Thermal and photoperiodic requirements of the seedling stage of three tropical forest species

Air temperature and photoperiod play an important role in the seedling development for tropical forest species.Both variables are sensitive to climate,and so evaluating thermal and photoperiodic effects on seedling development is fundamental,especially for climate change studies.Methods to quantify thermal time and the energy required for plants to reach a development stage include air temperature and cardinal temperatures.The photoperiod will also affect physiological reactions of a plant and thus its development.Here we evaluated the six thermal time methods widely used to compute thermal requirement,and identified the influence of the photoperiod from the 2015 and2016 growing seasons and 12 sowing dates in Itajubá,Minas Gerais state,Brazil,on seedling development of three native tropical forest species Psidium guajava L.(Myrtaceae),Citharexylum myrianthum Cham.(Verbenaceae),and Bixa orellana L.(Bixaceae).The method used to quantify thermal time influenced the analytical results of seedling development;the one that considered three cardinal temperatures and compared them with the mean air temperature(Method5)performed better in computing thermal requirements.The influence of photoperiod on seedling development was inconclusive for the three species,but all three developed better in mild temperatures(between 13.3℃and 26.9℃)with a photoperiod shorter than 13 h.

Agronomic and Physiological Responses of Rice (<i>Oryza sativa</i>L.) under Different Water Management Systems, Fertilizer Types and Seedling Age

A field experiment was conducted to evaluate the agronomic and physiological responses of rice under different water management systems, types of fertilizer and seedling age. This experiment was done at the farm of Agri Park, College of Agriculture, Central Experimental Station (CES), Crop Science Cluster of the University of the Philippines Los Banos, College Laguna during 2013. The strip-split plot design with three replications was used with the two types of fertilizer (vermicompost and chemical fertilizer), water management (with and without standing water) and two seedling ages (10 and 14-d old) were the treatments in the experiment. Chemical fertilizer produced the highest grain yield, total dry matter (TDM), leaf area index (LAI), net assimilation rate (NAR) and crop growth rate (CGR). Most of these characters significantly increased in 10-d old seedlings with chemical fertilizer without standing water. The shorter phyllochron and higher root pulling resistance (RPR) were observed in 10-d old seedlings without standing water. For the variety NSIC Rc 216, the use of 10-d old seedlings grown without standing water with chemical fertilizer is the optimum conditions for the better growth and high productivity.

Variability and Synchronism of Leaf Appearance and Leaf Elongation Rates of Eleven Contrasting Rice Genotypes

Leaf appearance and leaf elongation rates in rice play an essential role in determining the development of the plants’ architecture which affects their adaptability to varying environments. This study aimed to characterize the rates of leaf appearance and elongation on all leaves of the main culms of rice plants for 11 contrasting varieties and to determine if the decrease in the leaf appearance rate was related to a simultaneous decrease in the rate of leaf elongation. Forty four 13-L pots were sown with one plant from one genotype and laid out in 4 randomized complete blocks. The experiment, conducted inside a greenhouse, was repeated twice. The increase in length of the leaves expanding on the main stems was monitored daily until flag leaf. Data were used to estimate the rates of leaf appearance and leaf elongation. Significant variability in the rate of leaf appearance, rate of leaf elongation, and leaf length was found across varieties. The kinetics of leaf appearance had linear phases intermediated by a curvilinear phase, without sharp changes in the phyllochron duration. Maximal leaf elongation rate (LER) of all genotypes (except for one) increased linearly with leaf rank until it reached its maximum value at leaf 8 to 10 (11 - 12 for Azucena) where it stabilized before decreasing linearly with leaf rank for the last leaves. Finally, both rates of leaf appearance and leaf elongation evolved with time more smoothly than expected so no sharp decrease in LER occurred at the time of the decrease in leaf appearance rate of the last leaves. However, the trilinear model fits the data well enough to remain useful in efficiently comparing the leaf appearance kinetics of contrasting varieties.

Effect of Varying Temperature Regime on Phyllochron in Four Warm-Season Pasture Grasses

Using accumulated temperature measures to predict plant development may provide guidance on timing of management practices to minimize competition between warm and cool-season components of mixed pastures. However, temperature and plant development relationships for warm-season pasture grasses common in the southern Great Plains of the USA have not been extensively studied. Under controlled environment conditions, base temperature (Tbase) values were determined for Big bluestem (Andropogon gerardii Vitman), Indiangrass (Sorghastrum nutans, (L.) Nash), Little bluestem (Schizachyrium scoparium (Michx) Nash) and, Sideoats grama (Bouteloua curtipendula (Michx) Torr). Measures of the accumulated temperature requirement for the phyllochron (leaf appearance interval) were made under a range of temperature regimes for these same species. Mean Tbase was 8.1&degC and differences among species were not significant (P > 0.05). Within temperature regimes mainstem leaf appearance was closely and linearly related to accumulated temperature above Tbase. Increase of 7.5&degC in night temperature increased phyllochron by a mean of 43%, but similar increase in day temperature only increased phyllochron by 16%. Phyllochron increased by 6.4&degC leaf-1 for each 1&degC increase in daily mean temperature within the range of 15.0&degC to 22.5&degC. If accumulated temperature measures are to monitor reliably the development of warm-season grasses, allowance must be made for changes in phyllochron as the growing season progresses.