Search

PREMISE OF THE STUDY Continental-scale disjunctions and associated drivers is a core research interest in biogeographic studies. Here, we selected a species-rich Australian plant genus (Calytrix; Myrtaceae) as a case study to investigate these patterns. The endemic Australian starflower genus has a disjunct distribution across the mesic fringes of the continent and is largely absent from the arid centre. METHODS We used high-throughput sequencing to generate unprecedented resolution and near complete species-level nuclear and plastid phylogenies for Calytrix. BioGeoBEARS and biogeographic stochastic mapping were used to infer ancestral areas, the relative contributions of vicariance and dispersal events, and directionality of dispersal. KEY RESULTS Present-day disjunctions in Calytrix are explained by a combination of scenarios: (1) retreat of multiple lineages from the continental centre to the more mesic fringes as Australia became progressively more arid, with subsequent extinction in the centre, and also (2) origination of ancestral lineages in southwestern Australia (SWA) for species-rich clades. The SWA biodiversity hotspot is a major diversification centre and the most common source area of dispersals, with multiple lineages originating in SWA and subsequently spreading to the adjacent arid Eremaean region. CONCLUSIONS Our results suggest major extinction, as a result of cooling and drying of the Australian continent in the Eocene-Miocene, shaped the present-day biogeography of Calytrix. We hypothesise that this peripheral vicariance pattern, which is similar to the African Rand flora, may explain the disjunctions of many other Australian plant groups. Further studies with densely sampled phylogenies are required to test this hypothesis. This article is protected by copyright. All rights reserved.

The need for sustainable agricultural practices to meet the food, feed, and fuel demands of a growing global population while reducing detrimental environmental impacts has driven research in multi‐faceted approaches to agricultural sustainability. Perennial cropping systems and microbial biofertilizer supplements are two emerging strategies to increase agricultural sustainability that are studied in tandem for the first time in this study. During the establishment phase of a perennial switchgrass stand in SW Montana, USA, we supplemented synthetic fertilization with a nitrogen‐fixing cyanobacterial biofertilizer (CBF) and were able to maintain aboveground crop productivity in comparison to a synthetic only (urea) fertilizer treatment. Soil chemical analysis conducted at the end of the growing season revealed that late‐season nitrogen availability in CBF‐supplemented field plots increased relative to urea‐only plots. High‐throughput sequencing of bacterial/archaeal and fungal communities suggested fine‐scale responses of the microbial community and sensitivity to fertilization among arbuscular mycorrhizal fungi, Planctomycetes, Proteobacteria, and Actinobacteria. Given their critical role in plant productivity and soil nutrient cycling, soil microbiome monitoring is vital to understand the impacts of implementation of alternative agricultural practices on soil health.

© 2021 John Wiley & Sons, Ltd.Basins with hydrological modifications pose challenges in hydrological modelling, especially when there are limited data about basin characteristics. Models, however, are vital if we are to identify undisturbed hydrological conditions and evaluate the extent of modifications. In this study, we used SWAT to model the hydrological processes in a semi-arid closed basin, where basin hydrology was heavily modified with reservoirs and irrigation canals and drains. Modelling was also challenging due to limited data about basin characteristics and irrigation management. We modelled the hydrological processes using topographic, land use/cover, soil and climate data. The auto-irrigation tool in SWAT, which determines the timing and amount of irrigation based on the plant water stress factor, was used to represent irrigation. We successfully calibrated/validated the model for streamflow and reservoir storage and confirmed it further by analysing simulated water volumes in wetlands collecting drainage flows. We used the model to simulate the undisturbed hydrologic state and the effects of intensified irrigation. This study showed that SWAT can provide reasonable predictions of hydrological processes in agricultural basins where the natural flow regime is altered by man-made structures. Simulations with the model revealed that the construction of reservoirs followed by land use changes and intensified irrigation have affected streamflows and downstream ecosystems significantly.

As the third most important greenhouse gas, nitrous oxide (N2O) poses a significant threat to global warming and the ozone layer. However, the effects of precipitation changes on N2O emissions in arid areas remain unclear, particularly in desert steppe environments. Therefore, an in situ control experiment was conducted from July 2018 to July 2020 to examine the N2O emissions with changes in precipitation in the Urat Desert Steppe, northwestern China. The results showed that the N2O emission rate was relatively low in this desert steppe, at −0.04 to +15.0 μg N m−2 hr−1 with an annual flux of 0.20 ± 0.03 kg N ha−1. An increasing trend of N2O emission was observed in the early growing season (February to June 2019) when the precipitation was increased by 40% and 60% of its natural level. In contrast, no significant change in N2O emissions was observed when the precipitation was decreased during the same period. During the middle and late growing season and in the nongrowing season, precipitation changes did not significantly affect N2O emissions. In particular, no significant change in the annual N2O flux was observed during the entire observation period whether the precipitation was increased or decreased. Furthermore, the results of a structural equation model showed that the most important controlling factor for N2O emission is an abundance of key functional ammonia monooxygenase genes of ammonia-oxidizing archaea, which are restricted by the soil NH4+-N content, followed by abundances of key functional NO2− reductase (nirK) and N2O reductase (nosZ) genes. In contrast, the indirect effect of soil moisture on the abundance of nosZ compensated for the direct effect of soil moisture on N2O emissions. These results show that the primary and secondary origins of N2O emissions are soil ammonia oxidation and soil denitrification processes, respectively. In these two processes, N2O emissions are influenced more by the abundance of key functional microorganisms than by soil moisture, which might be limited mainly by the available soil nitrogen. Overall, the N2O emissions in the desert steppe environment were not sensitive to precipitation changes and were regulated mainly by nitrogen-related key functional microorganisms.

1. Carbon (C) loss due to soil erosion is a major issue in semi-arid grasslands. The extent of soil erosion is determined by soil properties and vegetation structure, especially during the non-growing season. In many Inner Mongolian grasslands, intensive land-use, such as overgrazing and mowing, has severely reduced plant cover and damaged soil structure, which has exacerbated soil C loss by erosion. At the same time, increasing winter snowfall due to climate change is stimulating plant growth and altering plant composition. However, we do not know how changes in winter snow cover interact with land-use practices to regulate soil C loss due to erosion. 2. Here, we conducted a 6-year snow manipulation experiment under different land-use practices (control; moderately mowed, MM; heavily mowed, HM) to measure net changes in soil depth, soil C, plant biomass and vegetation structure. 3. After 6 years, soil C loss under ambient snow was three times greater in the MM and four times greater in the HM treatment compared with controls during non-growing season. However, deepened winter snow alleviated erosion-induced soil C loss by 14%, 47%, 16% in the controls, MM and HM treatments respectively. 4. The severity of soil C loss declined with increasing above-ground biomass (AGB), surface root biomass and vegetation structure. Vegetation structure and AGB explained more of the variation in soil C loss than surface root biomass, possibly because a complex canopy and plant cover increases overall surface roughness, thereby reducing soil C loss. Intensified land-use reduced AGB, surface root biomass and vegetation structure, but deepened snow increased overall surface roughness by promoting AGB. Hence, our study demonstrates that deepened snow can alleviate soil C loss due to land-use practices by promoting AGB. A free Plain Language Summary can be found within the Supporting Information of this article.

Global warming has exacerbated desertification in arid regions. Exploring the environmental variables and microbial communities that drive the dynamics of geographic patterns of desert crops is important for large-scale standardization of crops that can control desertification. Here, predictions based on future climate data from CMIP6 show that a steady expand in the suitable production areas for three desert plants (Cistanche deserticola, Cynomorium songaricum and Cistanche salsa) under global warming, demonstrating their high adaptability to future climate change. We examined the biogeography of three desert plant soil bacteria communities and assessed the environmental factors affecting the community assembly process. The α-diversity significantly decreased along elevated latitudes, indicating that the soil bacterial communities of the three species have latitude diversity patterns. The neutral community model evaluated 66.6% of the explained variance of the bacterial community in the soil of desert plants and Modified Stochasticity Ratio

Trade-offs exist for xerophytic shrubs between functional traits, involving in water loss and assimilate accumulation, can contribute to its survival and growth rate regulation in arid environments. However, growth analysis based on plant functional traits has been focused on the study of herbs and woody species. It is still unclear how the functional traits of xerophytic shrubs regulate their growth rate. In this study, we selectedeight xerophytic shrubs as samples to analyze the regulation process of the functional traits of shrubs on growth rate. Plants were cultivated for three years, and three harvests (every one year) were carried out. Factors explaining between-species differences in relative growth rate (RGR) varied, depending on whether different ages were considered. The results showed that RGR was positively correlated with net assimilation rate, but there was a significant negative correlation with leaf area ration (LAR), specific leaf area (SLA), and leaf biomass ratio in the age 1. However, in the age 2, RGR showed a significant positive correlation with the morphological traits (i.e., leaf area ration and specific leaf area), but not with physiological traits (i.e., net assimilation rate) and leaf biomass allocation. Our results suggested that the fluctuation of environmental factors affects the regulation path of the plant functional traits on RGR of xerophytic shrubs. However, the analysis of causality model showed that no matter in which age, net assimilation rate and leaf area ration principally drive the variation in RGR among xerophytic shrubs.

Conifers prevail in the canopies of many terrestrial biomes, holding a great ecological and economic importance globally. Current increases in temperature and aridity are imposing high transpirational demands and resulting in conifer mortality. Therefore, identifying leaf structural determinants of water use efficiency is essential for predicting physiological impacts due to environmental variation. Using synchrotron-generated microtomography imaging, we extracted leaf volumetric anatomy and stomatal traits in 34 species across conifers with a special focus on Pinus, the richest conifer genus. We show that intrinsic water use efficiency (WUEi ) is positively driven by leaf vein volume. Needle-like leaves of Pinus, as opposed to flat leaves or flattened needles of other genera, showed lower mesophyll porosity, decreasing the relative mesophyll volume. This led to increased ratios of stomatal pore number per mesophyll or intercellular airspace volume, which emerged as powerful explanatory variables, predicting both stomatal conductance and WUEi . Our results clarify how the three-dimensional organisation of tissues within the leaf has a direct impact on plant water use and carbon uptake. By identifying a suite of structural traits that influence important physiological functions, our findings can help to understand how conifers may respond to the pressures exerted by climate change.

Many regions across the globe are shifting to more arid climates. For shallow lakes, decreasing rainfall volume and timing, changing regional wind patterns and increased evaporation rates alter water regimes so that dry periods occur more frequently and for longer. Drier conditions may affect fauna directly and indirectly through altered physicochemical conditions in lakes. Although many studies have predicted negative effects of such changes on aquatic biodiversity, empirical studies demonstrating these effects are rare. Global warming has caused severe climatic drying in southwestern Australia since the 1970s, so we aimed to determine whether lakes in this region showed impacts on lake hydroperiod, water quality, and α, β and γ diversity of lake invertebrates from 1998 to 2011. Seventeen lakes across a range of salinities were sampled biennially in spring in the Wheatbelt and Great Southern regions of Western Australia. Multivariate analyses were used to identify changes in α, β and γ diversity and examine patterns in physicochemical data. Salinity and average rainfall partially explained patterns in invertebrate richness and assemblage composition. Climatic drying was associated with significant declines in lake depth, increased frequency of dry periods, and reduced α and γ diversity (γ declined from ~300 to ~100 taxa from 1998 to 2011 in the 17 wetlands). In contrast, β diversity remained consistently high, because each lake retained a distinct fauna. Mean α diversity per-lake declined both in lakes that dried and lakes that did not dry out, but lakes which retained a greater proportion of their maximum depth retained more α diversity. Accumulated losses in α diversity caused the decline in γ diversity likely through shrinking habitat area, fewer stepping stones for dispersal and loss of specific habitat types. Biodiversity loss is thus likely from lakes in drying regions globally. Management actions will need to sustain water depth in lakes to prevent biodiversity loss.

Megaherbivores (adult body mass > 1000 kg) are suggested to disproportionately shape ecosystem and Earth system functioning. We systematically reviewed the empirical basis for this general thesis and for the more specific hypotheses that 1) megaherbivores have disproportionately larger effects on Earth system functioning than their smaller counterparts, 2) this is true for all extant megaherbivore species and 3) their effects vary along environmental gradients. We furthermore explored possible biases in our understanding of megaherbivore impacts. We found that there are too few studies to quantitatively evaluate the general thesis or any of the hypotheses for all but the African savanna elephant. Following this finding, we performed a qualitative vote counting analysis. Our synthesis of this analysis suggests that megaherbivores can elicit strong impacts on, for example, vegetation structure and biodiversity, and all the elephant species promote seed dispersal. We were, however, unable to evaluate whether these effects are disproportionate to smaller large herbivores. Although environmental conditions can mediate megaherbivore impact, few studies quantified the effect of rainfall or soil fertility on megaherbivore impacts, precluding prediction of megaherbivore effects on the Earth system, particularly under future climates. Moreover, our review highlights major taxonomic, thematic and geographic biases in our understanding of megaherbivore effects. Most of the studies focused on African savanna elephant impacts on vegetation structure and biodiversity, with other megaherbivores and Earth system functions comparatively neglected. Studies were also biased towards semi-arid and relatively fertile systems, with the arid, high-rainfall and/or nutrient-poor parts of the megaherbivores' distribution ranges largely unrepresented. Our findings highlight that the empirical basis of our understanding of the ecological effects of extant megaherbivores is still limited for all species, except the African savanna elephant, and that our current understanding is biased towards certain environmental and geographic areas. We further outline a detailed, urgently needed avenue for future research.

Changes in precipitation regimes have significant effects on soil carbon (C) cycles; however, these effects may vary in arid versus humid areas. Additionally, the corresponding details of soil C cycles in response to altered precipitation regimes have not been well documented. Here, a meta-analysis was performed using 845 pairwise observations (control vs. increased or decreased precipitation) from 214 published articles to quantify the responses of the input process of exogenous C, the contents of various forms of C in soil, and the soil-atmosphere C fluxes relative to increased or decreased precipitation. The results showed that the effects of altered precipitation regimes did not differ between rainfall and snowfall. Increased precipitation significantly enhanced the soil C inputs, pools and outputs by 18.17%, 18.50%, and 21.04%, respectively, while decreased precipitation led to a significant decline in these soil C parameters by 10.18%, 9.96%, and 17.98%, respectively. The effects of increased precipitation on soil C cycles were more significant in arid areas (where mean annual precipitation, MAP

Net ecosystem gas exchange (NEE), a balance between gross ecosystem primary productivity (GPP) and ecosystem respiration (ER), is an important indicator of terrestrial ecosystem CO2 sink or source. Increasing frequency in droughts during different periods of the growing season may affect terrestrial ecosystem carbon (C) balance. However, detecting how drought timing controls ecosystem C processes is insufficiently explored because it is a challenge to accurately monitor and forecast drought dynamics. In a 5-year (2015–2019) precipitation manipulation experiment in a temperate steppe in northern China, we imposed a 60% decrease in precipitation in the early (April–June, DEP) and late (July–September, DLP) growing seasons in plots under rainout shelters to simulate drought occurrence timing. The responses of GPP, ER and NEE to DEP and DLP were examined to determine how the timing of decreased precipitation affects CO2 fluxes. Both DEP and DLP reduced GPP and ER. Decreased precipitation in the late growing season reduced NEE due to a greater decline in GPP than ER. In contrast, the lack of an effect of DEP on NEE can be attributed to a proportional decline in GPP and ER. Reduced normalized difference vegetation index (NDVI) and GPP induced by decreased precipitation explained the decline in GPP and ER respectively. Drought in the late growing season weakened the ecosystem C sink. The result indicates a low resistance in net C uptake to DLP. However, we did not find evidence that previous precipitation decreases resulted in a lower overall rate of ecosystem C exchange, indicating a high resilience in C processes in this semi-arid grassland. Synthesis and applications. Our study provides solid evidence that drought in the late growing season weakens ecosystem C sink in the semi-arid grassland. The findings suggest that management practices aimed at enhancing water availability during the late growing season should be preferred for increasing C sequestration.

Long-term studies are required to reveal responses by long-lived, top-order predator populations to ongoing seasonal fluctuations. However, such investigations are rare in the Australian context. Between 2009 and 2019, the breeding density and productivity of an arid and a mesic wedge-tailed eagle Aquila audax population, each occupying an area of 2800 km2, were compared (11–98 pairs monitored annually). Breeding pairs spaced themselves evenly in both study areas, with no significant difference between the average arid zone nearest-neighbour distance of 5.32 ± 1.98 km (n = 44) and that determined for the mesic zone (4.88 ± 2.32 km, n = 54). This similarity in spacing suggests a maximum average density is tolerated by these territorial raptors. By contrast, annual breeding success (proportion of pairs fledging young) and productivity (fledged young per pair) differed significantly between the two populations, with rainfall (but not temperature) influencing reproduction. In the arid zone, the proportion of successful pairs per occupied breeding home range was consistently low each year (mean = 12 ± 7% fledged broods per pair, range 0–26%) and positively correlated with annual rainfall. In the mesic zone, it was consistently high each year (mean = 69 ± 9%, range 57–91%) and not significantly correlated with annual rainfall. Overall productivity figures showed similar differences, with 0.13 and 0.77 fledglings per pair per year for arid (n = 9 years) and mesic (n = 11 years) eagles, respectively. Such low arid zone productivity, the lowest ever recorded for the species, could have long-term implications in the face of the increased frequency of extreme weather events. That breeding density can be independent of climatic factors provides new insight into the way a large Aquila species integrates with Australia’s predominantly arid environment. This study provides an important baseline data set for continued research on long-term occupancy and productivity trends.

• Savin juniper is an excellent species for desertification control in arid and semi-arid areas, where it typically establishes under the protection of nurse plants. Ultimately, established plants emerge into full sunlight as they grow, and this transition is accompanied by an increase in the preponderance of scale-like vs. needle-like leaf forms. • To test how age and variable sunlight environments affect shade tolerance in savin juniper, we established a pot study under field conditions with two age cohorts (1- and 4-year-old rooted scions) and three sunlight regimes (10%, 50% and 100% light transmittance). We measured growth, leaf parameters, photosynthesis, chlorophyll fluorescence and foliar pigments on a monthly basis (seven growing months per year, from 2015 to 2017). • Overall, there was little interaction for all variables, and both cohort and light regime had significant effects. Leaf form and spacing varied continuously, tending towards shorter, more closely spaced and more appressed scale leaves with higher dry leaf mass per area in older plants or under higher sunlight. There were no clear age-related patterns in carotenoids but both cohort and light had significant effects on gas exchange and chlorophyll fluorescence variables. • Savin juniper shows an intermediate tolerance to shade that changes with growth in that younger plants were less tolerant of full sun than older plants, consistent with its reliance on nurse plants for ultimate establishment in the open.

Gasterophilus spp. have been found to be widespread in reintroduced Przewalski's horses in the Kalamaili Nature Reserve (Northwest China). However, data on the annual variation in Gasterophilus infections are lacking. To analyze the epidemiological features and determine the cause of the annual variation in Gasterophilus infections, we treated 110 Przewalski's horses with ivermectin and collected Gasterophilus larvae from fecal samples each winter from 2007 to 2019. All 110 Przewalski's horses studied were found to be infected by Gasterophilus spp., and a total of 141 379 larvae were collected. Six species of Gasterophilus were identified with the following prevalence: G. pecorum (100%), G. nasalis (96.36%), G. nigricornis (94.55%), G. haemorrhoidalis (56.36%), G. intestinalis (59.09%), and G. inermis (3.64%). The mean infection intensity of Gasterophilus spp. larvae in Przewalski's horses was 1285 ± 653. G. pecorum (92.96% ± 6.71%) was the most abundant species. The intensity of Gasterophilus spp. (r = -0.561, P < 0.046) was significantly correlated with winter precipitation. Our findings confirmed that, in the Kalamaili Nature Reserve, gasterophilosis is a severe parasitic disease in Przewalski's horses. Winter precipitation at the beginning of the year can indirectly affect the intensity and composition of Gasterophilus spp. in Przewalski's horses at the end of the year. Therefore, the water-related ecological regulation should be carried out to help reduce the parasite infection of Przewalski's horses.

Ascension Island has had a long intermittent record of instrumental weather recording. Here, we develop monthly records of mean temperature and precipitation totals (for 1924-2020 when an almost complete record is available) from the three principal recording sites: the capital Georgetown and two gauges at Wideawake Airfield. Although some of the data are in global climate databases, we have sourced as much data as possible from the primary sources in the United Kingdom, the United States and from the island itself. Air temperature shows statistically significant warming since 1950 of 0.54°C and since 1979 of 0.40°C, and agrees closely with sea surface temperatures, taken from the seas around the island, back to the start of the island series in 1924. Although the island is too small to be in Reanalyses, the warming trends of air temperatures from these products also agree, but the absolute air temperature values are about 1°C cooler than measured on the island. Annual precipitation on the island indicates it is very arid, with a long-term average of only 165mm. Occasionally, heavy monthly precipitation totals occur (always between February and June) which bring severe damage to the island’s infrastructure and ecosystems. The heaviest monthly total was 334mm for April 1985.

Climate change is expected to promote biological invasions. Invasive species often undergo adaptive evolution, but whether invasive species show greater evolutionary potential than their native counterparts under climate change has rarely been evaluated. We conducted experimental evolution trials comparing the evolution of physiological performance (light-saturated photosynthetic rate, Amax ) of coexisting and closely related (1) invasive-native species pairs from Arid, Alpine, and Antarctic ecosystems, and (2) an invasive-naturalized species pair from a Mediterranean ecosystem differing in invasiveness. Experiments were conducted over three generations and under four environments of temperature and water availability resembling typical and climate change conditions in each ecosystem. Amax increased across generations for most species. Invasive species from Arid, Alpine, and Antarctic ecosystems showed similar, greater, and lesser evolution of Amax than their native counterparts, respectively. The Mediterranean invasive species showed greater evolution of Amax than its naturalized congener. Similar patterns were observed in all four experimental environments for each ecosystem, suggesting that comparable responses may be expected under climate change scenarios. All study species showed a positive association between Amax and reproductive output. Results suggest that invasive plants and their native (or naturalized) counterparts would show similar evolutionary responses of physiological performance to global warming and drought.

Interannual variability in precipitation has increased globally as climate warming intensifies. The increased variability impacts both terrestrial plant production and carbon (C) sequestration. However, mechanisms driving these changes are largely unknown. Here, we examined mechanisms underlying the response of aboveground net primary production (ANPP) to interannual precipitation variability in global drylands with mean annual precipitation (MAP)

Microbially-explicit models may improve understanding and projections of carbon dynamics in response to future climate change, but their fidelity in simulating global-scale soil heterotrophic respiration (RH ), a stringent test for soil biogeochemical models, has never been evaluated. We used statistical global RH products, as well as 7,821 daily site-scale RH measurements, to evaluate the spatio-temporal performance of one first-order decay model (CASA-CNP) and two microbially-explicit biogeochemical models (CORPSE and MIMICS) that were forced by two different input datasets. CORPSE and MIMICS did not provide any measurable performance improvement; instead, the models were highly sensitive to the input data used to drive them. Spatial variability in RH fluxes was generally well simulated except in the northern middle latitudes (~50°N) and arid regions; models captured the seasonal variability of RH well, but showed more divergence in tropic and arctic regions. Our results demonstrate that the next generation of biogeochemical models shows promise, but also needs to be improved for realistic spatio-temporal variability of RH . Finally, we emphasize the importance of net primary production, soil moisture, and soil temperature inputs, and that jointly evaluating soil models for their spatial (global scale) and temporal (site scale) performance provides crucial benchmarks for improving biogeochemical models.