JIA-2019-11

2523 ZHOU Tian-mei et al. Journal of Integrative Agriculture 2019, 18(11): 2521–2533 a 21° roof angle. 2.2. Experimental design Seeds were briefly sterilized by soaking in 55°C H 2 O for 15 min and then 30°C for 6 h. Seeds were germinated in a growth incubator, which was maintained at 25°C for two days under lights. The germinating seeds were sowed in a nursery tray (540 mm×280 mm) containing 72 cells. Each cell has a dimension of 45 mm high, 40 mm×40 mm wide at the top and 20 mm×20 mm at bottom. For each cultivar, three replicas with 144 seedlings per replica were applied to each treatment and were sowed in six trays based on a randomized block design. Seedlings were managed according to the conventional method; except that the water content of media was maintained between 85 to 90% at the seedling emergence stage, and between 65 to 85% at the seedling stage using plug weighing method (Wang 2003, 2005; Zhang et al . 2004). After cotyledons were expanded, seedlings were sprayed once every two days with quarter-, half-, or full-strength of Hoagland nutrient solution: quarter- strength at the cotyledon stage, half-strength at the one-leaf stage, and full-strength after the two-leaf stage (Li et al . 2008). No diseases occurred and no chemical applications were needed. Different batches of seedlings of tomatoes and cabbages sowed at different planting dates were used for developing or validating the models and listed in Table 1. 2.3. Measurements of environmental parameters and plant growth characteristics Environmental data acquisition Photosynthetically active radiation (PAR) and temperature data were auto-collected by a TNHY Agricultural Environment Detector (Zhejiang Top Instrument Co., China). The detector was placed in the greenhouse with a similar height to the seedlings. Environmental data were automatically collected every 10 s and an hourly mean value was calculated. Determination of seedling growth indexes Indexes were measured every five days beginning on the fifth day after sowing. A total of seven measurements have been made. For each measurement, ten seedlings were selected randomly from each block, and height, stem diameter, as well as fresh and dry mass were determined for each seedling. 2.4. Development of growth simulation models When nutrient and relative humidity are maintained constantly, plant growth and developmental processes are mainly affected by thermal effectiveness (TE) and PAR. The product of TE and PAR is defined as TEP (Zhang et al . 2009; Li et al . 2011) and used for development of growth simulation models in this study. The models established here quantitatively analyze the influence of temperature and PAR interactions on the growth and development of tomato and cabbage seedlings. Calculation of product of relative TE and PAR (TEP) The effect of temperature on seedling growth and development was calculated based on daily relative thermal effectiveness (RTE), defined as the proportion of crops grown for one day under actual temperature conditions in comparison with optimal temperature conditions. The model used a three- segment type function to represent the relationship between temperature and RTE based on the three fundamental temperature points for tomato and cabbage seedlings (Table 2). The values of daily RTE are between 0 and 1. When the temperature is below the lower development threshold temperature ( Tb ) or above the higher development threshold temperature ( Tm ), RTE will be 0; when the temperature is between the lower optimum temperature threshold ( Tob ) and the upper optimum temperature threshold ( Tou ), RTE will be 1; when the temperature is between Tb and Tob , RTE increases linearly with the increase of temperature; and when the temperature is between Tou and Tm , RTE decreases linearly with the increase of temperature. The specific calculation method of RTE is shown in eq. (1) (Li et al . 2005; Yuan et al . 2005). ( T < Tb ) ( T − Tb )/( Tob − Tb ) ( Tb ≤ T < Tob ) ( Tob ≤ T ≤ Tou ) ( Tm − T )/( Tm − Tou ) ( Tou < T ≤ Tm ) ( T > Tm ) 0 1 0 RTE ( T )= (1) where RTE ( T ) represents the relative thermal effectiveness when the temperature is T ; Tb is the lower development threshold temperature; Tob is the lower optimum temperature threshold; Tou is the upper optimum temperature threshold; Tm is the higher development temperature threshold. The three fundamental temperature points of tomato and cabbage seedlings are shown in Table 2. The combined effects of temperature and illumination on the growth and development of seedlings can be calculated as the product of RTE and PAR (TEP). The accumulated Table 1 Cultivars and sowing date of tomato and cabbage for parametrization or validation of models Crop Cultivar Sowing time (yr-mon-d) Model parametrization Model validation Tomato Jinlingmeiyu 2014-9-18 2014-9-28 Hezuo 903 2014-9-28 2015-4-23 Cabbage Sugan 27 2015-4-23 2015-5-12 Bochun 2015-4-23 2015-5-12