Short Communication 

Propagation of Dillenia  suffruticosa  (Griff.) Martelli Stem Cuttings Using Plant Hormones: A Promising Approach to Supply Plantlets to Revegetate Degraded Tropical Heath Forests in Brunei Darussalam

OPEN ACCESS                                                                                                                                                 Research Journal of Botany

ISSN 1816-4919 

DOI: 10.3923/rjb.2017.32.37

Short Communication

Propagation of Dillenia  suffruticosa  (Griff.) Martelli Stem Cuttings Using Plant Hormones: A Promising Approach to Supply Plantlets to Revegetate Degraded Tropical Heath Forests in Brunei Darussalam

1S. Matali, 1N. Abidin, 1W.H. Tuah, 2A.M.Q. Pg Yusof, 1H.H. Mohd Din, 1H. Taha, 1R.S. Sukri and 1F. Metali

1Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Brunei Darussalam 2Department of Biotechnology, UCSI University, No. 1, Jalan Menara Gading, UCSI Heights, Cheras, 5600 Kuala Lumpur, Malaysia

Abstract

Background and Objective: Dillenia suffruticosa  (Griff.) Martelli is abundantly thriving in various forest types in Brunei Darussalam, including the tropical Bornean heath forests. This study aimed to investigate the plant hormones that can be used to propagate stem cuttings of D.suffruticosa, which is a promising approach to supply plantlets to revegetate degraded tropical heath forests. Methodology: Stem cuttings of D.suffruticosa were treated using three single auxin hormone: 0.1% Indole Acetic Acid (IAA), 0.1% Indole Butyric Acid (IBA) and 0.2% Naphthalene Acetic Acid (NAA) and 5 commercially available rooting hormones: Yates, Clonex and Seradix 1, 2 and 3 and planted in a medium containing a mixture of equal parts black soil and perlite. The survival and rooting percentages, number and lengths of roots produced and number and surface areas of new leaves were assessed at 4-weekly intervals until week 16. Results: Results indicated that the cuttings treated with single auxin treatments (mainly 0.2% NAA and 0.1% IAA) had higher survival and rooting percentages, longer roots, larger leaf surface areas and produced more leaves than those cuttings treated with commercial rooting hormones. Conclusion: It is concluded that compared to commercial rooting hormones, 0.2% NAA and 0.1% IAA were the most effective auxin hormones in promoting survival and growth of Dillenia suffruticosa cuttings.

Key words: Bornean heath forests, IAA, IBA, NAA, rehabilitation, rooting hormones, vegetative propagation, auxins
 

Received: September 08, 2016               Accepted: October 31, 2016                  Published: December 15, 2016
 

Citation: S. Matali, N. Abidin, W.H. Tuah, A.M.Q. Pg Yusof, H.H. Mohd Din, H. Taha, R.S. Sukri and F. Metali, 2017. Propagation of Dillenia  suffruticosa  (Griff.) Martelli stem cuttings using plant hormones: A promising approach to supply plantlets to revegetate degraded tropical heath forests in Brunei Darussalam. Res. J. Bot., 12: 32-37.
 

Corresponding Author: F. Metali, Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Brunei Darussalam Tel: +6732463001
 

Copyright: © 2017 S. Matali et al .  This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.
 

Competing Interest: The authors have declared that no competing interest exists.
 

Data Availability: All relevant data are within the paper and its supporting information files.

INTRODUCTION 

Heath and Peat Swamp Forests of Brunei Darussalam, which cover 3,500 and 90,000 ha of the country’s total land area, respectively are unique in terms of their biodiversity and ecosystem features1. In the Belait District of Brunei Darussalam, two types of tropical heath forests exist: Kerangas (on higher and drier areas) and kerapah (on permanently waterlogged and lower areas)2,3. These forests are intermixed with the Peat Swamp Forests at Lumut and Badas and some of them occur along the Brunei Liquefied Natural Gas Company (BLNG) water pipelines that carry water from the Belait River to the BLNG plant in Lumut (pers. obs). In 2013, a 20 m wide fire corridor was created along the BLNG Pipeline Road as a preventive measure to reduce fire threats to the water pipelines (BLNG, pers. com.). However, the removal of vegetation cover has conversely increased the risk of fires to the dry and exposed peat within the fire corridor. As such, there is currently an urgent need to revegetate this fire corridor especially with increasing frequencies of dry spells and droughts that have increased fire incidences.

Cleared   and   degraded   forests   created   from anthropogenic disturbances take a long time to recover naturally, thus supplementing their regeneration through rehabilitation and reforestation activities using tree planting methods are necessary4. Wildings and stem cuttings of native plant species have been widely used to revegetate degraded lands and forests5,6. A rapidly growing number of rooted stem cuttings of plants has been vegetatively propagated and used in many reforestation programmes7,8.

An investigation on the vegetative propagation of Dillenia suffruticosa  (Griff.) Martelli, an abundant shrub that is native to Brunei Darussalam9 was conducted. Dillenia  suffruticosa from the family Dilleniaceae was chosen because it is a potential candidate for rehabilitation of degraded lands due to its ability to grow in various habitats including roadsides, secondary forests, open sites in undisturbed forest, peat swamps,  heath  forests,  white  sands  and  also  well  drained and eroded soils10. Dille nia s u ffr u tic o s a  can be used to stabilise  slopes  in  preventing  landslides11.  Since  obtaining D.  suffruticosa   seedlings  via  seed  propagation  is  difficult and almost impossible12, using auxins: Naphthalene Acetic Acid (NAA) and Indole Acetic Acid (IAA) in stem cuttings seem to be the best option to produce plantlets9.

This study investigated the different hormones (either using single auxin or commercially available plant rooting hormones) that could increase the survival and rooting percentages as well as root and leaf production of D. suffruticosa  stem cuttings. Therefore, the main aim of the study was to determine which hormone could be used for the mass propagation of D. suffruticosa  and thus, help to rapidly supply plantlets for the revegetation of degraded heath forests in Brunei Darussalam.


MATERIALS AND METHODS
 
Sampling of stem cuttings: A total of 150 softwood stem cuttings of Dillenia suffruticosa (Griff.) Martelli were collected from the heath forests within the Universiti Brunei Darussalam campus (4E58’41.5”N, 114E53’39.8”E) and along the Muara-Tutong highway (4E58’59.81”N, 114E54’20.34”E). A maximum of two leafy softwood stem cuttings (8-12 cm) were sampled per plant to reduce any damage to the wild stock plants.
 
Preparation of stem cuttings: Similar to Abidin and Metali9, all organs on the stem cuttings were removed to ensure they concentrate their energy in forming root and shoot instead of producing reproductive organs. A replicate of 10 cuttings were treated with single auxin hormones, 0.2% Naphthalene Acetic Acid (NAA), 0.1% Indole Acetic Acid (IAA) and 0.1% Indole Butyric Acid (IBA) and 20 cuttings with commercial rooting hormone powders, Seradix 1, 2, 3 and Yates and rooting hormone gel, Clonex, using a quick-dip method9,13. The auxins and their respective concentrations were selected and prepared by following Abidin and Metali9, whereas the commercial hormones were purchased from the local markets. The active constituent (s) of Seradix (unknown concentrations) and Clonex (0.3%) was IBA and Yates were 0.005% IAA and 0.002% NAA. Distilled water was used as a control treatment.

All stem cuttings were planted into square plastic pots containing autoclaved growth media of equal parts black soil and perlite. The pots were placed on the benches in a plant house  with misted conditions and the benches with pots were covered with a PVC plastic cover to maintain high relative humidity. The temperatures, relative humidity and light intensities recorded in the plant house were between 22-29EC, 80-90% and 300 µmoL mG2 secG1 (Apogee Quantum MQ-200 PAR Meter, Apogee Instruments, USA), respectively. After 6 weeks, the cuttings were re-potted into large pots with only black soils. The pots were subsequently transferred to a plant shade with temperatures between 22-34EC, relative humidity of 60-75% and light intensities of 450 µmol mG2 secG1. Fertilizers (NPK, 15:15:15) were added into the potted soil every 4 weeks and watered twice a day.

Assessment of cuttings and statistical analysis: The cuttings were assessed every 4 weeks until the 16th week for their percentages of survival and rooting, number and lengths of new roots produced and number and surface areas of new leaves. All statistical analyses were conducted using R version 3.3.014. Differences in the number of roots, root lengths, number of leaves and leaf surface areas between the different hormones were determined using one-way ANOVA and Tukey’s HSD tests. Assumptions of normality and equal variances were checked during one-way ANOVA and were not violated.

RESULTS
Stem  cuttings  treated  with  single  auxin  treatments (i.e., 0.2% NAA, 0.1% IAA and 0.1% IBA) had 100% survival recorded throughout the 1st 12 weeks  (Table  1). However, by week 16, only stem cuttings treated with 0.2% NAA remained at 100% survival. Stem cuttings treated with auxins produced roots  faster  with  100%  rooting  percentage  achieved  by week 4 when treated with 0.2% NAA and 100% rooting achieved by week 8 when treated with 0.1% IAA (Table 1). Cuttings treated with 0.1% IBA produced roots more slowly compared to the other hormone treatments, reaching only 90%  rooting by week 16. In contrast, percentage survival for all stem cuttings treated with commercial rooting hormones fell considerably to 40% and below by week 4, except for cuttings treated with Yates (Table 1). Percentage survival for all commercial rooting hormones reached 0% survival by week 12, except Yates-treated stems. None of the cuttings treated with commercial hormones (except Yates) had successfully rooted (Table 1). 

Cuttings treated with 0.2% NAA recorded significantly higher production of roots (Fig. 1a) and significantly longer root lengths (9.34±1.42 cm, Fig. 1b) than the other plant hormones. In contrast, cuttings treated with 0.1% IAA had significantly higher number of new leaves produced (10 new leaves, Fig. 1c) and significantly larger leaf surface area (166±48.6 cm2, Fig. 1d). Cuttings treated with distilled water (control) and all commercial rooting hormones (except for Yates) did not successfully produce any roots and leaf,  thus no data for these treatments were recorded by week 16.

Table 1: Survival percentages and rooting percentages of Dillenia suffruticosa stem cuttings treated with different hormones (0.2% Naphthalene Acetic Acid (NAA), 0.1% Indole Acetic Acid (IAA), 0.1% Indole Butyric Acid (IBA), Yates, Clonex, Seradix 1, 2 and 3) and distilled water as the control treatment at an interval of 4 weeks until week 16

Fig. 1(a-d): Variation in the (a) Number of roots produced, (b) Length of roots, (c) Number of new leaves produced and (d) Surface area of leaves of Dillenia suffruticosa stem cuttings treated with plant hormones (0.2% NAA, 0.1% IAA, 0.1% IBA, Yates, Clonex and Seradix 1, 2 and 3) and distilled water as the control treatment. Mean value is denoted by the diamond-shaped symbol. Different letters indicate significant difference between treatments (p<0.001). Dillenia suffruticosa stem cuttings treated with Clonex, Seradix and Control had zero mean values for all 4 parameters. Only data at week 16 were presented

Higher percentage survival of cuttings treated with Yates compared to the other commercial rooting hormones used in this study could be due to the presence of both NAA and IAA as the active ingredients in Yates. However, due to its very low concentrations (0.005% IAA and 0.002% NAA), stem cuttings treated with Yates recorded lower rooting and survival percentages in week 16 and the effect was not clear-cut as those of single NAA and IAA hormone treatment. Kebede et al. 16 also reported that at low concentrations of NAA and IBA hormones, root productions were also low. Various studies have reported that different concentrations of hormones differentially affected survival, rooting percentage, leaf and roots production of cuttings17-20. Copes and Mandel21 noted that a combination of NAA and IBA did not significantly increase root and leaf productions compared to the significant effects achieved with one hormone treatment, NAA or IBA, which was consistent with the present findings.

In this study, stem cuttings treated with Clonex rooting hormone gel which contained 0.3% IBA had negative results on survival, root and leaf production compared to 0.1% synthetic IBA treatment. This finding was similar to studies of stem cuttings propagation of three tropical species, whereby cuttings treated with commercial rooting hormone Clonex also showed lower rooting percentage compared to cuttings treated with synthetic IBA22 and this could possibly be due to high IBA concentrations in Clonex.

The use of single auxins (especially 0.2% NAA) will result in a high survival rate of stem cuttings. The stem cutting technique with plant hormone will produce plantlets that will be used in the revegetation of tropical degraded heath forests in Brunei Darussalam. Raising plantlets from vegetative propagation using plant hormones then consecutively using them to revegetate forests are not new7,8. There is a possibility that the revegetation programme in Lumut using D. suffruticosa will also be extended to the Peat Swamp forests as this species is well known to be grown in many forest habitats10.

It is concluded that Dillenia suffruticosa stem cuttings grow better when treated with single auxin treatment than using commercial root-promoting hormones. Synthetic auxins, in particular 0.2% NAA and 0.1% IAA are more suitable for use in the mass propagation of D. suffruticosa stem cuttings. D. suffruticosa plantlets can be rapidly mass produced using stem cutting techniques with a single auxin treatment (mainly NAA and IAA), which can then be transplanted to the degraded heath forests in Lumut. The suitability of this species in the revegetation and rehabilitation programme will be further assessed via field monitoring of planted stem cuttings.

Dillenia suffruticosa (Griff.) Martelli (Daun Sempur)




Wickramathilake et al., /Journal of Tropical Forestry and Environment Vol. 3, No. 02 (2013) 66-75 

Impacts of Woody Invader Dillenia suffruticosa (Griff.) Martelli on Physio- chemical Properties of Soil and, Below and Above Ground Flora

 B.A.K. Wickramathilake 1*, T.K. Weerasinghe 2 and S.M.W. Ranwala 3

1 Department of Zoology, Open University of Sri Lanka, Nawala, Nugegoda 2 Department of  Botany, The Open University of Sri Lanka, Nawala, Nugegoda 3 Department of Plant Sciences, University of Colombo, Colombo 03

Date Received: 20-04-2013  Date Accepted: 29-10-2013 

Abstract 

Dillenia suffruticosa (Griffith) Martelli, that spreads fast in low-lying areas in wet zone of Sri Lanka is currently listed as a nationally important Invasive Alien Species that deserves attention in ecological studies. Thus, impact of this woody invader on physical, chemical properties of soil and below and above ground flora was investigated. Five sampling sites were identified along a distance of 46km from Avissawella to Ratnapura. At each site, two adjacent plots [1m x10m each for D. suffruticosa present (D+) and absent (D-)] were outlined. Physical and chemical soil parameters, microbial biomass and number of bacterial colonies in soil were determined using standard procedures and compared between D+ and D- by ANOVA using SPSS. Rate of decomposition of D.suffruticosa leaves was also determined using the litter bag technique at 35% and 50% moisture levels. Above ground plant species richness in sample stands was compared using Jaccard and Sorenson diversity indices. Decomposition of D. suffruticosa leaves was slow, but occurred at a more or less similar rate irrespective of moisture content of soil. Particle size distribution in D+ soil showed a much higher percentage of large soil particles.  Higher % porosity in D+ sites was a clear indication that the soil was aerated.  The pH was significantly lower for D+ than D- thus developing acidic soils whereas conductivity has been significantly high making soil further stressed. The significant drop in Cation Exchange Capacity (CEC) in D+ soil was a remarkable finding to be concerned with as it correlated with fertility of soil. Significantly higher values of phosphates reported in D+ soil support the idea that plant invaders are capable to increase phosphates in soil.

Higher biomass values recorded for D+ sites together with higher number of bacterial colonies could be related to the unexpectedly recorded higher Organic Carbon. Both  the  Jaccard  and  Sorenson   indices indicated  that D+  and  D-  sites  were dissimilar with respect to  above ground  plant  species  richness.  Thus, changes in above ground vegetation and soil properties due to the invasion were identified and further studies are needed for determining the degree of soil deterioration due to the invasive behavior of D. suffruticosa.

Key words: Dillenia suffruticosa, soil properties, Sri Lanka, invasive species, microbial biomass

1. Introduction

Invasive alien Species (IAS) cause tangible ecological and economic damages by altering goods and services provided by the environment (Charles and Dukes, 2007, Parker, 1999, Primental et al., 2000). One major reason for these irreparable and irreversible impacts of IAS has been related to their ability to modify physical resources of the environment in ways that differ from resident plant associations (Ehrenfeld, 2004, Weidenhamer  and Callaway, 2010). Many invasive plant species have high specific leaf areas, faster growth rates and increased leaf nutrient concentrations relative to the resident species of the same sites, and these traits change soil properties via modifying rates of decomposition and nutrient cycling in the soil environment (Allison and Vitousek, 2004). Additionally, allelopathic, defensive, or antimicrobial chemicals of plant invaders act as novel weapons and play a vital role in uniquely affecting the biogeochemistry of the soil to maintain the dominance of plant invaders (Callaway and Ridenour, 2004, Laio et al., 2008). There is much evidence that invasive plant species can modify physical or chemical attributes of soil, including inputs and cycling of nitrogen and other elements (Laio et al., 2008, Nicholas et al., 2008, Parker et. al., 1999, Walker and Smith, 1997).

For many years knowledge on impacts of IAS in Sri Lanka was mostly based on anecdotal observations, but in recent years empirical evidences on many aspects of IAS have been multiplied. Although studies on the impacts of plantation crops and many agricultural crops on  Sri Lankan soils have been studied (Weerasinghe, 2012, Weerasinghe  and Weerasinghe, 2007),   impacts of many  IAS, both on soil and  native species remain understudied (Jayaratne  and Ranwala, 2010). Para, (Dillenia suffruticosa (Griffith) Martelli., Family - Dilleniaceae) is one  such example.

Dillenia suffruticosa, native to East Asia, was introduced to Sri Lanka as an ornamental plant to Royal Botanical Gardens in 1882 from Boneo.  It is a light demanding woody shrub that could grow up to 6m tall  in open lands in moist soil, thus proliferated fast as dense stands  in the wet-low  country of Sri  Lanka inhabiting  many marshy/semi- marshy areas (including abandoned paddy fields) in Kalutara, Galle  and Ratnapura  districts, posing a threat to native biota. Shade provided by its large leaves hinder undergrowth and accumulation of litter created a favourable habitat for mosquitoes, thus raising human health issues in the surroundings. When growing in riparian habitats it influenced sedimentation rates (Ranwala, 2011). These  impacts listed D. suffruticosa as a nationally important IAS over the last ten years (Wijesundara, 1999, 2010). It  was also recognized as an alternate host for Oil palm nettle caterpillar Setoranitens in  Malaysia  (Lim et al., 2001). However, important uses of D.suffruticosa have also been documented. Ability to staunch bleeding  (Ahmed and Holdsworth, 1995), antifungal (Johnny et al., 2011, Wiart et al., 2004) and phyto- remediation (Rahim et. al., 2011 ) properties, usage of live poles as an effective and economical means of slope stabilization in  bio-engineering (Abdullah et al., 2012, Prasad et al., 2012, Sasan et al., 2009) are among them.

Control through utilization has been suggested as an eco - friendly approach in IAS management (Geesing et.al.,2004) but at the same time, concern on IAS as ecosystem engineers (Crooks, 2002, Walker and  Smith, 1997) cannot be neglected.  As IAS alter structure and function of invaded ecosystems by modifying physical, chemical and biological resources, impact analysis is considered very important. Despite the widespread global attention on IAS, studies on their qualitative and quantitative consequences on the environment have not been well documented in many countries (Callaway and Maron, 2006, Jayaratne  and Ranwala, 2010, Richardson and Van-Wilgen, 2004). In this context, we describe some impacts of D. suffruticosa on its immediate neighborhood through this paper.

The present work examined changes in physical, chemical properties of soil and below and above ground flora between stands with and without D. suffruticosa. Hence the study was conducted with the following objectives. Firstly, to  determine  the  decomposition  time  and  rate  of  leaves  of  D. suffruticosa. Secondly  to identify  the effects of  D. suffruticosa  on physical  parameters  of soil such as particles-size  distribution, bulk density, porosity percentage and chemical parameters such as pH, conductivity, cation exchange capacity  and nutrients (mainly Nitrates and Phosphates)  in soil.   Thirdly, to recognize the effect of D. suffruticosa on below ground flora (microbial biomass and bacterial colonies of soil) and above ground vegetation in invaded sites.

2. Materials and Methods  

2.1 Study sites 

Sampling  sites,  S1-S5  were  selected at  a  total  distance of  46 km  along  the  High  Level  Road   between  Awissawella  and  Ratnaputa  based  on  visual  observation  of  presence  of  D. suffruticosa. At each site, two 1m x10m size adjacent plots were randomly outlined to represent presence (D+) and absence (D-) of D. suffruticosa.  The regional climate of the study sites was wet, humid and warm with an annual average rainfall > 2500mm, overall year round temperature approximately at 30oC.  The stands contained Red Yellow Podsolic soils.

2.2 Determination of time and rate of decomposition of D. suffruticosa leaves

Fifty Nylon mesh bags (8cm ×10cm, pore size 0.25mm2) each containing 2g of leaf matter were prepared using air dried mature leaves of D. suffruticosa. Bags were sealed and kept buried (3 per pot) approximately 5cm beneath in 16 pots containing soil obtained from natural habitat of D. suffruticosa. Two bags were kept out of water at room temperature (30oC). To simulate natural moisture contents of soil, two equal sets of pots were maintained at 35% and 50% moisture levels under greenhouse conditions (30oC). At 14 day intervals, 3 litter bags  were  removed  from  each set of pots  and separately  washed  several  times followed by air  drying for  seven  days.  Residues were carefully taken out, oven dried at 700C until a constant weight was obtained. The mean mass loss of residues was calculated and plotted against decomposition time. Time taken for 50% loss of the initial mass (t50) was obtained for each moisture level.  Decomposition  rate  was  calculated by log n (Wt/W0)  =  log nW0-Kt50 ,where Wt= Weight  of  residue  remaining  at  time  t50, W0 = Initial  weight  of  residues, t50  = Time  taken  for  50%  loss  of  the  initial  mass, K = decomposition rate,  according to Anderson  and  Ingram  (1993).

2.3 Determination of physical and chemical properties of soil

A composite soil sample was obtained from each of the plots twice a year (6 month intervals). Physical parameters of soil such as particles-size distribution, water retention capacity, bulk density, porosity % and chemical parameters such as pH, conductivity, cation exchange capacity and nutrient levels (mainly Nitrates and Phosphates) were tested in D+ and D- according to Hess, (1971). Data  analyses for each parameter were  done  by  two way Analysis  of  Variance  using  SPSS  software  (Version 16) to assess the significant (P= 0.05)  impacts occurred due to the presence of D. suffruticosa  during sampling times.

2.4 Determination of the changes in below and above ground flora due to the presence of D. suffruticosa.

Soil samples obtained for above physical and chemical analyses were also used to compare below ground flora such as microbial biomass and number of different bacterial colonies between D+ and D- soil. Microbial biomass was measured using fumigation incubation technique as per Jenkinson and Powlson (1976) while number of bacterial colonies was enumerated according to Robert et. al., (1957).

To identify the effect on above ground flora, height and crown cover percentage of D. suffruticosa and   number of undergrowth plant species  was recorded in  D+ and D- plots at each site.  Similarity of above ground vegetation between D+ and D- plots was  compared for each site by  Jaccard  [ISJ  = c/( a+ b+ c)*100] and  Sorenson  [ISs = c /½( a+ b)*100] similarity coefficients (Muleller Dombois and Ellenburg, 1974)  where  a and b  were species richness in D+ and D- plots respectively and c = number of species common to both D+ and D-.

3. Results

3.1 Time and rate of decomposition of D. suffruticosa leaves 

Dillenia suffruticosa leaves decomposed at a rate of 0.014g/day and 0.011g/day respectively at 35% and 50% moisture levels taking 98 and 126 days for a 50% weight loss (Figure 1).

Decomposition Time (days)

Figure 1: Remaining weight of dried D. suffruticosa leaves during decomposition at 35% and 50% moisture levels

3.2 Change in physical and chemical properties of soil 

Our results indicated that D. suffruticosa tend to increase the percentage of large particles in soil (Figure 2a) simultaneously and significantly increasing the porosity of soil (Figure 2b).  However, bulk density and water retention capacity did not vary significantly between D+ and D- soil.  It was also found that there was no influence of the time of data collection on soil parameters investigated above.

Figure 2: Change of a) particle size distribution >1mm, and, b)   Percentage porosity in D+ and D- soils.

The pH of the soil was significantly reduced (6.00 vs 6.40, P=0.05) and conductivity of soil was significantly increased (25.64 vs 18.24, P=0.05) by the presence of D. suffruticosa.  Further, the Cation Exchange Capacity was significantly affected (Figure 3a) while an increase in % Organic Carbon in D+ plots also observed (Figure
3b).
Invasion of D. suffruticosa significantly increased the Phosphate content of soil. There was no significant change in the Nitrate content due to the presence of the woody invader (Figure 4).

Figure 3: Change in   a) Cation Exchange Capacity   b) Percentage Organic carbon in soil between  D. suffruticosa present and absent stands

Figure 4:  Change in Nitrate and Phosphate contents in soil by D. suffruticosa

3.3 Changes in below and above ground   flora due to presence of D. suffruticosa

The microbial biomass (Figure 5) and the number of bacterial colonies reported from soil was relatively high in D+ plots (166 x105 vs 97x 105 g1-soil, P=0.05) indicating that the invader promoted the existence of diverse micro flora in soil.
Observations revealed that presence of D. suffruticosa had significantly changed the composition and richness of undergrowth plant species under its stands. Further, it was noticed that species richness of undergrowth vegetation was inversely related to crown cover of D. suffruticosa which was about 2-3m tall in fully grown shrubs. At 100% crown cover no undergrowth was found. Both  the  Jaccard  and  Sorenson   indices confirmed that D+  and  D-  sites  were dissimilar   with   regard to  plant  species  richness (Table 1).

Figure 5: Change in microbial biomass in soil between D. suffruticosa present and absent stands

Table 1.
Similarity coefficients obtained for D+ and D- plots at five sampling sites. ISJ= Jaccard Similarity coefficient and ISS= Sorenson Similarity coefficient

4. Discussion  
Invasive Alien plant species impose multitude of impacts on structure and function of the ecosystem through direct or indirect effects on abiotic and biotic components of the environment (Charles and Dukes, 2007, Parker et. al., 1999, Walker and Smith, 1997) and our results are also in favor of  this idea to a certain extend.

Plant invaders, mainly through their litter and root exudates change soil structure and nutrient cycles, mobilize and/or chelate nutrients, modify soil nutrient pools and diversity of soil biota. These effects on soil biogeochemistry are not only closely linked to the nutrient stoichiometry and secondary metabolites of leaf tissues but also the rate of decomposition of plant litter which play a pivotal role in releasing nutrients and chemicals into soil (Ehrenfeld, 2003, 2004, Weidenhamer and Callaway, 2010). Single species litter dynamics have shown that rate of litter decomposition and nutrient cycling are closely correlated with site environmental conditions (particularly climate), litter chemistry, composition of soil biota and the moisture content of soil (Swift et.al., 1979). As proven by our results, ability of D. suffruticosa to decompose its litter in a more or less same rate at high and low moisture levels (under the same environmental conditions) could be attributed to its broad tolerance limits (Allison and Vitousek, 2004) to withstand commonly prevailing moisture fluctuations of the soil. In such instances the invader is said to pose a threat to native species by delaying decomposition of their litter as many native species require substantial amount of water to efficiently decompose leaf litter in wet and warm environments (Facelli and Picket, 1999).

Presence of a large proportion of easily decomposable substances in plant tissues is reflected by higher decomposition rates of litter and this characteristic serves as a trait of invasiveness.  However, according to our results D. suffruticosa exhibited a  slow decomposition rate (average  of  12.5mg/day  and (t50) 105 days) compared to  Lantana camara (rate  126 mg/day  and t50- 11 days)  and  Croton lacciferus (average  rate  154 mg/day  and t50- 09 days)  under more or less similar climatic and soil conditions (Ranwala, unpublished data). Although litter quality was not investigated in this work, according to Hirobi et al., (2004), low nutrients (N= 8.7, P= 0.19, K= 1.83, Ca= 7.09, Mg=2.16 mg g-1) and high amount of acid insoluble residue (368.2 mg g-1) in D. suffruticosa leaves were responsible for slow decomposition rates.

Our results proved that the presence of D. suffruticosa structurally alter soil by creating larger soil particles and many air pores, thus making the soil much aerated. Acidity and high conductivity of soil under D. suffruticosa stands further indicated that the soil chemistry was affected probably be due to the accumulation of more H+ ions, minerals released from litter, inputs of CO2 into substrate and or release of secondary metabolites/exudates by the invader (Kelly et. al., 1998). However, further work is required to comment on the mechanism. As proven by our results, Cation Exchange Capacity (CEC), which plays a major role in deciding the fertility status of soil, was also affected by the presence of D. suffruticosa. Significantly decreased CEC of soil in D. suffruticosa   stands was a major evidence to show that mobility of nutrients has been affected by the invasive plant. Reduced CEC in the present study is an important finding to be concerned with as this could directly interfere with the absorbance and exchange of nutrients of any native species in the neighborhood.  Increased organic carbon content exhibited by the plots with D. suffruticosa in our results served as an indication of the species potential of increasing soil organic carbon stock and hence soil fertility in invaded sites.    However, addition of carbon stimulates soil microbial growth, which in turn accumulates soil nitrogen in their biomass limiting the availability of nitrogen to plants in many instances (Vitousek, 1982). The study was not able to identify any difference in nitrate content between D+ and D- soils but in available phosphates.  This finding correlates with Martin et. al., (2009) which states that higher content of soil phosphates was common in many terrestrial invasions. However, further research is needed to ascertain whether this elevated phosphorus was brought through the invasive plant (Weidenhamer and Callaway, 2010) or activated by soil microbial biomass. This increase could also be attributed to the increased acidity which may assist to convert non soluble phosphate to soluble phosphates in the soil environment (Hedley et. al., 1983).

Movement of nutrients in soil is biologically mediated, thus changes in soil microbiota could be linked to changes in nutrient cycling of soil (Katherine et.al., 2006). At the same time, the abundance, composition and activity of the decomposing community is directly influenced by the plant and its litter resource (Couteaux et al., 1995, El-Shatnawi and Mukhadmeh, 2001, Kourtev et al., 2002). Higher microbial biomass observed in D+ soils in this study may have also contributed to alter soil chemical properties under D. suffruticosa stands, but, further investigations on microbial composition are required to comment on this change. As soil is degraded with the increase of unfavorable microorganisms in soil (Katherine et.al., 2006), it would be worthy to investigate on the changes in populations of favourable or  unfavourable microorganisms  between D+ and D- soil.

In general diversity, density of plants is expected to be high in places where ample sunlight is supplied (Bazzaz and Picket, 1980). It was clearly understood that D. suffruticosa suppress undergrowth plant species richness/composition by physically shading the floor and probably suppressing establishment and growth of seedlings of the resident species. Many IAS alter species assemblages in communities; reduce abundance and richness of the neighborhood by increasing above and below ground competition for resources such as light and nutrients and by exuding secondary metabolites through roots and plant litter (Meier and Bowman, 2008, Vilà and Weiner, 2004, Yurkonis et. al., 2005, Xiong and Nilsson, 1999). These prevent seedling establishment, inhibit growth and development of resident plant species thereby creating feedbacks for continued invasion in many ecosystems.

Our work also confirmed that the woody invader, D. suffruticosa modify its neighborhood by altering soil properties and above ground community composition.

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