Linking root and soil microbial stress metabolism to watershed biogeochemistry under rapid, year-round environmental change

Climate change

climate change

A change in the average conditions — such as temperature and rainfall — in a region over a long period of time.

Source: NASA Climate Kids Source

is occurring rapidly in northern forests, where air temperatures and precipitation are rising, but winter snowpack is shrinking, leading to more frequent soil freeze/thaw cycles in winter. These contrasting changes in soil temperature-moisture regimes are a major stressor for plant roots and soil microorganisms and can lead to changes in cycling of carbon and nutrients through whole forested ecosystems.

ecosystem

A natural community of plants, animals, and other living organisms and the physical environment in which they live and interact.

Source: A student's guide to Global Climate Change Source

Warming during the growing season may destabilize and release soil carbon

soil carbon

The measurable amount carbon dioxide stored in soil. It is the primary indicator of soil health, and it impacts the chemical, physical, and biological characteristics of the soil.

Source: Science Direct Source

(C) and nitrogen

nitrogen

Nitrogen, represented by the symbol N and atomic number 7, is a colorless, odorless, and tasteless gas that constitutes approximately 78% of Earth's atmosphere. It is vital for all life forms, as it is a fundamental part of amino acids, proteins, and DNA.

Source: Source

(N) into soil solution, but the severe thermal impact of soil freeze/thaw cycles in winter could magnify (in the case of N) or reverse (in the case of C) these losses. The combination of warming and increased freeze/thaw cycles appear to initially induce oxidation-reduction stress that selects for anaerobic N cycling-microbes and metal oxidizers, while shifting the majority of aerobic microbial C-cycling activity into deeper soil layers during winter. Soil microbes

microbe

Microbes are tiny living things that are found all around us and are too small to be seen by the naked eye. They live in water, soil, and in the air.

Source: NIH Source

are also evolving under these extreme conditions to increase decomposition of plant and soil C, but decrease decomposition of organic P, potentially decoupling C, N, and P outputs to associated aquatic ecosystems. These climate change effects on microbial metabolism could impact the export of dissolved organic matter and nutrients in ways that may explain longer-term changes in stream water chemistry and productivity of forested watersheds,

watershed

An area of land that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually flows to the lowest point in a basin.

Source: USGS Source

yet are poorly represented in ecosystem models. The objective of this proposed research is to improve mechanistic understanding and model representation of the combined effects of warming during the growing season and soil freeze/thaw cycles in winter on belowground biogeochemical cycles in northeastern forests. Our overarching hypothesis is that under climate change across seasons, microbes and plants exhibit a trade-off between stress metabolism and soil C, N, and P uptake and assimilation (short term) and biomass

biomass

Material that comes from living things, including trees, crops, grasses, and animals and animal waste. Some kinds of biomass, such as wood and biofuels, can be burned to produce energy.

Source: EPA Global Climate Change Source

stabilization (longer term) that scales up to impact soil carbon and nutrient export at the watershed-level.

To test this hypothesis, we propose a model-data integration study using the Climate Change Across Seasons Experiment (CCASE) at the Hubbard Brook Experimental Forest (HBEF) and a complementary plot-to-watershed-level biogeochemistry

biogeochemistry

Studies the cycle of key elements like carbon, nitrogen, and phosphorus within Earth's systems. It explores how these elements interact and the factors influencing their cycles.

Source: Oak Ridge Biogeochemical Dynamics Source

model, PnET-BGC. At CCASE, replicate field plots receive one of three climate treatments: growing season warming (+5°C above ambient), warming + freeze/thaw cycles (+5°C above ambient in growing season plus up to four freeze/thaw cycles in winter), and reference conditions (no treatment). We propose to couple new seasonal belowground biogeochemistry measurements at CCASE (net and gross C, N, and P fluxes

flux

The amount of some type of particle or energy crossing a unit area per unit time.

Source: NRC Library Source

and rates of plant- and microbial-derived DOC/N/P production in soil solution) in organic and mineral soil horizons, with -omics data on soil microbial communities (population genomics,

genomic

An interdisciplinary field of science that focuses on the structure, function, evolution, mapping, and editing of genomes.

Source: energy.gov Source

metagenomics, metabolomics) to reconstruct potential plant and microbial C, N, and P metabolism and export to the HBEF watershed over the past decade. To quantify the evolutionary trajectory of microbial evolution in situ during this time period, we will combine soil metagenomics datasets with new high-throughput characterizations of trait and gene evolution in individual soil bacteria and fungi collected from CCASE. To develop an integrated, scale-aware understanding of the consequences of evolving microbial stress and resource use traits for forest nutrient and C retention, we will incorporate both immediate and evolved responses of microbial C, N, and P cycling into new versions of PnET-BGC by applying an evolutionary algorithm to control specific C, N and P flux fluxes. Outputs of the revised PnET-BGC will be validated with over 40 years of existing forest C, N, and P pool and flux data from HBEF watersheds. By leveraging the versatile PnET-BGC model with a genes-to-ecosystems analysis of C, N, and P cycling at CCASE, this research will test our conceptual understanding of plant and microbial physiology responses to severe, compounding soil temperature perturbations across seasons, as well as the utility of a forest stand-level manipulative climate change experiment to understand the biogeochemical dynamics of a forest watershed undergoing rapid environmental change.