Altered Rainfall Research Articles

Seed Regeneration in Taxus baccata: Unveiling Ecological Restrictions and Paving the Way for Future Studies.

Taxus baccata, commonly known as English yew, is an evergreen tree native to regions ranging from Ireland and Sweden to Morocco, Algeria, and northern Iran. This species is of special concern due to habitat loss from human activities, including forest management, leading to declining populations. A 4-year monitoring study was conducted to investigate the factors behind the poor seed regeneration of yew. We examined seed germination, dormancy, desiccation tolerance, and seed predation as potential contributors to this issue. Our study proposed potential seed predation by frugivores and granivores, along with morphophysiological dormancy, as primary reasons for poor regeneration. Despite high seed production and seed availability in certain years, germination did not improve, likely due to the small size of the yew seed embryos, which prolongs dormancy. Yew seeds are desiccation-tolerant, water-permeable, and lack physical germination barriers, making seed predation a significant limiting factor. In conclusion, the natural regeneration of yew is hampered by potential seed predation, morphophysiological dormancy, and environmental factors such as altered temperature and rainfall patterns, which change the dormancy-breaking process. Further research is needed to quantify seed predation and explore its impact on seedling survival.

Understanding competition between two invasive woody plants of India under an altered rainfall regime

Understanding competition between two invasive woody plants of India under an altered rainfall regime

Climate-Smart Horticultural Practices: Building Resilience in a Changing Environment: A Scoping Review

Climate change disrupts weather patterns, intensifies water scarcity and exacerbates pest and disease pressures, posing a significant threat to horticultural production systems. This scoping review explores a range of climate-smart practices to enhance adaptation and resilience within the sector. Core practices like water-efficient irrigation, heat stress mitigation strategies, and adjustments to cropping patterns for altered rainfall are investigated. Integrated pest management is presented as a cornerstone for sustainable pest control. The review further explores the potential of precision agriculture, controlled-environment agriculture, and vertical farming to optimize resource use and mitigate climate risks. Beyond technical solutions, the review emphasizes continuous research and development for breeding climate-resistant varieties, refining existing practices, and exploring novel technologies. It advocates for an integrated approach, tailoring climate smart practices to specific contexts and socioeconomic considerations. Knowledge-sharing initiatives, training programs, economically viable technologies, and supportive government policies are identified as crucial for widespread adoption, particularly among smallholder farmers. The paper concludes with a call for collaboration among researchers, extension services, policymakers, and producers. By fostering knowledge dissemination, technology transfer, and financial incentives, stakeholders can empower farmers to adapt and thrive in a changing climate. Through collective action and unwavering commitment to innovation, the horticultural sector can ensure a secure and sustainable future for food production.

Disinfection by-product formation potential in response to variability in dissolved organic matter and nutrient inputs: Insights from a mesocosm study

Changes in rainfall patterns driven by climate change affect the transport of dissolved organic matter (DOM) and nutrients through runoff to freshwater systems. This presents challenges for drinking water providers. DOM, which is a heterogeneous mix of organic molecules, serves as a critical precursor for disinfection by-products (DBPs) which are associated with adverse health effects. Predicting DBP formation is complex due to changes in DOM concentration and composition in source waters, intensified by altered rainfall frequency and intensity. We employed a novel mesocosm approach to investigate the response of DBP precursors to variability in DOM composition and inorganic nutrients, such as nitrogen and phosphorus, export to lakes. Three distinct pulse event scenarios, mimicking extreme, intermittent, and continuous runoff were studied. Simultaneous experiments were conducted at two boreal lakes with distinct DOM composition, as reflected in their color (brown and clear lakes), and bromide content, using standardized methods. Results showed primarily site-specific changes in DBP precursors, some heavily influenced by runoff variability. Intermittent and daily pulse events in the clear-water mesocosms exhibited higher haloacetonitriles (HANs) formation potential linked to freshly produced protein-like DOM enhanced by light availability. In contrast, trihalomethanes (THMs), associated with humic-like DOM, showed no significant differences between pulse events in the brown-water mesocosms. Elevated bromide concentration in the clear mesocosms critically influenced THMs speciation and concentrations. These findings contribute to understanding how changing precipitation patterns impact the dynamics of DBP formation, thereby offering insights for monitoring the mobilization and alterations of DBP precursors within catchment areas and lake ecosystems.

Revisiting the bucket model: Long‐term effects of rainfall variability and nitrogen enrichment on net primary production in a desert grassland

Abstract The predicted intensification of the North American Monsoon is expected to alter growing season rainfall patterns in the southwestern United States. These patterns, which have historically been characterized by frequent small rain events, are anticipated to shift towards a more extreme precipitation regime consisting of fewer, but larger rain events. Furthermore, human activities are contributing to increased atmospheric nitrogen deposition throughout this dryland region. Alterations in rainfall size and frequency, along with changes in nitrogen availability, are likely to have significant consequences for above‐ground net primary production (ANPP) and plant community dynamics in drylands. The conceptual bucket model predicts that a shift towards fewer, but larger rain events could promote greater rates of ANPP in these regions by maintaining soil moisture availability above drought stress thresholds for longer periods during the growing season. However, only a few short‐term studies have tested this hypothesis, and none have explored the interaction between altered rainfall patterns and nitrogen enrichment. To address this knowledge gap, we conducted a 14‐year rainfall addition and nitrogen fertilization experiment in a northern Chihuahuan Desert grassland to explore the long‐term impacts of changes in monsoon rainfall size and frequency, along with chronic nitrogen enrichment, on ANPP (measured as peak biomass) and plant community dynamics. Contrary to bucket model predictions, small frequent rain events promoted comparable rates of ANPP to large infrequent rain events in the absence of nitrogen enrichment. It was only when nitrogen limitation was alleviated that large infrequent rain events resulted in the greatest ANPP. Furthermore, we found that nitrogen enrichment had the greatest impact on plant community composition under the small frequent rainfall regime. Synthesis. Our long‐term field experiment highlights limitations of the bucket model by demonstrating that water and nitrogen availability sequentially limit dryland ecological processes. Specifically, our findings suggest that while water availability is the primary limiting factor for above‐ground net primary production in these ecosystems, nitrogen limitation becomes increasingly important when water is not limiting. Moreover, our findings reveal that small frequent rain events play an important but underappreciated role in driving dryland ecosystem dynamics.

Forest Cover and Locality Regulate Response of Watershed Discharge to Rainfall Variability in Caribbean Region

Reforestation often occurs when the economy shifts from agriculture to industry and services such as tourism. However, there is a lack of coherent knowledge and investigation about the impact of reforestation in the tropics on hydrological variability as well as flood risks. It is unclear how changes in forest cover and pattern will affect flood risks and watershed response to future altered rainfall intensity. This study uses the Soil Water Assessment Tool (SWAT+) to simulate the impact of reforestation, the locality of forest, and the concentrated rainfall on the hydrology of the largest watershed in Puerto Rico. SWAT+ is a computer model simulating watershed hydrology driven by meteorological input and the characteristics of soils and land use. We hypothesized that increased forest cover, especially at low elevation range, would reduce flood risk and that reduced rain days while maintaining the mean annual rainfall invariant would increase stream discharge variability. We found that reforestation significantly reduced large discharges but increased small discharges; that forest at low elevation tended to reduce large and extreme discharges in comparison with forest at high elevation; and that more concentrated rainfall not only increased the rainfall variability but also increased the discharge variability. However, both the impact of shifting forest locality and the response of watershed to altered rainfall intensity strongly depended on geophysical factors such as ranges of elevation and slope. Moving forests to lower elevation in subbasins with steeper slopes showed a stronger reduction in extreme discharges than in subbasins with flatter slopes. On the other hand, subbasins with steeper slopes tended to response more strongly to more concentrated rainfall with greater increase in discharge variability than subbasins with flatter slopes. To cope with future increased climate variability, our results favor reforestation at lower elevation for watershed with large elevation ranges and steep slopes.

Inconsistent using FLOOD and Flooding Development of EPA SWMM for Assessing Flood Occurrences in Vulnerable Urban Watershed Considering Extreme Rainfall Events

Urban flood, commonly known as urban water congestion, is a type of water hazard that poses significant challenges for urban residents and water management experts. Chittagong, an essential economic hub in Bangladesh, renowned for its role as a port city, comprises a diverse range of land use, including residential, industrial, and commercial sectors. The Chaktai canal, an important element of Chittagong drainage system, is connected to the Karnaphuli river, playing a vital role in managing drainage by handling a substantial portion of the city water. Therefore, this research evaluated the operational efficiency of a specific drainage network under the influence of altered rainfall events using the Storm Water Management Model (SWMM). Using ArcGIS 10.4, the land use pattern of the area was researched, incorporating data from field surveys and secondary sources. SWMM 5.1 integrated watershed data, and further simulation was carried out to estimate runoff in various sub-catchments and drainage network limitations during heavy rain. During the intense monsoon period, the tool determined the average runoff depth, considering backwater effects and robust tidal surges, resulting in a depth of 3.3m compared to 2.6m in the dry season. This research evaluated the influence of impervious land use changes on urban drainage systems. While meteorological factors alone render drainage network sufficient in dry periods, the outfall shows vulnerability during the rainy season, with an allowance of only 0.7m, jeopardizing the catchment through flood. It contributed a schematic sub-catchment representation, emphasizing that flood events depend on volume runoff and peak flow in urban drainage system. SWMM model was used to illustrate the catchment surface runoff and interconnected node depths via conduits, as well as the current catchment scenario comprehensively.

Drought experiments need to incorporate atmospheric drying to better simulate climate change

Abstract Climate models predict more frequent, prolonged, and extreme droughts in the future. Therefore, drought experiments varying in amount and duration across a range of biogeographical scenarios provide a powerful tool for estimating how drought will affect future ecosystems. Past experimental work has been focused on the manipulation of meteorological drought: Rainout shelters are used to reduce precipitation inputs into the soil. This work has been instrumental in our ability to predict the expected effects of altered rainfall. But what about the nonrainfall components of drought? We review recent literature on the co-occurring and sometimes divergent impacts of atmospheric drying and meteorological drying. We discuss how manipulating meteorological drought or rainfall alone may not predict future changes in plant productivity, composition, or species interactions that result from climate change induced droughts. We make recommendations for how to improve these experiments using manipulations of relative humidity.

Altered rainfall greatly affects enzyme activity but has limited effect on microbial biomass in Australian dryland soils

Drylands support a substantial proportion of the worlds biodiversity and are important to food production but are sensitive to changes in rainfall regimes. Altered rainfall has been shown to impact plant growth and soil microbial activity in drylands but the longer-term effect on belowground communities and biogeochemical cycles remains uncertain. We explored how four years of reduced and increased rainfall influenced soil total and available carbon (C), nitrogen (N) and phosphorus (P) content, microbial biomass and potential extracellular enzyme activity under field conditions at six dryland sites in eastern Australia. The study coincided with a severe 3-year drought that resulted in low standing plant biomass and soil C content at all sites. Microbial biomass attributes varied considerably across sites, with rainfall treatment effects limited to decreased fungal biomass and lower fungal:bacterial ratios in semi-arid Nyngan and reduced fungal:bacterial ratios and microbial biomass C in semi-arid Quilpie in reduced treatments compared with increased rainfall plots. Similarly, available soil C, N and P varied considerably among sites, with more available N and P at four and all sites, respectively, in reduced rainfall treatments particularly when compared with increased rainfall treatments. Rainfall treatments consistently influenced enzyme activity across all sites, with higher rates in increased rainfall plots indicative of greater microbial activity and enhanced nutrient cycling. Enzymatic activity associated with N cycling showed a negative relationship with available N while enzymes associated with P cycling related positively to available C and negatively to available P. This indicates that microbes invested more in production of enzymes associated with less available nutrients. Enzyme activity was not related to microbial biomass suggesting a disconnect between biomass and enzyme production and that rainfall treatments altered the ecosystem's specific enzyme activity (activity per unit of microbial biomass). Our results suggest that altered rainfall consistently impacted dryland ecosystem function, but that microbial biomass is a poor proxy for rainfall-induced changes in soil processes.

Severe Prolonged Drought Favours Stress-Tolerant Microbes in Australian Drylands

Drylands comprise one-third of Earth’s terrestrial surface area and support over two billion people. Most drylands are projected to experience altered rainfall regimes, including changes in total amounts and fewer but larger rainfall events interspersed by longer periods without rain. This transition will have ecosystem-wide impacts but the long-term effects on microbial communities remain poorly quantified. We assessed belowground effects of altered rainfall regimes (+ 65% and -65% relative to ambient) at six sites in arid and semi-arid Australia over a period of three years (2016–2019) coinciding with a significant natural drought event (2017–2019). Microbial communities differed significantly among semi-arid and arid sites and across years associated with variation in abiotic factors, such as pH and carbon content, along with rainfall. Rainfall treatments induced shifts in microbial community composition only at a subset of the sites (Milparinka and Quilpie). However, differential abundance analyses revealed that several taxa, including Acidobacteria, TM7, Gemmatimonadates and Chytridiomycota, were more abundant in the wettest year (2016) and that their relative abundance decreased in drier years. By contrast, the relative abundance of oligotrophic taxa such as Actinobacteria, Alpha-proteobacteria, Planctomycetes, and Ascomycota and Basidiomycota, increased during the prolonged drought. Interestingly, fungi were shown to be more sensitive to the prolonged drought and to rainfall treatment than bacteria with Basidiomycota mostly dominant in the reduced rainfall treatment. Moreover, correlation network analyses showed more positive associations among stress-tolerant dominant taxa following the drought (i.e., 2019 compared with 2016). Our result indicates that such stress-tolerant taxa play an important role in how whole communities respond to changes in aridity. Such knowledge provides a better understanding of microbial responses to predicted increases in rainfall variability and the impact on the functioning of semi-arid and arid ecosystems.

Deforestation-induced changes in rainfall decrease soybean-maize yields in Brazil

Whereas the global demand for food, fiber and energy is increasing, the capacity of ecosystems services to sustain agricultural production is being compromised worldwide. Brazil is a global food supplier that has benefitted from agricultural intensification in the past decades. At the same time, expansion of cropland has led to deforestation that, in turn, is increasingly affecting rainfall patterns thereby influencing crop yields. This study examines how loss in forest cover has impacted agricultural yields through change in rainfall. To do so, we use modelled data on changes in rainfall patterns due to deforestation as input to a crop model. We assess yield changes within the soybean-maize double cropping system, the country's most relevant agricultural system, in five states within the Amazon and Cerrado biomes. Findings revealed that soybean and maize yields would have been respectively 6.6 % and 9.9 % higher per year in the last decade if rainfall patterns hadn't been altered by deforestation from 1982 onwards. Although agricultural efficiency improved between 2011 and 2020, it was insufficient to offset the negative effect of altered rainfall on yields. Our paper reveals the link between deforestation and crop yields, emphasizing the need to preserve forest cover for agricultural resilience and food security. It reinforces the critical role of forests in regulating the water cycle, particularly in the face of climate change-induced warmer and drier conditions that can impact agricultural production and other human activities.

Invasion by Hyptis suaveolens modifies the effects of altered rainfall variability on nutrient cycling across seasons in a dry tropical grassland experiment

ABSTRACT Ecosystems often recover rapidly when changes in climatic conditions are moderate, but extreme changes may push the ecosystem beyond its biological threshold, resulting in rather profound changes in its functioning and species composition. We experimentally evaluated how the ecosystem functioning of tropical grassland may change under changing precipitation variability by investigating shifts in soil properties and their relation to plant invasions. We found that soil moisture, soil pH, inorganic N content (NO3 - N + NH4 - N), N mineralization rate, and soil CO2 flux increase with a rise in rainfall. Moreover, the grassland plots invaded by Hyptis suaveolens, particularly those with increased precipitation, demonstrated elevated mineralization rates, substantial nutrient accumulation, and a reduced microbial biomass in comparison to the uninvaded plots. Our study highlighted that, following soil moisture (SM) and soil temperature (ST), N mineralization emerged as the third primary driver of soil CO2 flux. Enhanced precipitation led to increased N mineralization and subsequent CO2 emissions. The results indicate that escalated CO2 flux in invaded plots could be linked to invasive H. suaveolens adverse effects on soil processes, potentially leading to short-term inefficient nutrient cycling and elevated CO2 emissions, with potential consequences for the overall stability of the ecosystem.

Responses of nematode abundances to increased and reduced rainfall under field conditions: A meta‐analysis

AbstractEcosystems are projected to experience altered precipitation patterns associated with climate change, with some areas becoming wetter and others drier. Both above‐ and belowground communities will be impacted by such rainfall changes, yet research has predominantly focused on the flora and fauna aboveground. Still, there is a growing body of literature for the effects of altered precipitation on soil fauna. Nematodes are diverse and abundant in most soils, represent multiple trophic levels, and influence essential soil processes, making this group a good proxy for broader impacts on soil food webs. Hence, we assessed the effects of increased and reduced rainfall amount on total and trophic‐level abundances of nematodes using a meta‐analytical approach based on 46 independent observations from 37 field studies and tested whether effects differed among ecosystem types and with treatment duration (<1 year, short term; >1 year, long term). Overall, total and trophic group's abundances, except fungal feeders, were negatively impacted by reduced rainfall irrespectively of treatment duration. Increased rainfall had a positive effect on total abundances and plant parasitic nematodes, but only in longer term studies (>1 year). The impacts of altered rainfall were consistent across the ecosystems studied; however, most studies focus on grasslands and deserts, making it difficult to draw broad generalizations. Reductions in rainfall are therefore likely to decrease soil nematode abundance, with less pronounced effects on fungal feeders. Increased rainfall, on the other hand, may favor plant parasites, likely due to increased plant productivity. Hence, projections of reduced rainfall will have significant negative impacts on nematode abundances, at least in grasslands and deserts, with cascading effects on soil processes.

Rainfall pulse regime drives biomass and community composition in biological soil crusts.

Future climates will alter the frequency and size of rain events in drylands, potentially affecting soil microbes that generate carbon feedbacks to climate, but field tests are rare. Topsoils in drylands are commonly colonized by biological soil crusts (biocrusts), photosynthesis-based communities that provide services ranging from soil fertilization to stabilization against erosion. We quantified responses of biocrust microbial communities to 12 years of altered rainfall regimes, with 60 mm of additional rain per year delivered either as small (5 mm) weekly rains or large (20 mm) monthly rains during the summer monsoon season. Rain addition promoted microbial diversity, suppressed the dominant cyanobacterium, Microcoleus vaginatus, and enhanced nitrogen-fixing taxa, but did not consistently increase microbial biomass. The addition of many small rain events increased microbial biomass, whereas few, large events did not. These results alter the physiological paradigm that biocrusts are most limited by the amount of rainfall and instead predict that regimes enriched in small rain events will boost cyanobacterial biocrusts and enhance their beneficial services to drylands.

The Diversity of Soil Bacteria and Fungi Under Altered Nitrogen and Rainfall Patterns in a Temperate Steppe.

The response of soil microorganisms to altered nitrogen (N) and rainfall patterns plays an important role in understanding ecosystem carbon and nitrogen cycling processes under global change. Previous studies have separately focused on the effects of N addition and rainfall on soil microbial diversity and community composition. However, the combined and interactive impact of N addition and rainfall on soil microbial diversity and function mediated by plant and soil processes have been poorly investigated for grassland ecosystems. Here, we conducted a field experiment with simulated N addition (N addition: 10 g N m–2yr–1) and altered rainfall pattern [control, rainfall reduction (compared to control –50%); rainfall addition (compared to control + 50%)] to study their interactive effects on soil microbial diversity and function in a temperate steppe of Inner Mongolia. Our results showed that N addition and rainfall addition significantly increased soil bacterial diversity, and the bacterial diversity was positively correlated with soil microbial biomass nitrogen, inorganic nitrogen, and Stipa krylovii root exudate C:N ratio, Allium polyrhizum root exudate C and N, and A. polyrhizum root exudate C:N ratio. N addition and rainfall reduction significantly reduced fungal diversity, which correlated closely with soil microbial biomass carbon and the C:N ratio of A. polyrhizum root exudates. Bacteria were mainly eutrophic r-strategists, and the responses of bacterial function guilds to the interaction between N addition and rainfall pattern were not significant. However, the arbuscular mycorrhizal fungi (AMF), in the functional classification of fungi, were significantly reduced under the condition of N addition and rainfall reduction, and the absolute abundance of the phylum Glomeromycota increased under rainfall addition, suggesting that AMFs are sensitive to altered N and rainfall patterns over short timescales (1 year). Collectively, our results have important implications for understanding the plant–soil–microbe system of grasslands under climate change.

Insensitivity of Ecosystem Productivity to Predicted Changes in Fine‐Scale Rainfall Variability

AbstractChanges in rainfall associated with climate change are expected to affect the tightly coupled water‐carbon ecosystem dynamics. Here, we study the effects of altered rainfall at 33 sites in North America, as projected by the high‐resolution/high‐fidelity (∼4 km, 1 hr) continental‐wide Weather Research Forecasting (WRF) convection‐permitting model under a high‐emission scenario (RCP 8.5). We make use of a stochastic weather generator to extend WRF outputs, accounting for natural variability and simultaneously separate the changes in total rainfall, its seasonality, and its intraseasonal pattern. We used these rainfall scenarios to study ecosystem responses with the state‐of‐the‐art Tethys‐Chloris terrestrial biosphere model. Model simulations suggest that increases in mean annual rainfall dominate ecosystem responses at dry sites, while wet sites are less sensitive to rainfall changes. Sites of intermediate wetness face reductions in productivity, due to reduced growing season rainfall and increased water losses under altered seasonality, which outpace any possible benefits induced by increases in mean annual totals. Changes in the fine‐scale temporal structure of rainfall have an insignificant impact on ecosystem productivity and only alter hydrological dynamics, contradicting expectations based on some field experiments, which, however, are not tailored to directly quantify climate change impacts, but rather to understand the mechanisms leading to ecosystem responses. We further demonstrate how approaches following the “fewer but larger rainfall events” concept might exacerbate ecosystem responses.

Global patterns in culturable soil yeast diversity

SummaryYeasts, broadly defined as unicellular fungi, fulfill essential roles in soil ecosystems as decomposers and nutrition sources for fellow soil-dwellers. Broad-scale investigations of soil yeasts pose a methodological challenge as metagenomics are of limited use for identifying this group of fungi. Here we characterize global soil yeast diversity using fungal DNA barcoding on 1473 yeasts cultured from 3826 soil samples obtained from nine countries in six continents. We identify mean annual precipitation and international air travel as two significant correlates with soil yeast community structure and composition worldwide. Evidence for anthropogenic influences on soil yeast communities, directly via travel and indirectly via altered rainfall patterns resulting from climate change, is concerning as we found common infectious yeasts frequently distributed in soil in several countries. Our discovery of 41 putative novel species highlights the continued need for culture-based studies to advance our knowledge of environmental yeast diversity.

Divergent effects of biological soil crusts on soil respiration between bare patches and shrub patches under simulated rainfall in a desert ecosystem in Northwest China

The important role of biological soil crusts (biocrusts) in determining the soil carbon balance in dryland ecosystems under future climate change has been widely explored. However, when assessing the effects of biocrusts on soil respiration, few studies have considered biocrusts in bare soil patches and shrub soil patches. A field experiment was performed with five simulated rainfall addition events (0, 5, 15, 25, and 40 mm) in shrub and bare soil patches in June (early growing season, EGS), July (middle growing season, MGS) and September (late growing season, LGS) in 2016 and 2017. Our objective was to examine whether biocrusts at shrub and bare soil patches have the same effect on soil respiration under altered rainfall regimes. The results showed that the removal of biocrusts from bare patches reduced soil respiration by 15 % after rainfall amounts of 5–40 mm and increased the subsurface soil temperature and decreased the soil moisture after various rainfall treatments. However, in shrub patches, the removal of biocrusts led to a significant increase in soil respiration of 57 % and subsequent increases in subsurface soil temperature and moisutre. The discrepancy in the soil respiration response between the two types of patches might be attributable to the increase in soil infiltration after biocrust removal, with a greater stimulating increase in soil carbon emissions stimulated in the shrub patches than in the bare patches due to more the greater amounts of roots distributed under the former shrub patches. Our results indicate that the destruction of biocrusts in shrub patches may reduce the ability of biocrust ecosystems to become a net carbon sinks, with potentially negative consequences for ecosystem function and sustainability in water-limited regions.

Responses of soil N2 O emissions and their abiotic and biotic drivers to altered rainfall regimes and co-occurring wet N deposition in a semi-arid grassland.

Global change factors such as changed rainfall regimes and nitrogen (N) deposition contribute to increases in the emission of the greenhouse gas nitrous oxide (N2 O) from the soil. In previous research, N deposition has often been simulated by using a single or a series of N addition events over the course of a year, but wet N deposition actually co-occurs with rainfall. How soil N2 O emissions respond to altered rainfall amount and frequency, wet N deposition, and their interactions is still not fully understood. We designed a three-factor, fully factorial experiment with factors of rainfall amounts (ambient, -30%) rainfall frequency (ambient, ±50%) and wet N deposition (with/without) co-occurring with rainfall in semi-arid grassland mesocosms, and measured N2 O emissions and their possible biotic and abiotic drivers. Across all treatments, reduced rainfall amount and N deposition increased soil N2 O emissions by 35% and 28%, respectively. A significant interactive effect was observed between rainfall amount and N deposition, and to a lesser extent between rainfall frequency and N deposition. Without N deposition, reduced rainfall amount and altered rainfall frequency indirectly affected soil N2 O emissions by changing the abundance of nirK and soil net N mineralization, and the changes in nirK abundance were indirectly driven by soil N availability rather than directly by soil moisture. With N deposition, both the abundance of nirK and the level of soil water-filled pore space contributed to changes in N2 O emissions in response to altered rainfall regimes, and the changes in the abundance of nirK were indirectly driven by plant N uptake and nitrifier (ammonia-oxidizing bacteria) abundance. Our results imply that unlike wetter grassland ecosystems, reduced precipitation may increase N2 O emissions, and N deposition may only slightly increase N2 O emissions in arid and semi-arid N-limited ecosystems that are dominated by grasses with high soil N uptake capacity.

Altered precipitation and root herbivory affect the productivity and composition of a mesic grassland

BackgroundClimate change models predict changes in the amount, frequency and seasonality of precipitation events, all of which have the potential to affect the structure and function of grassland ecosystems. While previous studies have examined plant or herbivore responses to these perturbations, few have examined their interactions; even fewer have included belowground herbivores. Given the ecological, economic and biodiversity value of grasslands, and their importance globally for carbon storage and agriculture, this is an important knowledge gap. To address this, we conducted a precipitation manipulation experiment in a former mesic pasture grassland comprising a mixture of C4 grasses and C3 grasses and forbs, in southeast Australia. Rainfall treatments included a control [ambient], reduced amount [50% ambient] and reduced frequency [ambient rainfall withheld for three weeks, then applied as a single deluge event] manipulations, to simulate predicted changes in both the size and frequency of future rainfall events. In addition, half of all experimental plots were inoculated with adult root herbivores (Scarabaeidae beetles).ResultsWe found strong seasonal dependence in plant community responses to both rainfall and root herbivore treatments. The largest effects were seen in the cool season with lower productivity, cover and diversity in rainfall-manipulated plots, while root herbivore inoculation increased the relative abundance of C3, compared to C4, plants.ConclusionsThis study highlights the importance of considering not only the seasonality of plant responses to altered rainfall, but also the important role of interactions between abiotic and biotic drivers of vegetation change when evaluating ecosystem-level responses to future shifts in climatic conditions.