Monica Garcia

Detection of interannual vegetation responses to climatic variability using AVIRIS data in a coastal savanna in California

Ecosystem responses to interannual weather variability are large and superimposed over any long-term directional climatic responses making it difficult to assign causal relationships to vegetation change. Better understanding of ecosystem responses to interannual climatic variability is crucial to predicting long-term functioning and stability. Hyperspectral data have the potential to detect ecosystem responses that are undetected by broadband sensors and can be used to scale to coarser resolution global mapping sensors, e.g., advanced very high resolution radiometer (AVHRR) and MODIS. This research focused on detecting vegetation responses to interannual climate using the airborne visible-infrared imaging spectrometer (AVIRIS) data over a natural savanna in the Central Coast Range in California. Results of linear spectral mixture analysis and assessment of the model errors were compared for two AVIRIS images acquired in spring of a dry and a wet year. The results show that mean unmixed fractions for these vegetation types were not significantly different between years due to the high spatial variability within the landscape. However, significant community differences were found between years on a pixel basis, underlying the importance of site-specific analysis. Multitemporal hyperspectral coverage is necessary to understand vegetation dynamics.

Liposome entrapment and immunogenic studies of a synthetic lipophilic multiple antigenic peptide bearing VP1 and VP3 domains of the hepatitis A virus: a robust method for vaccine design

Multiple antigen peptides (MAP) have been demonstrated to be efficient immunological reagents for the induction of immune responses to a variety of infectious agents. Several peptide domains of the hepatitis A virus (HAV) capsid proteins, mainly VP1 and VP3, are the immunodominant targets for a protective antibody response. In the present study we analyse the immunogenic properties of a tetrameric heterogeneous palmitoyl‐derivatised MAP containing two defined HAV peptide sequences, VP1(11–25) and VP3(102–121), in rabbits immunised with either Freunds adjuvant or multilamellar liposomes. The immune response was evaluated with a specific enzyme immunoassay using MAP[VP1+VP3], VP1 and VP3 as targets. The avidity of the immune response was measured by a non‐competitive enzyme‐linked immunosorbent assay and by the surface plasmon resonance technology. Antisera raised against the lipo‐MAP peptide entrapped in liposomes demonstrated high avidity of binding with affinity rate constants approximately one order of magnitude greater than those obtained with the Freunds protocol.

Enhancement of the immunogenicity of a synthetic peptide bearing a VP3 epitope of hepatitis A virus

The immune responses elicited in mice by different forms of the VP3(110–121) B‐epitope of the hepatitis A virus (HAV) were studied. Different forms of incorporation in liposomes were tested, encapsulation, rather than surface exposure, being the best antigenic preparation. Three larger peptides of the VP3 epitope, two of them containing a hepatitis B virus T‐epitope, and a third containing a putative T‐epitope of HAV (VP3(102–121)) were assayed. While this latter T‐epitope induced an enhancement of the response against the VP3 B‐epitope, the artificially coupled T‐epitopes failed to induce a significant increase. The administration of two multiple antigenic peptide (MAP) constructs, the first containing the VP3(110–121) and VP1(11–25) HAV sequences and the second only the VP1(11–25) sequence, also suggested the presence of a T‐epitope, since the response against the VP1 peptide was increased in the first construct.

Liposomes as vehicles for the presentation of a synthetic peptide containing an epitope of hepatitis A virus.

Previous work from our group showed that the entrapment of HAV-related synthetic peptides into multilamellar liposomes yielded satisfactory immunoresponses when administered to mice. In the present work we report investigative results for several liposome formulations of a 20-mer peptide related to VP3 capsid protein of HAV. In this sense, the recently introduced surface plasmon resonance technique has been applied to compare the different strategies of association between the synthetic peptide and phospholipid vesicles and to demonstrate that no significant alteration in antigenicity is produced when the peptide sequence is covalently coupled to the surface of small unilamellar vesicles. In addition, conformational data obtained by the circular dichroism technique have shown a decrease in the helical contribution of peptide-once linked to phospholipid; probably this change is due to the restriction introduced at the N-terminus of the sequence when coupled to the derivatized phospholipids at the surface of vesicle bilayers.

Climate-driven variation in the intensity of a host-symbiont animal interaction along a broad elevation gradient.

Gradients of environmental stress may affect biotic interactions in unpredictable ways responding to climate variation, depending on the abiotic stress tolerance of interacting partners. Here, we study the effect of local climate on the intensity of feather mites in six mountain passerines along a 1400 m elevational gradient characterized by shifting temperature and rainfall. Although obligatory symbionts of warm-blooded organisms are assumed to live in mild and homeothermic environments, those inhabiting external, non-blood-irrigated body portions of the host organism, such as feather mites, are expected to endure exposure to the direct influence of a fluctuating climate. As expected, feather mite intensity declined with elevation in all bird species, a pattern that was also found in cold-adapted passerines that have typical alpine habits. The elevation cline was mainly explained by a positive effect of the average temperature upon mite intensity in five of the six species studied. Precipitation explained less variance in mite intensity than average temperature, and showed a negative correlation in half of the studied species. We found no climate-driven migration of mites along the wings of birds, no replacement of mite species along elevation gradients and no association with available food resources for mites (estimated by the size of the uropygial gland). This study suggests that ectosymbionts of warm-blooded animals may be highly sensitive to climatic variation and become less abundant under stressful environmental conditions, providing empirical evidence of the decline of specialized biotic interactions among animal species at high elevations.

Effect of chain length of HAV-VP3 synthetic peptides on its interaction with biomembrane models.

Shorter analogues of a continuous epitope of hepatitis A virus, VP3(110-121) peptide, failed to react with convalescent sera, indicating the importance of the entire peptide in the epitope structure. To better understand the influence of the structural properties of this 12-mer peptide epitope on its biological activity, the interaction of smaller peptide analogues with phospholipid biomembrane models was investigated by a combination of spectroscopic and biophysical techniques. In this article we describe our findings concerning the surface activity and the interaction of peptides with simple mono- and bilayer membranes composed of a zwitterionic phospholipid (dipalmitoyl phosphatidylcholine, DPPC), an anionic phospholipid (dipalmitoyl phosphatidylglicerol, DPPG), or a DPPC/DPPG mixture. The results indicate that the net negative charge of the peptide is in some way responsible of the specific interactions between VP3(110-121) and membrane phospholipids, and necessary to induce beta-type conformations upon vesicle interaction.

Mechanisms underlying the bioindicator notion: spatial association between individual sexual performance and community diversity.

The bioindicator notion is an appealing concept that has received more support in applied than in basic ecology, mostly due to the difficulty in deriving general ecological rules applicable to all target organisms. However, recognizing the mechanisms that determine the association between a particular species and the well-being of many other species is important for understanding the functioning of ecosystems and the relationship among different biological levels. We examined here the processes at the individual level that cause an association between species performance and biodiversity value, by analyzing attributes that can be studied in a variety of animals with sexual reproduction, namely breeding site selection and condition-dependent sexual signals. Our study model was the Capercaillie, an indicator of forest functioning and diversity, and the associated bird community, used here as a surrogate of broader forest biodiversity. At a regional scale Capercaillie occurrence was not associated with the most diverse forest patches, but at the scale of male spring territories the sexual display grounds (arenas) were located in the oldest and less disturbed forest portions, which also hosted the richest local bird communities. Social mechanisms and conspecific cueing likely concurred with habitat-driven processes in determining the long-term persistence of traditional display grounds, which were appealing to many other species because of their structural composition. Characteristics of male vocal display that honestly advertize male quality (low frequencies and rapid song rates) were significantly correlated with high diversity values, resulting in a spatial association between individual and community performances. Costly or risky activities such as reproductive or social behaviors, which more than other attributes match gradients in habitat quality, are therefore contributing to functionally connect individuals with ecosystem health.

Optical Remote Sensing for Soil Mapping and Monitoring

This chapter focuses on the use of optical remote sensing in the wavelength domain of visible and near infrared and shortwave infrared. It gives an overview of the principal issues concerning the use of these techniques for soil mapping and monitoring, including different spectral (multispectral and hyperspectral data) and spatial scales (laboratory, field, and image). It also analyze several aspects needed for the use of these type of data, like the information contain on a spectral signature, the main sources of uncertainty or the methods and approaches commonly used. At last it gives an overview of the common uses of soil spectroscopy showing in deeper detail the state of the art of its use for mapping soil properties, soil erosion, land degradation, and biological soil crust.

Estimating Latent and Sensible Heat Fluxes using the Temperature Vegetation Dryness Index and MODIS Data

In this work, daily latent heat (lambdaE_d) or evapotranspiration and sensible heat (H_d) fluxes were estimated from the TVDI (Temperature Vegetation Dryness Index) modified to account for climatic gradients (TVDI_t) using MODIS data in a Spanish region (Andalusia) with strong bioclimatic gradients. The TVDI_t was correlated (R=0.90) with field measured AWC (available water content). When reinterpreting TVDI_t as the ratio between actual and potential evapotranspiration to estimate surface energy fluxes, model vs. eddy covariance data from 2 semiarid sites were reasonable for H_d (R=0.94: RMSE=25.89 Wm^-2). For lambdaE_d RMSE was low (19.46 Wm^-2) but correlations were only significant after excluding summer dates (R=0.71) when transpiration is very low. Model accuracy is currently limited by the accuracy in Rn_d estimates (<27 Wm^-2) for which results at humid sites should be better than at semiarid sites.

Bridging Thermal Infrared Sensing and Physically‐Based Evapotranspiration Modeling: From Theoretical Implementation to Validation Across an Aridity Gradient in Australian Ecosystems

Thermal infrared sensing of evapotranspiration (E) through surface energy balance (SEB) models is challenging due to uncertainties in determining the aerodynamic conductance (gA) and due to inequalities between radiometric (TR) and aerodynamic temperatures (T0). We evaluated a novel analytical model, the Surface Temperature Initiated Closure (STIC1.2), that physically integrates TR observations into a combined Penman-Monteith Shuttleworth-Wallace (PM-SW) framework for directly estimating E, and overcoming the uncertainties associated with T0 and gA determination. An evaluation of STIC1.2 against high temporal frequency SEB flux measurements across an aridity gradient in Australia revealed a systematic error of 10–52% in E from mesic to arid ecosystem, and low systematic error in sensible heat fluxes (H) (12– 25%) in all ecosystems. Uncertainty in TR versus moisture availability relationship, stationarity assumption in surface emissivity, and SEB closure corrections in E were predominantly responsible for systematic E errors in arid and semi-arid ecosystems. A discrete correlation (r) of the model errors with observed soil moisture variance (r 5 0.33–0.43), evaporative index (r 5 0.77–0.90), and climatological dryness (r 5 0.60–0.77) explained a strong association between ecohydrological extremes and TR in determining the error structure of STIC1.2 predicted fluxes. Being independent of any leaf-scale biophysical parameterization, the model might be an important value addition in working group (WG2) of the Australian Energy and Water Exchange (OzEWEX) research initiative which focuses on observations to evaluate and compare biophysical models of energy and water cycle components. Plain Language Summary Evapotranspiration modeling and mapping in arid and semi-arid ecosystems are uncertain due to empirical approximation of surface and atmospheric conductances. Here we demonstrate the performance of a fully analytical model which is independent of any leaf-scale empirical parameterization of the conductances and can be potentially used for continental scale mapping of ecosystem water use as well as water stress using thermal remote sensing satellite data.