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1.
Adrian Ares Constance A. Harrington Thomas A. Terry Joseph M. Kraft 《Trees - Structure and Function》2008,22(5):603-609
The stable carbon (C) composition of tree rings expressed as δ13C, is a measure of intrinsic water-use efficiency and can indicate the occurrence of past water shortages for tree growth.
We examined δ13C in 3- to 5-year-old rings of Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) trees to elucidate if decreased water supply or uptake was a critical factor in the observed growth reduction
of trees competing with understory herb and shrub vegetation compared to those growing without competition. We hypothesized
that there would be no differences in δ13C of earlywood in trees growing in plots with competing vegetation and those in plots receiving complete vegetation control
during 5 years because earlywood formed early in the growing season when soil water was ample. We also hypothesized that δ13C in latewood which was formed during the later half of the growing season when precipitation was low, would be greater (less
negative) in trees in plots without vegetation control. We then separated early and latewood from rings for three consecutive
years and analyzed their δ13C composition. No significant differences in earlywood δ13C in years 3–5 were observed for trees in the two vegetation control treatments. δ13C of untreated latewood separated from wood cores was greater in 4- and 5-year-old rings of trees growing with competing vegetation
compared to trees growing without vegetation competition (i.e., −25.5 vs. −26.3‰ for year 4, and −26.1 vs. −26.8‰ for year
5). Results suggest that water shortages occurred in Douglas-fir trees on this coastal Washington site in the latewood-forming
portion of the growing season of years 4 and 5 in the no-vegetation control treatment. We also compared δ13C from untreated wood, crude cellulose extracted with the Diglyme–HCl method, and holocellulose extracted with toluene–ethanol
to see if the extraction method would increase the sensitivity of the analysis. δ13C values from the two extraction methods were highly correlated with those from untreated samples (r
2 = 0.97, 0.98, respectively). Therefore, using untreated wood would be as effective as using crude cellulose or holocellulose
to investigate δ13C patterns in young Douglas-fir. 相似文献
2.
M. Ohbo K. Katoh Y. Sasaki 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(5):305-309
Stimulatory effects of saturated fatty acids consisting of 4 (butyrate), 8 (octanoate), 12 (laurate) and 16 (palmitate) carbon
atoms, as well as acetylcholine on pancreatic amylase release were assessed in tissue segments isolated from sheep, rats,
hamsters, field voles and mice. The amount of amylase release induced by the fatty acids (1 μmol ⋅ l-1 to 10 mml ⋅ l-1) and by acetylcholine (10 nmol ⋅ l-1 to 100 μmol ⋅ l-1) increased in a concentration-dependent manner, and the maximum response in response to the fatty acids was obtained at the
maximal dose used. The maximum increase in amylase release in response to butyrate or octanoate was highly and significantly
(r=0.974, P<0.001) dependent on the log value of the mean body mass in the following order: sheep>rats>hamsters>field voles>mice. On
the other hand, the response to laurate and palmitate was variable among animal species. Addition of atropine (1.4 μmol ⋅ l-1) to the medium did not reduce the responses to octanoate stimulation, but significantly reduced acetylcholineinduced responses,
implying that the effects of the fatty acids were not mediated through activation of muscarinic acetylcholine receptors. Reduction
of calcium ion concentration in the medium significantly inhibited the responses induced by the fatty acids and acetylcholine,
suggesting that amylase release depends on extracellular calcium ions.
Accepted: 14 May 1996 相似文献
3.
Epibenthic brittle star assemblages were investigated on the northwestern Barents Sea shelf between 81° and 77°N in July
1991. At 9 drift stations in water depths between 80 and 360 m, series of 35–71 photographs, each depicting about 1 m2 of the seabed, were taken along transects of about 150- to 300-m length to assess abundances and spatial distribution patterns
of adult brittle stars (disc diameter ≥1 mm). Biomass values were derived by combining abundances with size-weight relationships
and size frequencies established using specimens from trawl catches. Six brittle star species were identified on the seabed
images. Ophiocten sericeum was the most abundant species on shallow shelf banks (≤100 m). Up to 2,800 individuals were counted on a single photograph;
median abundances per station ranged from 32 to 524 ind.m-2 and biomass from 0.3 to 5.0 g ash-free dry weight (AFDW) m-2. The spatial distribution along the transects (i.e. on the 100-m scale) was, however, extremely patchy. Disc diameters of
O. sericeum ranged between 1.6 mm and 15.4 mm. In deeper shelf habitats (>150 m), O. sericeum was rare or absent, and Ophiacantha bidentata dominated the brittle star fauna with median densities and biomasses of 2–49 ind.m-2 and 0.07–1.9 g AFDW m-2, respectively. Its disc diameters ranged from 2.9 to 14.4 mm. The other species (Ophiura sarsi, Ophiopholis aculeata, Ophioscolex glacialis, Ophiopleura borealis) occurred in distinctly lower numbers. Our findings provide further evidence that brittle stars dominate epibenthic communities
on Arctic shelves and locally reach very high abundances. Dense beds of Ophiocten sericeum seem to be a general phenomenon on high-Arctic shallow shelf banks.
Received: 30 March 1995/Accepted: 30 June 1995 相似文献
4.
为了解白头叶猴(Trachypithecus leucocephalus)的栖息地利用规律及其影响因素,2016年2月至2017年1月,采用瞬时扫描取样法对广西崇左白头叶猴国家级自然保护区一群白头叶猴的栖息地利用进行了研究。结果表明,白头叶猴对山体不同部位的利用存在显著性差异(χ2 =39.467,df=3,P<0.001),其中,对崖壁(56.75±9.55)%的利用比例最大,其次是对山坡(39.42±10.93)%和山顶(2.98±2.54)%的利用,而对山脚(0.84±1.47)%的利用频率最低。白头叶猴对不同微生境类型的利用存在差异(χ2=27.709,df=3,P<0.001),其中对乔木(49.37±12.31)%的利用比例最大,其次是裸岩(24.05±13.61)%,随后依次为藤本(15.48±8.01)%和灌木(10.87±5.45)%。白头叶猴主要在山坡上觅食,利用崖壁移动、休息,进行社会活动;主要利用裸岩进行社会活动,觅食、移动、休息主要发生在乔木上。从整体来看,白头叶猴在雨季对乔木的利用频率显著大于旱季(Z=-2.680,n=12,P=0.007);雨季在山坡觅食频率显著大于旱季(Z=-2.517,n=12,P=0.012),而在崖壁觅食频率刚好相反(Z=-2.842,n=12,P=0.004);白头叶猴雨季在乔木休息的频率显著大于旱季(Z=-2.355,n=12,P=0.019)。白头叶猴对栖息地的利用受到温度的影响。白头叶猴对乔木的总体利用频率随着平均温度的升高而增加(r=0.664,n=12,P=0.018);觅食时,对崖壁、裸岩的利用频率均与平均温度成负相关关系(崖壁:r=-0.685,n=12,P=0.014;裸岩:r=-0.600,n=12,P=0.039);休息时,对乔木的利用频率与平均温度呈正相关关系(r=0.650,n=12,P=0.022)。不同季节,白头叶猴对栖息地的利用方式不同。白头叶猴的栖息地利用模式可能是在觅食利益和捕食风险之间作出的权衡,并受到环境温度的影响。 相似文献
5.
Lianas, or woody climbing plants, are a major constituent of seasonally dry tropical forests, and are thought to impact negatively
their host trees. In this study we evaluated whether liana presence was associated with reduced leaf water potentials and
growth in adult Senna multijuga trees during the dry season in a lowland Bolivian forest. We used leaf water potentials in trees as a first approach to assess
trees’ water status, under the assumption that leaf water potentials become more negative when water losses (via transpiration)
exceed gains (by uptake). We measured relative growth in girth at 1.5 m height (gbh) to quantify tree growth. At the beginning
of the 1996 dry season (early June), we selected 20 S. multijuga trees 10–20 cm dbh, and measured their gbh. We also recorded pre-dawn and mid-day leaf water potentials in these trees. In
ten experimental trees all lianas were then cut, while the remaining trees were used as controls. Pre-dawn and mid-day water
potentials were re-measured 1 day after liana-cutting, and then every week in all trees for 1 month and then at 3 and 5 months,
until the beginning of the next rainy season (November); gbh was measured again in July 1997 to estimate relative growth rate.
Liana removal was associated with less negative pre-dawn (–0.3 vs –0.4 MPa) and mid-day (–0.5 vs –0.7 MPa) water potentials
in trees during the dry season. This difference appeared as early as 1 day after cutting, and disappeared once the rainy season
began. Liana-cut trees grew more (0.4 mm/mm year) than liana-uncut trees (0.2 mm/mm year). These findings suggest that lianas
may interfere with water availability to these trees during the dry season, and may also hinder tree growth.
Received: 16 November 1999 / Accepted: 23 March 2000 相似文献
6.
The environmental signals of stable carbon isotope in various tree-ring components of Pinus tabulaeformis 总被引:1,自引:0,他引:1
Linmin Ma Rena Duolikun Zhao Jianfu Giacomo Lorenzini 《Trees - Structure and Function》2011,25(3):435-442
Chinese pine (Pinus tabulaeformis) trees were sampled in the Helan Mountain, northwest China. The stable carbon isotope (δ13C) values of whole wood, holocellulose and alpha-cellulose in tree rings over 30 years (1968–1997) were measured to study
the δ13C response of different tree-ring components to past environmental change. There were obvious differences in the δ13C values of the three components. The Pearson correlation coefficient between the δ13C of alpha-cellulose and that of holocellulose was 0.547 (ρ < 0.01); between alpha-cellulose and whole wood, the coefficient was −0.126 (ρ > 0.10); between holocellulose and whole wood, the coefficient was −0.056. Correlation function analyses indicated that the
δ13C content of tree-ring alpha-cellulose correlated strongly with the average temperature from June to August (r = 0.427, ρ < 0.05), more than that of holocellulose (0.324, ρ < 0.10) or total wood (−0.245, ρ > 0.10). Significant correlations were observed between δ13C of tree-ring alpha-cellulose and the precipitation from the current year’s February to July (r = −0.514, ρ < 0.01) that were much higher than that of holocellulose (−0.481, ρ < 0.05) or total wood (−0.249, ρ > 0.10). A significant correlation (−0.545, ρ < 0.01) was also found between the ring width and the δ13C residual chronologies. These results suggest that more past environmental information is retained in the δ13C of tree-ring alpha-cellulose. Thus, the δ13C of alpha-cellulose of tree rings is the most suitable among the studied parameters for reconstructing the past climatic
conditions during the growing season. The δ13C values of other organic compounds in Pinus tabulaeformis xylem were affected by the external environment after carbon was fixed from the atmosphere. 相似文献
7.
Alcaligenes eutrophus JMP 134 was continuously (carbon-source-limited) grown on phenol to determine the maximum growth rates (μmax) as a function of the phenol assimilation pathways expressed. During growth on phenol as the sole source of carbon and energy,
an almost exclusive expression of the ortho cleavage pathway (catechol 1,2-dioxygenase) was observed at initially low growth rates. This allowed a μmax of 0.28 h-1. The induction of the meta cleavage pathway (catechol 2,3-dioxygenase), which appeared at around 0.25 h-1, resulted in a further increase in the growth rate to 0.40 h-1 after the enzyme activities of this pathway had been correspondingly expressed. Hence, two maximum growth rates, one for
the ortho and one for the meta cleavage pathway, exist for the growth of A. eutrophus JMP 134 on phenol. Growth on phenol was stimulated by formate, which served as an auxiliary energy source in this strain.
The simultaneous utilization of phenol and formate at a molar ratio of 1:5.2 resulted in an increase of the yield coefficient
from about 0.75 g dry mass/g phenol to 1.25 g/g. Furthermore, formate exerted a pronounced effect on the growth rate. At a
molar ratio of phenol to formate of 1:4.2, the growth rate was increased to 0.42 h-1, despite the exclusive induction of the ortho cleavage pathway. The meta cleavage pathway was expressed during growth on this substrate mixture at about 0.4 h-1. However, this did not enable a significant increase of the growth rate beyond 0.4 h-1. This is attributed to an exhaustion of the capacity for formate oxidation at this rate. The results are discussed with respect
to energy production capabilities when phenol is assimilated as an energy-deficient heterotrophic substrate.
Received: 13 November 1995/Received revision: 15 April 1996/Accepted: 22 April 1996 相似文献
8.
T. Matsunaga H. Sudo H. Takemasa Y. Wachi N. Nakamura 《Applied microbiology and biotechnology》1996,45(1-2):24-27
The cyanobacterium, Aphanocapsa halo-phytia MN-11, was immobilized in calcium alginate gel and coated on light-diffusing optical fibers (LDOF) for sulfated extracellular
polysaccharide production. Results indicated that sulfated extracellular polysaccharide production depends on the number of
immobilized cells and the light intensity. In addition, the production rate reached 116.0 mg (mg dry cells)-1 day-1 when the cells that were immobilized on LDOF were incubated under a light intensity of 1380 cd sr m-2 at a cell concentration of 1.0×108 cells/cm3 gel. Cells immobilized on LDOF produced about ten times more sulfated extracellular polysaccharide than those immobilized
in calcium alginate beads only (11.7 mg(mg dry cells)-1 day-1).
Received: 31 March 1995/Revised last revision 12 June 1995/Accepted 26 July 1995 相似文献
9.
Soil Nutrients Limit Fine Litter Production and Tree Growth in Mature Lowland Forest of Southwestern Borneo 总被引:1,自引:0,他引:1
Efforts to improve models of terrestrial productivity and to understand the function of tropical forests in global carbon
cycles require a mechanistic understanding of spatial variation in aboveground net primary productivity (ANPP) across tropical
landscapes. To help derive such an understanding for Borneo, we monitored aboveground fine litterfall, woody biomass increment
and ANPP (their sum) in mature forest over 29 months across a soil nutrient gradient in southwestern Kalimantan. In 30 (0.07 ha)
plots stratified throughout the watershed (∼340 ha, 8–190 m a.s.l.), we measured productivity and tested its relationship
with 27 soil parameters. ANPP across the study area was among the highest reported for mature lowland tropical forests. Aboveground
fine litterfall ranged from 5.1 to 11.0 Mg ha−1 year−1 and averaged 7.7 ± 0.4 (mean ± 95 C.I.). Woody biomass increment ranged from 5.8 to 23.6 Mg ha−1 year−1 and averaged 12.0 ± 2.0. Growth of large trees (≥60 cm dbh) contributed 38–82% of plot-wide biomass increment and explained
92% of variation among plots. ANPP, the sum of these parameters, ranged from 11.1 to 32.3 Mg ha−1 year−1 and averaged 19.7 ± 2.2. ANPP was weakly related to fine litterfall (r
2 = 0.176), but strongly related to growth of large trees at least 60 cm dbh (r
2 = 0.848). Adjusted ANPP after accounting for apparent “mature forest bias” in our sampling method was 17.5 ± 1.2 Mg ha−1 year−1.Relating productivity measures to soil parameters showed that spatial patterning in productivity was significantly related
to soil nutrients, especially phosphorus (P). Fine litterfall increased strongly with extractable P (r
2 = 0.646), but reached an asymptote at moderate P levels, whereas biomass increment (r
2 = 0.473) and ANPP (r
2 = 0.603) increased linearly across the gradient. Biomass increment of large trees was more frequently and strongly related to
nutrients than small trees, suggesting size dependency of tree growth on nutrients. Multiple linear regression confirmed the
leading importance of soil P, and identified Ca as a potential co-limiting factor. Our findings strongly suggest that (1)
soil nutrients, especially P, limit aboveground productivity in lowland Bornean forests, and (2) these forests play an important,
but changing role in carbon cycles, as canopy tree logging alters these terrestrial carbon sinks.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
A small-scale, “no-use zone policy” has been implemented since 1992 at Eilat’s Coral Nature Reserve (Northern Red Sea). Six
years later, the status of this closed-to-the-public reef area was compared to two nearby open-to-the-public sites, by evaluating
populations of the scleractinian coral Stylophora pistillata in the strolling zone (0.5–1.5 m depth). Results from the open sites show that: (1) Live coral cover was three times lower
than at the closed site; (2) numbers of small colonies (recruits) were significantly higher than in the closed site, while
numbers of medium and large size colonies (geometric mean radius, rˉ>4.1 cm) per m2 were significantly lower; (3) maximum rˉ was almost half than that in the closed site (9.6 cm versus 16.7 cm); (4) average number of broken colonies was three times
higher than in the closed site; (5) significantly fewer colonies were partially dead. The latter result may reflect senescence
processes in the large colonies of the closed site. Although colony breakage is reduced, it appears that the “no-use zone”
policy is not sufficient for protecting small reef areas. The intense exploitation of Eilat’s coral reef by the tourist industry
requires’ in addition to the conventional protective measures, the initiation of novel management solutions such as reef restoration
by sexual and asexual recruits.
Accepted: 11 August 1999 相似文献
11.
Douglas-fir trees from 39 open-pollinated families at four test locations were assessed to estimate heritability of modulus of elasticity (MOE) and basic density. After trees were felled, sound velocity was measured on 4-m logs with the Director HM200. Disks were taken to estimate dry and green wood density; dynamic MOE was estimated as green density × (sound velocity)2. Heritability estimates of MOE (across-site h
2=0.55) were larger than those for total height (0.15) and diameter at breast height (DBH; 0.29), and similar to those for density (0.59). Negative genetic correlations were found for MOE with height (r
A=−0.30) and DBH (r
A=−0.51), and were similar to those found for density with height (r
A=−0.52) and DBH (r
A=−0.57). The partial correlations of height with MOE and density, while holding DBH constant, were positive, implying that the observed negative correlations between height and the wood properties were a function of the high positive correlation between height and DBH and the strong negative correlations between DBH and the wood properties. Taper [DBH/(height−1.4)] was found to be negatively associated with MOE. Selection for MOE may produce greater gains than selection for density because MOE had a larger coefficient of additive variation (9.6%) than density (5.1%). Conversely, selection for growth may have a more negative impact on MOE than density because of the greater genetic variation associated with MOE. Family mean correlations of the wood quality traits with stem form and crown health were mostly nonsignificant. 相似文献
12.
Shinta Ohashi Naoki Okada Tadashi Nobuchi Somkid Siripatanadilok Teera Veenin 《Trees - Structure and Function》2009,23(4):813-822
We measured radial variation of carbon isotope composition and vessel traits in tree species in seasonally dry forests of
Northeast Thailand to explore a more reliable and amenable method of tropical dendrochronology for trees that lack visually
detectable and consistent growth rings. Six Dipterocarpaceae species (3 Shorea, 2 Dipterocarpus, and 1 Hopea species) with indistinct or irregular growth rings and teak (Tectona grandis), a species which forms distinct growth rings, were examined. The δ13C value variations in all species showed annual cyclicity. Dipterocarpaceae species usually marked the lowest values of δ13C in the middle of the growing season, whereas teak had the lowest values at nearly the end of the growing season. Since the
growing season of the species examined almost corresponds to the rainy season in the study area, the δ13C variation was likely caused by the change in moisture availability. The different variation pattern of teak was attributable
to its stronger dependence on 13C-enriched reserved material early in the growing season. Changes in tree vessel traits for all species examined also showed
annual cyclicity. Dipterocarpaceae species showed significant correlation between δ13C values and vessel measurements. Vessel lumen (mean area, tangential and radial diameter, and proportion of total area) had
a negative correlation, whereas vessel frequency showed a positive correlation. The correlations indicated that changes in
vessel traits were caused by the seasonal variation of moisture available to the trees. Thus, we concluded that methods using
wood anatomy, as well as δ13C, have great potential for use as tools in tropical dendrochronology within the context of seasonal climate. 相似文献
13.
Water source partitioning among trees growing on shallow karst soils in a seasonally dry tropical climate 总被引:7,自引:0,他引:7
The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known.
In northern Yucatan (Mexico), trees withstand 4–6 months of annual drought in spite of the small water storage capacity of
the shallow karst soil. We hypothesized that adult evergreen trees in Yucatan tap the aquifer for a reliable supply of water
during the prolonged dry season. The naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in
soil, bedrock, groundwater and plant stem water were used to determine the sources of water used by native evergreen and drought-deciduous
tree species. While the trees studied grew over a permanent water table (9–20 m depth), pit excavation showed that roots were
largely restricted to the upper 2 m of the soil/bedrock profile. At the peak of the dry season, the δ18O signatures of potential water sources for the vegetation ranged from 4.1 ± 1.1‰ in topsoil to −4.3 ± 0.1‰ in groundwater.
The δ18O values of tree stem water ranged from −2.8 ± 0.3‰ in Talisia
olivaeformis to 0.8 ± 1‰ in Ficus cotinifolia, demonstrating vertical partitioning of soil/bedrock water among tree species. Stem water δ18O values were significantly different from that of groundwater for all the tree species investigated. Stem water samples plotted
to the right of the meteoric water line, indicating utilization of water sources subject to evaporative isotopic enrichment.
Foliar δ13C in adult trees varied widely among species, ranging from −25.3 ± 0.3‰ in Enterolobium cyclocarpum to −28.7 ± 0.4‰ in T. olivaeformis. Contrary to initial expectations, data indicate that native trees growing on shallow karst soils in northern Yucatan use
little or no groundwater and depend mostly on water stored within the upper 2–3 m of the soil/bedrock profile. Water storage
in subsurface soil-filled cavities and in the porous limestone bedrock is apparently sufficient to sustain adult evergreen
trees throughout the pronounced dry season. 相似文献
14.
The aim of this study was to determine the effects of nitrogen (N) fertilization methods on root distribution and mineral element concentrations of White Marsh grapefruit (Citrus paradisi MacFadyen) trees on sour orange (C. aurantium Lush) rootstock on a poorly drained soil. At 0–15 cm depth of soil, root density was significantly greater for trees receiving 112 kg N ha-1 yr-1 as dry granular broadcast than those receiving the same amount of N as fertigation. Of the total roots in the top 60 cm soil, >75% was at 0–15 cm and <10% was at 30–60 cm. Root density was greatest near the emitter. Nitrogen concentration of roots was greater for the trees which received fertigation as compared to the trees which received dry fertilizer broadcast or no N. 相似文献
15.
M. Raeini-Sarjaz N. N. Barthakur N. P. Arnold 《International journal of biometeorology》1997,40(2):81-85
Leaf movements of bush bean plants were studied at the relatively low photon flux density of 0.2 mmol/m2 per s, and air temperatures of 25° and 35° C in a growth chamber. A beta-ray gauge system was used to monitor continuously
pulvinus water status and bending. Leaf angles were below the horizontal and were linearly related to the soil water content
(R≥−0.91 at 25° C and R≥−0.93 at 35° C). The beta-ray transmission maxima coincided with the stem temperature minima in darkness and vice versa when
brightness prevailed as the growth chamber temperature varied with the photoperiod. Leaf angle increased linearly with increased
beta-ray transmission. The Q10 temperature coefficient, a measure of the metabolic energy requirement for leaf movement between 25° and 35° C was estimated
at 1.8, and the corresponding mean Arrhenius constant at 423 kJ/mol for bush bean.
Received: 19 July 1996 / Accepted: 9 September 1996 相似文献
16.
Transpiration and whole-tree conductance in ponderosa pine trees of different heights 总被引:17,自引:0,他引:17
M. G. Ryan B. J. Bond B. E. Law R. M. Hubbard D. Woodruff E. Cienciala J. Kucera 《Oecologia》2000,124(4):553-560
Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree
water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine
if transpiration (E) and whole-tree conductance (g
t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m–2 (leaf area, projected) s–1 for the 12-m trees and 0.57 mmol m–2 (leaf area) s–1 for the 36-m trees. When photosynthetically active radiation (I
P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m–2 (ground) s–1), differences in E were more pronounced: 2.4 mmol m–2 (leaf area) s–1 for the 12-m trees and 1.2 mmol m–2 s–1 for the 36-m trees, yielding g
t of 140 mmol m–2 (leaf area) s–1 for the 12-m trees and 72 mmol m–2 s–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June
and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g
t in the taller trees also likely lowers photosynthesis during the growing season.
Received: 19 April 1999 / Accepted: 23 March 2000 相似文献
17.
The objective of this study was to assess fermentation product, growth rate and growth yield responses of Selenomonas ruminantium HD4 to limiting and non-limiting ammonia concentrations. The ammonia half-inhibition constant for S. ruminantium in batch culture was 296 mM. Cells were grown in continuous culture with a defined ascorbate-reduced basal medium containing
either 0.5, 5, 25, 50, 100 or 200 mM NH4Cl and dilution rates were 0.07, 0.14, 0.24 or 0.40 h-1. Ammonia was the growth-limiting nutrient when 0.5 mM NH4Cl was provided and the half-saturation constant was 72 μM. Specific rates of glucose utilization and fermentation acid carbon
formation were highest for 0.5 mM NH4Cl. Lactate production (moles per mole of glucose disappearing) increased at the fastest dilution rate (0.40 h-1) for 5.0 mM NH4Cl while acetate and propionate decreased when compared to slower dilutions (0.07 and 0.14 h-1). Lactate production remained low while acetate and propionate remained high for all dilution rates when NH4Cl concentrations were 25 mM or greater. Yield (Y
Glc and Y
ATP) were nearly doubled when NH4Cl was increased from 0.5 mM (25.1 g cells/mol glucose used and 13.9 g cells/mol ATP produced respectively) to the higher
concentrations. Y
Glc was highest at 25 mM and 50 mM NH4Cl (48.2 cells/mol and 43.1 cells/mol respectively) as was Y
ATP (23.2 cells/mol and 20.8 cells/mol respectively). Y
NH3 was highest at the lowest NH4Cl concentration. The maximal fermentation product formation rate occurred at a growth-limiting ammonia concentration, while
maximal glucose and ATP bacterial yields occurred at non-growth-limiting ammonia concentrations. Given the growth response
of this ruminal bacterium, it is possible that maximization of ruminal bacterial yield may necessitate sacrificing the substrate
degradation rate and vice versa.
Received: 5 December 1995/Received revision: 2 April 1996/Accepted: 22 April 1996 相似文献
18.
S. L. Chown 《Polar Biology》1996,16(3):171-178
The Diptera are one of the dominant insect consumer groups on sub-Antarctic islands and are thought to contribute significantly
to terrestrial ecological processes at many of these islands. The life-cycle of Paractora trichosterna and its contribution to kelp degradation at Husvik Harbour, South Georgia were therefore investigated in the laboratory and
in two artificial wrack beds in the field. Duration of the larval stage was approximately 2 months at 10°C, during which time
larvae attained a maximum individual mass of ca. 90 mg. Larvae had a relative consumption rate of 0.734 mg dry mass kelp mg
dry mass larva-1 day-1. Based on this rate and information on larval densities of P. trichosterna, and a smaller species, Antrops truncipennis, kelp consumption was estimated to be 714–870 g dry mass kelp m-2 over the 7-week study period. During this time, kelp dry biomass declined to 30% of its original value, both in a bed protected
from trampling by vertebrates and in an exposed one. P. trichosterna was directly responsible for 12% of this loss in the protected bed and 20% in the exposed one. A. truncipennis was responsible for an additional 3% loss in the exposed bed and 8% in the protected one. These fly species therefore contributed
significantly to kelp degradation. Differences in biomass of the larvae and adults of the two species between the beds suggested
that P. trichosterna prefers more exposed wrack than does A. truncipennis.
Received: 27 March 1995/Accepted: 4 July 1995 相似文献
19.
The synthesis of poly(3-hydroxyalkanoates) (PHA) by Pseudomonas putida KT2442 growing on long-chain fatty acids was studied in continuous cultures. The effects of the growth rate on the biomass
and polymer concentration were determined and it was found that the PHA concentrations decreased with increasing growth rates.
The highest volumetric productivity was 0.13 g PHA l-1 h-1 at a specific growth rate (μ) of 0.1 h-1. The molecular mass of the polymer remained constant at all growth rates but changes in the monomeric composition of the
PHA synthesized were observed. Variation of the carbon to nitrogen (C/N) ratio of the substrate feed at μ=0.1 h-1 revealed optimal PHA formation at C/N=20 mol/mol. In order to optimize PHA production P. putida KT2442 was cultivated to high cell densities in oxygen-limited continuous cultures. In this way a maximum biomass concentration
of 30 g/l containing approximately 23% PHA was achieved. This corresponds to a volumetric productivity of 0.69 g l-1 h-1.
Received: 14 December 1995 / Received revision: 18 April 1996 / Accepted: 22 April 1996 相似文献
20.
Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In
contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter)
are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to
the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed
litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other
canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall
to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest
(40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m−2 y−1), and reached 1,288 g m−2 y−1 in the old-growth forest and 934 g m−2 y−1 in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth
forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially
to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest
values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative),
probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and
leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent
on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional
with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially
high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical
forests so far. 相似文献