Understanding the low photosynthetic rates of sun and shade coffee leaves: bridging the gap on the relative roles of hydraulic, diffusive and biochemical constraints to photosynthesis

PLoS One. 2014 Apr 17;9(4):e95571. doi: 10.1371/journal.pone.0095571. eCollection 2014.

Abstract

It has long been held that the low photosynthetic rates (A) of coffee leaves are largely associated with diffusive constraints to photosynthesis. However, the relative limitations of the stomata and mesophyll to the overall diffusional constraints to photosynthesis, as well as the coordination of leaf hydraulics with photosynthetic limitations, remain to be fully elucidated in coffee. Whether the low actual A under ambient CO2 concentrations is associated with the kinetic properties of Rubisco and high (photo)respiration rates also remains elusive. Here, we provide a holistic analysis to understand the causes associated with low A by measuring a variety of key anatomical/hydraulic and photosynthetic traits in sun- and shade-grown coffee plants. We demonstrate that leaf hydraulic architecture imposes a major constraint on the maximisation of the photosynthetic gas exchange of coffee leaves. Regardless of the light treatments, A was mainly limited by stomatal factors followed by similar limitations associated with the mesophyll and biochemical constraints. No evidence of an inefficient Rubisco was found; rather, we propose that coffee Rubisco is well tuned for operating at low chloroplastic CO2 concentrations. Finally, we contend that large diffusive resistance should lead to large CO2 drawdown from the intercellular airspaces to the sites of carboxylation, thus favouring the occurrence of relatively high photorespiration rates, which ultimately leads to further limitations to A.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coffea / metabolism*
  • Coffea / physiology
  • Photosynthesis / physiology
  • Plant Leaves / metabolism*
  • Plant Leaves / physiology
  • Ribulose-Bisphosphate Carboxylase / metabolism
  • Sunlight*

Substances

  • Ribulose-Bisphosphate Carboxylase

Grants and funding

This research was supported by the Foundation for Research Assistance of the Minas Gerais State, Brazil (Fapemig, Grant APQ-01138-12), by the National Council for Scientific and Technological Development (CNPq) (Grants 302605/2010-0 and 475780/2012-4) to FMD, and by Plan Nacional (Spain) (GrantAGL2009-07999) to JG. A PhD scholarship granted by CNPq to SCVM is also gratefully acknowledged. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.