The mobilization and transport of newly fixed carbon are driven by plant water use in an experimental rainforest under drought.

Non-structural carbohydrates (NSCs) are building blocks for biomass and fuel metabolic processes. However, it remains unclear how tropical forests mobilize, export, and transport NSCs to cope with extreme droughts. We combined drought manipulation and ecosystem 13CO2 pulse-labeling in an enclosed rainforest at Biosphere 2, assessed changes in NSCs, and traced newly assimilated carbohydrates in plant species with diverse hydraulic traits and canopy positions. We show that drought caused a depletion of leaf starch reserves and slowed export and transport of newly assimilated carbohydrates below ground. Drought effects were more pronounced in conservative canopy trees with limited supply of new photosynthates and relatively constant water status than in those with continual photosynthetic supply and deteriorated water status. We provide experimental evidence that local utilization, export, and transport of newly assimilated carbon are closely coupled with plant water use in canopy trees. We highlight that these processes are critical for understanding and predicting tree resistance and ecosystem fluxes in tropical forest under drought.

Carbon dynamics during long-term starving poplar trees-the importance of older carbohydrates and a shift to lipids during survival.

Carbon (C) assimilation can be severely impaired during periods of environmental stress like drought or defoliation, making trees heavily dependent on the use of C reserve pools for survival; yet, dynamics of reserve use during periods of reduced C supply are still poorly understood. We used stem girdling in mature poplar trees (Populus tremula L. hybrids), a lipid-storing species, to permanently interrupt phloem C transport and induced C shortage in the isolated stem section below the girdle and monitored metabolic activity during three campaigns in the growing seasons of 2018, 2019, and 2021. We measured respiratory fluxes (CO2 and O2), NSC concentration, the respiratory substrate (based on isotopic analysis and CO2/O2 ratio) and the age of the respiratory substrate (based on radiocarbon analysis). Our study shows that poplar trees can survive long periods of reduced C supply from the canopy by switching in metabolism from recent carbohydrates to older storage pools with a potential mixture of respiratory substrates, including lipids. This mechanism of stress resilience can explain why tree decline may take many years until death occurs.

Stochastic and deterministic interpretation of pool models.

Carbon and element cycling models can be expressed in terms of the dynamics of individual particles or collection of them in aggregated pools. In both cases, the models represent the same dynamics and provide similar predictions. The time required for individual particles to pass through a system, that is, the transit time, can be obtained from both approaches. Pool models can be analyzed from a stochastic or a deterministic point of view.

Low-cost chamber design for simultaneous CO2 and O2 flux measurements between tree stems and the atmosphere.

Tree stem CO2 efflux is an important component of ecosystem carbon fluxes and has been the focus of many studies. While CO2 efflux can easily be measured, a growing number of studies have shown that it is not identical with actual in situ respiration. Complementing measurements of CO2 flux with simultaneous measurements of O2 flux provides an additional proxy for respiration, and the combination of both fluxes can potentially help getting closer to actual measures of respiratory fluxes. To date, however, the technical challenge to measure relatively small changes in O2 concentration against its high atmospheric background has prevented routine O2 measurements in field applications. Here, we present a new and low-cost field-tested device for autonomous real-time and quasi-continuous long-term measurements of stem respiration by combining CO2 (NDIR-based) and O2 (quenching-based) sensors in a tree stem chamber. Our device operates as a cyclic-closed system and measures changes in both CO2 and O2 concentration within the chamber over time. The device is battery powered with a >1-week power independence, and data acquisition is conveniently achieved by an internal logger. Results from both field and laboratory tests document that our sensors provide reproducible measurements of CO2 and O2 exchange fluxes under varying environmental conditions.

Starch and lipid storage strategies in tropical trees relate to growth and mortality.

Non-structural carbon (NSC) storage (i.e. starch, soluble sugras and lipids) in tree stems play important roles in metabolism and growth. Their spatial distribution in wood may explain species-specific differences in carbon storage dynamics, growth and survival. However, quantitative information on the spatial distribution of starch and lipids in wood is sparse due to methodological limitations. Here we assessed differences in wood NSC and lipid storage between tropical tree species with different growth and mortality rates and contrasting functional types. We measured starch and soluble sugars in wood cores up to 4 cm deep into the stem using standard chemical quantification methods and histological slices stained with Lugol's iodine. We also detected neutral lipids using histological slices stained with Oil-Red-O. The histological method allowed us to group individuals into two categories according to their starch storage strategy: fiber-storing trees and parenchyma-storing trees. The first group had a bigger starch pool, slower growth and lower mortality rates than the second group. Lipid storage was found in wood parenchyma in five species and was related to low mortality rates. The quantification of the spatial distribution of starch and lipids in wood improves our understanding of NSC dynamics in trees and reveals additional dimensions of tree growth and survival strategies.

Effectiveness and safety of perampanel monotherapy for focal and generalized tonic-clonic seizures: Experience from a national multicenter registry.

OBJECTIVE: To assess the effectiveness and tolerability of perampanel (PER) monotherapy in routine clinical practice for the treatment of focal onset and generalized tonic-clonic seizures (GTCS). METHODS: This multicenter, retrospective, observational study was conducted in patients aged ≥12 years treated with PER as primary monotherapy or converted to PER monotherapy by progressive reduction of background antiepileptic drugs. Outcomes included retention, responder, and seizure-free rate after 3, 6, and 12 months and tolerability throughout the follow-up. RESULTS: A total of 98 patients (mean age = 49.6 ± 21.7 years, 51% female) with focal seizures and/or GTCS were treated with PER monotherapy for a median exposure of 14 months (range = 1-57) with a median dose of 4 mg (range = 2-10). The retention rates at 3, 6, and 12 months and last follow-up were 93.8%, 89.3%, 80.9%, and 71.4%, respectively. The retention rates according to the type of monotherapy (primary vs conversion) did not differ (log-rank P value = .57). Among the 98 patients, 61.2% patients had seizures throughout the baseline period, with a median seizure frequency of 0.6 seizures per month (range = 0.3-26). Responder rates at 3, 6, and 12 months were 79.6%, 70.1%, and 52.8%, respectively, and seizure freedom rates at the same points were 62.7%, 56.1%, and 41.5%. Regarding the 33 patients who had GTCS in the baseline period, 87.8% were seizure-free at 3 months, 78.1% at 6 months, and 55.1% at 12 months. Over the entire follow-up, PER monotherapy was generally well tolerated, and only 16% of patients discontinued PER due to adverse events (AEs). Female patients were found to be at a higher risk of psychiatric AEs (female vs male odds ratio = 2.85, 95% confidence interval = 1-8.33, P = .046). SIGNIFICANCE: PER demonstrated good effectiveness and a good safety profile when used as primary therapy or conversion to monotherapy at relatively low doses, in a clinical setting with patients with focal seizures and GTCS.

Probability distributions of nonstructural carbon ages and transit times provide insights into carbon allocation dynamics of mature trees.

●In trees, the use of nonstructural carbon (NSC) under limiting conditions impacts the age structure of the NSC pools. We compared model predictions of NSC ages and transit times for Pinus halepensis, Acer rubrum and Pinus taeda, to understand differences in carbon (C) storage dynamics in species with different leaf phenology and growth environments. ●We used two C allocation models from the literature to estimate the NSC age and transit time distributions, to simulate C limitation, and to evaluate the sensitivity of the mean ages to changes in allocation fluxes. ●Differences in allocation resulted in different NSC age and transit time distributions. The simulated starvation flattened the NSC age distribution and increased the mean NSC transit time, which can be used to estimate the age of the NSC available and the time it would take to exhaust the reserves. Mean NSC ages and transit times were sensitive to C fluxes in roots and allocation of C from wood storage. ●Our results demonstrate how trees with different storage traits are expected to react differently to starvation. They also provide a probabilistic explanation for the 'last-in, first-out' pattern of NSC mobilization from well-mixed C pools.

Nonannual tree rings in a climate-sensitive Prioria copaifera chronology in the Atrato River, Colombia.

In temperate climates, tree growth dormancy usually ensures the annual nature of tree rings, but in tropical environments, determination of annual periodicity can be more complex. The purposes of the work are as follows: (1) to generate a reliable tree-ring width chronology for Prioria copaifera Griseb. (Leguminoceae), a tropical tree species dwelling in the Atrato River floodplains, Colombia; (2) to assess the climate signal recorded by the tree-ring records; and (3) to validate the annual periodicity of the tree rings using independent methods. We used standard dendrochronological procedures to generate the P. copaifera tree-ring chronology. We used Pearson correlations to evaluate the relationship of the chronology with the meteorological records, climate regional indices, and gridded precipitation/sea surface temperature products. We also evaluated 24 high-precision 14C measurements spread over a range of preselected tree rings, with assigned calendar years by dendrochronological techniques, before and after the bomb spike in order to validate the annual nature of the tree rings. The tree-ring width chronology was statistically reliable, and it correlated significantly with local records of annual and October-December (OND) streamflow and precipitation across the upper river watershed (positive), and OND temperature (negative). It was also significantly related to the Oceanic Niño Index, Pacific Decadal Oscillation, and the Southern Oscillation Index, as well as sea surface temperatures over the Caribbean and the Pacific region. However, 14C high-precision measurements over the tree rings demonstrated offsets of up to 40 years that indicate that P. copaifera can produce more than one ring in certain years. Results derived from the strongest climate-growth relationship during the most recent years of the record suggest that the climatic signal reported may be due to the presence of annual rings in some of those trees in recent years. Our study alerts about the risk of applying dendrochronology in species with challenging anatomical features defining tree rings, commonly found in the tropics, without an independent validation of annual periodicity of tree rings. High-precision 14C measurements in multiple trees are a useful method to validate the identification of annual tree rings.