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101.
Summary The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects. 相似文献
102.
Relative importance of photosynthetic traits and allocation patterns as correlates of seedling shade tolerance of 13 tropical trees 总被引:34,自引:0,他引:34
Kaoru Kitajima 《Oecologia》1994,98(3-4):419-428
Among 13 tropical tree species on Barro Colorado Island, species with high seedling mortality rates during the first year in shade had higher reltive growth rates (RGR) from germination to 2 months in both sun (23% full sun) and shade [2%, with and without lowered red: far red (R:FR) ratio] than shade tolerant species. Species with higher RGR in sun also had higher RGR in shade. These interspecific trends could be explained by differences in morphological traits and allocation paterns among species. Within each light regime, seedlings of shade-intolerant species had lower root: shoot ratios, higher leaf mass per unit area, and higher leaf area ratios (LAR) than shade tolerant species. In contrast, leaf gas exchange characteristics, or acclimation potential in these traits, had no relationship with seedling mortality rates in shade. In both shade tolerant and intolerant species, light saturated photosynthesis rates, dark respiration, and light compensation points were higher for sungrown seedlings than for shade-grown seedlings. Differences in R:FR ratio in shade did not affect gas exchange, allocation patterns, or growth rates of any species. Survival of young tree seedlings in shade did not depend on higher net photosynthesis or biomass accumulation rates in shade. Rather, species with higher RGR died faster in shade than species with lower RGR. This trend could be explained if survival depends on morphological characteristics likely to enhance defense against herbivores and pathogens, such as dense and tough leaves, a well-established root system, and high wood density. High construction costs for these traits, and low LAR as a consequence of these traits, should result in lower rates of whole-plant carbon gain and RGR for shade tolerant species than shade-intolerant species in shade as well as in sun. 相似文献
103.
Deborah Faria Mateus Luís Barradas Paciencia Marianna Dixo Rudi Ricardo Laps Julio Baumgarten 《Biodiversity and Conservation》2007,16(8):2335-2357
The traditional shade cacao plantations (cabrucas) of southern Bahia, Brazil, are biologically rich habitats, encompassing
many forest-dwelling species. However, a critical question for the conservation management of this specific region, and the
highly fragmented Atlantic forest in general, is to what extent the conservation value of cabrucas relies on the presence
of primary forest habitat in the landscape. We investigated the relative importance of cabrucas and forests for the conservation
of five diverse biological groups (ferns, frogs, lizards, birds and bats) in two contrasting landscapes in southern Bahia,
one dominated by forest with some interspersed cabrucas, and one dominated by cabrucas with interspersed forest fragments.
The community structure (richness, abundance and diversity) of all biological groups differed between cabrucas and forests,
although these differences varied among groups. A high number of forest species was found in the cabrucas. However, there
were pronounced differences between the two landscapes with regard to the ability of cabrucas to maintain species richness.
Irrespective of the biological group considered, cabrucas located in the landscape with few and small forest fragments supported
impoverished assemblages compared to cabrucas located in the landscape with high forest cover. This suggests that a greater
extent of native forest in the landscape positively influences the species richness of cabrucas. In the landscape with few
small forest fragments interspersed into extensive areas of shade cacao plantations, the beta diversity of birds was higher
than in the more forested landscape, suggesting that forest specialist species that rarely ventured into cabrucas were randomly
lost from the fragments. These results stress both the importance and the vulnerability of the small forest patches remaining
in landscapes dominated by shade plantations. They also point to the need to preserve sufficient areas of primary habitat
even in landscapes where land use practices are generally favorable to the conservation of biodiversity. 相似文献
104.
Nearly 40% of the remaining Atlantic Forest in southern Bahia state, Brazil, is a rustic agroforest of cacao (Theobroma cacao). These traditional shade plantations, locally known as ‘cabrucas’, are habitats for forest dwelling species. Here we investigated
the potential role of this traditional crop as a support for bat assemblages in southern Bahia, establishing the extent to
which the bat community structure found in this agricultural system is influenced by the proximity of forest tracts. We compared
the bat community attributes (richness, diversity and dominance) and species-level response (capture frequency) between native
forest tracts and shade cacao plantations located in two distinct landscapes, which varied in total amount of forest (patch
sizes and total forested area) and in their proximity to forest tracts. The cabrucas contiguous to forest tracts showed a
rich and abundant bat community, with samples showing capture rates, species richness, diversity and evenness significantly
higher than those reported for forest tracts. This situation changes, however, when shade plantations are located at some
distance from forest tracts ( > 1000 m). Bat communities in these isolated cabrucas are less diverse than those found in forests
and nearby cabrucas, but in both cases, species usually associated with pristine habitats were found. These findings suggest
that cabrucas per se are not forest surrogates, and their potential to harbor forest dwelling bat species is closely linked with the existence
of nearby forest tracts that may act as a source for species populations. Therefore, the entire landscape should be considered
for management, taking into account that maintenance of cabrucas together with the preservation and restoration of forest
patches is probably direly needed if one wishes to conserve the bat diversity in southern Bahia for the long term. 相似文献
105.
106.
Contrasting modes of light acclimation in two species of the rainforest understory 总被引:10,自引:0,他引:10
In tropical rainforests, the increased light associated with the formation of treefall gaps can have a critical impact on
the growth and survivorship of understory plants. Here we examine both leaf-level and whole-plant responses to simulated light
gap formation by two common shade-tolerant shrubs, Hybanthus prunifolius and Ouratea lucens. The species were chosen because they differed in leaf lifespans, a trait that has been correlated with a number of leaf-
and plant-level processes. Ouratea leaves typically live about 5 years, while Hybanthus leaves live less than 1 year. Potted plants were placed in the understory shade for 2 years before transfer to a light gap.
After 2 days in high light, leaves of both species showed substantial photoinhibition, including reduced CO2 fixation, F
v/F
m and light use efficiency, although photoinhibition was most severe in Hybanthus. After 17 days in high light, leaves of both species were no longer photoinhibited. In response to increased light, Ouratea made very few new leaves, but retained most of its old leaves which increased photosynthetic capacity by 50%. Within a few
weeks of transfer to high light, Hybanthus had dropped nearly all of its shade leaves and made new leaves that had a 2.5-fold greater light-saturated photosynthetic
rate. At 80 days after transfer, the number of new leaves was 4.9-fold the initial leaf number. After 80 days in high light, Hybanthus had approximately tenfold greater productivity than Ouratea when leaf area, photosynthetic capacity, and leaf dark respiration rate were all taken into account. Although both species
are considered shade tolerant, we found that their growth responses were quite different following transfer from low to high
light. The short-lived Hybanthus leaves were quickly dropped, and a new canopy of sun leaves was produced. In contrast, Ouratea showed little growth response at the whole-plant level, but a greater ability to tolerate light stress and acclimate at the
leaf level. These differences are consistent with predictions based on leaf lifespan and are discussed within the context
of other traits associated with shade-tolerant syndromes.
Received: 25 March 1999 / Accepted: 16 August 1999 相似文献
107.
遮荫处理对梅叶冬青叶片形态、光合特性和生长的影响 总被引:1,自引:0,他引:1
为了解遮荫环境对梅叶冬青(Ilex asprella)生长和光合特性的影响,采用遮荫网的方法模拟85%、56%和全光照等3种光照环境,研究了遮荫对其生长、光合参数以及生物量等的影响。结果表明,经一年遮荫处理后,梅叶冬青的叶绿素a、b和叶绿素总量都随着遮荫强度的增加而显著增高,胡萝卜素含量则显著降低。与对照相比,56%遮荫处理显著提高梅叶冬青的最大净光合速率和光饱和点,分别提高了17.6%和25.2%,但是85%遮阴处理则显著降低最大净光合速率和光饱和点,分别降低了18.2%和24.1%,两种遮荫处理均显著降低了光补偿点。叶长、叶宽、比叶面积、单片叶面积和叶片含水量均随着遮荫强度的增加而显著增加,而叶片厚度则显著减小。遮荫处理明显抑制整株生物量增长,减小根冠比,但是株高、冠幅和径向生长随遮荫处理时间不同而有所变异。因此,梅叶冬青有耐荫偏阳的特性,在林下种植时需及时调控乔冠层的透光率,一般应大于44%。 相似文献
108.
We compared the CO2- and light-dependence of photosynthesis of four tree species (Acer rubrum, Carya glabra, Cercis canadensis, Liquidambar styraciflua) growing in the understory of a loblolly pine plantation under ambient or ambient plus 200 μl l–1 CO2. Naturally-established saplings were fumigated with a free-air CO2 enrichment system. Light-saturated photosynthetic rates were 159–190% greater for Ce. canadensis saplings grown and measured under elevated CO2. This species had the greatest CO2 stimulation of photosynthesis. Photosynthetic rates were only 59% greater for A. rubrum saplings under CO2 enrichment and Ca. glabra and L. styraciflua had intermediate responses. Elevated CO2 stimulated light-saturated photosynthesis more than the apparent quantum yield. The maximum rate of carboxylation of ribulose-1,5-bisphosphate
carboxylase, estimated from gas-exchange measurements, was not consistently affected by growth in elevated CO2. However, the maximum electron transport rate estimated from gas- exchange measurements and from chlorophyll fluorescence,
when averaged across species and dates, was approximately 10% higher for saplings in elevated CO2. The proportionately greater stimulation of light-saturated photosynthesis than the apparent quantum yield and elevated rates
of maximum electron transport suggests that saplings growing under elevated CO2 make more efficient use of sunflecks. The stimulation of light-saturated photosynthesis by CO2 did not appear to correlate with shade-tolerance ranking of the individual species. However, the species with the greatest
enhancement of photosynthesis, Ce. canadensis and L. styraciflua, also invested the greatest proportion of soluble protein in Rubisco. Environmental and endogenous factors affecting N partitioning
may partially explain interspecific variation in the photosynthetic response to elevated CO2.
Received: 16 February 1999 / Accepted: 30 August 1999 相似文献
109.
Photosynthetic sunfleck utilization potential of understory saplings growing under elevated CO<Subscript>2</Subscript> in FACE 总被引:3,自引:0,他引:3
Few studies have evaluated elevated CO2 responses of trees in variable light despite its prevalence in forest understories and its potential importance for sapling
survival. We studied two shade-tolerant species (Acer rubrum, Cornus florida) and two shade-intolerant species (Liquidambar styraciflua, Liriodendron tulipifera) growing in the understory of a Pinus taeda plantation under ambient and ambient+200 ppm CO2 in a free air carbon enrichment (FACE) experiment. Photosynthetic and stomatal responses to artificial changes in light intensity
were measured on saplings to determine rates of induction gain under saturating light and induction loss under shade. We expected
that growth in elevated CO2 would alter photosynthetic responses to variable light in these understory saplings. The results showed that elevated CO2 caused the expected enhancement in steady-state photosynthesis in both high and low light, but did not affect overall stomatal
conductance or rates of induction gain in the four species. Induction loss after relatively short shade periods (<6 min) was
slower in trees grown in elevated CO2 than in trees grown in ambient CO2 despite similar decreases in stomatal conductance. As a result leaves grown in elevated CO2 that maintained induction well in shade had higher carbon gain during subsequent light flecks than was expected from steady-state
light response measurements. Thus, when frequent sunflecks maintain stomatal conductance and photosynthetic induction during
the day, enhancements of long-term carbon gain by elevated CO2 could be underestimated by steady-state photosynthetic measures. With respect to species differences, both a tolerant, A. rubrum, and an intolerant species, L. tulipifera, showed rapid induction gain, but A. rubrum also lost induction rapidly (c. 12 min) in shade. These results, as well as those from independent studies in the literature, show that induction dynamics
are not closely related to species shade tolerance. Therefore, it cannot be concluded that shade-tolerant species necessarily
induce faster in the variable light conditions common in understories. Although our study is the first to examine dynamic
photosynthetic responses to variable light in contrasting species in elevated CO2, studies on ecologically diverse species will be required to establish whether shade-tolerant and -intolerant species show
different photosynthetic responses in elevated CO2 during sunflecks. We conclude that elevated CO2 affects dynamic gas exchange most strongly via photosynthetic enhancement during induction as well as in the steady state.
Received: 1 April 1999 / Accepted: 16 August 1999 相似文献
110.
Leaf construction cost, nutrient concentration, and net CO2 assimilation of native and invasive species in Hawaii 总被引:10,自引:0,他引:10
To examine the predictability of leaf physiology and biochemistry from light gradients within canopies, we measured photosynthetic
light-response curves, leaf mass per area (LMA) and concentrations of nitrogen, phosphorus and chlorophyll at 15–20 positions
within canopies of three conifer species with increasing shade tolerance, ponderosa pine [Pinus ponderosa (Laws.)], Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and western hemlock [Tsuga heterophylla (Raf.) Sarg.]. Adjacent to each sampling position, we continuously monitored photosynthetically active photon flux density
(PPFD) over a 5-week period using quantum sensors. From these measurements we calculated FPAR: integrated PPFD at each sampling
point as a fraction of full sun. From the shadiest to the brightest canopy positions, LMA increased by about 50% in ponderosa
pine and 100% in western hemlock; Douglas fir was intermediate. Canopy-average LMA increased with decreasing shade tolerance.
Most foliage properties showed more variability within and between canopies when expressed on a leaf area basis than on a
leaf mass basis, although the reverse was true for chlorophyll. Where foliage biochemistry or physiology was correlated with
FPAR, the relationships were non-linear, tending to reach a plateau at about 50% of full sunlight. Slopes of response functions
relating physiology and biochemistry to ln(FPAR) were not significantly different among species except for the light compensation
point, which did not vary in response to light in ponderosa pine, but did in the other two species. We used the physiological
measurements for Douglas fir in a model to simulate canopy photosynthetic potential (daily net carbon gain limited only by
PPFD) and tested the hypothesis that allocation of carbon and nitrogen is optimized relative to PPFD gradients. Simulated
photosynthetic potential for the whole canopy was slightly higher (<10%) using the measured allocation of C and N within the
canopy compared with no stratification (i.e., all foliage identical). However, there was no evidence that the actual allocation
pattern was optimized on the basis of PPFD gradients alone; simulated net carbon assimilation increased still further when
even more N and C were allocated to high-light environments at the canopy top.
Received: 12 August 1998 / Accepted: 25 March 1999 相似文献