Study On The Plant Architecture And Development Of Different Cotton Cultivars Based On PAR Spatial Distribution In Canopies

The spatial distribution of PAR(Photosynthetically Active Radiation) in canopies of cotton(G hirsutum L.) directly reflects the group structure and the characters of plant architecture, and then affects cotton’s growth, dry matter production and yield formation. In present research, ten cotton cultivars with three kinds of different plant architecture(compact type, slightly compact type, incompact type) were chosen as research objects, and the PAR spatial distribution in canopies of different development stage were measured accurately with a grid sampling method. Afterwards the spatial heterogeneity of PAR distribution was analyzed qualitatively and quantificationally by the Semivariograms and the Kriging interpolation which were based on the principles and methods of Spatial Statistics, with the ultimate purpose to quantize the plant architecture and the spatial-temporal heterogeneity of PAR distribution in canopy. At the same time, researches on characters of agronomic trait development, such as LAI, biomass production and economic yield, were correlated with the objective of investigating the influence of PAR on cotton growth.The results showed that the i PAR distribution in canopy had a high spatial heterogeneity, a good spatial continuity and a strong spatial autocorrelation. The values of C/Sill in semivariogram were all higher than 0.75, which demonstrated that the heterogeneity of i PAR distribution mainly caused by the plant architecture factors. And the degrees of variation increased with the plant type from compact types to incompact ones, and through entire development stage it rised at first then declined. Depended on the fitting results of semivariance models, the Gaussian semivariogram model was most suitable for fitting the spatial and temporal heterogeneity of i PAR distribution in the canopy, whose determination coefficients(R2) were all above 0.94.The intensity of solar radiation declined with the depth of the canopy, and the i PAR was increased. Furthermore, it was slower in middle position of the cotton rows than that closed to the rows, which showed a “V” type. For cultivars with an incompat plant architecture, i PAR rised the fastest in the top of canopy, and the PAR interception mainly concentrated in the upper canopy. While for cultivars with slightly compact plant architecture, i PAR distribution was more homogeneous, and the growth rate was uniform. However, for compact plant type, more radiation transmitted across the canopy and failed to capture by the leaves, so the PAR interception was less than others, and the growth rate of i PAR was slow. At the squaring stage, the plants were small, and the rows were not sealing. At the boll-open stage, plants came to senesecence, and leaves came to dry and fell off. At those two stages, the canopy structures were sparser, which leaded to that the variation of i PAR distribution among different cultivars was unconspicuous. However, at the flowering and boll-setting stage, the canopy was closured, and the structure varied obviously for different plant architecture, which resulted in a great difference of the PAR distribution characters in the canopy.For incompact plant-type cultivars, LAI was higher through entire growth period than other cultivars, and the i PAR was also higher, the duration of the growth period was also longer. During the growth stage, they could intercept more solar radiation, and produced more biomass, but their RUE(Radiation Use efficiency) was not higher. It showed that the more dry matter production for cultivars with a incompact plant architecture was mainly attributed to the more accumulated PAR interception. Through the growth period, LAI and i PAR were increased firstly and then declined, which fitted a binomial expression. Furthermore, a significant positive correlation with a exponential relationship was finded between LAI and i PAR. The development of the biomass accumulation was accord with a logisitic model, and a positive linear regression was fitted between the cumulative biomass and the i PAR accumulation. The times when LAI, i PAR and the rate of biomass accumulation came to the highest all appeared at the full-blossom stage, while the time for compact plant-type cultivars was a little early than other cultivars with incompact plant-type.