Effects of Drought Stress on Photosynthetic and Physiological Characteristics of Juglans mandshurica Seedlings in Different Soil Substrates
JI Li, HAN Jiao, WANG Fang, WANG Jun, SONG Di, ZHANG Li-Jie, QI Yong-Hui, YANG Yu-Chun
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To investigate the response of photosynthetic physiological characteristics in seedlings of Juglans mandshurica under water stress in different soil substrates, In this study, two-year seedlings of J.mandshurica were used as research objects, and an experiment was conducted to set four water gradients(normal water supply CK, mild stress T1, moderate stress T2 and severe stress T3, and 80%, 60%, 40%, 20% field water capacity, respectively) in three soil substrates(humus, loam, sandy-loam) by pot controlled water method respectively. The chlorophyll, malondialdehyde(MDA), proline(Pro), antioxidant enzymes(POD, SOD, CAT)and photosynthesis indicators were determined in all treatments. The results showed that the chlorophyll content and Chl a/b were significantly decreased with increase of stress intensity(P<0.05). After 60 d of persistent water stress, the Chl a and Chl b content were 65.41% and 51.57% lower than those of CK, respectively. The order of chlorophyll content in the three matrices was:humus>loam>sandy-loam. With the increase of stress intensity, the proline(Pro) and malondialdehyde(MDA) content of seedlings were significantly increased, and Pro content in T3 in sandy-loam soil was 83.37 mg·g-1, which was highest among all treatment, and was 86.32% higher than CK. The activities of superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) of seedlings significantly increased with increase of stress intensity in humus soil. However, the SOD activity in loam soil increased first and then decreased. In general, the net photosynthetic rate(Pn), transpiration rate(Tr) and stomatal conductance(Gs) of seedlings decreased with increase of the stress intensity in three soil substrates. However, the stomatal limitation and non-stomatal limitation of seedling leaves in different soil substrates were different. The intercellular CO2 concentration(Ci) of T3 treated leaves was lowest in humus at 12:00, while in loam and sandy loam were 10:00. There was a significant positive correlation between soil total nitrogen, total phosphorus, permeation rate and transpiration rate and chlorophyll content(P<0.05), and reach a significant negative correlation between soil bulk density and chlorophyll content(P<0.05). Soil substrate and water stress had significant effects on the physiological characteristics and photosynthesis of J.mandshurica seedlings. Severe stress caused serious damage to the chlorophyll, osmotic substances and enzyme system of seedlings, and decreased the photosynthetic productivity of J.mandshurica seedlings. The seedlings in humus and loam have better drought resistance.