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691.
The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility
in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under
similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha-1 in the H. sonora stand to 27.2 Mg ha-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked
by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing
leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing
leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment
of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral
soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship
was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration
than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar
texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of
covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have
had different influences on the concentration of available nutrients in soil. 相似文献
692.
Michael R. Blatt 《Planta》1990,180(3):445-455
Evidence of a role for abscisic acid (ABA) in signalling conditions of water stress and promoting stomatal closure is convincing, but past studies have left few clues as to its molecular mechanism(s) of action; arguments centred on changes in H+-pump activity and membrane potential, especially, remain ambiguous without the fundamental support of a rigorous electrophysiological analysis. The present study explores the response to ABA of K+ channels at the membrane of intact guard cells ofVicia faba L. Membrane potentials were recorded before and during exposures to ABA, and whole-cell currents were measured at intervals throughout to quantitate the steady-state and time-dependent characteristics of the K+ channels. On adding 10 M ABA in the presence of 0.1, 3 or 10 mM extracellular K+, the free-running membrane potential (V
m) shifted negative-going (–)4–7 mV in the first 5 min of exposure, with no consistent effect thereafter. Voltage-clamp measurements, however, revealed that the K+-channel current rose to between 1.84- and 3.41-fold of the controls in the steady-state with a mean halftime of 1.1 ± 0.1 min. Comparable changes in current return via the leak were also evident and accounted for the minimal response inV
m. Calculated atV
m, the K+ currents translated to an average 2.65-fold rise in K+ efflux with ABA. Abscisic acid was not observed to alter either K+-current activation or deactivation.These results are consistent with an ABA-evoked mobilization of K+ channels or channel conductance, rather than a direct effect of the phytohormone on K+-channel gating. The data discount notions that large swings in membrane voltage are a prerequisite to controlling guard-cell K+ flux. Instead, thev highlight a rise in membranecapacity for K+ flux, dependent on concerted modulations of K+-channel and leak currents, and sufficiently rapid to account generally for the onset of K+ loss from guard cells and stomatal closure in ABA. 相似文献
693.
Water-storage capacity was measured inThuja occidentalis L.,Tsuga canadensis (L.) Carr., andAcer saccharum Marsh. during the dehydration of stem segments 1.5–2.5 cm in diameter. Stem water potential was measured with a temperature-corrected
stem hygrometer and cavitations were detected acoustically. Water loss was measured by weight change. Dehydration isotherms
consistently displayed three phases. The first phase, from water potential (Ψ) 0 to about −0.2 MPa, had a high capacitance
(C>0.4kg water lost· (1 of tissue)−1· MPa−1) and we have attributed this high C to capillary water as defined by Zimmermann (1983, Xylem structure and the ascent of
sap, Springer-Verlag). The second phase from Ψ=−0.5 to about −2.0 had the lowest C values (<0.02 kg·l−1·MPa−1) and was accompanied by a few cavitation events. This phase may have been a transition zone between capillary storage and
water released by cavitation events as well as water drawn from living cells of the bark. The third phase also had a high
C (about 0.07–0.22kg·l−1·MPa−1) and was associated with many cavitation events while Ψ declined below about −2.5 MPa; we presume the high capacitance was
the consequence of water released by cavitation events. We discuss the ecological adaptive advantage of these three phases
of water-storage in trees. In moist environments, water withdrawn from capillary storage may be an important fraction of transpiration,
but may be of little adaptive advantage. For most of the growth season trees draw mainly on elastic storage, but stem elastic
storage is less than leaf elastic storage and therefore unlikely to be important. In very dry environments, water relased
by cavitation events might be important to the short-term survival of trees. 相似文献
694.
Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures
of O2 (pO2; 1–80%, v/v, in N2) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO2 tested. In sub-ambient pO2 (1 and 2.5%) nodules contained specific activities of uricase (urate: O2 oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those
from air. On a cell basis, uninfected cells in nodules from 1% O2 contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in
sub-ambient O2, the activities of other enzymes of ureide synthesis were relatively unaffected by pO2. Short-term effects of pO2 on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO2 (1, 2.5 or 5%, v/v in N2) and15N2. Despite a fall in total15N2 fixation, ureide synthesis and export was maintained at a high level except in 1% O2 where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules
which allow the balance between O2 supply and demand to be maintained over a wide range of pO2, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of
fixed nitrogen.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance
Bureau postgraduate fellowship (to F.D.D.). 相似文献
695.
David A. Hill 《Primates; journal of primatology》1990,31(1):33-50
The social relationships of adult male rhesus macaques (Macaca mulatta) in Group I of the Cayo Santiago colony were studied over a period of 14 months. Relationships were found in which adult
males and sexually mature females were persistently close to one another in nonsexual contexts, both within and across seasons.
Males of long tenure and high dominance rank tended to have more female partners, and more persistent relationships, than
more recent immigrants of lower rank. Correlations with length of tenure were stronger than those with dominance rank. Closely-related
females tended to have persistent relationships with the same male. In most cases the female was primarily responsible for
maintaining proximity in non-sexual contexts.
Dyads which were persistently within 5 m of each other in the birth season were more likely to form a consortship in the subsequent
mating season than those which had a brief relationship. A similar tendency was apparent in the 1 m data but it was not statistically
significant. There was no association between persistent proximity during the birth season and the occurrence of long, or
multiple consortships, nor with the maintenance of proximity or direction of grooming between consort partners. The pattern
of consortships was not closely related to the formation of persistent relationships in the subsequent birth season. Females
occasionally received protection from their male partners and, in some cases, spent more time in the feeding corral with them
than did other females.
Affiliative relationships can be very enduring and may have long-term benefits that were not apparent during the study period. 相似文献
696.
Cortical microtubules (MTs) in protoplasts prepared from tobacco (Nicotiana tabacum L.) BY-2 cells were found to be sensitive to cold. However, as the protoplasts regenerated cell walls they became resistant
to cold, indicating that the cell wall stabilizes cortical MTs against the effects of cold. Since poly-l-lysine was found to stabilize MTs in protoplasts, we examined extensin, an important polycationic component of the cell wall,
and found it also to be effective in stabilizing the MTs of protoplasts. Both extensin isolated from culture filtrates of
tobacco BY-2 cells and extensin isolated in a similar way from cultures of tobacco XD-6S cells rendered the cortical MTs in
protoplasts resistant to cold. Extensin at 0.1 mg·ml−1 was as effective as the cell wall in this respect. It is probable that extensin in the cell wall plays an important role
in stabilizing cortical MTs in tobacco BY-2 cells. 相似文献
697.
698.
699.
A brief pulse of red light (R) given to darkgrown seedlings ofArabidopsis thaliana (L.) Heyn. potentiates rapid synthesis of chlorophyll upon transfer to continuous white light. The time course for potentiation
of rapid greening shows that a R pulse in the LF (low fluence) range has maximal effect within a few hours, and that there
is a small VLF (very low fluence) component as well. Partial reversal of the effect of R by far-red light (FR) indicates that
the pulse acts through phytochrome. As it does in the wild-type (WT), a pulse of R accelerates greening of long-hypocotyl
(hy) mutants. The extent of induction by the R pulse was about the same in the WT and in allhy mutants studied. Reversibility by FR was greatly decreased in thehy-1 andhy-2 strains. It is possible that these mutants contain a species of phytochrome with defective phototransformation kinetics.
If there is such a defective phytochrome species, it nevertheless appears to be active in the potentiation of rapid greening.
Dedicated to Professor Hans Mohr on the occasion of his 60th birthday 相似文献
700.
Nodules of cowpea (Vigna unguiculata (L.) Walp. cv. Vita 3:Bradyrhizobium CB 756) from 28-d-old plants cultured for 23 d with their root systems maintained in O2 levels from 1 to 80% (v/v, in N2) in the external gas phase showed a range of structural changes which have been interpreted in relation to an over- or under-supply
of O2. A response to the partial pressure of O2 in the gas phase (pO2) was noted with respect to nodule size, lenticel development, the relative distributions of cortical and infected central
tissue, the differentiation of cortex, especially the inner cortex, the frequency and size of infected and uninfected interstitial
cells, the volume of extracellular spaces both in cortex and infected tissue, and in the frequency of bacteroids. As a consequence
of these changes the surface area of inner cortex relative to the nitrogenase-containing units of fixing tissue (infected
cells or bacteroids) was increased by as much as 20-fold. Effectiveness of bacteroid functioning increased from 0.10 ± 0.02
· 10-9 μmol acetylene reduced per bacteroid in air-grown nodules to 0.9 ± 0.16 · 10-9 (same units) per bacteroid in those cultured in 1% O2.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian International Development
Assistance Bureau postgraduate fellowship (to F.D.D.). The authors wish to thank Dr. W.F.C. Blumer for his considerable help
with morphometric analysis, Dr. J. Kuo for guidance in the use of histological techniques, and to Dr. J.S. Pate for the suggestion
that lenticel development might be quantified by surface staining of nodules. 相似文献