Using a biochemical C₄ photosynthesis model and combined gas exchange and chlorophyll fluorescence measurements to estimate bundle‐sheath conductance of maize leaves differing in age and nitrogen content

Abstract

Bundle-sheath conductance (gbs) affects CO2 leakiness, and, therefore, the efficiency of the CO2-concentrating mechanism (CCM) in C4 photosynthesis. Whether and how gbs varies with leaf age and nitrogen status is virtually unknown. We used a C4-photosynthesis model to estimate gbs, based on combined measurements of gas exchange and chlorophyll fluorescence on fully expanded leaves of three different ages of maize (Zea mays L.) plants grown under two contrasting nitrogen levels. Nitrogen was replenished weekly to maintain leaf nitrogen content (LNC) at a similar level across the three leaf ages. The estimated gbs values on leaf-area basis ranged from 1.4 to 10.3 mmol m -2 s -1 and were affected more by LNC than by leaf age, although gbs tended to decrease as leaves became older. When converted to resistance (rbs = 1/gbs), rbs decreased monotonically with LNC. The correlation was presumably associated with nitrogen effects on leaf anatomy such as on wall thickness of bundle-sheath cells. Despite higher gbs, meaning less efficient CCM, the calculated loss due to photorespiration was still low for high-nitrogen leaves. Under the condition of ambient CO2 and saturating irradiance, photorespiratory loss accounted for 3-5% of fixed carbon for the highnitrogen, versus 1-2% for the low-nitrogen, leaves.

Bundle-sheath leakiness and intrinsic water use efficiency of a perennial C4grass are increased at high vapour pressure deficit during growth

“…Also, we observed an N effect on ϕ that responded to short-term variation of CO 2 levels: high N supply increased ϕ of leaves at ambient to low CO 2 levels ( C a ≤390 μmol mol −1 ). Further, ϕ responded dynamically to short-term changes of [CO 2 ], in support of theoretical predictions of C 4 photosynthesis models (von Caemmerer and Furbank, 1999; Yin et al , 2011). Lastly, across treatments, a positive correlation between WUE i and leakiness was evident, pointing to a trade-off between WUE i and energy use efficiency of this species.…”

“…The response of ϕ to short-term variation of [CO 2 ] has been predicted by model analyses (von Caemmerer and Furbank, 1999; Kiirats et al , 2002; Ghannoum, 2009; Yin et al , 2011). Although these models were designed for estimating gas exchange rate rather than leakiness, the present results supported the theoretical predictions.…”

“…Using the fitted parameters ( a′ and b′ ) of each CO 2 response curve, CO 2 -saturated net assimilation rate ( A sat ) was obtained as ( a′ + c′ ), and carboxylation efficiency (CE) was calculated as b′ ( a′ + c′ ) (the initial slope of the A – C i curve). For CO 2 response curves of C 4 leaves, A sat is proportional to Rubisco activity, while CE is proportional to the PEP carboxylase activity (von Caemmerer and Furbank, 1999; Yin et al , 2011). The ratio of A sat to CE was calculated to indicate the ratio of Rubisco to PEPc activities.…”

“…However, model analyses suggested an increase of leakiness with increasing C i (von Caemmerer and Furbank, 1999; Kiirats et al , 2002; Ghannoum, 2009; Yin et al , 2011), while (the few) experimental studies using the carbon isotope approach showed no clear response of leakiness to C i (Henderson et al , 1992; Pengelly et al , 2012). …”

Antisense Reduction of NADP-Malic Enzyme in Flaveria bidentis Reduces Flow of CO2 through the C4 Cycle

“…Although attempts have been made to estimate bundle sheath resistance by varies techniques, great uncertainty exists about the actual magnitude of this resistance. We assumed a value of 333 m 2 s 21 mol 21 bar 21 (which is within the range of estimates made by Yin et al [2011] for maize) to estimate C s (Fig. 7).…”