UNH Today

Melissa Knorr: Passionate About Soil Science and Global Change

UNH College of Life Sciences and Agriculture (COLSA) research scientist Melissa Knorr is driven by a passion for studying soil and unlocking its mysteries. Knorr has managed Serita Frey’s soil microbial ecology lab since 2002, focusing on soil carbon cycling and global change—specifically how various global change pressures impact soil’s complex microbial communities. Her research offers insights that help protect ecosystems and mitigate climate change. One of her key areas of work is at the Harvard Forest Long-Term Ecological Research site, where she has contributed to multiple global change experiments since joining UNH in 2002.

Knorr first became interested in soil science during her undergraduate studies at Ohio State University.

“My first experience learning about soils was through a volunteer position in a terrestrial ecology lab while an undergraduate,” Knorr shared. “Once I started there, I never left the field of soil science!”

Since then, understanding the complexities and importance of soil has become Knorr’s long-term focus, especially in the context of global change.

“A small amount of soil—a teaspoon—can contain a billion organisms and several meters of fungal hyphae,” Knorr explained. “The activity of these organisms is a primary feedback to climate—for example, through CO₂ production—and their complex interactions with each other and their environment are essential to predicting future climate.”

Knorr received the COLSA Research Support Staff Award in 2010 and the Dean’s Award for Distinction in 2024. Outside of work, she continues her passion for the earth by spending time in her garden, foraging for mushrooms, and exploring local hiking trails.

New England’s forests are confronting multiple environmental challenges, including historically high rates of atmospheric nitrogen deposits and rising temperatures due to climate change. And while scientists have studied these two variables independent of each other, identifying how rising temperatures leads to carbon loss in our Northeastern forests and increased nitrogen deposits results in carbon buildup, few studies have examined the dual effects of both – until now. A research team from the University of New Hampshire used data from a 16-year study at the Harvard Forest Long-Term Ecological Research (LTER) site in Massachusetts and found that when soil warming temperatures and increases in soil nitrogen levels were combined, soil carbon storage remained stable due to underground plant inputs from roots. These results challenge conclusions from single-factor studies and suggest that the loss of soil carbon in Northeastern forests impacted by climate change may be lower than previously predicted.

Over the past century, New England’s average temperature has risen by 1.7°F. And while rates of nitrogen deposits are declining, they are still 5-6 times higher than pre-industrial levels. This excess nitrogen, deposited onto ecosystems through rain and snowfall, can harm forests by damaging plant health and acidifying waterways. The UNH study, which was recently published in Nature Ecology & Evolution, revealed that while warming and nitrogen enrichment together increased soil respiration – the process by which plant roots and soil microbes release carbon dioxide (CO₂) into the atmosphere – overall soil carbon storage remained stable, thanks to greater carbon inputs from plants.

“What is most exciting about this study is that it’s one of the longest-running experiments to look at two global change pressures instead of just focusing on one,” said Melissa Knorr, a lab research supervisor with UNH’s College of Life Sciences and Agriculture (COLSA) and the paper’s lead author. “This is particularly important to study in the Northeast, where the region has experienced greater nitrogen deposition historically, and now faster warming than in other parts of the country.”

Study leads Knorr and Serita Frey, a professor in UNH’s Department of Natural Resources and the Environment and a scientist with the New Hampshire Agricultural Experiment Station, exposed soils at the Harvest Forest site to continuous warming of 5°C and nitrogen fertilization of 5 grams per square meter per year. Previous work at the Harvard Forest site documented that soil warming alone leads to significant carbon loss, whereas long-term soil nitrogen enrichment results in carbon accumulation.

“Plants, particularly through root turnover – the natural process where plant roots grow, die and decompose – and increased plant growth and activity, add new carbon to the soil,” said Frey. “And while microbial activity breaks down organic matter, releasing CO₂, we observed that enhanced plant carbon inputs below ground – caused by warmer temperatures and increased nitrogen – help maintain soil carbon levels, counteracting what would otherwise have been a significant net loss of carbon from the soil.”

Frey added, “This finding especially highlights the importance of plant-soil interactions in forest ecosystems and how these processes could be key to managing forests and ensuring that they continue to act as carbon sinks by absorbing CO₂ and reducing its concentration in our atmosphere.”

“The resilience of soil carbon storage observed in this study carries important implications for forests' role in combating climate change and offsetting rising atmospheric carbon dioxide levels here in the Northeast,” said Knorr.

“By challenging previous predictions from studies that looked at only one factor alone, this research offers a fuller picture of how ecosystems respond to multiple stressors,” Knorr said, adding that “the study offers insights that could inform conservation strategies to enhance carbon sequestration and preserve forest health across the Northeast.”

This work is co-authored by Melissa A. Knorr, Alexandra R. Contosta, Eric W. Morrison, Thomas J. Muratore, Mark A. Anthony, Iuliana Stoica, Kevin M. Geyer, Myrna J. Simpson and Serita D. Frey.

Support for this research comes from the U.S. National Science Foundation Long Term Ecological Research Program and a Long-Term Research in Environmental Biology grant.