Ozone flux in Glycine max (L.) Merr.: Sites of regulation and relationship to leaf injury

Summary Hood and Dare cultivars of soybean, Glycine max (L.) Merr., vary in their foliar response to ozone. The physiological basis of this variation was investigated as a function of leaf age through an analysis of ozone flux data, leaf developmental morphology, and analogue modelling techniques. At all concentrations (0.25–0.58 l l^-1) and exposure times (1–4 h), resistance to O₃ flux in the gas phase of the diffusive pathway (i.e., boundary layer and stomate) did not account fully for variation in pollutant uptake rates into the leaf interior. Ozone molecules experienced a residual resistance to diffusion that is not shared by effluxing water vapor molecules. Residual resistance to O₃ flux increased with pollutant concentration and exposure time and was associated with age-dependent differences in foliar O₃ response. Leaf morphology data, including stomatal frequency and the ratio of internal to external surface area, did not help explain cultivar or age-dependent differences in O₃ flux. The extent of foliar injury was not consistently related to the magnitude of O₃ flux into the leaf interior. An analysis of the residual resistance to O₃ flux suggests that the gas and liquid phase pathways for O₃, water vapor, and carbon dioxide are not identical.     

Transpiration rate and intercellular diffusive resistance in the tobacco leaf

The increase in the measured transpiration rate in tobacco leaves due to the experimentally decreased humidity of the bulk air was found to be significantly lower than the theoretical value calculated from the change of water vapour concentration gradients. Boundary layer and stomatal diffusive resistances remained unchanged under experimental conditions with no change of net photosynthetic CO₂ uptake. This suggests an increase in intercellular diffusive resistance with an increase in water vapour concentration gradient which is the driving force of water vapour diffusive part of transpiration flux. The increase can be ascribed to the lengthening of intercellular diffusive pathway as steeper water vapour concentration gradient in intercellular spaces results in an increased evaporating surface of intercellular cells thus moving the effective plane of vaporization in leaf mesophyll further inwards. Due to different and independent changes of concentration gradients for water vapour and CO₂, different length of intercellular diffusive pathways for CO₂ and water vapour may be expected.     

Stomatal uptake and stomatal deposition of ozone in isoprene and monoterpene emitting plants

Volatile isoprenoids were reported to protect plants against ozone. To understand whether this could be the result of a direct scavenging of ozone by these molecules, the stomatal and non-stomatal uptake of ozone was estimated in plants emitting isoprene or monoterpenes. Ozone uptake by holm oak (Quercus ilex, a monoterpene emitter) and black poplar (Populus nigra, an isoprene emitter) was studied in whole plant enclosures (continuously stirred tank reactors, CSTR). The ozone uptake by plants was estimated measuring ozone concentration at the inlet and outlet of the reactors, after correcting for the uptake of the enclosure materials. Destruction of ozone at the cuticle or at the plant stems was found to be negligible compared to the ozone uptake through the stomata. For both plant species, a relationship between stomatal conductance and ozone uptake was found. For the poplar, the measured ozone losses were explained by the uptake of ozone through the stomata only, and ozone destruction by gas phase reactions with isoprene was negligible. For the oak, gas phase reactions of ozone with the monoterpenes emitted by the plants contributed significantly to ozone destruction. This was confirmed by two different experiments showing a) that in cases of high stomatal conductance but under low CO(2) concentration, a reduction of monoterpene emission was still associated with reduced O(3) uptake; and b) that ozone losses due to the gas phase reactions only can be measured when using the exhaust from a plant chamber to determine the gas phase reactivity in an empty reaction chamber. Monoterpenes can therefore relevantly scavenge ozone at leaf level contributing to protection against ozone.     

Sensitivity of infrared water vapor analyzers to oxygen concentration and errors in stomatal conductance

Use of infrared analyzers to measure water vapor concentrations in photosynthesis systems is becoming common. It is known that sensitivity of infrared carbon dioxide and water vapor analyzers is affected by the oxygen concentration in the background gas, particularly for absolute analyzers, but the potential for large errors in estimates of stomatal conductance due to effects of oxygen concentration on the sensitivity of infrared water vapor analyzers is not widely recognized. This work tested three types of infrared water vapor analyzers for changes in sensitivity of infrared water vapor analyzers depending on the oxygen content of the background gas. It was found that changing from either 0 or 2% to 21% oxygen in nitrogen decreased the sensitivity to water vapor for all three types of infrared water vapor analyzers by about 4%. The change in sensitivity was linear with oxygen mole fraction. The resulting error in calculated stomatal conductance would depend strongly on the leaf to air vapor pressure difference and leaf temperature, and also on whether leaf temperature was directly measured or calculated from energy balance. Examples of measurements of gas exchange on soybean leaves under glasshouse conditions indicated that changing from 21% to 2% oxygen produced an artifactual apparent increase in stomatal conductance which averaged about 30%. Similar errors occurred for `conductances' of wet filter paper. Such errors could affect inferences about the carbon dioxide dependence of the sensitivity of photosynthesis to oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

A new technique for measurement of water permeability of stomatous cuticular membranes isolated from Hedera helix leaves

Transpiration of cuticular membranes isolated from the lower stomatous surface of Hedera helix (ivy) leaves was measured using a novel approach which allowed a distinction to be made between gas phase diffusion (through stomatal pores) and solid phase diffusion (transport through the polymer matrix membrane and cuticular waxes) of water molecules. This approach is based on the principle that the diffusivity of water vapour in the gas phase can be manipulated by using different gases (helium, nitrogen, or carbon dioxide) while diffusivity of water in the solid phase is not affected. This approach allowed the flow of water across stomatal pores ('stomatal transpiration') to be calculated separately from the flow across the cuticle (cuticular transpiration) on the stomatous leaf surface. As expected, water flux across the cuticle isolated from the astomatous leaf surface was not affected by the gas composition since there are no gas-filled pores. Resistance to flux of water through the solid cuticle on the stomatous leaf surface was about 11 times lower than cuticular resistance on the astomatous leaf surface, indicating pronounced differences in barrier properties between cuticles isolated from both leaf surfaces. In order to check whether this difference in resistance was due to different barrier properties of cuticular waxes on both leaf sides, mobility of 14C-labelled 2,4-dichlorophenoxy-butyric acid 14C-2,4-DB) in reconstituted cuticular wax isolated from both leaf surfaces was measured separately. However, mobility of 14C-2,4-DB in reconstituted wax isolated from the lower leaf surface was 2.6 times lower compared with the upper leaf side. The significantly higher permeability of the ivy cuticle on the lower stomatous leaf surface compared with the astomatous surface might result from lateral heterogeneity in permeability of the cuticle covering normal epidermal cells compared with the cuticle covering the stomatal cell surface.     

In Situ Estimates of Variable Plant Resistance to Water Flux in Ilex opaca Ait

Xylem pressure potentials and stomatal diffusion resistances were measured in the field in Ilex opaca Ait. during days which differed in temperature and vapor pressure deficit. Water flux into leaves was calculated by combining the field data with laboratory determinations of the relation between tissue water deficit and water potential. Estimates of apparent plant resistance were then calculated from fluxes and differences between soil water potential and xylem tension. The resistance depended strongly on water flux, dropping by a factor of over 7 from low to high water flow rates. This extends the generality of variable plant resistances measured in controlled environment studies to I. opaca as it occurs naturally in the field. The relation of apparent plant resistance to water flux as estimated in this study can be useful in simulation models which calculate water uptake to leaves as a flux driven by a difference in soil and leaf water potentials across a resistance between the bulk soil and the leaf.     

Plant transpiration at high elevations: Theory,field measurements,and comparisons with desert plants

Summary The influence of elevational changes on plant transpiration was evaluated using leaf energy balance equations and well-known elevational changes in the physical parameters that influence water vapor diffusion. Simulated transpirational fluxes for large leaves with low and high stomatal resistances to water vapor diffusion were compared to small leaves with identical stomatal resistances at elevations ranging from sea level to 4 km. The specific influence of various air temperature lapse rates was also tested. Validation of the simulated results was accomplished by comparing actual field measurements taken at a low elevation (300 m) desert site with similar measurements for a high elevation (2,560 m) mountain research site. Close agreement was observed between predicted and measured values of transpiration for the environmental and leaf parameters tested.Substantial increases in solar irradiation and the diffusion coefficient for water vapor in air (D _wv) occurred with increasing elevation, while air and leaf temperatures, the water vapor concentration difference between the leaf and air, longwave irradiation, and the thermal conductivity coefficient for heat in air decreased with increasing elevation. These changes resulted in temperatures for sunlit leaves that were further above air temperature at higher elevations, especially for large leaves. For large leaves with low stomatal resistances, transpirational fluxes for low-elevation desert plants were close to those predicted for high-elevation plants even though the sunlit leaf temperatures of these mountain plants were over 10°C cooler. Simulating conditions with a low air temperature lapse rate (0.003° C m^-1 and 0.004° C m^-1) resulted in predicted transpirational fluxes that were greater than those calculated for the desert site. Transpiration for smaller leaves decreased with elevation for all lapse rates tested (0.003° C m^-1 to 0.010° C m^-1). However, transpirational fluxes at higher elevations were considerably greater than expected for all leaves, especially larger leaves, due to the strong influence of increased solar heating and a greater D _wv. These results are discussed in terms of similarities in leaf structure and plant habit observed among low-elevation desert plants and high-elevation alpine and subalpine plants.     

Stomatal cavity modulates the gas exchange of Sorghum bicolor (L.) Moench. grown under different water levels

This work aimed to evaluate the effects of lower water levels on leaf intercellular spaces and to assess their relations with the gas exchange, anatomy, and growth of Sorghum bicolor. Experiments were conducted in a greenhouse, in which plants were subjected to three water conditions (ten replicates, n = 30): well-irrigated, decreased irrigation, and limited irrigation. Lower water levels had no significant effect on the growth of S. bicolor but increased the biomass of the roots. Moreover, the number of leaves, leaf area, and leaf size as well as the chlorophyll content were not affected by lower water levels, and no significant changes were detected for whole plant photosynthesis, transpiration, or stomatal conductance. The water content of the plants and the water potential remained unchanged. However, compared with other treatments, the decreased irrigation decreased water loss and increased the water retention. Lower water levels increased the intercellular CO₂ percentage, mesophyll area, and proportion of stomatal cavities and promoted minor changes in leaf tissue and stomatal traits. The increased stomatal cavities provided higher CO₂ uptake and prevented excessive water loss. Thus, modifications to the intercellular spaces promoted conditions to avoid excessive water loss while concurrently improving CO₂ uptake, which are important traits for drought-tolerant plants.

     

Effect of Cyclic Variations in Gas Exchange under Constant Environmental Conditions on the Ratio of Transpiration to Net Photosynthesis

Simultaneous cyclic variation in rates of both net photosynthesis and transpiration were induced in attached leaves of cotton and pepper plants under constant environmental conditions. The cyclic variations in photosynthesis and transpiration were found to be in phase, and the ratio net photosynthetic rate/transpiration rate remained constant over a wide range of gas exchange rates. A similar constancy of this ratio was also found as gas exchange rates declined following excision of a sunflower leaf, which was not initially cycling, in air. These results suggested that change in stomatal aperture was the only controlling factor involved and that it was affecting both processes proportionately. Visible loss of leaf turgur and measurable water stress developed in both pepper and cotton at peak exchange rates, but the gas exchange ratio remained constant. The failure of water stress and increased stomatal aperture to lower the gas exchange ratio suggested an absence of any significant leaf mesophyll resistance (r′_m) to inward diffusion of CO₂. The possibility that r′_m was low is discussed generally, and in relation to the use of chemical antitranspirants to raise the gas exchange ratio. Within the limits of the experiments, water stress apparently had no direct adverse effect on rates of net photosynthesis. The gas exchange ratio did not rise as exchange rates declined. Ultimately, at very low exchange rates, the ratio fell, declining to zero in cotton, but not in pepper. This decline was attributed to the onset of significant gas exchange through the cuticle, which was apparently less permeable to CO₂ than to water vapour. Positive net cuticular photosynthesis therefore probably does not occur in cotton. Except at very low exchange rates, the gas exchange ratio was higher in cotton than in pepper; it was similar in sunflower and cotton.     

Mesophyll Resistance and Carboxylase Activity: A Comparison under Water Stress Conditions

The response of several leaf gas exchange parameters were monitored with decreasing leaf water potential in Phaseolus vulgaris L. leaflets. These included photosynthesis, transpiration, CO₂ compensation point, ribulose 1,5-diphosphate carboxylase activity, boundary layer plus stomatal, and mesophyll resistance to diffusion of CO₂. Mesophyll resistance was calculated under two assumptions: (a) the CO₂ concentration at the chloroplast was zero, and (b) it was equal to the CO₂ compensation point.     

Development of a photosynthesis model with an emphasis on ecological applications

Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to describe net photosynthesis daily time courses in Prunus armeniaca. Net photosynthesis rates are calculated in response to incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance measured at five minute intervals. The steady-state calculations closely approximate the observed net photosynthesis rates for a broad range of weather conditions and leaf stomatal behavior.     

小麦和大豆叶片的气孔不均匀关闭现象

用14CO2放射自显影的方法研究了田间小麦和大豆叶片在水分胁迫下的气孔关闭状况。正常浇水的小麦和大豆叶片呈现出对14CO2的均匀吸收。在小麦与大豆"片水势分别降至-1．75和-1．32MPa的土壤干旱条件下,两种作物叶片都发生气孔不均匀关闭。离休叶片在空气中快速脱水易引起气孔不均匀关闭。正常供水小麦叶片在晴天中午明显的光合午休时,无CO2的不均匀吸收。某些晴天中午,在大豆光合午休低谷时段观察到较明显的气孔不均匀关闭,用气体交换资料计算出的细胞间隙CO2浓度并不随气孔年度的降低而下降,反而略有回升。     

Gas Exchange and Water Use Efficiency of Adenophora lobophylla (Campanulaceae) at Different Altitudes on the East Boundary of the Qing- Zang Plateau

Field measurements were made of leaf net photosynthetic rate (Pn), apparent quantum yield (AQY), dark respiration (Rd), transpiration (Tr), water use efficiency (WUE), stomatal conductance (Gs), intercellular CO2 concentration (Ci), leaf temperature (TI), stomatal density, air temperature (Ta) and relative soil water content (SWC) for Adenophora lobophylla Hong in August, 1996. The species grows in the region from an altitude of 2 300 m to 3 400 m on the eastern boundary of the Qing-Zang Plateau in Sichuan Province, China. Leaf gas exchange, water use efficiency and plasticity of populations in field were compared among different altitudes to evaluate the possible interactions between adaptation of A. lobophylla and environmental factors in these habitats. Pn and AQY at low altitudes were lower than those at high altitudes. They strongly responded to SWC and Ta. On the other hand, Rd at low altitudes was higher than that at high altitudes because of the higher air temperature there. The growth rates at low altitudes were associated with the increases in Rd and a relevant less Pn. Stomata showed strong responses to leaf-to-air vapor pressure deficit at the leaf surface (Vpdl) and Tl in these habitats. Increasing stomatal limitations to photosynthesis appeared to be responsible for the reduction in Pn at high Tl, Vpdl and low available soil water for A. lobophylla at low ahitudes. Nonstomatal limitation to photosynthesis also happened at extreme soil water deficits and high Tl and Vpdl at an altitude of 2 300 m. Tr had a close relationship with stomatal conductance and was also affected by leaf temperature and leaf-to-air vapor pressure deficit at the leaf surface among habitats grown in different ahitudes. WUE increased with altitude. Increasing stomatal densities showed different plasticity of A. lobophylla as altitude increased. SWC and Ta appeared to be important factors to limit carbon assimilation in A. lobophylla at low altitudes, primarily through the process of stomatal closure. The overall results are in consistence with the hypothesis that strong pressure from tmfavorable environmental factors to gas exchange and wateruse of A. lobophylla may prevent their population expansion at low altitudes, which indicate that the above-mentioned restrictions might lead to the endangerment of A. lobophylla.     

OZONE SENSITIVITY OF LEAVES: RELATIONSHIP TO LEAF WATER CONTENT,GAS TRANSFER RESISTANCE,AND ANATOMICAL CHARACTERISTICS

Relative water content, resistance to gas transfer, stomatal spacing, and other characteristics of primary bean leaves were studied in relation to ozone sensitivity and injury. Cells of primary bean leaves are maximally sensitive to ozone exposure 9–10 days after germination under our experimental conditions. The stage of maximum sensitivity was not correlated with changes in stomatal number or resistance on either adaxial or abaxial leaf surfaces. It was deduced that bean leaf sensitivity was a function of more internal circumstances, and gas exchange was never the limiting factor through the developmental period studied. Changes in resistance were not significantly altered by ozone levels that produced no visible injury. After exposure to high ozone doses, a decrease in adaxial resistance occurred apparently as a result of palisade and epidermal cell lysis. Normally most gas exchange occurs through the adaxial surface. A 10 % decrease in relative water content accompanying a 60-min ozone exposure of 0.55 ppm could not be explained physiologically on the basis of cell injury as no visible leaf injury occurred.     

不同浇水量对毛乌素沙地沙柳幼苗气体交换过程及其光化学效率的影响

 利用毛乌素沙地优势灌木沙柳(Salix psammophila)幼苗,研究气体交换及其PSⅡ的光化学效率对4种浇水量响应。结果表明：不同浇水量明显影响沙柳幼苗净光合速率、蒸腾速率、气孔导度、胞间CO2浓度和叶片温度日变化动态;除幼苗叶片温度随着浇水量的增加而降低外,其它以上因素均随浇水量的增加而增大。浇水量少时,幼苗净光合速率明显有“午睡”现象,而充足浇水能有效消除幼苗净光合速率的“午睡”现象;浇水量增加降低了沙柳幼苗光补偿点,提高了饱和光强和表观量子效率;浇水量显著影响幼苗的PSⅡ光化学效率,随着浇水量减少,幼苗的最大荧光、可变荧光、最大荧光比和最大光化学效率逐渐减小。相关分析反映了在不同施水量处理下,环境因子光合有效辐射、大气温度、大气饱和水汽压差及其生理变量气孔导度、叶片温度、胞间CO2浓度均显著影响幼苗净光合速率。     

Gasometric method of water deficit measurement in leaves

A gasometric method was developed for measuring water deficit in leaves. For a leaf at full turgor the amount of water penetrating into the tissue after removing the air from intercellular spaces by means of a vacuum pump, is equal in volume to the gas removed from the intercellular spaces. In a leaf with a water deficit the amount of the infiltrating water is greater than the removed gas volume by the amount egual to the water deficit. Determination of the volumes of the gas removed and penetrating water enables water deficit, if any, to be calculated. Comparative measurements carried out on five plant species confirmed the correctness of the method suggested. Reduction of the measuring time allowed to eliminate completely the sources of errors associated with the growth of tissue and loss of dry weight during respiration.     

Stomatal constraints may affect emission of oxygenated monoterpenoids from the foliage of Pinus pinea

Dependence of monoterpenoid emission and fractional composition on stomatal conductance (G(V)) was studied in Mediterranean conifer Pinus pinea, which primarily emits limonene and trans-beta-ocimene but also large fractions of oxygenated monoterpenoids linalool and 1,8-cineole. Strong decreases in G(V) attributable to diurnal water stress were accompanied by a significant reduction in total monoterpenoid emission rate in midday. However, various monoterpenoids responded differently to the reduction in G(V), with the emission rates of limonene and trans-beta-ocimene being unaffected but those of linalool and 1,8-cineole closely following diurnal variability in G(V). A dynamic emission model indicated that stomatal sensitivity of emissions was associated with monoterpenoid Henry's law constant (H, gas/liquid phase partition coefficient). Monoterpenoids with a large H such as trans-beta-ocimene sustain higher intercellular partial pressure for a certain liquid phase concentration, and stomatal closure is balanced by a nearly immediate increase in monoterpene diffusion gradient from intercellular air-space to ambient air. The partial pressure rises also in compounds with a low H, but more than 1,000-fold higher liquid phase concentrations of linalool and 1,8-cineole are necessary to increase intercellular partial pressure high enough to balance stomatal closure. The system response is accordingly slower, and the emission rates may be transiently suppressed by low G(V). Simulations further suggested that linalool and 1,8-cineole synthesis rates also decreased with decreasing G(V), possibly as the result of selective inhibition of various monoterpene synthases by stomata. We conclude that physicochemical characteristics of volatiles not only affect total emission but also alter the fractional composition of emitted monoterpenoids.     

Leaf diffusion resistance, illuminance, and transpiration

Stepwise increases in fluorescent illuminance, imposed as a single variable in a controlled environment, induced progressive stomatal opening in 8 plant species, as evidenced by a consistent decrease in leaf diffusion resistance (R_L), ranging from 15 to 70 sec cm⁻¹ in darkness to about 1 sec cm⁻¹ at approximately 40 kilolux. The minimum R_L values were the same for the upper and the lower epidermis, provided that stomatal density was adequate. Saturation illuminance was not achieved in any species; extrapolation indicates that 50 kilolux would bring about full stomatal opening (R_L ≤ 0.1 sec cm⁻¹).

In 4 species, reasonable agreement was obtained in a controlled environment between transpiration as measured by weight loss and that calculated from determination of (a) the difference in water vapor density from leaf to air, (b) the boundary layer resistance, and (c) the leaf diffusion resistance. This result confirms the physical validity of the resistance measurement procedure.

     

Computer-based studies of diffusion through stomata of different architecture

BACKGROUND AND AIMS: The influence of stomatal architecture on stomatal conductance and on the developing concentration gradient was explored quantitatively by comparing diffusion rates of water vapour and CO(2) occurring in a set of three-dimensional stoma models. The influence on diffusion of an internal cuticle, a sunken stoma, a partially closed stoma and of substomatal chambers of two different sizes was considered. METHODS: The study was performed by using a commercial computer program based on the Finite Element Method which allows for the simulation of diffusion in three dimensions. By using this method, diffusion was generated by prescribed gas concentrations at the boundaries of the substomatal chamber and outside of the leaf. The program calculates the distribution of gas concentrations over the entire model space. KEY RESULTS: Locating the stomatal pore at the bottom of a stomatal antechamber with a depth of 20 microm decreased the conductance significantly (at roughly about 30 %). The humidity directly above the stomatal pore is significantly higher with the stomatal antechamber present. Lining the walls of the substomatal chamber with an internal cuticle which suppresses evaporation had an even stronger effect by reducing the conductance to 60 % of the original value. The study corroborates therefore the results of former studies that water will evaporate preferentially at sites in the immediate vicinity to the stomatal pore if no internal cuticle is present. The conductance decrease affects only water vapour and not CO(2). Increasing the substomatal chamber increases CO(2) uptake, whereas transpiration increases if an internal cuticle is present. CONCLUSIONS: Variation of stomatal structure may, with unchanged pore size and depth, profoundly affect gas exchange and the pathways of liquid water inside the leaf. Equations for calculation of stomatal conductance which are solely based on stomatal density and pore depth and size can significantly overestimate stomatal conductance.     

冬小麦叶片气孔导度模型水分响应函数的参数化

植物气孔导度模型的水分响应函数用来模拟水分胁迫对气孔导度的影响过程, 是模拟缺水环境下植物与大气间水、碳交换过程的关键算法。水分响应函数包括空气湿度响应函数和土壤湿度(或植物水势)响应函数, 该研究基于田间实验观测, 分析了冬小麦(Triticum aestivum)叶片气孔导度对不同空气饱和差和不同土壤体积含水量或叶水势的响应规律。一个土壤水分梯度的田间处理在中国科学院禹城综合试验站实施, 不同水分胁迫下的冬小麦叶片气体交换过程和气孔导度以及其他的温湿度数据被观测, 同时观测了土壤含水量和叶水势。实验数据表明, 冬小麦叶片气孔导度对空气饱和差的响应呈现双曲线规律, 变化趋势显示大约1 kPa空气饱和差是一个有用的阈值, 在小于1 kPa时, 冬小麦气孔导度对空气饱和差变化反应敏感, 而大于1 kPa后则反应缓慢; 分析土壤体积含水量与中午叶片气孔导度的关系发现, 中午叶片气孔导度随土壤含水量增加大致呈现线性增加趋势, 但在平均土壤体积含水量大于大约25%以后, 气孔导度不再明显增加, 而是维持在较高导度值上下波动; 冬小麦中午叶片水势与相应的气孔导度之间, 随着叶水势的增加, 气孔导度呈现增加趋势。根据冬小麦气孔导度对空气湿度、土壤湿度和叶水势的响应规律, 研究分别采用双曲线和幂指数形式拟合了水汽响应函数, 用三段线性方程拟合了土壤湿度响应函数和植物水势响应函数, 得到的参数可以为模型模拟冬小麦的各类水、热、碳交换过程采用。