act-dog

Scientists conducted a study to examine how sunlight intensity (the percent of maximum possible sunlight) affects seedling growth and survival. Study Seeds were collected from a certain species of plant growing in a temperate grassland. The seeds were planted and grown in identical conditions for 2 months. Then 800 similar-sized seedlings were selected, and each was transplanted into its own pot. All the pots were identical and contained the same amount of a particular soil. The pots were equally divided into 4 groups (Groups 1−4), and then all the groups of pots were placed next to each other in the temperate grassland. In 3 of the groups, all the pots in a group were covered by the same number of layers of a plastic mesh to reduce sunlight intensity. The number of layers was different for each of those 3 groups. Table 1 Sunlight Group intensity 1 10% 2 25% 3 50% 4 100% The seedlings were then grown for the next 10 weeks, during which all the pots were watered daily with the same amount of water. At 10 weeks, the surviving plants were harvested, and the average dry mass of the plants in each group was determined. The seedlings that did not survive were counted, and the seedling mortality (the percent of seedlings that did not survive to 10 weeks) was also determined for each group. The results are shown in Table 2. Table 2 Average Seedling dry mass mortality Group (g) (%) 1 0.18 8 2 0.58 3 3 0.80 2 4 0.57 6 Table adapted from Marina Semchenko et al., “Positive Effect of Shade on Plant Growth: Amelioration of Stress or Active Regulation of Growth Rate?” ©2011 by British Ecological Society.