| Summary: | 碩士 === 國立嘉義大學 === 園藝學系研究所 === 103 === Citrus is thought very sensitive to drought stress; however, drought stress not only limits crop development and yield but significantly impairs photosynthesis. This study investigated the effects of hydrogel amendments on photosynthesis of ʻPokanʼ mandarin (Citrus reticulata Blanco) under drought stress. 2-year-old ʻPokanʼ was grown in added hydrogels (1, 3 and 6 g·L-1 Alcosorb®; A1, A3 and A6) to pot medium and non-hydrogels added was used as control. All treatments except control were non-irrigation for 33 days, and then rewatering 2000 mL on the 34th day and control was irrigation everyday. Hydrogels treatment significantly increased 7-20% medium volumetric water content at first day. After 33 days drought stress, A1, A3 and A6 medium volumetric water content were 0.0%, 4.6% and 12.4% left, respectively. Hydrogels treatment medium volumetric water content after rewatering significantly increased, and A6 had the highest (58.5%) among all treatments on 45th day. Hydrogels treatment improved ʻPokanʼ photosynthesis during drought stress, leading to A1, A3 and A6 were 1.1, 1.7 and 2.2 µmol·m-2·s-1, respectively. On 45th day (after rewatering), A6 (3.9 µmol·m-2·s-1) had significantly higher photosynthesis than CK (3.5 µmol·m-2·s-1), A1 and A3 (3.6 µmol·m-2·s-1 both). Added 6 g·L-1 hydrogels to pot medium had the highest medium water content and significantly improved ʻPokanʼ leaf photosynthesis. 2-year-old ʻPokanʼ pot seedlings were divided into 6 g·L-1 hydrogels (A6), and non-hydrogels (D) for 33 days non-irrigation and then rewatering 2000 mL on 33th day, and CK with irrigation everyday. A6 treatment had the highest medium water content at first day and 45th day which were 58.1% and 54.3%, respectively. Non-irrigation of A6 and D treatment decreased to 0% at 39th day and 24th day, respectively. ʻPokanʼ leaf chlorophyll index decreased during non-irrigation period; A6 treatment decreased slower than D treatment. Leaf chlorophyll index of A6 treatment were 75.7 and 61.8 at first day and 33th day. Leaf chlorophyll index of D treatment were 73.7 and 55.2 at first day and 33th day. On 33th day, non-irrigation treatment of leaf chlorophyll index significantly lower than CK (73.3). After rewatering, A6 and D treatment still lower than CK, which were 69.4, 66.0 and 70.9, respectively. A6, D, and CK leaf Fv/Fm were 0.733, 0.563, and 0.807. CK was significantly higher than non-irrigation treatment, and D treatment leaf Fv/Fm was the lowest. A6 treatment can delay ʻPokanʼ leaf photosynthesis rate decreased in drought stress, and leaf stomatal conductance, transpiration rate, Rubisco acitivity were similar. Physiological indicators exhibit that added hydrogel in ʻPokanʼ pot medium can delay effect by drought stress. Hydrogel can absorb large quantities of water, to save irrigation cost and avoid waste of water resources. Under drought stress, to add 6 g·L-1 hydrogels can improve Citrus reticulata Blanco photosynthesis in pot medium.
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