Establishment of exotic invasive species causes many negative implications in restoration programmes such as out competing native species, thereby altering the structure, composition and function of the target ecosystem. Although Alstonia macrophylla is an exotic invasive tree species in Sri Lanka, its impact on native flora is undermined due to its timber value. The influence of A. macrophylla on the composition and dynamics of new recruits in an eleven-year-old restoring pine plantation (RP) was investigated and compared to a 25???30-year-old unrestored Pine plantation (UP) in Hantana, Sri Lanka. In both stands, the dominant species and the highest densities in all life stages (seedlings, saplings and trees) of the woody plants were represented by A. macrophylla. This species survived better than the non-Alstonia species in RP, than in UP, and was well represented in all diameter at breast height (dbh) classes in RP. The negative correlation between rainfall and mortality of Alstonia and non-Alstonia was stronger in UP than that in RP. The study concludes that considering life history strategies and invasive behavior of A. macrophylla in pine conversion programmes, they must be managed at different time scales (short, mid and long term) using silvicultural techniques to achieve restoration goals in the mountainous regions of Sri Lanka.

Both native and non‐native bamboo populations can expand their distributions in a rather irregular manner, inflicting changes in native vegetation with potential consequences for litter‐dwelling arthropod communities. To our knowledge, no studies have been undertaken to explore the impacts of bamboo spread on litter‐dwelling arthropods. This study examined the impacts of Bambusa bambos, a spreading native bamboo species, on abundance and order richness of litter‐dwelling arthropods in tropical moist evergreen forests. Bamboo‐rich and non‐bamboo forests were compared in three study sites at Moragahakanda in the Central Province of Sri Lanka. Arthropods were sampled from leaf litter and individuals were categorised into their respective orders. Arthropod abundance and order richness were higher in bamboo‐rich forests than in non‐bamboo forests across all sites, indicating more hospitable micro‐habitat conditions following bamboo spread. Litter‐dwelling arthropods belonging to orders Blattodea, Hymenoptera, Diptera, Lepidoptera and Orthoptera were either more prevalent or more frequently associated with bamboo‐rich forests than non‐bamboo forests, suggesting a potential shift in community structure. The abundance and order richness of litter‐dwelling arthropods in non‐bamboo forests was explained by environmental variables, whilst no such associations were observed in bamboo‐rich forests. The overall findings indicate that the spread of bamboo may facilitate litter‐dwelling arthropods and cause a compositional shift in taxonomic assemblages, perhaps as a result of changes in the micro‐habitat conditions on the forest floor.

Exposing plants to gradually increasing stress and to abiotic shock represents two different phenomena. The knowledge on plants' responses following gradually increasing stress is limited, as many of the studies are focused on abiotic shock responses. We aimed to investigate how cowpea (Vigna unguiculata (L.) Walp.) plants respond to three common agricultural abiotic stresses: hypoxia (applied with the increasing time of exposure to nitrogen gas), salinity (gradually increasing NaCl concentration), and water deficit (gradual decrease in water supply). We hypothesized that the cowpea plants would increase in tolerance to these three abiotic stresses when their intensities rose in a stepwise manner. Following two weeks of treatments, leaf and whole-plant fresh weights declined, soluble sugar levels in leaves decreased, and lipid peroxidation of leaves and roots and the levels of leaf electrolyte leakage increased. Polyphenol oxidase activity in both roots and leaves exhibited a marked increase as compared to catalase and peroxidase. Leaf flavonoid content decreased considerably after hypoxia, while it increased under water deficit treatment. NO emission rates after 3 h in the hypoxically treated plants were similar to the controls, while the other two treatments resulted in lower values of NO production, and these levels further decreased with time. The degree of these changes was dependent on the type of treatment, and the observed effects were more substantial in leaves than in roots. In summary, the responses of cowpea plants to abiotic stress depend on the type and the degree of stress applied and the plant organs.

Rice (Oryza sativa L.) and barley (Hordeum vulgare L.) are the cereal species differing in tolerance to oxygen deficiency. To understand metabolic differences determining the sensitivity to low oxygen, we germinated rice and barley seeds and studied changes in the levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), activities of the enzymes involved in their scavenging, and measured cell damage parameters. The results show that alcohol dehydrogenase activity was higher in rice than in barley embryos providing efficient anaerobic fermentation. Nitric oxide (NO) levels were also higher in rice embryos indicating higher NO turnover. Both fermentation and NO turnover can explain higher ATP/ADP ratio values in rice embryos as compared to barley. Rice embryos were characterized by higher activity of S-nitrosoglutathione reductase than in barley and a higher level of free thiols in proteins. The activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase) in imbibed embryos were higher in rice than in barley, which corresponded to the reduced levels of ROS, malonic dialdehyde and electrolyte leakage. The observed differences in metabolic changes in embryos of the two cereal species differing in tolerance to hypoxia can partly explain the adaptation of rice to low oxygen environments.

High demand has increased the exploitation of medicinal plants from the wild. Insufficient information on germination and seedling development hinders the propagation of such plants. Thus, seed germination and seedling development of three medicinal species in the family Acanthaceae were studied. Seeds were collected during their peak dispersal period. Seed moisture content (SMC) was determined using the oven dry method. Seed germination and effect of 500 ppm GA treatment and dry storage on germination were studied. Seedlings were transferred to three potting media, viz, sand: coir dust: compost, sand: compost, sand: coir dust and sand: garden soil (in equal ratio) and raised until 45 days in a greenhouse. Number of leaves and height of plants were measured in 7-day intervals. Fresh weight, root, shoot and leaf dry weights were measured after 45 days. SMC of all the studied species was < 15%, revealing that they are orthodox. Thus, no special conditions are needed to store them. Rhinacanthus polonnaruwensis seeds had a T50 < 30 days, indicating that they have no dormancy. Barleria prionitis and Andrographis paniculata seeds were dormant as the T50 was > 30days. Germination increased > 80 % after GA3 treatment and dry storage. Therefore, seeds of B. prionitis and A. paniculata have non-deep physiological dormancy. Dry storage for 1 and 3 months could be recommended for these two species, respectively. Seedlings of all three-study species showed high growth performance in the sand: garden soil potting medium which could be recommended to grow these species. These information will be useful to germinate and grow these three species for large-scale commercial pursoses.

Enrichment of monoculture plantations with broad-leaved species convert poorly managed exotic plantations into mixed species woodlands with enhanced ecosystem services. However, the effect of enrichment planting on the recruitment of plant diversity is poorly understood. This study aims to investigate the effect of enrichment planting in an eleven-year-old restored Pine (Pinus caribaea Morelet) plantation (RP) and a 25-30-year-old unrestored Pine plantation (UP) in Hantana, Sri Lanka. All naturally regenerated woody species were tagged, identified, and counted. The height and the diameter at breast height were measured. Nearly four times more woody species emerged from RP than UP. However, majority of species in both RP and UP were represented by the exotic invasive tree species Alstonia macrophylla Wall. ex G. Don. The mean density of seedlings of woody species was higher in RP than UP. The Shannon-Wiener diversity index was higher in RP than UP for all different life stages. Endemics were only recorded in RP. Since improved plantation structure and higher diversity was recorded in RP than UP, thinning followed by enrichment planting can be used to restore monoculture Pine plantation into mixed species plantations.

Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain (ETC) that has a lower affinity for oxygen than does cytochrome (cyt) oxidase. To investigate the role(s) of AOX under different oxygen conditions, wild-type (WT) Nicotiana tabacum plants were compared with AOX knockdown and overexpression plants under normoxia, hypoxia (near-anoxia), and during a reoxygenation period following hypoxia. Paradoxically, under all the conditions tested, the AOX amount across plant lines correlated positively with leaf energy status (ATP/ADP ratio). Under normoxia, AOX was important to maintain respiratory carbon flow, to prevent the mitochondrial generation of superoxide and nitric oxide (NO), to control lipid peroxidation and protein S-nitrosylation, and possibly to reduce the inhibition of cyt oxidase by NO. Under hypoxia, AOX was again important in preventing superoxide generation and lipid peroxidation, but now contributed positively to NO amount. This may indicate an ability of AOX to generate NO under hypoxia, similar to the nitrite reductase activity of cyt oxidase under hypoxia. Alternatively, it may indicate that AOX activity simply reduces the amount of superoxide scavenging of NO, by reducing the availability of superoxide. The amount of inactivation of mitochondrial aconitase during hypoxia was also dependent upon AOX amount, perhaps through its effects on NO amount, and this influenced carbon flow under hypoxia. Finally, AOX was particularly important in preventing nitro-oxidative stress during the reoxygenation period, thereby contributing positively to the recovery of energy status following hypoxia. Overall, the results suggest that AOX plays a beneficial role in low oxygen metabolism, despite its lower affinity for oxygen than cytochrome oxidase.

Monitoring growth performance of newly recruited plant species after applying several silvicultural treatments in monoculture plantations is important to evaluate the success of forest restoration. This study was conducted in 2015 to determine the growth performance of the naturally regenerated woody plant species in an unrestored (UP) and a restored (RP) Pinus caribaea Morelet plantation, in lower Hantana, Sri Lanka. In RP, partial thinning of pines followed by enrichment planting of four broad-leaved tree species in 2003 and total thinning of pines was initiated in 2009. In both sites fifteen plots (5x5m) and within each of them three subplots (1x1m) were demarcated randomly. The height of seedlings (SE, <50 cm in height) in subplots and height of saplings (SA1= 50-129 and SA2=130-300 cm in height) and trees (TR, >300 cm in height) and dbh of SA2 and TR in all the plots were recorded. Collectively, 417 individuals (RP=298, UP=119) representing 28 species (RP=24, UP=12) and 22 plant families (RP=18, UP=13) survived by the end of the six months. The mean monthly increment of height (MMIH)of survived species in RP was higher for all the life forms except for SE (SE=1.35, SA1=1.61, SA2= 1.38, TR= 4.45 cmmo-1) than in UP (SE=2.06, SA1= 0.17, SA2= 0.00, TR= 1.65 cmmo-1). The MMIH of trees was significantly higher in RP than UP. The mean monthly increment of dbh (MMID) of survived individuals in RP was higher for both SA2 (0.017 cm per mo-1) and TR (0.027 cm per mo-1) than in UP (SA2= 0.0007, TR= 0.024 cmmo-1). The MMID of SA2 was significantly higher in RP than UP Of the 24 species tested in all four life form categories in RP, 19 (SE=39%, SA1=56%, SA2=69%, TR=85% of the species)had MMIH exceeding 1 cm mo-1while eight (SA2=5%, TR=26%) had dbh increment exceeding 0.05 cm mo-1. In UP, only five species (SE=60%, SA1=100%, SA2=25%, TR=77%of the species) had MMIH exceeding 1cm while one species (Alstonia macrophylla)(SA2=25%, TR=22%) had MMID exceeding0.05 cm mo-1. As the growth performance of the naturally regenerated woody species in RP was higher than UP, we conclude that restoration of pine plantation in mountainous regions of Sri Lanka, using silvicultural techniques is successful in achieving restoration goals.Keywords: Growth performance, Natural regeneration, Pinus plantation, Restoration