IntroductionClimate change is predicted to intensify droughts in tropical regions. However, the extent to which drought intensification and the subsequent changes in root exudate (RE) composition reshape soil prokaryotic communities (SPC) remains poorly understood.MethodsWe conducted a 69-day incubation to determine the effects of repeated exposure to severe drought and RE application on the SPC activity and structure in soils under old-growth forests and pastures from southwestern Amazonia. At the beginning of each cycle, microcosms received either artificial RE solution or sterile water; following drying, microcosms were either kept at 30% water holding capacity (WHC) for 18 days, representing the regional WHC in the dry season, or at 5% WHC, simulating severe drought.ResultsDrought intensity and RE availability were the primary drivers of changes in SPC composition and activity. The lowest prokaryotic diversity values were observed in the severe drought treatment with +RE addition for both land-uses. After wetting, +RE microcosms showed higher SPC activity due to the utilization of the supplemented REs. Carbon availability interacted with land-use specific characteristics and partially buffered drought effects on SPC composition in pastures. The SPCs from both land-uses were well-adapted to regional drought conditions. However, repeated severe drought caused significant community shifts towards dominance of a few drought-resistant families.DiscussionIntensifying droughts can reduce prokaryotic diversity and reassemble tropical soil communities toward drought-tolerant taxa, with RE inputs amplifying pos-wetting activity yet exacerbating diversity losses under severe stress. Such changes may compromise ecosystem stability and soil functions under future precipitation regimes.

The Earth's surface is in constant change due to biotic and abiotic processes. During the last decades awareness arose that these biotic and abiotic processes might intensely interfere. Biogenic weathering, the acceleration of mineral weathering by autotroph-symbiont couples fuelled by photoassimilates for the sake of an equilibrated nutrient supply of involved biota, potentially drives denudation rates at ecosystem level. Our experiment aimed to examine how aridity affects biogenic weathering. The study was conducted along a gradient in Chile from humid to hyperarid climate (Atacama Desert), where photoassimilate production is increasingly limited by water stress. We hypothesize that biogenic weathering would cease if a threshold between element loss from denudation and energy demand for additional nutrient element mobilization by biogenic weathering is crossed, as competition between life for these elements becomes less intense when water supply limits biomass growth increasingly. We buried mesh bags containing freshly broken minerals, including biotite, muscovite and apatite along the gradient in Chile on granitic bedrock. Unexpectedly and in contrast to our initial hypothesis, we found that mineral weathering rates driven by mycorrhizal fungi under arid conditions were even proportionally higher, indicating a comparatively higher investment of photoassimilates into biogenic weathering by desert plants than by mediterranean, suggesting an adaptive mechanism. Additionally, biogenic weathering occurred at constant rates over a depth of up to 2.3 m, illustrating the constant mining of mycorrhizal fungi, irrespective of overall biological activity along the soil profile. The relative importance of biogenic weathering in arid climates furthermore points towards a fundamental function of biogenic weathering beyond nutrient mobilization by suggesting a regulatory role in overcoming long periods of missing soil water that prevent nutrient exchange from the soil matrix.

Quickly identifying and characterizing isolates from extreme environments is currently challenging while very important to explore the Earth ' s biodiversity. As these isolates may, in principle, be distantly related to known species, techniques are needed to reliably identify the branch of life to which they belong. Proteotyping these environmental isolates by tandem mass spectrometry offers a rapid and cost-effective option for their identification using their peptide profiles. In this study, we document the first high-throughput proteotyping approach for environmental extremophilic and halophilic isolates. Microorganisms were isolated from samples originating from high-altitude Andean lakes (3700-4300 m a.s.l.) in the Chilean Altiplano, which represent environments on Earth that resemble conditions on other planets. A total of 66 microorganisms were cultivated and identified by proteotyping and 16S rRNA gene amplicon sequencing. Both the approaches revealed the same genus identification for all isolates except for three isolates possibly representing not yet taxonomically characterized organisms based on their peptidomes. Proteotyping was able to indicate the presence of two potentially new genera from the families of Paracoccaceae and Chromatiaceae/Alteromonadaceae, which have been overlooked by 16S rRNA amplicon sequencing approach only. The paper highlights that proteotyping has the potential to discover undescribed microorganisms from extreme environments.

Diverse microbiota inhabit some of Earth's most extreme arid regions, enduring in environments where survival seems improbable. Despite numerous reports of microorganisms across the Atacama Desert—the oldest and driest desert on Earth—our understanding of how they adapt to extreme conditions in its hyperarid core remains limited. Prior systematic studies of the hyper-arid core have relied upon targeted gene sequencing (e.g., 16S rDNA), limiting inference of microbial community structure and function. Here we show that a diverse core group of microbes can be found in the hyperarid core, enabled by processing of large sample volumes linked to low-input metagenomic sequencing of 50 soil samples along a 450 km south-north transect. Linking gene function to soil geochemistry revealed a tipping point related to potential adaptive strategies. Our findings challenge the notion that microbial activity in the hyperarid core is predominantly transient. Among the diversity of metabolic pathways detected, we found evidence of gene circuits that encode proteins capable of using atmospheric trace gases to produce metabolic water and generate energy. Growing evidence of this previously under-recognized capability may extend the known range of habitability for soil microbial communities, with implications for the search for life beyond Earth, such as on Mars or arid exoplanets.

Despite knowing better, water-stable aggregates like pseudosands are still disintegrated into their clay- and silt-sized bits and pieces to serve standardization in texture determination. Lacking yet a viable alternative, this deliberately committed mistake seems the contemporary best practice for modeling purposes, which is far from being ideal. Here, we propose this misconception to be a major cause for flawed process understanding of tropical soils, leading to substantial uncertainties in model development. There is enough evidence as to why pseudosands are neither sand nor the plain sum of their clay- and silt-sized units and should therefore better be defined as an additional soil texture class for which properties have yet to be examined across the tropics.

Understanding the behavior of water in extreme environments is crucial in assessing its habitability potential. This study investigates the water uptake and release of nitrate and nitrate salt mixtures under Martian and Atacama Desert-like conditions. The Atacama serves as a Mars analogue due to its hyper-arid climate and shared salt composition. This study determines deliquescence and efflorescence relative humidities (DRH and ERH, respectively) for pure magnesium nitrate hexahydrate (Mg(NO3)(2)6H(2)O) as a function of temperature and perchlorate/nitrate mixtures at various ratios at 248 K. Finally, the effects of magnesium sulfate anhydrous (MgSO4) on Mg(NO3)(2)6H(2)O are also investigated. Pure Mg(NO3)(2) DRH varied with temperature (80% RH at 223 K to 63% at 268 K), while ERH remained constant at 24% RH across temperatures. When mixed with perchlorate, the DRH values were lowered, reaching values close to 40% RH. The less deliquescent MgSO4 had minimal impact on Mg(NO3)(2) water uptake when mixed in equimolar ratios. The laboratory DRH conditions did not align with conditions found on Mars, indicating that the salt mixtures are unlikely to deliquesce under Martian conditions found at Gale Crater. However, the warmer temperatures of the Atacama may favor water uptake. Therefore, the DRH and ERH data were applied to two sites in the Atacama. Conditions in the Atacama support water uptake by nitrates in the fall/winter seasons, allowing for the possibility of metastable brines persisting for extended periods. Thus, although nitrates may enhance habitability in the Atacama, they may play less of a role in habitability on Mars.

IntroductionEukaryotic algae in the top few centimeters of fellfield soils of ice-free Maritime Antarctica have many important effects on their habitat, such as being significant drivers of organic matter input into the soils and reducing the impact of wind erosion by soil aggregate formation. To better understand the diversity and distribution of Antarctic terrestrial algae, we performed a pilot study on the surface soils of Meseta, an ice-free plateau mountain crest of Fildes Peninsula, King George Island, being hardly influenced by the marine realm and anthropogenic disturbances. It is openly exposed to microbial colonization from outside Antarctica and connected to the much harsher and dryer ice-free zones of the continental Antarctic. A temperate reference site under mild land use, SchF, was included to further test for the Meseta algae distribution in a contrasting environment.MethodsWe employed a paired-end metabarcoding analysis based on amplicons of the highly variable nuclear-encoded ITS2 rDNA region, complemented by a clone library approach. It targeted the four algal classes, Chlorophyceae, Trebouxiophyceae, Ulvophyceae, and Xanthophyceae, representing key groups of cold-adapted soil algae.ResultsA surprisingly high diversity of 830 algal OTUs was revealed, assigned to 58 genera in the four targeted algal classes. Members of the green algal class Trebouxiophyceae predominated in the soil algae communities. The major part of the algal biodiversity, 86.1% of all algal OTUs, could not be identified at the species level due to insufficient representation in reference sequence databases. The classes Ulvophyceae and Xanthophyceae exhibited the most unknown species diversity. About 9% of the Meseta algae species diversity was shared with that of the temperate reference site in Germany.DiscussionIn the small portion of algal OTUs for which their distribution could be assessed, the entire ITS2 sequence identity with references shows that the soil algae likely have a wide distribution beyond the Polar regions. They probably originated from soil algae propagule banks in far southern regions, transported by aeolian transport over long distances. The dynamics and severity of environmental conditions at the soil surface, determined by high wind currents, and the soil algae’s high adaptability to harsh environmental conditions may account for the high similarity of soil algal communities between the northern and southern parts of the Meseta.

<p class="p1">Losses in above- and belowground biodiversity are linked to changes in land use practices and immediately affect processes in the upper soil horizons. Theoretically, these superficial changes are reversible unless a tipping point on an ecosystem level was crossed. This safety net of functional redundancy facilitates the return of vital soil functions and processes to the initial state. Little is known about how deep these changes have reached into the subsoil over time, because early warning indicators of a tipping point being about to be crossed are still sparse. This is especially important for the tropics, as soils are typically intensively weathered and nutrient depleted, therefore, plants relying largely on nutrients from below. Net nitrous oxide (N<span class="s1"><sub>2</sub></span>O) emission rates from the soil surface have proved to be valid proxies for detecting the crossing of tipping points in soil biogeochemistry. Here, we advanced this approach by looking deeply into the soil and reveal that potential greenhouse gas (GHG) production and consumption are useful proxies to estimate how deep the loss of aboveground biodiversity has already impacted soil microbial processes. We performed incubation experiments on forest and pasture soils stemming from shallow as well as 1 m deep profiles from the Peruvian Amazon Basin to determine the production and consumption potential of the GHGs at different water holding capacities. We expected pasture soils to have lost direct carbon(C)-related connections to deeper soil horizons. In forests, roots with different and greater depths also connect deeper soil layers. Therefore, in greater depth, carbon dioxide (CO<span class="s1"><sub>2</sub></span>) production declined faster under pastures than under forests because C limitations are reached sooner. In the surface, grasses are well known for their input of C and increased CO<span class="s1"><sub>2</sub></span> production. Since old pastures are limited in nitrogen (N), almost no N<span class="s1"><sub>2</sub></span>O should be produced, possibly increasing the potential to take up N<span class="s1"><sub>2</sub></span>O. However, denitrification is a heterotrophic process also dependent on available C, therefore, the potentials of N<span class="s1"><sub>2</sub></span>O production and consumption in deeper forest soils were larger with increasing water holding capacity. These findings could indicate that losses in aboveground biodiversity due to forest conversion can have profound impacts on soil microbial processes, extending also to deeper soil layers while altering the connection of the subsoil to the top.</p>

Humans play an interconnecting role in social-ecological systems (SES), they are part of these systems and act as agents of their destruction and regulation. This study aims to provide an analytical framework, which combines the concept of SES with the concept of tipping dynamics. As a result, we propose an analytical framework describing relevant dynamics and feedbacks within SES based on two matrixes: the “tipping matrix” and the “cross-impact matrix.” We take the Southwestern Amazon as an example for tropical regions at large and apply the proposed analytical framework to identify key underlying sub-systems within the study region: the soil ecosystem, the household livelihood system, the regional social system, and the regional climate system, which are interconnected through a network of feedbacks. We consider these sub-systems as tipping elements (TE), which when put under stress, can cross a tipping point (TP), resulting in a qualitative and potentially irreversible change of the respective TE. By systematically assessing linkages and feedbacks within and between TEs, our proposed analytical framework can provide an entry point for empirically assessing tipping point dynamics such as “tipping cascades,” which means that the crossing of a TP in one TE may force the tipping of another TE. Policy implications: The proposed joint description of the structure and dynamics within and across SES in respect to characteristics of tipping point dynamics promotes a better understanding of human-nature interactions and critical linkages within regional SES that may be used for effectively informing and directing empirical tipping point assessments, monitoring or intervention purposes. Thereby, the framework can inform policy-making for enhancing the resilience of regional SES.

Studies of hyper‐arid sites contribute to our understanding on how life adapted to extreme conditions. They are often used to further deduce implications for extraterrestrial biology by the so‐called analogue site‐approach. The Atacama Desert, Chile, is one of the most prominent analogue sites despite its neighboring productive ecosystems due to its hyper‐aridity and geochemical features resembling Martian environments. We hypothesize that many drivers of extremophile life in analogue sites are only mistakenly attributed to aridity alone, thus obscuring a clear view of the far more complex process interactions originating in nearby earthly ecosystems. To test this, we investigated 54 soil profiles up to 60 cm of soil depth along of four transects in the Atacama Desert, either running parallel (S‐N) or perpendicular (W‐E) to the Andes. Our objective was to reveal the processes controlling the formation of soil organic carbon (SOC) as the most reliable proxy for microbial life in order to understand the boundary conditions of life in extreme habitats. Further, we aimed at identifying analogue sites as uncompromised as possible by external influences of for example, vegetated or marine ecosystems. We found a mixture of influences driving habitable conditions on gradients perpendicular to the Andes, for example, fog and precipitation scavenging caused by altitudinal variations and differing proximity to the Pacific Ocean, while transects parallel to the Andes were much less biased by external factors. Our results show that studies on life under extreme conditions should clarify the explanatory strength of the investigated factors by a gradient study approach.

The western Amazon is particularly sensitive to drought since precipitation is common even during "dry season". The combination of increasing land use pressure and droughts due to climate change makes the scenario of this ecosystem likely to cross or having crossed tipping points. We argue that nitrous oxide (N2O) emissions can be used to identify the crossing of tipping points in soils, particularly those related to N-cycling. This hypothesis is being tested within the BMBF funded Project PRODIGY, which will show that under stress microbial functional diversity in soils are a safety-net for ecosystems. The survey area (MAP) spreads across three countries (Peru, Brazil and Bolivia). Lab and field experiments are used to test our hypothesis based on the observations that N2O emission under tropical pasture shift after 10 years in use. Pre-measurement modeling is used to optimize measurement designs. Replicated above-ground biodiversity levels (n=4) will be sampled in each country. The soil will also be used for lab drought manipulation experiments to unravel underlying mechanisms. Measured values have shown to be lower than expected and simulated rates. Maybe because tipping points at different spacial and temporal scales are crossed faster than in temperate regions and biogeochemistry is less understood? Results from this investigation will allow the improvement of N2O models for tropical soils.

Global warming in the Antarctic Peninsula, Maritime Antarctica, within the past 45 years has accelerated rapid glacier retreatment, forming temporal gradients of soil development that concurs with the colonization of the ice-free soils by phototrophs. In the past decade the paradigm emerged that above- and belowground processes are interconnected, e.g. recently gained carbon fuels microbial activity and thus drives soil organic matter built-up and decomposition as well as mineral weathering. Studies of carbon allocation for Antarctic ecosystems, occurring in harsh conditions are lacking. Little is also known about the contribution of bacteria and fungi to decomposition of different soil carbon pools with different turnover rates in these soils, which is of utmost importance for the prediction of the future feedback of the Antarctic carbon balance to climate change. We followed soil horizon formation, soil organic carbon accumulation and carbon exchange with the atmosphere along a gradient of phototrophs of different trophic complexity level at King George Island by combining soil chemical analyses, field CO2 flux measurements, C-13 in situ labeling and molecular methods (PLFA and metabolomics). Our study revealed that colonization of the ice-free soils by vascular plant (Deschampsia antarctica) was leading to the formation of well-developed soil, with high contents of organic carbon and with a relatively high rates of photosynthesis and CO2 soil efflux. The soils sampled under D. antarctica showed the impact of this higher plant on the soil organic matter, containing significantly higher amounts of carbohydrates and amines, presumably as a result of root exudation. As determined by the C-13 labeling experiment more than 15% of the carbon recently assimilated by D. antarctica was transferred belowground, with a major flow into soil fungi. This suggests that not bacteria, but rather fungi preferentially and faster utilize the recently assimilated low molecular compounds allocated to the soil. Probably, successful performance of vascular plants in Maritime Antarctica may significantly foster biological weathering via enhanced microbial activity.

Climate warming is severely affecting maritime Antarctica, causing accelerated glacier retreat and thus leading to an ongoing exposure of once ice- covered land. This initiates a succession of plant and soil development. Nevertheless, the temporal dynamics and controlling factors of these processes, like C and N status of soils and the effect of root exudation are widely unknown under these harsh climatic conditions. Topsoil samples from three different sites of a chronological soil sequence in the forefront of a retreating glacier of the Fildes Peninsula, King George Island, were collected and incubated at 2 °C for three weeks. To mimic the influence of C and N containing root exudates (primers) on the mineralization of soil C, we added 13C labeled glucose or alanine and compared CO2 evolution in comparison to samples without C and N addition. Soil microbes covered up to 90% of their C demand for anabolic functions with the added C-sources in the case of late soil successions while it was only 50% for the young soils. These findings were independent of the form of primer. Both primers increased the mineralization of soil carbon in the young soils as compared to the control. For the later stages of soil development, we found negative priming which was strongest for the latest stage. These results give evidence for a clear shift in the microbial community of the three investigated sites. While sites with initial soil formation seem to be dominated by k-strategists with low turnover rates that rather use complex C-sources, a significant number of r-strategists in the soils of the older sites uses simple C-substrates very efficiently. As this leads to a relative decrease in SOM mineralization for the late stages of soil development, it is questionable if higher plants can improve their nutrition by stimulating free living soil microbes with root exudates or if they rather have to rely on mycorrhiza.

In many pristine ecosystems there seems to be negative nutrient budget existent, meaning that export exceeds the input received by aeolian deposition and physico-chemical weathering. Such ecosystems should degrade rather quickly, but are often found surprisingly stable on the long run. Our hypothesis was that this nutrient gap is an artefact caused by not considering the contribution of photoassimilatory-mediated biogenic weathering to the overall nutrient input, which might constitute an additional, energetically directed and demand driven pathway. Here, we firstly evaluated the evolution of mutualistic biogenic weathering along an Antarctic chronosequence and secondly compared the biogenic weathering rates under mycorrhized ecosystems over a global gradient of contrasting states of soil development. We found the ability to perform biogenic weathering increasing along its evolutionary development in photoautotroph-symbiont interaction and furthermore a close relation between fungal biogenic weathering and available potassium across all 16 forested sites in the study, regardless of the dominant mycorrhiza type (AM or EM), climate, and plant-species composition. Our results point towards a general alleviation of nutrient limitation at ecosystem scale via directional, energy driven and on-demand biogenic weathering.

Background: Maritime Antarctica is severely affected by climate change and accelerating glacier retreat forming temporal gradients of soil development. Successional patterns of soil development and plant succession in the region are largely unknown, as are the feedback mechanisms between both processes. Here we identify three temporal gradients representing horizontal and vertical glacier retreat, as well as formation of raised beaches due to isostatic uplift, and describe soil formation and plant succession along them. Our hypotheses are (i) plants in Antarctica are able to modulate the two base parameters in soil development, organic C content and pH, along the temporal gradients, leading to an increase in organic carbon and soil acidity at relatively short time scales, (ii) the soil development induces succession along these gradients, and (iii) with increasing soil development, bryophytes and Deschampsia antarctica develop mycorrhiza in maritime Antarctica in order to foster interaction with soil.Results: All temporal gradients showed soil development leading to differentiation of soil horizons, carbon accumulation and increasing pH with age. Photoautptroph succession occurred rapidly after glacier retreat, but occurrences of mosses and lichens interacting with soils by rhizoids or rhizines were only observed in the later stages. The community of ground dwelling mosses and lichens is the climax community of soil succession, as the Antarctic hairgrass D. antarctica was restricted to ornithic soils. Neither D. antarctica nor mosses at the best developed soils showed any sign of mycorrhization.Conclusion: Temporal gradients formed by glacier retreat can be identified in maritime Antarctic, where soil development and plant succession of a remarkable pace can be observed, although pseudo-succession occurs by fertilization gradients caused by bird feces. Thus, the majority of ice-free surface in Antarctica is colonized by plant communities which interact with soil by litter input rather than by direct transfer of photoassimilates to soil.