easy-to-measure” proxy for light-saturated
photosynthetic rates to facilitate modeling forest carbon cycling. Across all species in this study, the strongest correlation
was between nitrogen content expressed on an area basis (mmol m–2, N
area) and light-saturated P
max rate (μmol m–2 s–1, P
maxarea) (r
2=0.511). However, within a given species, leaf nitrogen was not tightly correlated with photosynthesis. Our sampling design
minimized intra-specific leaf-level variation (i.e., leaves were taken only from the top of the canopy and at only one point
in the season). This implies that easy-to-measure trends in nitrogen content of leaves may be used to predict the species-specific
light-saturated P
max rates.
Received: 16 March 1996 / Accepted: 16 August 1996 相似文献
5.
The increased frequency of heavy rains as a result of global climate change can lead to flooding and changes in light availability
caused by the presence of thick clouds. To test the hypothesis that reduction in light availability can alleviate the harmful
effects of soil flooding on photosynthesis, the authors studied the effects of soil flooding and acclimation from high to
low light on the photosynthetic performance of Eugenia uniflora. Seedlings acclimated to full sunlight (about 35 mol m−2 d−1) for 5 months were transferred to partial sunlight (about 10 mol m−2 d−1) and were either subjected to soil flooding or not flooded. Chlorophyll fluorescence was measured throughout the flooding
period and leaf gas exchange was measured 16 days after flooding was initiated. Minimal fluorescence yield (Fo) was significantly
higher and the quantum efficiency of open PSII centres (Fv/Fm) was significantly lower in flooded than in non-flooded plants
in full sunlight. Sixteen days after flooding was initiated, stomatal conductance (gssat) and net photosyntheses expressed on a leaf area (Asat-area), weight (Asat-wt) and chlorophyll (Asat-Chl) basis decreased in response to soil flooding. Flooding decreased stomatal conductance by similar amounts in full and partial
sunlight, but Asat-area in partial and full sunlight was 3.4 and 16.8 times lower, respectively, in flooded than in non-flooded plants. These results
indicate that changes from full to partial sunlight during soil flooding can alleviate the effects of flooding stress on photosynthesis
in E. uniflora seedlings acclimated to full sunlight. The responses of photosynthesis in trees to flooding stress may be dependent on changes
in light environment during heavy rains. 相似文献
6.
Carlos Eduardo Aragón Maritza Escalona Roberto Rodriguez Maria Jesús Cañal Iris Capote Danilo Pina Justo González-Olmedo 《In vitro cellular & developmental biology. Plant》2010,46(1):89-94
In vitro physiology and carbon metabolism can be affected by the sink–source relationship. The effect of different sucrose concentrations
(10, 30, and 50 g L−1), light intensities (80 and 150 μmol m−2 s−1), and CO2 levels (375 and 1,200 μmol mol−1) were tested during plantain micropropagation in temporary immersion bioreactors. Activities of pyruvate kinase, phosphoenol
pyruvate carboxylase, and the photosynthesis rate were recorded. From the morphological and practical point of view, the best
results were obtained when plants were cultured with 30 g L−1 sucrose, 80 μmol m−2 s−1 light intensity, and 1,200 μmol mol−1 CO2 concentration. This treatment improved leaf and root development, reduced respiration during in vitro culture, and increased starch level at the end of the hardening phase. In addition to that, the number of competent plants
was increased from 80.0% to 91.0% at the end of the in vitro phase and the survival percentage from 95.71% to 99.80% during ex vitro hardening. 相似文献
7.
Spatial and daily variation in photosynthetic water-use efficiency was examined in leaves of Betula pendula Roth with respect to distribution of hydraulic conductance within the crown, morphological properties of stomata, and water
availability. Intrinsic water-use efficiency (A
n/g
s) was determined from gas-exchange measurements performed both in situ in a natural forest stand and on detached shoots under
laboratory conditions. In intact foliage, sun leaves demonstrated significantly higher (P < 0.001) A
n/g
s than shade leaves, as photosynthesis in the lower canopy was chronically limited by low light availability. However, this
difference reversed in the mid-day period under sufficient irradiance (I > 800 μmol m−2 s−1): A
n/g
s averaged 28.8 and 24.0 μmol mol−1 (P < 0.01) for shade and sun leaves, respectively. This last finding coincided with the data obtained in laboratory conditions:
under equivalent leaf water supply and light, A
n/g
s in shade foliage was greater (P < 0.001) than in sun foliage across a wide range of irradiance. Thus, shade foliage of B. pendula is characterized by inherently higher A
n/g
s than sun foliage, associated with more conservative stomatal behavior, and lower soil-to-leaf (K
T) and leaf hydraulic conductances. Under unlimited light conditions, a within-crown trade-off between A
n/g
s and K
T becomes apparent. Differences in stomatal conductance between the detached shoots from sunlit and shaded canopy layers were
largely attributable to the variation in stomatal morphology; significant relationships were established with characteristics
combining stomatal size and density (relative stomatal surface, stomatal pore area index). Stomatal morphology is very likely
involved in long-term adjustment of photosynthetic WUE. 相似文献
8.
Canopy structure and vertical patterns of photosynthesis and related leaf traits in a deciduous forest 总被引:37,自引:0,他引:37
Canopy structure and light interception were measured in an 18-m tall, closed canopy deciduous forest of sugar maple (Acer saccharum) in southwestern Wisconsin, USA, and related to leaf structural characteristics, N content, and leaf photosynthetic capacity. Light attenuation in the forest occurred primarily in the upper and middle portions of the canopy. Forest stand leaf area index (LAI) and its distribution with respect to canopy height were estimated from canopy transmittance values independently verified with a combined leaf litterfall and point-intersect method. Leaf mass, N and A
max per unit area (LMA, N/area and A
max/area, respectively) all decreased continuously by over two-fold from the upper to lower canopy, and these traits were strongly correlated with cumulative leaf area above the leaf position in the canopy. In contrast, neither N concentration nor A
max per unit mass varied significantly in relation to the vertical canopy gradient. Since leaf N concentration showed no consistent pattern with respect to canopy position, the observed vertical pattern in N/area is a direct consequence of vertical variation of LMA. N/area and LMA were strongly correlated with A
max/area among different canopy positions (r2=0.81 and r2=0.66, respectively), indicating that vertical variation in area-based photosynthetic capacity can also be attributed to variation in LMA. A model of whole-canopy photosynthesis was used to show that observed or hypothetical canopy mass distributions toward higher LMA (and hence higher N/area) in the upper portions of the canopy tended to increase integrated daily canopy photosynthesis over other LMA distribution patterns. Empirical relationships between leaf and canopy-level characteristics may help resolve problems associated with scaling gas exchange measurements made at the leaf level to the individual tree crown and forest canopy-level. 相似文献
9.
The photosynthetic responses of the tropical tree species Acacia nigrescens Oliv. grown at different atmospheric CO2 concentrations—from sub-ambient to super-ambient—have been studied. Light-saturated rates of net photosynthesis (A
sat) in A. nigrescens, measured after 120 days exposure, increased significantly from sub-ambient (196 μL L−1) to current ambient (386 μL L−1) CO2 growth conditions but did not increase any further as [CO2] became super-ambient (597 μL L−1). Examination of photosynthetic CO2 response curves, leaf nitrogen content, and leaf thickness showed that this acclimation was most likely caused by reduction
in Rubisco activity and a shift towards ribulose-1,5-bisphosphate regeneration-limited photosynthesis, but not a consequence
of changes in mesophyll conductance. Also, measurements of the maximum efficiency of PSII and the carotenoid to chlorophyll
ratio of leaves indicated that it was unlikely that the pattern of A
sat seen was a consequence of growth [CO2] induced stress. Many of the photosynthetic responses examined were not linear with respect to the concentration of CO2 but could be explained by current models of photosynthesis. 相似文献
10.
Geometrical similarity analysis of photosynthetic light response curves, light saturation and light use efficiency 总被引:1,自引:0,他引:1
Light absorption and use efficiency (LAUE mol mol−1, daily gross photosynthesis per daily incident light) of each leaf depends on several factors, including the degree of light
saturation. It is often discussed that upper canopy leaves exposed to direct sunlight are fully light-saturated. However,
we found that upper leaves of three temperate species, a heliophytic perennial herb Helianthus tuberosus, a pioneer tree Alnus japonica, and a late-successional tree Fagus crenata, were not fully light-saturated even under full sunlight. Geometrical analysis of the photosynthetic light response curves
revealed that all the curves of the leaves from different canopy positions, as well as from the different species, can be
considered as different parts of a single non-rectangular hyperbola. The analysis consistently explained how those leaves
were not fully light-saturated. Light use optimization models, called big leaf models, predicted that the degree of light
saturation and LAUE are both independent of light environment. From these, we hypothesized that the upper leaves should not
be fully light-saturated even under direct sunlight, but instead should share the light limitation with the shaded lower-canopy
leaves, so as to utilize strong sunlight efficiently. Supporting this prediction, within a canopy of H. tuberosus, both the degree of light saturation and LAUE were independent of light environment within a canopy, resulting in proportionality
between the daily photosynthesis and the daily incident light among the leaves. 相似文献
11.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
12.
We compared variation in sun-canopy leaf anatomy, morphology and photosynthetic rates of coexisting woody species (trees and
lianas) in an 8-year-old secondary forest (SF) and mature forest (MF) in the wet season in Xishuangbanna, SW China. Variability
of leaf traits of 66 species within growth-form groups in each forest was quantified using coefficients of variation (CV).
For the mean values, the woody species in the SF had significantly higher leaf thickness and stomatal density, but lower nonmesophyll/mesophyll
ratios than those in the MF. The average leaf area and leaf mass area (LMA) in the studied woody species did not change greatly
during the successional process, but differed significantly between the growth forms, with trees having higher values than
lianas. The light-saturated photosynthetic rate per unit leaf area (A
a) of the woody species in the SF ranged from 11.2 to 34.5 μmol m−2 s−1, similarly to pioneer tree species from literature data in southeast Asia. The A
a and photosynthetic nitrogen-use efficiency (PNUE) were significantly higher than those in the MF; whereas A
a in the MF ranged between 9 to 21 μmol m−2 s−1, with similar values between lianas and trees. For all woody species in both SF and MF, there were no significant differences
in the average values of the CV of all measured variables for both lianas and trees. However, considerable variation in leaf
anatomy, morphology, and photosynthetic rates within both growth forms and forests existed, as well as substantial variation
in leaf size and stomatal density. We concluded that the tropical woody species formed a heterogeneous functional group in
terms of leaf morphology and physiology in both secondary and mature forests. 相似文献
13.
Arne Sellin Eele Õunapuu Eve Kaurilind Meeli Alber 《Trees - Structure and Function》2012,26(3):821-831
Variation in leaf and shoot hydraulic conductance was examined on detached shoots of silver birch (Betula pendula Roth), cut from the lower third (shade leaves) and upper third of the crown (sun leaves) of large trees growing in a natural
temperate forest stand. Hydraulic conductances of whole shoots (K
S), leaf blades (K
lb), petioles (K
P) and branches (i.e. leafless stem; K
B) were determined by water perfusion using a high-pressure flow meter in quasi-steady state mode. The shoots were exposed
to irradiance of photosynthetic photon flux density of 200–250 μmol m−2 s−1, using different light sources. K
lb depended significantly (P < 0.001) on light quality, canopy position and leaf blade area (A
L). K
lb increased from crown base to tree top, in parallel with vertical patterns of A
L. However, the analysis of data on shade and sun leaves separately revealed an opposite trend: the bigger the A
L the higher K
lb. Leaf anatomical study of birch saplings revealed that this trend is attributable to enhanced vascular development with increasing
leaf area. Hydraulic traits (K
S, K
B, K
lb) of sun shoots were well co-ordinated and more strongly correlated with characteristics of shoot size than those of shade
shoots, reflecting their greater evaporative load and need for stricter adjustment of hydraulic capacity with shoot size.
K
S increased with increasing xylem cross-sectional area to leaf area ratio (Huber value; P < 0.01), suggesting a preferential investment in water-conducting tissue (sapwood) relative to transpiring tissue (leaves),
and most likely contributing to the functional stability of the hydraulic system, essential for fast-growing pioneer species. 相似文献
14.
Leaf carbon isotope discrimination (Δ13C) varies with the balance between net photosynthesis (A) and stomatal conductance (g
s
). Inferences that can be made with Δ13C are limited, as changes could reflect variation in A and/or g
s
. Investigators have suggested that leaf δ18O enrichment above source water (Δ18O) may enable differentiation between sources of variation in Δ13C, as leaf Δ18O varies with transpiration rate (E), which is closely correlated with g
s
when leaves experience similar leaf to air vapor pressure differences. We examined leaf gas exchange of Salix arctica at eight sites with similar air temperatures and relative humidities but divergent soil temperatures and soil water contents
near Pituffik, Greenland (76°N, 38°W). We found negative correlations at the site level between g
s
and Δ18O in bulk leaf tissue (r
2 = 0.62, slope = −17.9‰/mol H2O m−2 s−1, P = 0.02) and leaf α-cellulose (r
2 = 0.83, slope = −11.5‰ mol H2O m−2 s−1, P < 0.01), consistent with the notion that leaf water enrichment declines with increasing E. We also found negative correlations at the site-level between intrinsic water-use efficiency (iWUE) and Δ13C in bulk leaf tissue (r
2 = 0.65, slope = −0.08‰/μmol CO2 /mol H2O, P = 0.02) and leaf α-cellulose (r
2 = 0.50, slope = −0.05 ‰/[μmol CO2 /mol H2O], P = 0.05). When increasing Δ13C was driven by increasing g
s
alone, we found negative slopes between Δ13C and Δ18O for bulk leaf tissue (−0.664) and leaf α-cellulose (−1.135). When both g
s
and A
max increased, we found steeper negative slopes between Δ13C and Δ18O for bulk leaf tissue (−2.307) and leaf α-cellulose (−1.296). Our results suggest that the dual isotope approach is capable
of revealing the qualitative contributions of g
s
and A
max to Δ13C at the site level. In our study, bulk leaf tissue was a better medium than leaf α-cellulose for application of the dual
isotope approach. 相似文献
15.
Sotiris Haliapas Traianos A. Yupsanis Thomas D. Syros George Kofidis Athanasios S. Economou 《Acta Physiologiae Plantarum》2008,30(6):807-815
Petunia × hybrida was grown under high (H), medium (M) and low (L) light intensity [photoperiod; 16 h d−1, photosynthetic photon flux density (PPFD); 360, 120 and 40 μmol m−2 s−1, respectively] as well as under end-of-day (EOD) red (R) and far-red (FR) light quality treatments [photoperiod; 14.5 h d−1, PPFD; 30 μmol m−2 s−1 EOD; 15 min, Control (C) light; without EOD light treatment]. Shoot growth, leaf anatomical and photosynthetic responses
as well as the responses of peroxidase (POD) isoforms and their specific activities following transition to flowering (1–6 weeks)
were evaluated. Flower bud formation of Petunia × hybrida was achieved at the end of the 4th week for H light treatment and on the end of the 6th week for FR light treatment. No flower
bud formation was noticed in the C and R light treatments. H and M light treatments induced lower chlorophyll (Chla, Chlb,
Chla+b) concentrations in comparison to L light. On the other hand R and FR light chlorophyll content were similar to C light.
Photosynthetic parameters [CO2 assimilation rate (A), transpiration rate (E) and stomatal conductance (g
s) values] were higher in the H light treated plants in comparison to M and L light treated plants. A, E and g
s values of R and FR light were similar to C light plants. Leaf anatomy revealed that total leaf thickness, thickness of the
contained tissues (epidermis, palisade and spongy parenchyma) and relative volume percentages of the leaf histological components
were differently affected within the light intensity and the light quality treatments. POD specific activities increased from
the 1st to the 6th week during transition to flowering. Native-PAGE analysis revealed the appearance of four anionic POD (A1–A4) isoforms in all light treatments. On the basis of the leaf anatomical, photosynthetic and plant morphological responses,
the production of high quality Petunia × hybrida plants with optimal flowering times could be achieved through the control of both light intensity and light quality. The
appearance of A1 and A2 anionic POD isoforms could be also used for successful scheduling under light treatments. 相似文献
16.
Light acclimatisation capabilities of Elodea nuttallii at nearly ambient DIC conditions were investigated by determining growth characteristics, main photosynthetic parameters
and pigmentation of plants incubated at 5 different irradiances (10–146 μmol photons m−2 s−1). Positive net growth was observed under all light treatments tested. Maximum ratio root versus shoot (r:s) of 1.86 was achieved
at medium irradiances (72–94 μmol photons m−2 s−1), whereas at low (10 μmol photons m−2 s−1) and high irradiances (146 μmol photons m−2 s−1) r:s was significantly lower (0.39 and 1.05, respectively). With respect to main photosynthetic parameters, an increase of
light compensation points (E
c), attended by decreasing ratios of light saturation points of photosynthesis (E
k)/irradiance were observed. E
c values were comparable to other low-light adapted macrophytes, which indicate that E. nuttallii can be regarded as a low-light adapted plant, under photorespiratory conditions. This was also confirmed by maximum E
k values of just 73 μmol photons m−2 s−1. Further support was achieved from pigmentation and non-photochemical quenching (NPQ) data, both indicating rather limited
acclimatisation ability at light treatments above 90 μmol photons m−2 s−1. These results are discussed with respect to the competitive abilities of E. nuttallii under nearly ambient (photorespiratory) DIC conditions, especially in dense stands and turbid phytoplankton-dominated waters. 相似文献
17.
Anne C. Lang Werner H?rdtle Helge Bruelheide Wenzel Kr?ber Matthias Schr?ter Henrik von Wehrden Goddert von Oheimb 《Ecological Research》2012,27(1):181-189
The aim of this study was to analyse the relation of horizontal and vertical canopy structure to tree functional diversity
of a highly diverse subtropical broad-leaved slope forest, stratified for different successional stages. This is of particular
interest because many key ecosystem processes and functions are related to the arrangement of forest canopies. We assessed
the effect of stand-related functional diversity (FDQ, measured as Rao’s quadratic entropy of leaf traits), together with other environmental variables on horizontal [measured
as relative crown projection areas (CPAr)] and vertical [relative crown overlap, coefficients of variation (CV) of crown positioning variables] structure of the upper
canopy at the local neighbourhood level. The analyses with mixed effects models revealed a negative relation (p = 0.025; estimate −0.07) between FDQ and CPAr. No significant effect of FDQ on vertical canopy structure has been found (p > 0.05). The findings are discussed with regard to resource partitioning and niche differentiation of canopy and sub-canopy
species. Successional stage positively impacted the CV of crown length (p = 0.019; estimate 0.03) but did not affect other response variables. The sloping terrain strongly influenced vertical canopy
structure as revealed by the significant effect of slope inclination on CV of crown length (p = 0.004; estimate −0.05) and of slope aspect on CV of mean crown height (p = 0.036; estimate −0.03). The high complexity of vertical crown positioning depending on the heterogeneous sloping terrain
of the study area may have obscured relations of FDQ to vertical canopy structure. 相似文献
18.
Seasonal courses of leaf CO2 gas exchange in a growing season were examined in saplings ofThujopsis dolabrata var.hondai andQuercus mongolica var.grosseserrata in a cool temperate deciduous forest. Between the two tree species there were no large differences in the light compensation
point of leaf photosynthesis, except for the season of new leaf expansion. However, light-saturated rates of net photosynthesis
were obviously high inT. dolabrata var.hondai. EvergreenT. dolabrata var.hondai saplings had large photosynthetic production in two seasons, before the emergence of new foliage and after foliage fall of
the overstory deciduous trees, because of the significantly high solar radiant energy penetrating under the forest canopy
during the seasons. Saplings of deciduousQ. mongolica var.grosseserrata were heavily shaded throughout the growing season by foliage of the overstory trees, which resulted in a low daily surplus
production. The annual surplus production of leaves in the growing season was estimated to be 2300 mmol CO2 m−2 inT. dolabrata var.hondai and −100 mmol CO2 m−2, slightly negative, inQ. mongolica var.grosseserrata. These results supported the high survivability ofT. dolabrata var.hondai saplings and the high mortality ofQ. mongolica var.grosseserrata in the deciduous forest. 相似文献
19.
Barton D. Clinton Chris A. Maier Chelcy R. Ford Robert J. Mitchell 《Trees - Structure and Function》2011,25(6):997-1007
In 20-year-old longleaf pine, we examined short-term effects of reduced live leaf area (A
L) via canopy scorching on sap flow (Q; kg H2O h−1), transpiration per unit leaf area (E
L; mm day−1), stem CO2 efflux (R
stem; μmol m−2 s−1) and soil CO2 efflux (R
soil; μmol m−2 s−1) over a 2-week period during early summer. R
stem and Q were measured at two positions (1.3-m or BH, and base of live crown—BLC), and R
soil was measured using 15 open-system chambers on each plot. E
L before and after treatment was estimated using Q measured at BLC with estimates of A
L before and after scorching. We expected Q to decrease in scorched trees compared with controls resulting from reduced A
L. We expected R
stem at BLC and BH and R
soil to decrease following scorching due to reduced leaf area, which would decrease carbon supply to the stem and roots. Scorching
reduced A
L by 77%. Prior to scorching, Q at BH was similar between scorch and control trees. Following scorching, Q was not different between control and scorch trees; however, E
L increased immediately following scorching by 3.5-fold compared to control trees. Changes in E
L in scorched trees corresponded well with changes in VPD (D), whereas control trees appeared more decoupled over the 5-day period following treatment. By the end of the study, R
stem decreased to 15–25% in scorched trees at both stem positions compared to control trees. Last, we found that scorching resulted
in a delayed and temporary increase in R
soil rather than a decrease. No change in Q and increased E
L following scorching indicates a substantial adjustment in stomatal conductance in scorched trees. Divergence in R
stem between scorch and control trees suggests a gradual decline in stem carbohydrates following scorching. The absence of a strong
R
soil response is likely due to non-limiting supplies of root starch during early summer. 相似文献
20.
Predicting vegetation water content in wheat using normalized difference water indices derived from ground measurements 总被引:2,自引:0,他引:2
Vegetation water content (VWC) is an important variable for both agriculture and forest fire management. Remote sensing technology
offers an instantaneous and non-destructive method for VWC assessment provided we can relate in situ measurements of VWC to
spectral reflectance in a reliable way. In this paper, based on radiative transfer models, three new normalized difference
water indices (NDWI) are proposed for VWC [fuel moisture content (FMC), and equivalent water thickness (EWT)] estimation,
taking both leaf internal structure and dry matter content into account. Reflectance at 1,200, 1,450 and 1,940 nm were selected
and normalized with reflectance at 860 nm to establish three water indices, NDWI1200, NDWI1450 and NDWI1940. Good correlations were observed between FMC (R
2 = 0.65–0.80) and EWT (both at the leaf scale, R
2 = 0.75–0.81 for EWTL and at the canopy scale, R
2 = 0.80–0.83 for EWTC) at various stages of wheat crop development. 相似文献