Belowground Responses Research Articles

Weed encroachment affects soil organic carbon stock in bermudagrass pastures

AbstractWeed encroachment indicates pasture degradation and is a major challenge for adequate pasture management. Additionally, it might compromise the soil organic carbon (SOC) stock, affecting global climate change. Common bermudagrass [Cynodon dactylon (L.) Pers.] is a worldwide grown forage species, but broadleaf weed species often encroach during the warm season without appropriate weed management. Spiny pigweed (Amaranthus spinosus L.) is one of the widely encountered weeds in pastures across the globe. We quantified the SOC in bermudagrass pastures encroached with different levels of spiny pigweed after 3 years. Different methods (fixed depth vs. equivalent soil mass [ESM] approaches) were evaluated for SOC estimates. The treatments were paddocks free of weeds (weed‐free), paddocks with weeds established in alternated strips (weed‐strips), and paddocks with weeds spread throughout the whole area (weed‐infested) in a randomized complete block design with four replicates. Bermudagrass herbage accumulation rate (HAR) and belowground responses were evaluated as explanatory variables. Spiny pigweed encroachment reduced the bermudagrass HAR and belowground biomass accumulation. The fixed depth method overestimated the SOC in the topsoil layer, while differences between ESM approaches were negligible. The SOC concentration was greater in weed‐free than weed‐infested areas. The cumulative SOC stock (0–15 cm) estimated on an ESM basis was 15% lower in weed‐infested pastures (33.6 Mg ha−1) compared to weed‐free or weed‐strips (39.5 Mg ha−1). Spiny pigweed encroachment in bermudagrass pastures significantly impacts the soil in the short term, leading to lower SOC stocks compared to weed‐free pastures.

Decoupling of plant and microbial communities following long‐term removal of an invasive grass

Ecosystem function can be shaped by the relationship between plant and soil microbial communities. When invasive plants disrupt these plant–soil feedbacks, they can leave soil legacy effects that persist even after removal. However, such legacy effects vary among species, and links between aboveground and belowground recovery after invasive plant removal remain unclear. We examined the potential legacy effects of the invasive yellow bluestem (Bothriochloa ischaemum var. songarica) in a grassland in central Texas, USA. In a 9‐year removal experiment, we measured the diversity and composition of plant and soil microbial communities in invaded plots (dominated by the invasive grass), removal plots (where the invasive was continually removed), and native‐dominated plots. With only passive recovery (i.e. no active seeding or planting), plant richness, native grass cover, and native forb cover in removal plots became similar to native‐dominated plots in 1–3 years, although species composition was still different 8 years after removal. In contrast, soil microbial diversity and composition did not differ among the treatments, including no differences between invaded and native‐dominated plots. Plant species composition may be influenced by dispersal limitations because removal plots are still surrounded by the invasive grass. The observed decoupling between aboveground and belowground responses to invasion and removal efforts could be due to the soil microbial community's resistance to influence by the invasive grass. These results suggest that microbial soil legacy effects will likely not limit grassland restoration and that active seeding or planting may be required for a more complete restoration of native plant communities after yellow bluestem removal.

Aboveground-belowground linkages across vegetation degradation gradients differ among native eucalypt communities.

Native vegetation degradation impacts soil communities and their functions. However, these impacts are often studied by comparing soil biotic attributes across qualitatively defined, discrete degradation levels within a single plant community at a specific location. Direct quantification of the relationships between vegetation and soil attributes across continuous degradation gradients and at larger scales is rare but holds greater potential to reveal robust patterns in aboveground-belowground linkages that may apply across different plant communities. We investigated how native vegetation attributes relate to soil communities and their functions across a degradation gradient within three native temperate eucalypt woodland and forest communities that differed in soil nutrient availabilities. Across remnant patches of native vegetation in the Sydney Basin bioregion, we established plots representing different levels of decline in their vegetation quality (i.e., increased exotics and canopy changes) compared to relevant reference communities. In those plots, we assessed soil community groups (microbes and fauna), carbon (C) and nutrient cycling (litter decomposition, enzyme activity, and phosphate and nitrate accumulation rates), soil pH, texture and vegetation attributes (composition, structure, and function). Our unique study design revealed that the relationships between vegetation degradation and soil biota across the food web (i.e., AM fungi, Fungi:bacteria ratio, Gram-positive bacteria, total nematodes) were highly dependent on the plant community. However, the degradation impacts on soil functions (i.e., total enzyme activity, and phosphate availability) were mostly consistent, suggesting their potential as belowground indicators of ecosystem degradation, with a notable positive association observed in phosphate availability rates. Additionally, the effects of vegetation degradation on soil biota and their functions appeared stronger in the nutrient-poor plant communities, suggesting greater vulnerability of their belowground components. Our findings call for caution when generalizing belowground responses to degradation and for further research on how nutrient availability mediates the impacts of degradation on aboveground-belowground linkages.

Rapid Increase in Soil Respiration and Reduction in Soil Nitrate Availability Following CO2 Enrichment in a Mature Oak Forest.

In the future, with elevated atmospheric CO2 (eCO2), forests are expected to increase woody biomass to capture more carbon (C), though this is dependent on soil nutrient availability. While young forests may access unused nutrients by growing into an unexplored soil environment, it is unclear how or if mature forests can adapt belowground under eCO2. Soil respiration (R s) and nutrient bioavailability are integrative ecosystem measures of below-ground dynamics. At Birmingham's Institute of Forest Research Free Air CO2 Enrichment (BIFoR FACE) facility, we investigated the effects of eCO2 (+150 ppm above ambient) on a mature oak forest during the first year of exposure. We observed an annual Rs increase of ∼21.5%; 996 ± 398 g C m-2 year-1 (ambient) to 1210 ± 483 g C m-2 year-1 (eCO2). The eCO2 impact was greater on belowground nutrient cycling, with monthly nitrate availability decreasing by up to 36%. These results show that high C uptake resulted in higher soil respiration with a concomitant decrease in the level of soil nitrate during the first year. These belowground responses and their long-term dynamics will have implications for the carbon budget of mature forest ecosystems in changing climate.

EFFECT OF WILDFIRE ON BELOWGROUND FAUNAL COMMUNITIES IN VARIABLE LANDSCAPES: A COMPREHENSIVE REVIEW

Wildfires are increasingly frequent and severe globally, with profound impacts on ecosystems. While the effects of fire on aboveground communities are well-documented, less is known about the responses of belowground fauna. This comprehensive review synthesizes current knowledge on how wildfires affect soil-dwelling organisms across diverse landscapes. We examine the direct and indirect impacts of fire on various faunal groups, including microarthropods, nematodes, and earthworms, and explore how landscape variability influences these effects. The review highlights the complex interplay between fire intensity, soil properties, and faunal community composition. We discuss the implications of these findings for ecosystem recovery and resilience, and identify critical knowledge gaps to guide future research. Understanding the responses of belowground communities to wildfire is crucial for developing effective post-fire management strategies and predicting long-term ecosystem changes in a warming world.

Long-Term Soil Warming Drives Different Belowground Responses in Arbuscular Mycorrhizal and Ectomycorrhizal Trees.

The ability of trees to acquire soil nutrients under future climate conditions will influence forest composition and function in a warmer world. Rarely are multiple belowground carbon allocation pathways measured simultaneously in large global change experiments, restricting our understanding of how trees may shift their allocation of resources to different nutrient acquisition mechanisms under future climates. Leveraging a 20-year soil warming experiment, we show that ectomycorrhizal (EM) trees reduce mycorrhizal colonization and root exudation while increasing fine root biomass, while arbuscular mycorrhizal (AM) trees largely maintained their belowground carbon allocation patterns in warmer soils. We suggest that AM trees may be better adapted to thrive under global warming due to higher rates of nitrogen mineralization in warmer soils and the ability of their mycorrhizal symbiont to acquire mineralized inorganic nutrients, whereas EM trees may need to alter their belowground carbon allocation patterns to remain competitive as global temperatures rise.

Integrated above and below-ground responses of the gypsum specialist Helianthemum squamatum (L.). to drought

Integrated above and below-ground responses of the gypsum specialist Helianthemum squamatum (L.). to drought

Belowground plant competition: uncoupling root response strategies of peas.

Belowground plant competition has been shown to induce varying responses, from increases to decreases in root biomass allocation or in directional root placement. Such inconsistencies could result from the fact that root allocation and directional growth were seldom studied together, even though they might represent different strategies. Moreover, variations in belowground responses might be due to different size hierarchies between plants, but this hypothesis has not been studied previously. In a greenhouse rhizobox experiment, we examined the way both root allocation and directional root placement of Pisum sativum are affected by the size and density of Festuca glauca neighbours, and by nutrient distribution. We found that root allocation of P. sativum increased with the density and size of F. glauca. By contrast, directional root placement was unaffected by neighbour size and increased either towards or away from neighbours when nutrients were patchily or uniformly distributed, respectively. These results demonstrate that directional root placement under competition is contingent on the distribution of soil resources. Interestingly, our results suggest that root allocation and directional placement might be uncoupled strategies that simultaneously provide stress tolerance and spatial responsiveness to neighbours, thus highlighting the importance of measuring both when studying belowground plant competition.

Measuring leaf and root functional traits uncovers multidimensionality of plant responses to arbuscular mycorrhizal fungi.

While many studies have measured the aboveground responses of plants to mycorrhizal fungi at a single time point, little is known about how plants respond belowground or across time to mycorrhizal symbiosis. By measuring belowground responses and growth over time in many plant species, we create a more complete picture of how mycorrhizal fungi benefit their hosts. We grew 26 prairie plant species with and without mycorrhizal fungi and measured 14 functional traits to assess above- and belowground tissue quality and quantity responses and changes in resource allocation. We used function-valued trait (FVT) modeling to characterize changes in species growth rate when colonized. While aboveground biomass responses were positive, the response of traits belowground were much more variable. Changes in aboveground biomass accounted for 60.8% of the variation in mycorrhizal responses, supporting the use of aboveground biomass response as the primary response trait. Responses belowground were not associated with aboveground responses and accounted for 18.3% of the variation. Growth responses over time were highly variable across species. Interestingly, none of the measured responses were phylogenetically conserved. Mycorrhizal fungi increase plant growth in most scenarios, but the effects of these fungi belowground and across time are more complicated. This study highlights how differences in plant allocation priorities might affect how they utilize the benefits from mycorrhizal fungi. Identifying and characterizing these differences is a key step to understanding the effects of mycorrhizal mutualisms on whole plant physiology.

Fine root production and turnover rate responses to long-term warming and nitrogen addition in a semi-arid grassland

Fine root production and turnover rate responses to long-term warming and nitrogen addition in a semi-arid grassland

Allocation, morphology, physiology: multiple aspects of above- and below-ground responses to water table stress, duration of drainage in alpine wetland plants (Carex muliensis)

Allocation, morphology, physiology: multiple aspects of above- and below-ground responses to water table stress, duration of drainage in alpine wetland plants (Carex muliensis)

Patterns and mechanisms of belowground carbon responses to changes in precipitation

Abstract It is well known that aboveground productivity usually increases with precipitation. However, how belowground carbon (C) processes respond to changes in precipitation remains elusive, although belowground net primary productivity (BNPP) represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere. This paper reviews the patterns of belowground C processes (BNPP and soil C) in response to changes in precipitation from transect studies, manipulative experiments, modeling and data integration and synthesis. The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation, which is largely different from linear response for aboveground productivity. C allocation, root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect patterns of belowground C processes in response to changes in precipitation. At last, we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation.

Contrasting plant transcriptome responses between a pierce-sucking and a chewing herbivore go beyond the infestation site

BackgroundPlants have acquired a repertoire of mechanisms to combat biotic stressors, which may vary depending on the feeding strategies of herbivores and the plant species. Hormonal regulation crucially modulates this malleable defense response. Jasmonic acid (JA) and salicylic acid (SA) stand out as pivotal regulators of defense, while other hormones like abscisic acid (ABA), ethylene (ET), gibberellic acid (GA) or auxin also play a role in modulating plant-pest interactions. The plant defense response has been described to elicit effects in distal tissues, whereby aboveground herbivory can influence belowground response, and vice versa. This impact on distal tissues may be contingent upon the feeding guild, even affecting both the recovery of infested tissues and those that have not suffered active infestation.ResultsTo study how phytophagous with distinct feeding strategies may differently trigger the plant defense response during and after infestation in both infested and distal tissues, Arabidopsis thaliana L. rosettes were infested separately with the chewing herbivore Pieris brassicae L. and the piercing-sucker Tetranychus urticae Koch. Moderate infestation conditions were selected for both pests, though no quantitative control of damage levels was carried out. Feeding mode did distinctly influence the transcriptomic response of the plant under these conditions. Though overall affected processes were similar under either infestation, their magnitude differed significantly. Plants infested with P. brassicae exhibited a short-term response, involving stress-related genes, JA and ABA regulation and suppressing growth-related genes. In contrast, T. urticae elicited a longer transcriptomic response in plants, albeit with a lower degree of differential expression, in particular influencing SA regulation. These distinct defense responses transcended beyond infestation and through the roots, where hormonal response, flavonoid regulation or cell wall reorganization were differentially affected.ConclusionThese outcomes confirm that the existent divergent transcriptomic responses elicited by herbivores employing distinct feeding strategies possess the capacity to extend beyond infestation and even affect tissues that have not been directly infested. This remarks the importance of considering the entire plant’s response to localized biotic stresses.

Belowground Response of a Bahiagrass Pasture to Long-Term Elevated [CO2] and Soil Fertility Management.

Effects of rising atmospheric CO2 concentration [CO2] on pastures and grazing lands are beginning to be researched, but these important systems remain understudied compared to other agronomic and forest ecosystems. Therefore, we conducted a long-term (2005-2015) study of bahiagrass (Paspalum notatum Flüggé) response to elevated [CO2] and fertility management. The study was conducted at the USDA-ARS, National Soil Dynamics Laboratory open-top field chamber facility, Auburn, AL. A newly established bahiagrass pasture was exposed to either ambient or elevated (ambient + 200 µmol mol-1) [CO2]. Following one year of pasture establishment, half the plots received a fertilizer treatment [N at 90 kg ha-1 three times yearly plus P, K, and lime as recommended by soil testing]; the remaining plots received no fertilization. These treatments were implemented to represent managed (M) and unmanaged (U) pastures; both are common in the southeastern US. Root cores (0-60 cm depth) were collected annually in October and processed using standard procedures. Fertility additions consistently increased both root length density (53.8%) and root dry weight density (68.2%) compared to unmanaged plots, but these root variables were generally unaffected by either [CO2] or its interaction with management. The results suggest that southern bahiagrass pastures could benefit greatly from fertilizer additions. However, bahiagrass pasture root growth is unlikely to be greatly affected by rising atmospheric [CO2], at least by those levels expected during this century.

Symbiotic mycorrhizal types affect patterns of tree aboveground and belowground C allocation in Northeast China

BackgroundGiven the ubiquitous nature of mycorrhizal symbioses, different symbiotic fungi have obvious differences in structure and function, which may affect associated tree aboveground and belowground C allocation dynamics. However, the mechanisms underlying tree aboveground and belowground C allocation and its response to symbiotic mycorrhizal types and other factors (e.g., resource availability) remain poorly understood.ResultsWe used forest inventory data to explore the potential mechanism of tree aboveground and belowground C allocation patterns in Northeast China. Our results showed that tree-fungal symbioses were related to the patterns of tree C allocation. The ratio of aboveground to belowground C pool was significantly higher in ectomycorrhizal (EM)-associated trees than that in arbuscular mycorrhizal (AM)-associated trees. Symbiotic mycorrhizal types were associated with the responses of tree aboveground and belowground C allocation to different factors, such as mean annual precipitation (MAP) and mean annual temperature (MAT). Almost all factors significantly increased aboveground C allocation in AM-associated trees but significantly decreased it in EM-associated trees. Moreover, after controlling the other factors, the effects of climate factors (MAT and MAP) on the C allocation of AM- and EM-associated trees were similar. Increases in MAT and MAP significantly increased belowground and aboveground C allocation, respectively.ConclusionsOur results demonstrate symbiotic mycorrhizal types play an important role in controlling tree aboveground and belowground C allocation and dynamics.

Are absorptive root traits good predictors of ecosystem functioning? A test in a natural temperate forest.

Trait-based approaches provide a useful framework to predict ecosystem functions under intensifying global change. However, our current understanding of trait-functioning relationships mainly relies on aboveground traits. Belowground traits (e.g. absorptive root traits) are rarely studied although these traits are related to important plant functions. We analyzed four pairs of analogous leaf and absorptive root traits of woody plants in a temperate forest and examined how these traits are coordinated at the community-level, and to what extent the trait covariation depends on local-scale environmental conditions. We then quantified the contributions of leaf and absorptive root traits and the environmental conditions in determining two important forest ecosystem functions, aboveground carbon storage, and woody biomass productivity. The results showed that both morphological trait pairs and chemical trait pairs exhibited positive correlations at the community level. Absorptive root traits show a strong response to environmental conditions compared toleaf traits. We also found that absorptive root traits were better predictors of the two forest ecosystem functions than leaf traits and environmental conditions. Our study confirms the important role of belowground traits in modulating ecosystem functions and deepens our understanding of belowground responses to changing environmental conditions.

Spore traits mediate disturbance effects on arbuscular mycorrhizal fungal community composition and mutualisms.

Trait-based approaches in ecology are powerful tools for understanding how organisms interact with their environment. These approaches show particular promise in disturbance and community ecology contexts for understanding how disturbances like prescribed fire and bison grazing influence interactions between mutualists like arbuscular mycorrhizal (AM) fungi and their plant hosts. In this work we examined how disturbance effects on AM fungal spore community composition and mutualisms were mediated by selection for specific functional spore traits at both the species and community level. We tested these questions by analyzing AM fungal spore communities and traits from a frequently burned and grazed (bison) tallgrass prairie system and using these spores to inoculate a plant growth response experiment. Selection for darker, pigmented AM fungal spores, changes in the abundance and volume of individual AM fungal taxa, and altered sporulation, were indicators of fire and grazing effects on AM fungal community composition. Disturbance associated changes in AM fungal community composition were then correlated with altered growth responses of Schizachyrium scoparium grass. Our work shows that utilization of trait-based approaches in ecology can clarify the mechanisms that underly belowground responses to disturbance, and provide a useful framework for understanding interactions between organisms and their environment.

Soil origin impacts Acacia longifolia above and belowground development: water and nutrition as players

Context Acacia longifolia is an aggressive invader, disrupting habitats and communities worldwide. Understanding what drives its expansion is of paramount importance. Key functional traits include fast growth and the presence of bacterial symbionts performing nitrogen fixation. Aims To address early plant development of A. longifolia under different soils and growth conditions (water and nutrition availability), establishing the key factors that influence above and belowground responses. Methods Plants were grown in pots with soils collected from forest, agricultural and dune areas in relative proximity, in a controlled experiment designed to study water effect and nutrient availability on early growth. Growth parameters included shoot and root length, nodule number and weight. Bacteria were isolated from nodules for genetic diversity evaluation. Photosynthetic pigments and isotopic nitrogen and carbon analyses were performed to address nitrogen fixation and photosynthesis. Key results Soil origin influenced plant growth and bacterial diversity. Largest plant development was achieved in forest soils with added nutrition and water. Plants from agricultural soil displayed higher aboveground development; however, belowground nodule number and bacterial biodiversity decreased, possibly due to anthropogenic activities. Forest soil promoted belowground development and bacterial diversity. In dune soils overall growth was lower and nitrogen fixation was higher. Conclusion Abiotic factors influenced juvenile acacia development; nutrition acts as a growth enhancer, and soil origin, including its microbial communities, can be considered a development modulator. Bacterial diversity varied according to soil type. Implications Several above and belowground interactions showed the need for an integrative perspective to understand acacias invasive potential.

Moister soils at elevated CO2 stimulate root biomass but suppress aboveground biomass production in Lolium perenne

Context Increases in atmospheric carbon dioxide concentration ([CO2]) drive increases in biomass production via impacts on photosynthesis and water use. In grasslands, the scale of this stimulation is related to soil water availability. Recently, it has become clear that the way precipitation controls elevated CO2 (eCO2) effects on grassland biomass is strongly seasonal but no mechanism yet exists to explain these observations. Aims The aims of this study were to determine how seasonal water availability affects aboveground, belowground and total biomass responses of a perennial ryegrass pasture to [CO2]. Methods We established the TasFACE2 experiment in a well-fertilised perennial ryegrass (Lolium perenne) monoculture with four seasonal irrigation schedules and three [CO2]. Key results The total biomass production of perennial ryegrass pasture was strongly stimulated by eCO2, but this extra biomass was preferentially allocated to belowground growth. The relationship between soil water content and aboveground biomass varied seasonally but there was a strong positive relationship between soil water content and root biomass production in all seasons. Conclusions Increases in soil moisture caused by eCO2 contributed to increases in root growth, but root biomass production was also stimulated directly by eCO2. Restriction of irrigation, therefore, suppressed the belowground response to eCO2 and created a non-linear response of biomass to CO2 concentration. Implications Antagonistic above- and belowground responses mean that the rising [CO2] might not increase pasture production in the manner generally predicted.

Root traits rather than functional diversity of soil microorganisms respond to drought and plant species composition in Mediterranean shrubland species

Belowground responses are critical in understanding how plants cope with the predicted increase in drought intensity and frequency in the Mediterranean region, because plant root systems compete with each other and interact with soil microbial communities under limiting water availability. However, the combined responses of plant roots and soil microorganisms to drought are not well understood. Using an experimental approach, we addressed the question of how recurrent drought and different combinations of two individuals from three common Mediterranean plant species (Quercus coccifera, Cistus albidus, and Brachypodium retusum) affect root characteristics and soil microbial activity. We hypothesized that drought effects on root characteristics and associated soil microbial communities are stronger when plant individuals of the same species compete for limiting water compared to inter-specific competition. Root morphological traits were more affected by the species identity of the neighbor individual than by recurrent severe drought, particularly in B. retusum, which may in part explain the higher survival previously observed for this species. On the other hand, drought and plant composition had little effect on root-associated soil microbes’ ability to use a wide range of different carbon substrates. Overall, our results did not confirm stronger effects of intra- compared to interspecific competition on the root and microbial responses, but showed strong species identity effects.