Summary Red spruce (Picea rubens Sarg.) trees growing at high elevation in the northeastern United States have experi-enced decline in recent years but seedlings have proved to be relatively tolerant of a wide range of environmental stresses in controlled studies. One possible reason for the wide tolerance to stress in seedlings is their inherently large pool of carbohy-drate reserves, which is available for maintenance during and regrowth after periods of stress. We tested for the effects of foliar N and exposure to ozone on foliar carbohydrate reserves of 20-year-old naturally regenerated saplings. The trees were maintained in native soil in 360-l containers for 5 years before the experiment. The year before the experiment, trees were fertilized with N,P,K to provide a population of trees from N deficient to N sufficient. As foliar N decreased below 0.9%, length of current-year shoots and specific needle area of cur-rent-year needles declined. Foliar N concentration was corre-lated with foliar sugar and starch concentrations, but relationships varied with time of year. Before bud break, foliar carbohydrates and N, in general, were positively correlated, and date of bud break was delayed in N-deficient trees. During active growth, foliar soluble sugars and N were positively correlated, but starch concentrations were negatively corre-lated with N. By late September, neither starch nor sugar concentration was correlated with N concentration. Ozone and foliar N concentrations did not interact to change foliar carbo-hydrate concentrations or shoot and needle growth in this relatively short-term study.
Keywords bud break, carbohydrate reserves, Picea rubens, shoot length, specific needle area, stress tolerance.
Introduction
Plants of low-resource environments have slow growth, low potential for resource capture, effective chemical defenses, and a high capacity for storage reserves (Grime 1977, Chapin 1991). Storage reserves are essential for survival in environ-ments where resources are low or highly variable because they allow for maintenance during and growth after periods of
resource limitation. But the cost of maintaining reserves is reduced growth (Chapin et al. 1990).
Retention of leaves for longer than one growth period, ever-greenness, has been proposed as an adaptation to resource limited systems that allows plants either to take advantage of ‘‘suitable conditions during generally unfavorable periods’’ (Moore 1984) or to store limiting resources such as nitrogen (Rundel and Parsons 1980). In temperate and boreal forests, survival of evergreen foliage through the winter depends on the development of cold tolerance, which is associated with changes in the quality and quantity of foliar carbohydrates (Senser et al. 1971). The ability of photosynthetic tissue to survive winter provides evergreen trees with the capacity to fix and store carbon before bud break. At bud break these carbon reserves are available for rapid growth of new foliage.
Foliar carbohydrate reserves of evergreen trees change sea-sonally with changes in photosynthetic activity, growth and cold tolerance (Little 1970, Senser et al. 1971, Kramer and Kozlowski 1979). These changes in foliar carbohydrates re-flect changes in source--sink strengths and are most predictable in evergreens such as red spruce (Picea rubens Sarg.) that have preformed shoots (fixed growth) and one annual period of shoot growth (Friedland et al. 1988, Alscher et al. 1989, McLaughlin et al. 1990, Amundson et al. 1992). For example, in the spring, newly fixed photosynthate is stored in stems and foliage as starch because of low sink strength and can, at that time, account for up to 30% of foliar dry weight (Alscher et al. 1989). By autumn, total soluble sugar content increases to above 10% of needle dry weight, whereas starch content drops nearly to zero (Alscher et al. 1989). This shift in the allocation of carbohydrates is associated with the cold hardening process (Senser et al. 1971).
Because of the importance of foliar carbohydrate reserves for maintenance during and growth after periods of resource limitation, any stress that reduces carbohydrate reserves could potentially affect the tree’s ability to respond to subsequent stress. Many environmental stresses have been shown to alter foliar carbohydrate contents. The air pollutant, ozone, reduces foliar starch concentrations of red spruce (Amundson et al.
Influence of foliar N on foliar soluble sugars and starch of red spruce
saplings exposed to ambient and elevated ozone
ROBERT G. AMUNDSON,
1,2ROBERT J. KOHUT
1and JOHN A. LAURENCE
11 Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY 14853, USA 2 Present address of corresponding author:1616 SW Harbor Way #403, Portland, OR 97201, USA
Received June 14, 1994
1991, Woodbury et al. 1992) and other evergreens (Meier et al. 1990, Paynter et al. 1991) as does water stress (Meier et al. 1990, Amundson et al. 1993). In contrast, N deficiency is frequently associated with elevated foliar starch concentra-tions in angiosperms (Waring et al. 1985, Chapin et al. 1986, Pell et al. 1990, Chapin 1991, Thompson et al. 1992) and gymnosperms (Ericsson 1979, Adams et al. 1986), presumably because low N availability reduces starch demand and growth faster than the capacity to fix carbon (Chapin 1991).
Many forested ecosystems are N limited (Vitousek 1982) and are exposed seasonally to elevated ozone (McLaughlin 1985). Because these two stresses have opposite effects on foliar carbohydrates, the stresses should interact. Pell et al. (1990) exposed radish (Raphanus sativa L.) to varying concen-trations of ozone and N and found interactive effects on foliar carbohydrates. They also observed a strong positive relation-ship between the ratio of sink to source mass and the amount of total nonstructural carbon in the sink organ, suggesting a functional relationship between carbohydrate concentrations in sink organs and relative strengths of source and sink.
The primary goals of the present study were to determine if foliar N alters foliar carbohydrate reserves of red spruce and, if so, to test if foliar N interacts with ozone to change these reserves. To test for effects of foliar N on foliar carbohydrate reserves, foliar N and carbohydrates of a group of red spruce saplings with a wide range of foliar N were monitored before and during exposure to ambient and elevated ozone.
Materials and methods Tree selection and maintenance
Naturally regenerated saplings of red spruce were selected in September 1985 at a site located approximately 16 km west of Mount Katahdin, Maine, that had been clear-cut in 1977. Soils at the site were Typic Haplorthods derived from glacial till. Selected trees were 1.0 to 1.5 m in height, relatively uniform in architecture without extensive branching induced by animal browsing, open-grown and not suppressed by adjacent trees, and could be removed without undue damage to roots. The selected trees were root-pruned by shovel approximately 0.5 m from the stem in September 1985. Root pruning was intended to stimulate regrowth of roots into the soil to be lifted so that transplant shock would be reduced.
In May 1986, native soil from the B horizon at the site was used to fill 360-l pots to within 25--30 cm of the lip of the pot. Trees with the O and E soil horizons intact were removed from the ground with shovels at the root pruning line. Each tree was placed in a pot and, if necessary, additional soil surface mate-rial was used to fill the pot to the rim. The trees were trans-ported to Ithaca, New York, and were maintained under 50% shade cloth (black polypropylene) until July 25, 1986. After that date they were unshaded. At the end of the 1986 growing season, the pots were partially buried in the ground and mulched with bark to the rim. The trees were watered as needed during the growing seasons of 1987, 1988, 1989 and 1990. On July 3, 1991, all trees were sprayed with Bifenthrin (0.6 g l−1 of wettable powder, FMC Corp., Philadelphia, PA) to
control spider mites. All trees were infrequently sampled for carbohydrates and nutrients from August 1987 through Octo-ber 1990 and routinely through SeptemOcto-ber 1991.
Foliar N, degree of bud swelling and fertilization
Foliage was sampled for nutrient analyses on October 30, 1990 and May 16, July 17 and September 27, 1991. On each sample date, foliage was cut, immediately wrapped in aluminum foil, frozen in liquid nitrogen, freeze-dried, ground to pass a 40-mesh screen, and subsequently analyzed for N by the micro-Kjeldahl technique by staff of the Department of Pomology at Cornell University (Grubinger et al. 1983).
On May 26, 1991, each tree was visually assessed for degree of bud swelling. The following four categories were used: no swelling, some swelling, most buds very swollen, and greater than 10 % of buds with needles beyond the bud scales (break-ing).
Before 1990, the trees were not fertilized. In August 1990, 13 of the 18 trees were fertilized with N,P,K (Peters, 15-16-17) to deliver 4 g of N per tree. Foliar N content of current-year foliage sampled in October 1990 was used to select six trees for each of the following groups: low (0.59--0.82%), interme-diate (0.87--1.03%), and high (1.04--1.22%). To assure ade-quate N for development of 1991 foliage, all trees were fertilized on April 12, 1991 with 13.3 g Peters N,P,K (15-16-17) to provide 2, 2.1 and 2.3 g as N, P and K, respectively. Trees in the low-, intermediate- and high-N groups received 1, 2 and 4 g, respectively, of additional N as ammonium nitrate. On July 5, 1991, all trees were fertilized with 4.5 g Peters N,P,K (15-16-17) with intermediate- and high-N groups receiving an additional 2 and 5 g N, respectively, as ammonium nitrate.
Ozone exposures
Ozone (produced from bottled oxygen) was added to three of the six nonfiltered (NF) open-top chambers (Kohut et al. 1987) daily from May 20, 1991 until September 27, 1991. The ozone treatments consisted of three chambers receiving NF air and three chambers receiving NF air with ozone added to produce twice ambient (2×) ozone concentrations from 1 h after sunrise to 1 h before sunset. During the experiment, ozone monitors were checked periodically against a transfer standard to assure the accuracy of the measurements.
Additionally, loss of ozone in the Teflon sampling lines was determined three times during the experiment and monitoring data were adjusted accordingly.
Tree watering
During the period when water was withheld, predawn and midmorning branch water potentials were routinely monitored on 1991 stems with a Scholander-type pressure chamber (Model B, Soil Moisture Equipment Inc., Santa Barbara, CA). Trees were rewatered when mean predawn water potentials declined below −2.0 MPa.
Needle and shoot morphology
Lengths and weights of shoots and weights and projected areas of needles were determined on 1991 branches on several dates after needle and branch growth had stopped. Projected needle areas were determined with an image analyzer (AgVision System, Decagon Devices, Pullman, WA, USA) after they were removed from stems by rapid immersion in liquid N.
Carbohydrates
Carbohydrates were determined by cutting four to six shoots with 1990 or 1991 needles between 1100 and 1130 h Eastern Daylight Time and preparing the tissue by the same protocol as described for N determination. Total soluble sugars were extracted from ground tissue with 12/5/3 methanol/chloro-form/water (v/v/v) (Haissig and Dickson 1979). Sugar concen-tration of the methanol--water phase of the extract was measured by the anthrone reaction (Yemm and Willis 1954). The starch or insoluble fractions were suspended in 4 ml of 0.10 M acetate--0.02 M NaF buffer, pH 4.5, placed in a boiling water bath for 15 min and then cooled. One ml of buffer containing 15 units of amyloglucosidase (EC 3.2.1.3) was added to the residue, and the mixture incubated at 50 °C for 24 h. Glucose was determined by the glucose oxidase system (Haissig and Dickson 1979, Ou-Lee and Setter 1985).
Experimental design and data analysis
Two ozone treatments, nonfiltered air (NF) and twice ambient (2×), constituted the main plots. Ozone treatments were ran-domly assigned to six open-top chambers; thus, ozone effects were tested over the replicate chambers (i.e., chambers nested within ozone regimes). The 18 experimental trees were divided into low-, intermediate- and high-N groups with six individu-als per group. Three trees, one from each N group, were randomly assigned to each chamber. Foliar N concentrations were not discrete and so could not be incorporated into the design as a second factor; instead N was included as a covariate where appropriate and tested by SAS GLM (SAS Institute Inc., Cary, NC). Sugar and starch concentrations (analyzed sepa-rately at each date) were tested for a response to ozone by one-way ANOVA, whereas the relationships between foliar N
and carbohydrates were tested by regression analyses (Minitab Inc, Boston, MA).
Results
Ozone exposure
Ozone exposures were conducted from 1 h after sunrise to 1 h before sunset from May 20 until September 27, 1991. Seasonal 12-h-mean ozone concentrations (0800 to 2000 h) for NF and 2× treatments were 0.045 and 0.088 µl l−1, and maximum 1-h averages for both were 0.112 and 0.241 µl l−1, respectively (Table 1). Visible symptoms normally associated with ozone injury were not detected on trees in either ozone treatment.
Influence of foliar N on foliar carbohydrates and date of bud break
Foliar N concentrations of 1990 foliage ranged from 0.59 to 1.22% on October 30, 1990 and generally declined from Oc-tober 1990 to September 1991 (Table 2). Nitrogen concentra-tions of 1991 foliage varied little from July to September 1991 and were similar within age class and N treatment in trees exposed to the NF and 2× treatments (Table 2).
Soluble sugar and starch concentrations of 1990 stems and starch concentrations of 1990 needles sampled on April 30, 1991 were positively correlated with N concentrations of 1990 foliage sampled on May 16, 1991 (Table 3), whereas soluble sugar concentrations of 1990 foliage were positively, but poorly, correlated with N concentrations of 1990 foliage (Ta-ble 3). Between April 30 and May 16, foliar starch concentra-tions increased in all trees, whereas sugar concentraconcentra-tions declined marginally. On May 16, starch concentrations of 1990 foliage ranged from 175 to 272 mg gDW−1 and were not corre-lated with foliar N concentrations. In contrast, sugar concen-trations declined in all trees over the same period (1 to 24 mg gDW−1 and were more positively correlated with foliar N con-centrations on May 16 than on April 30 (r = 0.74 versus 0.37, Table 3). On May 26, buds on five of six trees in the low-N group had not begun to swell, whereas buds on trees with higher foliar N were swelling or breaking. Trees in the low-N group had a significantly lower degree of bud swelling than trees in the two higher N groups (Table 2, P = 0.001).
Influence of foliar N and ozone on carbohydrates and shoot and needle growth
Sugar and starch concentrations were similar in trees exposed to either NF or 2× ozone treatments regardless of date
(Ta-Table 1. Ozone exposure statistics for 12-h interval from 0800 to 2000 h EDT between May 20 and September 27, 1991.
TreatmentOzone concentration (µl l−1)
12-h Average24-h AverageMax 1-hTotal hours
ble 4). Starch concentrations of 1991 foliage were negatively correlated with foliar N concentrations on July 17 (r = 0.84, Table 3). In contrast, sugar concentrations of 1991 foliage on the same date were positively, but poorly, correlated with foliar N concentrations (r = 0.46, Table 3). Similar trends were noted in 1990 foliage (Table 3). These relationships were not altered by exposure to ozone. By September 27, 1991, neither sugar nor starch concentration of 1991 foliage was correlated with foliar N concentration or prior ozone exposure.
Foliar starch concentrations of current-year foliage were lower on August 20, 1991 compared to current-year foliage on the same trees measured on August 16, 1989 (Table 4, P = 0.001). In contrast, mean sugar concentrations of current-year foliage on August 16, 1989 were similar to those of current-year foliage monitored on August 20, 1992 (Table 4).
Lengths of 1991 shoots increased with increasing N concen-trations in trees exposed to NF or 2× ozone (Figure 1). Mean lengths of 1991 shoots of trees exposed to 2× ozone sampled from August 20 to September 27 tended to be longer than those of NF-treated trees (4.67 versus 4.30 cm, P = 0.095). Mean projected leaf area to dry weight ratio (specific leaf area) of 1991 foliage was positively correlated with mean foliar N concentration (Figure 2). Ozone did not affect specific leaf area of 1991 foliage (2× = 29.8 versus 28.6 cm2 g−1 for NF, P = 0.47).
Exposure to ozone did not significantly affect predawn branch water potentials of trees that were not watered for 2 weeks from August 20 to September 3 (August 20, NF = −1.31
± 0.25 MPa, 2× = −1.58 ± 0.12 MPa, P = 0.35; September 3, NF = −2.13 ± 0.25 MPa, 2× = −2.50 ± 0.25 MPa, P = 0.22). Table 2. Foliar N concentration of the low-, intermediate- and high-N groups within the NF and 2× ozone treatments. Values are means with SDs in parentheses. Degrees of bud swelling on May 26, 1991 were as follows: 1 = no swelling, 2 = little swelling, 3 = very swollen, and 4 = breaking.
TreatmentN ContentBud swellingNitrogen (% DW)
1990 Foliage1991 Foliage
Oct 90May 91Sept 91July 91Sept 91
NFLow1.670.660.660.640.700.68 (1.2)(0.09)(0.11)(0.13)(0.13)(0.11) Intermediate30.880.710.690.780.81 (1)(0.01)(0.08)(0.02)(0.04)(0.09) High31.100.990.981.111.12 (1)(0.05)(0.05)(0.08)(0.13)(0.13)
2×Low10.820.750.690.700.73 (0)(0.00)(0.06)(0.09)(0.05)(0.07)
Table 3. Relationships between foliar N concentration (N, %) and stem or foliar sugar or starch concentration before, during and after shoot growth. Relationships with P-values less than 0.05 are indicated with an asterisk (*).
DateTissueAgeEquationrP-value Pre-bud break
April 30Stem90Starch = 31.6 + 20.5 N0.680.036* Sugar = 25.0 + 16.6 N0.660.048*
Needle90Starch = 78.0 + 66.3 N0.650.028* Sugar = 74.6 + 7.9 N0.370.382
May 16Needle90Starch = 201 + 8.3 N0.140.840 Sugar = 55 + 19.4 N0.740.005*
Shoot growth period
July 17Needle91Starch = 410 − 710 N + 323 N20.840.001* Sugar = 66.8 + 17.2 N0.460.198
Needle90Starch = 41.2 − 11 N − 16.1 N20.630.117 Sugar = 81.1 + 10.3 N0.430.243
Cold hardening period
Discussion
Evergreen foliage has been proposed as an adaptation to re-source limited environments by extending the period of carbon fixation (Moore 1984) and by increasing the ability of the plant to store limiting resources such as N (Rundel and Parsons 1980). The increase in foliar carbohydrate reserves before bud break supports the former proposal. Because N concentrations of all older foliage were not determined, the latter hypothesis could not be tested. Clearly, foliar N and carbohydrate concen-trations indicated changing relationships between these two variables as source and sink strengths changed.
Relationships between foliar N and foliar carbohydrate reserves and growth
Foliar N concentrations of the experimental trees ranged from deficient to sufficient for saplings and mature red spruce in the northeastern USA (Friedland et al. 1988, Fernandez and
Struchtemeyer 1990, Amundson et al. 1992) and were gener-ally lower than those reported for red spruce saplings in the southern Appalachians (McLaughlin et al. 1991).
Assessment of 1991 stem lengths verified that trees with current-year foliage below 0.9% N had reduced growth. The positive correlation between foliar N concentrations and spe-cific leaf area (area weight−1) also indicates that N deficiency affects needle morphology. The decrease in specific needle area with decreasing N concentration cannot be explained by N influences on foliar starch because the same relationship was found when starch was depleted at the end of the growing season. A possible explanation is that N deficiency results in denser leaves as was shown for broadleaf species (Thompson et al. 1992); however, this could not be verified because meas-urements were not made on individual needles.
The relationship between foliar N and foliar carbohydrate reserves changed as source--sink strengths changed. Annually, red spruce experiences shifts in source--sink relationships that Table 4. Soluble sugar and starch concentrations of current-year foliage of red spruce saplings exposed to NF or 2× ozone before, during and after a period of water stress. The SEs are presented in parentheses. Trees were maintained under ambient ozone conditions until May 20, 1991. Comparisons between sugar and starch concentrations of current-year foliage measured on August 16, 1989 and August 20, 1991 for trees exposed to NF or 2× treatments in 1991 were as follows: P-values for sugar concentrations, 1989 versus 1991, NF = 0.563, 2× = 0.241; P-values for starch concentrations, 1989 versus 1991, NF = <0.001, 2× = 0.001.
Treatment19891991
Aug 16July 17Aug 20Aug 26Aug 30Sept 3Sept 27
Soluble sugars (mg gDW−1)
NF90 (6)87 (3)92 (9)97 (2)96 (1)108 (2)123 (2) 2×88 (10)79 (3)97 (8)96 (2)95 (1)101 (2)119 (2) P-value0.6190.0990.7450.6940.4020.1240.257 Starch (mg gDW−1)
Figure 1. Relationship between foliar N concentration (%) and 1991 shoot length of trees exposed to NF (j) or 2× (h) ozone. Measure-ments were made between August 20 and September 27, 1991. Equa-tion for relaEqua-tionship is stem length (cm) = 1.58 + 4.74 N − 1.57 %2,
r2 = 0.602, P-value = 0.001.
correspond to periods when (1) foliage is photosynthetically active before bud break (source > sink), (2) when shoot, cam-bium or root growth is vigorous (source = sink), and (3) when tolerance to cold is established and maintained (source ≤ sink).
Pre-bud break period
In mid to late March in Ithaca, NY, photosynthetic capacity of red spruce foliage increases rapidly from a midwinter low (R.G. Amundson, unpublished data). Also, chloroplasts short-en, unclump and move toward the plasmalemma (Fincher and Alscher 1992), whereas chlorophyll concentrations increase and carotenoid concentrations decrease (Amundson et al. 1991). The substantial photosynthetic capacity of red spruce up to 2 months before bud break results in large increases in carbohydrate storage in stems and foliage before bud break.
The positive correlation between stem and needle carbohy-drates and foliar N during late April indicates that stem and needle carbohydrate storage pools of N-deficient trees are filled later than those of trees with higher foliar N concentra-tions. The delay in bud break of N-deficient trees and positive relationships between stem and needle carbohydrates and fo-liar N before bud break suggest that date of bud break is either directly influenced by foliar N concentrations or delayed in N-deficient trees by inadequate carbohydrate reserves to ex-pand new foliage.
Active growth period
During the period of rapid shoot elongation, new foliage changes from importing to exporting carbon (Turgeon 1989) and thus ends its reliance on reserves from other tissues result-ing in a negative relationship between foliar N and foliar starch concentrations. Negative relationships between foliar N and starch have also been reported for Scots pine (Pinus sylvestris L.) (Ericsson 1979), willow (Salix aquatica Smith) (Waring et al. 1985) and sedge (Eriophorum vaginatum L.) (Chapin et al. 1986). Chapin (1991) suggests that starch accumulates in leaves of N-limited plants because there is sufficient N for continued carbon fixation but insufficient N to maintain nor-mal growth (sink strength declines). Reduced length of 1991 shoots and higher starch concentrations of 1991 foliage in the N-deficient trees supports that hypothesis.
In mid-August, starch concentrations were significantly lower than in the same trees in 1989 (Amundson et al. 1993) or in a similar group of trees in 1990 (Woodbury et al. 1992). The reduction probably resulted from fertilization in April and July (cf. Ericsson 1979, Waring et al. 1985, Chapin et al. 1986), most likely because the carbon that would be stored as starch was allocated to root growth. Allocation of carbon is controlled by source and sink strengths that vary with time, growth form and potential rate of growth (see Laurence et al. 1994, Pell et al. 1994). Thus, fertilization does not always reduce foliar carbohydrate reserves. We assume that foliar reserves were diverted to root growth by mid-August to increase nutrient acquisition, whereas soil temperatures were too low in late April--early May for root growth. Without a sink for the newly fixed photosynthate, starch reserves accumulated in twigs and foliage before bud break.
Cold hardening period
The loss of starch and increase in sugars by September 27 indicated that the trees were cold hardening (Parker 1959, Senser et al. 1971, Alscher et al. 1989). By then neither starch nor sugar concentration of current-year foliage was correlated with foliar N.
As expected, N deficiency had multiple effects on the growth capacity of red spruce. Foliar N concentrations are positively correlated with photosynthetic capacity in red spruce (Amundson et al. 1992) which may explain the delay in filling of foliar starch pools in late April. Furthermore, N deficiency reduced carbon fixation capacity of current-year foliage by delaying the date of bud break and by reducing shoot lengths and specific needle areas.
Effects of ozone on foliar carbohydrate reserves and growth Although we anticipated that N deficiency would raise foliar starch concentrations and thus predispose the trees to ozone-induced reductions in starch, it did not. Fertilization of the trees most likely resulted in reduced foliar starch concentra-tions during mid-August. Our data support the results of earlier studies where short-term exposure to ozone had minimal ef-fects on red spruce seedlings (Taylor et al. 1986, Alscher et al. 1989, Laurence et al. 1989). Although exposure to ozone for one growing season depressed foliar starch concentrations in shortleaf pine (Pinus echinata Mill.) (Paynter et al. 1991) and loblolly pine (Pinus taeda L.) (Meier et al. 1990), longer exposures were needed to reduce foliar starch concentrations in red spruce seedlings (Amundson et al. 1991) and saplings (Woodbury et al. 1992) that were not N limited.
Red spruce response to multiple stresses
Because N deficiency and ozone stress have opposite effects on foliar starch reserves, we postulated that the two stresses would have an interactive effect on foliar starch concentra-tions. Pell et al. (1990) found such interactions in a study of radish. However, no interactions between ozone exposure and foliar N concentrations were detected; the relatively low starch concentrations and short duration of the ozone exposure may have millitated against such an interaction.
Although N deficiency decreased shoot length and ozone tended to increase shoot length, it is unclear whether these two stresses would interact to change shoot length in the long term. Clearly, changes in shoot length would affect tree stature and thus light capture, carbon fixation and growth.
concen-trations declined during water stress (Amundson et al. 1993) suggest that starch reserves were used at that time to maintain cell integrity. Additionally, Hauslauden et al. (1990) found that foliar carbohydrate reserves may be diverted to the synthesis of antioxidant compounds in response to exposure to ozone, further reducing susceptibility to long-term exposures. The changing relationships between foliar N and starch and sugar concentrations as source and sink strengths changed suggest that these foliar reserves are mobilized in response to changing sink strengths, which vary with severity of the stress and the organ sensing that stress. Collectively the above factors result in the relative insensitivity of red spruce to short-term stress.
Acknowledgments
This research was supported by funds provided by the Electric Power Research Institute under contract RP2799-1, the Empire State Electric Energy Research Corporation, the Niagara Mohawk Power Corpora-tion, and the United States Forest Service. This paper has not been subject to Forest Service peer review and should not be construed to represent the policies of the Agency. We thank Horacio Buscaglia, Suzanne Fellows, Terry Lauver, Richard Raba and Paul Van Leuken for invaluable operational and technical support.
References
Adams, M.B., H.L. Allen and C.B. Davey. 1986. Accumulation of starch in roots and foliage of loblolly pine (Pinus taeda L.): effects of season, site and fertilization. Tree Physiol. 2:35--46.
Alscher, R.G., R.G. Amundson, J.R. Cumming, S. Fellows, J. Fincher, G. Rubin, P. van Leuken and L.H. Weinstein. 1989. Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by ozone. New Phytol. 113:211--223.
Amundson, R.G., R.G. Alscher, S. Fellows, G. Rubin, J. Fincher, P. van Leuken and L.H. Weinstein. 1991. Seasonal changes in the pigments, carbohydrates, and growth of red spruce as affected by exposure to ozone for two growing seasons. New Phytol. 118:125--137.
Amundson, R.G., J.L. Hadley, J. Fincher, S. Fellows and R.G. Alscher. 1992. Comparisons of seasonal changes in photosynthetic capacity, pigments, and carbohydrates of healthy sapling and mature red spruce and of declining and healthy red spruce. Can. J. For. Res. 22:1605--1616.
Amundson, R.G., R.J. Kohut, J.A. Laurence, S. Fellows and L. Co-lavito. 1993. Red spruce reversibly allocates starch to sugars in foliage during moderate water stress. Environ. Exp. Bot. 33:383--390.
Chapin III, F.S. 1991. Integrated responses of plants to stress. Bio-Science 41:29--36.
Chapin III, F.S., G.R. Shaver and R.A. Kedrowski. 1986. Environ-mental controls over carbon, nitrogen, and phosphorus fractions in
Eriophorum vaginatum in Alaska tussock tundra. J. Ecol.
74:167--195.
Chapin III, F.S., E.-D. Schulze and H.A. Mooney. 1990. The ecology and economics of storage in plants. Annu. Rev. Ecol. Syst. 21:423--447.
Ericsson, A. 1979. Effects of fertilization and irrigation on the sea-sonal changes of carbohydrate reserves in different age-classes of needle on 20-year-old Scots pine trees (Pinus sylvestris). Physiol. Plant. 45:423--429.
Fernandez, I.J. and R.A. Struchtemeyer. 1990. Correlation between element concentrations in spruce foliage and forest soils. Commun. Soil Sci. Plant Anal. 15:1243--1255.
Fincher, J. and R.G. Alscher. 1992. The effects of long-term ozone exposure on injury in seedlings of red spruce (Picea rubens Sarg.). New Phytol. 120:49--59.
Friedland, A.J., G.J. Hawley and R.A. Gregory. 1988. Red spruce foliar chemistry in northern Vermont and New York. Plant Soil 105:189--193.
Grime, A.D.M. 1977. Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat. 111:1169--1194.
Grubinger, B.P., P.L. Minotti, H.C. Wein and A.D. Turner. 1983. Tomato response to starter fertilizer, polyethylene mulch and level of soil phosphorus. J. Am. Soc. Hortic. Sci. 118:212--216. Haissig, B.E. and R.E. Dickson. 1979. Starch measurement in plant
tissue using enzymatic hydrolysis. Physiol. Plant. 47:151--157. Hauslauden, A., N.R. Madamanchi, S. Fellows, R.G. Alscher and R.G.
Amundson. 1990. Seasonal changes in antioxidants in red spruce as affected by ozone. New Phytol. 115:447--458.
Kohut, R.J., R.G. Amundson and J.A. Laurence. 1987. Evaluation of the effects of ozone and acidic precipitation, alone and in combina-tion, on the photosynthesis, nutricombina-tion, and growth of red spruce and sugar maple. In Acid Rain: Scientific and Technical Advances. Eds. R. Perry, R.M. Harrison, J.N.B. Bell and J.N. Lester. Selper Ltd., London, pp 588--595.
Kramer, P.J. and T.T. Kozlowski. 1979. Physiology of woody plants. Academic Press Inc., Orlando, FL, 811 p.
Laurence, J.A., R.J. Kohut and R.G. Amundson. 1989. Response of red spruce seedlings exposed to ozone and simulated acidic precipi-tation in the field. Arch. Environ. Contam. Toxicol. 18:285--290. Laurence, J.A., R.G. Amundson, A.L. Friend, E.J. Pell and P.J.
Tem-ple. 1994. Allocation of carbon in plants under stress: an analysis of the ROPIS experiments. J. Environ. Qual. 23:412--417.
Lauver, T., R.H. Mandl, R.J. Kohut and J.A. Laurence. 1990. A weighing lysimeter for determining water loss in red spruce sap-lings (Picea rubens Sarg.). Environ. Exp. Bot. 30:157--164. Little, C.H.A. 1970. Seasonal changes in carbohydrate and moisture
content in needles of balsam fir (Abies balsamea). Can. J. Bot. 48:2021--2028.
McLaughlin, S.B. 1985. Effects of air pollution on forests: a critical review. J.A.P.C.A. 14:512--534.
McLaughlin, S.B., C.P. Andersen, N.T. Edwards, W.K. Roy and P.A. Layton. 1990. Seasonal patterns of photosynthesis and respiration of red spruce saplings from two elevations in declining southern Appalachian stands. Can. J. For. Res. 20:485--495.
McLaughlin, S.B., C.P. Andersen, P.J. Hanson, M.G. Tjoelker and W.K. Roy. 1991. Increased dark respiration and calcium deficiency of red spruce in relation to acidic deposition at high-elevation southern Appalachian Mountain sites. Can. J. For. Res. 21:1234--1244.
Meier, S., L.F. Grand, M.M. Schoeneberger, R.A. Reinert and R.I. Bruck. 1990. Growth, ectomycorrhizae and nonstructural carbohy-drates of loblolly pine seedlings exposed to ozone and soil water deficit. Environ. Pollut. 64:11--17.
Moore, P.D. 1984. Why be an evergreen? Nature 312:703.
Ou-Lee, T-M. and T.L. Setter. 1985. Enzyme activities of starch and sucrose pathways and growth of apical and basal maize kernels. Plant Physiol. 79:848--851.
Parker, J. 1959. Seasonal variations in sugars of conifers with some observations on cold resistance. For. Sci. 5:56--63.
Pell, E.J., W.E. Winner, C. Vinten-Johansen and H.A. Mooney. 1990. Response of radish to multiple stresses. I. Physiological and growth responses to changes in ozone and nitrogen. New Phytol. 115:439--446.
Pell, E.J., P.J. Temple, A.L. Friend, H.A. Mooney and W.E. Winner. 1994. Compensation as a plant response to ozone and associated stresses: an analysis of ROPIS experiments. J. Environ. Qual. 23:429--436.
Rundel, P.W. and D.J. Parsons. 1980. Nutrient changes in two chapar-rel shrubs along a fire-induced age gradient. Am. J. Bot. 67:51--58. Seiler, J.R. and B.H. Cazell. 1990. Influence of water stress on the physiology and growth of red spruce seedlings. Tree Physiol. 6:69--77.
Senser, M., P. Dittrich, O. Kandler, A. Thanbichler and B. Kuhn. 1971. Isopenstudien über den Einfluss der Jahreszeit auf den Oligosac-charidumsatz bein Coniferen. Ber. Deutsch. Bot. Gesellschaft 84:445--455.
Taylor, G.E., R.J. Norby, S.B. McLaughlin, A.H. Johnson and R.S. Turner. 1986. Carbon dioxide assimilation and growth of red spruce (Picea rubens Sarg.) seedlings in response to ozone, precipitation chemistry, and soil type. Oecologia 70:163--171.
Thompson, W.A., P.E. Kriedemann and I.E. Craig. 1992. Photosyn-thetic response to light and nutrients in sun-tolerant and shade-tol-erant rainforest trees. I. Growth, leaf anatomy and nutrient content. Aust. J. Plant Physiol. 19:1--18.
Turgeon, R. 1989. The sink--source transition in leaves. Annu. Rev. Plant. Physiol. 40:119--138.
Vitousek, P.M. 1982. Nutrient cycling and nutrient use efficiency. Am. Nat. 119:553--572.
Waring, R.H., A.J.S. McDonald, S. Larsson, T. Ericsson, A. Wiren, E. Arwidsson, A. Ericsson and T. Lohammar. 1985. differences in chemical composition of plants grown at constant relative growth rates with stable mineral nutrition. Oecologia 66:157--160. Woodbury, P.B., R.G. Amundson, R.J. Kohut and J.A. Laurence. 1992.
Stomatal conductance, whole-tree water use, and foliar carbohy-drate status of red spruce saplings exposed to ozone, acid precipita-tion, and drought. In Transactions of the 1991 Air and Waste Management Association International Symposium on Tropo-spheric Ozone and the Environment II. Ed. R. Berglund. Air and Waste Management Association, Pittsburgh, PA, pp 618--628. Yemm, E.W. and A.J. Willis. 1954. The estimation of carbohydrates in
