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1.
Communities of ten species of tropical forest tree seedlings from three successional classes were grown at ambient and elevated CO2 in large open-top chambers on the edge of a forest in Panamá. Communities grew from 20?cm to approximately 2?m in height in 6 months. No enhancements in plant biomass accumulation occurred under elevated CO2 either in the whole communities or in growth of individual species. Reductions in leaf area index under elevated CO2 were observed, as were decreases in leaf nitrogen concentrations and increases in the C:N ratio of leaf tissue. Species tended to respond individualistically to elevated CO2, but some generalizations of how successional groupings responded could be made. Early and mid-successional species generally showed greater responses to elevated CO2 than late-successional species, particularly with respect to increases in photosynthetic rates and leaf starch concentrations, and reductions in leaf area ratio. Late-successional species showed greater increases in C:N ratios in response to elevated CO2 than did other species. Our results indicate that there may not be an increase in the growth of regenerating tropical forest under elevated CO2, but that there could be changes in soil nutrient availability because of reductions in leaf tissue quality, particularly in late-successional species. 相似文献
2.
Dirk Hölscher Christoph Leuschner Kerstin Bohman Marc Hagemeier Jana Juhrbandt Soekisman Tjitrosemito 《Trees - Structure and Function》2006,20(3):278-285
In the tropics, old-growth forests are converted to other land cover types at a high rate and young secondary forest may gain in importance. Information on associated changes in leaf gas exchange and other leaf traits can be valuable for modelling biogeochemical fluxes under altered land-use patterns. We studied in situ photosynthetic parameters and stomatal conductance for water vapour in eight abundant tree species of young secondary forest and eight tree species of natural old-growth forest in Central Sulawesi, Indonesia. In sun leaves, the average maximal stomatal conductance (g
smax) in the secondary forest (SF) species was 2.1 times higher than in the old-growth forest (OGF) species. Species with a high g
smax reduced g
s sharply when vapour pressure deficit of the air increased, whereas species with a low g
smax were much less sensitive to air humidity. For area-based photosynthetic capacity (A
max-area), the SF species had a 2.3 times higher average than the OGF species. For both, g
smax and A
max-area the variation among species was higher in the OGF than in the SF. When all tree species (n=16) are considered, species means of specific leaf area (SLA), leaf N concentration and leaf P concentration were significantly correlated with g
smax and A
max-area. The strong correlation between A
max-area and foliar P (r
2=0.8) is remarkable as the alluvial soils in the study region are rich in nutrients. If the eight OGF species are analysed separately, the only significant correlation was observed between SLA and mass-based A
max; in the SF species strong correlations were found between leaf size and A
max-area and g
smax. These results show that the conversion of old-growth forest to young secondary forest in Sulawesi significantly alters tree leaf gas exchange characteristics and that chemical and structural leaf traits can be used for the prediction of these changes. The best correlations between leaf gas exchange parameters and leaf traits were obtained by different traits in the SF species, the OGF species and the entire pool of studied species. 相似文献
3.
We investigated photosynthesis of five plant species growing in the understory at three sites (1,170-, 1,600- and 2,100-mm annual moisture inputs), along the geographical range of coastal California redwood forest, to determine whether greater inputs of rain and fog at northern sites enhance photosynthetic utilization of fluctuating light. Measurements of understory light environment and gas exchange were carried out to determine steady state and dynamic photosynthetic responses to light. Leaf area index ranged from 4.84 at the 2,100-mm site to 5.98 at the 1,170-mm site. Maximum rates of net photosynthesis and stomatal conductance (g) did not vary appreciably within species across sites. Photosynthetic induction after a change from low to high light was significantly greater in plants growing in lower light conditions regardless of site. Photosynthetic induction also increased with the rate of g in diffuse light, prior to the increase to saturating light levels. Post-illumination CO2 assimilation was the largest factor contributing to variation in C gain during simulated lightflecks. The duration of post-illumination photosynthetic activity, total CO2 assimilation per light received, and light use efficiency during simulated lightflecks increased significantly with moisture inputs in four out of five species. Increasing leaf N concentration with increasing moisture inputs in three out of five species, coupled with changes in leaf N isotopic composition with the onset of the summer fog season suggest that natural N deposition increases with rain and fog inputs and contributes to greater utilization of fluctuating light availability in coastal California redwood forests. 相似文献
4.
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
5.
为探究富氮环境中固氮(nitrogen-fixing leguminous trees,NLT)与非固氮豆科树种(non-nitrogen-fixing leguminous trees,n-NLT)的叶片养分利用策略差异,以华南地区5种NLT植物[水黄皮(Pongamia pinnata)、大叶相思(Acacia auriculiformis)、朱樱花(Calliandra haematocephala)、海南红豆(Ormosia pinnata)、台湾相思(Acacia confusa)]和3种n-NLT植物[油楠(Sindora glabra)、中国无忧花(Saraca dives)、银珠(Peltophorum tonkinense)]为对象,测定其单位质量叶片碳(C)、氮(N)和磷(P)含量及其比值、单位面积叶片最大净光合速率(Aarea)和叶片光合氮、磷利用效率(PNUE、PPUE)等功能性状。结果表明,NLT的单位质量叶片N、P含量和Aarea均显著高于n-NLT,而两者PNUE和PPUE无显著差异;尽管两类植物单位质量叶片C含量无显著差异,但NLT的叶片C:N和C:P显... 相似文献
6.
The role of CAM in high rainfall cloud forests: an in situ comparison of photosynthetic pathways in Bromeliaceae 总被引:2,自引:0,他引:2
Crassulacean acid metabolism (CAM), an advanced photosynthetic pathway conferring water conservation to plants in arid habitats, has enigmatically been reported in some species restricted to extremely wet tropical forests. Of these, epiphytic Bromeliaceae may possess absorbent foliar trichomes that hinder gas‐exchange when wetted, imposing further limitations on carbon dioxide (CO2) uptake. The hypothesis that the metabolic plasticity inherent to CAM confers an ecological advantage over conventional C3 plants, when constant rainfall and mist might inhibit gas‐exchange was investigated. Gas‐exchange, fluorometry and organic acid and mineral nutrient contents were compared for the bromeliads Aechmea dactylina (CAM) and Werauhia capitata (C3) in situ at the Cerro Jefe cloud forest, Panama (annual rainfall > 4 m). Daily carbon gain and photosynthetic nutrient use efficiencies were consistently higher for A. dactylina, due to a greater CO2 uptake period, recycling of CO2 from respiration and a dynamic response of CO2 uptake to wetting of leaf surfaces. During the dry season CAM also had water conserving and photoprotective roles. A paucity of CAM species at Cerro Jefe suggests a recent radiation of this photosynthetic pathway into the wet cloud forest, with CAM extending diversity in form and function for epiphytes. 相似文献
7.
Periodic measurements of gas‐exchange rates and determinations of foliar N and P concentrations were used for evaluating instantaneous water‐use efficiency and photosynthetic nutrient‐use efficiency in two co‐existing dwarf shrubs of different growth form (V. myrtillus, deciduous, and V. vitis‐idaea, evergreen) in a subalpine heath in the southern Alps of Italy. Those data were compared with cumulative assessments of water‐use efficiency and photosynthetic nutrient‐use efficiency obtained by measuring leaf carbon isotope discrimination in leaf tissues and by estimating nutrient resorption from senescing leaves. V. myrtillus presented higher dry‐weight based rates of net photosynthesis (Aweight) compared to V. vitis‐idaea. Aweight was positively correlated with foliar‐nutrient status and intercellular‐to‐ambient gradient in CO2 concentrations. Aweight was, furthermore, negatively correlated with leaf specific mass. Instantaneous photosynthetic nutrient‐use efficiency did not differ between the two species but the percentages of N and P pools resorbed from senescing leaves were somewhat higher in the deciduous species. The evergreen species showed lower P concentrations in senescing leaves which indicated a higher proficiency in resorbing phosphorus compared to the deciduous species. In addition, the evergreen species achieved a higher carbon gain per unit foliar N and P, due to a longer mean residence time of both nutrients. The two species did not differ from each other with respect to both instantaneous and long‐term water‐use efficiency. This was consistent with the climatic pattern, showing no sign of water deficiency through the growing season. Current‐year V. vitis‐idaea leaves had a significantly higher Δ13C compared to previous‐year leaves, possibly mirroring a long term acclimation of evergreen leaves, as far as they age, to the habitat conditions in the understory where evergreen species are usually confined within mixed dwarf‐shrub communities. 相似文献
8.
Summary Laboratory and field gas exchange measurements were made on C3 (Scirpus olneyi Gray) and C4 (Spartina patens (Ait.) Mahl., Distichlis spicata (L.) Green) species from an irregularly flooded tidal marsh on the Chesapeake Bay. Laboratory measurements were made on plants grown from root stocks that were transplanted to a greenhouse and grown under high light and high nutrient conditions. The two C4 species were similar in their laboratory gas exchange characteristics: both had higher net carbon exchange rates, higher mesophyll conductances, higher photosynthetic temperature optima and lower leaf conductances than the C3 species. The laboratory photosynthetic water use efficiency of the C4 species was approximately three times that of the C3 species.Field gas exchange responses of the above species were measured in situ a Chesapeake Bay tidal marsh. Despite differences in biological potential measured in the laboratory, all three species had similar in situ carbon exchange rates on a leaf area basis. On a dry weight basis, leaves of the two C4 species had about 1.4 times higher light saturated CO2 assimilation rates than the C3 species. Light saturation of CO2 exchange occurred at photosynthetic photon flux densities of 80 n Einstein cm-2s-1, compared with 160 n Einstein cm -2s-1 in the laboratory grown plants. Spartina patens and Scirpus olneyi had similar daily CO2 assimilation rates, but the daily transpiration rate of the C3 species was almost twice that of the C4 species. Spartina patens showed greater seasonal decrease in photosynthesis than Distichlis spicata and Scirpus olneyi. The two C4 grass species maintained higher mesophyll conductances and photosynthetic water use efficiencies than the C4 sedge. 相似文献
9.
We measured rates of leaf senescence and leaf level gas exchange during autumnal senescence for seedlings of five temperate forest tree species under current and elevated atmospheric CO2 concentrations and low- and high-nutrient regimes. Relative indices of whole canopy carbon gain, water loss and water use efficiency through the senescent period were calculated based on a simple integrative model combining gas exchange per unit leaf area and standing canopy area per unit time. Seedlings grown under elevated [CO2] generally had smaller canopies than their current [CO2]-grown counterparts throughout most of the senescent period. This was a result of smaller pre-senescent canopies or accelerated rates of leaf drop. Leaf-level photosynthetic rates were higher under elevated [CO2] for grey birch canopies and for low-nutrient red maple and high-nutrient ash canopies, but declined rapidly to values below those of their current [CO2] counterparts by midway through the senescent period. CO2 enrichment reduced photosynthetic rates for the remaining species throughout some or all of the senescent period. As a result of smaller canopy sizes and reduced photosynthetic rates, elevated [CO2]-grown seedlings had lower indices of whole canopy end-of-season carbon gain with few exceptions. Leaf level transpiration rates were highly variable during autumnal senescence and neither [CO2] nor nutrient regime had consistent effects on water loss per unit leaf area or integrated whole canopy water loss throughout the senescent period. Indices of whole canopy, end-of-season estimates of water use efficiency, however, were consistently lower under CO2 enrichment, with few exceptions. These results suggest that whole canopy end-of-season gas exchange may be altered significantly in an elevated [CO2] world, resulting in reduced carbon gain and water use efficiency for many temperate forest tree seedlings. Seedling growth and survivorship, and ultimately temperate forest regeneration, could be reduced in CO2-enriched forests of the future. 相似文献
10.
Abstract. The impact of grazing pressure on gas exchange of Periploca laevigata was studied in relation to its nutritional status. P. laevigata, a woody and highly palatable shrub, is an important forage species in the dry season in Cabo de Gata Natural Park (Almeria, SE Spain) where this study was carried out. Seasonal and diurnal courses of net photosynthesis, transpiration and stomatal conductance were measured in the field. In addition, soil and plant nutrient status were measured as potential factors influencing leaf photosynthetic levels. Early in the growing season, ungrazed P. laevigata had higher photosynthetic activity than grazed plants suggesting that the defoliated plants were still recovering from herbivore damage in the previous summer. Later in the growing season grazed P. laevigata had higher photosynthetic activity than ungrazed plants, suggesting higher metabolic activity and a possible investment in chemical defences. Concentrations of P and N in the soil were higher in the grazed area. The nutrient concentration of the leaves of P. laevigata was similar in grazed and ungrazed plants. 相似文献
11.
Ilyas Siddique Vera Lex Engel John A. Parrotta David Lamb Gabriela B. Nardoto Jean P. H. B. Ometto Luiz A. Martinelli Susanne Schmidt 《Biogeochemistry》2008,88(1):89-101
Failures in reforestation are often attributed to nutrient limitation for tree growth. We compared tree performance and nitrogen
and phosphorus relations in adjacent mixed-species plantings of contrasting composition, established for forest restoration
on Ultisol soil, originally covered by tropical semi-deciduous Atlantic Forest in Southeast Brazil. Nutrient relations of
four tree species occurring in both planting mixtures were compared between a legume-dominated, species-poor direct seeding
mixture of early-successional species (“legume mixture”), and a species-diverse, legume-poor mixture of all successional groups
(“diverse mixture”). After 7 years, the legume mixture had 6-fold higher abundance of N2-fixing trees, 177% higher total tree basal area, 22% lower litter C/N, six-fold higher in situ soil resin-nitrate, and 40%
lower in situ soil resin-P, compared to the diverse mixture. In the legume mixture, non-N2-fixing legume Schizolobium parahyba (Fabaceae-Caesalpinioideae) had significantly lower proportional N resorption, and both naturally regenerating non-legume
trees had significantly higher leaf N concentrations, and higher proportional P resorption, than in the diverse mixture. This
demonstrate forms of plastic adjustment in all three non-N2-fixing species to diverged nutrient relations between mixtures. By contrast, leaf nutrient relations in N2-fixing Enterolobium contortisiliquum (Fabaceae-Mimosoideae) did not respond to planting mixtures. Rapid N accumulation in the legume mixture caused excess soil
nitrification over nitrate immobilization and tighter P recycling compared with the diverse mixture. The legume mixture succeeded
in accelerating tree growth and canopy closure, but may imply periods of N losses and possibly P limitation. Incorporation
of species with efficient nitrate uptake and P mobilization from resistant soil pools offers potential to optimize these tradeoffs. 相似文献
12.
Cyclobalanopsis glauca is a dominant species in mid-subtropical forest, and usually plays an important role in forest ecosystems. However, it often suffers redundant precipitation or water stress, which often concurs with high temperature, nutrient depletion and strong irradiance. The study presented in the paper hypothesized that soil water exerted strong influence on leaf gas exchange and traits. The objective of this study was to clarify the effect of soil water changes on photosynthetic characteristics and leaf traits and their relationships of C. glauca seedlings growing on nutrient-rich and nutrient-poor soil at three water levels. The study measured the specific leaf area (SLA), nitrogen content, chlorophyll concentrations and photosynthetic light response curve. Its results showed that there were no differences in leaf size, leaf dry weight, SLA, leaf dry matter content, Leaf nitrogen concentration and Leaf chlorophyll between the two soil nutrient treatments, while these parameters differed significantly among different water levels for either of the treatments. There were large variations in leaf photosynthetic parameters and leaf traits among the different water treatments, indicating different response patterns of C. glauca seedling and its adaptation to the different soil water conditions. There were no significant differences in light-saturated photosynthetic rate (Amax) and apparent quantum yield (Ø) between the nutrient-rich and nutrient-poor soils, which indicated that the C. glauca seedlings could maintain similar capacities in different soils that differed in nutrient condition. As to the relation between the photosynthesis and leaf traits, the Amax and PNUE were positively correlated with the SLA, respectively, but the SLA had significant negative relationship with the leaf N (P<0.01) in nutrient-rich soil. In contrast, both Amax and PNUE were significantly negatively correlated with the SLA, respectively (P<0.01); and the SLA was not significantly positively correlated with the leaf nitrogen concentration of the nutrient-poor soil (P>0.05). The specific leaf areas (SLA), nitrogen and chlorophyll concentrations as well as other photosynthetic features were influenced in a coordinative manner by the soil water. The relation among the Amax, PNUE and the Nmass, SLA could be described as a binomial equation and a liner negative regression for the nutrient-rich and nutrient-poor soil, respectively. In conclusion, soil water was more constraining factor than the soil nutrient to the photosynthesis of C. glauca seedlings, nutrient-rich soil could offset some negative influence resulting from soil water deficit on LSP and LCP. Factors affecting the variations of photosynthetic characteristics and leaf traits of C. glauca seedlings differed between the nutrient-rich and nutrient-poor soils. 相似文献
13.
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
14.
The influence of environmental gradients on the foliar nutrient economy of forests has been well documented; however, we have little understanding of what drives variability among individuals within a single forest stand, especially tropical forests. We evaluated inter‐ and intra‐specific variation in nutrient resorption, foliar nutrient concentrations and physical leaf traits of nine canopy tree species within a 1‐ha secondary tropical rain forest in northeastern Costa Rica. Both nitrogen (N) and phosphorus (P) resorption efficiency (RE) and proficiency of the nine tree species varied significantly among species, but not within. Both N and P RE were significantly negatively related to leaf specific strength. Green leaf N and P concentrations were strongly negatively related to leaf mass per area, and senesced leaf nutrient concentrations were significantly positively related to green leaf nutrient concentrations. This study reveals a strong influence of physical leaf traits on foliar nutrient and resorption traits of co‐occurring species in a secondary wet tropical forest stand. 相似文献
15.
Diaheliotropic leaf movement enhances leaf photosynthetic capacity and photosynthetic light and nitrogen use efficiency via optimising nitrogen partitioning among photosynthetic components in cotton (Gossypium hirsutum L.)
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H. Yao Y. Zhang X. Yi X. Zhang D. Fan W. S. Chow W. Zhang 《Plant biology (Stuttgart, Germany)》2018,20(2):213-222
- Phototropic leaf movement of plants is an effective mechanism for adapting to light conditions. Light is the major driver of plant photosynthesis. Leaf N is also an important limiting factor on leaf photosynthetic potential. Cotton (Gossypium hirsutum L.) exhibits diaheliotropic leaf movement. Here, we compared the long‐term photosynthetic acclimation of fixed leaves (restrained) and free leaves (allowed free movement) in cotton.
- The fixed leaves and free leaves were used for determination of PAR, leaf chlorophyll concentration, leaf N content and leaf gas exchange. The measurements were conducted under clear sky conditions at 0, 7, 15 and 30 days after treatment (DAT).
- The results showed that leaf N allocation and partitioning among different components of the photosynthetic apparatus were significantly affected by diaheliotropic leaf movement. Diaheliotropic leaf movement significantly increased light interception per unit leaf area, which in turn affected leaf mass per area (LMA), leaf N content (NA) and leaf N allocation to photosynthesis (NP). In addition, cotton leaves optimised leaf N allocation to the photosynthetic apparatus by adjusting leaf mass per area and NA in response to optimal light interception.
- In the presence of diaheliotropic leaf movement, cotton leaves optimised their structural tissue and photosynthetic characteristics, such as LMA, NA and leaf N allocation to photosynthesis, so that leaf photosynthetic capacity was maximised to improve the photosynthetic use efficiency of light and N under high light conditions.
16.
比较了异质养分环境中黍(Panicum miliaceum)叶片气体交换和光合养分利用效率。异质养分环境显著影响黍叶片气体交换;繁殖前期叶片光合速率、蒸腾速率、气孔导度和水分利用效率随环境中总养分水平变化的趋势与种子成熟期恰好相反;光合速率、蒸腾速率和气孔导度与叶氮含量成显著相关,而与叶磷含量和叶钾含量无显著相关;光合磷利用效率和光合钾利用效率受异质养分环境的显著影响,而光合氮利用效率对异质养分环境无显著反应。 相似文献
17.
Robin L. Chazdon 《Oecologia》1992,92(4):586-595
Summary Photosynthetic plasticity of two congeneric shrub species growing under natural field conditions was compared along transects spanning two canopy gaps in a Costa Rican rain forest. Piper arieianum is a shadetolerant species common in successional and mature forests, whereas P. sancti-felicis is a pioneer species abundant in abandoned clearings and large gaps. Twenty potted cuttings of each species were placed at regular intervals along two east-west transects crossing a small branch-fall gap and a large tree-fall gap. Along the transects, the percent of full sun photon flux density varied from less than 2% to 45%. After six months of growth under these conditions, leaves were monitored for incident photon flux density, photographic measures of light availability, photosynthetic capacity (Amax), leaf nitrogen content, leaf chlorophyll content, and specific leaf mass. Although both species demonstrated considerable plasticity in Amax across gap transects, P. sancti-felicis leaves had a superior capacity to track closely variation in light availability, particularly in the larger gap. For regressions of Amax on measures of light availability, P. sancti-felicis consistently showed a 3.5 to 5-fold higher coefficient of determination (R2) and a 3 to 4-fold higher slope than P. arieianum. In both species leaf nitrogen content per leaf area increased significantly with light availability, although P. sancti-felicis, again, showed a much stronger relationship between these variables. Across the transects, mean chlorophyll content per unit leaf area did not differ significantly between the species, whereas mean chlorophyll content per unit leaf dry mass was 3-times greater in leaves of P. sancti-felicis. Piper arieianum exhibited highly significant increases in chlorophyll a:b ratio with increased light availability, whereas P. sancti-felicis lacked significant variation in this trait across a gradient of light availability. Mean specific leaf mass did not vary significantly between species across the gap transects. The nature of the light acclimatory response differs quantitatively and qualitatively between these species. An important constraint on light acclimation of the shade-tolerant P. arieianum is its inability to increase photosynthetic nitrogen-use efficiency under conditions of high light availability. The lack of plasticity in chlorophyll a:b ratios does not restrict light acclimation of Amax in P. sancti-felicis. Leaves of P. arieianum exhibited symptoms of chronic photoinhibition in exposed microsites within the large gap. Species differences in the capacity to finely adjust Amax across a wide range of light conditions may be attributed to their maximum growth potential. Light acclimation in species with low maximum growth potential may be constrained at the cellular level by rates of protein and chlorophyll synthesis and at the whole-plant level by low maximum rates of uptake and supply of nutrients and water. For P. arieianum, restriction of photosynthetic plasticity is likely to limit competitive abilities of plants in high-light conditions of large gaps and clearings, whereas observed habitat restrictions for P. sancti-felicis do not appear to depend upon the highly-developed capacity for adjustment of Amax observed in this species. 相似文献
18.
Jean-Philippe Puyravaud Céline Dufour Subramanian Aravajy 《Journal of Biogeography》2003,30(7):1067-1080
Aim The objective of this study was to document succession from grassland thickets to rain forest, and to provide evidence for their potential as restoration tools. Location The Linganamakki region (State of Karnataka) of the Central Western Ghats of India. Method We selected thirty vegetation thickets ranging from 4 to 439 m2 in area in the vicinity of rain forest. The area of each small thicket was estimated as an oval using its maximum length and its maximum width. When the shape was irregular (mostly in large thickets) the limits of the thicket were mapped and the area calculated from the map. Plant species were identified, the number of individuals was estimated and their heights measured. Results There was a progression in the thickets from early to late successional species. Small thickets were characterized by ecotone species and savanna trees such as Catunaregam dumetorum. Savanna trees served as a nucleus for thicket formation. Colonizing species were mostly bird‐dispersed. As succession proceeded in larger thickets, the proportion of evergreen, late‐successional rain forest trees increased. The species composition of the large thickets differed depending on the species composition of reproductive adults in the nearby forested areas. The species within small thickets were also found in the large thickets. The nestedness in species composition suggested that species turnover was deterministic based on thicket size. Human disturbance (leaf and wood collection by the local populations) affected the species composition and the species–area relationship of thickets. Main conclusions Vegetation thickets are nodal centres for rain forest colonization within grasslands. They expand and replace savanna. Early successional bird‐dispersed species established around savanna trees followed by late‐successional rain forest trees dispersed from the nearby forest by birds. Restoration programmes that reproduce natural successional processes such as those observed in thickets will be more successful and less expensive than the methods currently being employed, where trees are individually planted in grassland. Wood harvesting is the only factor that prevents thicket growth and coalescence and hampers forest expansion. 相似文献
19.
Photosynthetic and gas exchange characteristics of dominant woody plants on a moisture gradient in an African savanna 总被引:4,自引:0,他引:4
Guy Franklin Midgley Julieta Nelida Aranibar† Khanyisa Brian Mantlana‡ Stephen Macko† 《Global Change Biology》2004,10(3):309-317
We determined key photosynthetic gas exchange parameters, and their temperature dependence, in dominant woody plants at four savanna sites on a moisture gradient in Botswana, southern Africa. Leaf stable carbon and nitrogen (N) isotope and morphological measures were made concurrently. Sampling of these predominantly non‐N‐fixing species took place during an exceptional rainfall season, representing near‐optimum conditions for primary production at these sites. The mean specific leaf area and leaf size were positively related to mean annual rainfall (MAR); species with larger leaves of lower density were more abundant in wetter sites. Almost all species at all sites showed high net light‐saturated photosynthetic rates (Amax?10 μmol CO2 m?2 s?1) due both to high CO2 carboxylation (Vc,max) and RubP‐regeneration capacity (Jmax). These high rates were associated with high values of leaf [N]. Across all sites, the temperature response of Amax showed no clear optimum, and a gradual drop from 25°C to 35°C, without notable temperature limitation at leaf temperatures in excess of 35°C. Dark respiration rate (Rday) across all species and sites increased exponentially with increasing leaf temperature. Species sampled at selected sites revealed a negative relationship between leaf δ13C (stable carbon isotope ratio) and MAR, suggesting higher leaf‐level water‐use efficiency at drier sites when integrated over the life of the leaf. At wetter sites, specific leaf [N] was lower and photosynthetic nitrogen‐use efficiency increased, a pattern reflected at the ecosystem level by less 15N enrichment of leaves at these sites. Taken together, the results suggest a switch from water‐use to nitrogen‐use efficiency constraints with increasing moisture availability. These constraints impact leaf form and function significantly, and may emerge at the ecosystem level in aspects of water and N cycling. 相似文献
20.
Carbon uptake by forests constitutes half of the planet’s terrestrial net primary production; therefore, photosynthetic responses
of trees to rising atmospheric CO2 are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics
and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment
in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September)
higher in CO2-enriched trees and showed no sign of down-regulation. Elevated CO2 had no effect on carboxylation efficiency (V
cmax) or maximal electron transport (J
max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO2 enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific
leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO2 (largely driven by Quercus). Because leaf area index did not change, the CO2-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO2 concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of
the additionally assimilated carbon remains uncertain. 相似文献