Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causalit

Alpine vascular plant species richness: The importance of daily maximum temperature and pH

ISSN:1385-0237ISSN:1573-505

UVS Observations of Ganymede During Juno Orbits 34 and 35 (invited)

Juno UVS, an ultraviolet spectrograph sensitive to wavelengths 68-210 nm, performed unique observations of Ganymede’s aurora and surface reflectance on the approach to Juno’s 34th and 35th perijoves (PJ). The combination of Juno’s 2 rpm spin rate, UVS’ 7.2° long “dog-bone” shaped slit, and the UVS scan mirror allows for the recording of 7.2° wide scans across Ganymede’s disk every 30 s. Through the wide slits we are able to capture integration times of 17 ms per spin for each resolution element in the observed swath. For the PJ34 Ganymede encounter on June 7, 2021 at 16:56:08 UTC, Juno UVS captured data during 16:52-16:56-17:04 UTC at altitudes varying from 1124-1044-6750 km. Over this time period Ganymede’s angular diameter varied from 89°-91°-33° on the sky, while the nadir solar phase angle varied from 148°-98°-32°. Juno UVS achieves a spatial resolution of ≈0.2° giving a best-case nadir spatial resolution of 4 km. The PJ34 UVS data provide a sparse, but high-resolution look at Ganymede’s aurora, and can be used to locate the last closed field lines to an accuracy of about one degree of latitude. For the PJ35 Ganymede encounter on July 20, 2021 at 16:48:30 UTC, Juno UVS captured data during 16:32-16:48-17:27 UTC. The increased observational period relative to the PJ34 encounter is due to the larger range, 52,610-49,999-67,060 km, making the angular extent of Ganymede only 5.5°-5.7-4.3° on the sky (at a nadir solar phase angle 99°-81°-44°) and the best-case nadir spatial resolution 175 km (comparable to HST imagery). UVS not only spatially resolved Ganymede, but also spectrally separates the prominent 130.4 and 135.6 nm O auroral emissions. We will present maps of the auroral and surface reflected emissions as well as maps of the 130.4/135.6 oxygen emission ratio

Methane distribution on Pluto as mapped by the New Horizons Ralph/MVIC instrument

International audienceThe data returned from NASA's New Horizons spacecraft have given us an unprecedented, detailed look at the Pluto system. New Horizons' Ralph/MVIC (Multispectral Visible Imaging Camera) is composed of 7 independent CCD arrays on a single substrate. Among these are a red channel (540-700 nm), near-infrared channel (780-975 nm), and narrow band methane channel (860-910 nm). By comparing the relative reflectance of these channels we are able to produce high-resolution methane "equivalent width" (based on the 890 nm absorption band) and spectral slope maps of Pluto's surface. From these maps we can then quantitatively study the relationships between methane distribution, redness, and other parameters like latitude and elevation. We find Pluto's surface to show a great diversity of terrains, particularly in the equatorial region between 30°N and 30°S latitude. Methane "equivalent width" also shows some dependence on elevation (while spectral slope shows very little)