Human-induced changes in atmospheric composition are expected to affect primary productivity across terrestrial biomes. Recent changes in productivity have been observed in many forest ecosystems, but low-latitude upper tree line forests remain to be investigated. Here, we use dendrochronological methods and isotopic analysis to examine changes in productivity, and their physiological basis, in Abies religiosa (Ar) and Pinus hartwegii (Ph) trees growing in high-elevation forests of central Mexico. Six sites were selected across a longitudinal transect (Transverse Volcanic Axis), from the Pacific Ocean toward the Gulf of Mexico, where mature dominant trees were sampled at altitudes ranging from 3200 to 4000 m asl. A total of 60 Ar and 84 Ph trees were analyzed to describe changes in growth (annual-resolution) and isotopic composition (decadal-resolution) since the early 1900s. Our results show an initial widespread increase in basal area increment (BAI) during the first half of the past century. However, BAI has decreased significantly since the 1950s with accentuated decline after the 1980s in both species and across sites. We found a consistent reduction in atmosphere to wood 13C discrimination, resulting from increasing water use efficiency (20–60%), coinciding with rising atmospheric CO2. Changes in 13C discrimination were not followed, however, by shifts in tree ring δ18O, indicating site- and species-specific differences in water source or uptake strategy. Our results indicate that CO2 stimulation has not been enough to counteract warming-induced drought stress, but other stressors, such as progressive nutrient limitation, could also have contributed to growth decline. Future studies should explore the distinct role of resource limitation (water vs. nutrients) in modulating the response of high-elevation ecosystems to atmospheric change.

Growth decline and divergent tree ring isotopic composition (δ13C and δ18O) contradict predictions of CO2stimulation in high altitudinal forests

Tropical and subtropical dendrochronology: Approaches, applications, and prospects

Neotropical Hypericum irazuense shrubs reveal recent ENSO variability in Costa Rican páramo

Methods and future directions for paleoclimatology in the Maya Lowlands

Drought in Guatemala has negative consequences for agriculture and potable water supplies, particularly in regions of the country with highly seasonal rainfall. General circulation models suggest that a decrease in both winter and summer rainfall over Central America is likely and imminent as a consequence of anthropogenic influences on the climate system. However, precipitation observations over the last several decades are equivocal. Here, we use an Abies guatemalensis tree-ring chronology from the Sierra de los Cuchumatanes to estimate January through March rainfall since the late seventeenth century. Our reconstruction shows that recent winter–spring rainfall from the region is not yet exceptional in the context of the last several centuries, has a significant yet variable decadal component, is associated with large-scale modes of ocean–atmosphere variability, and reveals evidence of past multiyear droughts.

Tree-ring reconstructed dry season rainfall in Guatemala

The continued expansion of dendroclimatology into Mesoamerica requires the identification and evaluation of species whose rings can be precisely dated and then statistically compared with precipita...

Annual chronology and climate response in Abies guatemalensis Rehder (Pinaceae) in Central America

287 Psychotropic medication in patients with end-stage cystic fibrosis

changed significantly from baseline to 6 months after ETI initiation (McNemar test p = 0.003) but was not statistically significantly different for the GAD-7 ( p = 0.073).Symptoms of 26 and 29 patients improved, and 17 and 14 experienced worsening symptoms for GAD-7 and PHQ-9, respectively.Conclusions: Findings demonstrated an overall improvement in GAD-7 and PHQ-9 scores 6 months after ETI initiation.Although a greater proportion of patients improved than worsened in terms of GAD-7 and PHQ-9 severity groups after 6 months of ETI, analyses are ongoing to better understand the factors that lead to mental health worsening in this subgroup of patients. 

479 Changes in psychotropic medication during first year of elexacaftortezacaftor-ivacaftor therapy

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Annual chronology and climate response in Abies guatemalensis Rehder (Pinaceae) in Central America

287 Psychotropic medication in patients with end-stage cystic fibrosis

479 Changes in psychotropic medication during first year of elexacaftortezacaftor-ivacaftor therapy