Leaves are sophisticated environmental sensors

A new international study shows that using plants as sensors of environmental change gives us another important tool for understanding the consequences of these changes for our life support systems.

Published in Nature Ecology and Evolution, a globally distributed experiment of grassland ecologists (Nutrient Network), at 27 sites in 4 continents, led by QUT’s Associate Professor Jennifer Firn found that critical plant nutrients (nitrogen, phosphorus and potassium) in leaves respond to fertilisation treatments as well as the climate and soils they are growing in.

Grasslands are one of the most extensive habitats in the world, they provide us with food, carbon storage and habitat for pollinators – 70 per cent of Australia are technically grassland and Australian grasslands are some of the most threatened ecosystems.

Professor Firn said “as our environment changes more quickly due to climate change, intensification of agriculture and land use change it is becoming more important to understand how grasslands all over the world are likely to respond.

“While ecologists and agricultural scientists have known for some time that individual species at individual locations can vary in the amounts of these nutrients in their leaves in response to fertilisation this is the first time that it has been confirmed experimentally across grasslands that experience very different climates and soil conditions,” Professor Firn said.

“When plants are fertilised they can use those extra nutrients to grow bigger and produce more flowers and seeds which can dilute the nutrients in their leaves, so a positive response of leaf nutrients to fertilisation was not guaranteed.

“A surprising result of this experiment was that Specific Leaf Area, a leaf trait that is commonly used to tell us about how plants defend themselves against herbivores and capture sunlight for growth, was unaffected by fertilisation and when grazing was stopped.

“So this critical measure of leaf architecture is not changing in the same consistent way as leaf nutrients with fertilisation. Leaf architecture is instead determined by climate and soil characteristics, so it may respond over a longer time frame than short-term fertilisation.”

Professor Firn described the impact of this study as “our society as a whole is consumed with human-made technology and for many reasons this is rightly so but this study’s results highlight we should not ignore the sophisticated technology in nature that is apparent around us every day—we just need to look harder.

“Plants kick start energy flow for all living organisms on our planet and it seems nature is providing us with meaningful signs of the impacts of our land-use decisions. We should also concentrate on finding ways to read these signs more effectively to build our understanding and ability to forecast tipping points.”

Professor Yvonne Buckley from Trinity College Dublin, a collaborator on this project, said:

“There are two ways that leaf nutrients can change in grassland communities, either the existing species leaves change to store more nutrients or the kinds of species which can survive in these new conditions change to species that naturally have higher leaf nutrients. We found that for nitrogen and potassium both of these things were happening but for phosphorus the species change pathway was not important.”

The paper describing this experiment is published in Nature Ecology & Evolution https://dx.doi.org/10.1038/s41559-018-0790-1

An interactive figure describing the results is available at https://evidentlyso.com.au/clients/qut/functionalTraits0120/

Blog post launched next week: https://natureecoevocommunity.nature.com/manage/posts/43150-leaf-traits-are-barometers-of-short-term-perturbations-in-grasslands-but-operating-instructions-apply

/University Release. View in full here.