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1.
We used pressure-volume analysis and dewpoint hygrometry to determine leaf water relation parameters of mangrove (Avicennia germinans L.) seedlings grown at salinities of 0, 8, 20 and 32 per thousand. Seedlings responded to an increase in salinity from 0 to 32 per thousand by an increase in leaf succulence as reflected in an increase in leaf water content per unit area from 300 to 360 g m(-2). Additionally, osmotic potential at full turgor decreased from -2.3 to -3.5 MPa and osmotic potential at zero turgor decreased from -2.7 to -4.3 MPa. Cell elasticity decreased as salinity increased from 0 to 32 per thousand, as indicated by a progressive increase in volumetric modulus of elasticity from 19 to 27 MPa. Increased leaf succulence enabled leaves to sequester large amounts of solutes without adversely increasing cell osmotic pressure. On the other hand, osmotic adjustment facilitated turgor maintenance as water potential diminished. Salinity-induced decreases in tissue elasticity generated greater water potential differences between leaves and soil under saline conditions than under non-saline conditions.  相似文献   

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Schrijvers  J.  Schallier  R.  Silence  J.  Okondo  J.P.  Vincx  M. 《Mangroves and Salt Marshes》1997,1(3):137-154
Many studies in the muddy intertidal zone of temperate regions haveindicated meiofaunal communities to be mainly affected by epibenthicpredation and disturbance rather than competition. Few studies, however,have dealt with mangrove sediments of tropical areas. In addition to aparallel study in a Ceriops tagal (Perr.) Rob. zone, a manipulativeexclusion technique was used to trace the dominant biological interactionsstructuring the meiobenthos of an East African Avicennia marina (Forsk.)Vierh. mangrove forest.The densities of the major meiobenthic taxa and nematode genera and abroad range of environmental factors were monitored over a depth profile forone year of caging. Cages (1 m2) excluded all epibenthos (> 2 mm)for one year and were procedurally controlled. Procedural and exclusioneffects were traced, using a factorial and mixed ANOVA design. Significant exclusion effects were indicated for oligochaetes and for oneof the dominant epistratal feeding nematode genera. They are discussed interms of epibenthic composition and density, feeding behaviour, foodresources, and the abiotic environment. The conclusion is that the observed meiobenthos (especially oligochaetesand nematodes) is influenced mainly by exploitative or resource competitionwith the epibenthos. The common food source was indicated to be muddydetritus and microalgae. Consequently, the role of the meiobenthos is mainlysituated in an isolated, detrital food web with only minor energy fluxes tothe epibenthos.  相似文献   

4.
Traditionally, poplars (Populus) have been planted to control erosion on New Zealand's hill-slopes, because of their capacity to dry out and bind together the soil, by reducing effective rainfall and increasing evapotranspiration and soil strength. However, the effect of widely spaced poplars on the partitioning of soil water and rainfall has not been reported. This study determined rainfall partitioning for 18 mid-spring days in a mature P. deltoides (Bart. ex Marsh, Clone I78)-pasture association (37 stems per hectare, unevenly spaced at 16.4 +/- 0.4 m) and compared it with a traditional open pasture system in grazed areas of a hill environment. Tree transpiration was measured by the heat pulse technique. A time-driven mathematical model was used to set a zero offset, adjust anomalous values and describe simultaneous sap velocity time courses of trees. The model showed that daylight sap flow velocities can be represented with a nonlinear Beta function (R(2) > 0.98), and differences in the parameters representing the initiation, duration and conformation of the sap velocity can be tested statistically to discern tree transpiration differences during the day. Evapotranspiration was greater for the poplar-pasture association than for the open pasture (2.7-3.0 versus 2.2 mm day(-1)). The tree canopy alone contributed 0.92 mm day(-1) as transpiration and 1.37 mm day(-1) as interception, whereas evapotranspiration of the pasture understory was only 0.4-0.6 mm day(-1). Despite the higher water use of the poplar-pasture association, soil water in the 0-300 mm soil stratum was higher than, or similar to, that of the open pasture. Tree shading decreased evapotranspiration and pasture accumulation under the trees.  相似文献   

5.
The black mangrove, Avicennia germinans, occurs sympatric withSpartina alterniflora in coastal Louisiana. Zonation exists alongan elevational gradient with A. germinans dominant at higherelevation creekbanks and S. alterniflora at interior, lowerelevation sites with greater depth and duration of flooding.Establishment of A. germinans seedlings was examined in cagesthat excluded predators and limited horizontal, but not vertical,movement of propagules by the tides and showed that blackmangrove could readily establish in the Spartina zone. Survivalof A. germinans seedlings after one year in cages was notsignificantly different between the two zones, and seedlings weresignificantly taller in the Spartina zone. Thus, neitherinundation per se nor other abiotic factors alone could accountfor the absence of A. germinans in the interior marsh. Althoughpropagules were dispersed into both zones, a net removal ofuncaged propagules from plots in the Spartina zone (–1.3 ± 0.6m-2 d-1) compared to a net addition to plots in the Avicennia zone (+0.5 ± 0.4 m-2d-1) indicated that retention of propagulesdiffered between zones. Causes of mortality were decay (Spartina> Avicennia zone), desiccation (Avicennia > Spartina zone), andpredation (Spartina > Avicennia zone). Although few propaguleswere completely consumed by predators (snails and crabs), damageto the cotyledons promoted decay. The results suggest that tidalaction limits retention and settlement of A. germinans propagulesin the Spartina zone, and a combination of predator damage andfrequent flooding leads to rapid decay of propagules that strandthere.  相似文献   

6.
Tank-bromeliads are discrete habitats which contain distinct aquatic communities, and which commonly occur in the neotropics. Because they span a broad range of ecological gradients in terms of habitat structure and amount of resources, researchers study the associations between the biodiversity of communities and these gradients in rainforests, where the very high species richness and densities within other continuous habitats makes it difficult to quantify animal communities. We analysed the diversity of aquatic insect communities in relation to different tank-bromeliad species in a primary rainforest (French Guiana) using artificial intelligence and complex optimization techniques to classify communities and model their determinants. First, the self-organizing map (neural network) was used to classify 158 bromeliads according to the quantitative structure of the insect communities. Catopsis berteroniana and Guzmania lingulata formed separate clusters of plants on the virtual map, while Vriesea splendens, Vriesea pleiosticha and Aechmea melinonii were grouped together in the remaining clusters. Some insect taxa occurred in all bromeliads, while other taxa were specific to a given species. Second, general linear modelling allowed us to specify the influence of the bromeliad species; water volume and volume of fine particulate organic matter inside of the tank; elevation above the ground; and sampling site on taxonomic richness and insect abundance. The number of taxa and individuals per plant increased with greater water volume, but the slope of the relationships depended on the bromeliad species. The significant influence of bromeliad species suggested that at similar water volumes different plant species had different taxon richness and insect abundance. Greater amounts of fine particulate organic matter were detrimental to community diversity in the tanks, probably because they decreased available space by clogging it and/or affected oxygen concentrations. The influence of tank-bromeliad species on the aquatic insect community was primarily related to their physical (and probably chemical) features rather than to species-specific associations sensu stricto. The classification of bromeliads with respect to animal species is likely to provide referential schemes for those biodiversity patterns to be expected under certain conditions, and may help to target model communities for subsequent experimental research.  相似文献   

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The native cacao trees (Theobroma cacao L.) in south-eastern French Guiana represent a noteworthy fraction of the genetic diversity of this species. Several scientific surveys have led to the collection of numerous accessions, which provides an opportunity for investigating the pattern of genetic diversity in natural populations. Using a capillary electrophoresis genotyping system, we fingerprinted 189 wild trees in 18 natural populations. Based on the 15 loci SSR profiles, we analyzed the intra- and inter-population variation and their relationship with control clones. The global allelic richness was 4.87 alleles per locus, but was 2.4 on average within individual populations; gene diversity was 0.368 and observed heterozygosity was low (0.160). Major structuring was discovered in the metapopulation of French Guianan wild cacao trees (Fst = 0.20), which could be explained by the biological characteristics of the cacao tree and the climatic events that affected the Guianan forests in the Quaternary period.  相似文献   

10.
–  • Chlorophyll meters such as the SPAD-502 offer a simple, inexpensive and rapid method to estimate foliar chlorophyll content. However, values provided by SPAD-502 are unitless and require empirical calibrations between SPAD units and extracted chlorophyll values.  相似文献   

11.

• Introduction  

Stem CO2 efflux (E s) is a significant component of total ecosystem respiration, but there is only scant information on seasonal variations in E s in tropical rainforests and on the main factors explaining these variations.  相似文献   

12.
Comparative water use by dryland trees in Parklands in Senegal   总被引:1,自引:1,他引:1  
Despite the clear evidence of competition for water between trees and crops, there have been very few studies comparing simultaneous water use by differing tree species in drylands. Comparative water use by dryland trees was measured in Senegal using heat balance gauges at the end of the wet season and in the dry season. Significant differences between tree species were found for maximum rates of water use per unit leaf area. Indigenous species may be better adapted to the dry environment than exotic species but the indigenous species Acacia seyal Del. used more water per unit leaf area than all other species. The exotic species Azadirachta indica Adr. Juss. consistently used less water per unit leaf area than most other species. There were significant differences in amounts of water used per unit leaf area by differing provenances of the same tree species. Water use in the dry season varied by a factor of three between two provenances of Acacia aneura F. Muell ex Benth. indicating potential to select provenances for drylands based on their water use characteristics. Absolute rates of water use as well as differences in sapflow between species were greatest when soils were moist suggesting that comparative sapflow studies will be most informative when carried out during the wet season. Water use rankings of the differing tree species were broadly maintained irrespective of season.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

13.
Pita P  Pardos JA 《Tree physiology》2001,21(9):599-607
Changes in leaf size, specific leaf area (SLA), transpiration and tissue water relations were studied in leaves of rooted cuttings of selected clones of Eucalyptus globulus Labill. subjected to well-watered or drought conditions in a greenhouse. Significant differences between clones were found in leaf expansion and transpiration. There was a significant clone x treatment interaction on SLA. Water stress significantly reduced osmotic potential at the turgor loss point (Pi0) and at full turgor (Pi100), and significantly increased relative water content at the turgor loss point and maximum bulk elastic modulus. Differences in tissue water relations between clones were significant only in the mild drought treatment. Among clones in the drought treatments, the highest leaf expansion and the highest increase in transpiration during the experiment were measured in those clones that showed an early and large decrease in Pi0 and Pi100.  相似文献   

14.
Summary Water in contact with wood surfaces is able to penetrate into the cellular structure by three routes: 1. As liquid water into cell lumena, by capillarity. — 2. As water vapour, by diffusion into cell lumena. — 3. As bound water, by diffusion within the cell wall.Transport from cell lumena into adjacent cell walls occurs rapidly by diffusion. In Scots pine (Pinus sylvestris) sapwood, it is shown that transport over short distances occurs much more rapidly by capillarity than by either of the diffusion processes. Treatment of wood with resin/wax water repellent formulations greatly reduces the rate of water flow due to capillarity and hence significantly cuts down the rate of dimensional change of specimens exposed to wet conditions.Swelling rates due to vapour phase and bound water diffusion were measured experimentally, and these data were used to predict the water sorption rates for specimens treated with a theoretically perfect water repellent, viz. that which excludes all liquid water.It was found experimentally that specimens immersed in water, after treatment with resin/wax water repellents, swelled more rapidly than predicted by the above procedure. This more rapid swelling is probably due to a certain amount of liquid water flow made possible by displacement of the hydrophobic film from cell wall surfaces (preferential wetting). It is suggested that the use of hydrophobic agents bonded chemically to the cell wall may be necessary to attain optimum water repellent effectiveness.  相似文献   

15.
Knowledge of the status and dynamics of soil N is essential to improving the production and management of silvopastoral system in the tropics. Soil N status and dynamics were analyzed as key factors affecting productivity and sustainability of a cut-and-carry silvopastoral system. The total soil N and N mineralization as affected by soil moisture and temperature were studied in a Gliricidia sepium (Jacq.) Walp – Dichanthium aristatum (Poir) C.E. Hubbard grassland association and in an adjacent open grassland located in a subhumid tropical region. The plot was installed in 1989 and the pruning residues and cut grass were removed from the site. No N fertilizer was applied. Total soil N increased at an average rate of 180 kg N ha−1 in the 0–0.2 m soil layer of the silvopastoral plot. Only a third of this value could be explained by the litter, nodule and root turnover. Nitrogen mineralization in both soils varied as a function of temperature but it was not affected by soil moisture. Even if mean soil temperature was 1 °C to 2 °C greater in the open grassland, the estimated daily rate of in-situ N mineralization was 20% greater in the silvopastoral system. Our results indicated that greater N mineralization in the silvopastoral system was due to greater soil biological activity associated with higher soil organic matter rather than due to more favorable soil temperature and water conditions. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

16.
Phillips N  Bergh J  Oren R  Linder S 《Tree physiology》2001,21(12-13):851-860
We investigated effects of nutrition and soil water availability on sap flux density, transpiration per unit leaf area (EL), and canopy stomatal conductance (GS) of Norway spruce (Picea abies L. (Karst.)) in northern Sweden during the 1996 growing season. Our objectives were to determine (1) if artificially imposed drought (65% rain diversion) reduces soil water sufficiently to cause physiological limitations to whole-tree and plot-scale water transport, and (2) whether increased capacity for water transport resulting from fertilization-induced increases in leaf (> 3-fold) and sapwood areas (> 2.3-fold) deplete soil water sufficiently to cause a negative feedback on GS and EL. We monitored soil water content (theta) and soil water potential (PsiS) in control (C), drought (D), fertilized (F) and irrigated + fertilized (IL) treatment plots, along with site meteorological conditions. Ten trees per plot were monitored for sap flow. Although there were significant treatment differences in mean daily EL (C > D > F; P < 0.01) and GS (C > D > F; P < 0.05), variation in absolute magnitudes was small. Therefore, transpiration differences on a unit ground area basis (EC) were nearly proportional to leaf area differences. Precipitation was well distributed throughout the study period and so PsiS remained high, except during short dry periods in Plot F when it declined rapidly. Thus, although soil water was not limiting to GS, EL or EC when precipitation was uniformly distributed throughout the growing season, we cannot conclude that water availability would not limit GS in fertilized stands if the seasonal distribution of precipitation were altered.  相似文献   

17.
Four new limonoids, named granatumins V–Y (1–4), belonging to the small group of limonoids with a C1–C29 oxygen bridge and a ∆8,30 double bond, were isolated from the seeds of an Indian mangrove, Xylocarpus granatum, collected in the swamp of Krishna estuary, Andhra Pradesh. The constitutions and absolute configurations of these compounds were established by extensive NMR investigations, single-crystal X-ray crystallography using Cu Kα radiation, and by the comparison of circular dichroism spectrum.  相似文献   

18.
Many evergreen mahogany (Swietenia macrophylla King) trees in the seasonally dry Bajo Paragua forest in northeast Bolivia carry substantial liana loads. Evergreen lianas may impede the growth of their host trees in various ways, including competition for water. Hypotheses tested were that water relations status differs (a) between lianas and their host trees, and (b) between trees infested with lianas that were cut 3.5 months previously (treated trees) and control trees with intact lianas. Diurnal measurements of stomatal conductance (g(s)) and leaf water potential (Psi) were made on canopy leaves of treated and control trees and lianas at the start and end of the dry season. Lianas had higher (less negative) Psi values (mean and predawn) and higher diurnal g(s) (expressed as mean or sum of diurnal values) than mahogany trees, indicating that lianas had a higher demand for, and ability to obtain, water than their host trees. Control and treated trees had a similar water relations status, suggesting that removal of lianas had no effect on the water relations of the trees, even at the end of the dry season. We conclude that either both life forms have conservative water relations that were unaffected by water availability in our study, or that the trees and lianas have access to sufficient and different sources of water because of differences in their rooting depths. Our data are consistent with studies of temperate species, indicating that lianas do not interfere with water availability to their host trees.  相似文献   

19.
Water use by mature trees of Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan var. raddiana growing in the northern Sahel was continuously recorded over 4 years. Water use was estimated from xylem sap flow measured by transient heat dissipation. Concurrently, cambial growth, canopy phenology, leaf water potential, climatic conditions and soil water availability (SWA) were monitored. In addition to the variation attributable to interannual variation in rainfall, SWA was increased by irrigation during one wet season. The wet season lasted from July to September, and annual rainfall ranged between 146 and 367 mm. The annual amount and pattern of tree water use were stable from year-to-year despite interannual and seasonal variations in SWA in the upper soil layers. Acacia tortilis transpired readily throughout the year, except for one month during the dry season when defoliation was at a maximum. Maximum water use of about 23 l (dm sapwood area)(-2) day(-1) was recorded at the end of the wet season. While trees retained foliage in the dry season, the decline in water use was modest at around 30%. Variation in predawn leaf water potential indicated that the trees were subject to soil water constraint. The rapid depletion of water in the uppermost soil layers after the wet season implies that there was extensive use of water from deep soil layers. The deep soil profile revealed (1) the existence of living roots at 25 m and (2) that the availability of soil water was low (-1.6 MPa) down to the water table at a depth of 31 m. However, transpiration was recorded at a predawn leaf water potential of -2.0 MPa, indicating that the trees used water from both intermediary soil layers and the water table. During the full canopy stage, mean values of whole-tree hydraulic conductance were similar in the wet and dry seasons. We propose that the stability of water use at the seasonal and annual scales resulted from a combination of features, including an extensive rooting habit related to deep water availability and an effective regulation of canopy conductance. Despite a limited effect on tree water use, irrigation during the wet season sharply increased predawn leaf water potential and cambial growth of trunks and branches.  相似文献   

20.
Soil moisture content from 0 to 2 m depth was monitored under 2–6 year old radiata pine (Pinus radiata) with three understoreys of bare ground, lucerne (Medicago sativa) and ryegrass/clover (Lolium perenne/Trifolium spp.) and under adjacent open-grown lucerne and ryegrass/clover pastures. By the fifth year soil moisture depletion/recharge pattern under the trees alone was similar to that under open pasture and under trees with pasture understoreys. Maximum plant available moisture storage was 207–223 mm in the top meter of this Templeton silt loam soil but only 69–104 mm at 1–2 m depth where coarse textures often predominated. Lucerne reduced soil moisture content (SMC) to lower levels during drier summers and extracted more water from 1 to 2 m depth than ryegrass/clover. Evapotranspiration (ET) during early summer when soil moisture was high was close to the Penman potential evapotranspiration (E p ), but the difference increased when SMC in the top meter dropped below 200 mm. The silvopasture treatments had higher ET in winter than pasture alone but this was still less than E p . Soil moisture deficits (SMD) at the end of each summer were sufficiently large to require slightly higher than normal winter rainfall and ET < E p to recharge the soil to field capacity before the next summer. The soil moisture results, taken together with root and growth data, suggest that trees and understorey pastures are complementary in the first three or four growing seasons but this balance subsequently declines in favor of the pine trees. Management options, to extend the period that understorey pastures are productive, include reducing tree stockings, more vigorous pruning, using competitive understoreys and changing from pines to deciduous trees. Research on new silvopastoral combinations is suggested.  相似文献   

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