Soil microbial communities regulate global biogeochemical cycles and respond rapidly to changing environmental conditions. However, understanding how soil microbial communities respond to climate ...change, and how this influences biogeochemical cycles, remains a major challenge. This is especially pertinent in alpine regions where climate change is taking place at double the rate of the global average, with large reductions in snow cover and earlier spring snowmelt expected as a consequence. Here, we show that spring snowmelt triggers an abrupt transition in the composition of soil microbial communities of alpine grassland that is closely linked to shifts in soil microbial functioning and biogeochemical pools and fluxes. Further, by experimentally manipulating snow cover we show that this abrupt seasonal transition in wide-ranging microbial and biogeochemical soil properties is advanced by earlier snowmelt. Preceding winter conditions did not change the processes that take place during snowmelt. Our findings emphasise the importance of seasonal dynamics for soil microbial communities and the biogeochemical cycles that they regulate. Moreover, our findings suggest that earlier spring snowmelt due to climate change will have far reaching consequences for microbial communities and nutrient cycling in these globally widespread alpine ecosystems.
Extracellular enzymes break down soil organic matter into smaller compounds and their measurement has proved to be a powerful tool to evaluate the functionality of soils. Urease is the enzyme that ...degrades urea and is widely considered to be a good proxy of nitrogen (N) mineralisation. But the methods available to measure this enzyme are time consuming; as such, urease is not commonly included in standard enzyme profiling of soils. We developed a fast, high throughput and reproducible colorimetric microplate technique to evaluate urease activity in soil. The method involves the incubation of soil slurries in 96-deepwell blocks with urea solutions and the measurement, by colorimetric reaction, of ammonium produced. We compared the new method with existing methods, yielding comparable results, and evaluated optimal conditions for urease analysis (soil slurry concentration, substrate concentration, incubation times and extractant salt concentration) in different grassland soils. The method proved to be a faster, higher throughput, and more precise alternative to existing methods for evaluating this important N-related enzyme.
•A new method was designed to measure urease activity in soil.•The method is fast, high throughput, and reproducible.•The new method proved to be a faster and more precise alternative to existing methods.
Root functional traits are known to influence soil properties that underpin ecosystem functioning. Yet few studies have explored how root traits simultaneously influence physical, chemical, and ...biological properties of soil, or how these responses are modified by common grassland perturbations that shape roots, such as defoliation and fertilisation.
Here, we explored how root traits of a wide range of grassland plant species with contrasting resource acquisition strategies (i.e. conservative vs. exploitative strategy plant species) respond to defoliation and fertilisation individually and in combination, and examined cascading impacts on a range of soil abiotic and biotic properties that underpin ecosystem functioning.
We found that the amplitude of the response of root traits to defoliation and fertilisation varied among plant species, in most cases independently of plant resource acquisition strategies. However, the direction of the root trait responses (increase or decrease) to perturbations was consistent across all plant species, with defoliation and fertilisation exerting opposing effects on root traits. Specific root length increased relative to non‐perturbed control in response to defoliation, while root biomass, root mass density, and root length density decreased. Fertilisation induced the opposite responses. We also found that both defoliation and fertilisation individually enhanced the role of root traits in regulating soil biotic and abiotic properties, especially soil aggregate stability.
Synthesis: Our results indicate that defoliation and fertilisation, two common grassland perturbations, have contrasting impacts on root traits of grassland plant species, with direct and indirect short‐term consequences for a wide range of soil abiotic and biotic properties that underpin ecosystem functioning.
摘要
众所周知，根系的功能性状会影响支撑生态系统功能的土壤性质。然而，很少有研究探讨各根系性状如何同时影响土壤的物理、化学和生物特性，以及这些反应如何被常见的草地扰动(例如落叶和施肥)所影响。
这篇文章探讨了落叶和施肥如何单独和共同地影响具有相反资源获取策略(即保守性策略与获取性策略)的各种草原植物物种的根系性状，并研究了对支撑生态系统功能的非生物和生物土壤特性的一系列级联影响。
我们发现根性状对落叶和施肥的反应幅度因植物种类而异，并在大多数情况下与植物资源获取策略无关。然而，所有研究的植物物种根性状对同一扰动的反应方向(增加或减少)都是一致的，并且落叶和施肥对根性性状具有相反的影响。相比于未扰动的对照组，落叶增加了比根长，但降低了根系生物量、根质量密度和根长密度。然而，施肥引起了相反的反应。我们还发现，落叶和施肥都单独地增强了根系性状在调节土壤生物和非生物特性中的作用，特别是土壤团聚体稳定性。
总体上，我们的研究结果表明，落叶和施肥这两种常见的草原扰动对草原植物物种的根性状具有截然不同的影响，并对支撑生态系统功能的各种土壤非生物和生物特性产生直接和间接的短期影响。
Our results indicate that defoliation and fertilisation, two common grassland perturbations, have contrasting impacts on root traits of grassland plant species, with direct and indirect short‐term consequences for a wide range of soil abiotic and biotic properties that underpin ecosystem functioning.
In the Peruvian Coastal Desert, an archipelago of fog oases, locally called lomas, are centers of biodiversity and of past human activity. Fog interception by a tree canopy, dominated by the legume ...tree tara (Caesalpinia spinosa), enables the occurrence in the Atiquipa lomas (southern Peru) of an environmental island with a diverse flora and high productivity. Although this forest provides essential services to the local population, it has suffered 90% anthropogenic reduction in area. Restoration efforts are now getting under way, including discussion as to the most appropriate reference ecosystem to use.
Genetic diversity of tara was studied in the Atiquipa population and over a wide geographical and ecological range. Neither exclusive plastid haplotypes to loma formations nor clear geographical structuring of the genetic diversity was found. Photosynthetic performance and growth of seedlings naturally recruited in remnant patches of loma forest were compared with those of seedlings recruited or planted in the adjacent deforested area. Despite the greater water and nitrogen availability under tree canopy, growth of forest seedlings did not differ from that of those recruited into the deforested area, and was lower than that of planted seedlings. Tara seedlings exhibited tight stomatal control of photosynthesis, and a structural photoprotection by leaflet closure. These drought-avoiding mechanisms did not optimize seedling performance under the conditions produced by forest interception of fog moisture.
Both weak geographic partitioning of genetic variation and lack of physiological specialization of seedlings to the forest water regime strongly suggest that tara was introduced to lomas by humans. Therefore, the most diverse fragment of lomas is the result of landscape management and resource use by pre-Columbian cultures. We argue that an appropriate reference ecosystem for ecological restoration of lomas should include sustainable agroforestry practices that emulate the outcomes of ancient uses.
Bio-fertilisation with plant growth promoting rhizobacteria (PGPR) can be extremely beneficial for plant development and growth under harsh environments. PGPR have been recently successfully applied ...in restoration programmes, but locally adapted strains are needed for successful outcomes. In this study, we evaluated the effect of bio-fertilisation with selected native PGPR strains on the growth and physiological response to drought of Caesalpinia spinosa (Mol.) Kuntze (tara), the main tree species of the Atiquipa forest, a highly valuable and unique ecosystem in the middle of the Atacama Desert in Peru. We compared the growth and physiological status of tara seedlings that were bio-fertilised with three PGPR strains, chemically fertilised and a non-fertilised control, under well-watered and under drought conditions. Seedlings inoculated with Pseudomonas sp. strain RC5.5 showed enhanced tolerance to drought, although under favourable, stress-free conditions it did not promote growth and only significantly increased quantum yield of photosystem II (Fv/Fm). On the other hand, chemical fertilisation highly enhanced plant growth, but led to substantial hydric demand under water limitation. Under drought, RC5.5 bio-fertilised plants showed lower reduction of leaf relative water content, net carbon assimilation rate, stomatal conductance, and a balanced shoot-to-root ratio compared with control plants. Therefore, strain RC5.5 is highlighted as a valuable candidate to be used as inoculant of tara in reforestation and restoration programmes in arid zones, in particular the Atiquipa forest, or in local tara plantations.
•Tara trees were inoculated with local bacterial strains with PGPR capacities.•Bio-fertilisation increased tara tolerance to drought.•Bio-fertilisation did not improve tree growth and morphology.•Chemical fertilisation produced a strong water stress and physiological imbalance.•Pseudomonas RC5.5 is selected as a good candidate to be used as inoculant in the field.
Mangrove ecosystems are important for carbon storage due to their high productivity and low decomposition rates. Waterways have experienced increased nutrient loads as a result of anthropogenic ...activities and it is unclear how this may affect carbon and nutrient cycles in downstream mangroves that receive these nutrient-rich waters. Using a laboratory-based incubation experiment, this study aimed to assess the effects of nutrient addition on the diversity and structure of mangrove soil bacterial communities, as well as biomass and activity of the soil microbial community, under different oxygen conditions. Bacterial community diversity and composition was characterised using 16S rRNA gene sequencing and microbial activity was examined through the measurement of microbial respiration and the activities of enzymes associated with organic matter decomposition. Nitrogen addition caused clear shifts in bacterial community composition, with decreases in bacterial diversity and the abundance of sulfate-reducing bacteria. Microbial biomass also decreased with nitrogen addition under reduced oxygen incubations. Changes in bacterial community structure were accompanied by changes in the activity of some enzymes involved in carbon, nitrogen, and phosphorus cycling. Under reduced oxygen conditions, nitrogen addition resulted in a significant increase in the microbial metabolic quotient but no accompanying change in microbial respiration, which was explained by a decrease in microbial biomass. The findings of this study indicate that nitrogen loading has potential implications for microbial communities and carbon and nutrient cycling in mangrove environments that warrant further investigation under field conditions.
•Nitrogen addition changed bacterial community composition and decreased diversity.•Nitrogen addition decreased abundance of sulfate-reducing bacteria.•Microbial biomass decreased and metabolic quotient increased with nitrogen addition.•Activity of enzymes involved in decomposition changed with nutrient addition.
Abstract
Soil microbial communities play a pivotal role in regulating ecosystem functioning. But they are increasingly being shaped by human-induced environmental change, including intense “pulse” ...perturbations, such as droughts, which are predicted to increase in frequency and intensity with climate change. While it is known that soil microbial communities are sensitive to such perturbations and that effects can be long-lasting, it remains untested whether there is a threshold in the intensity and frequency of perturbations that can trigger abrupt and persistent transitions in the taxonomic and functional characteristics of soil microbial communities. Here we demonstrate experimentally that intense pulses of drought equivalent to a 30-year drought event (<15% WHC) induce a major shift in the soil microbial community characterised by significantly altered bacterial and fungal community structures of reduced complexity and functionality. Moreover, the characteristics of this transformed microbial community persisted after returning soil to its previous moisture status. As a result, we found that drought had a strong legacy effect on bacterial community function, inducing an enhanced growth rate following subsequent drought. Abrupt transitions are widely documented in aquatic and terrestrial plant communities in response to human-induced perturbations. Our findings demonstrate that such transitions also occur in soil microbial communities in response to high intensity pulse perturbations, with potentially deleterious consequences for soil health.
Climate change is disproportionately impacting mountain ecosystems, leading to large reductions in winter snow cover, earlier spring snowmelt and widespread shrub expansion into alpine grasslands. ...Yet, the combined effects of shrub expansion and changing snow conditions on abiotic and biotic soil properties remains poorly understood. We used complementary field experiments to show that reduced snow cover and earlier snowmelt have effects on soil microbial communities and functioning that persist into summer. However, ericaceous shrub expansion modulates a number of these impacts and has stronger belowground effects than changing snow conditions. Ericaceous shrub expansion did not alter snow depth or snowmelt timing but did increase the abundance of ericoid mycorrhizal fungi and oligotrophic bacteria, which was linked to decreased soil respiration and nitrogen availability. Our findings suggest that changing winter snow conditions have cross‐seasonal impacts on soil properties, but shifts in vegetation can modulate belowground effects of future alpine climate change.
Climate change is disproportionately impacting mountain ecosystems, leading to large reductions in winter snow cover, earlier spring snowmelt and widespread shrub expansion into alpine grasslands. Using complimentary field experiments, we show that earlier snowmelt and reductions in snow cover have cross‐seasonal impacts on soil microbial communities and their functioning, with consequences for soil nutrient pools and fluxes. However, we also show that shifts in vegetation can modulate the belowground effects of future alpine climate change.
Photoprotection is a plant functional mechanisms to prevent photooxidative damage by excess light. This is most important when carbon assimilation is limited by drought, and as such, it entails a ...trade-off between carbon assimilation vs stress avoidance. The ecological adaptation of plants to local water availability can lead to different photoprotective strategies. To test this, we used different provenances of Caesalpinia spinosa (Mol.) Kuntze (commonly known as "tara") along a precipitation gradient. Tara is a Neotropical legume tree with high ecological and commercial value, found in dry tropical forests, which are increasingly threatened by climate change. Morphological and physiological responses of tara provenances were analyzed under three different treatments of drought and leaflet immobilization i.e., light stress, in a common garden greenhouse experiment. Tara quickly responded to drought by reducing stomatal conductance, evapotranspiration, photochemical efficiency, carbon assimilation and growth, while increasing structural and chemical photoprotection (leaflet angle and pigments for thermal dissipation). Leaflet closure was an efficient photoprotection strategy with overall physiological benefits for seedlings as it diminished the evaporative demand and avoided photodamage, but also entailed costs by reducing net carbon assimilation opportunities. These responses depended on seed origin, with seedlings from the most xeric locations showing the highest dehydration tolerance, suggesting local adaptation and highlighting the value of different strategies under distinct environments. This plasticity on its response to environmental stress allows tara to thrive in locations with contrasting water availability. Our findings increase the understanding of the factors controlling the functional ecology of tara in response to drought, which can be leveraged to improve forecasts of changes in its distribution range, and for planning restoration projects with this keystone tree species.
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