การประเมินพลวัตการเจริญเติบโตของรากยางพาราโดยเทคนิคมินิไรโซตรอน

Abstract

Water stress is the major constraint factor affecting on agricultural production especially water deficit and waterlogging conditions. This study aims to evaluate the physiological responses and fine root dynamics of rubber tree under water stress condition by using a minirhizotron technique. The study was conducted in 3 experiments. 1) Water deficit experiment, the study was carried out under glasshouse with CRD statistical design using RRIM 600 clone (1-year old) grown in rhizoboxs (1 plant/rhizobox). Plant materials were subjected with 3 regimes of watering: 1) control treatment (daily watering) 2) withholding water with 4-day interval (WH) and rewatering (RW) 3) withholding water with 8-day interval (WH) and rewatering (RW) under 3 replications during 32 days of the experimental period. Results showed that stomatal conductance and leaf water potential of rubber trees under the WH (8-day interval) and RW were significantly different lower than the WH and RW every 4-day interval and the daily watering treatment. Fine root length density in WH (8-day interval) and RW decreased at 0-40 cm depth while the remaining fine root growth was found at 40 - 100 cm soil depth. Linear regression of minirhizotron technique and gridline method was found low relationship among the treatments. Experiment 2, waterlogging experiment was examined on RRIM 600 and RRIT 251 clone, 8-month seedlings were grown in the plastic tank (5.3 cubic foot). The experiment was arranged as factorial design in CRD with 3 replications. Planting materials were subjected to 3 levels of waterlogging as waterings, surface waterlogging (SW) and partial waterlogging (PW) (10 cm above soil surface) compare with control (daily watering) for 42 days of experimental period. Results showed that stomatal conductance and leaf water potential of SW and PW treatment decreased during waterlogging in both of RRIM 600 and RRIT 251 clones. After water draining, RRIM 600 clone exhibited shoot emergence, leading to higher recovery than RRIT 251. Fine root length density of live root decreased along 0-50 cm depth during waterlogging. The morphological adaptation was found in SW and PW by the development of lenticels, adventitious roots, aerenchyma and lenticels formation. Experiment 3, fine root dynamics was monitored with minirhizotron technique under field condition using clone RRIM 600 (16-year-old) in Songkhla province. Fine root dynamics was observed at 0-60 cm soil depth with minirhizotron technique. Transparent acrylic tubes were installed with 3 sampling trees during January 2014 - May 2015. Results showed that during the first dry season (February - April 2014), fine root length density was gradually increased until maximum fine root production occurrence during rainy season (October 2014) at 10-20 cm soil depth. The rate of maximum fine root production was 0.01 mm mm2 month1 in September 2014 and fine root mortality occurred 2 phases in August 2014 and December 2014. In 2015, at the earlier of dry season during (February-April) fine root production decreased again and tended to increase at the start of rainy season in May 2015. Fine root distribution estimated in year-round (February 2014- January 2015) was found highest at 20-30 cm depth. The increasing of fine root dynamics occurred after the full canopy development stage for 30 days. Dry rubber weight (g/t/t) increased to the peak period at late January 2014 continued to earlier February 2014, similarly found in January-February 2015 before leaf falling. Then, it decreased after leaf flushing. Rainfall and soil moisture were correlated with fine root dynamics at 40-60 cm depth (P<0.01). It was concluded that rubber tree adaptation under different water stress levels by using the minirhizotron technique was suitable to monitor fine root dynamics both in glasshouse and field condition