Increasing atmospheric CO2 and canopy temperature induces anatomical and physiological changes in leaves of the C4 forage species Panicum maximum

Abstract

Changes in leaf anatomy and ultrastructure are associated with physiological performance in the context of plant adaptations to climate change. In this study, we investigated the isolated and combined effects of elevated atmospheric CO 2 concentration ([CO 2 ]) up to 600 μmol mol -1 ( eC ) and elevated temperature ( eT ) to 2°C more than the ambient canopy temperature on the ultrastructure, leaf anatomy, and physiology of Panicum maximum Jacq. grown under field conditions using combined free-air carbon dioxide enrichment (FACE) and temperature free-air controlled enhancement (T-FACE) systems. Plants grown under eC showed reduced stomatal density, stomatal index, stomatal conductance ( g s ), and leaf transpiration rate ( E ), increased soil-water content ( SWC ) conservation and adaxial epidermis thickness were also observed. The net photosynthesis rate ( A ) and intrinsic water-use efficiency ( iWUE ) were enhanced by 25% and 71%, respectively, with a concomitant increase in the size of starch grains in bundle sheath cells. Under air warming, we observed an increase in the thickness of the adaxial cuticle and a decrease in the leaf thickness, size of vascular bundles and bulliform cells, and starch content. Under eCeT , air warming offset the eC effects on SWC and E , and no interactions between [CO 2 ] and temperature for leaf anatomy were observed. Elevated [CO 2 ] exerted more effects on external characteristics, such as the epidermis anatomy and leaf gas exchange, while air warming affected mainly the leaf structure. We conclude that differential anatomical and physiological adjustments contributed to the acclimation of P . maximum growing under elevated [CO 2 ] and air warming, improving the leaf biomass production under these conditions.

Elevated CO2 and warming change the nutrient status and use efficiency of Panicum maximum Jacq

“…However, some general responses may be highlighted. For example, increased [CO 2 ] decreases transpiration rates and increases photosynthesis in many species, thereby greatly increasing water use efficiency [6]. The fact that transpiration governs the root-ion contact of N, Ca, Mg and S [7] suggests that at high [CO 2 ], less absorption of these nutrients may occur.…”

Elevated CO2and warming change the nutrient status and use efficiency ofPanicum maximumJacq

“…While some species appear to be saturated under actual [CO 2 ], others are not necessarily saturated at this level [32]. Likewise, P. maximum exhibited an increase in photosynthesis as a function of [eCO 2 ] [6] and an increase in dry mass, although this result was dependent on the time of evaluation, in our experiment. The increase in shoot dry mass with heating is probably associated with higher efficiency of N, P, K, Ca and Mg use under this same condition (Fig 3).…”

“…However, the P dilution effect that occurred with increasing plant dry mass does not seem to have been influenced by the [CO 2 ] and warming treatments, given the similar slope values of the lines (Fig 4B). However, the increase in photosynthetic rate under elevated [CO 2 ] [6] can be associated with the Rubisco content. High [CO 2 ] is expected to increase the Rubisco concentration, and this will require more inorganic P to be transformed into organic P for Rubisco synthesis, which is an important component of rRNA involved in enzyme synthesis.…”

“…The following sources were used: simple superphosphate (18% P 2 O 5 ), potassium chloride (60% K 2 O), zinc sulphate (22% Zn), boric acid (17% B) and sodium molybdate (39% Mo). During the experimental period, the accumulated rainfall was 224 mm, and the average temperature was 25 °C, with minimum and maximum of 16 and 35 °C, respectively, while the average air relative humidity was 87% [6].…”

“…Experiments suggest that P. maximum would benefit by a 2°C warming under well-watered conditions, by exhibiting increased dry mass [11] and not showing increased stress indicators, such as malondialdehyde and hydrogen peroxide [12]. However, under heating, there was no increase in photosynthesis and transpiration [6,13], suggesting that under a warmed atmosphere, P. maximum may exhibit increased NUE. It was also observed that under heating, P. maximum exhibited an increase in the concentration of many amino acids, such as valine, threonine and phenylalanine, which have N in their structure [14].…”