Manjunatha H. Chandregowda: Grasses adjust their root traits during drought to reduce the negative impacts on aboveground productivity

In this new post, Manjunatha H. Chandregowda—a new ecological researcher working at the Hawkesbury Institute for the Environment, Western Sydney University, Australia—discusses his paper: Root trait shifts towards an avoidance strategy promote productivity and recovery in C3 and C4 pasture grasses under drought—recently shortlisted for the 2022 Haldane Prize for Early Career Researchers.

About the research

Human disruption of global carbon and nitrogen cycles has not only led to record-breaking atmospheric greenhouse gas concentrations but has also increased the occurrence of extreme climatic events. As climate models predict further increases in the frequency and severity of extreme events, producing sufficient food to feed our growing global population will be a major challenge in the coming decades. Climate-resilient food production practices require an improved understanding of the mechanisms underpinning plant species’ responses to predicted climatic conditions. Our research aims to help address this challenge.

Figure showing pastures exposed to climate extreme treatments at the Pastures and Climate Extremes (PACE) field facility at the Hawkesbury campus of Western Sydney University, Australia (credit: David Thompson)

Grasslands, including pastures and rangelands, cover ~40% of the Earth’s terrestrial surface area and provide the feedbase that supports global livestock production. Despite their extensive distribution, these grassy biomes are sensitive to changes in climate, with reduced rainfall and rising temperatures in many ecoregions having negative effects on forage production and associated food security. Understanding which plant traits and strategies are associated with climate adaptation and resilience can help inform future grassland management to support global food production in a drier climate. We addressed this challenge by evaluating traits that describe grass species’ responses to climate variability and disturbance. Most of our understanding of plant responses to drought stress has disproportionately relied on aboveground responses. However, plant roots directly sense changes in their growing environment and exhibit varied strategies to optimize water and nutrient acquisition. In order to optimize species selection—to increase the resilience of forage production under more extreme climate conditions—it is essential to quantify differences in root traits and trait flexibility across a range of forage species and functional groups.

Figure showing all six replicate shelters of the Pastures and Climate Extremes (PACE) field facility at the Hawkesbury campus of Western Sydney University, Australia (credit: David Thompson)

In this work, we addressed this knowledge gap by subjecting perennial forage grasses to extreme winter and spring drought to identify traits involved in their drought resistance and resilience strategies. This new knowledge on root traits and associated flexibility in response to severe drought can inform species selection and management decisions that enhance the resistance and resilience of grassland systems in the face of future, more extreme climates.

About the research

The main objective of this paper was to quantify root trait responses to future rainfall events. Taking place within a wider research programme exploring resistance and resilience strategies of forage grasses and legumes to future warmer and drier climates, this paper focused on understanding the role of root strategies of grass species in the context of extreme drought. In a field manipulation experiment in Southern Australia, we exposed several perennial C3 and C4 forage grasses to a simulated 6-month-long cool-season drought, and followed plant recovery after the drought was alleviated. We predicted that: (a) C3 and C4 grasses differ in their root trait responses to drought due to differences in their climates of origin and photosynthetic pathways: C3 grasses are expected to shift their root characteristics to avoid drought and C4 grasses to exhibit tolerance to drought; (b) aboveground recovery following drought is associated with belowground carbon storage in both C3 and C4 grasses.

Figures showing several members of the Pastures and Climate Extremes (PACE) team involved in experiment management (credit: David Thompson)

The key findings of this research paper are:

Manju preparing root samples for trait analysis at the Hawkesbury Forest Experiment field site at Western Sydney University, Australia (credit: Sally Power)

1. C3 and C4 grasses differ in their root traits, with C3 species normally exhibiting root traits in line with drought avoidance, while C4 species show drought tolerance strategies. However, during drought, both C3 and C4 grasses shifted their root traits towards drought avoidance by increasing the production of thinner roots with higher specific root length, lower tissue density and higher concentrations of soluble sugars and nitrogen in a species-specific manner.

2. While root trait plasticity towards increased production of thinner roots drives aboveground productivity during drought, the larger belowground carbon reserves determine the stronger recovery of aboveground biomass post-drought in both C3 and C4 functional groups.

    In conclusion, pasture grasses can adjust to drought by shifting their root traits for the higher acquisition of soil resources but in a species-specific manner. Understanding linkages between root traits and aboveground production can inform resistance and resilience strategies to drought in pasture grasses. This information can guide species and cultivar selection that enhance resistance and resilience and thus support climate-smart management of grazing lands by sustaining forage production in future drier climates.

    About the author

    Manju at the Pastures and Climate Extremes (PACE) field facility at the Hawkesbury campus of Western Sydney University, Australia (credit: David Thompson)

    I am an ecosystem ecologist studying the interface of plants and soil. In particular, I am interested in the mechanisms that enable plants to adjust to changes in their environment. Additionally, I am interested in how plant communities mediate climate and global change impacts on ecosystem processes. 

    I decided to become an ecologist after I finished my master’s degree in Drosophila genetics. My childhood days in a small village in the Western Ghats region in Southern India might have increased my motivation to switch to ecology. Having no formal training in ecology, finding a PhD position in ecology was challenging. However, following my MSc, I had the opportunity to work as a research assistant with leading ecologists in India, Prof. Mahesh Sankaran (National Centre for Biological Sciences, India) and Prof. Sumanta Bagchi (Indian Institute of Science, India). This experience greatly helped me on my journey to become an ecologist. I became involved in and led several research projects on understanding the effects of land use and global change factors on soil functions, which provided me with strong ecological foundations. This work provided me the opportunity to explore many regions of the Western Ghats, semiarid grasslands, and the alpine grasslands of the high Himalayas. These experiences also helped me win a competitive scholarship funded by Dairy Australia to pursue a PhD at the Hawkesbury Institute for the Environment, Western Sydney University, Australia.

    As a postdoctoral research fellow at the Hawkesbury Institute for the Environment, I continue my doctoral research on understanding climate resilience in pasture systems and the role of management practices in pasture adaptation to climate change—issues that are relevant globally as well as in Australia. Apart from my postdoctoral research, I am also involved in managing long-term global network sites, including Nutrient Network (NutNet), DroughtNet and DRI-grass (Drought and Root herbivore Interactions in a Grassland) in Richmond, near Sydney, Australia. 

    In the future, I look forward to working in less-managed ecosystems, which I believe are natural labs covering innate gradients of climatic and other environmental variables.

    Enjoyed the blogpost? Read the research here!

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