Abstract
Accurate estimations of the vertical leaf nitrogen (N) distribution within a rice canopy is helpful for understanding the nutrient supply and demand of various functional leaf layers of rice and for improving the predictions of rice productivity. A two-year field experiment using different rice varieties, N rates, and planting densities was performed to investigate the vertical distribution of the leaf nitrogen concentration (LNC, %) within the rice canopy, the relationship between the LNC in different leaf layers (LNCLi, i = 1, 2, 3, 4), and the relationship between the LNCLi and the LNC at the canopy level (LNCCanopy). A vertical distribution model of the LNC was constructed based on the relative canopy height. Furthermore, the relationship between different vegetation indices (VIs) and the LNCCanopy, the LNCLi, and the LNC vertical distribution model parameters were studied. We also compared the following three methods for estimating the LNC in different leaf layers in rice canopy: (1) estimating the LNCCanopy by VIs and then estimating the LNCLi based on the relationship between the LNCLi and LNCCanopy; (2) estimating the LNC in any leaf layer of the rice canopy by VIs, inputting the result into the LNC vertical distribution model to obtain the parameters of the model, and then estimating the LNCLi using the LNC vertical distribution model; (3) estimating the model parameters by using VIs directly and then estimating the LNCLi by the LNC vertical distribution model. The results showed that the LNC in the bottom of rice canopy was more susceptible to different N rates, and changes in the LNC with the relative canopy height could be simulated by an exponential model. Vegetation indices could estimate the LNC at the top of rice canopy. R705/(R717+R491) (R2 = 0.763) and the renormalized difference vegetation index (RDVI) (1340, 730) (R2 = 0.747) were able to estimate the parameter “a” of the LNC vertical distribution model in indica rice and japonica rice, respectively. In addition, method (2) was the best choice for estimating the LNCLi (R2 = 0.768, 0.700, 0.623, and 0.549 for LNCL1, LNCL2, LNCL3, and LNCL4, respectively). These results provide technical support for the rapid, accurate, and non-destructive identification of the vertical distribution of nitrogen in rice canopies.
Highlights
Nitrogen (N) is a key nutrient resource required for vegetation growth (Aerts and Chapin, 1999; Wang et al, 2005; Xu et al, 2012), which affects the development of important photosynthetic organs, enzymes (RuBisCO, etc.), and pigments (Gu et al, 2014)
The results showed that the LNC of the ith leaf layer (LNCLi) could be better simulated in different varieties, treatments, and growth stages by using the Leaf nitrogen concentration (LNC) vertical distribution model proposed in this study
We investigated the vertical distribution characteristics of the LNC within the rice canopy and the relationships of the LNCCanopy with the LNCLi and LNCALi and proposed an LNC vertical distribution model based on the relative canopy height
Summary
Nitrogen (N) is a key nutrient resource required for vegetation growth (Aerts and Chapin, 1999; Wang et al, 2005; Xu et al, 2012), which affects the development of important photosynthetic organs (leaves, etc.), enzymes (RuBisCO, etc.), and pigments (chlorophyll, etc.) (Gu et al, 2014). Hirose and Werger (1987) explained the mechanism (the optimization theory) of non-uniform vertical N distribution from the aspect of light distribution and indicated that leaves under better light conditions can obtain more N than those under poorer light conditions and can maximize the total photosynthesis in the canopy. Based on these results, Chen et al (1993) proposed the coordination theory, which advocates that there is a potential trade-off in the investment in structures that increase the capacity for light capture and carbon assimilation because of the huge N consumption by the above two processes
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