ALBERT

Description: Plant–microbial symbioses are widespread in nature and can shape the ecology and evolution of hosts and interacting symbionts. Fungal endophytes—fungi that live asymptomatically within plant tissues—are a pervasive group of symbionts well known for their role in mediating host-responses to biotic and abiotic stresses. However, they also may become pathogenic and often impose metabolic costs on hosts. Here, we examine the role of fungal endophytes in mediating responses of the host grass red fescue ( Festuca rubra ) to salt and herbivore stress. We collected 38 red fescue genotypes from within its native range on Akimiski Island, Nunavut, Canada, where it occurs in the supratidal region on the northern part of the island and is heavily grazed by nesting and brood-rearing snow geese ( Chen caerulescens caerulescens ) and Canada geese ( Branta canadensis ). We screened all plants for the presence of the systemic endophyte Epichloë festucae and sequenced the nonsystemic endophytic community on a subset of these plants. While we did not detect E. festucae , our plants instead were host to a diverse array of nonsystemic fungal endophytes. We then conducted a fully factorial greenhouse experiment where we crossed plant genotype (4 levels) with simulated grazing (clipped or unclipped), endophyte status (present or absent) and salinity (0, 32 or 64 ppt) to examine the ecological role of this endophytic community. Overall, the presence of nonsystemic endophytes increased plant survival, but only in the absence of salt or clipping. On the other hand, these endophytes reduced plant tolerance to simulated herbivory by 69% but had no effect on aboveground plant growth. Thus, our results identify a potential nonsystemic endophyte-mediated trade-off in host plant survival and tolerance to herbivory and suggest this trade-off may be altered by stressful abiotic conditions.

Description: The complexity involved in accurate estimation and numerical simulation of regional evapotranspiration (ET) can lead to inconsistency among techniques, usually attributed to methodological deficiencies. Here we hypothesize instead that discrepancies in ET estimates should be expected in some cases and can be applied to measure the effect of anthropogenic influences in developed river basins. We compare an ensemble of corrected ET estimates from land surface models with GRACE and MODIS satellite-based estimates in the intensively-managed Colorado River Basin to contrast the roles of natural variability and human impacts. Satellite-based approaches yield larger annual amplitudes in ET estimates than land surface model simulations, primarily during the growing season. We find a total satellite-based ET flux of 142 ± 7 MAF yr -1 , with 38% due to anthropogenic influences during summer months. We evaluate our estimates by comparison with reservoir storage and usage allotment components of the basin water management budget.

Description: Few biogeographic studies of dinoflagellate cysts include the near-shore estuarine environment. We determine the effect of estuary type, biogeography, and water quality on the spatial distribution of organic-walled dinoflagellate cysts from the Northeast USA (Maine to Delaware) and Canada (Prince Edward Island). A total of 69 surface sediment samples were collected from 27 estuaries, from sites with surface salinities 〉20. Dinoflagellate cysts were examined microscopically and compared to environmental parameters using multivariate ordination techniques. The spatial distribution of cyst taxa reflects biogeographic provinces established by other marine organisms, with Cape Cod separating the northern Acadian Province from the southern Virginian Province. Species such as Lingulodinium machaerophorum and Polysphaeridinium zoharyi were found almost exclusively in the Virginian Province, while others such as Dubridinium spp. and Islandinium ? cezare were more abundant in the Acadian Province. Tidal range, sea surface temperature (SST), and sea surface salinity (SSS) are statistically significant parameters influencing cyst assemblages. Samples from the same type of estuary cluster together in canonical correspondence analysis when the estuaries are within the same biogeographic province. The large geographic extent of this study, encompassing four main estuary types (riverine, lagoon, coastal embayment, and fjord), allowed us to determine that the type of estuary has an important influence on cyst assemblages. Due to greater seasonal variations in SSTs and SSSs in estuaries compared to the open ocean, cyst assemblages show distinct latitudinal trends. The estuarine context is important for understanding present-day species distribution, the factors controlling them, and to better predict how they may change in the future. A total of 69 surface sediments from 23 northeast USA estuaries, from Maine to Delaware and four estuaries from Prince Edward Island (Canada), were analyzed to determine the effect of estuary type, biogeography and water quality on the spatial distribution of organic walled dinoflagellate cysts. The spatial distribution of cyst taxa was found to reflect biogeographic provinces established by other marine organisms, with Cape Cod separating the northern Acadian province from the southern Virginian province. The large geographic extent of this study, encompassing four main estuary types (riverine, lagoon, coastal embayment, and fjord), allowed us to determine that the type of estuary is an important parameter influencing cyst assemblages.

Description: Soil water storage is a fundamental signal in the land hydrological cycle, and changes in soil moisture can affect regional climate. In this study, we used simulations from CMIP5 archives to investigate changes in the annual range of soil water storage under global warming at northern mid- and high-latitudes. Results show that future warming could lead to significant declines in snowfall, and a corresponding lack of snowmelt water recharge to the soil, which makes soil water less available during spring and summer. Conversely, more precipitation as rainfall results in higher recharge to soil water during its accumulating season. Thus, the wettest month of soil water gets wetter, and the driest month gets drier, resulting in an increase of the annual range and suggesting that stronger heterogeneity in global water distribution (changing extremes) could occur under global warming; this has implications for water management and water security under a changing climate.

Description: We present the first detailed analysis of H 3 + nightside emission from Jupiter, using data from the Cassini flyby in 2000–2001, producing the first jovian maps of nightside H 3 + emission, temperature and column density. Using these, we identify and characterise regions of H 3 + nightside emission, compared against past observations of H 3 + emission on the dayside. We focus our investigation on the region previously described as ‘mid-to-low latitude emission’, the source for which has been controversial. We find that the brightest of this emission is generated at jovigraphic latitudes similar to the most equatorward extent of the main auroral emission, but concentrated at longitudes eastward of this emission. The emission is produced by enhanced H 3 + density, with temperatures dropping away in this region. This emission has a loose association with the predicted location of diffuse aurora produced by pitch angle scattering in the north, but not in the south. This emission also lays in the path of sub-rotating winds flowing from the aurora, suggesting a transport origin. Some differences are seen between dayside and nightside sub-auroral emission, with dayside emission extending more equatorward, perhaps caused by the lack of sunlight ionisation on the nightside, and unmeasured changes in temperature. Ionospheric temperatures are hotter in the polar region (~1100-1500K), dropping away towards the equator (as low as 750K), broadly similar to values on the dayside, highlighting the dominance of auroral effects in the polar region. No equatorial emission is observed, suggesting that very little particle precipitation occurs away from the polar regions.

Description: Recent forest diebacks, combined with threats of future drought, focus attention on the extent to which tree death is caused by catastrophic events as opposed to chronic declines in health that accumulate over years. While recent attention has focused on large-scale diebacks, there is concern that increasing drought stress and chronic morbidity may have pervasive impacts on forest composition in many regions. Here we use long-term, whole-stand inventory data from southeastern U.S. forests to show that trees exposed to drought experience multiyear declines in growth prior to mortality. Following a severe, multiyear drought, 72% of trees that did not recover their pre-drought growth rates died within 10 yr. This pattern was mediated by local moisture availability. As an index of morbidity prior to death, we calculated the difference in cumulative growth after drought relative to surviving conspecifics. The strength of drought-induced morbidity varied among species and was correlated with drought tolerance. These findings support the ability of trees to avoid death during drought events but indicate shifts that could occur over decades. Tree mortality following drought is predictable in these ecosystems based on growth declines, highlighting an opportunity to address multiyear drought-induced morbidity in models, experiments, and management decisions.

Description: Earth science increasingly relies on computer-based methods and many government agencies now require further sharing of the digital products they helped fund. Earth scientists, while often supportive of more transparency in the methods they develop, are concerned by this recent requirement and puzzled by its multiple implications. This paper therefore presents a reflection on the numerous aspects of sharing code and data in the general field of computer modeling of dynamic Earth processes. Our reflection is based on ten years of development of an open-source model called RAPID that simulates the propagation of water flow waves in river networks. Three consecutive but distinct phases of the sharing process are highlighted here: opening, exposing, and consolidating. Each one of these phases is presented as an independent and tractable increment aligned with the various stages of code development and justified based on the size of the users community. Several aspects of digital scholarship are presented here including licenses, documentation, websites, citable code and data repositories, and testing. While the many existing services facilitate the sharing of digital research products, digital scholarship also raises community challenges related to technical training, self-perceived inadequacy, community contribution, acknowledgment and performance assessment, and sustainable sharing. This article is protected by copyright. All rights reserved.