Feedbacks of terrestrial ecosystems to atmospheric and climate change depend on soil ecosystem dynamics. Soil ecosystems can directly and indirectly respond to climate change. For example, warming ...directly alters microbial communities by increasing their activity. Climate change may also alter plant community composition, thus indirectly altering the soil communities that depend on their inputs. To better understand how climate change may directly and indirectly alter soil ecosystem functioning, we investigated oldâfield plant community and soil ecosystem responses to single and combined effects of elevated COâ, warming, and precipitation in Tennessee (USA). Specifically, we collected soils at the plot level (plant community soils) and beneath dominant plant species (plantâspecific soils). We used microbial enzyme activities and soil nematodes as indicators for soil ecosystem functioning. Our study resulted in two main findings: (1) Overall, while there were some interactions, water, relative to increases in COâ and warming, had the largest impact on plant community composition, soil enzyme activity, and soil nematodes. Multiple climateâchange factors can interact to shape ecosystems, but in our study, those interactions were largely driven by changes in water. (2) Indirect effects of climate change, via changes in plant communities, had a significant impact on soil ecosystem functioning, and this impact was not obvious when looking at plant community soils. Climateâchange effects on enzyme activities and soil nematode abundance and community structure strongly differed between plant community soils and plantâspecific soils, but also within plantâspecific soils. These results indicate that accurate assessments of climateâchange impacts on soil ecosystem functioning require incorporating the concurrent changes in plant function and plant community composition. Climateâchangeâinduced shifts in plant community composition will likely modify or counteract the direct impact of atmospheric and climate change on soil ecosystem functioning, and hence, these indirect effects should be taken into account when predicting the manner in which global change will alter ecosystem functioning.
Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities? In a 14 d ...laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g⁻¹ soil) to soils amended with and without ¹³C-labeled plant residue. We measured CO₂ respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR). Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g⁻¹) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g⁻¹) had no impact on plant residue decomposition, while greater concentrations of C (> 7.2 mg C g⁻¹) reduced decomposition (-50%). Concurrently, high exudate concentrations (> 3.6 mg C g⁻¹) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (< 3.6 mg C g⁻¹) increased metabolic activity rather than gene copy numbers. These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.
High elevation and latitude ecosystems are experiencing high levels of anthropogenic atmospheric warming. Climate warming may directly change soil microbial activity and alter ecosystem carbon ...dynamics and productivity, but increasing evidence suggests these responses may depend on other biotic factors such as plant community composition and abiotic factors such as moisture.
We examined how abiotic (warming) and biotic (presence of dominant plant species) factors interact to affect soil microbial processes. Our experiment deployed the independent and combined treatments of experimental warming and dominant plant species removal in a high and low elevation montane meadows. We analysed multiple soil microbial responses to warming and the presence of a dominant plant at three times throughout the growing season, including soil respiration, microbial metabolic functional diversity, microbial biomass carbon and nitrogen, and extracellular enzyme potential activity.
Overall, there were few independent microbial responses to either the warming or the removal treatments. There was a significant interaction between warming and the removal of a dominant plant species, where microbial biomass and the activity of some microbial enzymes were lower in warmed plots where the dominant species was removed relative to control plots.
The effect of warming on extracellular enzyme activity was typically observed only at the high‐elevation site. In contrast, we found that effects of warming were consistent across the growing season, despite strong temporal variation in microbial properties.
Our results emphasize the need to further consider soil microbial responses to warming under multiple environments, including shifts in both biotic and abiotic factors, to aid in predictions of carbon dynamics under future global change.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
Many serious ecosystem consequences of climate change will take decades or even centuries to emerge. Long-term ecological responses to global change are strongly regulated by slow processes, such as ...changes in species composition, carbon dynamics in soil and by long-lived plants, and accumulation of nutrient capitals. Understanding and predicting these processes require experiments on decadal time scales. But decadal experiments by themselves may not be adequate because many of the slow processes have characteristic time scales much longer than experiments can be maintained. This article promotes a coordinated approach that combines long-term, large-scale global change experiments with process studies and modeling. Long-term global change manipulative experiments, especially in high-priority ecosystems such as tropical forests and high-latitude regions, are essential to maximize information gain concerning future states of the earth system. The long-term experiments should be conducted in tandem with complementary process studies, such as those using model ecosystems, species replacements, laboratory incubations, isotope tracers, and greenhouse facilities. Models are essential to assimilate data from long-term experiments and process studies together with information from long-term observations, surveys, and space-for-time studies along environmental and biological gradients. Future research programs with coordinated long-term experiments, process studies, and modeling have the potential to be the most effective strategy to gain the best information on long-term ecosystem dynamics in response to global change.
Abstract
As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter ...decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.
Ecosystems containing multiple nonnative plant species are common, but mechanisms promoting their co-occurrence are understudied. Plant-soil interactions contribute to the dominance of singleton ...species in nonnative ranges because many nonnatives experience stronger positive feedbacks relative to co-occurring natives. Plant-soil interactions could impede other nonnatives if an individual nonnative benefits from its soil community to a greater extent than its neighboring nonnatives, as is seen with natives. However, plant-soil interactions could promote nonnative co-occurrence if a nonnative accumulates beneficial soil mutualists that also assist other nonnatives. Here, we use greenhouse and field experiments to ask whether plant-soil interactions (1) promote the codominance of two common nonnative shrubs (
Ligustrum sinense
and
Lonicera maackii
) and (2) facilitate the invasion of a less-common nonnative shrub (
Rhamnus davurica
) in deciduous forests of the southeastern United States. In the greenhouse, we found that two of the nonnatives,
L. maackii
and
R. davurica
, performed better in soils conditioned by nonnative shrubs compared to uninvaded forest soils, which suggests that positive feedbacks among co-occurring nonnative shrubs can promote continued invasion of a site. In both greenhouse and field experiments, we found consistent signals that the codominance of the nonnatives
L. sinense
and
L. maackii
may be at least partially explained by the increased growth of
L. sinense
in
L. maackii
soils. Overall, significant effects of plant-soil interactions on shrub performance indicate that plant-soil interactions can potentially structure the co-occurrence patterns of these nonnatives.
Abstract
Winters in snow-covered regions have warmed, likely shifting the timing and magnitude of nutrient export, leading to unquantified changes in water quality. Intermittent, seasonal, and ...permanent snow covers more than half of the global land surface. Warming has reduced the cold conditions that limit winter runoff and nutrient transport, while cold season snowmelt, the amount of winter precipitation falling as rain, and rain-on-snow have increased. We used existing geospatial datasets (rain-on-snow frequency overlain on nitrogen and phosphorous inventories) to identify areas of the contiguous United States (US) where water quality could be threatened by this change. Next, to illustrate the potential export impacts of these events, we examined flow and turbidity data from a large regional rain-on-snow event in the United States’ largest river basin, the Mississippi River Basin. We show that rain-on-snow, a major flood-generating mechanism for large areas of the globe (Berghuijs
et al
2019
Water Resour. Res.
55
4582–93; Berghuijs
et al
2016
Geophys. Res. Lett.
43
4382–90), affects 53% of the contiguous US and puts 50% of US nitrogen and phosphorus pools (43% of the contiguous US) at risk of export to groundwater and surface water. Further, the 2019 rain-on-snow event in the Mississippi River Basin demonstrates that these events could have large, cascading impacts on winter nutrient transport. We suggest that the assumption of low wintertime discharge and nutrient transport in historically snow-covered regions no longer holds. Critically, however, we lack sufficient data to accurately measure and predict these episodic and potentially large wintertime nutrient export events at regional to continental scales.
Ecological succession drives large-scale changes in ecosystem composition over time, but the mechanisms whereby climatic change might alter succession remain unresolved. Here, we asked if the effects ...of atmospheric and climatic change would alter tree seedling emergence and establishment in an old-field ecosystem, recognizing that small shifts in rates of seedling emergence and establishment of different species may have long-term repercussions on the transition of fields to forests in the future.
We introduced seeds from three early successional tree species into constructed old-field plant communities that had been subjected for 4 years to altered temperature, precipitation, and atmospheric CO(2) regimes in an experimental facility. Our experiment revealed that different combinations of atmospheric CO(2) concentration, air temperature, and soil moisture altered seedling emergence and establishment. Treatments directly and indirectly affected soil moisture, which was the best predictor of seedling establishment, though treatment effects differed among species.
The observed impacts, coupled with variations in the timing of seed arrival, are demonstrated as predictors of seedling emergence and establishment in ecosystems under global change.
Atmospheric and climatic change can alter plant biomass production and plant community composition. However, we know little about how climate change-induced alterations in biomass production affect ...plant species composition. To better understand how climate change will alter both individual plant species and community biomass, we manipulated atmospheric CO₂, air temperature, and precipitation in a constructed old-field ecosystem. Specifically, we compared the responses of dominant and subdominant species to our climatic treatments, and explored how changes in plant dominance patterns alter community evenness over 2 years. Our study resulted in four major findings: (1) all treatments, elevated CO₂, warming, and increased precipitation increased plant community biomass and the effects were additive rather than interactive, (2) plant species differed in their response to the treatments, resulting in shifts in the proportional biomass of individual species, which altered the plant community composition; however, the plant community response was largely driven by the positive precipitation response of Lespedeza, the most dominant species in the community, (3) precipitation explained most of the variation in plant community composition among treatments, and (4) changes in precipitation caused a shift in the dominant species proportional biomass that resulted in lower community evenness in the wet relative to dry treatments. Interestingly, compositional and evenness responses of the subdominant community to the treatments did not always follow the responses of the whole plant community. Our data suggest that changes in plant dominance patterns and community evenness are an important part of community responses to climatic change, and generally, that such compositional shifts can alter ecosystem biomass production and nutrient inputs.
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