Response of Douglas-fir seedlings to a brief pulse of 15N-labeled nutrients

The temporal distribution of soil nutrients is heterogeneous, and thus the uptake, storage and later remobilization of brief nutrient pulses may be critical for growth in nutrient-limited habitats. We investigated the response of 2-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings receiving a low nutrient supply to a 15-day nutrient pulse (containing 250 ppm nitrogen (N) as 10 atom % 15NH4 15NO3). The nutrient pulse was imposed in late July, toward the end of the seedlings' third growing season, and subsequent changes in dry mass and N content over the following 3 months were determined from destructive harvests. We tested three hypotheses: (1) N from the nutrient pulse is rapidly assimilated and accumulated primarily in needles and roots; (2) this accumulated N is later remobilized to support new growth; and (3) the nutrient pulse leads to a larger second flush of shoot growth. Seedlings increased their N content by 175 mg (67%) in response to the nutrient pulse. Nitrogen was taken up preferentially into younger tissues, especially the secondary flush and current-year roots. Immediately after the nutrient pulse, tissue N concentrations were high and supported subsequent increases in dry mass. Over 3 months, seedlings receiving the nutrient pulse added twice as much dry mass as control seedlings, and even after 3 months of growth, N concentrations remained greater than in controls. Current-year and older needles were the only components whose dry mass did not increase over this period. The nutrient pulse increased the size of the second flush, but it was still a minor component of increments in dry mass (approximately 10% of the total dry mass increment) and N content (23%). The relatively modest increases in N content during autumn could be accounted for by soil uptake and there was no evidence that N was remobilized to support growth of new tissues. Short-term (15 days) elevated N uptake led to sustained growth in the long term (> 3 months), and thus growth rate was to a large extent decoupled from current nutrient supply.     

Nutrition and bud removal affect biomass and nutrient allocation in Douglas-fir and western red cedar

Seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata J. Donn ex D. Don) were grown at high (250 mg l(-1)) and low (20 mg l(-1)) nitrogen (N) supply for a year. Before the second growing season, half of the seedlings in each nutrient treatment were allocated to the other treatment. Half of the seedlings in each nutrient treatment then had all growing points removed. Biomass and N, phosphorus (P) and potassium (K) concentrations of old and new shoots and roots were measured three times in the second year to test the interaction of current-year and previous-year nutrient supply on biomass and nutrient allocation in these two species with different growth habits. Pruned seedlings served as controls. Unpruned seedlings of both species increased in height throughout the second growing season, except for Douglas-fir in the N250 --> N20 treatment. Repeated pruning did not prevent new shoot growth, but resulted in a 12 to 52% reduction in biomass of new shoots and new and old roots. Seedlings receiving a low N supply in the first growing season were more severely affected by pruning than seedings receiving a high N supply. Growth was reduced more by pruning in western red cedar than in Douglas-fir. Concentrations of N, P and K were higher in pruned seedlings than in unpruned seedlings. Although dry weights of all plant parts in all treatments increased throughout the second growing season, some retranslocation of N, P and K was observed from old shoots of both species in the N250 --> N20 and N20 --> N20 treatments after August. Quantities of N, P and K retranslocated were greatest in seedlings grown the previous year in the high-N treatment.     

Biomass and nutrient allocation in Douglas-fir and amabilis fir seedlings: influence of growth rate and nutrition

Allocation of biomass and nutrients to shoots and roots was followed for three years in fast and slow growing populations of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a fast growing pioneer species, and amabilis fir (Abies amabilis Dougl. ex J. Forbes), a slow growing shade-tolerant species. Seedlings were grown for three seasons in five nutrient treatments containing varying proportions of nitrogen and phosphorus (N:P). In both species, growth was greatest in the 250:20 N:P treatment followed by the 100:60 and 100:20 treatments. Vector analysis showed that, in both species, relative to the 100:20 treatment, seedlings in the 20:20 treatment were N deficient and seedlings in the 100:4 treatment were P deficient, i.e., where deficiency is defined to mean that an increase in nutrient supply increases nutrient content, nutrient concentration and plant dry weight. Seedlings in the 100:60 treatment had a higher P content than seedlings in the 100:20 treatment but the same dry weight, indicative of what Timmer and Armstrong (1987) termed luxury consumption. No nutrient retranslocation was observed in either species until the third growing season. In Douglas-fir, the greatest percentage of nutrients was exported from one-year-old shoots between May and July of the third growing season to support new growth. The total amount and percent of nutrients retranslocated was higher in Douglas-fir than in amabilis fir. Amabilis fir seedlings also exported N and P from older shoots, but this was later partially replenished. In both species, P retranslocation was greatest in treatments with a high N:P ratio. Nitrogen retranslocation was greatest in amabilis fir seedlings in treatments with a low N:P ratio, and greatest in Douglas-fir seedlings in the 250:20 and 100:60 treatments. Potassium retranslocation was correlated with seedling size. Douglas-fir retranslocated more of its shoot N reserves into new growth at the expense of older needles when soil fertility was high and sinks were strong. Otherwise, both species preferentially translocated the elements in short supply. Thus, retranslocation varied with the ecological characteristics of species, the relative availability of soil nutrients and sink strength.     

Biomass and nutrient allocation in Douglas-fir and amabilis fir seedlings: influence of growth rate and temperature

Allocation of biomass and nutrients to current-year and one-year-old shoots and roots of two-year-old conifer seedlings with differing rates of growth was studied. Differences in growth rate were achieved by selecting fast- and slow-growing populations of the relatively fast- and slow-growing conifer species, Pseudotsuga menziesii (Mirb.) Franco and Abies amabilis Dougl. ex Loud, respectively. Environmentally controlled differences in growth rate were induced by placing half of the seedlings in a 10 degrees C growth chamber and half in a 20 degrees C growth chamber in their second growing season. Seedling samples were harvested in May, before the temperature treatment, and in July and November of the second growing season, and biomass and nutrient concentrations of current-year and one-year-old shoots and roots were determined. Seedling biomass and nutrient allocation differed among the high-growth treatments. Seedlings exhibiting high growth in response to the 20 degrees C treatment and faster growing populations within species both showed increased allocation to new shoots, whereas seedlings of the fast-growing species showed greater allocation to old shoots than to new shoots. Increased growth increased nutrient uptake, but nutrient concentration decreased with growth rate as a result of dilution, so that faster-growing seedlings had greater nutrient-use efficiency than slower-growing seedlings. Retranslocation of P and K was seen in the second year only in slow-growing populations at 10 degrees C. Nutrient concentrations of one-year-old plant parts decreased in the second year, indicating new growth was a stronger sink for nutrients than second-year growth.     

Decomposition responses of pine (Pinus massoniana) needles with two different nutrient-status to N deposition in a tropical pine plantation in southern China

? The effect of nitrogen (N) deposition on the decomposition of pine (Pinus massoniana) needles in a tropical pine plantation was studied. The pine needles with two different nutrient status (nutrient-rich and nutrient-poor) were used, followed by 3-levels of N treatments (Control: no N addition, Low- N: 5 g N m^?2 y^?1, and Medium-N: 10 g N m^?2 y^?1 experimental inputs), which had been applied for 26 months continuously before this experiment and continued throughout the decomposition measurement.

? The main objective was to test the hypothesis that decomposition of nutrient-rich needles would be more sensitive to cumulative N deposition than the decomposition of nutrient-poor needles.

? Nitrogen addition had negative effect on mass loss, and the release of N and P from decomposing nutrient-rich needles but little or no effect on the decomposition of nutrient-poor needles. In addition, a negative effect in the initial decomposition phase and a positive effect in later decay stages were found on C release. The negative effect was stronger on nutrient-rich needles than on nutrient-poor needles, but the reverse was true for the positive effect.

? Our results suggest that response of litter decomposition to N deposition may vary depending on the nutrient status of the litter.

     

Foliar nitrogen concentrations and natural abundance of (15)N suggest nitrogen allocation patterns of Douglas-fir and mycorrhizal fungi during development in elevated carbon dioxide concentration and temperature

Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir) seedlings were grown in a 2 x 2 factorial design in enclosed mesocosms at ambient temperature or 3.5 degrees C above ambient, and at ambient CO2 concentration ([CO2]) or 179 ppm above ambient. Two additional mesocosms were maintained as open controls. We measured the extent of mycorrhizal infection, foliar nitrogen (N) concentrations on both a weight basis (%N) and area basis (Narea), and foliar delta15N signatures (15N/14N ratios) from summer 1993 through summer 1997. Mycorrhizal fungi had colonized nearly all root tips across all treatments by spring 1994. Elevated [CO2] lowered foliar %N but did not affect N(area), whereas elevated temperature increased both foliar %N and Narea. Foliar delta15N was initially -1 per thousand and dropped by the final harvest to between -4 and -5 per thousand in the enclosed mesocosms, probably because of transfer of isotopically depleted N from mycorrhizal fungi. Based on the similarity in foliar delta15N among treatments, we conclude that mycorrhizal fungi had similar N allocation patterns across CO2 and temperature treatments. We combined isotopic and Narea data for 1993-94 to calculate fluxes of N for second- and third-year needles. Yearly N influxes were higher in second-year needles than in third-year needles (about 160 and 50% of initial leaf N, respectively), indicating greater sink strength in the younger needles. Influxes of N in second-year needles increased in response to elevated temperature, suggesting increased N supply from soil relative to plant N demands. In the elevated temperature treatments, N effluxes from third-year needles were higher in seedlings in elevated [CO2] than in ambient [CO2], probably because of increased N allocation below ground. We conclude that N allocation patterns shifted in response to the elevated temperature and [CO2] treatments in the seedlings but not in their fungal symbionts.     

Photosynthetic activity in winter needles of the evergreen tree Taxus cuspidata at low temperatures

Photosystems harvest light energy, yet this energy cannot be efficiently employed for CO(2) assimilation at the below-freezing temperatures to which plants are typically exposed during winter in the temperate and boreal zones. To elucidate the mechanisms whereby this energy is dissipated, I evaluated performance of photosystems in winter needles of the evergreen tree Taxus cuspidata Sieb. et Zucc. Chloroplasts were localized adjacent to plasma membranes in needle cells in summer, whereas they congregated together in the centers of the cells during winter. When winter needles were acclimated to a temperature of 20 degrees C, their chloroplasts gradually dispersed to the edges of the cells, as in the summer. Acclimation-dependent relocalization coincided with changes in CO(2) uptake. Examination of photosystem II fluorescence kinetics in winter needles indicated that the quinone electron acceptor (Q(A)) reduction rate exceeded the Q(A) oxidation rate at low temperatures. The majority of Q(A) remained reduced even when winter needles were subjected to a temperature of -5 degrees C at low irradiance.     

氮肥对盆栽欧洲水青冈生物量和营养分配的影响(英文)

调查了施加氮肥(15NH4和15NO3)处理后在两个连续生长季内欧洲水青冈(Fagus sylvatica L.)幼苗地上部分和地下部分的生物量和营养元素分配。盆栽欧洲水青冈幼苗培养于温室大棚内,培养土样取自相邻的三种林分:欧洲水青冈,挪威赤松,欧洲水青冈-赤松混交林。结果表明,氮肥(15N)处理对欧洲水青冈营养元素分配没有显著影响,施加氮素形式决定自身流入植物库的情况。欧洲水青獭收氮素主要以硝态氮的形式,因此,尽管植物体内保存的硝态氮和氨态氮并没有统计差异,但是叶片中硝态氮明显减少。施加硝态氮对欧洲水青冈氮素恢复的影响要大于施加氨态氮。与欧洲水青冈茎、粗根相比,优质根系对氮素(15N)固定是一个缓慢过程。表8图1参40。     

Biomass and nutrients allocation in pot cultured beech seedlings： influence of nitrogen fertilizer

Allocation of biomass and nutrient elements including Nitrogen to above and belowground compartments of beech seedlings (Fagus sylvatica L.) treated by labeled nitrogen fertilizer in the form of ¹⁵NH₄ and ¹⁵NO₃ were investigated at the end of two successive growing seasons. Pot cultured beech seedlings were grown at a green house on intact soil cores sampled from three adjacent stands including beech, Norway spruce and mixed beech-spruce cultures of Solling forest, Germany. Comparing biomass allocation and nutrients concentrations of the seedlings between the control and ¹⁵N-fertilized treatments revealed no significant effect of N fertilization on nutrients uptake by seedlings over the experiment. The form of N input influenced its movement into plant pools. It was demonstrated that beech seedlings take up nitrogen mainly in the form of nitrate, which is then reduced in the leaves, although the differences between the retention of NO₃ ^?-N and NH₄ ⁺-N in plants were not statistically significant. Percent recoveries of ¹⁵N in trees were typically greater after ¹⁵NO₃ than after ¹⁵NH₄ additions. It was indicated that immobilization of 15N tracer in fine roots was a slower process comparing other plant compartments such as stem and coarse roots, but a powerful sink for N during the course of study.     

Five-year vegetation control effects on aboveground biomass and nitrogen content and allocation in Douglas-fir plantations on three contrasting sites

Despite widespread use of intensive vegetation control (VC) in forest management, the effects of VC on allocation of biomass and nutrients between young trees and competing vegetation are not well understood. On three Pacific Northwest sites differing in productivity, soil parent material, and understory vegetation community, we evaluated year-5 effects of presence/absence of 5 years of VC on allocation of aboveground biomass and nitrogen (N) between planted Douglas-fir (Pseudotsuga menziesii var. menziesii) and competing vegetation. Equations for predicting bole, branch, foliar, and total dry weights based on stem diameter at a height of 15 cm and total tree height did not differ significantly among sites or by presence or absence of VC. This contrasts with previous research, using diameter at breast height rather than at 15 cm, which found that separate equations were warranted for trees with and without competing vegetation. Estimated whole-tree biomass among the six site/VC combinations ranged from 0.8 to 7.5 Mg ha⁻¹, and increases in tree biomass associated with VC ranged from 62% to 173% among sites. Among the three sites, there were positive, linear relationships between soil total N content to a depth of 60 cm and both N content of aboveground vegetation (trees plus competing vegetation) and Douglas-fir foliar N concentration. Tree N content increased by 8.4, 8.2, and 40.0 kg N ha⁻¹ with VC at the three sites, whereas competing vegetation N content decreased with VC by 0.9, 18.8, and 32.0 kg N ha⁻¹, respectively, at the same sites. Thus, VC did not lead to a direct compensatory tradeoff between aboveground N content of trees and other vegetation. However, soil N content was linearly related to N accumulation and plant growth across the three sites. In addition to differences in N availability among sites, the effect of VC on the redistribution of resources among trees and competing vegetation also was influenced by vegetation community composition and efficacy of VC treatments.     

Photosynthetic responses to lightflecks ofFagus crenata seedlings grown in a gap and understory of a deciduous forest

Photosynthetic responses to a series of 1-min lightflecks (1,000μmol m⁻² s⁻¹) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50μmol m⁻² s⁻¹) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively. The maximum net photosynthetic rate (P _Nmax) and maximum stomatal conductance (g _smax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25μmol m⁻²s⁻¹, the net photosynthetic rate (P ₂₅) and stomatal conductance (g _s25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic rate (P _N ) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase inP _N at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses to lightflecks. The higher ratios ofP ₂₅/P _Nmax andg _s25/g _smax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and stomatal limitations than the gap seedlings under low light conditions. The ratios ofP _N /P _Nmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUE _s) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings when the background PPFD was 25μmol m⁻² s⁻¹. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions than the gap seedlings although the net carbon gain of single lightflecks (CG _s) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUE _s between understory seedlings at a background PPFD of 25μmol m⁻² s⁻¹ and gap seedlings at a background PPFD of 50μmol m⁻² s⁻¹. However,CG _s in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments. This study was funded by the research project, Evaluation of Total CO₂ Budget in Forest Ecosystems, coordinated by the Ministry of Agriculture, Forestry and Fisheries of Japan.     

Comparison of 5th- and 14th-year Douglas-fir and understory vegetation responses to selective vegetation removal

The effects of early vegetation management on the survival and growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] were examined 5 and 15 years after planting in the Oregon Coast Range. Our first objective was to document the effects of vegetation species competition upon key ecosystem properties. The second objective was to document the effects of vegetation removal during early Douglas-fir stand establishment upon long-term tree growth and on biomass production by vegetation components. Seven levels of manual vegetation removal were maintained for the first 5 years after planting: 0%, 25%, 50%, 75%, and 100% shrub removal; and 100% shrub removal combined with 50% or 100% herbaceous vegetation removal. Shrub and herb removal did not affect Douglas-fir survival at year five, but treatments providing less than 75% shrub removal significantly reduced Douglas-fir survival by year 15. Removing shrubs and herbs completely (100S + 100H) during the 5 years following tree planting allowed successful tree establishment, with a 366% increase in biomass accumulation per hectare for Douglas-fir in that treatment at the end of 14 years of growth. At 15 years stand age, even with shrub removal alone, a 304% gain in tree biomass per hectare was obtained compared to no vegetation removal (NVR). By stand age 15 years, any increase in the degree of understory removal beyond 75% did not contribute significantly to additional tree survival and growth. The understory vegetation on NVR treatment plots and the herbaceous vegetation on 100% shrub removal (100S) treatment plots, contained >90% and >80% of aboveground biomass N at 5 years, respectively, indicating possible competition for soil N. Soil moisture was not different among treatments at 5 years. Complete vegetation removal (100S + 100H) for 5 years resulted in a significant increase in soil bulk density (P < 0.05), a significant decrease in total soil C (P < 0.05) and no change in total soil N in the upper 15 cm of the mineral soil. By 14 years, however, only the soil bulk density remained greater (P < 0.05) on the 100S + 100H treatment. We conclude that greater tree survival and growth occurred with at least 75% shrub removal. Our results suggest that managers may have substantial flexibility in maintaining a partial understory component suitable for ecosystem productivity, canopy cover and wildlife habitat, while maintaining forests productive for timber resources.     

Phytohormones and their metabolites during long shoot development in Douglas-fir following cone induction by gibberellin injection

Changes in plant hormones and metabolites in long-shoot stems of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) during cone induction by gibberellic acid (GA) treatment were analyzed by high performance liquid chromatography-electrospray ionization tandem mass spectrometry in multiple reaction monitoring mode. A mixture of GA(4) and GA(7), including small amounts of GA(3) and GA(1), was stem-injected into each tree in amounts of 0, 4, 40 or 400 mg. One week after injection, concentrations of GA(4), GA(7) and GA(3) were elevated in all GA-treated samples. The ratio of GA(4) to GA(7) decreased significantly at Week 3. Absolute concentrations of all gibberellins declined sharply at Week 3 after GA application. After 5 weeks, GA(1) and GA(4) were below detection limits in all samples, and GA(7) and GA(3) were found only in the samples from trees treated with 40 or 400 mg of GA. Endogenous indole-3-acetic acid (IAA) concentrations increased following GA injection, and peaked at Week 2 or Week 3 in the trees treated with 40 or 400 mg GA, respectively. Injection of 400 mg of GA brought about a twofold increase in IAA concentration compared with control values. Injection of 40 and 400 mg of GA caused significant increases in stem dry mass in Week 5. Seed orchard data revealed that injection of either 40 or 400 mg GA enhanced female cone formation, whereas male cone formation was enhanced only by 400 mg GA. Slight decreases in concentrations of abscisic acid (ABA) and isopentenyl adenosine were observed after GA application. No significant changes were detected in the concentrations of ABA metabolites except for a slight decrease in the concentration of 7'-hydroxy ABA. The concentration of ABA declined during the growing season and the concentration of ABA glucose ester increased correspondingly.     

Simulation of carbon and water budgets of a Douglas-fir forest

The forest growth/hydrology model FORGRO–SWIF, consisting of a forest growth and a soil water model, was applied to quantify the inter-annual variability of the carbon and water budgets of a Douglas-fir forest (Pseudotsuga menziessii (Mirb.) Franco) in The Netherlands. With these budgets, the water use efficiency, the amount of water needed to fix a certain amount of carbon, and its variability was estimated. After testing the model performance in simulating daily carbon and transpiration fluxes, and soil water contents of this forest ecosystem, the model was applied to a 10-year period of meteorological data. Two forest parameterisations were used: the non-thinned situation of 1995, and the thinned situation in 1996. Relations between forest water use and forest growth were quantified with the model. The model performed satisfactory, an R² value for daily carbon fluxes of 0.58 and for daily transpiration fluxes 0.81. The forest showed to be a clear carbon sink, in the climax situation between 1000 and 1210 g C m⁻² per year. In the thinned situation the carbon uptake was more than halved to values between 430 and 620 g C m⁻² per year. The calculated yearly WUE’s for the forest were between 2.5 and 4.3 g C m⁻² mm⁻¹ and for the total ecosystem between 1.1 and 2.0 g C m⁻² mm⁻¹. The thinned forest had clearly lower WUE’s than the non-thinned forest. The importance of including interception evaporation as forest water use is discussed, and the results showed the importance of integration of forest growth and forest water use for calculating yearly carbon and water budgets.     

Estimates of pollen contamination and selfing in a coastal Douglas-fir seed orchard

Seed orchards are the link from tree breeding to reforestation programs and are theoretically expected to function as closed, perfect populations, ensuring gain and diversity are consistently and predictively delivered as improved seed and seedlings. Seed orchard populations often deviate from panmixia due to fertility variation, reproductive asynchrony, and gene flow, leading to reduced seed crops genetic quality. Here, as a part of multiyear monitoring study, we used DNA fingerprinting (simple sequence repeat markers) to assess a Douglas-fir (Pseudotsuga menziesii) seed orchard's seed crop genetic quality (2009 seed crop). The studied seed crop was produced under ambient temperature (i.e. no reproductive phenology manipulation) and pollination was augmented by pollen from within orchard's pollen donors. DNA fingerprinting of the parental population (66 parents) along with 207 gametophyte (1n) – embryo (2n) pairs of random bulk sample of seed allowed parentage (maternal and paternal) assignment and the direct assessment of pollen contamination (0.18 ± 0.027) and selfing (0.17 ± 0.025) rates as well as parental (pollen, ovule and individual parent) gametic contribution was compared to a previous year's crop (2005). The extended reproductive phenology coupled with variable within-orchard pollen availability has created opportunities for both self and foreign pollen to be successful at various times resulting in the seemingly paradoxical scenario of high selfing and gene flow. These results (2005 and 2009) allowed comparison of seed orchard's crop management practices and are expected to provide scientific foundations to effective seed crops genetic quality improvement.     

Three dimensional distribution of needle and stem surface area in a Douglas-fir

The distribution of needles and branches in the crown of a 14-m tall Douglas-fir was investigated for the purpose of developing a three-dimensional structure for use with radiation transfer models. We found a linear relationship between the basal area of main branches originating at the bole and the total one-sided planimetric surface area of the foliage attached to each branch. A similar linear relationship was found between the branch basal area and the mass of stem material on the branch. Total silhouette area (needles plus branch material) did not vary significantly horizontally along the branch length, but stem surface area declined linearly from near the bole to the branch tip. Needle surface silhouette area and leaf area index increased along the main branch from near the bole to the branch tip. Silhouette leaf area (STAR) did not vary along the main branch. The needle area density (NAD) (m(2) m(-3)) was calculated for each of the lower 11 whorls; the vertical distribution of NAD increased from the base of the bole to the top of the crown.     

Physiological responses of needles of Pinus massoniana elite families to phosphorus stress in acid soil

Pinus massoniana Lamb. is a major timber species widely planted in the South China, where the soil is acidic and deficient in phosphorus (P) due to fixation by aluminum and iron. Understanding the physiological responses to rhizospheric insoluble P is essential for enhancing plantation productivity. Thus, a sand culture experiment was conducted with four levels of P treatment (0, 5, 20 g insoluble P and 10 g soluble P), and 11 P. massoniana elite families. Physiological responses were measured after two months of stress. Compared to the normal soluble P treatment, the insoluble P treatment significantly reduced the proline content and the APase activity in the needles, while it significantly increased the catalase activity by 1.3-fold and malondialdehyde content by 1.2-fold. Soluble protein content was unaffected by the treatments, but chlorophyll content was significantly lower in P-deprived treatment compared with soluble and insoluble P treatments. These physiological responses also exhibited highly significant variation among families (p < 0.01). The findings suggest that increased catalase activities in the presence of insoluble P might be involved in the activation of an anti-oxidation defense mechanism that scavenges the reactive oxygen species elicited by the stress. And this response has a strong genetic control that can be exploited to identify desirable genotypes.     

不同光照条件下红松幼苗光合作用诱导反应的研究

无论光通量密度(PPFD)为200靘ol穖-2穝-1还是500靘ol穖-2穝-1,生长在林冠下的红松幼苗光合速率达稳定净光合速率的50%和90%的诱导时间均长于全光条件下生长苗木。全光下生长的红松幼苗在PPFD为500靘ol穖-2穝-1时的诱导反应较PPFD为200靘ol穖-2穝-1时缓慢,而林冠下生长苗木则恰好相反。表明林冠下生长红松幼苗的光合作用诱导期与光斑强度有关。图3参6。     

Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation

The phloem-feeding aphid Essigella californica represents a potential threat to the productivity of Pinus radiata plantations in south-eastern Australia. Five- and nine-year-old field trials were used to characterize the effects of artificial and natural aphid-induced (E. californica) defoliation, respectively, on shoot photosynthesis and growth. Photosynthetic capacity (A(max)) was significantly greater following a 25% (D25) (13.8 μmol m(-2) s(-1)) and a 50% (D50) (15.9 μmol m(-2) s(-1)) single-event upper-crown artificial defoliation, 3 weeks after defoliation than in undefoliated control trees (12.9 μmol m(-2) s(-1)). This response was consistently observed for up to 11 weeks after the defoliation event; by Week 16, there was no difference in A(max) between control and defoliated trees. In the D50 treatment, this increased A(max) was not sufficient to fully compensate for the foliage loss as evidenced by the reduced diameter increment (by 15%) in defoliated trees 36 weeks after defoliation. In contrast, diameter increment of trees in the D25 treatment was unaffected by defoliation. The A(max) of trees experiencing upper-crown defoliation by natural and repeated E. californica infestations varied, depending on host genotype. Despite clear differences in defoliation levels between resistant and susceptible genotypes (17 vs. 35% of tree crown defoliated, respectively), growth of susceptible genotypes was not significantly different from that of resistant genotypes. The observed increases in A(max) in the lower crown of the canopy following attack suggested that susceptible genotypes were able to partly compensate for the loss of foliage by compensatory photosynthesis. The capacity of P. radiata to regulate photosynthesis in response to natural aphid-induced defoliation provides evidence that the impact of E. californica attack on stem growth will be less than expected, at least for up to 35% defoliation.