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1.
Photosynthetic characteristics, leaf longevity and biomass accumulation of a threatened herb species, Arisaema heterophyllum, were studied in the understory of a riparian forest and at a neighboring deforested open site for 3 years in order to understand
the combined effects of light and water availability. Light availability was 2- to 4-fold higher at the deforested than at
the forest site during the growing season of the species, and precipitation varied considerably over the 3 years. Despite
the difference in water availability among the years (dry in 1994 and 1996, and wet in 1995), the species showed a strong
acclimation to the different light environments. Light-saturated assimilation rate on a leaf area basis, leaf mass area ratio
(LMA), and relative growth rate (RGR) were all higher at deforested site. While a positive correlation between individual
RGR and microsite light availability was found in the wet year, no correlation was found in the dry years, and mean RGR was
significantly lower in the dry year at both sites. Leaf longevity, photosynthetic capacity on a leaf mass basis, dark respiration
rate, and leaf conductance, varied considerably from year to year, especially in the plants at the open site, probably depending
on water availability. In the dry years plants at the deforested sites showed a lower photosynthetic rate and leaf conductance
under unwatered than under watered conditions. These results suggest that the water availability in a given year may strongly
affect light acclimation and annual RGR of the herb species in natural habitats, even under mesic climate conditions.
Received: 15 February 1997 / Accepted: 20 May 1997 相似文献
2.
P.W. Rundel A.C. Gibson G.S. Midgley S.J.E. Wand B. Palma C. Kleier J. Lambrinos 《Plant Ecology》2002,169(2):179-193
We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species
in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding
extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats
(associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in
a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species
in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange
and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination
(Δ) of 3.7–7.5‰ through C3 species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved
amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the
rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during
the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season
water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic
water use efficiency (as estimated from the inverse of c
i
:c
a ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water
potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet
years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano
shrublands to adjacent national parks to ensure the persistence of these important communities.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Differential use of large summer rainfall events by shrubs and grasses: a manipulative experiment in the Patagonian steppe 总被引:17,自引:0,他引:17
In the Patagonian steppe, years with above-average precipitation (wet years) are characterized by the occurrence of large
rainfall events. The objective of this paper was to analyze the ability of shrubs and grasses to use these large events. Shrubs
absorb water from the lower layers, grasses from the upper layers, intercepting water that would otherwise reach the layers
exploited by shrubs. We hypothesized that both life-forms could use the large rainfalls and that the response of shrubs could
be more affected by the presence of grasses than vice versa. We performed a field experiment using a factorial combination
of water addition and life-form removal, and repeated it during the warm season of three successive years. The response variables
were leaf growth, and soil and plant water potential. Grasses always responded to experimental large rainfall events, and
their response was greater in dry than in wet years. Shrubs only used large rainfalls in the driest year, when the soil water
potential in the deep layers was low. The presence or absence of one life-form did not modify the response of the other. The
magnitude of the increase in soil water potential was much higher in dry than in humid years, suggesting an explanation for
the differences among years in the magnitude of the response of shrubs and grasses. We propose that the generally reported
poor response of deep-rooted shrubs to summer rainfalls could be because (1) the water is insufficient to reach deep soil
layers, (2) the plants are in a dormant phenological status, and/or (3) deep soil layers have a high water potential. The
two last situations may result in high deep-drainage losses, one of the most likely explanations for the elsewhere-reported
low response of aboveground net primary production to precipitation during wet years.
Received: 23 January 1997 / Accepted: 19 November 1997 相似文献
4.
Ramírez N 《American journal of botany》2002,89(5):836-842
Reproductive phenology of 171 plant species belonging to 57 families of angiosperms was studied according to life-forms in four habitat types in a savanna-forest mosaic on the Venezuelan Central Plain. Flowering, unripe fruit, and mature fruit patterns were affected significantly according to life-forms and habitats respectively. Production of flowers, unripe fruits, and mature fruits showed marked seasonality for all habitats except for the forest. Flowering peaked during the rainy season, and fruiting peaked toward the end of the rainy season. The savanna and the disturbed area had similar proportions of species that flowered over the year. The percentage of species with unripe fruits produced throughout the year was more seasonal for the disturbed area than for the other habitats. Mature fruit patterns showed an increase during the late rainy season for the ecotone and savanna. A large number of herbaceous (annual and perennial) and liana species flowered during the wet season, and a smaller fraction flowered during the dry season; and trees, shrubs, and epiphytes increased flowering activity during the dry season. Unripe fruit patterns were similar to those of flowering for all life-forms, however, tree species were less seasonal. Mature fruit production by shrubs peaked in the period of maximum rainfall, while the peak for perennial herbs was in the late rainy season and the peak for annual herbs was during the transition between the rainy season and the dry season. The largest proportion of tree and liana species with ripe fruits occurred during the dry season. Differences among phenological patterns in habitats were caused mainly by life-forms and promote a wider distribution of reproductive events in habitats and overall community in the Venezuelan Central Plain. 相似文献
5.
Juan P. Ferrio José Luis Araus Ramon Buxó Jordi Voltas Jordi Bort 《Vegetation History and Archaeobotany》2005,14(4):510-517
Carbon isotope discrimination (Δ13C) in charred grains from archaeological sites provides reliable information about water availability of ancient crops. However,
as cereals are cultivated plants, they may reflect not only climatic fluctuations, but also the effect on water status of
certain agronomic practices, such as sowing in naturally wet soils or irrigation. In this work, we propose a methodological
approach to combine Δ13C data from different plant species, in order to discriminate between climate-derived and anthropogenic effects on ancient
crops. We updated previous models for estimating water inputs from Δ13C of cereal grains of Hordeum vulgare and Triticum aestivum/durum, and we applied them to published data from several archaeological sites, including samples from the Neolithic to the present
day in northeast and southeast Spain, as well as from the Neolithic site of Tell Halula (northwest Syria). We found an important
decrease in water availability from the Neolithic to the present time in the three areas of study, especially clear for the
two driest areas (southeast Spain and northwest Syria). Potential differences in water management practices between wheat
and barley, as well as between cereal and legume crops (Vicia faba and Lens culinaris), are also discussed on the basis of the comparison of Δ13C values across several archaeological sites. 相似文献
6.
Increases in Desert Shrub Productivity under Elevated Carbon Dioxide Vary with Water Availability 总被引:2,自引:1,他引:1
David C. Housman Elke Naumburg Travis E. Huxman Therese N. Charlet Robert S. Nowak Stanley D. Smith 《Ecosystems》2006,9(3):374-385
Productivity of aridland plants is predicted to increase substantially with rising atmospheric carbon dioxide (CO2) concentrations due to enhancement in plant water-use efficiency (WUE). However, to date, there are few detailed analyses
of how intact desert vegetation responds to elevated CO2. From 1998 to 2001, we examined aboveground production, photosynthesis, and water relations within three species exposed
to ambient (around 38 Pa) or elevated (55 Pa) CO2 concentrations at the Nevada Desert Free-Air CO2 Enrichment (FACE) Facility in southern Nevada, USA. The functional types sampled—evergreen (Larrea tridentata), drought-deciduous (Ambrosia dumosa), and winter-deciduous shrubs (Krameria erecta)—represent potentially different responses to elevated CO2 in this ecosystem. We found elevated CO2 significantly increased aboveground production in all three species during an anomalously wet year (1998), with relative
production ratios (elevated:ambient CO2) ranging from 1.59 (Krameria) to 2.31 (Larrea). In three below-average rainfall years (1999–2001), growth was much reduced in all species, with only Ambrosia in 2001 having significantly higher production under elevated CO2. Integrated photosynthesis (mol CO2 m−2 y−1) in the three species was 1.26–2.03-fold higher under elevated CO2 in the wet year (1998) and 1.32–1.43-fold higher after the third year of reduced rainfall (2001). Instantaneous WUE was also
higher in shrubs grown under elevated CO2. The timing of peak canopy development did not change under elevated CO2; for example, there was no observed extension of leaf longevity into the dry season in the deciduous species. Similarly,
seasonal patterns in CO2 assimilation did not change, except for Larrea. Therefore, phenological and physiological patterns that characterize Mojave Desert perennials—early-season lags in canopy
development behind peak photosynthetic capacity, coupled with reductions in late-season photosynthetic capacity prior to reductions
in leaf area—were not significantly affected by elevated CO2. Together, these findings suggest that elevated CO2 can enhance the productivity of Mojave Desert shrubs, but this effect is most pronounced during years with abundant rainfall
when soil resources are most available. 相似文献
7.
M. Zunzunegui M. C. Díaz Barradas F. Aguilar F. Ain Lhout A. Clavijo F. García Novo 《Plant and Soil》2002,247(2):271-281
The relationship between water availability and plant growth response in Halimium halimifolium (L.) Willk throughout two years with contrasted precipitation (300 and 850 mm) was examined by measuring vegetative growth and midday leaf water potential in four sandy soil sites with different water availability in Doñana National Park, Spain. H. halimifolium, Cistaceae is mostly restricted to sandy substrates close to coastal Mediterranean areas. At Doñana National Park this species is the main component of stable sand vegetation. Vegetative growth started in March, ending in July. The maximum shoot elongation rate (110 mm/year) and number of branches (8.3 branches/year) occurred in plants growing in the most hygrophytic site (MN) in both the wet and dry years. Plants at this site exhibited higher midday water potentials throughout the year. In contrast, the minimum shoot elongation rate (40 mm/year) and midday water potential (–4.0 MPa) occurred in Monte Intermedio plants (MI) in the dry year, although the water table was shallower than in Monte Blanco (MB). In the wet year the minimum shoot and branch elongation were recorded in MB. The number of leaves per branch for a single main shoot was higher (55 leaves/branch) in the driest area (MB), but these leaves had the smallest area. ANOVA showed significant differences in growth response and midday water potential between the four sites. A stepwise multiple linear regression showed that midday water potential, water table depth and monthly average temperature were the variables most closely associated with shoot elongation rate. We conclude that under severe dryness, the expected patterns of greater growth in sites with better water supply may differ from compared with the expected growth pattern in normal conditions. 相似文献
8.
Changes in drought response strategies with ontogeny in Quercus rubra: implications for scaling from seedlings to mature trees 总被引:1,自引:0,他引:1
We investigated scaling of physiological parameters between age classes of Quercus rubra by combining in situ field measurements with an experimental approach. In the in situ field study, we investigated changes
in drought response with age in seedlings, juveniles, and mature trees of Q. rubra. Throughout the particularly dry summer of 1995 and the unusually wet summer of 1996 in New England, we measured water potential
of leaves (ΨLeaf) and gas exchange of plants at three sites at the Harvard Forest in Petersham, Massachusetts. In order to determine what
fraction of the measured differences in gas exchange between seedlings and mature trees was due to environment versus ontogeny,
an experiment was conducted in which seedlings were grown under light and soil moisture regimes simulating the environment
of mature trees. The photosynthetic capacity of mature trees was three-fold greater than that of seedlings during the wet
year, and six-fold greater during the drought year. The seedling experiment demonstrated that the difference in photosynthetic
capacity between seedlings and mature trees is comprised equally of an environmental component (50%) and an ontogenetic component
(50%) in the absence of water limitation. Photosynthesis was depressed more severely in seedlings than in mature trees in
the drought year relative to the wet year, while juveniles showed an intermediate response. Throughout the drought, the predawn
leaf water potential (ΨPD) of seedlings became increasingly negative (–0.4 to –1.6 MPa), while that of mature trees became only slightly more negative
(–0.2 to –0.5 MPa). Again, juveniles showed an intermediate response (–0.25 to –0.8 MPa). During the wet summer of 1996, however,
there was no difference in ΨPD between seedlings, juveniles and mature trees. During the dry summer of 1995, seedlings were more responsive to a major rain
event than mature trees in terms of ΨLeaf , suggesting that the two age classes depend on different water sources. In all age classes, instantaneous measurements of
intrinsic water use efficiency (WUEi), defined as C assimilation rate divided by stomatal conductance, increased as the drought progressed, and all age classes
had higher WUEi during the drought year than in the wet year. Mature trees, however, showed a greater ability to increase their WUEi in response to drought. Integrated measurements of WUE from C isotope discrimination (Δ) of leaves indicated higher WUE in
mature trees than juveniles and seedlings. Differences between years, however, could not be distinguished, probably due to
the strong bias in C isotope fractionation at the time of leaf production, which occurred prior to the onset of drought conditions
in 1995. From this study, we arrive at two main conclusions:
Received: 14 July 1999 / Accepted: 10 January 2000 相似文献
9.
Yvonne Eva-Maria Barbara Bohr Peggy Giertz Yedidya Rakotomalala Ratovonamana Jörg Ulrich Ganzhorn 《International journal of primatology》2011,32(4):901-913
Climate change will impose new constraints on the distribution of species through desertification. Small-scale endemists common
in biodiversity hotspots such as Madagascar are especially threatened. Among them are the gray-brown mouse lemurs (Microcebus griseorufus), which occupy the driest habitats in Madagascar of all Microcebus spp. We studied impacts of aridity on this species to identify critical factors for distributional limits. Accordingly, we compared
populations of 2 adjacent habitats that differ in their humidity levels. We found that the more humid habitat provided more
high-quality food and maintained a higher population density of Microcebus griseorufus, with individuals in better condition compared to the drier habitat. At the end of the wet, but not in the dry season, Microcebus griseorufus adjusted its home range size to local food plant density, which indicates that individuals optimize food intake in the wet
season to prepare for the dry season. We found a negative exponential relationship between food plant density and home range
size, which suggests an upper limit for the size of home ranges. According to this relationship, individuals from the drier
habitat could not compensate for reduced food availability by enlarging their home range beyond this threshold. Thus, in case
of declining food availability during the wet season due to a generally drier climate, individuals will not be able to extend
their home ranges to include more food resources, and hence to accumulate enough fat reserves for the dry season. In consequence,
they will have to migrate toward more mesic refugia. Migration, however, requires habitat connectivity, which is scarce in
Madagascar’s largely anthropogenic and heavily fragmented landscape. Our data suggest that upper limits in home range sizes
can limit a species’ ability to adapt to increasing aridity. 相似文献
10.
Summary Eight Hawaiian Dubautia species grow in habitats as varied as exposed lava, dry scrub, mesic forest, wet forest, and bog. These species also differ in diploid chromosome number, with four species having 13 pairs of chromosomes and four species having 14 pairs. This ecological and chromosomal variation is paralleled by significant interspecific variation in tissue elastic properties. The four 13-paired species from dry habitats exhibit significantly lower tissue elastic moduli near full hydration (E
i) than the four 14-paired species from mesic to wet habitats. Values of E
i range from 2 to 4 MPa among the former species and from 9 to 18 MPa among the latter species. The turgor dependence of the elastic modulus also differs markedly between the two groups of species. As a result of these differences in tissue elastic properties, the capacity for maintaining high turgor pressures as tissue water content decreases is much greater in the 13-paired species from dry habitats than in the 14-paired species from mesic to wet habitats. These results indicate that the evolutionary diversification of the Dubautia species has been accompanied by a significant degree of change at the physiological level. 相似文献
11.
The ability to appropriately modify physiological and morphological traits in response to temporal variation should increase
fitness. We used recombinant hybrid plants generated by crossing taxa in the Piriqueta caroliniana complex to assess the effects of individual leaf traits and trait plasticities on growth in a temporally variable environment.
Recombinant hybrids were used to provide a wide range of trait expression and to allow an assessment of the independent effects
of individual traits across a range of genetic backgrounds. Hybrid genotypes were replicated through vegetative propagation
and planted in common gardens at Archbold Biological Station in Venus, Florida, where they were monitored for growth, leaf
morphological characters, and integrated water use efficiency (WUE) (C isotope ratio; δ13C) for two successive seasons. Under wet conditions only leaf area had significant effects on plant growth, but as conditions
became drier, growth rates were greatest in plants with narrow leaves and higher trichome densities. Plants with higher WUE
exhibited increased growth during the dry season but not during the wet season. WUE during the dry season was increased for
plants with smaller, narrower leaves that had higher trichome densities and increased reflectance. Examination of alternative
path models revealed that during the dry season leaf traits had significant effects on plant growth only through their direct
effects on WUE, as estimated from δ13C. Over the entire growing season, plants with a greater ability to produce smaller and narrower leaves with higher trichome
densities in response to reduced water availability had the greatest growth rate. These findings suggest that plants making
appropriate changes to leaf morphology as conditions became dry had increased WUE, and that the ability to adjust leaf phenotypes
in response to environmental variation is a mechanism by which plants increase fitness. 相似文献
12.
Modulation of relative growth rate and its components by water stress in Mediterranean species with different growth forms 总被引:7,自引:0,他引:7
Effects of water availability on seedling growth were analysed in eight Mediterranean species naturally occurring in the Balearic
Islands. Seedlings were grown outdoors during summer under two irrigation treatments: field capacity and 35% of field capacity.
The relative growth rate (RGR) strongly depended on the growth form, from highest values in herbs to lowest in woody perennials.
The main component associated with interspecific variation in RGR was the specific leaf area (SLA), and a quantitative grouping
of the different growth forms appeared along the regression line between both parameters. The slow-growing species, i.e. woody
perennial shrubs, had the lowest SLA and the fast-growing perennial herbs, the highest, while woody semi-deciduous shrubs
appeared intermediate. Decreases in RGR due to water stress were analysed in terms of the relative contribution of the leaf
mass ratio (LMR), SLA and the net assimilation rate (NAR). Pooling all species, the decrease in RGR caused by water deficit
was mainly explained by decreases in SLA. However, this general pattern was strongly dependent of growth form. Thus, in the
woody perennial plants, the decrease in RGR was accompanied by a three-fold decrease in NAR which, however, increased in perennial
herbs. SLA increased with decreasing water supply in woody perennial plants, and decreased in woody semi-deciduous shrubs
and perennial herbs. Finally, decreases in LMR partly explained decreases in RGR in perennial herbs and woody perennial shrubs.
This different response of the different growth forms may reflect differences in seedling adaptation and surviving strategies
to drought periods. 相似文献
13.
Jinhuan Liu Dehui Zeng Don Koo Lee Zhiping Fan Lei Zhong 《Frontiers of Biology in China》2008,3(3):332-337
Six leaf traits, i.e., fresh mass (FM), dry mass (DM), leaf dry matter content (DMC), area (AR), specific leaf area (SLA)
and thickness (TH) from 23 plant species in the southeastern Keerqin Sandy Lands, China were measured. The results show that
leaf traits of herbs were more diversified than those of shrubs and trees and average SLA tended towards a decreasing trend
from herbs to shrubs to trees. On the contrary, DMC and DM show an upward trend from herbs to shrubs to trees. No apparent
difference was found in TH. Except forDMand TH, there were significant variations in SLA and DMC among three different growth
forms. Moreover, a significant correlation was found between SLA and DMC. It is concluded that SLA and DMC could be used to
predict species position along a resource use gradient.
__________
Translated from Chinese Journal of Ecology, 2006, 25: 921–925 [译自: 生态学杂志] 相似文献
14.
We tested the hypothesis that life forms (trees, shrubs, forbs, and mosses; deciduous or evergreen) can be used to group
plants with similar physiological characteristics. Carbon isotope ratios (δ13C) and carbon isotope discrimination (Δ) were used as functional characteristics because δ13C and Δ integrate information about CO2 and water fluxes, and so are useful in global change and scaling studies. We examined δ13C values of the dominant species in three boreal forest ecosystems: wet Picea mariana stands, mesic Populus tremuloides stands, and dry Pinus banksiana stands. Life form groups explained a significant fraction of the variation in leaf carbon isotope composition; seven life-form
categories explained 50% of the variation in δ13C and 42% of the variation in Δ and 52% of the variance not due to intraspecific genetic differences (n=335). The life forms were ranked in the following order based on their values: evergreen trees<deciduous trees=evergreen
and deciduous shrubs=evergreen forbs<deciduous forbs=mosses. This ranking of the life forms differed between deciduous (Populus) and evergreen (Pinus and Picea) ecosystems. Furthermore, life forms in the Populus ecosystem had higher discrimination values than life forms in the dry Pinus ecosystem; the Picea ecosystem had intermediate Δ values. These correlations between Δ and life form were related to differences in plant stature
and leaf longevity. Shorter plants had lower Δ values than taller plants, resulting from reduced light intensity at lower
levels in the forest. After height differences were accounted for, deciduous leaves had higher discrimination values than
evergreen leaves, indicating that deciduous leaves maintained higher ratios of intracellular to ambient CO2 (c
i/c
a) than did evergreen leaves in a similar environment within these boreal ecosystems. We found the same pattern of carbon isotope
discrimination in a year with above-average precipitation as in a year with below-average precipitation, indicating that environmental
fluctuations did not affect the ranking of life forms. Furthermore, plants from sites near the northern and southern boundaries
of the boreal forest had similar patterns of discrimination. We concluded that life forms are robust indicators of functional
groups that are related to carbon and water fluxes within boreal ecosystems.
Received: 15 April 1996 / Accepted: 16 November 1996 相似文献
15.
Teresa Navarro Jalal El Oualidi Mohammed Sghir Taleb Virginia Pascual Baltasar Cabezudo 《Flora》2009,204(9):658-672
This study describes the dispersal traits and dispersal patterns of 51 perennial plant species belonging to 19 families in an oro-Mediterranean thorn cushion plant formation on the High Atlas, Morocco. Diaspore type, mass, number, antitelechoric mechanisms and dispersal time were studied with respect to growth forms, dispersal modes and spatial dispersal. Species spanned 105 range of diaspore mass, which coincided with those found in other high mountain regions. Diaspore mass was significantly higher in trees and shrubs than in semi-shrubs and perennial herbs. Barochorous and zoochorous species are more likely to have heavy diaspores, whereas anemochorous and ballistic species have a medium diaspore mass and semachorous and ombro-hydrochorous species have low diaspore mass. Diaspore number was significantly higher in trees and shrubs than in semi-shrubs and perennial herbs. The barochorous, ombro-hydrochorous and zoochorous species tended to produce higher diaspore numbers than species with other dispersal modes. Bradyspory was well-developed by trees and large shrubs dispersed by biotic vectors. Synaptospermy was represented by its long dispersal component. Myxospermy was significantly associated with semi-shrubs and perennial herbs with restricted spatial dispersal. It seems that ombro-hydrochory combined with myxospermy and a high number of light seeds is an efficient mechanism that ensures successful establishment of the most typical and endemic thorn cushion plant species, such as Alyssum, Vella and Ormenis. In our study area, the highest dispersal availability was synchronized with the dry summer season (July–August) and the beginning of the rainy months (September). The dispersal peak for the wind-dispersed species, which is the most effective primary dispersal mode, occurs during the dry season, while dispersal for the biotic-dispersed species takes place throughout the year. 相似文献
16.
Manuel T. Lerdau N. Michele Holbrook Harold A. Mooney Paul M. Rich Julie L. Whitbeck 《Oecologia》1992,92(2):166-171
Summary We investigated relationships between light availability, diel acid fluctuation, and resource storage in the arborescent cactus Opuntia excelsa growing in western Mexico. We compared canopy and understory individuals from a deciduous forest as well as open-grown plants of the same approximate size as those in the understory. During the wet season light availability and daily fluctuations in titratable acidity (an index of carbon uptake) were lower in the understory than in unshaded habitats. In the dry season all plants had reduced levels of acid fluctuation, with the smallest individuals, regardless of habitat, showing the greatest reduction. These data suggest that light availability in the forest understory constrains carbon assimilation during the wet season, but that a factor associated with plant size, possibly water status, limits carbon gain during the dry season. Plants in all habitats remained physiologically active for at least five months into the dry season. We suggest that this was possible due to the maintenance of constant concentrations of water and nitrogen in the photosynthetically active chlorenchyma. Parenchyma in terminal cladodes showed a different seasonal pattern of resource storage; water content and nitrogen concentration were reduced from the wet to the dry season in the parenchyma. Using the parenchyma to supply photosynthetic tissues during times of reduced resource availability allows O. excelsa to assimilate carbon during times of the year when most other trees in the forest are leafless. 相似文献
17.
喀斯特季节性雨林植物叶片碳同位素组成及水分利用效率 总被引:1,自引:0,他引:1
研究喀斯特季节性雨林不同生境代表性树种及同一树种不同生境下叶片δ13C值及水分利用效率(WUE),丰富喀斯特季节性雨林物种生态位分化及物种共存理论,可为喀斯特地区石漠化治理树种选择及配置提供参考.结果表明: 喀斯特季节性雨林树种叶片δ13C值的范围为-34.13‰~-29.69‰,平均值为(-31.40±1.19)‰,WUE的范围为9.08~58.76 μmol·mol-1,均值为41.79 μmol·mol-1,低于更高纬度的亚热带和暖温带森林,但高于更低纬度的热带雨林和同一纬度的非喀斯特季节性雨林;从洼地到山顶,随着干旱指数的增加,不同生境代表性树种的水分利用效率逐渐增大;同一树种δ13C值和WUE也是从洼地到山顶逐渐增高.树种水分利用效率除了与气候等因子相关外,还与植物所处生境的地质背景、水分可利用性相关.同一气候条件下,喀斯特区植物的水分利用效率要高于非喀斯特区、干旱生境植物的水分利用效率高于湿润生境,说明不同的水分利用效率是喀斯特地区植物适应不同生境、实现多物种共存的策略之一. 相似文献
18.
Mediterranean-type climate (MTC) regions around the world are notable for cool, wet winters and hot, dry summers. A dominant vegetation type in all five MTC regions is evergreen, sclerophyllous shrubland, called chaparral in California. The extreme summer dry season in California is moderated by a persistent low-elevation layer of marine fog and cloud cover along the margin of the Pacific coast. We tested whether late dry season water potentials (Ψ(min)) of chaparral shrubs, such as Arctostaphylos species in central California, are influenced by this coast-to-interior climate gradient. Lowland coastal (maritime) shrubs were found to have significantly less negative Ψ(min) than upland interior shrubs (interior), and stable isotope (δ(13)C) values exhibited greater water use efficiency in the interior. Post-fire resprouter shrubs (resprouters) had significantly less negative Ψ(min) than co-occurring obligate seeder shrubs (seeders) in interior and transitional chaparral, possibly because resprouters have deeper root systems with better access to subsurface water than shallow-rooted seeders. Unexpectedly, maritime resprouters and seeders did not differ significantly in their Ψ(min), possibly reflecting more favorable water availability for shrubs influenced by the summer marine layer. Microclimate and soil data also suggest that maritime habitats have more favorable water availability than the interior. While maritime seeders constitute the majority of local Arctostaphylos endemics, they exhibited significantly greater vulnerability to xylem cavitation than interior seeders. Because rare seeders in maritime chaparral are more vulnerable to xylem cavitation than interior seeders, the potential breakdown of the summer marine layer along the coast is of potential conservation concern. 相似文献
19.
Patchy desert shrubs magnify the horizontal heterogeneities of carbon source and nutrient availability in an arid ecosystem,
significantly affecting the abundance and activity of the soil microbial community. Since each shrub species develops special
ecophysiological adaptations to the extreme harsh desert environments, previous studies elucidated that the effects of perennial
shrubs on microbial diversity are unequal. The aim of the present study, conducted in the Negev Desert, Israel, was to illustrate
the vertical changes of soil microbial community functionality in the root zone of perennial shrubs. Soil samples were collected
from the 0–50 cm depth at 10-cm intervals under the canopy of Zygophyllum dumosum, Hammada scoparia, and from the open spaces between them, in the wet and dry seasons. Soil moisture and organic matter exhibited a significant
(P < 0.001) plant and depth dependence. The mean basal respiration rates and microbial biomass in soils collected beneath perennial
shrubs were relatively higher than the control during the wet season, however, a contrasting trend was observed at some soil
depths during the dry season. Relatively high abundance and activity of aromatic and carboxylic acid utilizers were observed
in the vicinity of perennial shrubs, and the values recorded during the dry season were generally higher than the corresponding
values during the wet season. In addition, a “mirror effect” in vertical changes of the community-level physiological profile
was observed between Z. dumosum and H. scoparia. This study demonstrated the stratification of the functional aspects in soils under the canopy of perennial shrubs, thus
indicating that the scattered distribution of vegetation not only causes horizontal heterogeneities of the microbial community
in an arid system, but also that the ecophysiological adaptations developed by xerophytes regulate the abundance and saprotrophic
functionality of microorganisms in the root zone. 相似文献
20.
Sylvain Delagrange Catherine Potvin Christian Messier Lluis Coll 《Trees - Structure and Function》2008,22(3):337-349
To improve establishment yield and carbon accumulation during reforestation, analyses of species adaptations to local environments
are needed. Here we measured, at the individual scale, links between biomass accumulation and multiple-level tree traits:
biomass partitioning, crown morphology and leaf physiology. The study was carried out on one- and three-year-old individuals
of five tropical tree species assigned to pioneer (P) or non-pioneer (NP) functional groups. Among the species, Cedrela odorata, Luehea seemannii and Hura crepitans showed the greatest biomass accumulation. On our seasonally dry site, species performance during the first year was dependent
on a greater investment in above-ground foraging, while performance after three years was mainly related to water relations.
However, large biomass accumulations were not simply associated with an efficient water use but also with contrasting water
uses, based on inter-specific relationships. Generally, greater carbon isotope discrimination (Δleaf) was related to greater allocation to roots. Species with high Δleaf generally showed high leaf potential nitrogen use efficiency (PNUE), suggesting that lower water use efficiency (WUE) increases
the efficiency of photosynthetically active N. Also, PNUE was negatively correlated to leaf mass per area (LMA), implying
that photosynthetically active N is diluted as total leaf mass increases. Finally, no distinction in measured traits, including
biomass accumulation, was observed between the two functional groups. 相似文献