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Phyllosphere microorganisms are essential for plant growth and health. Although there are an increasing number of studies showing that the composition of phyllosphere communities varies among different plant species, it remains unclear whether and how their bacterial and fungal community composition predictably varies with plant traits and leaf age. In this study, we used high-throughput sequencing to explore the diversity and composition of phyllosphere communities in needles of different ages (originating from different cohorts) for three evergreen coniferous species (Pinus koraiensis, Picea koraiensis, and Abies nephrolepis). Our results indicated that Gammaproteobacteria (bacteria) and Dothideomycetes (fungi) were dominant in newly formed needles, whereas Actinobacteria (bacteria) and Eurotiomycetes (fungi) were dominant in perennial needles. Tree species identity and needle age were the main factors explaining the variations of the α diversity (species richness of phyllosphere communities) and β diversity (dissimilarity among phyllosphere communities). In particular, we found that leaf dry matter content, leaf mass per area, and total phosphorus content emerged as key predictors of composition and diversity of phyllosphere microbial communities, underscoring the major influence of tree species identity and needle age on phyllosphere communities through changes in plant functional traits. Finally, we found that the interaction between tree species identity and needle age also contributed significantly to explaining the diversity and composition of phyllosphere communities, probably because differences in plant functional traits or environmental conditions between new and perennial needles depend on tree growth rates and resource acquisition strategies. These findings provide new insights into the mechanisms of community assembly among different evergreen tree species and offer a better understanding of the interactions between plant traits and phyllosphere microorganisms during needle aging. [ABSTRACT FROM AUTHOR]

Copyright of Mustafa Kemal University Journal of Agricultural Sciences / Mustafa Kemal Üniversitesi Tarım Bilimleri Dergisi is the property of Mustafa Kemal University, Faculty of Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background and aims Foliar water uptake (FWU) has been documented in many species and is increasingly recognized as a non-trivial factor in plant–water relationships. However, it remains unknown whether FWU is a widespread phenomenon in Pinus species, and how it may relate to needle traits such as the form and structure of stomatal wax plugs. In this contribution, these questions were addressed by studying FWU in current-year and 1-year-old needles of seven Pinus species. Methods We monitored FWU gravimetrically and analysed the needle surface via cryo-scanning electron microscopy. Additionally, we considered the effect of artificial wax erosion by application of the surfactant Triton X-100, which is able to alter wax crystals. Key results The results show for all species that (1) FWU occurred, (2) FWU is higher in old needles compared to young needles and (3) there is substantial erosion of stomatal wax plugs in old needles. FWU was highest in Pinus canariensis , which has a thin stomatal wax plug. Surfactant treatment enhanced FWU. Conclusions The results of this study provide evidence for (1) widespread FWU in Pinus , (2) the influence of stomatal wax plugs on FWU and (3) age-related needle surface erosion. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a toxic metalloid, which has been increasingly used in the brake lining of vehicles, and increased concentrations have been found in soils near abundant traffic. However, since very few investigations of Sb accumulation in urban vegetation have been undertaken there exists a knowledge gap. We studied the concentrations of Sb in leaves and needles of trees in the Gothenburg City area, Sweden. In addition, lead (Pb), also associated with traffic, was investigated. Sb and Pb concentrations of Quercus palustris leaves at seven sites with contrasting traffic intensity varied substantially, correlated with the traffic-related PAH (polycyclic aromatic hydrocarbon) air pollution at the sites and increased during the growing season. Sb but not Pb concentrations were significantly higher in needles of Picea abies and Pinus sylvestris near major roads compared to sites at larger distances. In Pinus nigra needles at two urban streets both Sb and Pb were higher compared to an urban nature park environment, emphasising the role of traffic emissions for these elements. A continued accumulation of Sb and Pb in three years old needles of Pinus nigra, two years old needles of Pinus sylvestris and eleven years old needles of Picea abies was observed. Our data suggest a pronounced link between traffic pollution and Sb accumulation in leaves and needles, where the particles carrying Sb seem not to be transported very far from the source. We also conclude that there exists a strong potential for Sb and Pb bioaccumulation over time in leaves and needles. Implications of these findings are that increased concentrations of toxic Sb and Pb are likely to prevail in environments with high traffic intensity and that Sb can enter the ecological food chain by accumulation in leaves and needles, which is important for the biogeochemical cycling.

In the semiarid sandy region of Northeast China, Mongolian pine (Pinus sylvestris var. mongolica) suffers dieback after the age of 35, while Japanese red pine (Pinus densiflora) and Chinese pine (Pinus tabuliformis) stay healthy. Foliar nutrient retranslocation reflects the nutrient conservation and utilization mechanism of plants in response to their habitats. However, the nutrient retranslocation strategies employed by three Pinus tree species to cope with nutrient limitations remain largely unknown. For this study, we investigated the seasonal variations in nitrogen (N) and phosphorus (P) concentrations of Mongolian pine, Japanese red pine, and Chinese pine plantations in terms of the green needles of all ages, senesced needles, and soil. Further, the N retranslocation efficiency (NRE), and P retranslocation efficiency (PRE), and correlations between the N:P ratios of needles and soil were analyzed. The results showed that, except for the spring NRE in 1-year-old needles of Mongolian pine, the spring NRE and PRE in 1- and 2-year-old needles of the three tree species were greater than zero. The autumn PRE was higher than zero for Mongolian pine, but lower than zero for Japanese red pine and Chinese pine. Among the three Pinus species, Mongolian pine showed greater spring PRE in 2-year-old needles, and PRE from 1- to 2-yearold needles, and from 2-year-old needles to litter. However, Japanese red pine had higher P concentrations and lower N:P ratios in senesced needles, while greater PRE was found in Chinese pine litter. Significant relationships between the N:P ratios were found in the current year and 1-year-old needles and soil in the Mongolian pine plantation, while there was an insignificant relationship between the N:P ratios of the needles and soil in the Chinese pine plantation. Thus, for Mongolian pine, the removal of P from needles in autumn, and higher P translocation from older needles under P-deficient soil may have contributed to the tree dieback. In contrast, Japanese red pine and Chinese pine stored P in their needles during autumn. Japanese red pine returned more P to the soil via litter, while Chinese pine maintained N:P homeostasis and increased P withdrawal prior to needle abscission. [ABSTRACT FROM AUTHOR]

Needle experience large variations in photosynthetic rates in response to cone presence and needle aging. Exploring the interaction effect of these factors on photosynthetic traits is helpful to understand the source-sink relationship between needles and cones. Here, we examined the impact of needle age on needle CO2 assimilation rate (Pn), needle mass per area (LMA), and needle concentration of soluble sugars, starch, total non-structural carbohydrates ([NSC]), nitrogen ([N]) and phosphorus ([P]) in cone‐bearing branches (reproductive branches) and branches without cones (vegetative branches) of Pinus koraiensis. We also compared instantaneous photosynthetic N-use efficiency (PNUE) and P-use efficiency (PPUE) in reproductive and vegetative branches. Our results showed that needles in reproductive branches had lower Pn, [N], [P], PNUE and PPUE than the needles in vegetative branches, but higher [NSC] and LMA. The differences between branch types were similar across needle ages, despite a clear effect of aging on photosynthetic traits: Pn, [N], [P], PNUE and PPUE decreased with increasing needle age, whereas LMA increased and [NSC] did not change with needle age. Unexpectedly, these results suggest that Pn in needles of reproductive branches is limited by NSC accumulation, and that N and P needed for cone development come from adjacent needles/reproductive branches while NSC come from more distant organs. These results shed light on the source-sink transport of carbon, N and P between needles and cones and are helpful for eventually predicting and improving crop size in Pinus koraiensis. [ABSTRACT FROM AUTHOR]

Non-structural carbohydrates (NSCs), including soluble sugar (SS) and starch (ST), are essential for the growth and survival of plants. However, few studies have investigated the effects of phenology, needle age, and life history together on NSCs. We measured NSCs of leaves for 120 Pinus koraiensis individuals of various sizes (0.3–100 cm diameter at breast height, DBH) across needle age and during three leaf development periods to evaluate the effects of phenology, needle age, and life history on NSCs. Concentration ranges were 6.60–12.07, 2.38–8.90 and 10.97–16.18 g·100 g−1 dry mass for SS, ST, and NSC, respectively. Needle age accounted for most of the variations (42.2%-84.4%) of NSCs, followed by phenology (9.2%-46.8%), while life history accounted for only a small proportion. In general, NSC reached its maximum value during the leaf unfolding period and the shift between SS and ST occurred during the leaf fall period. The slope of NSC with phenology generally increased with increasing needle age (absolute value). With increasing needle age, NSC and its components showed gradual upward trends. The slope of NSC with needle age decreased with leaf development (except during the leaf fall period). Life history had significant effects on NSCs in the leaf fall period for both current year and perennial needles, and in the leaf unfolding period only for the current year needles. Needle age significantly affected the correlations of NSC and SS (or ST) only at the leaf unfolding period. Phenology had significant effects on the correlations of NSC and SS (or ST) only for current year needle. Our results clearly showed that the variations of NSC and its components were highly dependent on needle age, followed by phenology. Unexpectedly, the effects of life history on NSCs were much less than those of needle age and phenology. Therefore, needle age and phenology dominate over life history in influencing NSCs, and the ecological significance of NSCs variations need to be reconsidered by effects of incorporating needle age and phenology.

Leaf functional traits are essential for the growth and adaptation of trees to environmental changes. However, how needle traits and trait–trait relationships respond to different nitrogen (N) addition rates and leaf ages remain unclear for evergreen coniferous species. Our study aimed to investigate the effects of N addition and leaf age on needle traits and their bivariate correlations. Understanding resource utilization and distribution strategies during tree growth under the background of increased N deposition is important. We conducted a six-year manipulative field experiment in a Pinus koraiensis plantation in northeastern China with variable N addition levels: control (no N addition, CK); 20 kg N ha−1yr−1 (low-N, LN); 40 kg N ha−1yr−1 (medium-N, MN); and 80 kg N ha−1yr−1 (high-N, HN). The needle trait data were collected in September. The morphological traits, i.e., specific leaf area (SLA) and leaf dry matter content (LDMC); and chemical traits, i.e., leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), and leaf nonstructural carbohydrates (NSC) concentrations, were measured to investigate the changes in needle traits and their bivariate correlations. We found that N addition and needle age significantly affected needle traits, and the effect of needle age was much stronger than that of N addition. N addition and needle age had no significant interaction effects on any of the traits except for the LNC. Due to the dispersal trait values of current-year needles, there were almost no significant bivariate correlations between traits under different N addition rates. The SLA–LDMC and LDMC–LNC relationships were found to differ among the various N addition rates, and other trait trait relationships may be relatively stable because of the weak plasticity of older needles. Additionally, needle age significantly affected the slope of the SLA–LDMC relationship and the elevation of the LDMC–LPC and NSC–LNC relationships, indicating differences in the ecological strategies of needles at different ages. In summary, our findings emphasize that trait–trait relationships in current-year and older needles were inconsistent in response to N addition and that the optimal allocation of resources in needles was based on their functional needs during leaf aging. • Both nitrogen addition and needle age have significant effects on needle traits of Pinus koraiensis. • Needle age is the main source of trait variations compared with nitrogen addition. • The trait–trait relationships in current-year and older needles are inconsistent in response to nitrogen addition. • Needle age significantly modify the trait–trait relationships. [ABSTRACT FROM AUTHOR]

Abstract Background For capital breeding Lepidoptera, larval food quality is a key determinant of their fitness. A series of studies have suggested that the larval host species or varieties dramatically impact their development and reproductive output. However, few studies have reported the role of foliar age and adult mating success has often been ignored in these studies. In this paper, the influence of host species and needle age on larval performances, adult mating behavior and fitness consequences has been studied using a capital breeding caterpillar, Dendrolimus punctatus Walker (Lepidoptera:Lasiocampidae). Results In larval performance trial, a strong effect of larval host species and needle age was found on survivorship, developmental duration, body weight, percentage of adult emergence, and growth index, but not on percentage of female progeny. In adult mating trial, larval host species and needle age also significantly affected mating latency and mating duration, but not mating success. In adult fitness trial, female fecundity, longevity and fitness index, but not oviposition duration and fertility, influenced by larval host species and needle age. Conclusions These results reveal the importance of larval host species and needle age on larval performance and adult reproductive fitness in this capital breeding insect and provide strong evidence that old needles of masson pine P. massoniana is the best host for D. punctatus.

Aims Given the importance of resorption in nutrient conservations, nutrient resorption should change with leaf age if resorption depends on nutrient content, and if nutrient content changes with leaf age. However, no study has addressed this issue. Methods Here, we measured N and P concentrations of needles of different ages in two woody evergreen conifer species—white spruce (Picea glauca Voss.) and balsam fir (Abies balsamea Mill.)—to determine the effects of needle aging on nutrient resorption. Important Findings For both species, N and P concentrations were higher in newer needles than in older needles. Nutrient resorption efficiency, i.e. percentage of nutrients resorbed during senescence, also declined significantly with needle age from 73 to 22% in these two evergreen conifer species. The difference in nutrient resorption between old and young needles may be attributed to the size of N and P sink tissues, which is likely to decrease with needle age. These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species. [ABSTRACT FROM AUTHOR]

Pine (Pinus) species exhibit extensive variation in needle shape and size between juvenile (primary) and adult (secondary) needles (heteroblasty), but few studies have quantified the changes in needle morphological, anatomical and chemical traits upon juvenile-to-adult transition. Mediterranean pines keep juvenile needles longer than most other pines, implying that juvenile needles play a particularly significant role in seedling and sapling establishment in this environment. We studied needle anatomical, morphological and chemical characteristics in juvenile and different-aged adult needles in Mediterranean pines Pinus halepensis Mill., Pinus pinea L. and Pinus nigra J. F. Arnold subsp. salzmannii (Dunal) Franco hypothesizing that needle anatomical modifications upon juvenile-to-adult transition lead to a trade-off between investments in support and photosynthetic tissues and that analogous changes occur with needle aging albeit to a lower degree. Compared with adult needles, juvenile needles of all species were narrower with 1.6- to 2.4-fold lower leaf dry mass per unit area, and had ∼1.4-fold thinner cell walls, but needle nitrogen content per dry mass was similar among plant ages. Juvenile needles also had ∼1.5-fold greater mesophyll volume fraction, ∼3- fold greater chloroplast volume fraction and ∼1.7-fold greater chloroplast exposed to mesophyll exposed surface area ratio, suggesting overall greater photosynthetic activity. Changes in needle traits were similar in aging adult needles, but the magnitude was generally less than the changes upon juvenile to adult transition. In adult needles, the fraction in support tissues scaled positively with known ranking of species tolerance of drought (P. halepensis > P. pinea > P. nigra). Across all species and needle and plant ages, a negative correlation between volume fractions of mesophyll and structural tissues was observed, manifesting a trade-off between biomass investments in different needle functions. These results demonstrate that within the broad trade-off, juvenile and adult needle morphophysiotypes are separated by varying investments in support and photosynthetic functions. We suggest that the ecological advantage of the juvenile morphophysiotype is maximization of carbon gain of establishing saplings, while adult needle physiognomy enhances environmental stress tolerance of established plants. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir ( Cunninghamia lanceolata ) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ 13 C) and oxygen (δ 18 O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ 13 C and declined δ 18 O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ 13 C and a constant needle δ 18 O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ 13 C, δ 18 O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a toxic metalloid, which has been increasingly used in the brake lining of vehicles, and increased concentrations have been found in soils near abundant traffic. However, since very few investigations of Sb accumulation in urban vegetation have been undertaken there exists a knowledge gap. We studied the concentrations of Sb in leaves and needles of trees in the Gothenburg City area, Sweden. In addition, lead (Pb), also associated with traffic, was investigated. Sb and Pb concentrations of Quercus palustris leaves at seven sites with contrasting traffic intensity varied substantially, correlated with the traffic-related PAH (polycyclic aromatic hydrocarbon) air pollution at the sites and increased during the growing season. Sb but not Pb concentrations were significantly higher in needles of Picea abies and Pinus sylvestris near major roads compared to sites at larger distances. In Pinus nigra needles at two urban streets both Sb and Pb were higher compared to an urban nature park environment, emphasising the role of traffic emissions for these elements. A continued accumulation of Sb and Pb in three years old needles of Pinus nigra , two years old needles of Pinus sylvestris and eleven years old needles of Picea abies was observed. Our data suggest a pronounced link between traffic pollution and Sb accumulation in leaves and needles, where the particles carrying Sb seem not to be transported very far from the source. We also conclude that there exists a strong potential for Sb and Pb bioaccumulation over time in leaves and needles. Implications of these findings are that increased concentrations of toxic Sb and Pb are likely to prevail in environments with high traffic intensity and that Sb can enter the ecological food chain by accumulation in leaves and needles, which is important for the biogeochemical cycling., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

Key message: Needle age class explains most of the variability in maritime pine leaf traits. Needle size and area are related to climate and foliar nutrients. Specific leaf area is highest in stands with high site index and nutrient concentrations. Abstract: Needle size, leaf traits and site parameters were studied in 31 Pinus pinaster plots (93 trees) located in Galicia (NW Spain). All needles were classified according to age class, and foliar nutrients were analyzed for each tree and age class. Needle age significantly affected the needle length (NLength), needle width (NWidth), needle thickness (NThickness), leaf area (projected A and total A), specific leaf area (SLA and SLA), needle tissue density ( N), N per unit leaf area (NN), average dry weight ( D) and moisture content ( M). The age class effect was the most important factor for assessing the variability in leaf dimensions. A regression model developed to predict the NLength in age class 1 indicated the importance of climate and nutritional conditions. An important proportion of the variation (25.2 %) in NLength for age classes 1 and 2 can be predicted only with spring precipitation. The SLA was positively affected by concentrations of foliar nutrients, particularly K (FK), and showed a rather high level of plasticity considering that maritime pine is a light demanding species. The SLA in the stands under study was higher than that of provenances from drier areas. SLA was higher in plots located at low elevations, with good site index and nutritional status of K and Mg (FMg). Boosted regression tree analysis showed that FN contributed most to explaining needle traits. FN concentration was negatively correlated with N, SLA and site index. [ABSTRACT FROM AUTHOR]

Trees can remove particulate matter from the atmosphere, improving air quality and providing ecosystem services. Particle removal capacity is known to differ between tree species, but the influence of environmental factors on the removal capacity is still unclear. In this study, we measured particle capture efficiency (Cp) of Norway spruce ( Picea abies (L.) Karst.) in wind tunnel experiments under three watering treatments (well watered, moderate drought, and severe drought) and determined needle characteristics (stomatal conductance and density, wax condition, and needle area) that affect particle uptake. Trees were exposed in the wind tunnel to 0.7 μm (geometric mean diameter) NaCl particles with a mass concentration of 1 mg·m−3, and the Cp of the tree was determined for the current-year (C) and previous-year (C+1) needles. Overall, the Cp was significantly higher for C+1 needles than for C needles for all watering treatments. There was also a trend for higher Cp of C+1 needles of less watered trees, but this was not observed for C needles. We suggest that greater erosion of the wax layer of C+1 needles compared with C needles increases hydrophilicity of the C+1 needle surface and this, in interaction with low stomatal conductance, led to the higher Cp. [ABSTRACT FROM AUTHOR]

The effects of elevated CO (700 ppm) and/or elevated O (80 ppb) on different-age needles of Pinus tabulaeformis were studied in open top chambers. Elevated CO increased needle dry weight, net photosynthetic rate, and maximum quantum yield of photosystem II in previous and current-year needles. Elevated O significantly decreased dry weight, net photosynthetic rate, and maximum quantum yield of photosystem II only in previous-year needles. Elevated O increased hydrogen and malondialdehyde content in previous-year needles, but did not significantly increase hydrogen peroxide content in current-year needles, which indicated that oxidative stress induced by elevated O was more severe in previous-year needles than in current-year needles. Our results showed that the adverse effect of elevated O in needles of P. tabulaeformis was ameliorated by elevated CO. [ABSTRACT FROM AUTHOR]

As one of the three major five-leaved pines in the northern hemisphere, Pinus koraiensis is the most important dominant tree species in the natural mixed-broadleaved Korean pine forests. However, the regeneration of P. koraiensis under the canopy of secondary forest stands is poor because of the light limitation. This study was conducted to understand how P. koraiensis seedlings adapt to different light intensities and what would be the optimum light level for their establishment and growth. Three repetition plots with four light intensities (15%, 30%, 60% and 100% of the natural incident irradiances, achieved by suspending layers of black nylon net above and surrounding the plots) were set up under natural climate conditions in a montane region in eastern Liaoning Province, Northeast China. A total of 80 P. koraiensis seedlings with similar height and root collar diameter were transplanted into four plots. After one year of acclimation to the specific light conditions, the seasonal variations of the photosynthetic variables and needle traits of the current and one-year-old needles, and the growth parameters were observed under four light intensities. The results indicated that: (1) The seedling at 60% treatment exhibited the greatest growth, which agreed with the response of the light-saturated photosynthetic rates ( A) and the dark respiration rate ( R) in the current and one-year-old needles, i.e., R at 60% treatment was significantly lower than that at 100% treatment, but A did not differ between the seedlings at 100% and 60% treatments. (2) The P. koraiensis seedlings have a certain photosynthetic plasticity to adapt the light conditions by adjusting their needle traits and regulating the physiological processes, because A, R, light saturation point and compensation point, the needle mass area, needle nitrogen and chlorophyll contents were significantly ( p<0.05) correlated with the light intensities. Especially, A at 100% and 60% treatments was significantly higher ( p<0.05) than that at 30% and 15% treatments for both current and one-year-old needles. (3) The needles of different ages played a commutative role during the growing season, i.e., the one-year-old needles played a major role for the photosynthesis in the early growing season; the current year needles did in the later growing season. This ensured the effective photosynthesis throughout the growing season. These findings suggest that P. koraiensis is the in-between heliophilous and shade-tolerant tree species at least for the seedlings up to 8 years. [ABSTRACT FROM AUTHOR]

Norway spruce (Picea abies (L.) Karst) trees are affected by ongoing climate change, including warming and exposure to phytotoxic levels of ozone. Non-volatile terpenoids and volatile terpenoids (biogenic organic volatile compounds, BVOCs) protect spruce against biotic and abiotic stresses. BVOCs also affect the atmosphere's oxidative capacity. Four-year-old Norway spruce were exposed to elevated ozone (EO) (1.4 × ambient) and warming (1.1 °C + ambient air) alone and in combination on an open-field exposure site in Central Finland. Net photosynthesis, needle terpenoid concentrations and BVOC emissions were measured four times during the experiment's second growing season: after bud opening in May, during the mid-growing season in June, and after needle maturation in August and September. Warming increased terpene concentrations in May due to advanced phenology and decreased them at the end of the growing season in matured current-year needles. Ozone enhanced these effects of warming on several compounds. Warming decreased concentrations of oxygenated sesquiterpenes in previous-year needles. Decreased emissions of oxygenated monoterpenes by warming and ozone alone in May were less prominent when ozone and warming were combined. A similar interactive treatment response in isoprene, camphene, tricyclene and α-pinene was observed in August when the temperature and ozone concentration was high. The results suggest long-term warming may reduce the terpenoid-based defence capacity of young spruce, but the defence capacity can be increased during the most sensitive growth phase (after bud break), and when high temperatures or ozone concentrations co-occur. Reduced BVOC emissions from young spruce may decrease the atmosphere's oxidative capacity in the warmer future, but the effect of EO may be marginal because less reactive minor compounds are affected., (© The Author(s) 2022. Published by Oxford University Press.)

Knowledge on variations in stomata is useful in reflecting leaf physiological characteristics of CO uptake and water transpiration, and predicting the responses of plants to future climate change. Stomatal density and number of stomatal rows (current-year, 1- and 2-year-old needles) in relation to tree age (ranging from 25 to 320 years old), elevation (ranging from 738 to 1,380 m a.s.l.), and sun exposure (sun and shade exposure) were investigated in Pinus koraiensis trees. Stomatal density and number of stomatal rows in relation to tree age and elevation showed a humped curve with the maximum values at intermediate levels of tree age (210 years old) and elevation (1,050 m a.s.l.), respectively. Needle age but not sun exposure significantly affected the stomatal density across tree ages and elevations. Our results suggest that variations in stomatal density of Pinus koraiensis needles are related to ontogenetic growth and environmental factors. [ABSTRACT FROM AUTHOR]

Leaf traits and physiology are species-specific and various with canopy position and leaf age. Leaf photosynthesis, morphology and chemistry in the upper and lower canopy positions of Pinus koraiensis Sieb. et Zucc and Quercus mongolica Fisch. ex Turoz in broadleaved Korean pine forest were determined in September 2009. Canopy position did not significantly affect light-saturated photosynthetic rate based on unit area ( P) and unit dry mass ( P), apparent quantum yield (α), light compensation point (LCP), light saturation point (LSP); total nitrogen (N), phosphorus (P), carbon (C), and chlorophyll content (Chl) per unit dry mass; leaf dry mass per unit area (LMA) and photosynthetic nitrogen-use efficiency (PNUE) for P. koraiensis current-year needles and Q. mongolica leaves. While in P. koraiensis one-year-old needles, P, P, α and LCP in the upper canopy were lower than those in the lower canopy. The needles of P. koraiensis had higher Cm and LMA than leaves of Q. mongolica, but P, Chl and PNUE showed opposite trend. There were no differences in P, LSP, N, and P between the two species. Needle age significantly influenced photosynthetic parameters, chemistry and LMA of P. koraiensis needles except LCP, LSP and C. In contrast to LMA, P, P, N, P, Chl, and PNUE of one-year-old needles were significantly lower than those of current-year needles for P. koraiensis. The negative correlations between LMA and P, N, P, Chl, and positive correlations between P and N, P, Chl were found for P. koraiensis current-year needles and Q. mongolica leaves. Our results indicate that leaf nitrogen and phosphorus contents and nutrient absorption from soil are similar for mature P. koraiensis and Q. mongolica growing in the same environment, while difference in carbon content between P. koraiensis and Q. mongolica may be attributed to inherent growth characteristics. [ABSTRACT FROM AUTHOR]

• Needle age accounted for most of the variations of NSC and its components, followed by phenology. • Needle age and phenology had significant effects on the relationships of NSC and its components. • Life history accounted for only a small proportion in NSC and its components variations. Non-structural carbohydrates (NSCs), including soluble sugar (SS) and starch (ST), are essential for the growth and survival of plants. However, few studies have investigated the effects of phenology, needle age, and life history together on NSCs. We measured NSCs of leaves for 120 Pinus koraiensis individuals of various sizes (0.3–100 cm diameter at breast height, DBH) across needle age and during three leaf development periods to evaluate the effects of phenology, needle age, and life history on NSCs. Concentration ranges were 6.60–12.07, 2.38–8.90 and 10.97–16.18 g·100 g−1 dry mass for SS, ST, and NSC, respectively. Needle age accounted for most of the variations (42.2%-84.4%) of NSCs, followed by phenology (9.2%-46.8%), while life history accounted for only a small proportion. In general, NSC reached its maximum value during the leaf unfolding period and the shift between SS and ST occurred during the leaf fall period. The slope of NSC with phenology generally increased with increasing needle age (absolute value). With increasing needle age, NSC and its components showed gradual upward trends. The slope of NSC with needle age decreased with leaf development (except during the leaf fall period). Life history had significant effects on NSCs in the leaf fall period for both current year and perennial needles, and in the leaf unfolding period only for the current year needles. Needle age significantly affected the correlations of NSC and SS (or ST) only at the leaf unfolding period. Phenology had significant effects on the correlations of NSC and SS (or ST) only for current year needle. Our results clearly showed that the variations of NSC and its components were highly dependent on needle age, followed by phenology. Unexpectedly, the effects of life history on NSCs were much less than those of needle age and phenology. Therefore, needle age and phenology dominate over life history in influencing NSCs, and the ecological significance of NSCs variations need to be reconsidered by effects of incorporating needle age and phenology. [ABSTRACT FROM AUTHOR]

We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability. [ABSTRACT FROM AUTHOR]

The dynamics of six different needle parameters of Pinus sylvestris L. and Pinus ponderosa Dougl. ex P. & C. Laws. were examined retrospectively for a 112-year-old mixed stand in Brandenburg, Germany, using the needle trace method. Similarities were found in needle production, needle loss and needle density. However, needle age, needle retention and total number of needles revealed significant differences between the tree species, with higher values for P. ponderosa. Pinus ponderosa yielded approximately twice as much mean whole-crown needle dry mass as P. sylvestris. Furthermore, different branching systems could be detected between the species, with both pines following "Corner's rule". The results suggest that under identical growing conditions, P. ponderosa exhibits more efficient water use and can therefore maintain a bigger crown (as the basis for increased growth) than P. sylvestris. [ABSTRACT FROM AUTHOR]

Variation in annual radial and height increments (RI and HI, respectively) as well as the number of needles belonging to different needle sets of successive annual shoots, determined by the needle trace method (NTM), was studied retrospectively in Scots pine stands, one in southern Finland and two in Estonia. The connection between different needle sets and tree growth was studied by correlation and covariance analyses. The numbers of needles of the three youngest needle sets were positively correlated with growth, whereas the number of needles older than 3 years had no significant correlation. The covariance analysis emphasized the negative relationship of older needle sets with tree growth. It is generally concluded that the two or three youngest needle sets are important and all older needles minimally contribute to growth, possibly because of their small quantity. Older needles may remain on the tree if assimilation is impeded for some reason, e.g. due to premature loss in the two youngest needle sets. The trees having attached old needles grew less than those that had already totally lost these needle sets. [ABSTRACT FROM AUTHOR]

Methylbutenol is a 5-carbon alcohol that is produced and emitted by several species of pine in western North America, and may have important impacts on the tropospheric chemistry of this region. In the present study the response of methylbutenol basal emission rate (measured at a constant light intensity of 1500 µmol m−2 s−1 and temperature of 30 °C) to the light and temperature conditions of the growth environment was examined, using field-grown plants shielded with shade cloth of various densities. Methylbutenol basal emission rates increased linearly with the temperature of the growth environment but did not respond to the shading of foliage during growth and development. Both photosynthesis and basal methylbutenol emission rate declined in older needles; however, these declines appear to result from parallel but independent processes and not from basal MBO emission rate directly tracking photosynthetic rates. Older needles did not occupy cooler microenvironments within the canopy; and thus differing thermal microenvironment could not explain the reduced MBO emission in older needles. [ABSTRACT FROM AUTHOR]

We investigated the nutritional dynamics of Phaeocryptopus gaeumannii and the impact of nitrogen (N) fertilization of Douglas-fir (Pseudotsuga menziesii) on the production of P. gaeumannii fungal fruiting bodies. Emergence of P. gaeumannii fungal fruiting bodies (pseudothecia) in Douglas-fir stomata has been directly linked to premature needle loss, a symptom of Swiss needle cast disease. Douglas-fir trees (10-yr-old) naturally infected with P. gaeumannii were treated with soil applications of N fertilizer isotopically enriched with 15 N to increase foliar N and track the movement of N from the host to the fungus. Foliar N, free amino acids, percent of stomata occluded by pseudothecia, N isotope and carbon (C) isotope levels were assessed on treated and control trees. Higher foliar N resulted in increased %N and %C in P. gaeumannii, as well as increased fungal fruiting and thus disease severity. Comparisons of δ15N levels between P. gaeumannii pseudothecia and associated needles indicated an increase in δ15N of needles and a simultaneous decline in δ15 N of pseudothecia coupled with increased levels of foliar and fungal percentage N. These findings confirm that P. gaeumannii responds to host nutrient status and that increased N availability inside Douglas-fir needles is linked to increased severity of Swiss needle cast disease. [ABSTRACT FROM AUTHOR]

Abstract Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2 but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar Carea (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (δ13 C) caused by inputs of 13 C-depleted CO2 to estimate labile and structural C in needles of different ages in a four-year, closed-chamber mesocosm experiment in which Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO2 (ambient + 179 ppm). Declines in δ 13 C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The δ 13 C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second- and third-year needles, respectively, with higher proportions of new C in elevated than ambient CO2 chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second-year needles). Relative to ambient CO2 , elevated CO2 increased labile C in both first- and second-year needles. Relative to ambient temperature, elevated temperature diminished labile C in second-year needles but not in first-year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant-soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations... [ABSTRACT FROM AUTHOR]

ABSTRACT The effects of CO2 enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1-year-old needles of the same branch of field-grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open-top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO2 partial pressures. Photosynthetic rates of the 1-year-old needles made at the growth CO2 partial pressure averaged 10·5 ± 0·5 μmol m-2 s-1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m-2 s-1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1-year-old needles was reduced by 25% from 23·0 ± 1·8 μmol m-2 s-1 in the 36 Pa CO2 grown trees to 17·3 ± 0·7 μmol m-2 s-1 in the 65 Pa grown trees. Growth in elevated CO2 also resulted in a 25% reduction in Vcmax (maximum carboxylation rate), a 23% reduction in Jmax (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non-structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1-year-old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1-year-old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m-2. The current-year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO2. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field-grown trees and may be regulated by source-sink balance, sugar feedback mechanisms and nitrogen allocation. [ABSTRACT FROM AUTHOR]

Chrysomyxa rhododendri(DC.) De Bary is a needle rust with a host shift between Rhododendronsp. and Norway spruce (Picea abies(L.) Karst.), penetrating only the new developing flushes of the conifer. Because little is known about its effects on trees, we investigated several parameters related to photosynthesis in artificially infected 3-year-old Norway spruce seedlings. The potential efficiency of photosystem II (PSII; derived from chlorophyll fluorescence measurements) was reduced in infected current-year needles as soon as disease symptoms were visible, about three weeks after inoculation. Two weeks later, photosynthetic O2 evolution (Pmax) of infected needles was less than 20% of control needles, whereas respiratory O2 uptake (RD) was about three times higher than that of control needles. Nonstructural carbohydrate concentrations were about 60% of control values in all parts of the shoots of infected trees. Photosynthetic inhibition was associated with marked decreases in chlorophyll concentration and chlorophyll a/b ratio but only a small reduction in carotenoid concentration. In infected trees, Pmax of noninfected 1-year-old and 2-year-old needles was 50 and 80% higher than in the corresponding age class of needles of control trees. Estimation of potential daily net dry mass production, based on Pmax, RD, specific leaf area, carbon content and needle biomass, indicated that seedlings infected once were able to produce 60%, and those infected twice only 25%, of the dry mass of controls. We conclude that afforestation and regeneration of Norway spruce is seriously impaired in regions where seedlings are frequently attacked by Chrysomyxa. [ABSTRACT FROM PUBLISHER]

Epicuticular wax composition and its variation with needle age was analysed chemically. Needles were taken from conifers at the highest altitude of their local distribution. Quantitative and qualitative differences in the composition of the three conifer waxes were found. Increasing needle age influenced the wax composition in Pinus cembra and Picea abies. [ABSTRACT FROM AUTHOR]

The effects of CO2 enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressures. At this age trees were 3·5–4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO2 concentration [(pCO2)a] were lower in 1-year-old needles of trees grown at elevated CO2 concentrations than in those of trees grown at ambient (pCO2)a. At elevated CO2 concentrations Vcmax (maximum carboxylation rate) was reduced by 13% and Jmax (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO2)a of 4·68 ± 0·41 μmol m–2 s–1 and 6·15 ± 0·46 μmol m–2 s–1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO2)a were 6·2 ± 0·72 μmol m–2 s–1 at 36 Pa and 10·15 ± 0·64 μmol m–2 s–1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO2 treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO2)a in fully fexpanded needles of the current year... [ABSTRACT FROM AUTHOR]

Photosynthetic characteristics of 1- and 2-year-old needles were determined in excised shoots of maritime pine (Pinus pinaster Ait.) with an open gas exchange system. We used the nonlinear least mean squares method to derive values for quantum yield of electron transport (α), maximum carboxylation velocity (Vcmax), and maximum electron transport rate (Jmax), from photosynthetic response curves to light and CO2. Crown height had no significant effect on any of the parameters; however, Vcmax and Jmax, as well as α were 43, 26 and 35% higher, respectively, in 1-year-old needles than in 2-year-old needles. The main effect of irradiance on needles was a small decline in leaf concentrations of nitrogen and phosphorus from the top to the bottom of the canopy. Only Jmax demonstrated a linear relationship with both nitrogen content (R2 = 0.42) and irradiance at the shoot level. Because needle age accounted for most of the variability in photosynthesis, we incorporated needle age into the photosynthesis model of Farquhar et al. (1980). The modified model underestimated the daily assimilation rate of 1-year-old needles in the field, especially when assimilation rates were high. [ABSTRACT FROM PUBLISHER]

Larches ( Larix spp.), deciduous conifers, occur in the northern hemisphere in cold-temperate and boreal climates – an environment normally thought to favor evergreen tree species. We compare foliar carbon isotope discrimination (Δ), instantaneous water use efficiency, total foliar nitrogen concentration, and specific leaf area (for a subset of sites) between Larix spp. and co-occurring evergreen conifers at 20 sites throughout the natural range of larches. Except for Larix occidentalis in the xeric Intermountain West, USA, Δ is significantly ( P < 0.05) greater for larches than co-occurring evergreen conifers at 77% of the sites, suggesting that larches use water less efficiently. At elevations greater than 3000 m, the Δ of Larix spp. and co-occurring conifers converge, suggesting that water is not the limiting resource. Foliar nitrogen concentration and specific leaf area are two ecophysiological characteristics that are positively correlated with high photosynthetic capacity. Foliar nitrogen concentration is significantly greater for larches than evergreen conifers at 88% of the sites and specific leaf area is approximately three times greater for larches than co-occurring conifers. Future studies should examine the potential effect that global warming may have on the distribution of larch forests because the water use efficiency of larches is commonly less than co-occurring evergreen conifers and the boreal and high-latitude environments are likely to experience the greatest climate warming. [ABSTRACT FROM AUTHOR]

This study evaluated the contribution of different ages of foliage to the nutrient and carbon balance of black spruce ( Picea mariana (Mill.) B.S.P.) from a nutrient-poor peatland in Alberta. Seasonal patterns of foliar nitrogen and phosphorus concentration and content were examined in six needle cohorts up to 10 years old. Trees were treated to simulate excess nutrient deficiency (removal of all one-year-old foliage), nutrient excess (fertilized with 250, 50, 100 kg ha NPK split application in June and July), or left as controls. Gas exchange (net assimilation-Na, stomatal conductance-g, mesophyll conductance-g, water-use efficiency-WUE, dark respiration-RS) was measured on six different needle cohorts in several control trees in 1989 and 1990. Nitrogen and phosphorus concentration decreased with needle age. Foliar nutrient concentration fell from April to June and then was stable until September except for the fertilized trees where it increased. There was no evidence of greater than normal retranslocation of nutrients from older needles for defoliated trees or greater than normal nutrient loading in older needles of fertilized trees. NA, g, g, WUE, and RS were similar for all needles up to six or eight years old, these older needles having NA of 65% of current needles and similar RS. The results do not support to conclusion that older needles of black spruce are retained as an adaptation to nutrient stress. It does not appear that older needles serve as a nutrient storage site in conditions of excess nutrient availability or a greater than normal nutrient source during times of excess nutrient deficiency. It appears that the maintenance of long-livedfoliage in black spruce does not provide for greater flexibility in tree nutrient allocation. Their contribution to the carbon balance of the tree seems to be sufficient to explain their retention. [ABSTRACT FROM AUTHOR]

Rates of net photosynthesis and dark respiration were measured for detached needles of Pinus pumila trees growing on the Kiso mountain range in central Japan in 1987. Dependency of photosynthesis on light and temperature was examined in relation to needle age and season. The light saturation point of net photosynthesis was lower in 3- and 4-yr-old needles than that in current (flushed in 1987), 1- and 2-yr-old needles. P, net photosynthetic rates at 1000 μmol m s and 15°C, of needles from 1- to 4-yr-old generally decreased with needle age. P of 1- to 4-yr-old needles became higher in August than in other months, and P of current needles did so in September. Current needles showed high respiration rates (at 15°C) only in August. Optimum air temperatures for net photosynthesis at 1000 μmol m s were between 10 and 15°C for current and 1-yr-old needles. The temperature coefficient of dark respiration rates was 2.3-3.3 for current needles from August to October, and 2.2 for 1-yr-old needles in mid-July. [ABSTRACT FROM AUTHOR]

Remote sensing is one of the modern methods that have significantly developed over the last two decades and, nowadays, it provides a new means for forest monitoring. High spatial and temporal resolutions are demanded for the accurate and timely monitoring of forests. In this study, multi-spectral Unmanned Aerial Vehicle (UAV) images were used to estimate canopy parameters (definition of crown extent, top, and height, as well as photosynthetic pigment contents). The UAV images in Green, Red, Red-Edge, and Near infrared (NIR) bands were acquired by Parrot Sequoia camera over selected sites in two small catchments (Czech Republic) covered dominantly by Norway spruce monocultures. Individual tree extents, together with tree tops and heights, were derived from the Canopy Height Model (CHM). In addition, the following were tested: (i) to what extent can the linear relationship be established between selected vegetation indexes (Normalized Difference Vegetation Index (NDVI) and NDVIred edge) derived for individual trees and the corresponding ground truth (e.g., biochemically assessed needle photosynthetic pigment contents) and (ii) whether needle age selection as a ground truth and crown light conditions affect the validity of linear models. The results of the conducted statistical analysis show that the two vegetation indexes (NDVI and NDVIred edge) tested here have the potential to assess photosynthetic pigments in Norway spruce forests at a semi-quantitative level; however, the needle-age selection as a ground truth was revealed to be a very important factor. The only usable results were obtained for linear models when using the second year needle pigment contents as a ground truth. On the other hand, the illumination conditions of the crown proved to have very little effect on the model's validity. No study was found to directly compare these results conducted on coniferous forest stands. This shows that there is a further need for studies dealing with a quantitative estimation of the biochemical variables of nature coniferous forests when employing spectral data that were acquired by the UAV platform at a very high spatial resolution. [ABSTRACT FROM AUTHOR]

• Pruning caused an up-regulation in the net photosynthetic rates of remaining foliage. • The photosynthetic increase upon pruning occurred mainly in two youngest needles. • Pruning enhanced the investment of needle nitrogen to CO 2 fixing enzyme. • Pruning favored stomatal conductance and carboxylation rate of current-year-needle. • Understory removal had no effect on tree growth and needle photosynthesis. How tree growth and the underlying photosynthesis of leaves, especially those multi-aged leaves, change after the application of both pruning and understory removal remains unclear. In this study, the tree growth and photosynthetic responses of various-aged needles to pruning, understory removal and their interactions were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. The biochemical and stomatal limitations to photosynthesis was separated by the combined measurements of stable carbon (δ 13C) and oxygen (δ 18O) isotopes in needles. Our results showed that the tree growth rates did not respond to pruning, understory removal, and their interactions. Pruning significantly stimulated the net photosynthetic rates (P A) and stomatal conductance (g s) of remaining foliage (especially the current- and one-year-needles). Although pruning had no effect on needle total nitrogen (N) concentration, the concentrations of water-soluble N (N S), the ratio of water-soluble N to sodium dodecyl sulfate (SDS)-insoluble N (N S /N D), and the photosynthetic N use efficiency (PNUE) were higher in needles of pruned trees compared with the unpruned trees. A significant and positive correlation between PNUE and N S /N D was also detected. The constant δ 13C and declined δ 18O in the current-year-needles from pruned trees suggested that both the photosynthetic capacity and the g s were responsible for the enhancement in P A of the youngest needles. Conversely, in the previous year needles, δ 13C and δ 18O were not significantly different between the control and pruned trees. Consistent with the response of tree growth rate, the foliar photosynthesis also did not exhibit changes following understory removal in both pruned and unpruned stands. We highlighted that pruning caused an up-regulation in P A of remaining foliage, thereby mitigating the negative effects of canopy loss on carbon assimilation. [ABSTRACT FROM AUTHOR]