Exploring Relationships between Canopy Architecture, Light Distribution, and Photosynthesis in Contrasting Rice Genotypes Using 3D Canopy Reconstruction

Abstract

The arrangement of leaf material is critical in determining the light environment, and subsequently the photosynthetic productivity of complex crop canopies. However, links between specific canopy architectural traits and photosynthetic productivity across a wide genetic background are poorly understood for field grown crops. The architecture of five genetically diverse rice varieties-four parental founders of a multi-parent advanced generation intercross (MAGIC) population plus a high yielding Philippine variety (IR64)-was captured at two different growth stages using a method for digital plant reconstruction based on stereocameras. Ray tracing was employed to explore the effects of canopy architecture on the resulting light environment in high-resolution, whilst gas exchange measurements were combined with an empirical model of photosynthesis to calculate an estimated carbon gain and total light interception. To further test the impact of different dynamic light patterns on photosynthetic properties, an empirical model of photosynthetic acclimation was employed to predict the optimal light-saturated photosynthesis rate (P_max ) throughout canopy depth, hypothesizing that light is the sole determinant of productivity in these conditions. First, we show that a plant type with steeper leaf angles allows more efficient penetration of light into lower canopy layers and this, in turn, leads to a greater photosynthetic potential. Second the predicted optimal P_max responds in a manner that is consistent with fractional interception and leaf area index across this germplasm. However, measured P_max , especially in lower layers, was consistently higher than the optimal P_max indicating factors other than light determine photosynthesis profiles. Lastly, varieties with more upright architecture exhibit higher maximum quantum yield of photosynthesis indicating a canopy-level impact on photosynthetic efficiency.

Keywords: 3D reconstruction; MAGIC population; canopy architecture; crop productivity; light environment; photosynthesis; rice (Oryza spp.).

Figure 1

Plant height over the course of the experiment, calculated as the average of five measurements per plot. The means of three plots are shown with standard errors of the mean. M2, M4, M11, and M13 refer to Shan-Huang Zhan-2 (SHZ-2), IR4630-22-2-5-1- 3, 157 WAB 56-125, and Inia Tacuari, respectively.

Figure 2

Modeled cLAI, the area of leaf material (or mesh area) per unit ground as a function of depth through the canopy (i.e., distance from the top) at 12:00 h for (A) GS1 and (B) GS2. M2, M4, M11, and M13 refer to Shan-Huang Zhan-2 (SHZ-2), IR4630-22-2-5-1- 3, 157 WAB 56-125, and Inia Tacuari, respectively.

Figure 3

Modeled leaf inclination angles throughout depth (i.e., distance from the top) in the canopy. (A) GS1 and (B) GS2. Representations of M2 (left) and M13 (right) are shown at the side to make interpretation easier. As an additional visual aid, we have added lines of different angles which correspond to the leaf angles shown on the X-axis. The average triangle inclination angle throughout the horizontal subsection was calculated with respect to vertical, where a leaf inclination angle toward 0 indicates a more horizontal leaf and an inclination angle of 90 indicates a more vertical leaf. M2, M4, M11, and M13 refer to Shan-Huang Zhan-2 (SHZ-2), IR4630-22-2-5-1- 3, 157 WAB 56-125, and Inia Tacuari, respectively.

Figure 4

Modeled fractional interception as a function of depth in the canopy at 12:00 h for (A) GS1 and (B) GS2, using ray tracing data. Curves were calculated with step Δd = 1 mm. M2, M4, M11, and M13 refer to Shan-Huang Zhan-2 (SHZ-2), IR4630-22-2-5-1-3, 157 WAB 56-125, and Inia Tacuari, respectively.

Figure 5

Whole canopy acclimation model output. The acclimation model was run at 250 locations throughout canopy depth to predict the optimal P_max at each location throughout canopy depth (i.e., from the top of the canopy) dependent upon the light environment that it experienced, calculated via ray tracing. A moving average has been fitted to the data. (A) GS1 and (B) GS2. M2, M4, M11, and M13 refer to Shan-Huang Zhan-2 (SHZ-2), IR4630-22-2-5-1-3, 157 WAB 56-125, and Inia Tacuari, respectively.