Biological and geochemical controls on phosphorus bioavailability in arctic tundra

The National Science Foundation funded this three-PI/three institution collaborative project in August 2019. Research and sample collection will begin in Summer 2020, and Dr. Weintraub is currently recruiting a PhD student for this project. More details here.

Phosphorus (P) is a nutrient essential for life but its supply in the environment is often limited, resulting in P limitation to plant growth and/or decomposition in some environments. Plants and microorganisms take up P as dissolved phosphate in soil water. Phosphate is also removed from solution by binding with soil minerals. In particular, iron minerals strongly bind phosphate and may regulate its availability to plants and microorganisms. This project will investigate how geochemical and biological systems “compete” for phosphate in arctic tundra soils near Toolik Field Station, Alaska, where soil warming and permafrost thaw are altering carbon and water budgets, which in turn affects soil moisture and nutrient availability. This research is broadly important to understanding how soil properties (e.g., soil saturation and pH) affect this competition for phosphate and consequently influence plant growth and the ability of arctic ecosystems to serve as future carbon sources or sinks. The implications of this work extend beyond arctic systems and will increase the fundamental understanding of soil P availability.

Winter snow depth as a driver of microbial activity, nutrient cycling, tree growth and treeline advance in the Arctic

The National Science Foundation funded this three-PI/two-institution collaborative project in 2015. The field experiment was setup in September 2016, and research will continue through August 2020. Dr. Weintraub is currently recruiting a PhD student for this project and related follow-ups. More details here.

The position of the Arctic treeline is an important regulator of surface energy budgets, carbon cycling and subsistence resources in high latitude environments. It has long been thought that temperature exerts a direct control on the growth of treeline trees
 and the position of the treeline. However, our recent work in the Arctic with white spruce suggests that indirect effects of temperature on soil nutrient availability may be of equal
 or greater importance. These results highlight the importance of winter snow depth as a driver of tree growth. If our hypotheses are confirmed by our experimental manipulations, our findings will alter our predictions of where and when treelines
 may advance.

Cold soils at the treeline, particularly during
 winter, may limit microbial activity and nutrient availability to the point where trees are barely
 able to survive and grow.
Measurements made during winter have revealed that Arctic forests maintain snowpacks that are much deeper than observed at treeline. Trees are thought to trap snow and lead to a deeper snowpack, insulating the soil from cold air and allowing for greater overwinter microbial activity and greater nutrient mineralization. Indeed, we found a strong positive correlation between white spruce growth and winter snow depth. We are now conducting a field experiment to isolate the mechanisms underlying this correlation by using snowfences to manipulate winter snow depth and fertilizer to increase soil nutrient availability at three treelines that differ in soil moisture. To provide a test of the importance of temperature as a direct control
on treeline tree growth, we are experimentally warming tree shoots. We predict that both experimental snow and nutrient additions
will lead to large increases in microbial activity, photosynthesis, tree growth, seed quality,
seed production, seedling establishment and recruitment of new trees. We expect to observe
the greatest positive responses where soils are wet and cold. Meanwhile, we predict that
shoot warming will lead to negligible changes in growth. This research will elucidate the relationship between snow depth and soil nutrient availability, and determine the relative importance of nutrient and temperature limitations at treeline to white spruce—a dominant member of the boreal forest and the northernmost tree species in North America.

Microbial control of litter decay

The National Science Foundation funded this five-PI/four institution collaborative project (Weintraub lead PI & project director) in September 2009. That grant has ended, but this line of research continues in my lab, including a collaboration with the Pacific Northwest National Lab's Environmental Molecular Sciences Laboratory. Thus far, >15 publications and numerous training opportunities for several students have resulted from the Toledo component of this ongoing project.

There is growing interest in understanding the conditions under which soils gain or lose C, because soils actually contain more C than the atmosphere and could play either a mitigating or exacerbating role in global warming. Surprisingly, the microbial interactions with plant litter chemistry and nutrient availability controlling decomposition and soil C sequestration are not well understood, because of surprising gaps in our understanding of the mechanisms controlling decomposition. The goal of this research is to define these relationships with integrated field, laboratory, and modeling studies of the biochemical mechanisms driving interactions between soil C sequestration, plant litter chemistry, and microbial community composition and activity during decomposition.

We are investigating the functional links between decomposer microorganisms, litter chemistry, and temperature using experiments that manipulate C and temperature over the course of litter decomposition. Molecular studies are currently under way to further determine the community composition of active microorganisms capable of metabolizing specific chemical components of plant litter. Our next goal is to determine how communities and activities of soil organisms, microbial enzyme production, and the efficiency of enzymatic degradation of litter substrates are affected by temperature increases, particularly at low temperatures, when decomposition is inhibited. This research provides mechanistic insight into the impacts on plant litter decomposition from climate change.

Additionally, the outreach activities from this project included developing an the online Interactive Model Of Leaf Decomposition (IMOLD; Targeting grades 9-12, IMOLD starts with professionally animated lessons on the C cycle, litter decomposition, and microbes. Users are then directed to an interactive decomposition model allowing them to decompose different litters in the same environment, or the same litter in different environments. Lastly, IMOLD includes lab and classroom lesson plans developed by teachers. This educational resource is already being used in high school classrooms throughout the US.

Controls on phosphorus availability and runoff in agricultural fields

Phosphorus (P) is an essential nutrient for plants and is often added as fertilizer to farm fields. However, adding P to fields can be problematic because P mined from phosphate rock is a non-renewable resource—easily accessible sources are projected to peak in the year 2030 and, subsequently, become depleted. In addition, P added to agricultural fields can runoff into surface waters and contribute to harmful algal blooms, including the bloom that shut down the Toledo municipal water supply in August 2014.

The application of P fertilizers is often inefficient, as much of the P forms complexes with soil particles and is unavailable to plants. In addition, some of the P from previous fertilizer applications remains bound to soil particles from year to year, becoming “legacy P”. After several years of fertilization, a soil may become saturated with P, at which point the ability of soil particles to bind additional P becomes negligible. At this point, P inputs to surface waters may increase—either by erosion of soil particles into waterways, or by runoff of dissolved P that does not bind to P-saturated soils.

The goal of our research, which began in summer 2016 and is ongoing, is to determine if enhancing the activity of decomposer organisms during the plant growing season could stimulate the mobilization and uptake of legacy-P. Depleting the legacy P pool has the potential to help decrease the amount of P that farmers need to apply to their crops or can be leached into waterways.

Additionally, I was a member of the now-ended NSF funded Research Coordination Network on Phosphorus Sustainability (2015-2017) ( This gave me the opportunity to participate in developing new syntheses on P’s role in providing ecosystem services/disservices (e.g. MacDonald et al. 2016) and the role of legacy-P  (e.g. Rowe et al. 2015). Beyond providing opportunities for networking and publication, these syntheses help to inform our research on P management.

To view past research projects, please click here.

home analytical services
people interests data projects publications opportunities contact

Return to Michael Weintraub
Faculty Page
Copyright 2019 ESE Lab Return to Environmental
Sciences Department