摘要:

ABSTRACTTwo published models of canopy photosynthesis, MAESTRO and BIOMASS, are simulated to examine the response of tree stands to increasing ambient concentrations of carbon dioxide (Ca) and temperatures. The models employ the same equations to described leaf gas exchange, but differ considerably in the level of detail employed to represent canopy structure and radiation environment. Daily rates of canopy photosynthesis simulated by the two models agree to within 10% across a range of CO2concentrations and temperatures. A doubling ofCaleads to modest increases of simulated daily canopy photosynthesis at low temperatures (10% increase at 10°C), but larger increases at higher temperatures (60% increase at 30°C). The temperature and CO2dependencies of canopy photosynthesis are interpreted in terms of simulated contributions by quantum‐saturated and non‐saturated foliage. Simulations are presented for periods ranging from a diurnal cycle to several years. Annual canopy photosynthesis simulated by BIOMASS for trees experiencing no water stress is linearly related to simulated annual absorbed photosynthetically active radiation, with light utilization coefficients for carbon of ɛ= 1.66 and 2.07g MJ−1derived forCaof 350 and 700 μmol mol−1, r

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTRecent progress in improving the salt tolerance of cultivated plants has been slow. Physiologists have been unable to define single genes or even specific metabolic processes that molecular biologists could target, or pinpoint the part of the plant in which such genes for salt tolerance might be expressed. While the physiological might be expressed. While the physiological processes are undoubtedly complex, faster progress on unraveling mechanisms of salt tolerance might be made if there were more effort to test hypotheses rather than to accumulate data, and to integrate cellular and whole plant responses. This article argues that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme. Rather, the build‐up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growt

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTImages of chlorophyll fluorescence were used to demonstrate patchy stomatal closure at low humidities in leaves of well‐wateredXanthium strumariumplants. The pattern and extent of patchy stomatal closure were shown to be different for the two surfaces of amphistomatous leaves by taking images of leaves with CO2available to only one leaf was exposed to low humidity, patchiness was more extensive on that surface. Gas‐exchange experiments were also conducted to determine the apparent photosynthetic capacity of the mesophyll (photosynthesis rate at constantciwhen it was supplied with CO2through both surfaces or through each surface alone. These experiments showed declines in the apparent photosynthetic capacity of the mesophyll at low humidities that were consistent with patchy stomatal closure on one or both surfaces. The results suggest that patchy stomatal closure can be a factor in the steady‐state reponses of stomata to humidity. In amphistomatous leaves this is further complicated by the fact that patches on one epidermis may not coincide with those of the other su

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTPlants have the ability to dampen the effects of variability in water resources. Various mechanisms contribute to these properties: reduction of leaf area, increased rooting depth and stomatal conductance. To evaluate the differential roles and interactions of these mechanisms, we have built a model and simulated flows of water in Mediterranean evergreen scrub. The essential concept of this model is that the water status of the canopy is governed by the water lost by transpiration, the availability of soil water and the hydraulic resistances to water flow in soil and plant. The amount of water supplied by the roots is related to changes in water potential between the soil and the leaf. The amount of water lost to the atmosphere is regulated by an interaction between atmospheric demand and canopy water potential. Water uptake by plant is assumed equal to plant water loss. Leaf area appears to affect largely the annual water balance. The critical leaf water potential required to reduce the maximum stomatal conductance by half has a dominant effect on annual leaf water potential. Reducing rooting depth induces a new functional equilibrium for the plant. This new equilibrium is reached by decreasing leaf area and the critical leaf water potential. Our results show the complexity of interactions of these mechanisms and highlight the importance of the coordination between them. Finally, we suggest a reconsideration of these mechanisms in a context of the survival and long‐term persistence of the plan

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTDaily patterns of stomatal conductance (gs), xylem pressure potential (P) and canopy microclimatic variables were recorded on 11 sample days as part of a one‐year study of the water use ofEucalyptus grandisHill ex Maiden in the eastern Transvaal, South Africa. Measured gswas found to be largely controlled by quantum flux density (Q) and ambient vapour pressure deficit (D). Canopy conductance (gc) was determined for hourly intervals using gsmeasurements and leaf areas in four different canopy levels. A simple model was constructed to allow the prediction of gcand transpiration from Q, D and season of year. The model was used to estimate transpiration rates from 10 trees in a later study of similarly‐agedE. grandistrees, in which sap flow in each tree was measured using the heat pulse velocity (HPV) technique. Five of the trees were monitored on a summer day and five on a winter day. Correspondence between HPV sap flow and modelled transpiration was good for the summertime comparisons, but measured winter‐time sap flow rates were underestimated by the model, especially under conditions of high sap flow. The discrepancy is believed to result from having insufficient data from the conductance study to describe the response of gsto relatively high D in winter. Marked variation in transpiration per unit leaf area indicates that a relatively large number of trees must be sampled for the HPV technique to be used to obtain a mean rate for an entire stand in w

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe genusAnanashas its centre of origin in northern South America. In this area, several varieties ofAnanas comosusare widely cultivated, and a number of wild species are found growing under variable conditions of light intensity, soil fertility and water availability. Here we report detailed daily courses of titratable acidity, and malate, citrate and free‐sugars content of several cultivated varieties ofA. comosusand ofA. ananassoides, a closely related species growing on granitic rock‐outcrops in southern Venezuela. Day‐night oscillations of both malate and citrate were detected in plants growing under full sun, but malate was by far the most important organic anion associated with CAM performance in ail populations sampled. Fructose was the dominant compound in the neutral fraction, but only sucrose showed a consistent inverse relation with the cycle of titratable acidity. The diel oscillations of free sugars measured were not always enough to account for the amount of organic anions accumulated during the night. Plants cultivated under shady conditions always showed a lower night‐time increase in titratable acidity and organic acids, and also smaller oscillations in the amount of free sugars than sun exposed plants. In all populations growing under full sun, osmolality increased during the night, but it was not always possible to explain these changes on the basis of variations in molar concentrations of organic acids and sugars. Besides, no diel variations in the cations K+, Ca2+and Mg2+were detected. K+was always the dominant cation (K/Ca ratios ∼ 19), while Mg2+was always higher than Ca2+(M

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTLight gradients were measured in leaves that had different types of anatomical development of the mesophyll but similar pigment content. Leaves of the legume,Thermopsis montana, had columnar palisade and spongy mesophyll whereas leaves of the monocot,Smilacina stellata, had spongy mesophyll only. Light gradients were measured at 550 nm in both types of leaves when they were irradiated with collimated or diffuse light. When irradiated with collimated light, light gradients were steeper in leaves with spongy mesophyll in comparison to those that had palisade tissue. On the other hand, light gradients were similar between both leaf types when they were irradiated with diffuse light. Thus, columnar palisade cells facilitated the penetration of collimated light over diffuse light. These results suggest that palisade tissue may help distribute light more uniformly to chloroplasts within the leaf. Moreover, the functional significance of palisade tissue may be related to the amount of collimated light within the natural environment.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe effects of ultraviolet‐B (UV‐B between 290 and 320 nm) on photosynthesis and growth characteristics were investigated in field grown cassava (Manihot esculentumCrantz). Plants were grown at ambient and ambient plus a 5.5kJ m−2d−1supplementation of UV‐B radiation for 95 d. The supplemental UV‐B fluence used in this experiment simulated a 15% depletion in stratospheric ozone at the equator (0°N). Carbon dioxide exchange, oxygen evolution, and the ratio of variable to maximum fluorescence (Fv/Fm) were determined for fully expanded leaves after 64–76 d of UV‐B exposure. AH plants were harvested after 95 d of UV‐B exposure, assayed for chlorophyll and UV‐B absorbing compounds, and separated into leaves, petioles, stems and roots. Exposure to UV‐B radiation had no effect onin siturates of photosynthesis or dark respiration. No difference in the concentration of UV‐B absorbing compounds was observed between treatments. A 2‐d daytime diurnal comparison of Fvto Fmratios indicated a significant decline in Fv/Fmratios and a subsequent increase in photoinhibition under enhanced UV‐B radiation if temperature or PPF exceeded 35°C or 1800μmol m−2s−1, respectively. However, UV‐B effects on fluorescence kinetics appeared to be temporal since maximal photosynthetic rates as determined by oxygen evolution at saturated CO2and PPF remained unchanged. Although total biomass was unaltered with UV‐B exposure, alterations in the growth characteristics of cassava grown with supplemental UV‐B radiation are consistent with auxin destruction and reduced apical dominance. Changes in growth included an alteration of biomass partitioning with a significant increase in shoot/root ratio noted for plants receiving supplemental UV‐B radiation. The increase in shoot/root ratio was due primarily to a significant decrease in root weight (–32%) with UV‐B exposure. Because root production determines the harvest‐able portion of cassava, UV‐B radiation may still influence the yield of an important tropical agronomic species, even though photosynthesis

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe capacity for photosynthesis is often affected when plants are grown in air with elevated CO2partial pressure. We grewPhaseolus vulgarisL. in 35 and 65 Pa CO2and measured photosynthetic parameters. When assayed at the growth CO2level, photosynthesis was equal in the two CO2treatments. The maximum rate of ribulose‐1,5‐bisphosphate (RuBP) consumption was lower in plants grown at 65 Pa, but the CO2partial pressure at which the maximum occurred was higher in the high‐CO2‐grown plants, indicating acclimation to high CO2. The acclimation of RuBP consumption to CO2involved a reduction of the activity of RuBP carboxylase which resulted from reduced carbamylation, not a loss of protein. The rate of RuBP consumption declined with CO2when the CO2partial pressure was above 50Pa in plants grown under both CO2levels. This was caused by feedback inhibition as judged by a lack of response to removing O2from the air stream. The rate of photosynthesis at high CO2was lower in the high‐CO2‐grown plants and this was correlated with reduced activity of sucrose‐phosphate synthase. This is only the second report of O2‐insensitive photosynthesis under growth conditions for plants gr

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTPot culture studies were conducted using two drought‐tolerant and one susceptible cultivar of wheat (Triticum aestivumL.) under three different moisture regimes. Proton spin‐lattice relaxation time,T1, leaf water content, LWC, leaf water potential, Ψ, solute potential, Ψsand turgor potential, Ψpwere measured from 45 to 75 d after sowing at weekly intervals. The three cultivars did not differ significantly in their values of LWC, leaf water potential, and their components in the stressed and unstressed plants; but they did differ significantly in theirT1values both under stressed and unstressed conditions on all days of measurement, with the drought tolerant cultivars having a higherT1compared to the susceptible cultivar. This suggests that leaf waterT1is a better parameter for describing plant water status than the traditional water relation indices. The relation between Ψ andT1was logarithmic, indicating the similarity betweenT1and water activity of the cellula

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY