Leaf economics

Plant growth rate determines their vulnerability to changes

Published: Saturday 04 July 2015

each plant, like an entrepreneur, has an economic strategy for subsistence. Some plants live like the proverbial hare, following a live fast, die young strategy. Their leaves produce and consume energy quickly, making them more susceptible to weather changes or pest attacks. Other plants are tortoise-like, taking a live slowly and last longer approach.

These are the findings of a study conducted by 33 scientists from 15 countries. They categorised plants based on 'leaf economics'. "Leaves are like little factories. Each can make energy in a hurry, but at the risk of running down its equipment fast. Or, it can have a slow but steady output. It's a fundamental trade-off for every leaf, and this is what has been termed as leaf economics," says Ian Wright of Australia's Macquarie University, who is the lead author of the study (Nature, Vol 428, No 6985, April 22, 2004).

The research took roots in 1985, when Peter Reich, a professor at the us-based University of Minnesota, compared the rates at which different plants captured and stored energy through photosynthesis, and the speed at which they used energy during the respiration process. Reich noticed that two fast-growing plants, poplar trees and soybeans, were more susceptible to ozone pollution than the slow-growing pines. It's because poplars exchange gases faster than pines, Reich found. To probe further, along with his co-researchers, he decided to study 2,548 leafy plant species.

The team found that plants like 'hares' and 'tortoises' are found in all ecosystems. Moreover, leaves are built in accordance with their economic strategy. Those of fast-growing plants tend to be thin and full of nutrients like nitrogen and phosphorus. Slow growth, in contrast, allows for thick, sturdy leaves that resist weather changes and pest attacks.

According to the researchers, a plant's position on the continuum will help predict how it will respond to climate change. For example, if rainfall or nutrient levels increase, 'hares' like aspen would do well. But if conditions were to get drier, the slow-growing 'tortoises', such as spruce and other evergreens, would benefit. Similarly, if there is little sunlight available in the understory of a forest, the 'tortoises' can scale back their operations and live with it.

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