Plant Ecophysiology / Parasitic plant biology
Ecophysiology is a scientific discipline which aims to understand how plants and animals respond to environmental factors. Plants form the basis for life on earth, and are fundamentally important for our efforts to combat climate change and feed a growing population. Understanding the factors which limit plant productivity will be of critical importance in developing technologies and strategies for maintaining and improving yield. In my group, we are interested in the link between both biotic (living) and abiotic (non-living) stresses on plant carbon (C) and nitrogen (N) metabolism, and ultimately plant growth.
Find my publications at my Google Scholar page or learn more about our research below.
Effect of hemiparasite attachment to host plants
Parasitic plants are plants which abstract water and nutrients from their host, reducing host plant growth. Parasites can reduce agricultural yields by up to 100%, and are estimated to cause approximately $10 billion of damage to agriculture annually. Despite this, our understanding of the effects of parasitic plants on their host's physiology and biochemistry remains rudimentary.
Application of fertilizer to parasitized plants has been shown in some studies to reduce the effects of the parasite on the host, although it is not clear about whether this is a result of the host being more able to defend itself, or the parasite being less "hungry". A paper published by our lab in 2019 (Irving et al. 2019, here) supplied nutrients to the host (alfalfa; Medicago sativa) or parasite (Phtheirospermum japonicum) separately, finding elevated host-to-parasite carbon and nitrogen flux as a result of parasite nutrient deficit in young plants, while the host nutrient status seemed less important. In older plants, nutrient supply to the host could apparently suppress parasitism, while the nutrient status of the P. japonicum plant was not important.
Our current research in this area seeks to identify factors other than nutrient status which might affect the balance between the host and the parasite, and to identify the mechanisms by which parasitism can be suppressed.
Mechanism of damage by Orobanche minor
Holoparasites are plants which obtain all their nutrients from a host plant, with no capacity to live independently. One example is Orobanche minor, which lacks leaves and chlorophyll, and parasitizes clover plants. O. minor is an invasive species in Japan, introduced to the Kanto region around 100 years ago.
As a legume, clover has the ability to fix nitrogen gas (N2) from the environment, although this has a high energy cost. In 2019, we published a paper (Jokinen and Irving, 2019 here) which hypothesized that N deficit would have a greater effect in clover plants parasitized by O. minor than unparasitized plants, due to carbon abstraction by the parasite. Contrary to our expectations, we found that the negative effects of N deficit and parasitism were independent of each other.
Current work in our lab seeks to explore the basis for damage by the parasite, and whether this is a result of reduced nutrient uptake by unparasitised roots.
Differential root growth in grass plants
Differential roots growth is a phenomena whereby some species of plants increase root growth inside nutrient patches. Under nutrient limiting conditions, this has been shown to improve their competitive ability, allowing them to capture more nutrients and grow more rapidly than plants which don't exhibit differential root growth. However, the specific mechanisms of this behaviour are poorly understood and require more study.
One of my students is looking at how plants decide where to grow roots under conditions with multiple limiting nutrients, since most plants grow under conditions where nutrients are limiting and patchy in the environment. Since plants have limited capacity to explore the soil, it is important for them to invest their resources wisely, to maximise their ability to grow and reproduce.
A second student is looking at the effect of defoliation on differential root growth, and the implications of defoliation for plants' competitive ability. Root growth and maintenance is underpinned by carbon fixed by plant leaves, and the loss of leaves by grazing represents a huge challenge for grass plants. Leaf loss massively reduces the plant's photosynthetic capacity, and has been shown to suppress new roots growth. We are investigating the relative importance of defoliation, both for the plants ability to compete for light aboveground, and nutrients belowground.
D = doctoral, M = master, B = bachelor, while the number refers to their year of study.
- Maya Lackie (M2) - Effect of host C-status on the alfalfa-Phtheirospermum japonicum interaction
- Clarissa Francis Frederica (M2) - Does Phtheirospermum japonicum derive a benefit from multiple hosts?
- Mao Hattori (B4) - Does Orobanche damage its host by limiting nutrient uptake?
- Sayuki Mori (B4) - Effects of defolation on differential root growth in Poa annua and its implications for above- and below-ground competition
- Yanjinlkham Giimaa (B4) - How does plant root growth respond to patches of different nutrients?
- Ting-Yi Chu (B4) - Effects of nutrient supply to parasitized and unparasitized roots in the clover - Orobanche system