Hydraulic redistribution in forests: Spatial and temporal drivers of variation, and consequences for climate feedbacks

The amount of water stored in soils, and how this varies over time and with depth, controls the amount of carbon dioxide

carbon dioxide (CO2)

An important heat-trapping gas, also known as a greenhouse gas, that comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions.

Source: NASA Source

plants can photosynthesize and, subsequently, accumulate as stored carbon. During droughts, when there is little water in soils, plants close the leaf pores to prevent water loss to the dry air, but also limiting their ability to withdraw carbon dioxide from the atmosphere. With the ongoing changes in climate, droughts are becoming more common in many parts of the world. The computer simulation models scientists use to predict future climate and environmental change are still limited in their ability to accurately reproduce observed soil moisture and therefore carbon uptake by forest 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

One reason for this may be that these models do not realistically represent a process known as hydraulic redistribution, where plant roots transport water from wet to dry soils. During droughts, plants can access water stored deeper in the ground, transport the water through the root system, and release the water in shallower, dry soils where most nutrients the plants need are stored. After the water mixes with the nutrients, plants can use the nutrient-rich water to continue photosynthesizing longer than would be possible without hydraulic redistribution. In this project, the researchers will measure water content in different parts of the soil and plants to track the transportation of water in trees exposed to different levels of drought to detect and quantify hydraulic redistribution.The project will focus on species that have different levels of response to drought growing in hardwood forests of northern Indiana. The questions the researchers aim to answer are: Which species use hydraulic redistribution as a way to ease drought stress, and when? Do trees have to be a certain age or size before they are able to hydraulically redistribute water?To what extent does hydraulic redistribution alleviate water stress in trees and contribute to maintaining photosynthesis rates during droughts?The researchers will then use the measured data and the answers to those questions to generate better model representations of hydraulic redistribution in the DOE-sponsored E3SM

Energy Exascale Earth System Model (E3SM)

The Energy Exascale Earth System Model (E3SM) project includes Earth System Models, simulations, and predictions to investigate energy-relevant science using code optimized for DOE's advanced supercomputers.

Source: NVCL Web Page Source

climate simulation model. With this information, scientists can make predictions of how much less carbon plants take up during droughts under different climate scenarios.