Periodic Reporting for period 4 - SHIFTFEEDBACK (Ecosystem response to drought: unravelling the unexplored role of plant-soil feedback)
Reporting period: 2024-07-01 to 2024-12-31
Climate change is increasing the intensity and duration of droughts, and this has long-term negative impacts on Earth’s plant communities. Vegetation responses to drought vary and are linked to plant species diversity and community composition, but also to changes in soil microbial communities, that can feed back to plant growth and alter competitive interactions between plants. The EU-funded SHIFTFEEDBACK project investigated how changes in plant-soil feedback underlie strong shifts in plant community composition following drought. The project quantified the effects of plant-plant and plant-microbial interactions on plant growth and subsequent shifts in plant community composition in response to drought, and the mechanisms underlying changes in plant-microbial interactions. These findings elucidate the mechanisms through which drought affects plant community composition and ecosystem functioning beyond the duration of the drought.
The overall objectives of this project were:
Objective 1. Examining how drought affects plant community and soil microbial community composition and the implications for plant-soil feedback
Objective 2. Quantifying the effects of plant-plant and plant-microbial interactions on plant growth and subsequent shifts in plant community composition in response to drought
Objective 3: Disentangling the mechanisms underlying drought-induced changes in plant-soil feedback
The overall objectives of this project were:
Objective 1. Examining how drought affects plant community and soil microbial community composition and the implications for plant-soil feedback
Objective 2. Quantifying the effects of plant-plant and plant-microbial interactions on plant growth and subsequent shifts in plant community composition in response to drought
Objective 3: Disentangling the mechanisms underlying drought-induced changes in plant-soil feedback
To meet these objectives, we used a variety of experimental approaches.
To address Objective 1, we adopted and altered a long-term drought field experiment. This allowed us to test how 20 years of summer drought affects plant and soil microbial communities, and how these changes determine future plant growth and response to new drought. We found that chronic drought exposure strongly shifted the composition of both soil bacterial and fungal communities, and drought legacy reduced the amount of carbon stored in soils underneath older heather plants, through it effect on bacterial communities. These findings indicate that the active management of heathlands is essential not only for keeping aboveground vegetation dynamics, but also for maintaining below-ground soil nutrient and carbon pools. These findings have been published in Journal of Applied Ecology (Gliesch et al. 2024, output x).
To assess whether these changes in soil microbial communities as a result of chronic drought persistent after drought , and whether these changes affect the response of the ecosystem to a new drought, we subjected both control plots and drought legacy plots of this long-term experiment to a new drought treatment. We found that the persistent changes in soil bacterial and fungal communities did not recover, but that the effect of new drought on these communities was minimal. Drought legacy also shifted plant community composition, with the strongest effect of new drought on building stage Calluna. These findings highlight a mismatch between plant and soil microbial community response to drought. Importantly, we found that ecosystem CO2 fluxes were determined by shifts in plant community composition, and that drought legacy only had a minor effect on how ecosystem CO2 fluxes respond to a new drought.
To assess the effect of these persistent shifts in soil fungal and bacterial communities for future plant growth and community composition, we grew the grass Molinia caerulea and heather (Calluna vulgaris) in soils collected from underneath these species in drought and control plots, alone and in combination. We found that drought increased the invasion growth rate of Molinia, which is in line with our field observations that grasses and fast-growing forbs are increasing in abundance after drought.
To address Objective 2, we set up field drought experiments in six sites, representing a chronosequence of time since land-abandonment. In the third year of these field experiments, we performed a manipulation experiment within control plots, drought plots, and ‘after-drought’ plots to quantify the effects of plant-plant and plant-microbial interactions on plant growth in response to drought. These results show that the presence of plant-microbe interactions mitigates the effect of drought on plant growth, and promotes more facilitative interactions in early and late successional stages.
To address Objective 3, we set up a series of mechanistic experiments, ranging from large, outdoor pots with different plant communities, to individual species growing in the greenhouse. In our long-term, field-based mesocosm experiment we found that drought only shifts plant-soil feedback when plants are grown in communities in the feedback phase, and that in particular the fast-growing grass experienced more positive feedback under drought, which may explain the shift towards dominance of this plant species in response to drought. We also found, similar to the field experiments for Objective 1, that aboveground and belowground responses to drought show a mismatch.
In an experiment growing individual plants of 12 different species, grasses and forbs had negative plant-soil feedback, while legumes had neutral to positive feedback, but that overall, feedback was not affected by drought and only marginally predicted by root traits. In a separate experiment, we found that the feedback caused by root exudates was distinct from total feedback effects of individual plants, and we identified the bacterial and fungal taxa that are linked to these responses. These findings highlight that drought effects on plant-soil feedback may be community and trait-dependent.
To address Objective 1, we adopted and altered a long-term drought field experiment. This allowed us to test how 20 years of summer drought affects plant and soil microbial communities, and how these changes determine future plant growth and response to new drought. We found that chronic drought exposure strongly shifted the composition of both soil bacterial and fungal communities, and drought legacy reduced the amount of carbon stored in soils underneath older heather plants, through it effect on bacterial communities. These findings indicate that the active management of heathlands is essential not only for keeping aboveground vegetation dynamics, but also for maintaining below-ground soil nutrient and carbon pools. These findings have been published in Journal of Applied Ecology (Gliesch et al. 2024, output x).
To assess whether these changes in soil microbial communities as a result of chronic drought persistent after drought , and whether these changes affect the response of the ecosystem to a new drought, we subjected both control plots and drought legacy plots of this long-term experiment to a new drought treatment. We found that the persistent changes in soil bacterial and fungal communities did not recover, but that the effect of new drought on these communities was minimal. Drought legacy also shifted plant community composition, with the strongest effect of new drought on building stage Calluna. These findings highlight a mismatch between plant and soil microbial community response to drought. Importantly, we found that ecosystem CO2 fluxes were determined by shifts in plant community composition, and that drought legacy only had a minor effect on how ecosystem CO2 fluxes respond to a new drought.
To assess the effect of these persistent shifts in soil fungal and bacterial communities for future plant growth and community composition, we grew the grass Molinia caerulea and heather (Calluna vulgaris) in soils collected from underneath these species in drought and control plots, alone and in combination. We found that drought increased the invasion growth rate of Molinia, which is in line with our field observations that grasses and fast-growing forbs are increasing in abundance after drought.
To address Objective 2, we set up field drought experiments in six sites, representing a chronosequence of time since land-abandonment. In the third year of these field experiments, we performed a manipulation experiment within control plots, drought plots, and ‘after-drought’ plots to quantify the effects of plant-plant and plant-microbial interactions on plant growth in response to drought. These results show that the presence of plant-microbe interactions mitigates the effect of drought on plant growth, and promotes more facilitative interactions in early and late successional stages.
To address Objective 3, we set up a series of mechanistic experiments, ranging from large, outdoor pots with different plant communities, to individual species growing in the greenhouse. In our long-term, field-based mesocosm experiment we found that drought only shifts plant-soil feedback when plants are grown in communities in the feedback phase, and that in particular the fast-growing grass experienced more positive feedback under drought, which may explain the shift towards dominance of this plant species in response to drought. We also found, similar to the field experiments for Objective 1, that aboveground and belowground responses to drought show a mismatch.
In an experiment growing individual plants of 12 different species, grasses and forbs had negative plant-soil feedback, while legumes had neutral to positive feedback, but that overall, feedback was not affected by drought and only marginally predicted by root traits. In a separate experiment, we found that the feedback caused by root exudates was distinct from total feedback effects of individual plants, and we identified the bacterial and fungal taxa that are linked to these responses. These findings highlight that drought effects on plant-soil feedback may be community and trait-dependent.
Using a unique combination of long-term field experiments and controlled mechanistic experiments, our results show that drought has strong and persistent effects on soil microbial communities, and that the recovery of these communities lags behind that of aboveground communities. Moreover, our experiments show that these changes in soil microbial communities have implications for future plant growth and community composition. While the impacts of drought on plant-soil feedback were minimal when plants were grown individually, drought-induced shifts in soil microbial communities increased the competitiveness of fast-growing grasses after drought. However, when challenged with ongoing drought, drought-adapted microbiomes mitigated the impact of drought on plant growth. We also found that ecosystem CO2 uptake was determined by shifts in plant community composition but not by microbial communities, highlighting that drought-induced changes in microbial communities indirectly determine CO2 fluxes through affecting plant growth and community composition. These findings fundamentally advance our understanding of ecosystem response to drought, and provide mechanistic insight into the role of soil microbial communities in this response as well as in the consequences for C cycle feedbacks and future impacts of drought.