Evolutionary ecology of masting: mechanisms, models, and climate change.

Many perennial plants show mast seeding, characterized by synchronous and highly variable reproduction across years. We propose a general model of masting, integrating proximate factors (environmental variation, weather cues, and resource budgets) with ultimate drivers (predator satiation and pollination efficiency). This general model shows how the relationships between masting and weather shape the diverse responses of species to climate warming, ranging from no change to lower interannual variation or reproductive failure. The role of environmental prediction as a masting driver is being reassessed; future studies need to estimate prediction accuracy and the benefits acquired. Since reproduction is central to plant adaptation to climate change, understanding how masting adapts to shifting environmental conditions is now a central question.

Masting is uncommon in trees that depend on mutualist dispersers in the context of global climate and fertility gradients.

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands.

Carbon use strategies in shoot and acorn growth of two evergreen broadleaf trees unraveled by seasonal carbohydrate measurements and carbon isotope analysis.

Woody species have evolved carbon (C) storage processes that meet needs for reserves associated with asynchronies between C supply and demand. However, our understanding of storage dynamics is still elusive in mature trees, especially when reproduction is involved. Integrated analyses of isotope ratios, concentrations, and biomass may enhance understanding of stored C fractions' dynamics and roles. Thus, we monitored starch and soluble sugars (SSs), C isotope ratios, and biomass, in leaves, twigs and reproductive organs of two mature evergreen broadleaf trees, Quercus glauca and Lithocarpus edulis, for two years. During the growing season, no starch was observed in twigs, while constant starch levels were observed in leaves. Increase in SSs for winter hardening was earlier in L. edulis than in Q. glauca, in line with L. edulis acorns' earlier ripening. Decrease in SSs and increase in starch occurred simultaneously in the next spring. In addition, sucrose accounted for less than 10% of total SSs in leaves of both species, whereas mannose accounted for up to 75% in Q. glauca and myo-inositol up to 23% in L. edulis, indicating species specific sugar composition. These results indicate that seasonal variation of SSs fraction was more reflective to climatic change and NSC storage was less influenced by reproduction. No starch was detected in acorn organs of either Q. glauca or L. edulis except in ripening seeds. The biomass of ripe acorns was 1.7- and 6.4-fold greater than that of current-year twigs in Q. glauca and L. edulis, respectively. Bulk twigs and reproductive organs were ca. 1.0‰ 13C enriched relative to bulk leaves, which was lower than in deciduous trees. These results indicate that new photo-assimilate is the predominant C source for reproductive growth. These findings provide new insights into the dynamics of C storage in relation to reproduction in evergreen broadleaf trees.

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery.

The relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential.

Globally, tree fecundity exceeds productivity gradients.

Lack of tree fecundity data across climatic gradients precludes the analysis of how seed supply contributes to global variation in forest regeneration and biotic interactions responsible for biodiversity. A global synthesis of raw seedproduction data shows a 250-fold increase in seed abundance from cold-dry to warm-wet climates, driven primarily by a 100-fold increase in seed production for a given tree size. The modest (threefold) increase in forest productivity across the same climate gradient cannot explain the magnitudes of these trends. The increase in seeds per tree can arise from adaptive evolution driven by intense species interactions or from the direct effects of a warm, moist climate on tree fecundity. Either way, the massive differences in seed supply ramify through food webs potentially explaining a disproportionate role for species interactions in the wet tropics.

Safe femoral condyle range for the reverse Rigidfix femoral fixation device in anterior cruciate ligament reconstruction.

BACKGROUND: To determine the characteristics of cross-pin protrusion in patients treated with the reverse Rigidfix femoral fixation device for femoral tunnel preparation through the anteromedial portal in Arthroscopic anterior cruciate ligament reconstruction (ACLR), analyse the reasons for this outcome, and identify safety hazards of this surgical technique for improvement. METHODS: A retrospective analysis of patients who underwent ACLR using this technology at our hospital in 2018 was conducted. Patients with and without cross-pin protrusion were included in the protrusion positive and negative groups, respectively. The sex, age and imaging characteristics of the patients with cross-pin protrusion were identified, and the reasons for cross-pin protrusion were analysed. RESULTS: There were 64 and 212 patients in the protrusion positive and negative groups, respectively. The proportion of cross-pin protrusion cases was 23.19% (64/276). There was a significant difference in the ratio of males to females (P < 0.001, χ2 = 185.184), the mediolateral femoral condyle diameter (protrusion positive group, 70.59 ± 2.51 mm; protrusion negative group, 82.65 ± 4.16 mm; P < 0.001, t = 28.424), and the anteroposterior diameter of the lateral femoral condyle (protrusion positive group, 58.34 ± 2.89 mm; protrusion negative group, 66.38 ± 3.53 mm; P < 0.001, t = 16.615). The cross-pins did not penetrate the lateral femoral condyle cortex in patients with a mediolateral femoral condyle diameter ≥ 76 mm, but the cross-pins definitely penetrated the cortex when the diameter was ≤ 70 mm. The cross-pins did not penetrate when the anteroposterior lateral femoral condyle diameter was ≥ 66 mm, but the cross-pins definitely penetrated it when the diameter was ≤ 59 mm. CONCLUSION: The patients with cross-pin protrusion after reverse Rigidfix femoral fixation treatment to prepare the femoral tunnel through the anteromedial portal in ACLR were mainly females with small femoral condyles. For patients with a mediolateral femoral condyle diameter ≥ 76 mm and an anteroposterior lateral femoral condyle diameter ≥ 66 mm, there is no risk of cross-pin protrusion, so this technique can be used with confidence. LEVELS OF EVIDENCE: III.

lncRNA GAS8-AS1 downregulates lncRNA UCA1 to inhibit osteosarcoma cell migration and invasion.

BACKGROUND: Osteosarcoma (OS) is the most common type of primary bone tumor that mainly affects adolescents and young adults. The present study explored the role of lncRNA GAS8-AS1 in OS. METHODS: A total of 48 OS patients were selected from the 82 OS patients admitted by Luoyang Orthopedic Hospital of Henan Province between May 2010 and May 2013. Transient cell transfections, Transwell cell migration and invasion assay, RT-qPCR, and patient follow-up were carried out during the research. RESULTS: The results showed that GAS8-AS1 was downregulated, while UCA1 was upregulate in cancer tissues in comparison to adjacent non-cancer tissues of OS patients. GAS8-AS1 was not affected by clinical stage. Follow-up study showed that downregulated GAS8-AS1 in cancer tissues was closely correlated with poor survival. GAS8-AS1 and UCA1 were inversely correlated in cancer tissues. Overexpression of UCA1 failed to affect the expression of GAS8-AS1, while overexpression of GAS8-AS1 led to downregulated expression of UCA1 in OS cells, while the molecular mediators between these two lncRNAs are unknown. Overexpression of GAS8-AS1 did not affect OS cell proliferation but significantly inhibited cancer cell migration and invasion. Overexpression of UCA1 promoted the migration and invasion of OS cells and attenuated the effects of overexpressing GAS8-AS1. CONCLUSIONS: Therefore, GAS8-AS1 may inhibit OS cell migration and invasion by downregulating oncogenic UCA1.

The protective effects of bexarotene against advanced glycation end-product (AGE)-induced degradation of articular extracellular matrix (ECM).

Osteoarthritis (OA) is a common debilitating disease primarily characterised by excessive loss of the articular ECM, which is composed of up to 95% type II collagen. Among the factors that contribute to the pathogenesis of OA, the natural process of aging is regarded as the most significant risk factor. AGEs, which are extremely resilient to degradation, are produced in the body naturally as a result of the Maillard process of nonenzymatic glycation and are also introduced through diet and tobacco smoke. AGEs have a high affinity for collagen and therefore accumulate in joint tissues, where they induce increased expression of proinflammatory cytokines, chemokines, and degradative enzymes. Additionally, AGEs induce oxidative stress, which further exacerbates the degradative process. Type II collagen is targeted for degradation by matrix metalloproteinases (MMPs), particularly MMP-3 and MMP-13, and AGEs have been shown to trigger increased expression of these MMPs. The role of retinoid and rexinoid receptors as specific treatment targets has been receiving increasing attention. Bexarotene is a retinoid X receptor (RXR) agonist used for the treatment of T-cell lymphoma and other cancers which has displayed a favourable safety profile. Here, we examined the roles of RXR agonism using bexarotene on AGE-induced markers of OA, including oxidative stress, inflammatory response, and MMP-mediated degradation of type II collagen. Furthermore, we demonstrate that bexarotene inhibited phosphorylation of IκBα, thereby suppressing activation of the proinflammatory NF-κB cellular signalling pathway. These findings present a basis for selective targeting of RXR by bexarotene as a potential treatment of OA induced by AGEs.

Field transcriptome revealed a novel relationship between nitrate transport and flowering in Japanese beech.

Recent advances in molecular and genetic studies about flowering time control have been increasingly available to elucidate the physiological mechanism underlying masting, the intermittent and synchronized production of a large amount of flowers and seeds in plant populations. To identify unexplored developmental and physiological processes associated with masting, genome-wide transcriptome analysis is a promising tool, but such analyses have yet to be performed. We established a field transcriptome using a typical masting species, Japanese beech (Fagus crenata Blume), over two years, and analyzed the data using a nonlinear time-series analysis called convergent cross mapping. Our field transcriptome was found to undergo numerous changes depending on the status of floral induction and season. An integrated approach of high-throughput transcriptomics and causal inference was successful at detecting novel causal regulatory relationships between nitrate transport and florigen synthesis/transport in a forest tree species. The synergistic activation of nitrate transport and floral transition could be adaptive to simultaneously satisfy floral transition at the appropriate timing and the nitrogen demand needed for flower formation.

Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale.

The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

Springtime photoinhibition constrains regeneration of forest floor seedlings of Abies sachalinensis after a removal of canopy trees during winter.

A clear-cutting of canopy trees during winter often causes severe foliar damage during the following spring in forest floor seedlings of Abies sachalinensis, a typical shade-tolerant evergreen coniferous species. The maximum photochemical efficiency of photosystem II after an overnight dark adaptation showed a temporary decrease immediately before budbreak in 1-year-old shoots of A. sachalinensis seedlings grown under full sunlight in a nursery, suggesting "springtime photoinhibition" related to the phenology of evergreen coniferous species. In the field, a greater rate of canopy tree cutting during winter was associated with more severe photoinhibition in the following spring, immediately before budbreak, which subsequently resulted in a reduction in carbon gain in 1-year-old shoots, and consequently suppressed the growth of current-year shoots. Although photoinhibition under low temperature is a well-known factor to determine the survival rate of tree seedlings during winter in cool regions, the present study additionally proposes that the temporary increase in the susceptibility to photoinhibition in springtime i.e. "springtime photoinhibition" would be a constraint for the regeneration of coniferous seedlings especially when the canopy trees are removed during winter.

Influence of reproduction on nitrogen uptake and allocation to new organs in Fagus crenata.

The contributions of the internal nitrogen (N) cycle and N uptake from soil to growth in mature trees remain poorly understood, especially during reproduction. In order to elucidate how reproduction affects N uptake, allocation and remobilization, we applied pulse 15N labelling to three fruiting (F) and three non-fruiting (NF) Fagus crenata Blume trees after the leaves were fully unfurled. Three-year-old branches were sampled from upper crowns at about 2 week intervals until leaf fall. 15N content per organ dry mass (15Nexcess) and N concentration in all new shoot organs were determined. Fruiting led to greater 15Nexcess uptake from the soil during the first month following application. Cupules absorbed the highest fraction of 15Nexcess initially and nuts contained about half the 15Nexcess at the end of the growing season. Biomass of reproductive organs represented up to 70% of new shoot growth in F trees. This fruit burden led to 34% and 38% reduction in biomass and 15Nexcess, respectively, in mature leaves compared with NF trees. Moreover, the increment of 15Nexcess in new shoots of F relative to NF trees was lower than the increment of biomass between the two. These results indicate that N is a limiting resource during masting in F. crenata. 15Nexcess incorporated into nuts started to increase dramatically once 15Nexcess in leaves, branches and cupules hit seasonal maxima. Similar seasonal biomass growth patterns were also found in these organs, indicating that sink strength drives uptake and allocation of 15Nexcess between new shoot compartments. These results, together with translocation of 15Nexcess from cupules and senescing leaves to nuts (contributing to fruit ripening), suggest that a finely tuned growth phenology alleviated N limitation. Thus, fruiting did not influence the N concentration in leaves or branches. These reproduction-related variations in N uptake and allocation among new shoot compartments have implications for N dynamics in the plant-soil system.

Growth rate reduction causes a decline in the annual incremental trunk growth in masting Fagus crenata trees.

Tree trunk annual increments are markedly reduced in mast years. There are two hypotheses that could explain the mechanism for this phenomenon: (1) a reduction in the duration of growth due to switching the resource allocation from somatic growth to seed production; (2) reduction of growth rate due to resources being shared between somatic growth and reproduction simultaneously. In this study, we aimed to test these hypotheses in Fagus crenata  Blume from the point of view of resource allocation. The radial growth patterns in F. crenata during a year without reproduction (2014) and a masting year (2015) were monitored using a digital dendrometer. At the same time, shoot growth patterns were monitored by sampling branches from the top of the canopy. Data obtained using the digital dendrometer were fitted to a sigmoidal function, and the parameters of the function were evaluated with a hierarchal Bayesian approach; estimated parameters were used to represent the properties of trunk growth phenology. Trunk growth started synchronously just after leaf unfurling in both mass-fruiting (F15) and limited-fruiting (NF15) trees in 2014 and 2015. Reproduction reduced the growth rate in 2015. This was due to the resources being allocated for the development of cupules and for formation of relatively thick branches, both of which occurred simultaneously with trunk growth. There was no clear difference in the duration of radial growth between F15 and NF15 trees in the 2 years, although seed maturation started after trunk growth ceased. As a result, the annual trunk radius increment was reduced in the F15 trees in 2015. These results suggested that reduction of radial growth rate (Hypothesis 2) caused the reduction in annual trunk increment of reproducing trees of this species.

Short-stem prostheses in primary total hip arthroplasty: A meta-analysis of randomized controlled trials.

BACKGROUND: Short-stem (SS) prostheses require less resection of the femoral neck, produce a more physiological load pattern in the proximal femur, reduce stress shielding, and aid bone conservation and are, therefore, beneficial for young patients. Conventional cementless implants in total hip arthroplasty (THA) have shown excellent clinical results; however, it is unclear whether SS prostheses can obtain the same clinical and radiological outcomes. We conducted a meta-analysis of randomized controlled trials (RCTs) to evaluate whether SS prostheses are superior to conventional implants after primary THA. METHODS: We reviewed the literature published up to June 2016 from PubMed, Web of Science, and the Cochrane Library to find relevant RCTs comparing SSs and conventional stems in primary THA. Quality assessment was performed by 2 independent reviewers. The RevMan 5.3 software program of the Cochrane Collaboration was used to analyze the data. Random- or fixed-effect models were used to calculate standardized mean differences (SMDs) and 95% confidence intervals (CIs) for each comparison. RESULTS: Six RCTs involving 552 patients with 572 hips were identified. Strong evidence indicated that SS prostheses were more effective for reducing thigh pain than conventional implants (I = 46%, P = 0.002; risk ratio [RR], 95% CI 0.15, 0.04-0.49). However, there were no significant differences between the 2 groups in Harris Hip Scores (I = 0%, P = 0.84; SMD, 95% CI 0.02, -0.15-0.18), Western Ontario and McMaster Universities Osteoarthritis Index Scores (I = 0%, P = 0.35; SMD, 95% CI 0.09, -0.10-0.27), femoral offset of stem (I = 0%, P = 0.57; SMD, 95% CI 0.06, -0.16-0.29), and leg-length discrepancy (I = 79%, P = 0.88; SMD, 95% CI 0.04, -0.44-0.51). CONCLUSION: SS prostheses achieve the same clinical and radiological outcomes as conventional implants, and were superior in terms of reducing thigh pain. But whether the postoperative thigh pain applied in 2nd-generation cementless prosthesis still needs further large-scale multicenter studies with longer follow-up to confirm.

Reproduction-related variation in carbon allocation to woody tissues in Fagus crenata using a natural 13C approach.

The contribution of new photo-assimilates and stored carbon (C) to plant growth remains poorly understood, especially during reproduction. In order to elucidate how mast seeding affects C allocation to both reproductive and vegetative tissues, we measured biomass increase in each tissue, branch starch concentration and stable C isotope composition (δ13C) in bulk leaves, current-year shoots, 3-year branches and tree rings in fruiting and non-fruiting trees for 2 years, as well as in fruits. We isolated the effect of reproduction on C allocation to vegetative growth by comparing 13C enrichment in woody tissues in fruiting and non-fruiting specimens. Compared with 2‰ 13C enrichment in shoots relative to leaves from non-fruiting trees, fruiting reduced the enrichment to 1‰ and this reduction disappeared in the following year with no fruiting, indicating that new photo-assimilates are preferentially used for woody tissues even with fruiting burden. In contrast, fruits had up to 2.5‰ 13C enrichment at mid-summer, which dropped thereafter, indicating that fruit production relies on C storage early in the growing season then shifts to current photo-assimilates. At this tipping point, growth of shoots and cupules had almost finished and nuts had a second rapid growth period thereafter. Together with shorter shoots but higher biomass increment per length in fruiting trees than non-fruiting trees, these results indicate that the C limitation due to fruit burden is minimized by fine-tuning of allocation of old C stores and new photo-assimilates, along with the growth pattern in various tissues. Furthermore, fruiting had no significant effect on starch concentration in 3-year-old branches, which became fully depleted during leaf and flower flushing but were quickly replenished. These results indicate that reproduction affects C allocation to branches but not its source or storage. These reproduction-related variations in the fate of C have implications for evaluating forest ecosystem C cycles during climate change.

Parameterisation and validation of a resource budget model for masting using spatiotemporal flowering data of individual trees.

Synchronised and fluctuating reproduction by plant populations, called masting, is widespread in diverse taxonomic groups. Here, we propose a new method to explore the proximate mechanism of masting by combining spatiotemporal flowering data, biochemical analysis of resource allocation and mathematical modelling. Flowering data of 170 trees over 13 years showed the emergence of clustering with trees in a given cluster mutually synchronised in reproduction, which was successfully explained by resource budget models. Analysis of resources invested in the development of reproductive organs showed that parametric values used in the model are significantly different between nitrogen and carbon. Using a fully parameterised model, we showed that the observed flowering pattern is explained only when the interplay between nitrogen dynamics and climatic cues was considered. This result indicates that our approach successfully identified resource type-specific roles on masting and that the method is suitable for a wide range of plant species.

Nitrogen storage dynamics are affected by masting events in Fagus crenata.

It is generally assumed that the production of a large crop of seeds depletes stores of resources and that these take more than 1 year to replenish; this is accepted, theoretically, as the proximate mechanism of mast seeding (resource budget model). However, direct evidence of resource depletion in masting trees is very rare. Here, we trace seasonal and inter-annual variations in nitrogen (N) concentration and estimate the N storage pool of individuals after full masting of Fagus crenata in two stands. In 2005, a full masting year, the amount of N in fruit litter represented half of the N present in mature leaves in an old stand (age 190-260 years), and was about equivalent to the amount of N in mature leaves in a younger stand (age 83-84 years). Due to this additional burden, both tissue N concentration and individual N storage decreased in 2006; this was followed by significant replenishment in 2007, although a substantial N store remained even after full masting. These results indicate that internal storage may be important and that N may be the limiting factor for fruiting. In the 4 years following full masting, the old stand experienced two moderate masting events separated by 2 years, whilst trees in the younger stand did not fruit. This different fruiting behavior may be related to different "costs of reproduction" in the full masting year 2005, thus providing more evidence that N may limit fruiting. Compared to the non-fruiting stand, individuals in the fruiting stand exhibited an additional increase in N concentrations in roots early in the 2007 growing season, suggesting additional N uptake from the soil to supply resource demand. The enhanced uptake may alleviate the N storage depletion observed in the full masting year. This study suggests that masting affects N cycle dynamics in mature Fagus crenata and N may be one factor limiting fruiting.

Fruit production in three masting tree species does not rely on stored carbon reserves.

Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous (13)C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO2 enrichment system, we exposed trees to (13)C-depleted CO2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ(13)C values compared to control trees. δ(13)C analysis of new biomass during the first season after termination of the CO2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant (13)C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ(13)C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.

Leaf traits, shoot growth and seed production in mature Fagus sylvatica trees after 8 years of CO2 enrichment.

BACKGROUND AND AIMS: Masting, i.e. synchronous but highly variable interannual seed production, is a strong sink for carbon and nutrients. It may, therefore, compete with vegetative growth. It is currently unknown whether increased atmospheric CO(2) concentrations will affect the carbon balance (or that of other nutrients) between reproduction and vegetative growth of forest species. In this study, reproduction and vegetative growth of shoots of mature beech (Fagus sylvatica) trees grown at ambient and elevated atmospheric CO(2) concentrations were quantified. It was hypothesized that within a shoot, fruiting has a negative effect on vegetative growth, and that this effect is ameliorated at increased CO(2) concentrations. METHODS: Reproduction and its competition with leaf and shoot production were examined during two masting events (in 2007 and 2009) in F. sylvatica trees that had been exposed to either ambient or elevated CO(2) concentrations (530 µmol mol(-1)) for eight consecutive years, between 2000 and 2008. KEY RESULTS: The number of leaves per shoot and the length of terminal shoots was smaller or shorter in the two masting years compared with the one non-masting year (2008) investigated, but they were unaffected by elevated CO(2) concentrations. The dry mass of terminal shoots was approx. 2-fold lower in the masting year (2007) than in the non-masting year in trees growing at ambient CO(2) concentrations, but this decline was not observed in trees exposed to elevated CO(2) concentrations. In both the CO(2) treatments, fruiting significantly decreased nitrogen concentration by 25 % in leaves and xylem tissue of 1- to 3-year-old branches in 2009. CONCLUSIONS: Our findings indicate that there is competition for resources between reproduction and shoot growth. Elevated CO(2) concentrations reduced this competition, indicating effects on the balance of resource allocation between reproduction and vegetative growth in shoots with rising atmospheric CO(2) concentrations.

Height-related decreases in mesophyll conductance, leaf photosynthesis and compensating adjustments associated with leaf nitrogen concentrations in Pinus densiflora.

Hydraulic limitations associated with increasing tree height result in reduced foliar stomatal conductance (g(s)) and light-saturated photosynthesis (A(max)). However, it is unclear whether the decline in A(max) is attributable to height-related modifications in foliar nitrogen concentration (N), to mesophyll conductance (g(m)) or to biochemical capacity for photosynthesis (maximum rate of carboxylation, V(cmax)). Simultaneous measurements of gas exchange and chlorophyll fluorescence were made to determine g(m) and V(cmax) in four height classes of Pinus densiflora Sieb. & Zucc. trees. As the average height of growing trees increased from 3.1 to 13.7 m, g(m) decreased from 0.250 to 0.107 mol m(-2) s(-1), and the CO(2) concentration from the intercellular space (C(i)) to the site of carboxylation (C(c)) decreased by an average of 74 µmol mol(-1). Furthermore, V(cmax) estimated from C(c) increased from 68.4 to 112.0 µmol m(-2) s(-1) with the increase in height, but did not change when it was calculated based on C(i). In contrast, A(max) decreased from 14.17 to 10.73 µmol m(-2) s(-1). Leaf dry mass per unit area (LMA) increased significantly with tree height as well as N on both a dry mass and an area basis. All of these parameters were significantly correlated with tree height. In addition, g(m) was closely correlated with LMA and g(s), indicating that increased diffusive resistance for CO(2) may be the inevitable consequence of morphological adaptation. Foliar N per unit area was positively correlated with V(cmax) based on C(c) but negatively with A(max), suggesting that enhancement of photosynthetic capacity is achieved by allocating more N to foliage in order to minimize the declines in A(max). Increases in the N cost associated with carbon gain because of the limited water available to taller trees lead to a trade-off between water use efficiency and photosynthetic nitrogen use efficiency. In conclusion, the height-related decrease in photosynthetic performance appears to result mainly from diffusive resistances rather than biochemical limitations.