2016, DOI: 10.1111/nph.14307
Photosynthesis: ancient, essential, complex, diverse … and in need of improvement in a changing world
Ülo Niinemets, Joseph A. Berry, Susanne von Caemmerer, Donald R. Ort, Martin A. J. Parry, and Hendrik Poorter
The 17th International Congress on Photosynthesis Research covered an extraordinarily broad range of topics from submolecular‐scale biophysical details of energy transfer and basic chemistry of artificial photosynthesis to ecophysiology and crop physiology at whole leaf, whole plant and global scales. Recognizing that photosynthesis is the key source of energy for life on Earth and given the rapid pace of global environmental change, and the pressure of an increasing human population (e.g. Tilman et al., 2011; Alexandratos & Bruinsma, 2012), the photosynthesis research community faces two important challenges: (1) understanding the mechanisms, vulnerabilities and potentials for improvement of the photosynthetic process; and (2) developing better techniques for monitoring, modeling and rapid screening of photosynthesis at scales ranging from the individual genotype (Fiorani & Schurr, 2013) to fields, bread‐baskets (Guan et al., 2016; Pinto et al., 2016) and global vegetation units (Rogers et al., 2016). Addressing these challenges is essential to identify and incorporate new genetic improvements in the basic mechanism, and to understand and anticipate the role of photosynthesis in the responses of the global biosphere to climate and anthropogenic changes. In this regard we take note of the decision made this year by the European Space Agency (ESA) to build a satellite, Fluorescence Explorer (FLEX) mission, intended specifically for studies of photosynthesis by monitoring a product of photosynthesis, chlorophyll fluorescence. While this will provide an unprecedented new measurement capability, there remain many questions about how to relate this measurement to photosynthesis (Schlau‐Cohen & Berry, 2015) and this challenge will, no doubt, be a major issue in future congresses.
Another challenge to crop improvement is the fact that the photosynthetic process has been fine‐tuned by billions of years of natural selection, and is subject to deeply rooted genetic controls shaped in the native environments of the crop ancestors. These may be difficult to change and may not be optimal for current agro‐ecosystems. This was nicely demonstrated at the meeting by Lisa Ainsworth (USDA ARS, USA) who reported on mechanisms underlying the historical 80‐year improvement in soybean yield showing that soybean yield has been driven largely by a near doubling of harvest index. While the rate of carbon gain per unit leaf area has increased somewhat in modern soybean cultivars, it has been due to increased stomatal conductance and lower water‐use efficiency, rather than via increases in photosynthetic capacity (Koester et al., 2016). Yet, photosynthesis is the only yield determinant that is not close to its biological limits (Zhu et al., 2008; Ort et al., 2015), suggesting that increases in photosynthesis might indeed lead to increases in yield. In the following, we focus on meeting highlights pertaining to rate‐limiting processes for which improvements could increase crop yield, and on new advancements in monitoring and predictive modeling of plant photosynthesis.