giant tree by mullenkedheim/Flickr

For plant biomass, size and age beat climate

The size and age of plants have more of an impact on their productivity than temperature and precipitation do, a new study suggests.

Researchers combined a new mathematical theory with data from more than 1,000 forests around the world to show that climate has a relatively minor direct effect on net primary productivity, or the amount of biomass—wood or any other plant materials—that plants produce by harvesting sunlight, water, and carbon dioxide.

“A fundamental assumption of our models for understanding how climate influences the functioning of ecosystems is that temperature and precipitation directly influence how fast plants can take up and use carbon dioxide,” says Brian Enquist, professor in the ecology and environmental biology department at University of Arizona.

“Essentially, warm and wet environments are thought to allow plant metabolism to run fast, while cold and drier environments slow down metabolism and hence lower biomass production in ecosystems.

“This assumption makes sense, as we know from countless experiments that temperature and water control how fast plants can grow. However, when applied to the scale of entire ecosystems, this assumption appears to not be correct.”

Plant math

Published in Nature, the analysis reveals a new and general mathematical relationship that governs worldwide variation in terrestrial ecosystem net primary productivity. Plant size and plant age control most of the variation in plant productivity, not temperature and precipitation as traditionally thought.

“This general relationship shows that climate doesn’t influence productivity by changing the metabolic reaction rates underlying plant growth, but instead by determining how large plants can get and how long they can live for,” says postdoctoral researcher Sean Michaletz, the study’s lead author.

“This means that plants in warm, wet environments can grow more because their larger size and longer growing season enable them to capture more resources, not because climate increases the speed of their metabolism.”

Climate matters, too

The finding does not, however, mean that climate is unimportant for plant productivity. “Climate is still an important factor, but our understanding of how it influences ecosystem functioning has now changed,” Michaletz says.

The findings suggest that mathematical models used for predicting the effects of global climate change can be improved by accounting for the effects of plant size and plant age on net primary productivity.

“Understanding exactly how climate controls net primary production is important for understanding the plant-atmosphere feedbacks that control climate change,” Michaletz says.

“In other words,” Enquists adds, “to better predict how ecosystems will change with climate, we need to understand what influences the amount of plant biomass in a given area as well as its age.”

Researchers from Fujian Normal University in China and Kenyon College also contributed to the study.

Source: University of Arizona