The Relationship Between Maturation Size and Maximum Tree Size From Tropical to Boreal Climates.

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

Initial stomatal conductance increases photosynthetic induction of trees leaves more from sunlit than from shaded environments: A meta-analysis.

It has long been held that tree species/leaves from shaded environments show faster rate of photosynthetic induction than species/leaves from sunlit environments. But the evidence so far is conflicting and the underlying mechanisms are still under debate. To address the debate, we compiled a dataset for 87 tree species and compared the initial increasing slope during the first 2-minute induction (SA) and stomatal and biochemical characteristics between sun and shade species from the same study, and those between sun and shade leaves within the same species. In 77% of between-species comparisons, the species with high steady-state photosynthetic rate in the high light (Af) exhibited a larger SA than the species with low Af. In 67% within-species comparisons, the sun leaves exhibited a larger SA than the shade leaves. However, in only a few instances did the sun species/leaves more rapidly achieve 50% of full induction, with an even smaller SA, than the shade species/leaves. At both the species and leaf level, SA increased with increasing initial stomatal conductance before induction (gsi). Despite exhibiting reduced intrinsic water use efficiency in low light, a large SA proportionally enhances photosynthetic carbon gain during the first 2-minute induction in the sun species and leaves. Thus, in terms of the increase in absolute rate of photosynthesis, tree species/leaves from sunlit environments display faster photosynthetic induction responses than those from shaded environments. Our results call for re-consideration of contrasting photosynthetic strategies in photosynthetic adaption/acclimation to dynamic light environments across species.

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.