Study Claims Plants' Size, Age Impacts the Net Productivity More than Climate

Researchers at the University of Arizona found that climate alone is not the only strong determinant of plant productivity.

The new collaborated study combined a new mathematic theory of data retrieved from 1,000 forests across the world. They found that the size and age of plants had more impact on the net productivity of the plants, whereas temperature and precipitation has a relatively minor effect on the primary productivity or the amount of biomass 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," said Brian Enquist, a professor in the UA's Department of Ecology and Evolutionary Biology whose research lab led the study. "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 supports the previous findings that showed temperature and water regulate the rate at which plants grow. But, this theory is not valid when the scale is applied to the entire ecosystem.

The team tested the assumption on the scale of ecosystem for which they developed a novel mathematical theory that evaluated the significance of various hypothesized drivers of net primary productivity. Later, they evaluated this theory using a large new dataset that was gathered from 1,000 different forests located at various places across the world.

The analysis showed that a new mathematical link that governs the changes in terrestrial ecosystem net primary productivity worldwide. They noticed that it is the age and size of the plants that regulate most of the variation in plant productivity rather than temperature and precipitation as traditionally thought.

This general association highlights that climate alone does not influence productivity by changing the metabolic rates that triggers plant growth, but instead by determining how large plants can get and how long they can live for. This mean the plants growing in warmer and wet environments can grow more as their large size and longer growing season boost them to capture more resources and not because climate ups the rate of metabolism. This, however, does not indicate that climate is not a key factor for plant productivity.

"Climate is still an important factor," said postdoctoral researcher Sean Michaletz, "but our understanding of how it influences ecosystem functioning has now changed."

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

Enquist said, "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."

The finding was documented in the journal Nature.