Rising atmospheric CO₂ explains 26–52% of the recent delay in autumnal senescence in important forest and crop species

There is strong evidence to suggest that global warming is leading to an extended growing season by altering the timing of autumnal events such as bud set and leaf abscission 1,2,3, with important impacts on ecosystem productivity and global carbon cycling. However, while temperature is an important driver of spring phenological events, the relationship between temperature and autumn phenology is weak4. Here, we present results from three open-air field experiments in which elevated atmospheric CO2 concentration [CO2] at the concentration likely to exist in 2050, extended the growing season of: (1) three abundant North American forest trees; (2) the world’s most extensively grown broad-leaved crop (soybean); and (3) two European poplars. Across experiments and over multiple years, elevated [CO2] delayed autumnal declines in leaf area, chlorophyll concentration, photosynthesis and normalized vegetation difference index (NVDI) by 2-7 days for soybean and 5-15 days for trees. These findings indicate that [CO2] alters growing season length and the rise in atmospheric [CO2] over the past 30 years could explain 26-52% of the extended growing season now ascribed to warming3

Foliar Symptoms Triggered by Ozone Stress in Irrigated Holm Oaks from the City of Madrid, Spain

BACKGROUND: Despite abatement programs of precursors implemented in many industrialized countries, ozone remains the principal air pollutant throughout the northern hemisphere with background concentrations increasing as a consequence of economic development in former or still emerging countries and present climate change. Some of the highest ozone concentrations are measured in regions with a Mediterranean climate but the effect on the natural vegetation is alleviated by low stomatal uptake and frequent leaf xeromorphy in response to summer drought episodes characteristic of this climate. However, there is a lack of understanding of the respective role of the foliage physiology and leaf xeromorphy on the mechanistic effects of ozone in Mediterranean species. Particularly, evidence about morphological and structural changes in evergreens in response to ozone stress is missing. RESULTS: Our study was started after observing ozone -like injury in foliage of holm oak during the assessment of air pollution mitigation by urban trees throughout the Madrid conurbation. Our objectives were to confirm the diagnosis, investigate the extent of symptoms and analyze the ecological factors contributing to ozone injury, particularly, the site water supply. Symptoms consisted of adaxial and intercostal stippling increasing with leaf age. Underlying stippling, cells in the upper mesophyll showed HR-like reactions typical of ozone stress. The surrounding cells showed further oxidative stress markers. These morphological and micromorphological markers of ozone stress were similar to those recorded in deciduous broadleaved species. However, stippling became obvious already at an AOT40 of 21 ppm•h and was primarily found at irrigated sites. Subsequent analyses showed that irrigated trees had their stomatal conductance increased and leaf life -span reduced whereas the leaf xeromorphy remained unchanged. These findings suggest a central role of water availability versus leaf xeromorphy for ozone symptom expression by cell injury in holm oak