Large-scale insect outbreak homogenizes the spatial structure of ectomycorrhizal fungal communities

Ectomycorrhizal fungi (plant symbionts) are diverse and exist within spatially variable communities that play fundamental roles in the functioning of terrestrial ecosystems. However, the underlying ecological mechanisms that maintain and regulate the spatial structuring of ectomycorrhizal fungal communities are both complex and remain poorly understood. Here, we use a gradient of mountain pine beetle (Dendroctonus ponderosae) induced tree mortality across eleven stands in lodgepole pine (Pinus contorta) forests of western Canada to investigate: (i) the degree to which spatial structure varies within this fungal group, and (ii) how these patterns may be driven by the relative importance of tree mortality from changes in understory plant diversity, productivity and fine root biomass following tree death. We found that the homogeneity of the ectomycorrhizal fungal community increased with increasing tree death, aboveground understory productivity and diversity. Whereas, the independent effect of fine root biomass, which declined along the same gradient of tree mortality, increased the heterogeneity of the ectomycorrhizal fungal community. Together, our results demonstrate that large-scale biotic disturbance homogenizes the spatial patterns of ectomycorrhizal fungal communities

Fungal Community Response to Long-Term Soil Warming With Potential Implications for Soil Carbon Dynamics

The direction and magnitude of climate warming effects on ecosystem processes such as carbon cycling remain uncertain. Soil fungi are central to these processes due to their roles as decomposers of soil organic matter, as mycorrhizal symbionts, and as determinants of plant diversity. Yet despite their importance to ecosystem functioning, we lack a clear understanding of the long-term response of soil fungal communities to warming. Toward this goal, we characterized soil fungal communities in two replicated soil warming experiments at the Harvard Forest (Petersham, Massachusetts, USA) which had experienced 5 degrees C above ambient soil temperatures for 5 and 20 yr at the time of sampling. We assessed fungal diversity and community composition by sequencing the ITS2 region of rDNA using Illumina technology, along with soil C concentrations and chemistry. Three main findings emerged: (1) long-, but not short-term warming resulted in compositional shifts in the soil fungal community, particularly in the saprotrophic and unknown components of the community; (2) soil C concentrations and the total C stored in the organic horizon declined in response to both short- (5 yr) and long-term (20 yr) warming; and (3) following long-term warming, shifts in fungal guild relative abundances were associated with substantial changes in soil organic matter chemistry, particularly the relative abundance of lignin. Taken together, our results suggest that shifts with warming in the relative abundance of fungal functional groups and dominant fungal taxa are related to observed losses in total soil C

Data from: Positive effects of non-native grasses on the growth of a native annual in a southern California ecosystem

Fire disturbance is considered a major factor in the promotion of non-native plant species. Non-native grasses are adapted to fire and can alter environmental conditions and reduce resource availability in native coastal sage scrub and chaparral communities of southern California. In these communities persistence of non-native grasses following fire can inhibit establishment and growth of woody species. This may allow certain native herbaceous species to colonize and persist beneath gaps in the canopy. A field manipulative experiment with control, litter, and bare ground treatments was used to examine the impact of non-native grasses on growth and establishment of a native herbaceous species, Cryptantha muricata. C. muricata seedling survival, growth, and reproduction were greatest in the control treatment where non-native grasses were present. C. muricata plants growing in the presence of non-native grasses produced more than twice the number of flowers and more than twice the reproductive biomass of plants growing in the treatments where non-native grasses were removed. Total biomass and number of fruits were also greater in the plants growing in the presence of non-native grasses. Total biomass and reproductive biomass was also greater in late germinants than early germinants growing in the presence of non-native grasses. This study suggests a potential positive effect of non-native grasses on the performance of a particular native annual in a southern California ecosystem

pec_carlton_data

Files included: (1) pec_carlton_biomass_allocation_data.csv, (2) pec_carlton_environment_data.csv, (3) pec_carlton_germination_data.csv, (4) pec_carlton_growth_data.csv, (5) pec_carlton_non_natives_data.csv, (6) pec_carlton_scatterplot_abundance_data.cs

Comparison of biomass variables at final harvest (112 d) for <i>Cryptantha muricata</i> across three treatments.

<p><i>Notes</i>: <i>n</i> =  number of harvested individuals per treatment. Significant differences were tested using Tukey-Kramer post-hoc tests.</p><p><i>**P</i><0.01,</p><p>***<i>P</i><0.001,</p><p>****<i>P</i><0.0001.</p>†<p>Data were log-transformed.</p><p>Comparison of biomass variables at final harvest (112 d) for <i>Cryptantha muricata</i> across three treatments.</p

Number of live <i>Cryptantha muricata</i> on each of three grass removal treatments in the San Dimas Experimental Forest.

<p>Sample periods were from February to mid-May 2011. 1,500 seeds were hand dispersed per treatment on January 2011. 29 seeds germinated in the litter treatment, 32 in the control treatment, and 29 in the bare ground treatment. Red line represents where no further germination was observed on any plots after 10 weeks (day 70). Mortality of <i>C. muricata</i> was not observed until day 84 (right side of red line). All surviving individuals (Control, <i>n</i> = 17; Litter, <i>n</i> = 15; Bare Ground, <i>n</i> = 12) were harvested at 112 d.</p

Biomass allocation for (<i>n</i> = 8) early and (<i>n</i> = 9) late germinants of <i>Cryptantha muricata</i> on the control grass removal treatment in the San Dimas Experimental Forest at final harvest (112 d).

<p>Biomass allocation for (<i>n</i> = 8) early and (<i>n</i> = 9) late germinants of <i>Cryptantha muricata</i> on the control grass removal treatment in the San Dimas Experimental Forest at final harvest (112 d).</p

Linear mixed effects models with repeated measures describing effects of three grass manipulation treatments on air temperature at the soil surface in °C and soil water potential in MPa over four growing periods (day 70 to day 112).

<p>Linear mixed effects models with repeated measures describing effects of three grass manipulation treatments on air temperature at the soil surface in °C and soil water potential in MPa over four growing periods (day 70 to day 112).</p

Summary of linear mixed effects models for total, linear, and quadratic contrasts describing growth of <i>Cryptantha muricata</i> over four growing periods.

<p><i>Notes</i>: Number of individuals per treatment - Control (<i>n</i> = 17), Litter (<i>n</i> = 15), Bare Ground (<i>n</i> = 12).</p>†<p>Data were log-transformed.</p>‡<p>Data were square root transformed.</p><p>Summary of linear mixed effects models for total, linear, and quadratic contrasts describing growth of <i>Cryptantha muricata</i> over four growing periods.</p

Environmental factors measured on each of three grass removal treatments in the San Dimas Experimental Forest.

<p>Panel (A) represents air temperature at the soil surface and panel (B) represents soil water potential on each of the three grass removal treatments (Control, <i>n</i> = 25, Litter, <i>n</i> = 25, Bare Ground, <i>n</i> = 25). Data are represented by means ±SE.</p