Limitation of coffee leaf photosynthesis by stomatal conductance and light availability under different shade levels

Abstract

In agroforestry systems, the effect of shade trees on coffee net photosynthesis (A n ) has been the object of debates among coffee scientists. In this study, we undertook over 600 coffee A n ''spot'' measurements under four different artificial shade levels (100, 72, 45 and 19% of full solar irradiance) and analyzed limitations to A n by low light availability (photon flux density, PFD) and stomatal conductance (g s ). These gas exchange measurements were carried out during two consecutive coffee growing seasons in a commercial plantation in the Orosi valley of Costa Rica. Levels of A n were related to PFD and g s in order to calculate envelope functions which were used to establish PFD or g s limitations to A n . Under the growing conditions of the present trial, mean leaf A n remained stable for growth irradiance (GI) as low as 45% of full sun and decreased by *20% at 19% GI. Limitation to A n due to g s was strong in full sun and decreasing with increasing shade levels. On the other hand, limitation due to PFD remained at a similar level for all shade treatments. These different evolutions of limitations of A n by PFD and g s in response to shade explain the absence of a decrease in coffee leaf A n with a shade level up to 55%. Consequently, these results confirm that Arabica coffee is a shade-adapted plant with leaves that can maintain a high photosynthetic performance under low light availability.

Leaf Chlorophyll Fluorescence and Gas Exchange Response to Different Light Levels in <i>Platycerium bifurcatum<i/>

“…These observations of higher g s and higher A net have also been reported by other findings as in citrus plant (Medina et al, 2002). This has been explained by Franck and Vaast (2009) that this condition was linked to lower diffusional limitation. Lower E L value in T4 caused by the higher temperature received by the plants thus might lead to loss of water.…”

“…This result as evidence that lower value of g s might point towards to reduction on the A net value and this was parallel as g s principally affected the diffusional limitation (Larcher, 2003) shows leading in the stomatal limitation. Consequently, this result may due to this condition leads almost to stomatal closure in which stomatal closure generally will reduced the diffusion of ambient CO 2 into mesophyll (Elsheery and Cao, 2008.;Franck and Vaast, 2009), thus resulted in the A net reduction (Cornic, 2002). Higher value of g s in 2 and T3 associated to the high value of A net if compared to the exposed plants of T4.…”

Microclimate and development of Coffea canephora cv. Conilon under different shading levels promoted by Australian cedar (Toona ciliata M. Roem. var. Australis)

“…Therefore, the average intercept of 47% observed in this work is within the range proposed by those authors. Studies on arabica coffee grown under agroforestry systems have shown limitations for both stomatal conductance and light availability for coffee photosynthesis under shade levels above 45% (Franck and Vaast, 2009). Carelli et al (1999) observed significant reductions in photosynthesis and stomatal conductance with light interception of 80%; however, they found no differences in these variables with a light interception of 50%.…”

Impact of tree shading on the microclimate of a coffee plantation: a case study from the Peruvian Amazon

“…The higher humidity at the shaded area was in accordance with Barradas and Fanjul (1986), who explained it by higher output of water vapour produced by a much higher transpiration rate of canopy trees pumping water from lower soil layers. Additionally, shade of up to 55% is beneficial for coffee leaf photosynthesis as it maintains greater coffee net photosynthesis relative to plants in full sun via a significant attenuation of stomatal stress (Franck and Vaast, 2009). …”

“…In fact, C. arabica is shade-adapted, with leaves that can maintain a high photosynthetic performance under low light availability (Franck and Vaast, 2009), making it well-suited to heavily shaded systems. Agroforestry provides additional benefits not yielded by coffee plantations grown in full sun, including serving as a refuge for forest biota (Moguel and Toledo, 1999), reducing pressure for further forest conversion to agriculture (Noponen et al, 2013), serving as a source of fuel-wood and construction material (Rice, 2008), stabilizing microclimatic conditions (Lin, 2007;Siles et al, 2010a), and protecting the soil (Siebert, 2002).…”