Lower Mean Annual Precipitation Research Articles

Meta-analysis on the Effects of Nitrogen Addition on Soil Organic Carbon Content in Terrestrial Ecosystems

Several studies have demonstrated that the increased deposition of nitrogen(N) has significantly affected the content of soil organic carbon(SOC); however, the change significantly varies in different regions. In this study, Meta-analysis, Meta-regression, and linear regression were performed to systematically evaluate the effects of climate, soil properties, and field design factors on the responses of SOC to N addition based on 408 data points from 49 field experiments in China. The results revealed that the response of SOC to N addition was significantly positively correlated with the mean annual temperature(MAT) and mean annual precipitation(MAP) of the sample sites(P<0.05). In the regions with lower MAT(<3℃) or MAP(<500 mm), SOC significantly decreased after N addition. In the areas with higher MAT(>3℃) or MAP(>500 mm); however, SOC significantly increased. For soil properties, SOC significantly accumulated after N addition in the plots with a higher soil C:N ratio(>15) or acidic soil(pH<6.5) but less changed in the plots with a lower C:N ratio(≤ 15) or higher pH(≥ 6.5). For ecotype, after N addition, SOC decreased significantly in the grassland ecosystem(-5.34%) but less changed in the wetland ecosystem. SOC accumulated the most after N addition in the forest ecosystem(10.52%), particularly in the broad-leaved forest ecosystem(13.10%). Further analysis showed that the soil C:N ratio was the most important factor. For type of N application, the addition of ammonium nitrate or urea increased the SOC content significantly, but the effect of nitrate was not significant. In summary, when accurately evaluating, predicting, and analyzing the effects of N addition on SOC content, the effects of climatic characteristics and soil properties of sample sites and field design factors should be comprehensively considered.

Patterns and consequences of invasion of tropical montane forests by Cestrum aurantiacum Lindl. in the Western Ghats

In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics.

Identifying the Influencing Factors of Plastic Film Mulching on Improving the Yield and Water Use Efficiency of Potato in the Northwest China

Potato is an important crop in the Northwest China, however, its production is constrained by water scarcity. Plastic mulching film is an efficient technical measure to alleviate potato production restrictions. Therefore, studying the response of potato yield and water use efficiency to plastic mulching film is of great significance. The study conducted a meta-analysis to quantify the effect of plastic film on potato yield and water use efficiency in the Northwest. The study then quantified the effects of different levels of natural conditions (mean annual precipitation, mean annual accumulated temperature ≥ 10 °C), fertilizer application (nitrogen fertilizer, phosphate fertilizer, potassium fertilizer), cultivation measures (planting density, cultivation method, mulching method), and mulching properties (mulching color, mulching thickness) through subgroups analysis. Finally, the random forest model was used to quantify the importance of factors. Plastic film mulching increased yield by 27.17% and water use efficiency by 27.16%, which had a better performance under relatively lower mean annual precipitation, low mean annual accumulated temperature ≥ 10 °C, relatively lower fertilizer application, planting density of 15,000–45,000 plants·ha−1, ridge, and black mulching. Natural conditions, fertilization measures were vital to improve productivity. The research results can provide reference for agricultural management strategies of potato cultivation using plastic film in the Northwest China and other potato-producing areas.

Rapid drought-recovery of gas exchange in Caragana species adapted to low mean annual precipitation.

While variation in mean annual precipitation (MAP) of the native habitat of a species has been shown to determine the ability of a species to resist a hydraulic decrease during drought, it remains unknown whether these variations in MAP also influence the ability of a species to recover and survive drought. Leaf hydraulic and gas exchange recovery following drought and the underlying mechanisms of these responses in six Caragana species from habitats along a large precipitation gradient were investigated during rehydration in a common garden. The gas exchange of species from arid habitats recovered more rapidly during rehydration after mild, moderate and severe drought stress treatments than species from humid habitats. The recovery of gas exchange was not associated with foliar abscisic acid concentration, but tightly related to the recovery of leaf hydraulic conductance (Kleaf ). The recovery of Kleaf was associated with the loss of Kleaf during dehydration under mild and moderate drought stress, and to leaf xylem embolism formation under severe drought stress. Results pointed to the different ability to recover in gas exchange in six Caragana species post-drought is associated with the MAP of the species in its native habitat.

The mechanisms of rapid seed germination in Caragana species adapted to low mean annual precipitation

The mechanisms of rapid seed germination in Caragana species adapted to low mean annual precipitation

Effects of canopy density on understory plant diversity in Robinia pseudoacacia plantations on the Loess Plateau of China

To solve the problems of understory plant shortage and biodiversity reduction caused by high tree density of Robinia pseudoacacia plantations on the Loess Plateau in northwest China, we analyzed the data collected by field survey and from literatures. We used the upper boundary line method to examine the impacts of canopy density on understory plant diversity. Based on field survey at the Guanshan Forest Farm of Jingchuan County of Gansu Pro-vince, the species number of understory plants in R. pseudoacacia plantations was higher than that in natural grassland (91 vs. 78). The dominant species varied with canopy density, which was completely different from that of natural grassland. A comprehensive analysis of both literature data and field survey data showed that, when mean annual precipitation (MAP) <550 mm or >550 mm, the increases in canopy density first led to a stable understory plant coverage and then a sharp or slight decrease, and understory plant biomass showed a sharp and continuous decrease or a slight increase and then decrease. Understory plant species richness and other diversity indices (Shannon, Simpson, and Pielou indices) first increase and then decrease, with bigger variation range under lower MAP. In all, the characteristics (coverage, biomass and species diversity, etc.) of understory plant community in R. pseudoacacia plantations were strongly affected by canopy density, with higher sensitivity under lower MAP. There was a general threshold range of canopy density of 0.45-0.6. When canopy density was above or below this thre-shold range, it would lead to a rapid decrease of the most characteristics of understory plant community. Therefore, keeping canopy density within the rational range of 0.45-0.6 in the management of R. pseudoacacia plantations is the key to make all the above-mentioned understory plant characteristics at relatively high level.

Late Holocene fire and precipitation history of the Kashmir Himalaya: Inferences from black carbon in lake sediments

Throughout the human history, fire, climate, and human advancement had a very complicated relationship. Scientists have explored this relationship using different proxies such as black carbon, polycyclic aromatic hydrocarbons, and charcoal. In this study, black carbon (BC) concentrations and its isotopic compositions (δ13CBC) in a sediment core from the Wular Lake, Kashmir (India) were measured to understand the interactions of fire and human development in the Kashmir Himalaya during the late Holocene. As revealed through radiocarbon dating, the sediment core covered the time span from 3752 to 306 Cal years BP. Two major climate phases in the region were identified based on the relationship between mean annual precipitation and δ13CBC. The first phase, from 3752 to 1500 Cal year BP, was characterised by low mean annual precipitation (dry climate), which transitioned into a wetter phase with higher mean annual precipitation after 1500 Cal year BP until 306 Cal year BP. Within the dry phase, a phase of extreme dryness and minimum precipitation around ∼2500 Cal years BP was observed. The variability in BC concentrations in the sediments revealed dynamic fire history in the Kashmir Himalaya with occurrences of high fire events around 3000 Cal years BP, which gradually declined until 1500 Cal year BP then increase again. Our results, in combination with available studies from the region, suggested that forest fires in the Kashmir Himalaya were dominantly human-driven than due to large scale climate change.

Comparative study of biomass and morpho-physiological traits for different deciduous species in semi-arid afforestation region of Mongolia

Afforestation practices are useful tools for rehabilitating degraded lands in many parts of the world, as well as in Mongolia for protecting soil, water resources, and the potential of carbon sequestration to mitigate climate change. And so, regular investigation was conducted to determine the response and adaptation of Populus sibirica, Ulmus pumila, and Hippophae rhamnoides in terms of growth characteristics and leaf morpho-physiological traits to suggest and select effective and sustainable afforestation methods to suit Mongolia’s conditions. We measured the root collar diameter (RCD), height growth, leaf area (LA), specific leaf area (SLA), leaf biomass (LB), chlorophyll concentration and leaf water potential (ψ) of the selected species. Results showed that P. sibirica (135.3±6.81cm) height growth, stem, root and total biomass were higher among the studied species, but leaf and branch biomass was higher in U. pumila (93.46±5.10cm). However, leaf morphological parameters and chlorophyll content was higher for P. sibirica (330.56±56.81µg/ml) compared with other species. Leaf water potential was found lower for U. pumila and higher in H. rhamnoides. Therefore, we suggest that U. pumila is more adaptable to low mean annual precipitation regions, requiring less water and H. rhamnoides provide good financial source for local community as they yield fruits. Our findings are relevant to ensuring the sustainability of afforestation programs in semiarid conditions in Mongolia.

Higher resistance and resilience of bacterial growth to drought in grasslands with historically lower precipitation

Climate change is expected to alter precipitation regimes, resulting in longer periods of drought and heavier precipitation events. Even though the direct effect of water availability on soil microbial processes is well documented, the influence of precipitation legacy on microbial resistance and resilience to drought remains unclear. Using soils from a natural mean annual precipitation (MAP) gradient (∼550–950 mm yr−1) equipped with long-term (>8 yr) rain-out shelters, we investigated how the history of precipitation influenced microbial ‘resistance’ (tolerance to drying) and ‘resilience’ (ability to recover growth rates following rewetting) to drought. We found that bacterial growth was more resistant and resilient to drought in sites with lower MAP. In contrast, the precipitation-reduction treatments had no detectable influence on microbial drought resistance or resilience. The microbial carbon-use efficiency immediately after rewetting was higher in soils from lower precipitation sites. In contrast, the steady-state microbial growth rates and respiration (under standardized moisture conditions) were consistent along the precipitation gradient. The variation in microbial drought resistance and resilience across the precipitation gradient was linked to the microbial community structure. Taken together, our results suggest that historical precipitation regimes – and the associated differences in exposure to drought – had selected for bacterial communities that were more resistant and resilient to drought.

Rare bacterial biosphere is more environmental controlled and deterministically governed than abundant one in sediment of thermokarst lakes across the Qinghai-Tibet Plateau.

Thermokarst lakes are widely distributed in cold regions as a result of ice-rich permafrost thaw. Disentangling the biogeography of abundant and rare microbes is essential to understanding the environmental influences, assembly mechanisms, and responses to climate change of bacterial communities in thermokarst lakes. In light of this, we assessed the abundant and rare bacterial subcommunities in sediments from thermokarst lakes across the Qinghai-Tibet Plateau (QTP). The operational taxonomic unit (OTU) richness was more strongly associated with location and climate factors for abundant subcommunities, while more strongly associated with physicochemical variables for rare subcommunities. The relative abundance of abundant and rare taxa showed opposite patterns with abundant taxa having greater relative abundance at higher latitude and pH, but at lower mean annual precipitation and nutrients. Both the abundant and rare subcommunities had a clear distribution pattern along the gradient of latitude and mean annual precipitation. Abundant subcommunities were dominantly shaped by dispersal limitation processes (80.9%), while rare subcommunities were shaped almost equally by deterministic (47.3%) and stochastic (52.7%) processes. The balance between stochastic and deterministic processes was strongly environmentally adjusted for rare subcommunities, while not associated with environmental changes for abundant subcommunities. The results shed light on biogeography patterns and structuring mechanisms of bacterial communities in thermokarst lakes, improving our ability to predict the influences of future climate change on these lakes.

Community-level trachoma ecological associations and the use of geospatial analysis methods: Asystematic review.

BackgroundTrachoma is targeted for global elimination as a public health problem by 2030. Understanding individual, household, or community-associated factors that may lead to continued transmission or risk of recrudescence in areas where elimination has previously been achieved, is essential in reaching and maintaining trachoma elimination. We aimed to identify climatic, demographic, environmental, infrastructural, and socioeconomic factors associated in the literature with trachoma at community-level and assess the strength of their association with trachoma. Because of the potential power of geospatial analysis to delineate the variables most strongly associated with differences in trachoma prevalence, we then looked in detail at geospatial analysis methods used in previous trachoma studies.MethodsWe conducted a systematic literature review using five databases: Medline, Embase, Global Health, Dissertations & Theses Global, and Web of Science, including publications from January 1950 to January 2021. The review protocol was prospectively registered with PROSPERO (CRD42020191718).ResultsOf 35 eligible studies, 29 included 59 different trachoma-associated factors, with eight studies also including spatial analysis methods. Six studies included spatial analysis methods only. Higher trachomatous inflammation—follicular (TF) prevalence was associated with areas that: had lower mean annual precipitation, lower mean annual temperatures, and lower altitudes; were rural, were less accessible, had fewer medical services, had fewer schools; and had lower access to water and sanitation. Higher trachomatous trichiasis (TT) prevalence was associated with higher aridity index and increased distance to stable nightlights. Of the 14 studies that included spatial methods, 11 used exploratory spatial data analysis methods, three used interpolation methods, and seven used spatial modelling methods.ConclusionResearchers and decision-makers should consider the inclusion and potential influence of trachoma-associated factors as part of both research activities and programmatic priorities. The use of geospatial methods in trachoma studies remains limited but offers the potential to define disease hotspots and areas of potential recrudescence to inform local, national, and global programmatic needs.

Paleoclimate instabilities during late Oligocene - Early Miocene in SW Europe from new geochemical climofunctions based on soils with pedogenic carbonate

In this study, two new climofunctions based on major elements are proposed from the study of 28 modern alluvial soils with pedogenic carbonate from NE Spain. The first climofunction relates a base ratio (CaO, K 2 O) to the mean annual temperature (MAT), and the second one the clayeness ratio (Al 2 O 3 /SiO 2 ) to the mean annual precipitation (MAP). In both climofunctions, the use of the parent material ratio as normalizer gave the best results, taking into account the natural variability of alluvial deposits. Application of these climofunctions to 86 paleosols from Oligo-Miocene alluvial successions in southern France and central Spain was performed, and combined with morphological functions previously proposed, with the aim to build detailed paleoclimatic data for this key period of climate history. This work provides a high frequency record (range of 10s to 100 s kyr) of paleoclimate fluctuations, with estimated MAP from both methods very comparable (mean ~ 550 mm/yr). Estimated MAT and MARP (mean annual range of precipitations) mainly exhibit the same trends: 1) high values followed by a rapid decrease during the early Aquitanian (from 18.8 to 13.5 °C; from 80 to 20 mm), 2) a warming trend towards the middle Aquitanian (up to 16.6 °C, 90 mm), 3) a cooling (down to 13.4 °C, 40 mm) during the late Aquitanian – early Burdigalian. Comparisons with paleoclimate data from paleontological remains indicate similar MAT and two times lower MAP estimated from paleosols. However, consistency between estimated MAP from this study to previous paleopedological investigations in NE Spain suggests a regional climate pattern (southern France and central Spain) precursor of the Mediterranean conditions that developed during middle Neogene whereas humid conditions prevailed in the western coastal basins of Europe. Periods of large amplitude fluctuations in MARP and MAT are interpreted as reflecting the interrelation between the lower Miocene climate instability (Mi1, Mi1a events) and continental climate. • geochemical climofunctions (MAP and MAT) are proposed from modern alluvial soils. • performed on paleosols with pedogenic carbonate from the Oligo-Miocene. • both functions can be applied to truncated paleosols. • high resolution climate record.

Effect of conservation tillage on crop yield and soil organic carbon in Northeast China: A meta‐analysis

AbstractNortheast China, the important grain‐producing region in China, is under threat from soil degradation because of long‐term conventional tillage (CT). The adoption of conservation tillage is anticipated to restore soil fertility, maintain crop yields and enhance sustainability. However, the integrated effects of conservation tillage practice on crop yields and soil organic carbon (SOC) remain unclear. In this meta‐analysis of peer‐reviewed studies conducted in the Northeast China region, we assess crop yields and SOC values under no‐till, ridge tillage and subsoiling tillage practices. The results indicate that in areas with mean annual temperatures (MAT) below 3°C, crop yields were significantly (p &lt; .05) higher under ridge tillage (0.8%) and subsoiling tillage (13.1%) compared with CT, whereas yields reduced under no‐till (−3.7%). Ridge tillage generally had a similar effect on crop yield as no‐till, without the negative impact in colder regions. We also report that no‐till practice increased SOC concentrations by 24.1%, 43.9% and 17.4% in areas of higher temperature (MAT &gt; 6°C), low mean annual precipitation (MAP) (&lt;500 mm) and continuous cropping conditions, respectively. Ridge tillage and subsoiling tillage also had positive effects on SOC concentrations (to a lesser degree than no‐till), indicating that conservation tillage can enhance SOC in Northeast China. Overall, the implementation of different conservation tillage measures in Northeast China was found to enhance crop yields and sequester carbon. We recommend that ridge tillage is used in colder areas and that subsoiling tillage is used in rotation with other tillage measures to maintain crop yields.

Spatial variation of global surface soil rock fragment content and its roles on hydrological and ecological patterns

Rock fragments (RFs, material particles with diameter > 2 mm) are widely distributed in soils over globe. However, spatial pattern of RF content (RFC) and its roles on hydrological and ecological patterns have remained unclear at the global scale. In this study, based on the collected global datasets, we investigated the relationships between mean annual temperature (MAT), mean annual precipitation (MAP), elevation and RFC at 0–5 cm soil depth. In addition, we also examined the links of RFC to representative hydrological and ecological indicators (soil water content or SWC, and normalized difference vegetation index or NDVI, respectively). Results showed that through affecting the pedogenic and morphogenic processes, temperature, precipitation and elevation presented significant relationships with RFC over the globe. When MAT < 20 ℃, RFC decreased with MAT increasing, due to that high temperature could promote RF weathering and thus soil production; while when MAT > 20 ℃, RFC slightly increased with MAT increasing, due to that extreme high temperature induced arid condition would surpass soil production. RFC decreased with MAP increasing, because precipitation increased SWC and hydrologic flow and thus enhanced soil production. In addition, higher elevation zones usually had colder condition and greater loss of fine-textured soils due to erosion, and thus RFC increased with elevation increasing. Furthermore, a RFC threshold of about 0.2 m3 m−3 was identified. When RFC < 0.2 m3 m−3, existence of RFs may improve the soil pore structure and thus water and nutrient retention capacity. Therefore, higher SWC and NDVI were observed. However, when RFC > 0.2 m3 m−3, due to poor soil water and nutrient retention capacity, as well as lower MAT with higher elevation, or lower MAP, lower SWC and NDVI were observed. These findings can supplement the lack of knowledge on RFs and its effects from the global perspective.

Global patterns of leaf construction traits and their covariation along climate and soil environmental gradients.

Leaf functional traits and their covariation underlie plant ecological adaptations along environmental gradients, but there is limited information on the global covariation patterns of key leaf construction traits. To explore how leaf construction traits co-vary across diverse climate and soil environmental conditions, we compiled a global dataset including cell wall mass per unit leaf mass (CWmass ), leaf carbon (C) and calcium (Ca) concentrations, and specific leaf area (SLA) for 2348 angiosperm species from 340 sites world-wide. Our results demonstrated negative correlations between leaf C and Ca concentrations and between leaf C and SLA across diverse nongraminoid angiosperms. Leaf C concentration increased with increasing mean annual temperature (MAT) and mean annual precipitation (MAP) and with decreasing soil pH and calcium carbonate (CaCO3 ) concentration, whereas leaf Ca concentration and SLA exhibited the opposite responses to these environmental variables. The covariations of leaf Ca-C and of leaf SLA-C were stronger in habitats with lower MAT and MAP, and/or higher soil CaCO3 content. This global-scale analysis demonstrates that the leaf C and Ca concentrations and SLA together govern the C and biomass investment strategies in leaves of nongraminoids. We conclude that environmental conditions strongly shape leaf construction traits and their covariation patterns.

Element and isotope compositions of newly discovered dinosaur eggs and geochemical environmental instructions from the early Late Cretaceous of Xiuning Basin, China

ABSTRACT New umbellaoolithid and faveoloolithid eggs were discovered from the early Late Cretaceous deposit in the Xiuning Basin, Anhui Province, China, and the samples were examined for elemental and isotopic compositions to reconstruct the geochemical environment. The results show that the trace elements consist of Sr, Mn, Ti, Ba, As, La, Cr, Ni, Pb, Cu, Zn, Co and Ir. The abnormal Sr and Mn were deposited in the eggshell mainly through material exchange of dinosaurs, and the high Ir concentration of surrounding rocks in the Xiuning Basin is conformed to the early Late Cretaceous Ir anomaly. The δ13C compositions of eggshells suggest that the palaeovegetations are supposed to be −20.191‰ and −21.156‰ showing C3 plant and high CO2 concentration, as well as low mean annual precipitation. The δ18O compositions of eggshells indicate that the drinking water was mainly composed of meteoric water and plant leaf water, and the mean palaeotemperature was approximately 19°C. Based on the geochemical compositions of eggshells, the Ni content, the Sr/Ba ratio and the palaeoclimate index of surrounding rocks, the palaeoenvironment in the Xiuning Basin were dominated by alluvial fans and river systems with semi-arid climate in the early Late Cretaceous.

Variation in desert shrub foliar pH in relation to drought and salinity in Xinjiang, China

AbstractAimFoliar pH, an emerging plant functional trait, plays a key role in plant eco‐physiological processes. However, it remains unclear how foliar pH varies among plants with different preferences concerning soil salinity, and how it responds to drought stress in desert ecosystems.LocationXinjiang, northwestern China (40.24° N to 46.24° N, 80.66° E to 91.33° E).MethodsWe addressed variation in foliar pH in four desert shrub groups (i.e., euhalophytes, secretohalophytes, pseudohalophytes and glycophytes) with differing adaptive strategies to soil salinity in 29 sites in Xinjiang, China, and explored the effects of drought and saline stress on foliar pH variability.ResultsWe found that average foliar pH of desert shrubs was 5.54 ± 0.02, higher than that of shrubs from humid areas. At the functional group level, euhalophytes (5.65 ± 0.03) and glycophytes (5.61 ± 0.04) had significantly higher foliar pH than secretohalophytes (5.47 ± 0.03) and pseudohalophytes (5.39 ± 0.05). Coverage‐weighted mean foliar pH of glycophytes‐dominated communities was significantly higher (5.80 ± 0.18) than those of the halophytes‐dominated communities (5.34 ± 0.07 ~ 5.49 ± 0.07). Only in pseudohalophytes there was a significant relationship between foliar pH and both drought stress (i.e., low soil water stress coefficient, aridity index, and mean annual precipitation) and saline stress (shown by high soil electrical conductivity and soil pH). In contrast, secretohalophytes displayed opposite or non‐significant relationships between foliar pH and drought and saline stress. Compared with salinity indicators, drought exerted a much larger impact on foliar pH, particularly in pseudohalophytes and secretohalophytes.ConclusionsOur work documented a comprehensive analysis of foliar pH across halophyte and glycophyte shrub species, and found contrasting responses of foliar pH to drought and salinity in desert ecosystems, which can provide an alternative perspective for understanding the survival strategies of desert plants, and may also offer new insights into the population dynamics of desert shrub communities under global climate change.

Soil bacterial and eukaryotic co‐occurrence networks across a desert climate gradient in northern China

AbstractA vast portion of the surface of the Earth is desert and desertified land, where, due to the harsh natural environment, vegetation is generally scarce. Soil microbes play important roles in ecosystems and have been used as indicators of soil quality and health. However, microbial interactions in desert ecosystems remain poorly understood. In this study, we collected soil samples from 12 deserts in northern China, spanning four climate types representing distinct aridity gradients, to evaluate bacterial and eukaryotic co‐occurrence networks, and analyze environmental factors determining microbial interactions and their relationships with these factors. At the regional scale, bacterial and eukaryotic interactions strengthened with increasing mean annual precipitation (MAP). They were also influenced by soil total phosphorus and the normalized difference vegetation index. At the local scale, although soil‐, climate‐, and plant‐related factors significantly constrained bacterial and eukaryotic networks, their relative effects varied. Overall, eukaryotic communities formed smaller and less complex networks than bacterial communities. Both bacterial and eukaryotic networks were more complex in deserts with higher MAP, suggesting that they are more stable and play more important roles in biogeochemical cycling in these areas than in lower MAP deserts. Our results provide further evidence that altered precipitation gradient probably leads to unstable and vulnerable microbial communities. This study enhances our understanding of microbial community organization in desert ecosystems, while providing novel insights into soil health. These findings should prove valuable in the evaluation of land development and degradation processes.

Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties.

Soil nitrogen (N) availability is critical for grassland functioning. However, human activities have increased the supply of biologically limiting nutrients, and changed the density and identity of mammalian herbivores. These anthropogenic changes may alter net soil N mineralization (soil net Nmin ), that is, the net balance between N mineralization and immobilization, which could severely impact grassland structure and functioning. Yet, to date, little is known about how fertilization and herbivore removal individually, or jointly, affect soil net Nmin across a wide range of grasslands that vary in soil and climatic properties. Here we collected data from 22 grasslands on five continents, all part of a globally replicated experiment, to assess how fertilization and herbivore removal affected potential (laboratory-based) and realized (field-based) soil net Nmin . Herbivore removal in the absence of fertilization did not alter potential and realized soil net Nmin . However, fertilization alone and in combination with herbivore removal consistently increased potential soil net Nmin. Realized soil net Nmin , in contrast, significantly decreased in fertilized plots where herbivores were removed. Treatment effects on potential and realized soil net Nmin were contingent on site-specific soil and climatic properties. Fertilization effects on potential soil net Nmin were larger at sites with higher mean annual precipitation (MAP) and temperature of the wettest quarter (T.q.wet). Reciprocally, realized soil net Nmin declined most strongly with fertilization and herbivore removal at sites with lower MAP and higher T.q.wet. In summary, our findings show that anthropogenic nutrient enrichment, herbivore exclusion and alterations in future climatic conditions can negatively impact soil net Nmin across global grasslands under realistic field conditions. This is an important context-dependent knowledge for grassland management worldwide.

Multiproxy strategy for determining palaeoclimate parameters in the Ruby Ranch Member of the Cedar Mountain Formation

AbstractA multiproxy approach for evaluating palaeoclimate parameters in deep-time can result in improvements to inter-related factors affecting palaeohydrology. Here we utilize diverse geochemical tools to improve palaeoclimate estimates for the Cedar Mountain Formation (CMF). Prior research utilized stable carbon and oxygen isotopes to develop chemostratigraphic correlations to the late Aptian–early Albian, hypothesized aridity during a positive carbon isotope excursion (CIE) and estimated pCO2 through this event. This study refines estimates using petrographical analyses, bulk geochemical proxies for mean annual precipitation (MAP) and clumped isotope palaeothermometry. MAP rates range from 736 to 1042 mm a−1 with a slight decrease during the hypothesized aridity event. We interpret warm-biased temperatures (with an average of 32.9°C) that do not vary significantly through the study section. Carbonate nodules are likely to have precipitated in highly evaporative conditions as indicated by the presence of dolomite. Utilizing a simple Rayleigh fractionation model and two estimates of δ18O of water, we suggest that evaporation of 2–57% is necessary to result in an enriched end member δ18Ow. These data suggest that an increase in aridity is a result of lower MAP rates and greater evaporation during seasonal extremes. Lastly, revised pCO2 calculations suggest overestimates but indicate a shift towards greater concentrations during the positive CIE.