Báo cáo lâm nghiệp: "2 CO response curves can be a measured with field-portable closed-loop photosynthesis system"

Chia sẻ: Nguyễn Minh Thắng | Ngày: | Loại File: PDF | Số trang:5

Thêm vào BST

Báo xấu

43
lượt xem 1
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: 2 CO response curves can be a measured with field-portable closed-loop photosynthesis system...

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Báo cáo lâm nghiệp: "2 CO response curves can be a measured with field-portable closed-loop photosynthesis system"

CO response curves can be measured with 2 field-portable closed-loop photosynthesis system a J.T. Davis T.M. Ball 3 D.K. McDermitt J.M. Norman 2 2 T.J. Arkebauer *, J.M. Welles 2 J.M. 1 rkebauer elles c mer 1 nd S.R. Roerner S.R. 1 1 LI-COR, Inc., Lincoln, NE 68504, 2 Department of Agronomy, University of Nebraska, Lincoln, NE 68583, 3 Department of Forestry, Fisheries and Wildlife, University of Nebras!ka, Lincoln, NE 68583, and 4 Carnegie Institution of Washington, Stanford, CA 94305, U.S.A. Introduction with a fully controlled steady state system. The effects of system leaks and control of leaf temperature are discussed. Assimilation rate versus internal C0 re- 2 sponse curves provide an important tool for assessing the efficiency and capacity Materials and Methods of the photosynthetic system. Until recent- ly, measurement of C0 response curves 2 was limited to laboratory studies, where Data of Fig. 1 were obtained on well-watered soybeans (Glycine max (L.) Merrill, cv Hobbit) elaborate gas exchange systems were grown in soil and 12 in pots in a temperature- to mobile field laboratories. available, or controlled (27 ± 3°C) greenhouse in Lincoln, Here we report the use of a portable pho- NE. Measurements were made on upper cano- tosynthesis system (LI-6200, LI-COR, py fully exposed leaves when the plants were in the early pod-filling stage. PAR was supplied by Inc.) for measurement of response curves. one Metalarc 400 W lamp and one Lucolux 400 The LI-6200 uses a closed-loop design in W lamp in a single water-cooled luminaire (Sun- which varying C0 concentrations are pro- 2 brella, Environmental Growth Chambers, Cha- vided the leaf from the 2 C0 as removes grin Falls, OH). 1’he 1I chamber of the LI-6200 system. A typical measurement requires was mounted on a tripod and placed at a dis- tance beneath the lamp which gave the desired 10-25 min, depending upon chamber light intensity. Radiation from the lamp was fil- volume, leaf area and assimilation rate. tered with 1/4 in plexiglas and external air flow Response curves measured on well- was provided by a small 110 V fan. Response watered soybean and cotton with the LI- curves were constructed as described in results. 6200 are compared to those measured * Present address: Department of Soils, University of Wisconsin, Madison. Wl 53706. U.S.A. is consin, ** Present address: Systems Ecology Group, California State University, San Diego, CA 92t 20, U.S.A.
Data of Figs. 2, 3 and 4 were obtained on vegetative soybeans grown in vermiculite and 8 in pots in the greenhouse at Carnegie Institu- tion, Stanford, CA. Measurements made were in adjacent laboratory with the steady state an system described by Ball (1987), and with the LI-6200. Relative humidity sensor and IRGA calibrations were carefully compared and checked prior to measurement. PAR (1200-1300 UMO was supplied by a ) 1 S 2 - M I- high intensity projector lamp filtered with a dichroic mirror. Comparative measurements were made on the same leaflets. Data reported in Figs. 2, 3 and 4 were obtained with chamber relative humidity (RH) above 72% in both sys- tems. A response curve measured on soybean with the LI-6200 at ambient humidity (32%) deviated from a concomitant curve measured with the steady state system at about 70% RH. The pattern of photosynthesis rates and internal C0 concentrations suggested that stomatal 2 conductance was not uniform across the leaf at the lower humidity (Terashima et al., 1988; data not shown). Data of Fig. 5 were obtained on vegetative cotton grown in nutrient solution at 33°C, about 35% RH and 600 llmol 1 s 2 m- ’ light intensity. Further details pertaining to the the curve measured by continuous draw- measurements are given in the text. down is coincident with that measured after a 5 min equilibration at each C02 level, we conclude that the 2 methods are equivalent. Soybean leaflets are evidently Results able to maintain a quasi-steady state with slowly declining (0.01-1 ppm-s- ex- ) 1 a C0 concentration. Three other ternal 2 A baseline C0 response curve was mea- 2 experiments gave the same result. sured by placing a single soybean leaflet in the 1I assimilation chamber of the LI- To further evaluate results obtained with 6200 and allowing the leaflet to remove the LI-6200, response curves were mea- C0 until the compensation point was sured on soybeans with a steady state 2 reached. Assimilation rate, conductance system described by Ball (1987) and side- and internal C0 concentration were com- by-side measurements were made on the 2 puted every 5 ppm or so as the chamber same leaves under similar conditions with C0 mole fraction declined. This was 2 the LI-6200 (Fig. 2). Correspondence be- repeated 2 more times and all curves tween the 2 methods is generally excellent were coincident (data not shown). A 4th except that the C0 compensation point is 2 curve was prepared in which the C0 slightly overestimated by the LI-6200. At 2 mole fraction was held constant (± 5 low chamber C0 mole fractions, a large 2 ) 1 mol- ’ pmol for 5 min at 7 different levels C0 gradient exits between chamber air 2 and ambient air exaggerating chamber 2 C0 injector. Assimilation, using a conductance and C, were then measured leaks that are normally small. Leaks cause in transient mode by allowing the C0 an underestimation of the assimilation 2 mole fraction to decline a few ppm from rate, and consequently, an overestimation each of the preset levels (Fig. 1Since of the compensation point.
and correct each assimilation measure- ment as the chamber C0 mole fraction 2 declines. Both corrected and uncorrected data can be stored. As the experiments reported in Figs. 2-5 progressed, r declined from about 15 000 s to about 7000 s, presumably due to chamber gasket deterioration. The effects of leaks on the LI-6200 data from Fig. 2 are shown in Fig. 3 for 2 values of a. Chamber leaks have important effects at low chamber C0 mole fractions, but 2 negligible effects at ambient levels. In ordi- nary photosynthesis measurements where C0 concentrations are near ambient, 2 only small gradients exist to drive C0 dif- 2 fusion into the chamber, so chamber leaks are not a problem. However, when C0 2 response curves are being measured, leak tests should be performed regularly, and the data corrected accordingly. Fig. 4 Chamber leaks can be modeled by the shows the LI-6,200 data from Fig. 2 after following expression: the leak correction was applied. The cor- ) /dt er b am ch dc ((Cambient- G / chamber ’l’); respondence between the steady state and LI-6200 results is excellent. Similar where dCcnamber!dtis the C0 change rate 2 results were obtained in a 2nd experiment. due to chamber leaks (s-!), C is the ent i amb 2 C0 for 2 separate C0 mole fraction of ambient air sur- 2 curves response leaves of chamber-grown cotton were rounding the chamber (pmol or 1 mol- ’ measured late in the afternoon. Leaves pp Gchamber is the chamber C0 mole 2 m), were trimmed symmetrically about the fraction, and is the leak rate time r (s). A simple leak test can be constant performed by first reducing the chamber C0 mole fraction to 50-100 ppm using 2 the system C0 scrubber, and then 2 rate of C0 increase measuring the 2 with a filter paper leaf rep- (dCcnamber!dn lica in the chamber. Since the chamber C0 mole fraction is always known, and 2 the ambient C0 mole fraction is constant 2 and easily measured, r can be computed. We have found that a is constant and in- dependent of the C0 gradient for a given 2 set of conditions. Once r, G and chamber C are known, the leak rate can be t en i amb computed and subtracted from the mea- sured C0 change rate. The LI-6200 can 2 be programmed to calculate the leak rate
mid-vein prior to measurement. LI-6200 data were first obtained in the growth room, and then the plants were trans- ferred into fresh growth solution, taken down a cool, dimly lit outside hallway and into the laboratory, where steady state It is rapid and convenient inas- curves. measurements were performed. Results much as it does not require a series of for both the steady state system and LI- mixed gasses or long equilibration times, 6200 are shown in Fig. 5. Compensation and it can be performed with a compact points and initial slopes are in excellent and portable instrument. However, a major agreement, but maximum rates were question which remains is leaf tempera- higher when measured in situ with the LI- ture control. 6200. There is little doubt that the time of Leaf temperature control in the LI-6200 day and prior treatment of the plants affec- chamber relies on evaporative cooling of ted maximal rates measured with the stea- the leaf and passive heat exchange with dy state system. the environment. Since there is no active temperature control, leaf temperature increases, which might occur during a measurement lasting 20 min or more, are Discussion a matter of concern. As indicated in the figure legends, leaf temperature control in These and other experiments support the artificial environments is not a serious conclusion that well-watered C-3 plant problem. High intensity incandescent leaves are able to maintain a quasi-steady lamps which produce a narrow light beam state with respect to C0 mole fractions 2 be filtered with dichroic mirror. Such can a which change at the rates observed used to produce the light a source was in typical experiments (e.g., 0.01-1 data of Figs. 3-5. Clear plexiglas makes ). 1 ppm-s- Under these conditions, the an excellent IR filter for high intensity transient approach provides a valid discharge lamps. A plexiglas filter, along method for measuring C0 response 2 with an external fan and water-cooled
41 °C with an external fan, whereas the luminaire, effectively controlled leaf tem- chamber air temperature gradually in- perature increases under our HID lamp. creased to 44°C without the fan. With The problem is more serious in the field, proper techniques, temperature increases although it is not insurmountable. Davis can often be held to under 2-3°C. The et al. (1987) reported a chamber tempera- data of Brooks and Farquhar (1985) on ture increase of only 1.3°C while mea- spinach indicate that a 2°C temperature suring a C0 response curve on green 2 increase at 30°C would cause a 7% ash under full sun (1750 j1mol , 1 s 2 m- ’ increase in the photorespiratory C0 com- 2 35°C). In many cases, moderate chamber pensation point. and leaf temperature increases of 2-3°C measurement in full sun. during occur a Under unfavorable conditions, tempera- ture increases of up to 6°C have been References observed; this, of course, is unacceptable. Keeping the chamber cool and shaded Ball J.T. (1987) Calculations related to gas when not in use, and adequate transpi- exchange. In: Stomatal Function. (Zeiger E., ration rates, help to moderate temperature Farquhar G.D. t3< Cowan I.R., eds.), Stanford increases. University Press, Stanford, CA The infrared filters that work so well Brooks A. & Farquhar G.D. (1985) Effect of temperature on the C0 specificity of ribu- under artificial lights do not help very / 2 los-1,5-bisphosphate carboxylase/oxygenase much in the field because plant leaves and the rate of respiration in the light. Planta have relatively little absorptance in the 165, 397 near IR, and the solar spectrum has rela- Davis J.E., Arkebauer T.J., Norman J.M. & tively little energy in the longer wave Brandle J.R. (19137) Rapid field measurement of regions. However, an external fan does a the assimilatiorn rate versus internal C0 2 concentration relationship in green ash (Fraxi- surprisingly good job of moderating cham- the influence of pennsylvan:ica Marsh.): nus ber temperature increases. One of us Tree light intensity. PhysioL 3, 387 (JMN) found that when a Big Blue Stem Terashima I., Wong S.C., Osmond C.B. & Far- (Andropogon gerardii Vitman) leaf of about quhar G.D. (1988) Characterisation of non- 5 cm was enclosed in the 1/4I chamber 2 uniform photosynthesis induced by abscisic at an outside air temperature of 40°C, the acid in leaves having different mesophyll anatomies. Plant Cell Physiol. 29, 385 chamber air temperature remained near