Influence of Water Regimes and Potassium Chlorate on Floral Induction , Leaf Photosynthesis and Leaf Water Potential in Longan

This study verifies the influence of water regimes and potassium chlorate (KC1O3) on photosynthetic rate, flower emergence and media moisture content of longan trees. The trees were grown in 150 liters lysimeter tanks filled with fine sand. The experimental design was a 2x2 factorial in completely randomized design (CRD) with 2 factors; 1) two levels of water regimes (well-watered and water deficit) and 2) two levels of KClO3 at 10 and 0 g. The results revealed that the well-watered treatment produced faster days of terminal bud break than that of the water deficit treatment. The 10 g KClO3 treatment induced 91 % flower emergence at 35 days after commencing the treatment, while the 0 g KClO3 treatment had 82 % leaf flushing and had no flower emergence. Water deficit or KClO3 treatments reduced the net carbondioxide (CO2) exchange, transpiration and stomatal conductance rates. Moreover, the combination of well-watered and 0 g KClO3 treatments gave the greatest values of the parameters. The well-watered treatment had higher volumetric water content in the growing medium and leaf water potential than the water deficit treatment, while for the 10 g and 0 g KClO3 treatments had similar the media moisture content.


Introduction
Longan (Dimocarpus longan Lour.) is one of the most popular fruit crops of northern Thailand.Longan flowers from late December to late February and is harvested from late June to August.At the present, the main region of longan cultivation is in the upper northern part of the country, such as 'Daw', 'Haeo', 'Bieo Khieo' and 'Si Chomphu'.Floral induction is an important step of flowering and fruiting.Due to the fact that the soil moisture levels and levels of KClO 3 used vary from place to place, induction of flowering at certain times is necessary in longan production.There are many factors that control flowering in longan, such as temperature, tree health, cultivar, water stress and potassium chlorate.(Subhadrabandhu, 1990;Manochai et al., 2004;Davenport & Stern, 2005;Sritontip et al., 2005).
Water constitutes a major part of the tissue mass and is required for growth and development.Plant water status is a good indicator of plant health and how well adapted the plant is to its environment.Plant water status can provide information on potential crop yield or be used for irrigation strategy.The water potential of a plant governs transport across cell membranes.Water potential can be used to evaluate the water status of a plant and provides a relative index of water stress.Technological advancements have increased the relative ease and number of variations to measure water potential in plant or plant leaves.Water is the most important factor among the environmental factors affecting growth; it may reduce the growth rate, metabolic activities and leaf area www.ccsen (

Experiment Treatment
The experimental design was a 2x2 factorial in completely randomized design (CRD) with 4 replications, total of 16 longan tree pots, with water regimes of well-watered (WW) or water deficit (WD) and KClO 3 at 10 and 0 g.pot -1 .The WW treated plants were supplied daily with a constant volume of water of 30 liters throughout the experimental period.The WD treated plants received a starting amount of water of 15 liters (in the 30-liter capacity container) and were supplied daily until the water container was empty.Then, the container was refilled to the starting volume of 15 liters.The nutrient solution was replaced every 15 day.The longan trees at the fully mature leaf stage were treated with 10 g pot -1 KClO 3 mixed into the nutrient solution containers.The study was conducted in the lysimeters at the Agricultural Technology Research Institute, Rajamangala University of Technology Lanna, Lampang, Thailand from November 1, 2008 to January 31, 2009.

Data Collection
1. Percentage of flowering, the sixteenth longan trees were sampled for data.These data were the percentage and days to visible active buds.The data collection lasted 49 days after treatment.
2. Leaf photosynthesis and chlorophyll fluorescence were measured immediately after KClO 3 application and then monitored at 1, 4, 7, 10, 13, 17, 21, 28 and 35 days after KClO 3 application (4 leaves per tree were sampled).The measurements were made on the 3 rd or 4 th leaf position of the fully expanded mature compound leaves at 09.00 to 10.00 a.m.Chlorophyll fluorescence (Fv/Fm) was measured at the leaf using a plant efficiency analyzer (Model PEA, Hansatech Instruments, UK.).On the same leaf, net CO 2 exchange, transpiration, and stomatal conductance rates were measured using a portable steady-state leaf photosynthesis system at an irradiance of 1,200 µ mol m -2 s -1 PAR (Model LCA-4 with the PLC-4 leaf chamber; Analytical Development Company Ltd. (ADC), UK).

Data Analysis
The data was analyzed for statistical significance by using the Statistic 8 analytical software package (SXW Tallahassee, FL).The Least Significant Difference (LSD) was used to compare treatment differences with ANOVA (P<0.05).

The Effects of Water Regimes and KClO 3 on the Physiology of the Trees
The longan trees that were treated with well watered produced terminal bud break significantly earlier than that of water deficit.Different water regimes had no differences on percentage of floral emergence or leaf flushing measurements after commencement of treatment.Those treated with 10 g KClO 3 had greater floral emergence and lower leaf flushing.However, the 10 g and 0 g KClO 3 were similar in the days of terminal bud break.There was no interaction between the water regimes and KClO 3 treatments on days of terminal bud break, percentage of flower emergence or leaf flushing after treatment (Table 2).*Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Changes in the Leaf Photosynthesis Characteristics Caused by Water Regimes and KClO 3
The water deficit longan trees had efficiency of photosystem ΙΙ lower at 7, 10, and 28 days after commencement treatment.Moreover, the 10 g KClO 3 reduced the efficiency of photosystem II at 4, 7, 10 and 28 days after application (Table 3).The interaction effect showed that the well water with 0 g KClO 3 had the highest value for the efficiency of photosystem II (Table 4).The water deficit treatments decreased the net CO 2 exchange rate during 1 to 35 days after treatment and the 10 g KClO 3 had a net CO 2 exchange rate that was lower than the 0 g KClO 3 at 4, 7, 10, 13, and 21 days after treatment (Table 5).The interaction effect between water regimes and KClO 3 rates showed that the well water with 0 g KClO 3 had the greatest effect on the net CO 2 exchange rate of those treatments (Table 6).For changes in transpiration rate, the water deficit had lower transpiration rate than the well-watered at 7 and 10 days after treatment and the 10 g KClO 3 treatment depressed the transpiration rate at 4-17 days after treatment (Table 7).The interaction effect between water regimes and KClO 3 resulted that the well-watered with 10 g KClO 3 , the water deficit with 10 g KClO 3 and water deficit with 0 g KClO 3 treatments decreased the transpiration rate when compared with the well-watered with 0 g KClO 3 treatment (Table 8).The water deficit reduced the stomatal conductance at 7, 13, 17 and 28 days after treatment.A similar result was obtained with the 10 g KClO 3 where the stomatal conductance declined at 4, 7, 10, 13, 17 and 28 days after treatment (Table 9).The interaction effect between water regimes and KClO 3 rates showed that the well-watered with 0 g KClO 3 treatment had the greatest stomatal conductance after the beginning of the experiment (Table 10).
Table 9.Effects of water regimes and KClO 3 rates on the stomatal conductance rate (mol M -2 S -1 ) after treatment *Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Changes of Volumetric Water Content and Leaf Water Potential
The volumetric water content in the growing media after treatment showed that the water deficit reduced the moisture value while there was no effect between 10 g and 0 g KClO 3 treatment.In addition, there was no interaction among all the treatments (Table 11).
The leaf water potential after the start of a treatment showed that the well-watered had higher leaf water potential than that of water deficit at 10 to 35 days after treatment while there was no effect on that from 10 g and 0 g KClO 3 .
However, there was no interaction effect among treatments (Table 12).*Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Discussion
The full irrigation had faster the days of terminal bud break about 9 days.The well-watered and water deficit treatments gave approximately 43.34-47.82% of all buds flowered and 44.95-45.89% of leaf flushing.The reduction of the water amount had effect on time of terminal bud brake due to water deficiency was a factor that usually causes the limitation of growth and metabolic activity rates of the plant (Boland et al., 1993).Borchert (1994) reported that water deficit inhibited bud break and shoot growth in tropical tree.In the present study, the 91% of all buds flowered at 25-27 days after the application of KClO 3 .The off-season flowering in longan trees was induced by KClO 3 (Sritontip et al., 2005;Hegele et al., 2008;Davenport & Stern, 2005;Manochai et al., 2005).The KClO 3 application induced floral emergence and reduced leaf flushing, whereas the treatments without KClO 3 application did not induce flowering.The efficiency of photosystem II (Fv/Fm), leaf net CO 2 assimilation, transpiration and stomatal conductance rates were reduced in water deficit and KClO 3 application, except for the application of combination of full irrigation and without KClO 3 treatments.In longan trees treated with water deficit, KClO 3 , and a combination of water deficit and KClO 3 leaf photosynthesis decreased because water deficit caused closure of the stomata and reduced CO 2 assimilation and stem extension, leaf expansion, and fruit growth (Flore & Lakso, 1989;Menzel, 2005).The high photosynthesis rate indicated the optimal irrigation management for longan and low value was led to drought stress.The photosynthetic rate of apricot trees daily irrigated to 25% of field capacity was lowered by 55% compared to control trees (100% field capacity), while a 75% reduction in photosynthesis was observed in the rest of water deficit stressed treatments (Ruiz-Sanchez et al., 2000).Diurnal changes in leaf gas exchange in well-water and drought were studied in Tai So litchi trees.Stomata conductance and net CO 2 assimilation reached maximum values at 0700-0800 h, and were lower in drought trees than in the controls for most of the day (Menzel & Simpson, 1994;Menzel, 2005).Water stress decreased the net CO 2 assimilate in papaya (Marler et al., 1994).Induced reduction in net CO 2 assimilated and stomata conductance were also observed in Valencia orange trees (Syvertsen & Lloyd, 1994).In Kensington mango trees effective stomatal closure was reached at -1.2 and -3.0 MPa (Schaffer et al., 1994;Pongsomboon, 1991).The water deficit had a lower leaf water potential in longan trees at 10 days after treatment due to decreasing of moisture content in growing media.The reduction of leaf water potential decreased leaf photosynthesis characteristics in longan tree because water deficit led to decreasing turgor pressure (Akinci & Lösel, 2012).Moreover, Drought conditions are usually associated with a decrease in plant productivity and the course of growth leads to the increase of abscisic acid (ABA) and decrease of indole-3-acetic acid (IAA) and cytokinins (CKs), which may result in the early stoppage of branch growth in comparison with its natural trend (Bradford & Hsiao, 1982;Ferguson et al., 1992) The treatment with KClO 3 induced the longan flowering process and could be used for off-season longan production.The mechanism of how KClO 3 induces the flowering process in longan is not entirely understood.Some researches claimed that in plants, the chlorate (ClO 3 -) ion competitively inhibited the nitrate reductase enzyme and is reduced to chlorite (ClO 2 -) and hypochlorite (ClO -) (Duke, 1985;King, 1974).Furthermore, the reduction products chlorite (C1O 2 -) and hypochlorite (C1O -) were shown to be rapidly acting toxins that poisoned all plant cell types (Aberg, 1947).It was previously shown that KClO 3 application also decreased chlorophyll fluorescence and leaf gas exchange (Sritontip et al., 2010), the leaf photosynthesis considerably decreased up to 6 days after KClO 3 application and remained rather low compared to the control up to 11 days (Hegele et al., 2008), consequently, the detrimental effects of KClO 3 on the plant's photosynthetic system could be caused by the phytotoxic effect of ClO 2 -and ClO -.Thus, water deficit and KClO 3 treatments seemed to be the inhibiting factors of the photosynthetic efficiency.
Floral initiation in longan is dependent on cool temperature and some chemicals treatment.However, the leaf photosynthesis was reduced during flower induction stage by low temperature and KClO 3, whereas the longan trees can induce flowering after treatments, which probably account for the depression in leaf photosynthesis rate reposed during the floral initiation in subtropical tree species (Sritontip et al., 2010;Hegele et al., 2008).There is considerable evidence for the regulatory role of plant hormones controlling floral induction, particularly in perennial fruit trees.It has been reported for trees that an increase of CKs stimulates flower induction, while high levels of gibberellic acids (GAs) and IAA result in inhibition (Bangerth, 2009).Furthermore, it was found that CKs concentrations in terminal buds of longan increased, whereas IAA concentrations reduced during the first fourteen days after KClO 3 application and GAs also decreased at twenty days after treatment (Hegele et al., 2008).
Although, water deficit and KClO 3 decreased leaf photosynthesis, water deficit treatment reduced media volumetric water content and leaf water potential, while both KClO 3 concentrations did not significantly affect these parameters.

Conclusion
The water deficit delayed time of terminal bud break by 9 days, while, the full irrigation and water deficit treatments gave similar flowering and leaf flushing percentages.Whereas, the longan trees in treatments without KClO 3 application did not have floral emergence.The efficiency of photosystem II (Fv/Fm), leaf net CO 2 assimilation and transpiration rates, and stomata conductance were reduced in water deficit and with KClO 3 treatments.The volumetric water content and leaf water potential declined with the water deficit treatment, while there was no difference between 10 g and 0 g KClO 3 .
Although water deficit impacted on the efficiency of photosystem II (Fv/Fm), leaf net CO 2 assimilation and transpiration rates, and stomata conductance; it did not affect off-season flower induction by KClO 3 .Therefore off-season production during dry season or under controlled deficit irrigation seems to be feasible, at least, in terms of how effective KClO 3 is as a flower inducing agent.Irrigation management during further fruit development still requires detailed investigation in order to optimize yield and quality of off-season longan fruit.
the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Factors
the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.Table10.Interaction effect of water regimes and KClO 3 rates and on the stomatal conductance rate (mol M -2 0.03 b 0.04 b 0.04 b 0.04 b 0.06 ab 0.06 0.02 b 0

Table 1 .
Composition of the standard nutrient solution * used for longan trees growing in lysimeters

Table 2 .
Changes in terminal bud break, floral emergence and leaf flushing after start of the treatments

Table 4 .
Interaction effect of KClO 3 and water regime on chlorophyll fluorescence (Fv/Fm) of 'Daw' longan trees after treatment *Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Table 5 .
Effects of water regimes and KClO 3 rates on the net CO 2 exchange rate (µ mol M -2 S -1 ) after treatment Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Table 6 .
Interaction effect of water regimes and KClO 3 rates on the net CO 2 exchange rate (µ mol M -2 S -1 ) after treatment

Table 7 .
Effects of water regimes and KClO 3 rates on the transpiration rate (m mol M -2 S -1 ) after treatment

Table 8 .
Interaction effect of water regimes and KClO 3 rates on the transpiration rate (m mol M -2 S -1 ) after treatment

Table 11 .
Effects of KClO 3 and water regime on the volumetric water content of growing medium after treatments *Means within the column followed by the same letter were not significantly different at p=0.05 by LSD.NS = Non-significant.

Table 12 .
Effects of KClO 3 and water regime on the leaf water potential of longan trees after treatment