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Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

CSIRO Div. of Plant Industry, Australian Cotton Co-operative Research Center, Locked Bag 59, Narrabri, NSW 2390, Australia

View larger version (19K): [in a new window]   Fig. 1. Relationship between leaf assimilation rate measured at 2000 µmol m-2 s-1 (CAmax) and specific leaf nitrogen (SLN) of individual leaves for (a) Exp. P1 sown 13 Oct. 1999, (b) Exp. P2 sown 28 Oct. 2000 and (c) with both experiments combined. For comparison, the fitted curve of Reddy et al. (1997) is also presented in (c).

View larger version (20K): [in a new window]   Fig. 2. Relationships between leaf assimilation rate (CA) and light intensity (PAR) for three categories of specific leaf nitrogen (SLN) of individual leaves as measured in Exp. P2 (2000–2001).

View larger version (11K): [in a new window]   Fig. 3. Relationships of (a) leaf assimilation rate measured at 2000 µmol m-2 s-1 (CAmax) and (b) leaf CO2 assimilation rate measured in the dark (CAdark) plotted against specific leaf nitrogen (SLN) of individual leaves. These responses are derived from data of Exp. P2 (2000-2001) specifically used to measure the response of leaf assimilation rate to light intensity.

View larger version (17K): [in a new window]   Fig. 4. Calculated radiation use efficiency (RUE) versus observed RUE. Three approaches using the existing method of Hammer and Wright (1994) that scales from leaf photosynthesis to canopy RUE are compared. The first comparison (a, Approach 1) used the published functions in the Hammer and Wright (1994) that estimate carbon assimilation (CA) from light intensity, and uses the response for CAmax versus SLN taken from this study (Eq. [5]). The second comparison (b, Approach 2) used Eq. [9] for estimating CA from light intensity with the relationships of CAmax and CAdark to SLN being derived from the same data (Eq. [7] and [8]). The third comparison (c, Approach 3) is the same as the second approach but uses Eq. [5] instead of Eq. [7].

View larger version (25K): [in a new window]   Fig. 5. Calculated radiation use efficiency (RUE) compared to observed RUE. Values were calculated using either (i) a vertical SLN gradient within the canopy (SLNgrad), or (ii) a uniform vertical distribution. The method used here utilizes responses taken from this study (Eq. [5], [8], and [9]).

View larger version (13K): [in a new window]   Fig. 6. Sensitivity analysis of the scaling method: The predicted response of radiation use efficiency (RUE) to average canopy specific leaf nitrogen (SLN canopy) for (a) three different vertical SLN gradients within the canopy (SLNgrad), (b) two different average light extinction coefficients (k), and (c) a combination of three different canopy LAI with two different SLNgrad.