Environmental changes affect picoplanktonic composition in Antarctic Peninsula ponds

Antarctic Peninsula is experiencing one of the largest global warming events worldwide.Shallow water bodies generated by the melting of snow in summer are numerous,and they might act as sentinels of climate change due to their rapid response and ability to integrate catchment information.Shifts in climate can influence the structure of microbial communities which dominate these freshwaters ecosystems.Here,we characterize three ponds at Cierva Point(Antarctic Peninsula)by examining their physico-chemical and morphological characteristics and we explored how different factors modify the structure of the microbial community.We studied the abundance and biomass of heterotrophic bacteria,picocyanobacteria and picoeukaryote algae during January and February of two consecutive summers(2017 and 2018).We found that ponds had different limnological characteristics,due to their location,geomorphological features and presence of the surrounding flora and fauna.Physico-chemical parameters as well as microbial community differed between ponds,months and years.In 2017,most ponds were oligo to mesotrophic states.The larger accumulated rainfall(as a result of environmental changes on the Antarctic Peninsula)during 2018,particularly in February,causes nutrient runoff into water bodies.This affects those ponds with the highest seabird circulation,such as gentoo penguin,increasing eutrophication.As a result,picoplanktonic abundances were higher,and the community structure shifts to a largely heterotrophic bacteria dominated one.These results suggest that these communities could act as sentinels to environmental changes,anticipating a future with mostly hypertrophic ponds.

Impacts of brood parasitism by shiny cowbird Molothrus bonariensis on the breeding success of a small host, the black-backed water tyrant Fluvicola albiventer

The shiny cowbird Molothrus bonariensis parasitizes many species with different life-history traits and has a detrimental effect on the survival of the progeny of the hosts.In response,hosts have developed numerous antiparasitic defenses.Here,we examined the effects of brood parasitism by shiny cowbird on the clutch and brood sizes(83 nests)in a small host,the black-backed water tyrant Fluvicola albiventer.We also studied whether the death of parasite nestlings was related to the care of the foster parents and whether the host had any antiparasitic defense against the shiny cowbird.Our results indicate that brood parasitism significantly decreased the host hatching and fledging successes.The majority of nest failures(57%)were caused by brood parasitism.Shiny cowbird parasitism occurred in 52%of nests and the intensity of parasitism was 1.23±0.53 eggs per parasitized nest.Of the total host eggs,54%were damaged.During the incubation stage,20 nests(47%)were abandoned because of egg punctures by shiny cowbirds females.Only two parasitic fledglings were recorded,while the remaining nestlings either died from starvation(n=12)or predation(n=3).Foster parents abandoned parasitic nestlings between 5 and 10 days old.Our findings demonstrate that the shiny cowbird has very low rates of fledging success when parasitizing black-backed water tyrant.Also,parasitism had a high reproductive cost in the black-backed water tyrant because a very low proportion(7%)of the parasitized nests(n=43)were successful.

树种菌根类型通过细根生物量和凋落物动态影响土壤呼吸和土壤碳储存

热带森林是高生产力但同时也是脆弱的生态系统之一。一些全球范围的造林项目计划未来十年在热带地区种植数百万棵树。树种菌根类型影响森林土壤碳储存已成为共识,但在热带地区,树种菌根类型如何影响土壤呼吸(Rs)和碳储存,目前仍知之甚少。为研究树种菌根类型对Rs和土壤碳储存的影响,本实验在一个近30年热带同质园的3种丛枝菌根(AM)树种和3种外生菌根(EM)树种的单种林中,测量了其Rs和表层20 cm的碳含量,以及有关的生物因子(如根生物量、凋落物动态、土壤微生物)和非生物因子(如微气候)。研究结果表明,AM单种林的Rs、土壤碳含量,以及凋落物周转速率和细根生物量显著高于EM单种林。分析表明,与其他生物和非生物因子比较,树种菌根类型对Rs和土壤碳含量的影响最大。进一步分析表明,菌根类型是通过细根生物量和凋落物动态(凋落物产量、凋落物现存量、凋落物周转速率)直接和间接影响Rs和土壤碳含量。本研究结果强调了树种菌根类型对森林碳循环的影响,表明在热带地区种植AM树种可能比种植EM树种更能促进土壤固碳。

Abiotic and biotic drivers of struvite solubilization in contrasting soils

Phosphorus(P) limitation in the coming decades calls for the utilization of alternative fertilizers in agriculture. Struvite is a promising P source, but its potential role as a fertilizer is dependent on different physical, chemical, and biological properties, which are very heterogeneous in soil, complicating the prediction of the best soil conditions for its application. Here, we evaluated the solubility of struvite in soil, its redistribution into P fractions, and its potential abiotic and biotic drivers in 62 globally distributed soils with contrasting properties through an incubation assay. We found that after 40 d, about 35% of struvite P was redistributed into soil fractions more accessible to plants and microbes. Phosphorus redistribution from struvite was driven by a complex suite of soil physical, chemical, and microbial properties as well as environmental factors that varied across soils. Soil texture played a critical role in determining the redistribution of P in struvite-amended soils in soluble(H2O extraction), labile(NaHCO3 extraction), and moderately labile(NaOH extraction) fractions.In addition, the soil solution cation concentration was one of the most important drivers of available struvite-derived P fractions. The great importance of texture and cations in determining struvite-derived P fractions in soil was contrasted with the relatively minor role of pH. At the microbial level, the number of bacterial operational taxonomic units(OTUs) from the unfertilized soils that correlated with struvite-derived P fractions was higher than that of fungi. The number of OTUs that correlated with the struvite-derived soluble P fraction was dominated by fungi, whereas the number of OTUs that correlated with the struvite-derived labile P fraction was dominated by bacteria. Overall, this study provided a predictive framework for the potential use of struvite as a P fertilizer in contrasting soils.