ผลของสภาวะน้ำขังและสภาพร่มเงาต่อการเจริญเติบโตและการตอบสนองทางเสรีวิทยาของต้นกาแฟโรบัสต้า

Abstract

The recent heavy rainfall and flooding events in southern Thailand may have significant long-term impacts on coffee orchards. The vegetative growth of a Robusta coffee plant in the mixed-fruit tree orchard is affected by multiple environmental factors. Also, it is directly dependent on its capacity to the acclimation to abiotic stress conditions. This study was to evaluate the effects of short period waterlogging and light conditions on the characteristics of leaves and roots in Robusta coffee plants. In the first experiment, seedlings were subjected to three different conditions of substrate water availability; 0-day waterlogging, 15-day waterlogging and 30-day waterlogging. Seedlings of three commercial coffee cultivars (CP 2, CP 84-4 and CP 84-5) were used to measure the physiological responses to water stress in leaves and roots. In the second experiment, Robusta trees were subjected to two different conditions of light. Sampling and measurements were made using the youngest fully expanded leaves of lateral branches. A pair of leaves was selected based on leaf positions (1st, 3rd and 5th nodes). Under waterlogging conditions, the results showed that seedlings symptoms varied with the duration of waterlogging and different varieties. The CP 84-4 and CP 84-5 cultivars tended to had greater sensitivity to waterlogging than CP 2. Cultivars did not show changes in gas exchange parameters (photosynthetic rate, stomatal conductance and leaf water potential) due to waterlogging after 15 and 30 days of treatment. Meanwhile, all seedlings showed more severe symptoms such as including cortex sloughing, black and a lack of fibrous roots. The root damage also was excessive in waterlogged for 15 and 30 day periods. In addition, Robusta coffee leaves from trees grown in the shade had lower values for stomata size than leaves from trees grown in full sun light. Moreover, there were differed significantly between their leaf positions. Leaves developed at the 3rd and 5th node were larger in structure (leaf area, Specific leaf area and leaf mass per leaf area) than leaves development of leaves at the 1" node. Besides, the highest stomatal traits (stomata density and stomatal size) and leaf structure (leaf mass per leaf area, total chlorophyll per leaf area) were observed in the leave exposed to full sun condition. This study demonstrates that short period waterlogging and light conditions significantly influence on morpho-physiological characteristics of Robusta coffee leaves and roots. Also, these findings could apply a suitable environment for growth development of Robusta coffee in a mixed orchard.