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Strategies shrubby junipers adopt to tolerate drought differ by site

Drought-induced dieback episodes are globally reported among forest ecosystems but they have been understudied in scrublands. Chronically-stressed individuals are supposed to be more vulnerable prior to drought which triggers death. Drought-triggered dieback and mortality events affecting Mediterranean Juniperus phoenicea scrublands were analyzed in two sites with contrasting climate and soil conditions located in Spain. The radial growth patterns of coexisting living and dead junipers, including the calculation of growth statistics used as early-warning signals, quantified growth response to climate, were characterized and the wood C and O isotope discrimination was analyzed. In the inland, continental site with rocky substrates (Yaso, Huesca, N Spain), dead junipers grew less than living junipers about three decades prior to the dieback started in 2016. However, in the coastal, mild site with sandy soils (Doñana, Huelva, SW Spain), dead junipers were smaller but grew more than living junipers about two decades before the dieback onset in 2005. The only common patterns between sites were the higher growth coherence in both living and dead junipers prior to the dieback, and the decrease in growth persistence of dead junipers. Cool and wet conditions in the prior winter and current spring, and cool summer conditions enhanced juniper growth. In Doñana, growth of living individuals was more reduced by warm July conditions than in the case of dead individuals. Higher ?13C values in Yaso indicate also more pronounced drought stress. In Yaso, dead junipers presented lower ?18O values, but the opposite occurred in Doñana suggesting different changes in stomatal conductance prior to death. Warm summer conditions enhance evapotranspiration rates and trigger dieback in this shallow-rooted species, particularly in sites with a poor water-holding capacity. Chronic, slow growth is not always a reliable predictor of drought-triggered mortality. informacion[at]ebd.csic.es: Camarero et al (2020) Dieback and mortality of junipers caused by drought: Dissimilar growth and wood isotope patterns preceding shrub death. Agr Forest Meteorol 291, 108078. DOI 10.1016/j.agrformet.2020.108078


https://www.sciencedirect.com/science/article/pii/S0168192320301805?dgcid=author#ack0001
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Parasites help brine shrimp cope with arsenic habitat contamination

Parasites help brine shrimp cope with arsenic habitat contamination

Do parasites weaken their hosts' resilience to environmental stress? Not always, according to this study. Rather than weakening its brine shrimp intermediate host, tapeworm infection enhances the shrimps' ability to cope with arsenic contamination in the water, and the same holds true in the warmer waters predicted by climate change models. Brine shrimps were collected from a highly polluted estuary in Spain and their infection status with tapeworm larvae was determined. Samples were used for toxicity testing with arsenic. To their surprise, the researchers found that infected shrimp were consistently more resistant to arsenic than uninfected ones. This was true not only at 25 degrees Celsius (the temperature under which both samples were tested), but also at 29 degrees (tested on some of the shrimp from the larger May sample). Overall, the 4-degree increase—consistent with current climate-change predictions for the change in mean temperature—made the shrimp more vulnerable to arsenic toxicity. To examine how parasite infection might protect the shrimp against arsenic toxicity, the researchers collected another sample from the same location in May 2015. Infection details were similar to the May 2014 sample. Comparing infected and uninfected Artemia, they found increased numbers of fat-containing droplets in the infected shrimp. Parasite infection was also associated with significant changes in oxidative stress markers. Lipids such as those in lipid droplets are thought to be able to protect organisms against pollutants by sequestering toxins away from sensitive target sites—a principle known as 'survival of the fattest'. Regarding oxidative stress, the researchers speculate that the tapeworm parasites benefit from healthy intermediate hosts with high chances of becoming tasty food for flamingos, grebes and other final avian hosts. This study provides the first empirical evidence that parasites can increase resistance to metal or metalloid pollution, rather than decrease it. It is also the first study to consider the influence of temperature change on parasite-pollutant interactions. Results contradict the pre-existing view that pollution and parasites are stressors that both have negative effects on the health of free living organisms. informacion[at]ebd.csic.es: Sánchez et al (2016) When parasites are good for health: cestode parasitism increases resistance to arsenic in brine shrimps. PLoS Pathog 12(3): e1005459. doi:10.1371/journal.


http://dx.plos.org/10.1371/journal.ppat.1005459