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500 results for “semi-arid”
Hydrothermal conditions determine soil potential net N mineralization rates in arid and semi-arid grasslands
<p>Soil net nitrogen (N) mineralization is a key biogeochemical process influencing plant available N and net primary productivity (NPP) in terrestrial ecosystems. However, the spatial variations and controlling factors of soil net N mineralization (RPNM) in arid and semi-arid grasslands are less studied and unclear. In this study, we investigated the soil RPNM by performing a laboratory incubation experiment. Soil samples were collected from 30 sites in three east-west transects on the Inner Mongolia Plateau (MP), Loess Plateau (LP), and Tibetan Plateau (TP) along a 3,200 km arid and semi-arid grassland gradient, with each transect containing three different grassland types (meadow steppe, typical steppe, and desert steppe, respectively). Results showed that the average RPNM values ranged from -0.37 to 1.29 mg N kg–1 d–1, with a significantly lower RPNM found in the desert steppe (0.08 ± 0.01 mg N kg–1 d–1) compared with those in the meadow steppe (0.30 ± 0.03 mg N kg–1 d–1) and in the typical steppe (0.33 ± 0.03 mg N kg–1 d–1) in the MP and LP transects (p < 0.05). This difference could be explained by variations in climatic and soil factors, such as hydrothermal index (HT), the soil pH, soil organic matter (SOM) and precipitation. However, no significant differences in RPNM were found among different grassland types in the TP transect, possibly due to the similarly low microbial activity, as indicated by the MBC values. Across all three grassland transects, HT, SOM, and microbial variables were the major factors controlling RPNM, which together explained 20.7% of the variation in RPNM. Further SEM analysis indicated HT was an integral predictor of RPNM, directly or indirectly via SOM, under different conditions of precipitation and temperature. Our findings provide field evidence and parameters for biogeochemical cycling to better predict future N transformation processes under changing precipitation and temperature regimes across a wide range of arid and semi-arid grassland ecosystems.</p>
Effect of drought and nutrient availability on invaded plant communities in a semi-arid ecosystem
<p><span>Ecosystem functions are heavily dependent on the functional composition of the plant community, i.e., the functional traits of plants forming the community. This, on the one hand, depends on plant occurrence, but on the other hand depends on the intraspecific variability of functional traits of the species, which are influenced by climate and nutrient availability and affected by plant-plant interactions. To illustrate that, we studied the effects of drought and nitrogen addition (+ N), two important abiotic variables which are changing with ongoing global change, as well as their combined effect on the functional responses of grassland communities in semi-arid environments of Northern Africa comprising of natural and invasive species. We conducted a plot plant experiment where we planted three native species and one invasive plant species in artificial communities as of 5 individuals per species per plot. We exposed these communities to four different treatments: a drought treatment, a N-addition treatment, the combination between drought and N-addition as well as a control. To assess the performance of plants within treatments, we measured selected plant functional traits (plant height, specific leaf area (SLA), leaf dry matter content (LDMC), N content of the leaves (Nmass), specific root length (SRL) and root diameter) for all individuals occurring in our plots, and additionally assessed the above and belowground biomass for each plant individual. We found that the invasive species showed a higher performance (higher biomass accumulation, taller plants, higher SLA, Nmass, SRL and root diameter as well as lower LDMC) than the native species under drought conditions. The invasive species was especially successful with the combined impact of drought + N, which is a likely scenario in ongoing global change for our research area. Thus, plant functional traits might be a key factor for invasion success of plant species which will be even more pronounced under ongoing global change.</span></p>
The effects of temperature extremes on survival in two semi-arid Australian bird communities over three decades, with predictions to 2104
<p>Aim: Organisms in arid and semi-arid regions are frequently exposed to climatic extremes and accordingly among the most vulnerable to climate change. Studies of seasonal differences in vital rates, which mediate effects of climate on viability, are rare in arid species limiting ability to project population trends. We quantified survival patterns for two bird communities as a function of expo-sure to temperature extremes in winter and summer, then project survival patterns to 2104.</p> <p>Location: semi-arid eastern Australia</p> <p>Time period: 1986-2016; 1986-2104</p> <p>Major taxa studied: Birds</p> <p>Methods: Using mark recapture time-dependent Cormack-Jolly-Seber models and data for 37 species from two 30-year ringing programs, we tested for effects on 6-monthly survival of expo-sure to temperatures >38oC and <0oC. We then predicted future survival for different emission scenarios, testing whether changes in survival associated with warming winters would be suffi-cient to offset the effects of rising summer temperatures. Results: Survival probability declined strongly with increasing exposure to days >38oC and to a lesser extent to days <0oC, with temperature extremes explaining 43% and 13% of temporal varia-tion in survival among years, respectively. Summer survival patterns were similar across avian guilds but only survival of nectarivores declined in winter. Our models predict that gains in winter survival will not offset reductions in summer survival.</p> <p>Annual survival is predicted to decline sub-stantially by the end of the century: from 0.63 in 1986 to 0.43 in 2104 under an optimistic emis-sion scenario and to 0.11 under a pessimistic scenario. Main conclusions: We highlight the significance of temperature extremes for species' persistence in arid and semi-arid regions, comprising 70% of Australia's land mass, and 40% globally. Our demography-based results are consistent with physiological-based projections evaluating avian survival in arid and semi-arid regions globally and suggest rising summer temperatures pose a risk to population persistence in these regions. </p>
Climate mitigation potential and soil microbial response of cyanobacteria-fertilized bioenergy crops in a cool semi-arid cropland
<p>Bioenergy carbon capture and storage (BECCS) systems can serve as decarbonization pathways for climate mitigation. Perennial grasses are a promising second-generation lignocellulosic bioenergy feedstock, but optimizing their sustainability, productivity, and climate mitigation potential requires an evaluation of how nitrogen (N) fertilizer strategies interact with greenhouse gas (GHG) and soil organic carbon (SOC) dynamics. Further, crop and fertilizer choice can affect the soil microbiome which is critical to soil organic matter turnover, nutrient cycling, and sustaining crop productivity but these feedbacks are poorly understood due to the paucity of data from agroecosystems. Here, we examine the climate mitigation potential and soil microbiome response to establishing two functionally different perennial grasses, switchgrass (Panicum virgatum, C4), and tall wheatgrass (Thinopyrum ponticum, C3), in a cool semi-arid agroecosystem under two fertilizer applications, a novel cyanobacterial biofertilizer (CBF) and urea. Finally, we examine shifts in soil microbial composition resulting from crop establishment and fertilizer regime. We find that in contrast to the C4 crop, the C3 crop achieved 98% greater productivity and had a higher N use efficiency when fertilized and the CBF produced the same biomass enhancement as urea. Non-CO2 greenhouse gas fluxes across all treatments were low and we observed a three-year net loss of SOC under the C4 crop and a net increase under the C3 crop at a 0-30 cm soil depth regardless of fertilization. Further, we detected crop-specific changes in the soil microbiome, including an increased relative abundance of arbuscular mycorrhizal fungi under the C3, and potentially pathogenic fungi in the C4 grass. Taken together, these findings highlight the potential of CBF-fertilized C3 crops as a second-generation bioenergy feedstock in semiarid regions as a part of a climate mitigation strategy.</p>
Troubled waters: Water availability drives human-baboon encounters in a protected, semi-arid landscape
<p>Most animal habitats are affected by humans. While some species tolerate and even benefit from these changes, others suffer. Understanding when and how human-altered landscapes affect animal behavior, health, reproduction, and survival is essential to species management in a human-dominated world. Here we use 27 years of data on human-baboon encounters in a protected, semi-arid ecosystem in Kenya to: (i) identify spatial, environmental, and group-level predictors of baboon encounters with pastoralists; (ii) test whether human-built water sources alter baboon ranging patterns; and (iii) test if human encounters are linked to baboon survival, reproduction, and health. We find that the primary driver of human-baboon encounters is water availability. During dry periods, pastoralists migrate into baboon rangelands, leading to frequent human-baboon encounters, especially near water wells. Further, the baboons shift their ranges to encompass newly built wells and move away from abandoned, dried-up wells. Since 2006, a third of adult baboon deaths were linked to violent encounters with humans or their dogs. Human encounters were also linked to high infant mortality and parasite diversity in females (but this effect could not be disentangled from seasonal confounds). For wild baboons, life in protected, pastoralist conservancies presents a double-edged sword: human-built wells enable the baboons to access water during dry periods, but these wells lead to encounters with humans, which have become a common source of baboon mortality. Together, our results serve as a comprehensive case study of anthropogenic effects on wild primates, highlighting the complex interactions between humans and wildlife in protected areas.</p>
Figure 3 in A New Genus and Species of Earthworm (Oligochaeta: Megascolecidae) from Semi-Arid Australia
Figure 3. Right prostate gland of holotYpe.
Figure 2 in A New Genus and Species of Earthworm (Oligochaeta: Megascolecidae) from Semi-Arid Australia
Figure 2. Male field of holotYpe of Aridulodrilus molesworthae gen. et sp. nov.
Figure 1 in A New Genus and Species of Earthworm (Oligochaeta: Megascolecidae) from Semi-Arid Australia
Figure 1. Live extended specimen of Aridulodrilus molesworthae gen. et sp. nov.
Figure 6 in Host effect on morphology of the fruit fly Anastrepha zenildae (Diptera: Tephritidae) from the Semi-Arid region of Rio Grande do Norte
Figure 6. Wireframe Comparison of Discriminant Function Analysis of the wings of Anastrepha zenildae (Males and females) from Guava and Jua fruits. (A) Wing shape variation between female and male flies of the same host, in a semi-arid region. (B) between female and male flies from different hosts. GUAF = Females from Guava; GUAM = Males from Guava; JUAF = Females from Jua; JUAM = Males from Jua. Larger symbols: Centroids of each dataset.
Figure 4 in Host effect on morphology of the fruit fly Anastrepha zenildae (Diptera: Tephritidae) from the Semi-Arid region of Rio Grande do Norte
Figure 4. Principal component analysis (PCA) of the adult flies of Anastrepha zenildae (Males and females) from Guava and Jua fruits. GUAF = Females from Guava; GUAM = Males from Guava; JUAF = Females from Jua; JUAM = Males from Jua. Larger symbols: Centroids of each dataset.
Figure 5 in Host effect on morphology of the fruit fly Anastrepha zenildae (Diptera: Tephritidae) from the Semi-Arid region of Rio Grande do Norte
Figure 5. CanonicalVariable Analysis (CVA) of the wings of adult Anastrepha zenildae (Males and females) from Guava and Jua fruits (above), and the wireframes of wing shape for each investigated component (below). GUAF = Females from Guava; GUAM = Males from Guava; JUAF = Females from Jua; JUAM = Males from Jua. Wireframes in black represent displacement for each CV.
Figure 3 in Host effect on morphology of the fruit fly Anastrepha zenildae (Diptera: Tephritidae) from the Semi-Arid region of Rio Grande do Norte
Figure 3. Representation of landmarks in wing structure and consensus shape applied to Anastrepha zenildae with landmarks. 1 = intersection of humeral and costal veins; 2 = intersection of subcostal and costal vens; 3 = intersection of R1 and costal veins; 4 = intersection of R2+3 and costal veins; 5 = intersection of R4+5 and costal veins; 6 = intersection of M vein with wing margin; 7 = intersection of vein Cu1 with wing margin; 8 = intersection of vein A1+Cu2 and wing margin; 9 = intersection of A1 and Cu2 veins; 10 = intersection of M vein and base of bm cell; 11 = intersection of Cu1 and Cu2 veins; 12 = intersection of M and bm-cu veins; 13 = intersection of Cu1 and bm-cu veins; 14 = intersection of r-m and R4+5 veins; 15 = intersection of r-m and M veins; 16 = intersection of M and dm-cu veins; 17 = intersection of Cu1 and dm-cu veins.
Near real-time ultrahigh-resolution imaging from unmanned aerial vehicles for sustainable land use management and biodiversity conservation in semi-arid savanna under regional and global change (SAVMAP)
<p>To prevent aggravation of existing poverty in semi-arid savannas, a comprehensive concept for the sustainable adaptive management and use of these ecosystems under unprecedented conditions is needed. SAVMAP is an innovative, trans-, and inter-disciplinary initiative whose goal is to develop a valuable monitoring tool for both sustainable land-use management and rare species conservation (black rhinoceros) in semi-arid savanna in Namibia. SAVMAP uses near real-time ultrahigh-resolution photographic imaging (NURI) facilitated by unmanned aerial vehicles (UAVs) designed at EPFL.</p>
Woody cover and geology as stabilising forces in semi-arid savannas
<p>Data accompanying the paper:</p> <p>L.M. Vermeulen, B. Verbist, K. Van Meerbeek, J. Slingsby, P.N. Bernardino, B. Somers. 2024. Woody cover and geology as stabilising forces in semi-arid savannas.</p>
Fig. 42 in Diamonds in the rough: Ibotyporanga (Araneae, Pholcidae) spiders in semi-arid Neotropical environments
Fig. 42. Known geographic distribution of Brazilian species with plesiomorphic short procursus.
Shrub influence on soil carbon and nitrogen in a semi-arid grassland is mediated by precipitation and largely insensitive to livestock grazing
<p>Dryland (arid and semi-arid) ecosystems globally provide more than half of livestock production and store roughly one-third of soil organic carbon (SOC). Biogeochemical pools are changing due toshrub encroachment, livestock grazing, and climate change. We assessed how vegetation microsite, grazing, and precipitation interacted to affect SOC and total nitrogen (TN) at a site with long-term grazing manipulations and well-described patterns of shrub encroachment across elevation and mean annual precipitation (MAP) gradients. We analyzed SOC and TN in the context of vegetation cover at ungrazed locations within livestock exclosures, high-inten- sity grazing locations near water sources, and moderate-intensity grazing locations away from water. SOC was enhanced by MAP (p<0.0001), but grazing intensity had little effect regardless of MAP (p = 0.12). Shrubs enhanced SOC (300–1279 g C m2) and TN (27–122 g N m2), except at high MAP where the contribution or stabilization of shrub inputs relative to grassland inputs was likely diminished. Cover of perennial herbaceous plants and litter were significant predictors of SOC (r2 = 0.63 and 0.34, respectively) and TN (r2 = 0.64 and 0.30, respectively). Our results suggest that continued shrub encroachment in drylands can increase SOC storage when grass production remains high, although this response may saturate with higher MAP. In contrast, grazing – at least at the intensities of our sites – has a lesser effect. These effects underscore the need to understand how future climate and grazing may interact to influence dryland biogeochemical cycling.</p>
Responses of soil temperature, moisture, and respiration to five-year warming and nitrogen addition in a semi-arid grassland
<p><span>How climate warming interacts with atmospheric nitrogen (N) deposition to affect carbon (C) release from soils remains largely elusive, posing a major challenge in projecting climate change‒terrestrial C feedback. As part of a five-year (2006–2010) field manipulative experiment, this study was designed to examine the effects of 24-hour continuous warming and N addition on soil respiration and explore the underlying mechanisms in a semi-arid grassland on the Mongolian Plateau, China. Across the five years and all plots, soil respiration was not changed under the continuous warming, but was decreased by 3.7% under the N addition. The suppression of soil respiration by N addition in the third year and later could be mainly due to the reductions in the forb-to-grass biomass ratios. Moreover, there were interactive effects between continuous warming and N addition on soil respiration. Continuous warming increased soil respiration by 5.8% in the ambient N plots, but reduced it by 6.3% in the enriched N plots. Soil respiration was unaffected by N addition in the ambient temperature plots yet decreased by 9.4% in the elevated temperature plots. Changes of soil moisture and the proportion of legume biomass in the community might be primarily responsible for the non-additive effects of continuous warming and N addition on soil respiration.</span> This study provides empirical evidence for the positive climate warming‒soil C feedback in the ambient N condition. However, N deposition reverses the positive warming‒soil C feedback into a negative feedback, leading to decreased C loss from soils under a warming climate. Incorporating our findings into C-cycling models could reduce the uncertainties of model projections for land C sink and global C cycling under multifactorial global change scenarios.</p>
Resistance of termite mounds to variation in long-term fire regimes across semi-arid African savannas
<p>1. Fire regimes are expected to change with climate change, resulting in a crucial need to understand the specific ways in which variable fire regimes impact important contributors to ecosystem functioning, such as mound-building termites. Termite mounds and fire are both important agents of savanna ecosystem heterogeneity and functioning, but there is little understanding of how they interact across savanna types. 2. We used very high-resolution LiDAR remote sensing to measure the size, density, and distribution of termite mounds across approximately 1,300 ha of experimental burn plots in four South African savanna landscapes representing a wide range of fire treatments differing in seasonality and frequency of burning. 3. In nutrient-poor granitic savannas, fire had no impact on termite mound size, densities, and spatial distributions. In nutrient-rich basaltic savannas with high mammalian herbivore abundance and intermediate rainfall, very frequent fires caused a decrease in termite mound size, whereas in arid nutrient-rich basaltic savannas, fires that occurred at intermediate frequencies and in transitional seasons (i.e., late dry season and late wet season) decreased the degree of spatial overdispersal exhibited by mounds. 4. Overall, our results suggest that termite mounds are resistant to variation in fire seasonality and frequency, likely indicating that ecosystem services provided by mound-building termites will be unaffected by changing fire regimes. However, consideration of changes to termite mound size and distribution could be necessary for land managers in specific savanna types, such as nutrient-rich soils with high mammalian herbivore abundance.</p>
Data for: Nitrous oxide emissions from groundnut and millets farms in semi-arid peninsular India
<p>Nitrous oxide (N<sub>2</sub>O) emissions response curves for crops grown outside temperate regions have been rare and have thus far arrived at conflicting conclusions. Most studies reporting N<sub>2</sub>O emissions from tropical cropping systems have examined only one or two nitrogen fertilizer application rate(s) which precludes the possibility of discovering nonlinear changes in emission factors (EF, % of added N converted to N<sub>2</sub>O-N) with increasing fertilizer-N rates. To examine the relationship between N rates and N<sub>2</sub>O fluxes in a tropical region, we compared farming practices with three or four N rates for their yield-scaled impacts from three crops in peninsular India. We measured N<sub>2</sub>O fluxes during nine seasons between 2012 and 2015, with N application rates ranging between 0 and 70, 0 and 90, and 0 and 480 kg-N ha<sup>-1</sup> for foxtail-millet (<em>Setaria italica</em> L., locally called korra), groundnut (<em>Arachis hypogaea</em> L., also called peanut) and finger-millet (<em>Eleusine coracana</em> L., locally called ragi), respectively. In two cases, the highest N application rate greatly exceeded crop-N needs. Potential climate smart farming agricultural practices (with low/optimized N rates) led to a 50-150% reduction in N<sub>2</sub>O emissions intensity (per unit yield) along with a reduction of 0.2-0.75 tCO2e ha<sup>-1</sup> season<sup>-1</sup> as compared to high N conventional applications. We found a non-linear increase in N<sub>2</sub>O flux in response to increasing applied N for both N-fixing and non N-fixing crops and the extent of super-linearity for non N-fixing crops was much higher than what has been reported earlier. If a linear fit is imposed on our datasets, the emission factors (EFs) for finger-millet and groundnut were ~3.5% and ~1.8%, respectively. Our data shows that for low-N tropical cropping systems, even when they have low soil carbon content, increase in N use to levels just above crop needs to enhance productivity might lead to relatively small increase in N<sub>2</sub>O emissions as compared to the impact of equivalent changes in fertilizer-N use in systems fertilized far beyond crop N needs.</p>
Data for: Steal the rain: Interception loses and rainfall partitioning by a broad-leaf and a fine-leaf woody encroaching species in a southern African semi-arid savanna
<p><span>Woody plant encroachment (WPE) has been found to alter ecosystem functioning and services in savannas. In rain-limited savannas, increasing woody cover can reduce streamflow and groundwater by altering </span>evapotranspiration rates and rainfall partitioning<span>, but the ecological relevance of this impact is not well known. </span><span>This study quantified the altered partitioning of rainfall by two woody plant structural types (fine- and broad-leaved trees) across a gradient of encroachment in a semi-arid savanna in South Africa. Averaged across both plant functional types, loss of rainfall through canopy interception and subsequent evaporation roughly doubled (from 20.5</span> to <span>43.6% of total rainfall) with a roughly 13-fold increase in woody cover (from 2.4 to </span>31.4 m<sup>2</sup>/ha tree basal cover). Spatial partitioning changes comprised <span>fourfold increases in stemflow (from 0.8</span> to <span>3.9% of total rainfall) and a decline in throughfall proportion of about two-fifths (from 80.2% to 47.3% of total rainfall). </span>Changes in partitioning were dependent on plant functional type; rainfall interception by the fine-leaved multi-stemmed shrub <em>Dichrostachys</em> <em>cinerea</em> was almost double that of the broad-leaved tree <em>Terminalia sericea</em> at the highest levels of woody encroachment (i.e., 49.7% vs 29.1% of total rainfall intercepted at tree basal area of 31.4 m<sup>2</sup>/ha). Partitioning was also dependent on rainfall characteristics, with the proportion of rainfall intercepted inversely related to rainfall event size and intensity. Therefore, increasing tree cover in African grassy ecosystems reduces the amount of canopy throughfall, especially beneath canopies of fine-leaved species in smaller rainfall events. Rainfall interception traits may thus confer a selective advantage, especially for fine-leaved woody plant species in semi-arid savannas. </p>
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