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1.
Sap flux of five co-occurring tree species in a temperate broad-leaved forest during seasonal soil drought 总被引:1,自引:0,他引:1
Dirk Hölscher Oliver Koch Sandra Korn Ch. Leuschner 《Trees - Structure and Function》2005,19(6):628-637
In an old-growth forest in Central Germany, sap flux was studied in five broad-leaved tree species that were assumed to differ
in drought sensitivity. Under moist soil conditions, average daily sap flux density (J
s) in the outermost xylem varied by a factor of 2.3 among the species (67–152 g cm−2 per day, n=5 trees per species), and declined in the sequence Fagus sylvatica > Acer pseudoplatanus > Tilia cordata > Carpinus betulus > Fraxinus excelsior. Decreasing soil moisture content (Θ) resulted in linearly reduced J
s in four of the species. During a dry period, J
s was reduced by 44% in T. cordata, 39% in F. sylvatica, 37% in A. pseudoplatanus and 31% in C. betulus compared to sap flux at equal vapour pressure deficit (D) in the wet period. F. excelsior, the only ring-porous species studied, lacked a significant response in J
s to D and Θ. The relative reduction in water use during the dry period was not related to the assumed drought sensitivity of the
species as inferred from their abundance in natural woodlands. J
s was positively correlated with tree diameter at breast height (DBH) in three species but decreased with DBH in two species.
Dyeing experiments revealed that DBH accounted for 94% of the variation in sapwood area found in a bulk sample of all diffuse-porous
trees. This suggests that DBH is a reliable estimator of sapwood area of temperate diffuse-porous species irrespective of
species identity. In contrast, sap flux density was found to be greatly dependent on tree species. The estimated whole-plant
water use for diffuse-porous trees of a given diameter (49 cm) ranged between 74 and 168 kg per day per species under moist
soil conditions. Thus, in temperate mixed forests, species-specific differences in water use can result in a considerable
spatial heterogeneity of canopy transpiration. 相似文献
2.
Using constant heat sap flow sensors, xylem water fluxes in ten tree species and two liana species were monitored for 5–10
days during the beginning of the wet season in May, 1993. For a subset of the trees, a branch was also monitored at the top
of the crown for 5 days. Xylem flux (J
S) was related diurnally in all plants to vapor pressure deficit (D) measured within the upper-third of the canopy, and to incoming shortwave radiation R
S above the canopy. Cross-correlation analysis was used to estimate time lags between diurnal patterns of J
S and D or R
S, and between J
S in stems and branches. The maximum correlation coefficient from cross-correlation of J
S with R
S (range=0.57–0.92) was often higher than the maximum of J
S with D (range=0.43–0.89), indicating that diurnal J
S was more dependent on R
S than D. Time lags (lag corresponding to maximum correlation) of J
S at stem-base with D was shorter (0–45 min) than with radiation (5–115 min), highly variable within a species, and uncorrelated to the height
or exposure of tree crowns or liana in the canopy. On a stand level, not accounting for the diel lag between stem sap flux
and canopy flux resulted in errors in estimated canopy transpiration of up to 30%.
Received: 19 October 1998 / Accepted: 8 June 1999 相似文献
3.
A recently described phloem-bleeding technique was used to study seasonal changes in δ13C, sugar levels and the amino acid:sugar balance of phloem translocate of 2- to 3-year old trees of Eucalyptus globulus at a rain-fed site (Eulup) and a waste-effluent-irrigated site (Albany) in south-west Australia. δ13C of phloem sap from the Eulup site fluctuated widely between winter (−27.6‰) and peak summer stress (−20.2‰), compared with
a much smaller range of −28.4 to −26.3 at Albany. Seasonal changes in sugar concentrations in sap fluctuated closely with
those of phloem δ13C, with highest concentrations and least negative δ13C values at times of greatest soil water deficit. Molar ratios of amino acids to sugars in phloem sap were similar between
plantations in winter through to early summer. They then remained high at the nitrogen-rich effluent-treated site, but fell
dramatically once soils dried out at Eulup. Mature leaf dry matter sampled at peak yearly stress (early autumn) showed more
negative δ13C values than concurrently harvested phloem sap or recently initiated shoot apex dry matter, presumably because the sampled
foliage had laid down its structural carbon earlier under relatively unstressed winter/spring conditions. Differences between
Albany and Eulup were much greater for δ13C of phloem and new apical dry matter than for dry matter of mature foliage. Comparisons of δ13C signatures of phloem sap carbon with those of dry matter of nascent xylem tissues showed seasonal fluctuations in δ13C of phloem translocate which were mirrored a month or so later by those for xylem carbon. δ13C analyses of trunk growth rings from Eulup and Albany showed well-defined seasonal oscillations over the first 2 or 3 years
of growth until irrigation commenced at Albany. Fluctuations in δ13C at the latter site then became noticeably less pronounced than at Eulup. Future use of phloem sap δ13C and solute analyses for studying seasonal water and nutrient status of E. globulus is discussed.
Received: 9 April 1998 / Accepted: 20 August 1998 相似文献
4.
L. W. Zhu P. Zhao X. A. Cai X. P. Zeng G. Y. Ni J. Y. Zhang L. L. Zou T. T. Mei M. H. Yu 《Trees - Structure and Function》2012,26(2):535-542
Stem CO2 efflux (E
s) has been estimated from a temperature-related equation, but sap flux often affects measurements of E
s, which leads to misunderstanding real stem respiration. In order to observe the relationship between E
s and stem temperature and to analyze the effect of sap velocity on E
s, stem temperature, E
s and sap flux were measured from a subtropical Schima superba plantation in South China on three trees for consecutive 3 days in July and October 2009. Stem temperature, E
s and sap velocity were significantly higher in July than in October. Stem temperature could explain 17–41 and 54–75% variations
of E
s in July and October, respectively. A negative relationship between E
s and stem temperature was found during 1800–2300 hours in July. The daytime E
s was 9.2, 4.3 and 2.4% higher than the predicted for three trees in July, and this occurred only on Tree 1 in October. Sap
velocity was positively correlated with E
s for three trees in July, and the increase of E
s with the increase of sap velocity was only observed on Tree 1 in October. These results demonstrated that the occurrence
of sap flux could account for the increase of daytime E
s, and the effect of sap velocity on E
s varied with the seasons from the S. superba stem. 相似文献
5.
城市绿化树木具有多重生态效应, 其耗水量不容忽视。在不了解树干液流空间变异的前提下, 将点的测定值推广到整树或者林段尺度会产生很大的误差。为准确地确定整树耗水, 采用热消散探针法研究了夏秋季北京成年常绿树种油松(Pinus tabulaeformis)、雪松(Cedrus deodara)和刺槐(Robinia pseudoacacia)树干液流的空间变异特征及产生原因。各树种树干液流存在方位变异, 受树干靠南的方向受光较多、木材解剖特征和枝下高高度的影响, 油松和雪松液流密度与方位之间的关系较为固定, 而刺槐液流密度与方位之间的关系表现出随机性。不同方位每小时液流密度之间高度相关(p < 0.000 1)。因此, 可以基于这种关系准确地计算其他方位的液流(R2 > 0.91, p < 0.000 1)。油松和雪松树干液流的径向变异显著, 较深处和较浅处树干液流的日变化格局相似, 但是较深处的液流明显滞后于较浅处的树干液流, 且较浅处树干液流对环境因子的响应远高于深处的液流。不同深度树干液流之间密切相关, 因此可以利用较浅处的液流外推其他深度的液流(R2 > 0.89, p < 0.000 1)。然而, 同一棵树不同方位径向剖面特征不同, 雪松南向较深处的液流明显高于其他方位, 且滞后不显著, 这与树冠南向受光较多有关。结合误差分析, 采取北向15 mm和75 mm深处的液流密度均值来估算整树耗水较为准确。 相似文献
6.
Hydraulic Lift in Cork Oak Trees in a Savannah-Type Mediterranean Ecosystem and its Contribution to the Local Water Balance 总被引:3,自引:1,他引:2
Cathy Kurz-Besson Dennis Otieno Raquel Lobo do Vale Rolf Siegwolf Markus Schmidt Alastair Herd Carla Nogueira Teresa Soares David Jorge Soares David John Tenhunen João Santos Pereira Manuela Chaves 《Plant and Soil》2006,282(1-2):361-378
The aim of this study was to identify the sources and depth of water uptake by 15-years old Quercus suber L. trees in southern Portugal under a Mediterranean climate, measuring δ18O and δD in the soil–plant-atmosphere continuum. Evidence for hydraulic lift was substantiated by the daily fluctuations observed
in Ψs at 0.4 and 1 m depth and supported by similar δ18O values found in tree xylem sap, soil water in the rhizosphere and groundwater. From 0.25 m down to a depth of 1 m, δD trends
differed according to vegetation type, showing a more depleted value in soil water collected under the evergreen trees (−47‰)
than under dead grasses (−35‰). The hypothesis of a fractionation process occurring in the soil due to diffusion of water
vapour in the dry soil is proposed to explain the more depleted soil δD signature observed under trees. Hydraulically lifted
water was estimated to account for 17–81% of the water used during the following day by tree transpiration at the peak of
the drought season, i.e., 0.1–14 L tree−1 day−1. Significant relationships found between xylem sap isotopic composition and leaf water potential in early September emphasized
the positive impact of the redistribution of groundwater in the rhizosphere on tree water status. 相似文献
7.
Michael Nahm Andreas Matzarakis Heinz Rennenberg Arthur Geßler 《Trees - Structure and Function》2007,21(1):79-92
During the growing season of the exceptionally dry and warm year 2003, we assessed seasonal changes in nitrogen, carbon and
water balance related parameters of mature naturally grown European beech (Fagus sylvatica L.) along a North–South transect in Europe that included a beech forest stand in central Germany, two in southern Germany
and one in southern France. Indicators for N balance assessed at all four sites were foliar N contents and total soluble non-protein
nitrogen compounds (TSNN) in xylem sap, leaves and phloem exudates; C and water balance related parameters determined were
foliar C contents, δ13C and δ18O signatures. Tissue sampling was performed in May, July and September. The N related parameters displayed seasonal courses
with highest concentrations during N remobilization in May. Decreased total foliar N contents as well as higher C/N ratios
in the stands in central Germany and southern France compared to the other study sites point to an impaired N nutrition status
due to lower soil N contents and precipitation perception. TSNN concentrations in leaves and phloem exudates of all study
sites were in ranges previously reported, but xylem sap content of amino compounds in July was lower at all study sites when
compared to literature data (c. 1 μmol N mL−1). In September, TSNN concentrations increased again at the two study sites in southern Germany after a rain event, whereas
they remained constant at sites in central Germany and southern France which hardly perceived precipitation during that time.
Thus, TSNN concentrations in the xylem sap might be indicative for water balance related N supply in the beech trees. TSNN
profiles at all study sites, however, did not indicate drought stress. Foliar δ13C, but not foliar C and δ18O followed a seasonal trend at all study sites with highest values in May. Differences in foliar δ13C and δ18O did not reflect climatic differences between the sites, and are attributed to differences in altitude, photosynthesis and
δ18O signatures of the water sources. Except of low TSNN concentrations in the xylem sap, no physiological indications of drought
stress were detected in the trees analysed. We suppose that the other parameters assessed might not have been sensitive to
the drought events because of efficient regulation mechanisms that provide a suitable physiological setting even under conditions
of prolonged water limitation. The uniform performance of the trees from southern France and central Germany under comparably
dry climate conditions denotes that the metabolic plasticity of mature beech from the different sites studied might be similar. 相似文献
8.
Philip G. Oguntunde 《Plant and Soil》2005,278(1-2):371-383
Cassava (Manihot esculenta Crantz), a perennial woody shrub, is known to be highly productive under favourable conditions and produce reasonably well
under adverse conditions where other crops fail. Using constant heat sap flow sensors, sap flow density (F
d
) of cassava was monitored for 10 days in December 2002. Sap flow was highly correlated (R
2
=0.72, P<0.05) to incoming solar radiation (R
s) than to other climatic factors. Using cross-correlation analysis, no time shift was detected between F
d
and solar radiation, whereas vapour pressure deficit (VPD) lags F
d
by 110 min. Solar radiation and VPD together explained 83% of diurnal variation in sap flow. Whole-plant transpiration ranged
from 0.8 to 1.2 mm day−1 and daily canopy conductance (g
c), computed based on the inverted Penman–Monteith model, varied between 0.7 and 2.1 mm s−1 (mean = 1.4 ± 0.5 mm s−1). For the measurement period, characterized by high evaporative demand coupled with low available soil water, transpiration
accounted for 21% of the available energy and was only able to meet 24% of the atmospheric water demand. Average decoupling
factor (Ω) of 0.05±0.02 estimated suggested that a 10% change in g
c may lead to more than 9% change in transpiration which further supports the notion that stomata play significant role in
regulating cassava water use compared to other known mechanisms. Beyond light saturation (R
s
>300 W m−2) and at higher VPD (>1.0 kPa), wind effects on the canopy transpiration under water stress condition were low, while VPD
explains 94% of the observed variance in daily canopy conductance. 相似文献
9.
Alison F. Moldenke Ralph E. Berry Jeffrey C. Miller James G. Wernz 《Entomologia Experimentalis et Applicata》1997,84(2):157-163
We examined toxicity of acephate to third-instar gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), under different conditions of administration method, availability of food to larvae during bioassay, host plant, and activity of detoxifying enzymes. Larvae that had been fed field-collected foliage of white alder (Alnus rhombifolia Nutt.) were less susceptible 48 h after treatment with topically applied acephate if they were allowed to continue feeding on foliage during the bioassay period (LD50= 60.6 μg/g larva ) than if they were not (LD50= 13.5 μg/g larva ). All surviving larvae were replaced on their original food plant after the 48-h bioassay; of these, 14.4% of the larvae not fed during treatment died before pupation, compared with 1.3% of the larvae fed alder during treatment. The LD50 obtained for topically treated larvae reared and treated on Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, (51.1 μg/g larva) was comparable to that obtained for larvae fed alder (60.0 μg/g larva) throughout treatment. Larvae treated orally with acephate, however, were slightly more susceptible when reared on Douglas-fir (LC50, 20.3 ppm ) than when reared on alder (LC50, 27.0 ppm ). Post-treatment mortality in orally treated larvae was 10.3% in those fed alder and 9.5% in those fed Douglas-fir. Higher cytochrome P-450 activities in larvae reared on Douglas-fir apparently did not enhance tolerance to acephate. Both sexes of orally treated larvae took significantly longer to pupate than did controls on both foliage types, as did topically treated males fed Douglas-fir. Pupal weight generally was slightly, but not always significantly, higher in treated than untreated larvae under all dietary and treatment regimes. 相似文献
10.
In Vitis vinifera L. berries, the onset of ripening (known as “veraison”) involves loss of turgor (P) in the mesocarp cells. We hypothesized
that P loss was associated with an accumulation of apoplastic solutes in mesocarp tissue prior to veraison. Apoplastic sap
was extracted from the mesocarp by centrifugation at the appropriate gravity to measure the apoplast solute potential (ΨsA) and assay the sap composition. The ΨsA was about −0.2 MPa early in development, decreased about 1.0 MPa by veraison, and continued to decrease during ripening to
almost −4.0 MPa by the end of berry development. Potassium, malate, tartrate, proline, glucose, fructose, and sucrose were
quantified in apoplastic sap. The calculated contribution of these solutes was about 50% of the total ΨsA preveraison, but increased to about 75% as fructose and glucose accumulated during ripening. The contribution of the estimated
matric potential to apoplast water potential decreased during development and was only 1.5% postveraison. We conclude that
high concentrations of solutes accumulated in the mesocarp apoplast prior to veraison, and that P loss was a direct result
of decreased ΨsA. Because ΨsA decreased before veraison, our findings suggest that apoplast solutes play an important role in the events of cellular metabolism
that lead to the onset of ripening. 相似文献
11.
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
12.
Richard J. Pruell Bryan K. Taplin Jonathan D. Karr 《Environmental Biology of Fishes》2012,93(1):61-71
Isotopic ratios of fish otoliths have been used in numerous studies as natural tags or markers to aid in the study of connectivity
among fish populations. We investigated the use of spatial and temporal changes in the stable carbon and oxygen isotope ratios
of otoliths to differentiate juvenile habitats of winter flounder (Pseudopleuronectes americanus). Young-of-the-year (YOY) juvenile winter flounder were collected annually over a three-year period from 18 stations along
the coast of Rhode Island, USA. Sagittal otoliths were removed from fish and analyzed for stable carbon (13C/12C or δ13C) and oxygen (18O/16O or δ18O) isotope ratios using continuous flow isotope ratio mass spectrometry. Differences in isotope ratios were observed among
stations and along salinity gradients in the Narragansett Bay estuary and an estuarine river system (Narrow River). Overall,
the isotope ratio patterns observed among stations were consistent over the three sampling years; however, differences were
noted in isotope ratios and the magnitude of the isotope ratio gradients among years. Significant positive correlations were
noted between salinity and δ13C for two of the three years. For each of the three years sampled there was a highly significant positive correlation (2002,
r = 0.93, P < 0.01; 2003, r = 0.85, P < 0.01; 2004, r = 0.97, P < 0.01) between δ18O and the salinity of the collection site. Also, there was a significant negative correlation between the number of months
of above average river flow and δ18O for the three sampling years (r = 0.99, P < 0.05). These findings suggest that yearly changes in the volume of freshwater inputs to these estuarine habitats may be
related to the differences observed in otolith δ18O isotope ratios. Because of these year-to-year differences, sampling of each cohort may be necessary in order to use this
isotopic technique for winter flounder connectivity studies. 相似文献
13.
Increased use of stable isotope analysis to examine food-web dynamics, migration, transfer of nutrients, and behavior will likely result in expansion of stable isotope studies investigating human-induced global changes. Recent elevation of atmospheric CO2 concentration, related primarily to fossil fuel combustion, has reduced atmospheric CO2 δ13C (13C/12C), and this change in isotopic baseline has, in turn, reduced plant and animal tissue δ13C of terrestrial and aquatic organisms. Such depletion in CO2 δ13C and its effects on tissue δ13C may introduce bias into δ13C investigations, and if this variation is not controlled, may confound interpretation of results obtained from tissue samples collected over a temporal span. To control for this source of variation, we used a high-precision record of atmospheric CO2 δ13C from ice cores and direct atmospheric measurements to model modern change in CO2 δ13C. From this model, we estimated a correction factor that controls for atmospheric change; this correction reduces bias associated with changes in atmospheric isotopic baseline and facilitates comparison of tissue δ13C collected over multiple years. To exemplify the importance of accounting for atmospheric CO2 δ13C depletion, we applied the correction to a dataset of collagen δ13C obtained from mountain lion (Puma concolor) bone samples collected in California between 1893 and 1995. Before correction, in three of four ecoregions collagen δ13C decreased significantly concurrent with depletion of atmospheric CO2 δ13C (n ≥ 32, P ≤ 0.01). Application of the correction to collagen δ13C data removed trends from regions demonstrating significant declines, and measurement error associated with the correction did not add substantial variation to adjusted estimates. Controlling for long-term atmospheric variation and correcting tissue samples for changes in isotopic baseline facilitate analysis of samples that span a large temporal range. 相似文献
14.
For base-paired nucleic acids, variations in 1
J
NH and the imino 1H chemical shift are both dominated by hydrogen bond length. In the absence of molecular alignment, the 1
J
NH coupling for the imino proton then can be approximated by 1
J
NH = (1.21Hz/ppm)δH − 103.5 ± 0.6 Hz, where δH represents the chemical shift of the imino proton in ppm. This relation permits imino residual dipolar couplings (RDCs) resulting
from magnetic susceptibility anisotropy (MSA) to be extracted from measurement of (1
J
NH + RDC) splittings at a single magnetic field strength. Magnetic field-induced RDCs were measured for tRNAVal and the alignment tensor determined from magnetic-field alignment of tRNAVal agrees well with the tensor calculated by summation of the MSA tensors of the individual nucleobases.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Jinfa Ying, Alexander Grishaev and Michael P. Latham contributed equally to this work. 相似文献
15.
Geographic patterns of intraspecific variations in traits related to photosynthesis and biomass were examined in two separate
common garden experiments using seed collected from 26 Sitka alder (Alnus sinuata Rydb.) and 18 paper birch (Betula papyrifera Marsh.) populations from climatically diverse locations in British Columbia, Canada. Exchange rates of carbon dioxide and
water vapour were measured on 2-year-old seedlings to determine the maximum net instantaneous photosynthetic rate, mesophyll
conductance, stomatal conductance, and photosynthetic water use efficiency. Height, stem diameter, root and shoot dry mass
and fall frost hardiness data were also obtained. Mean population maximum photosynthetic rate ranged from 10.35 to 14.57 μmol
CO2 m–2 s–1 in Sitka alder and from 14.76 to 17.55 μmol CO2 m–2 s–1 in paper birch. Based on canonical correlation analyses, populations from locations with colder winters and shorter (but
not necessarily cooler) summers had higher maximum photosynthetic rates implying the existence of an inverse relationship
between leaf longevity and photosynthetic capacity. Significant canonical variates based on climatic variables derived for
the seed collection sites explained 58% and 41% of variation in the rate of photosynthesis in Sitka alder and paper birch,
respectively. Since growing season length is reflected in date of frost hardiness development, an intrinsic relationship was
found between photosynthetic capacity and the level of fall frost hardiness. The correlation was particularly strong for paper
birch (r=–0.77) and less strong for Sitka alder (r=–0.60). Mean population biomass accumulation decreased with increased climate coldness. These patterns may be consequential
for evaluation of the impact of climate change and extension of the growing season on plant communities.
Received: 12 July 1999 / Accepted: 24 November 1999 相似文献
16.
Jeffrey M. Klopatek 《Plant and Soil》2007,294(1-2):157-167
Litterfall and fine root production were measured for three years as part of a carbon balance study of three forest stands
in the Pacific Northwest of the United States. A young second-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stand, a second-growth Douglas-fir with red alder (Alnus rubra Bong.) stand, and an old-growth (∼550 years) Douglas-fir stand were monitored for inputs of carbon and nitrogen into the
soil from litterfall and fine root production, as well as changes in soil C and N. Fine root production and soil nutrient
changes were measured through the use of soil ingrowth bags containing homogenized soil from the respective stands. Litterfall
biomass was greatest in the Douglas-fir-alder stand (527 g m−2 yr−1) that annually returned nearly three times the amount of N as the other stands. Mean residence time for forest floor material
was also shortest at this site averaging 4.6 years and 5.5 years for C an N, respectively. Fine root production in the upper
20 cm ranged from 584 g m−2 in the N rich Douglas-fir-alder stand to 836 g m−2 in the old-growth stand. Fine root production (down to one meter) was always greater than litterfall with a below:above ratio
ranging from 3.73 for the young Douglas-fir stand to 1.62 for the Douglas-fir-alder stand. The below:above N ratios for all
three stands closely approximate those for biomass. Soil changes in both C and N differed by site, but the soil C changes
in the old-growth stand mirrored those obtained in an ongoing CO2 flux study. Results from the soil ingrowth bags strongly suggest that this method provides a simple, but sufficient device
for measuring potential fine root biomass production as well as soil chemical changes. 相似文献
17.
Liubov Volkova Lauren T. Bennett Andrew Merchant Michael Tausz 《Trees - Structure and Function》2010,24(2):351-362
We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under moderate and high light regimes to short-term water deficit followed by rewatering. Under adequate water supply,
morphological and photosynthetic characteristics differed between species. D. antarctica, although putatively the more shade and less drought adapted species, had greater chlorophyll a/b ratio, and greater water use efficiency and less negative δ13C. Both species were susceptible to water deficit regardless of the light regime showing significant decreases in photosynthetic
parameters (A
max, V
cmax, J
max) and stomatal conductance (g
s
) in conjunction with decreased relative frond water content (RWC) and predawn frond water potential (Ψpredawn). During the water deficit period, decreases in g
s
in both species started one day later, and were at lower soil water content, under moderate light compared with high light.
D. antarctica under moderate light was more vulnerable to drought than all other plants as was indicated by greater decreases in Ψpredawn, lowest stomatal conductance, and photosynthetic rates. Both tree fern species were able to recover after a short but severe
water stress. 相似文献
18.
Chemical Exchange Saturation Transfer (CEST) is an MRI approach that can indirectly detect exchange broadened protons that
are invisible in traditional NMR spectra. We modified the CEST pulse sequence for use on high-resolution spectrometers and
developed a quantitative approach for measuring exchange rates based upon CEST spectra. This new methodology was applied to
the rapidly exchanging Hδ1 and Hε2 protons of His57 in the catalytic triad of bovine chymotrypsinogen-A (bCT-A). CEST enabled
observation of Hε2 at neutral pH values, and also allowed measurement of solvent exchange rates for His57-Hδ1 and His57-Hε2
across a wide pH range (3–10). Hδ1 exchange was only dependent upon the charge state of the His57 (k
ex,Im+ = 470 s−1, k
ex,Im = 50 s−1), while Hε2 exchange was found to be catalyzed by hydroxide ion and phosphate base (
k\textOH - k_{{{\text{OH}}^{ - } }} = 1.7 × 1010 M−1 s−1,
k\textHPO42 - k_{{{\text{HPO}}_{4}^{2 - } }} = 1.7 × 106 M−1 s−1), reflecting its greater exposure to solute catalysts. Concomitant with the disappearance of the Hε2 signal as the pH was
increased above its pK
a, was the appearance of a novel signal (δ = 12 ppm), which we assigned to Hγ of the nearby Ser195 nucleophile, that is hydrogen bonded to Nε2 of neutral His57. The
chemical shift of Hγ is about 7 ppm downfield from a typical hydroxyl proton, suggesting a highly polarized O–Hγ bond. The
significant alkoxide character of Oγ indicates that Ser195 is preactivated for nucleophilic attack before substrate binding.
CEST should be generally useful for mechanistic investigations of many enzymes with labile protons involved in active site
chemistry. 相似文献
19.
Glenn L. Butterfoss Eugene F. DeRose Scott A. Gabel Lalith Perera Joseph M. Krahn Geoffrey A. Mueller Xunhai Zheng Robert E. London 《Journal of biomolecular NMR》2010,48(1):31-47
Methionine residues fulfill a broad range of roles in protein function related to conformational plasticity, ligand binding,
and sensing/mediating the effects of oxidative stress. A high degree of internal mobility, intrinsic detection sensitivity
of the methyl group, and low copy number have made methionine labeling a popular approach for NMR investigation of selectively
labeled protein macromolecules. However, selective labeling approaches are subject to more limited information content. In
order to optimize the information available from such studies, we have performed DFT calculations on model systems to evaluate
the conformational dependence of 3
J
CSCC, 3
J
CSCH, and the isotropic shielding, σiso. Results have been compared with experimental data reported in the literature, as well as data obtained on [methyl-13C]methionine and on model compounds. These studies indicate that relative to oxygen, the presence of the sulfur atom in the
coupling pathway results in a significantly smaller coupling constant, 3
J
CSCC/3
J
COCC ~ 0.7. It is further demonstrated that the 3
J
CSCH coupling constant depends primarily on the subtended CSCH dihedral angle, and secondarily on the CSCC dihedral angle. Comparison
of theoretical shielding calculations with the experimental shift range of the methyl group for methionine residues in proteins
supports the conclusion that the intra-residue conformationally-dependent shift perturbation is the dominant determinant of
δ13Cε. Analysis of calmodulin data based on these calculations indicates that several residues adopt non-standard rotamers characterized
by very large ~100° χ3 values. The utility of the δ13Cε as a basis for estimating the gauche/trans ratio for χ3 is evaluated, and physical and technical factors that limit the accuracy of both the NMR and crystallographic analyses are
discussed. 相似文献
20.
I. N. Ktitorova O. V. Skobeleva K. G. Agaltsov 《Russian Journal of Plant Physiology》2012,59(1):120-128
The root growth rate in barley (Hordeum vulgare L.) seedlings was measured in parallel with temporal changes in longitudinal (δl) and transverse (δD/D) cell-wall extensibilities and membrane hydraulic conductivity (L
p) in the root extension zone. The root growth rate and biophysical parameters examined were sensitive to UV-B irradiation
of shoots or roots and to excessive content of ammonium, glutamate, or nickel in the nutrient medium. The root responses to
the above treatments were compared with the effects of abscisic acid, salicylate, hydrogen peroxide, diethylstilbestrol, α-naphthyl
acetate, oryzalin, and ionomycin. The progressive reduction of root growth under the action of various stressors was accompanied
by typical temporal patterns of the growth zone parameters: the δl extensibility declined monotonically, while δD/D and L
p changed nonmonotonically, exhibiting the reversion from the initial decrease to the eventual increase above the control values.
The decline of δl indicated that the root growth suppression was mainly due to changes in cell-wall mechanical properties caused probably by
disorganization of cortical microtubules. It was found that the decline in δD/D and L
p was caused primarily by the appearance of oxidative stress, disorders in cytoplasmic H+ homeostasis in root cells, and the consequent transient activation of the plasmalemmal H+-pump. Conversely, the increase in δD/D and L
p upon the abrupt retardation of root growth was presumably caused by the increase in cytoplasmic Ca2+ content, disassembling of cortical microtubules, and by partial inhibition of the plasmalemmal H+-pump. The reversion of δD/D and L
p changes upon progressive reduction of root growth can be used as an indicator to distinguish moderate and severe stress conditions
in the root growth zone. Furthermore, this reversion indicates the increasing disbalance in the homeostasis of reactive oxygen
species, cytosolic Ca2+, and cytosolic H+ upon severe stress. 相似文献