Interactions between plants and soil microbes influence plant nutrient transformations, including nitrogen (N) fixation, nutrient mineralization, and resource exchanges through fungal networks. Physical disturbances to soils can disrupt soil microbes and associated processes that support plant and microbial productivity. In low resource drylands, biological soil crusts ("biocrusts") occupy surface soils and house key autotrophic and diazotrophic bacteria, non-vascular plants, or lichens. Interactions among biocrusts, plants, and fungal networks between them are hypothesized to drive carbon and nutrient dynamics; however, comparisons across ecosystems are needed to generalize how soil disturbances alter microbial communities and their contributions to N pools and transformations. To evaluate linkages among plants, fungi, and biocrusts, we disturbed all unvegetated surfaces with human foot trampling twice yearly in dry conditions from 2013-2018 in cyanobacteria-dominated biocrusts in Chihuahuan Desert grassland and shrubland ecosystems. Our study included microbial communities and N pools sampled at different time points in the disturbance treatments at one or both sites. We began our sampling after observations in April 2018 that the chlorophyll a content was at least double in control than disturbed plots in both ecosystems (Chung et al. 2019). Stomping occurred in May, and we collected soil and plant samples in June 2018 for N pools and soil and root fungal abundance. We collected additional soil samples in September 2018 and conducted the 15N tracer experiment to observe rates of N transfer from biocrust to plants before the fall stomp treatment in October. We collected chlorophyll a samples and soils for sequencing bacteria in September of 2019, also before the fall stomp treatment.
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Disturbance to biocrusts decreased cyanobacteria, N ‐fixer abundance, and grass leaf N but increased fungal abundance
Interactions between plants and soil microbes influence plant nutrient transformations, including nitrogen (N) fixation, nutrient mineralization, and resource exchanges through fungal networks. Physical disturbances to soils can disrupt soil microbes and associated processes that support plant and microbial productivity. In low resource drylands, biological soil crusts (“biocrusts”) occupy surface soils and house key autotrophic and diazotrophic bacteria, non‐vascular plants, or lichens. Interactions among biocrusts, plants, and fungal networks between them are hypothesized to drive carbon and nutrient dynamics; however, comparisons across ecosystems are needed to generalize how soil disturbances alter microbial communities and their contributions to N pools and transformations. To evaluate linkages among plants, fungi, and biocrusts, we disturbed all unvegetated surfaces with human foot trampling twice yearly from 2013–2019 in dry conditions in cyanobacteria‐dominated biocrusts in the Chihuahuan Desert grassland and shrubland ecosystems. After 5 years, disturbance decreased the abundances of cyanobacteria (especially
- PAR ID:
- 10364961
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 103
- Issue:
- 4
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We used field mesocosms in which the potential for fungal connections between biocrusts and roots remained intact or were impeded by mesh. We imposed a precipitation regime of small, frequent or large, infrequent rain events. We used15N to track fungal‐mediated nitrogen (N) transfer. We quantified microbial carbon use efficiency and plant and biocrust production and N content.
Fungal connections with biocrusts benefitted plant biomass and nutrient retention under favourable (large, infrequent) precipitation regimes but not under stressful (small, frequent) regimes, demonstrating context dependency in the fungal loop. Translocation of a15N tracer from biocrusts to roots was marginally lower when fungal connections were impeded than intact. Under large, infrequent rains, when fungal connections were intact, the C:N of leaves converged towards the C:N of biocrusts, suggesting higher N retention in the plant, and plant above‐ground biomass was greater relative to the fungal connections‐impeded treatment. Carbon use efficiency in both biocrust and rooting zone soil was less C‐limited when connections were intact than impeded, again only in the large, infrequent precipitation regime.
Synthesis . Although we did not find evidence of a reciprocal transfer of C and N between plants and biocrusts, plant production was benefited by fungal connections with biocrusts under favourable conditions. -
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Conceptual context: Species interactions may couple the resource dynamics of different primary producers and may enhance productivity by reducing loss from the system. In low-resource systems, this biotic control may be especially important for maintaining productivity. In drylands, the activities of vascular plants and biological soil crusts can be decoupled in space because biocrusts grow on the soil surface but plant roots are underground, and decoupled in time due to biocrusts activating with smaller precipitation events than plants. Soil fungi are hypothesized to functionally couple the plants and biocrusts by transporting nutrients. We studied whether disrupting fungi between biocrusts and plants reduces nitrogen transfer and retention and decreases primary production as predicted by the fungal loop hypothesis. Additionally, we compared varying precipitation regimes that can drive different timing and depth of biological activities. Methodological approach: We used field mesocosms in which the potential for fungal connections between biocrusts and roots remained intact or were impeded by mesh. We imposed a precipitation regime of small, frequent or large, infrequent rain events. We used 15N to track fungal-mediated nitrogen (N) transfer. We quantified microbial carbon use efficiency and plant and biocrust production and N content.more » « less
