Aboveground Community Composition Research Articles

Coastal dune management affects above and belowground biotic characteristics.

Dune vegetation mediates dune-building through trapping wind-blown sand and reduces dune erosion by attenuating wave energy via above- and belowground biomass. Despite the role of vegetation in dune functions, the amount and distribution of biomass within a dune remains poorly quantified due to a lack of ample data. Our objectives were to determine the effects of management history and elevation on (1) dune belowground biotic structure and aboveground community composition and (2) to determine best predictors of belowground biomass. We sampled belowground biomass and sedimentology across the dune profile at sites in the Outer Banks, North Carolina, USA. Dunes were classified as either unmanaged (no anthropogenic interventions) or managed (sand fencing, vegetation planting, dune construction). Living belowground biomass was higher in unmanaged dunes and decreased with depth. Non-living belowground biomass was 50% higher than living biomass and with greater abundance in unmanaged dunes. Elevation was a significant covariate of living and non-living belowground biomass, vegetative cover and species richness. Plant community composition varied less in managed dunes and differed significantly from unmanaged dunes. Vegetative cover, species richness, elevation, sedimentology and management history were predictors of belowground biomass. These results underscore the influence of management and geomorphology on dune plant communities, which may influence erosion resistance.

Plant species and soil depth differentially affect microbial diversity and function in grasslands

AbstractIntroductionGrassland ecosystems are a major store of terrestrial carbon (C), yet little is known about their capacity to cycle and store C in deeper soil horizons. Further, it is unclear how plant community composition within agricultural grasslands mediates this capacity and influences microbial community composition. We investigated whether the aboveground community composition in intensively managed agricultural grasslands influenced belowground microbial community composition, abundance, respiration and enzyme activities with depth.Materials and MethodsSoil was sampled in four soil layers: A (0–15 cm), B (15–30 cm), C (30–60 cm) and D (60–90 cm) in monocultures of six grassland species and a mixture of all six. Functional capacity was measured through enzymatic and substrate‐induced respiration assays, and microbial abundance and diversity were assessed via quantitative polymerase chain reaction and sequencing (16S, Internal transcribed spacer), respectively.ResultsMicrobial abundance and C cycling enzyme activity decreased and community composition changed, along the soil depth gradient, regardless of the plant community. Microbial abundance was not significantly influenced by plant community type across the entire soil depth profile. However, prokaryotic community composition was significantly influenced by plant community in the top 15 cm of soil, and fungal community composition was significantly influenced between 15 and 30 cm in depth. Plant community types mediated the rate at which C cycling enzyme activity decreased along the soil depth gradient, and selected C cycling enzymes were significantly more active at 15–60 cm depth when Cichorium intybus (a deep rooting species) was present.ConclusionThis study provides an improved understanding of how agricultural grassland communities affect the soil microbiome with depth; this has potential implications for the management of these systems for enhanced soil health. Our work indicates the potential for multispecies mixtures with deep rooting species to be a practical strategy to increase C cycling capacity in deeper soil layers within grasslands, which may have implications for policy goals related to C storage.

Soil seed banks provide a storage effect in post-logging regrowth forests of southeastern Australia

Despite the importance of soil seed banks in diversity maintenance, our understanding of plant response to changes in resource availability is largely limited to above-ground vegetation. We investigated how forest structure and edaphic properties influenced the above-ground vegetation and soil seed banks following logging in montane regrowth forests dominated by Eucalyptus regnans in the Central Highlands of southeastern Australia. We surveyed above-ground vegetation, soil seed banks, forest structure and soil properties across 20 harvest units, aged 16 to 20 years. A total of 80 species were identified in above-ground vegetation with 72 species in the soil seed bank, with only 34% of species co-occurring in both species’ pools. Climate, soil, topography, and light availability shaped plant composition but the relative importance of these properties varied among individual species and pools of diversity (combined, above-ground, soil seed bank, life form). Annual heat moisture index (AHMI) was the most important factor that influenced plant community composition across all species pools with individual species positively associated with AHMI. Acacia, but not Eucalyptus stem density further moderated plant response via effects on both light availability and soil nitrogen at the stem exclusion phase of stand development. Structurally mediated controls on above-ground community composition flow through to the soil seed bank via above-ground diversity effects on below-ground composition. For the combined species pool, individual species were most frequently related to Acacia stem density that on average explained 20% of model variation. Soil nutrients accounted for most of the model variation for individual species in above-ground (26%), soil seed bank (20%) and non-woody (32%) pools of diversity, with AHMI accounting for most of the model variation for woody species (18%). The differential response of individual species and community composition to gradients in resource availability across different pools of species diversity and life forms clearly demonstrates a storage effect in wet temperate forests of southeastern Australia that promotes post-disturbance recruitment and persistence. Our work suggests logging interacts with broad environmental controls to shape species diversity. The key role of Acacia stem density as a biotic filter of plant diversity provides opportunity to shape future plant diversity through management interventions such as thinning in the early stages of stand development. With native forest harvesting of these forests set to end from 2024, our findings provide important information on future patterns of plant diversity as logged forests recover over time, opportunities for management interventions in shaping plant composition, and potential impacts of future wildfire.

Aboveground community composition and soil moisture play determining roles in restoring ecosystem multifunctionality of alpine steppe on Qinghai-Tibetan Plateau

Alpine steppe is one of the most important grassland ecosystems on Qinghai-Tibetan Plateau (QTP), which has been greatly degraded in past decades. However, few studies have paid attention to the ecosystem multifunctionality (EMF) of restored degraded alpine steppes. Four treatments of alpine steppes (degraded alpine steppes, cultivated alpine steppes, fenced alpine steppes and intact alpine steppes) were investigated to explore the effect of treatment, biotic (above- and belowground community composition) and abiotic factors (pH and soil moisture) on restoring nine ecosystem functions (above- and belowground plant biomass, plant nitrogen content, soil organic carbon, soil nitrogen, soil phosphorus, soil microbial biomass carbon, microbial biomass nitrogen and microbial biomass phosphorus) and EMF of alpine steppe ecosystem in Madoi County of Qinghai Province, China. Our results showed that both grassland cultivation and fencing significantly promoted EMF of the degraded alpine steppes. Aboveground plant community composition was more significantly correlated with EMF of the alpine steppes than belowground soil community composition in the process of ecological restoration. Combining abiotic factors with biotic factors could improve the ability to explain EMF than biotic factors alone. Overall, aboveground community composition and soil moisture played determining roles in restoring EMF of alpine steppes.

Grazing exclusion erodes the forbs functional group without altering offspring recruitment composition in a typical steppe

AbstractThe underlying mechanism of grazing exclusion on grassland community structure and dynamics may be determined by offspring recruitment. However, little is known about the role of plant functional groups in community recruitment. A chronosequence of grazing‐excluded grasslands was selected to analyze the aboveground community composition and offspring recruitment based on plant functional groups. Grazing exclusion significantly increased grasses biomass (111.7–480.7%), height (95.6–241.8%), and coverage (84.8–148.5%) and decreased grasses density (10.2–59.7%). Grazing exclusion eroded total species richness (13.2–25.0%) and forbs richness (16.6–39.4%). Grazing exclusion shifted the dominance from forbs to grasses. Grasses functional group (GFG) determined community structure, but forbs functional group (FFG) regulated species diversity in typical steppe. Clonal recruitment played a decisive role in the community regeneration, especially tiller recruit mode by GFG. Grazing exclusion had different effects on offspring recruitment of grasses and FFG. Total asexual, grasses asexual, and tiller offspring density both first significantly increased and then significantly decreased with grazing exclusion time. Forbs asexual offspring density did not significantly decrease in 10‐ and 20‐year grazing exclusion grasslands but significantly reduced after 30 years. Change in community dominance caused by grazing or grazing exclusion did not alter the tiller recruitment dominance in this area. Our results indicate that grazing exclusion presents a negative effect on community regeneration and biodiversity conservation in the studied typical steppe.

Proximate grassland and shrub-encroached sites show dramatic restructuring of soil bacterial communities.

BackgroundChanges in aboveground community composition and diversity following shrub encroachment have been studied extensively. Recently, shrub encroachment was associated with differences in belowground bacterial communities relative to non-encroached grassland sites hundreds of meters away. This spatial distance between grassland and shrub sites left open the question of how soil bacterial communities associated with different vegetation types might differ within the same plot location.MethodsWe examined soil bacterial communities between shrub-encroached and adjacent (one m apart) grassland soils in Chinese Inner Mongolian, using high-throughput sequencing method (Illumina, San Diego, CA, USA).ResultsShrub-encroached sites were associated with dramatic restructuring of soil bacterial community composition and predicted metabolic function, with significant increase in bacterial alpha-diversity. Moreover, bacterial phylogenic structures showed clustering in both shrub-encroached and grassland soils, suggesting that each vegetation type was associated with a unique and defined bacterial community by niche filtering. Finally, soil organic carbon (SOC) was the primary driver varied with shifts in soil bacterial community composition. The encroachment was associated with elevated SOC, suggesting that shrub-mediated shifts in SOC might be responsible for changes in belowground bacterial community.DiscussionThis study demonstrated that shrub-encroached soils were associated with dramatic restructuring of bacterial communities, suggesting that belowground bacterial communities appear to be sensitive indicators of vegetation type. Our study indicates that the increased shrub-encroached intensity in Inner Mongolia will likely trigger large-scale disruptions in both aboveground plant and belowground bacterial communities across the region.

Rapid recovery of soil bacterial communities after wildfire in a Chinese boreal forest

Fires affect hundreds of millions of hectares annually. Above-ground community composition and diversity after fire have been studied extensively, but effects of fire on soil bacterial communities remain largely unexamined despite the central role of bacteria in ecosystem recovery and functioning. We investigated responses of bacterial community to forest fire in the Greater Khingan Mountains, China, using tagged pyrosequencing. Fire altered soil bacterial community composition substantially and high-intensity fire significantly decreased bacterial diversity 1-year-after-burn site. Bacterial community composition and diversity returned to similar levels as observed in controls (no fire) after 11 years. The understory vegetation community typically takes 20–100 years to reach pre-fire states in boreal forest, so our results suggest that soil bacteria could recover much faster than plant communities. Finally, soil bacterial community composition significantly co-varied with soil pH, moisture content, NH4+ content and carbon/nitrogen ratio (P < 0.05 in all cases) in wildfire-perturbed soils, suggesting that fire could indirectly affect bacterial communities by altering soil edaphic properties.

Abiotic drivers and plant traits explain landscape‐scale patterns in soil microbial communities

The controls on aboveground community composition and diversity have been extensively studied, but our understanding of the drivers of belowground microbial communities is relatively lacking, despite their importance for ecosystem functioning. In this study, we fitted statistical models to explain landscape-scale variation in soil microbial community composition using data from 180 sites covering a broad range of grassland types, soil and climatic conditions in England. We found that variation in soil microbial communities was explained by abiotic factors like climate, pH and soil properties. Biotic factors, namely community-weighted means (CWM) of plant functional traits, also explained variation in soil microbial communities. In particular, more bacterial-dominated microbial communities were associated with exploitative plant traits versus fungal-dominated communities with resource-conservative traits, showing that plant functional traits and soil microbial communities are closely related at the landscape scale.

Effects of grazing on the soil properties and C and N storage in relation to biomass allocation in an alpine meadow

Livestock grazing is one of the most important factors influencing the above-ground community composition and structure in a natural grassland ecosystem. Different grazing intensities also have the potential to alter soil C and N storage substantially in grasslands. We conducted a field community study and soil analyses to determine the effects of different grazing intensities on the above-ground community and soil properties in an alpine meadow on the Tibetan Plateau. Our results showed the following: (i) the vegetation height, coverage, and above-ground biomass significantly declined with increased grazing intensity, but the species richness reached the highest level in a moderate-grazing intensity meadow; (ii) grazing had a significant positive effect on soil properties in that the soil moisture content, soil organic carbon concentration, soil total nitrogen concentration, soil available nitrogen, soil total phosphorus, and soil available phosphorus significantly increased with increased grazing pressure; and (iii) soil C and N storage also significantly increased with increased grazing pressure; altogether, these increases had a significant positive cor relation with the increase of below-ground biomass allocation. Our results indicated that higher grazing intensity might have a potentially positive effect to increase the soil C and N storage in alpine meadows. However, from a long-term perspective, moderate grazing may help to achieve a balance between species diversity protection, livestock production and soil C and N management.

Rooting depth and above-ground community composition in Kalahari sand woodlands in western Zimbabwe

Abstract:The pattern of coarse-root distribution was analysed in the woody plant community along a 200-m edaphic gradient on a Kalahari sand woodland catena in Zimbabwe. The root systems of 45 trees and shrubs were excavated, mapped, and digitized to analyse rooting depth and architecture. Patterns of change in the above-ground community were also identified along this transect. Rooting depth increased, and the centre of mass of the root profile shifted towards the maximum rooting depth as a function of distance up the catena. The data also suggest that interspecific variation in rooting depth may increase up the catena. The below-ground pattern was accompanied by above-ground changes: species richness and basal area also increased up the catena. It is hypothesized that increasing soil depth allows greater coexistence of alternative water-use strategies, resulting in the observed increase in species richness up the catena.

Community Composition and Regeneration of Lake Wales Ridge Wiregrass Flatwoods in Relation to Time-since-Fire

most structurally important species in the community significantly varied among postfire age groups; wiregrass (Aristida beyrichiana) frequency was lowest in long-unburned stands, but average cover of saw palmetto (Serenoa repens) increased with time-since-fire. Plant species presence remained relatively constant across all stands. Estimated species richness and diversity did not change significantly with time-since-fire. Species composition of the seed bank did not closely resemble the aboveground community composition. Most species present in the seed bank (63%) were not found growing in any stand. Most wiregrass flatwoods species (89%) are capable of vegetative recovery and many (54%) were found to recover only vegetatively after fires. Although few significant shifts in plant species presence were detected along a gradient in fire history that spanned thirty years, important structural changes occurred, which eventually can have substantial impacts in fire suppressed communities. Species that recover vegetatively after fires, but are not present in the seed bank, could be lost from long-unburned flatwoods.