Research Article | Open Access
Seasonal Variation of the Canopy Structure Parameters and Its Correlation with Yield-Related Traits in Sugarcane
Population structure determines sugarcane yield, of which canopy structure is a key component. To fully understand the relations between sugarcane yield and parameters of the canopy structure, 17 sugarcane varieties were investigated at five growth stages. The results indicated that there were significant differences between characterized parameters among sugarcane populations at different growth stages. During sugarcane growth after planting, leaf area index (LAI) and leaf distribution (LD) increased, while transmission coefficient for diffuse radiation (TD), mean foliage inclination angle (MFIA), transmission coefficient for solar beam radiation penetration (TR), and extinction coefficient () decreased. Significant negative correlations were found between sugarcane yield and MFIA, TD, TR, and at the early elongation stage, while a significant positive correlation between sugarcane yield and LD was found at the same stage. A regression for sugarcane yield, with relative error of yield fitting less than 10%, was successfully established: sugarcane yield = 2380.12 + 46.25 × LD − 491.82 × LAI + 1.36 × MFIA + 614.91 × TD − 1908.05 × TR − 182.53 × + 1281.75 × LD − 1.35 × MFIA + 831.2 × TR − 407.8 × + 8.21 × MFIA − 834.50 × TD − 1695.49 × .
Sugarcane (Saccharum spp. hybrids), with economical importance, has by far the highest yield in crops. Since vegetative stalks are targeted in sugarcane harvest, population structure forms the basis of sugarcane yield. The population structure refers to the dynamics of the distribution and arrangement of each single plant, total leaf area, total plant number, and total root weight in time and space. The crop canopy structure plays a key role in the population structure because it directly affects not only the interception of sunlight but also the photosynthetic efficiency and crop yield of the population through the influence on microenvironment of water, heat, and atmosphere on the canopy [1–3]. Therefore, the light use efficiency of a crop population is directly related to its canopy structure. The biological yield of a crop and its organ distributions are the ultimate results of the canopy structure, which will be reflected in photosynthetic characteristics. There is vital significance for the exploration of appropriate population structure and the cultivation of high-yield and high-quality crops through the study on canopy structure . The leaf morphologies and population structures of other crops such as rice, wheat, and cotton have already been investigated [5–11].
The cultivation of an optimized population structure to improve optical radiation distribution within the canopy and to increase energy utilization is the basis for high yield in crops. The main indices for light radiation within the crop canopy are leaf area index (LAI), mean foliage inclination angle (MFIA), transmission coefficient for diffuse radiation (TD), transmission coefficient for solar beam radiation penetration (TR) in different altitude angles and azimuth angles, extinction coefficient (), and leaf distribution (LD). It is reported there is a close relationship among these indices [5–11]. Canopy light interception can be influenced by the LAI, and it rises along with the increasing LAI. Light interception peaks when LAI is at its optimum. The photosynthetic rate can be affected by the light interception and an appropriate increase in light interception rate of a population can improve the photosynthetic capacity and thus increase production [6–10]. Canopy value at all levels reflects vertical distribution of the leaf area and leaf angle and also the vertical diminishing status of canopy light. In recent years, the investigation on the canopy structure of crops has been greatly facilitated due to the emergence of canopy image analysis techniques. Moreover, the population structure characteristic values such as LAI, MFIA, TD, TR in different altitude angles and azimuth angles, , and LD were successfully determined .
Sugarcane is not only a main sugar crop but also an important energy one. The selection of yield and quality-related traits is a key for breeding superior sugarcane varieties. The relationships between leaf morphologies and yields or sucrose contents in sugarcane have been explored [12–15]. However, ecophysiological studies on relationships between characteristics of the canopy structure and sugarcane growth as well as yields have been rarely reported [12–14]. Currently, there is no report on the effects of sugarcane leaf morphology and its spatial distribution on radiation characteristics of canopy.
From all the above, the prediction of sugarcane yield-related traits in population structure at different growth stages is significant in theory and practice for breeding high-yield sugarcane varieties. The canopy spaces and light distributions of different sugarcane populations were investigated in the present study. The relationships between structural characteristics and their yield-related traits were also revealed among different varieties. This study aims to provide references for breeding of high-yield sugarcane varieties on the basis of high-quality population structure.
2. Materials and Methods
The tested sugarcane varieties were FN94-0403, FN94-0744, FN95-1726, FN96-0907, FN98-10100, ROC10, GT94-116, GT95-118, GT96-211, GT96-44, GT97-18, MT70-611, YT92-1287, YT96-107, YT9-6794, YT96-835, and YT96-86. These varieties were planted in the farm of Sugarcane Research Institute, Fujian Agriculture and Forestry University (longitude: 119.23 E, latitude: 26.08 N), as a randomized complete block design. There were three rows for each variety, with the amount of 45,000 sugarcane two-bud sets per hm−2. The plot area was 31.35 m2, with the row length of 9.5 meter and the row space of 1.1 meter. Field management level was slightly higher than that of the local production fields, with timely cultivator earth, fertilization, irrigation, and pest control. During field management, the same pilot and the same technical measure should be completed on the same day.
The canopy structure parameters of sugarcane were determined by CI-100 digital plant canopy imager (Washington, USA) at the stages of seedling (May), tillering (June), early elongation (July), rapid elongation (August), and late elongation (September), respectively. The measured indices include LAI, MFIA, TD, TR, , and LD. Fifteen plants of each variety were randomly selected for measurement on canopy structure parameters with three replicates. In mid-November, plant height, stalk diameter, and stalk number for all tested varieties were measured. Single stem weight and cane yield were calculated according to the following formulas: single stem weight = 0.785 × plant height × stalk diameter2, cane yield = single stem weight × effective stalk number per unit area.
The measurement was conducted according to established methods [1–3]. During evening time when sunshine was not particularly strong and the sky remained cloudless, observation stick with a fish-eye probe was installed centrally between the rows and was adjusted to exclude any influence from the outside including shadows. Five images were taken in each district. Software for plant canopy analysis, provided by U.S. CID, Inc. (Washington, USA), was applied to calculate the canopy structure parameters. During measurement, LD was represented by distribution frequency of the leaf within each azimuth. The leaf blade azimuth is the angle between the normal direction of leaf surface projection and the direction North; this was then divided clockwise into four directions 90° between each other. and TR were derived according to zenith angle, which was the angle between the target direction and the zenith direction. In this study, CI100 fish-eye lens were set as the observation point, and four angles, 27°, 45°, 63°, and 81°, were determined from the beginning of 9° to 18° zenith angle.
2.3. Statistical Analyses
The variance analysis, factor analysis, and regression analysis were performed on the means of data by DPS statistical software .
3. Result and Analysis
3.1. Seasonal Changes of Population Structure Characteristics of Sugarcane Varieties
3.1.1. Leaf Area Index (LAI)
Sugarcane LAIs varied significantly at different growth stages. As seasons change, the LAIs of all varieties increased (Table 1). There was no significant difference in LAI between sugarcane varieties at seedling (May) and tillering stages (June), but at the early elongation stage (July) there was a significant difference. The average LAIs of FN94-0403, FN98-10100, GT96-44, GT94-116, FN96-0907 and MT70-611 at the early elongation stage (July) were larger than those of YT96-794, YT96-835, YT96-107, and GT95-118. There was a relatively small difference in LAI between sugarcane varieties at the rapid elongation stage (August) and the late elongation stage (September). At the rapid elongation stage, the largest average LAI was MT70-611, while the smallest average LAIs were YT96-794 and ROC10. At the late elongation stage (September), the largest average LAIs were GT95-118 and FN98-10100, while the smallest average LAI was YT96-794.
|Notes: the lowercase letters denote significant differences at the level of 0.05.|
3.1.2. Mean Foliage Inclination Angle (MFIA)
There were significant differences in the sugarcane MFIAs at different growth stages (Table 2). As seasons changed, the maximum MFIA appeared at the seedling stage (May), while the minimum one appeared at the rapid elongation stage (August). There was no significant difference in MFIA between sugarcane varieties at seedling stage (May), tillering stage (June), and the rapid elongation stage (August), but there was a significant difference at the early elongation stage (July). Compared to those of GT95-118, ROC10, and FN95-1726 at the early elongation stage (July), the MEIAs of FN94-0403 and MT70-611 were smaller. There were large differences in the average MFIA among sugarcane varieties at the late elongation stage (September). The MFIAs of three sugarcane varieties, FN96-0907, GT97-18, and FN94-0403, were larger than those of another two sugarcane varieties, GT96-44 and YT96-107.
|Notes: the lowercase letters denote significant differences at the level of 0.05.|
3.1.3. Transmission Coefficient for Diffuse Radiation (TD)
There were significant differences in the sugarcane TD at different growth stages (Table 3). As seasons changed, the maximum TD appeared at the seedling stage (May), while the minimum TD was found at the late elongation stage (September). There was no significant difference in TD between sugarcane varieties at the seedling stage, the tillering stage (June), the rapid elongation stage (August), and the late elongation stage (September), but there was a significant difference at the early elongation stage (July). The TD of GT95-118 at the early elongation stage (July) was larger than other sugarcane varieties including FN98-10100.