Eddy covariance captures four‐phase crassulacean acid metabolism (CAM) gas exchange signature in Agave

Abstract

Mass and energy fluxes were measured over a field of Agave tequilana in Mexico using eddy covariance (EC) methodology. Data were gathered over 252 d, including the transition from wet to dry periods. Net ecosystem exchanges (FN,EC ) displayed a crassulacean acid metabolism (CAM) rhythm that alternated from CO2 sink at night to CO2 source during the day, and partitioned canopy fluxes (FA,EC ) showed a characteristic four-phase CO2 exchange pattern. Results were cross-validated against diel changes in titratable acidity, leaf-unfurling rates, energy exchange fluxes and reported biomass yields. Projected carbon balance (g C m(-2) year(-1) , mean ± 95% confidence interval) indicated the site was a net sink of -333 ± 24, of which contributions from soil respiration were +692 ± 7, and FA,EC was -1025 ± 25. EC estimated biomass yield was 20.1 Mg (dry) ha(-1) year(-1) . Average integrated daily FA,EC was -234 ± 5 mmol CO2 m(-2) d(-1) and persisted almost unchanged after 70 d of drought conditions. Regression analyses were performed on the EC data to identify the best environmental predictors of FA . Results suggest that the carbon acquisition strategy of Agave offers productivity and drought resilience advantages over conventional semi-arid C3 and C4 bioenergy candidates.

Shifts in gene expression profiles are associated with weak and strong Crassulacean acid metabolism

“…Whereas photosynthetic pathway—CAM or C 3 —is often portrayed as a binary trait, a variety of intermediate phenotypes ranging between full C 3 and CAM have been described. Constitutive CAM plants such as Agave are defined as species that rely on the CAM pathway constantly, regardless of even prolonged abiotic stress (Owen et al., ) (although an abundance of water can amplify C 3 carbon fixation in many constitutive CAM species) (Nobel, ). Weak CAM encompasses a variety of phenotypes, including facultative CAM (the ability to switch from C 3 to CAM under abiotic stress such as salt or drought, as found in Clusia [Borland et al., ; Lüttge, ], Mesembryanthemum [Winter and Ziegler, ; Cushman et al., ], and some Yucca species [Heyduk et al., 2016]), CAM cycling (recycling of respired CO 2 at night with daytime C 3 carbon fixation [Ting and Burk, ; Sipes and Ting, ]), and CAM idling (complete closure of stomata concomitant with recycling respired CO 2 [Sipes and Ting, ]).…”

Modelling evapotranspiration using the modified Penman-Monteith equation and MODIS data over the Albany Thicket in South Africa

“…The study area presents interesting space for testing the model since it is located in a dry landscape dominated by succulent vegetation. It has been established that such vegetation type has high water storage capacity within its tissues and has a very high water use efficiency [23][24][25] . These characteristics predispose the land-atmosphere water vapour transfer to be strongly coupled to plant phenological dynamics.…”

“…This suggests that the observed ET may not be necessarily related to SWC measured by soil moisture sensors buried at 25 mm below the surface. It is well established that the convergent evolution of thicket vegetation similar to the study site has resulted in high water storage in plant tissues to allow plant function during extended periods of moisture deficit 23,25 . In addition, during the calibration period ET was about 35% greater than rainfall received.…”

“…These results suggest that stomatal conductance is relatively high in the AT. There is a general belief that such thicket vegetation tends to close stomata during daylight hours to optimise water use 24,25 . As such, one would have envisaged relatively low stomatal conductance in such vegetation which lead to low ET.…”

Model approaches to advance crassulacean acid metabolism system integration

“…A number of complex CAM phenotypes demonstrate remarkable physiological and ecological plasticity which still engender intriguing research questions (Yang et al, 2015;Winter et al, 2015;Borland et al, 2018;Edwards, 2019;Winter, 2019). In strong CAM species such as Kalanchoe daigremontiana, Agave tequilana and Tillandsia usneoides the strength and duration of the intermediate Phases II and IV (respectively early morning and late afternoon) are adversely affected by a degree of drought, but can be restored quickly upon rehydration (Owen et al, 2016). Plasticity, as represented by facultative CAM, has also been documented for woody dicotyledonous species such as Clusia minor, temperate perennial herbs such as Sedum telephium and many members of the Aizoaceae which can rapidly and reversibly undergo CAM induction (Borland and Griffiths, 1990;Borland et al, 1992;Haag-kerwer et al, 1992;Dodd et al, 2002;Winter, 2019).…”