One of the core research objectives in our lab is to understand how climate and soils shape the way that plants use water and nitrogen during photosynthesis. Because photosynthesis is such a fundamental process, regulating flows of energy on a global scale, it is crucial that we understand how and why photosynthesis changes across environments. A recent paper led by PhD student Jennifer Paillassa (University du Québec à Trois-Rivières) and co-authored by several past and current lab members, explores how site climate and soil properties (e.g. pH, depth, and texture) jointly determine the balance between nitrogen and water use, on the basis of least-cost optimality theory.
Least-cost theory posits that plants should aim to minimise the summed costs of photosynthetic water use and nitrogen use, which should depend on the environmental conditions. (For more information, read these two key papers: Wright et al. 2003 and Prentice et al. 2014). For example, soil fertility generally increases with soil pH, such that plants on high pH soils should have lower nitrogen costs than plants on low pH soils, resulting in higher carboxylation (nitrogen use) at a given transpiration rate (water use). Deeper soils hold more water than shallow soils, and thus produce lower water costs, while soils with high silt content retain nutrients and water more effectively than sandy soils while releasing both resources more easily than clayey soils.
There was strong support for our key predictions that higher pH (higher fertility) would reduce nitrogen costs relative to water costs, and that plants on deeper and more silt-rich soils would exhibit the reverse trend. We also explored the interaction between climate and soil as a predictor of Ci:Ca, the ratio of leaf intercellular to ambient CO2, which integrates nitrogen and water use. In more climatically arid environments, greater soil depth and silt content reduced water costs relative to nitrogen costs.
The key message is that climate and soil properties jointly influence how plants balance nitrogen and water during photosynthesis, and that future studies should consider both. Stay tuned for more information regarding the role of soil phosphorus in the economics of leaf photosynthesis!
Follow the link to read the paper:
Paillassa, J., Wright, I.J., Prentice, I.C., Pepin, S., Smith, N.G., Ethier, G., Westerband, A.C., Lamarque, L.J., Han, W., Cornwell, W.K. and Maire, V., 2020. When and where soil is important to modify the carbon and water economy of leaves. New Phytologist. doi.org/10.1111/nph.16702 https://doi.org/10.1111/nph.16702
The Wright Lab (Western Sydney University) 