Current-year Foliage Research Articles

Alternative method for estimating aboveground net primary productivity applied to balsam fir stands in eastern Canada

Aboveground net primary productivity (ANPP) was measured in three balsam fir (Abies balsamea (L.) Mill.) forests on a climatic transect extending from southern New Brunswick ("warm" study area) to central Quebec ("cool" study area). Annual foliar production was estimated with a relationship between cross-sectional area at breast height of the current-year annual xylem ring and the mass of current-year foliage, using data obtained by harvesting trees at the beginning of the study. This relationship differed among study areas. Annual branch production was determined from annual foliar production and the ratio of annual branch production to annual foliar production. The ratio of branch to foliar production was estimated from intensive measurement of a sample of branches collected at the end of the study period; it varied among years but was similar for all study areas. ANPP was 3.36 Mg C·ha–1·year–1 at the warm study area, 3.73 Mg C·ha–1· year–1 at the mid-transect study area, and 3.04 Mg C·ha–1·year–1 at the cool study area. These estimates of ANPP were greater than those estimated using a conventional method of summing up increment and litterfall. On average, the conventional estimate of ANPP was 83% of the estimate using relationships described above. Because net ecosystem productivity is the difference between NPP and heterotrophic respiration, a 17% underestimate of NPP can have a substantial effect on the estimate of carbon-sink activity of a forest.

Integrating within-crown variation in net photosynthesis in loblolly and slash pine families.

We examined photosynthetic characteristics of two fast- and two slow-growing half-sib families of both loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii var. elliottii Engelm.) on two sites in northern Florida to: (1) quantify variation in light-saturated net photosynthesis (Amax) associated with vertical crown position and foliage age; (2) quantify the amount and distribution of leaf area by foliage age class; and (3) determine whether photosynthetic indices, ranging from leaf-level through whole-crown Amax, were related to growth differences among species and families. In both species, leaf-level Amax was higher in more recently formed foliage both within the same year (where Amax in the third flush averaged 10 to 30% higher than Amax in the first flush) and between years (where Amax in current-year foliage averaged 20 to 40% higher than Amax in 1-year-old foliage). When expressed on a leaf area basis, Amax of current-year foliage was higher in slash pine than in loblolly pine, but Amax expressed on a mass basis did not differ between species. Loblolly pine had higher whole-tree leaf area than slash pine, whereas whole-tree Amax did not differ between species. When the mean values for fast-growing families were compared with the mean values for slow-growing families, there were no differences in leaf-level characteristics, whereas at the whole-tree level, fast-growing families had higher leaf area and whole-tree Amax than slow-growing families in both species. When comparisons were made among the individual fast- and slow-growing families, however, results were more variable. In both species, stem volume growth was strongly correlated with whole-tree Amax, with most of the strength of the correlation deriving from the relationship between volume growth and tree leaf area.

Soil disturbance and five-year tree growth in a montane alternative silvicultural systems (MASS) trial

Ground-based forestry practices can negatively affect soil productivity by altering the physical, chemical, and biological properties of soil. The effect of soil disturbance on soil properties and tree growth was evaluated following single-pass hydraulic excavator and multiple-pass combined excavator and flexible track grapple skidder forwarding in four silvicultural systems treatments: Clearcut (CC), Green Tree Retention (GT), Patch Cut (PC), and Uniform Shelterwood (SW). The effectiveness of an excavator soil-rehabilitation technique (tilling) in decompacting skidtrails (i.e., reducing soil bulk density) and nutrient availability was also evaluated. Western hemlock (Tsuga heterophylla (Raf.) Sarg.) and amabilis fir (Abies amabilis Dougl. Ex. Forbes) seedlings were planted on undisturbed plots, within tracks and between tracks of skidtrails, and in rehabilitated trails within the four harvesting treatments in the spring of 1994. Seedling growth was measured after five growing seasons, and nutrient concentrations of current-year foliage were determined at the end of the fourth growing season. Seedling survival and growth was generally reduced by soil disturbances associated with skid-trails. Effects of disturbance on physical properties of soil (e.g., compaction, puddling) and disruption of drainage were the most likely causes. Nutrient deficiencies do not appear to be a factor. Nonetheless, nitrogen concentrations were lower in current-year foliage taken from rehabilitation treatments than from either undisturbed or skidtrail treatments. Effectiveness of soil rehabilitation varied. In well-drained deeper soils, tilling reduced soil bulk density to levels below those of undisturbed soils and, in the short-term (five years), improved tree growth. In wetter conditions, rehabilitation treatment decreased survival and growth of both species. Thus specific rehabilitation (tilling) prescriptions should not be universally applied across a landscape. Key words: Abies amabilis, Tsuga heterophylla, foliar analysis, soil bulk density, soil compaction, soil rehabilitation

Severe red spruce winter injury in 2003 creates unusual ecological event in the northeastern United States

Abundant winter injury to the current-year (2002) foliage of red spruce (Picea rubens Sarg.) became apparent in the northeastern United States in late winter of 2003. To assess the severity and extent of this damage, we measured foliar winter injury at 28 locations in Vermont and surrounding states and bud mortality at a subset of these sites. Ninety percent of all trees assessed showed some winter injury, and trees lost an average of 46% of all current-year foliage. An average of 32% of buds formed in 2002 were killed in association with winter injury. Both foliar and bud mortality increased with elevation and with crown dominance, and bud mortality increased with greater foliar injury. Foliar injury in 2003 at a plantation near Colebrook, New Hampshire, was more than five times the typical levels for 9 previous years of measurement and more than twice that measured for another high-injury year. Plantation data also indicated that bud mortality in 2003 was greater than previously documented and that persistent winter injury was associated with increased tree mortality. Comparisons of our data with past studies for two sites with native red spruce also indicated that damage in 2003 was greater than other recently reported, high-injury years. Because heavy foliar and bud losses can severely disrupt the carbon economies of trees, the 2003 winter injury event could lead to further spruce decline and mortality, particularly among dominant trees at higher elevations.

Nitrogen uptake and turnover in riparian woody vegetation.

The nutrient balance of streams and adjacent riparian ecosystems may be modified by the elimination of anadromous fish runs and perhaps by forest fertilization. To better understand nitrogen (N) dynamics within stream and riparian ecosystems we fertilized two streams and their adjacent riparian corridors in central Idaho. On each stream two nitrogen doses were applied to a swathe approximately 35 m wide centered on the stream. The fertilizer N was enriched in 15N to 18 per thousand. This enrichment is light relative to many previous labeling studies, yet sufficient to yield a traceable signal in riparian and stream biota. This paper reports pre-treatment differences in delta15N and the first-year N response to fertilizer within the riparian woody plant community. Future papers will describe the transfer of allochthonous litter N to the stream and its subsequent processing by stream biota. Pre-treatment delta15N differed between the two creeks (P=0.0002), possibly due to residual salmon nitrogen in one of the creeks. Pre-treatment delta15N of current-year needles was enriched compared to leaf litter, which was in turn enriched compared to needles aged 4 years and older. We conclude that fractionation due to retranslocation occurs in at least two phases. The first phase, which optimizes allocation of N in younger needle age classes, is distinctly different from the second, which conserves N prior to abscission. The delta15N difference between creeks was eliminated by the fertilization (P=0.42). In the two dominant conifer species, Abies lasiocarpa and Picea engelmannii, most fertilizer N was found in the current-year foliage; little was found in older needles and none was detected in litter (P=0.53). The only N-fixing shrub species, Alnus incana, took up only a small amount of fertilizer N [mean percent N derived from fertilizer (%Ndff) 5.0+/-1.6% (SE)]. Far more fertilizer N was taken up by other deciduous shrubs (mean %Ndff=33.9+/-4.5%). Fertilizer N made up 25% (+/-4.2%) of the N in deciduous shrub litter. These results demonstrate the feasibility of light labeling with 15N and the potential influence of riparian plant species composition on stream nutrient dynamics via allochthonous leaf litter inputs.

Foliar nutrients and induced susceptibility: genetic mechanisms of Douglas-fir resistance to western spruce budworm defoliation

We conducted greenhouse defoliation experiments with clones of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) over 3 years to assess the role of foliar nutrients as a resistance mechanism to western spruce budworm (Choristoneura occidentalis Freeman) defoliation. The grafted clones were derived from mature trees (i.e., ortets) that showed resistance or susceptibility to budworm defoliation in the forest. Current-year foliage was analyzed for concentrations of nitrogen (N), sugars (sucrose + fructose + glucose), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), copper (Cu), iron (Fe), and zinc (Zn). We computed rank correlations between foliar nutrient levels in the ortets and their corresponding clones to test the null hypothesis that foliar chemistry does not have a genetic basis (H01). Foliar concentrations of sugars and P were under genetic control to some degree, but concentrations of other nutrients were not. We used analysis of variance to test the null hypotheses that foliar chemistry does not change in response to budworm defoliation (H02) and that it is not different between resistant and susceptible clones (H03). We rejected H02 for sugars, P, K, Mn, and Zn; defoliation by the budworm changed levels of these nutrients and had divergent effects on concentrations of P, K, and Zn in resistant clones. We concluded that induced susceptibility, whereby defoliation alters foliar nutrients to make trees more favorable for insect feeding, appears to be an important determinant of Douglas-fir resistance to the western spruce budworm. Failure to reject H03 implies that previously reported differences between the foliar nutrient levels in resistant Douglas-firs and those in susceptible Douglas-firs in the forest are probably caused by induced susceptibility.

Monthly leaf area index estimates from point-in-time measurements and needle phenology for Pinus taeda

Leaf area index (LAI) of loblolly pine (Pinus taeda L.) trees of the southern United States varies almost twofold interannually; loblolly pine, essentially, carries two foliage cohorts at peak LAI (September) and one at minimum (March–April). Herein, we present an approach that may be site invariant to estimate monthly LAI for loblolly pine using point-in-time measurements from a LI-COR LAI-2000 plant canopy analyzer (PCA). Our analyses used needle accretion and abscission data from monthly needle counts and destructive harvest data from a replicated 2 × 2 factorial experiment of water and nutrition amendments. No significant treatment effects on relative needle accretion or abscission were observed. Cohort (interannual) differences in needle accretion were found but appeared trivial. Cohort year had variable effects on needle abscission. Abscission of current-year foliage began in July and continued through November of the third year; however, only 7%–9% remained 23 months following bud initiation. A treatment-invariable regression of PCA measurements on cohort foliage biomass (r2 [Formula: see text] 0.98) was used to estimate annual cohort LAI. We derived monthly estimates of LAI from cohort accretion and abscission and cohort LAI. Monthly estimates of LAI for loblolly pine, using point-in-time measurements from the PCA, appear possible, although further testing is required.

Site temperatures influence seasonal changes in terpene composition in Douglas-fir vegetative buds and current-year foliage

Over a 3-year period (1998–2000), variations in terpene composition was measured in vegetative buds of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) from six sites varying in elevation and geographic location with sampling from early spring to midsummer. Eleven terpenes were found in virtually all samples (tricyclene, α-pinene, camphene, sabinene, β-pinene, myrcene, Δ-3-carene, limonene, β-phellandrene, terpinolene, and bornyl acetate) and represented an average of 87% of the total terpenes. In each year, composition of the terpene mix varied significantly (P [Formula: see text] 0.05) for all sites and dates, with some significant site and date interactions. Degree-day accumulations were calculated for all sites and years. Patterns of change in terpene composition between sites, areas, and years were strongly related to the temperature regimes associated with site and year.

Impact of old foliage removal, simulating defoliation by the balsam fir sawfly, on balsam fir tree growth and photosynthesis of current-year shoots

To investigate the effect of defoliation by the balsam fir sawfly ( Neodiprion abietis) on current-year growth and photosynthesis, all 1-year-old and older foliage were removed by manual clipping before the start of the growing season from balsam fir seedlings cultivated at two levels of fertilization. Measurements carried out late in the same growing season showed that both defoliation and withholding fertilizer reduced current-year foliar dry weight, shoot length, needle size, and stem xylem radial width, as well as total foliar dry weight, and root dry weight. Defoliation increased the projected area to weight ratio, nitrogen concentration, net photosynthetic rate per unit of dry weight, and ratio of photosynthesis to internal CO 2 concentration in current-year needles. In contrast, withholding fertilizer did not alter the projected area to weight ratio and decreased the nitrogen concentration, net photosynthetic rate per unit of dry weight, and ratio of photosynthesis to internal CO 2 concentration. Both defoliation and withholding fertilizer also decreased the number of current-year needles produced in the growing season following treatment. The results indicate that (1) the reduction in total photosynthesizing biomass caused by removing old foliage is much greater than the biomass of old foliage removed due to decreased production of current-year foliage, and (2) old foliage removal stimulates net photosynthesis in current-year shoots, probably by improving foliar nitrogen relations. Removing old foliage reduced the total photosynthesizing biomass more, and stimulated net photosynthesis of remaining foliage less, than the removal of current-year foliage measured in earlier studies, which helps explain why tree recovery is slower following defoliation by the balsam fir sawfly than after spruce budworm ( Choristoneura fumiferana) attack.

Growth recovery in young, plantation white spruce following artificial defoliation and pruning

Defoliation by the spruce budworm (Choristoneura fumiferana (Clem.)) was simulated by artificially defoliating trees in a plantation of 12-year-old white spruce (Picea glauca (Moench) Voss) over a 2-year period and then allowing the trees to recover for 3 years. Four treatments were applied: control (C); removal of 50% of the current-year foliage (50); removal of all current-year shoots (100P); and removal of all current-year shoots and some older foliage age-classes (100P+). All treatments increased shoot production. Trees in the 100P treatment completely recovered their foliage mass after 1 year, but trees in the 50 treatment were still affected after 3 years of recovery. Trees in the 100P+ treatment showed poor recovery rates in foliage mass. Only the trees in the 50 treatment completely recovered height growth. After 2 years of defoliation, specific volume increment was reduced by 21.3, 58.1, and 75.3% for the 50, 100P, and 100P+ treatments, respectively. After 3 years of recovery, specific volume increment in the 50 treatment recovered completely, while the 100P and 100P+ treatments were reduced by 34.2 and 79.9%, respectively. Because of the release of suppressed buds following both needle loss only and shoot loss, white spruce may be a reforestation candidate for areas having a high probability of budworm outbreaks.

Growth and leaf nutrient responses of loblolly and slash pine families to intensive silvicultural management

Intra-specific variation in foliar nutrient response to fertilization treatments and associated growth performance is largely unknown in southern pines. Sixteen open-pollinated families from each of three pine taxa—genetically improved loblolly pine (PTI; Pinus taeda), improved slash pine (PEI; Pinus elliottii var. elliottii), and unimproved slash pine (PEU)—were planted in two locations under a common split–split plot experimental design in north Florida. At each site, two levels of silvicultural treatments (low intensity—no fertilization; high intensity—fertilization and weed control) were implemented. Vector analysis suggested that N, P, and K were nutrients mostly commonly limiting growth, while Mg and Ca were generally not deficient for the three taxa over four different sampling periods during the growing season. The period of highest nutrient demand occurred during the growing season from June to September, with deficiencies easing throughout the remainder of the year. Differential family responses in foliar nutrient levels (especially N and P) were closely associated with current-year foliage biomass production and annual height growth for the three taxa. PTI and PEI families with constant, but minor, foliar N and P deficiencies during the growing season had higher foliage biomass production and height increments than those exhibiting excess, dilution, or severe deficiency. PEU families generally had lower nutrient requirements than PTI and PEI families. Differences in nutrient demand for growth existed between PEU and PEI. Differences between PEI and PEU in foliar nutrient response to intensive management from this study, along with findings in growth performance and crown structure, suggested that PEI had growth strategies more closely aligned with PTA than with PEU. Significant intra-specific differences in growth and nutritional characteristics also indicated that family forestry could be a viable option suited for intensive plantation management because family-specific fertilizer prescriptions may be needed to further improve stand growth.

Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore.

Two field studies were carried out to determine the influence of Abies balsamea foliage age on the preference and performance of larvae of Neodiprion abietis, a specialist Diprionid sawfly. Preference was determined by examining N. abietis defoliation on all age classes of foliage. Performance was estimated using larval survival, cocoon weights and the percentage of adults that were females. Neodiprion abietis preference for, and performance on, current-year foliage was very low, peaked on 2 or 3-year-old foliage, and declined on older foliage. Thus, sawfly feeding preference was adaptive. However, survival and cocoon weight were highest when sawflies were allowed to feed on all age classes of foliage, demonstrating that an insect specialist may perform better when feeding on several age classes of foliage from a single host plant species. These results indicate that either different larval instars have different nutritional requirements, or that food mixing provides the best diet, permitting the herbivore to obtain needed nutrients while avoiding ingestion of toxic doses of secondary metabolites. In addition, our results suggest that limited availability of varied foliage has more negative consequences for N. abietis females than for males, as the percentage of survivors that were females decreased when juvenile mortality was high. Our results emphasize the importance of considering non-linear changes in foliar quality as leaves age on herbivore preference and performance, and demonstrate how a herbivore can use this variability to maximize its fitness.

Effects of chronic N fertilization on foliar membranes, cold tolerance, and carbon storage in montane red spruce

We evaluated the influence of protracted low-level nitrogen (N) fertilization on foliar membrane-associated calcium (mCa), sugar and starch concentrations, membrane stability, winter cold tolerance, and freezing injury of red spruce (Picea rubens Sarg.) trees growing in six experimental plots on Mount Ascutney, Vermont. For 12 consecutive years before this evaluation, each plot received one of three treatments: 0, 15.7, or 31.4 kg N·ha–1·year–1supplied as NH4Cl. In comparison with trees from control plots, the current-year foliage of trees from N-addition plots had lower mCa concentrations, higher levels of electrolyte leakage, reduced cold tolerance, and greater freezing injury. Levels of mCa, membrane stability, and cold tolerance did not differ between N treatments, but trees in high-N treated plots experienced greater freezing injury. Although no differences in carbohydrate nutrition were detected in September, foliar sugar and starch concentrations from trees in N-treated plots were higher than control plot trees in January. We propose that foliar mCa deficiencies reduced cell membrane stability, decreased cold tolerance, and increased freezing injury for trees in N addition plots relative to controls. Declines in mCa may also help account for increases in respiration previously measured. Because soil, root, and mycorryhizal conditions were not evaluated, it is unknown how treatment-induced changes in these compartments may have influenced the alterations in foliar mCa and physiological parameters measured in this study.

Does nutrition-related stress carry over to spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) progeny?

Three different patterns of feeding of sixth-instar spruce budworm, Choristoneura fumiferana Clemens were simulated in the laboratory. Larvae were fed artificial diets whose nitrogen and total soluble sugar contents varied according to levels similar to those found in three types of balsam fir, Abies balsamea (L.) Miller foliage (current-year foliage from middle and lower crown sections and one-year-old foliage). The biological performance of offspring was studied according to the nutrition of their parents. Although food quality had no impact on pupal weight of female parents and individual mean egg weight, progeny fitness was influenced by parental nutrition. Old foliage simulated diet, poor in nitrogen, clearly affected the early larval development of progeny, especially the percent of egg hatch and first-instar survival. Lower crown current-year foliage simulated diet, with low total soluble sugar content, reduced the first-instar survival of the progeny. However, the selective pressure exerted by low food qualities on the parental generation and on the early stages of their progenies resulted in C. fumiferana populations having higher tolerance to starvation and higher survival after the diapause period. These results highlighted the potentially direct and indirect effects of C. fumiferana parental nutrition on the next generation. The patterns of feeding of parental generations would appear to affect the quality and size of subsequent populations through several selections on the different life-history stages of both generations.

Simulated root freezing in the nursery: effects on the growth and physiology of containerized boreal conifer seedlings after outplanting

The effects of induced root freezing injury on 2+0 white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) BSP), and jack pine (Pinus banksiana Lamb.) seedlings were studied. Hardened seedlings were exposed to freezing during the fall and cold stored until planting. Seedlings were planted in spring on two field sites with different soil moisture levels (wet or dry). Seedling morphology and physiology were measured periodically during the first growing season, and mortality was evaluated at the end of the season. With the exception of June measurements on the wet site, where daytime water potential fell as low as –2.0 MPa, root damage did not seriously affect shoot water potential. Generally, stomatal conductance decreased with increasing root damage. Net photosynthesis on both sites decreased between 22 and 39% with increasing root damage. Root damage did not affect the ratio of intercellular to ambient CO2concentration. As well, reductions in the nitrogen concentration of current-year foliage with increasing root damage were observed, suggesting that the observed reductions in net photosynthesis were caused by nonstomatal factors. Root growth was greater on the wet site than on the dry site, particularly between August and October, when mean soil minimum temperatures were lower on the dry site. On both sites, aerial dry mass was only slightly affected by root damage in July and August, but the effect of damage became more pronounced in October on the wet site. Black spruce and white spruce seedling mortality began being affected when approximately 50% of the root systems were damaged, while jack pine mortality was affected starting at 40% damage. Root damage levels of 50% caused 2.0 and 1.5 cm reductions in annual height increment of white spruce and black spruce, respectively, and 40% damage caused a reduction of 1.0 cm in annual height increment of jack pine.

The role of monoterpenes in resistance of Douglas fir to western spruce budworm defoliation.

We conducted defoliation experiments with 7- to 8-year-old clones of Douglas fir [Pseudotsuga menziesii (Mirb.) Franco var. glauca] to assess the role of monoterpenes as a resistance mechanism to western spruce budworm (Choristoneura occidentalis Freeman) defoliation. The grafted clones were derived from mature trees that showed resistance or susceptibility to budworm defoliation in the forest. All clones were exposed to either budworm defoliation or nondefoliation treatments in 1998 and 1999 under greenhouse conditions. We found that the total concentration of monoterpenes in current-year foliage varied greatly between two consecutive years in clones in the greenhouse and in their corresponding mature trees in the forest. Fractional composition of different monoterpenes was similar between different years and between clones and mature trees, indicating genetic control of this trait. Two different defoliation experiments were conducted to assess the importance of budburst phenology as a factor determining host plant resistance. In the 1998 experiment, budworm feeding was matched to the budburst of each individual plant. Monoterpene concentration was high in 1998, and budworm potential fitness was greater on clones from the resistant mature trees that had lower concentrations of total monoterpenes. In the 1999 experiment, budworm feeding was matched to budburst of the whole population of plants in order to mimic conditions similar to insects feeding on trees in the field. The concentration of monoterpenes was low in 1999, and budworm fitness was not related to monoterpenes. Total monoterpene concentration was negatively related to foliar nitrogen concentration, suggesting that C/N balance may affect monoterpene synthesis in needles. However, tree growth was not related to total monoterpene concentration. We concluded that expression of differences in budworm resistance among Douglas fir genotypes might be caused by interactions among multiple resistance mechanisms such as needle monoterpenes and tree budburst phenology.

Testing the ecophysiological basis for the control of monoterpene concentrations in thinned and unthinned balsam fir stands across different drainage classes.

Stand thinning across different soil drainage types was used to test the ecophysiological basis for the control of foliar monoterpenes in current-year foliage of balsam trees [Abies balsamea (L.) P. Mill.] the year following treatment. Photosynthetic capacity (A max) was greater on mesic sites than on sub-hygric and hydric sites (1.81, 1.33 and 0.88 µmol m-2 s-1, respectively) and greater in mid-July than at the end of June (1.86 vs 0.77 µmol m-2 s-1). Foliar N was greater on thinned plots than control plots (2.6 vs 2.2g m-2); starch was greater on mesic control plots than mesic thinned plots (16.3 vs 10.9g m-2); and total soluble sugars (TSS) were higher in mid-July than at the end of June (16.5 vs 12.8g m-2). Total monoterpenes, as well as five individual monoterpenes, showed a complex interaction between site drainage class, thinning treatment and time of sampling (P<0.05). For all sites and dates combined, total monoterpenes were negatively correlated with specific leaf area (r 2=0.46), and positively but weakly correlated with A max (r 2=0.35), foliar N (r 2=0.29) and TSS (r 2=0.24). Total monoterpenes were not correlated with the different measures of carbon to nitrogen ratio as predicted by the carbon-nutrient balance hypothesis. Our results offer partial support to the different hypotheses proposing that foliage having greater resource availability, enzymatic machinery and potential for building storage structures will have greater monoterpene content. However, the strength of the relationships with monoterpenes often varied with sampling date, suggesting that phenological development may play a strong role in determining which factors control monoterpenes at a given time.

Application of response surface methodology and ANOVA to detect pollution effects on photosynthetic response under varying temperature and light regimes

Studies of air pollution effects on plant physiological responses to diurnal changes in environmental conditions are complex, and thus, require efficient statistical design and valid data analysis. Here, we aim at demonstrating the use of a response-surface methodology (RSM) including least square regression and canonical analyses in combination with a two-way ANOVA to quantify net photosynthetic ( A n) response of ponderosa pine ( Pinus ponderosa Dougl. ex Laws) seedlings to different levels of rain acidity, ozone, temperature, and light conditions. Seedlings were exposed to four combinations of two rain (pH 5.1 and 3) and two ozone (ambient, and twice-ambient) regimes. The rain treatment was applied to foliage only on a weekly basis from January to April 1992. The ozone treatment was applied from September 1991 to November 1992. A n responses of current- and 1-year-old foliage to nine combinations of three temperatures (18, 25, 32°C) and three light regimes (250, 500, 1000 μmol photons m −2 s −1) were measured between 0800 and 1900 h from 18 August to 7 September 1992. A completely randomized design, replicated twice, was used for the assignment of rain-by-ozone combinations (main plots). Foliage age classes were sub-plots within the main plots, temperature levels were sub-plots within foliage age classes, and light levels were sub-plots within temperature levels. Response surface models of A n response to temperature and light levels were constructed per rain-by-ozone combination for each foliage age. β Temp, β Temp 2 , β Light, A n mean , A n max , temperature at A n max , and light at A n max were calculated or estimated. The effects of rain pH and ozone on these variables were then quantified using a two-way ANOVA. No significant rain-by-ozone or ozone effect was detected for any response. Rain of pH 3 decreased A n mean in current-year foliage only.

Effects of Short-term, High Exposure to Chlorine Gas on Morphology and Physiology of Pinus ponderosa andPseudotsuga menziesii

Following an accidental spill, acute morphological and physiological effects of chlorine gas exposure were evaluated on two conifer species, Pseudotsuga menziesii(Mirb.) Franco and Pinus ponderosa(L.), growing in a montane, coniferous forest in the Rocky Mountains, USA. Foliar injury, consisting of chlorosis, necrotic mottling and necrosis was observed only on foliage that was directly exposed to chlorine gas. Necrotic needles of both species defoliated during the months immediately following exposure. Buds of both species within 50m of the gas release were killed; this gave rise to secondary shoot growth for Pseudotsuga menziesii. Cuticular injury was assessed by measuring droplet contact and retention angles on 1-year-old foliage (directly exposed) and current-year foliage (which flushed after the gas cloud had subsided). Chlorine gas exposure led to smaller droplet contact angles on needles in both age classes of Pseudotsuga menziesii(P<0.0001), but not on Pinus ponderosa. Moreover, exposure led to increased cuticular water loss and decreased total water content of needles in both age classes of Pseudotsuga menziesii, and for 1-year-old needles of Pinus ponderosa(P<0.0001). On exposed trees, needles in both age classes had lowerFv / Fmratios (P<0.0001), suggesting reductions in photosynthetic efficiency. Thus, exposure of needles to chlorine gas may lead to increased drought susceptibility and damage to chloroplast membranes in conifers, and may have a negative influence on tree growth. Importantly, plant responses to chlorine gas are species-specific and are influenced by variation between sites and the stochastic movement of chlorine gas clouds.

Morphological and stomatal responses of Norway spruce foliage to irradiance within a canopy depending on shoot age

Morphological and stomatal responses of Norway spruce ( Picea abies) foliage to light availability were studied in respect to shoot age. Needle minor diameter ( D 1, anatomical width), major diameter ( D 2, anatomical thickness), dry weight ( M), and tissue density index ( I D) increased, and needle flatness ( Fl) and specific leaf area (SLA) decreased with foliage age, while shade foliage demonstrated higher morphological plasticity as compared to sun foliage. Needle minor diameter, dry weight, and the ratio of total to projected leaf area increased, and needle flatness and specific leaf area decreased with daily average photosynthetic photon flux density ( Q D). The current-year foliage exhibited the highest variation with irradiance, while the morphological plasticity decreased with needle ageing. The morphological characteristics of needles were independent of irradiance if Q D was above 300 μmol m −2 s −1. D 1 was the only linear needle characteristic which significantly changed with light availability within a canopy, and thus determined needle flatness, SLA, as well as the ratio of total to projected leaf area (TLA/PLA). Needle flatness was a characteristic responding most sensitively to the photosynthetic photon flux density, R 2 was 0.68, 0.44, and 0.49 for the current-year, 1-year-old, and 2-year-old foliage, respectively. TLA/PLA ranged from 2.2 to 4.0 depending on D 1. Variation in SLA in response to light availability can be attributed to changes both in needle shape and tissue density. Stomatal responses to photosynthetic photon flux density ( Q P) depended on foliage type (sun or shade) and age. Sun needles demonstrated higher daily maximum leaf conductances to water vapour compared to shade needles. The shade needles responded more sensitively to changes in Q P at dawn and sunset than the sun needles, while older needles of both foliage types exhibited faster stomatal responses. The light-saturation of leaf conductance ( g L) was achieved by 20 μmol m −2 s −1 for shade foliage, and approximately by 50 μmol m −2 s −1 for sun foliage. As a rule, g L changed in response to irradiance faster in the evening, i.e. at decreasing irradiance. Stomata were not usually completely closed in the dark before sunrise and after sunset, the phenomenon being more pronounced in older shoots and sun needles. Nightly water losses from spruce foliage are attributable primarily to older shoots, and are related to age-dependent changes in stomatal responsiveness.