Elevated physiological plasticity in xerophytic-deciduous shrubs as demonstrated in their variable maximum carboxylation rate

A plant’s photosynthetic capacity is typically reflected by its maximum carboxylation rate (Vcmax), which varies with time and plant functional type. In what way Vcmax in a xerophytic-shrub species changes in response to variation in its desert habitat remains poorly understood. In this study, Vcmax was continuously monitored in a common desert-shrub species, Artemisia ordosica, with a portable photosynthetic system over seven growing seasons from 2013 to 2019. Vcmax’s annual and interannual variations were subsequently assessed in conjunction with a meta-analysis carried out as a separate study. Vcmax in the species did not show a distinct seasonal pattern over the seven growing seasons. It rather displayed extensive year-to-year variations in the seasonal peak and its associated timing, exhibiting greater plasticity as compared with other plant functional types. Seasonal variation in Vcmax was primarily controlled by leaf nitrogen content per area (Narea) in a positive, linear manner, with the relationship’s sensitivity varying as a function of soil volumetric water content (VWC). Interannual variation in Vcmax was regulated by annual mean VWC, also in a positive, linear manner. The effect of Narea on Vcmax was amplified during the leaf-expanding stage of the shrub. Given severe drought anticipated under continued climate change, xerophytic shrubs are believed sufficiently malleable to acclimatize to ongoing environmental change in deserts.