Increased Seedling Survival Research Articles

Overexpression of heat shock protein gene PfHSP21.4 in Arabidopsis thaliana enhances heat tolerance

Nuclear-encoded chloroplast small heat shock proteins (Cp-sHSPs) play important roles in plant stress tolerance due to their abundance and diversity. Their functions in Primula under heat treatment are poorly characterized. Here, expression analysis showed that the Primula Cp-sHSP gene, PfHSP21.4, was highly induced by heat stress in all vegetative and generative tissues in addition to constitutive expression in certain development stages. PfHSP21.4 was introduced into Arabidopsis, and its function was analysed in transgenic plants. Under heat stress, the PfHSP21.4 transgenic plants showed increased heat tolerance as shown by preservation of hypocotyl elongation, membrane integrity, chlorophyll content and photosystem II activity (Fv/Fm), increased seedling survival and increase in proline content. Alleviation of oxidative damage was associated with increased activity of superoxide dismutase and peroxidase. In addition, the induced expression of HSP101, HSP70, ascorbate peroxidase and Δ1-pyrroline-5-carboxylate synthase under heat stress was more pronounced in transgenic plants than in wild-type plants. These results support the positive role of PfHSP21.4 in response to heat stress in plants.

Direct and indirect effects of tree canopy facilitation in the recruitment of Mediterranean oaks

Summary Tree recruitment in Mediterranean ecosystems is strongly limited at the seedling stage by drought. Increasing evidence shows the critical positive role of the canopy nurse effect on seedling survival which results from direct and indirect, positive and negative interactions between species. Most studies, however, have only focused on the effects of tree canopy on water and light, ignoring other critical factors affecting seedling regeneration, such as canopy effects on high temperatures and the competing herb biomass. Here, we evaluate how tree canopy cover and removal of herbs affect the survival and growth of seedlings of two dominant Mediterranean Quercus species during a 3‐year study. We use an integrated model that combines several data sets to quantify and predict regeneration dynamics along environmental gradients of soil moisture, temperature and light. Low soil moisture, increased soil temperature and herb biomass negatively affected seedling survival of both Quercus species. Seedling growth was positively associated with increasing soil moisture and light. Although tree canopy cover directly facilitated seedling survival in both Quercus species, it also negatively affected herb biomass and thus indirectly facilitated the survival of Quercus suber, but not of Quercus ilex seedlings at low levels of soil moisture. Overall, tree canopies increased seedling survival but not growth during the establishment phase, mainly by ameliorating the effects of low soil moisture and high temperatures. Tree canopy indirectly facilitated survival of Q. suber seedlings by negatively affecting the competing herb layer. Synthesis and applications. To improve tree recruitment and conserve Mediterranean Quercus woodlands, the removal of herbs should be integrated into management plans for dry habitats. Interactions between abiotic and biotic factors may also effect the regeneration of these tree species. In particular, a healthy tree canopy will become important for providing conditions to facilitate seedling establishment if these habitats become drier and warmer, as predicted by some climate change scenarios.

Survival, Growth and Cu Accumulation by Non-Mycorrhizal and Mycorrhizal Jatropha curcas L. Seedlings or Cuttings in a Grassland and in Mine Tailing Soils

Jatropha curcas has been identified as an alternate source for biofuel, and thus requires immediate establishment of plantations in areas not utilized for food production such as in mine tailings sites. Screenhouse experiments were conducted to determine the survival, growth and copper (Cu) accumulation of non-mycorrhizal or mycorrhizal J. curcas seedlings or cuttings grown in oven sterilized grassland soil from Caliraya, Laguna and in mine tailing soils from Paracale, Camarines Norte and Mogpog, Marinduque. Grassland soil was sterilized in an oven for three days at 100˚C prior to use. Seedlings or cuttings were either uninoculated or inoculated with Mykovam or MineVAM mycorrhizal inoculants. Results show that Paracale soil supported the highest survival and best growth of seedlings or cuttings. In Mogpog soil, all seedlings died before two months except those inoculated with Mykovam while all cuttings died on the third month. Non-mycorrhizal seedlings did not survive in Caliraya soil while mycorrhizal inoculation increased seedling survival and growth. Cuttings did not respond to inoculation, probably due to low mycorrhizal infection (≤14 %) as compared to seedlings (≤100 %). Mykovam promoted higher survival and better plant growth than MineVAM because of its higher root colonization. Cu accumulation was higher in the roots of mycorrhizal plants and the lowest was in the leaves especially in the Mykovam-inoculated plants. In conclusion, Mykovam inoculated J. curcas grew better with higher survival rate than the control thus this imply that rehabilitation of grasslands in Caliraya, Laguna and mine tailing areas in Paracale, Camarines Norte can be done for its potential for biofuel production. However, field trials should be conducted.

Seed photosynthesis enhances Posidonia oceanica seedling growth

Posidonia oceanica seeds demonstrate photosynthetic activity during germination as well as throughout seedling development, a fact which suggests that seed photosynthesis can influence seedling growth. This study examines the contribution of seed photosynthesis to changes in leaf and root biomass, the concentration of seed carbohydrate reserves (free sugars and starch) and elemental C, N and P content in seedlings exposed to different light/dark treatments. Green seeds attached to seedlings remained photosynthetically active for three months and photosynthetic activity in the seeds enhanced seedling growth in leaves and roots. It was estimated that ca. 29.26% of leaf biomass and ca. 42.31% of root biomass production was due to seed photosynthetic activity. Photosynthesis occurred at a higher rate in seeds than in leaves during early seedling growth, and extreme light limitation reduced the mobilization of carbon reserves stored in the seeds. These adaptations control leaf self‐shading and plant competition in well‐established P. oceanica beds while also promoting increased seedling survival rates in open, uncolonised areas where clonal growth is limited.

Fire-free natural regeneration in water limited Pinus halepensis forests: a silvicultural approach

We aimed to elucidate environmental and silvicultural factors that determine the extent of fire-free natural regeneration in east Mediterranean Pinus halepensis forests. The specific aims were to study the potential and identify bottlenecks for natural regeneration and examine the effects of overstory thinning and site preparation treatments. We integrated four experiments conducted in diverse ecoregions in Israel ranging from semiarid to subhumid. Seedling emergence and survival were traced for 2–4 years in Mishmar Ha’Emek Forest (MHF) with annual rainfall of 604 mm; Shaharia Forest (SF)—435 mm; and Yatir Forest (YF)—280 mm. Effects of thinning treatments: clearcut, 100 tree, 200 tree ha−1 and control—310 tree ha−1, were examined in MHF. Effects of site preparation treatments: soil scarification and herb clipping were examined in SF. Density of emerged seedlings varied among ecoregions and was linked to average annual rainfall. Within ecoregions, emerged seedling density was higher on north-facing slopes than on south-facing slopes and was strongly related to stand characteristics (e.g., stem basal area) and seed rain. Seedling survival rate of about 20 % was recorded in MHF while no seedling survival was observed in YF and SF during the study years. Thinning treatments reduced seed rain and emerging seedling density, but increased seedling survival and growth. Recruitment 4 years after thinning was highest in the 100 tree ha−1 treatment and lowest in the control. In SF, seedling survival was limited mainly by herbaceous vegetation and was improved by soil scarification and herb clipping. Silvicultural implications are discussed.

English

Management and transmission of four seed-borne pathogenic fungi namely,Colletotrichum trifolii,  Rhizoctonia solani, Fusarium equiseti and F. incarnatum were investigated on alfalfa plants. The pathogenicity test on alfalf plant showed that R. solaniand C. trifolii caused  high percentages of rotted seeds and seedlings mortality (26.45, 26.1% and 31.6,  21.1% , respectively). However, no significant differences were observed between the treatments with F. equiseti and F. incarnatum when compared with the control treatment. Transmission of the pathogenic fungi from seed to mature plant of alfalfa was investigated in this study. Results indicate that the recovery percentages of the tested pathogens gradually decreased from root apex up to the first internodes below the shoot tip, but did not reach to the shoot apex. In order to control these fungi, different concentrations of sodium metabisulphite (SM), sodium salicylate (SS) and hydroquinone (HQ) were tested in vitro. Treatment with SM at 10 mM completely inhibited the growth of all isolated fungi. Under greenhouse conditions, soaking alfalfa seeds in a water solution of hydroquinone at 12mM showed to be the most effective treatment in reducing seed rot and seedling mortality percentages and increasing seedling survival percentages. Application of the tested treatments presented significant increases in growth parameters, photosynthetic pigments (chlorophyll a and b and carotenoids) in leaves and total phenol in alfalfa plants. This study therefore recomended the use of HQ and SM as potential and promising antifungal agents in  the protection of alfalfa plants against the tested seed-borne fungi.   Key words: Pathogenicity, Colletotrichum trifolii, Rhizoctonia solani, Fusarium equiseti, F. incarnatum, transmission, hydroquinone, sodium metabisulphite and sodium salicylate.

Effects of Media Formulation on the Growth and Morphology of Ectomycorrhizae and Their Association with Host Plant

Tricholoma matsutake and Rhizopogon roseolus form ectomycorrhizal (ECM) association with their host plant on natural habitats. The main objective of this study was to test mycelial growth, morphology, and host plant survival both in vitro and in vivo when treated with enriched media. Aseptically germinated seedlings of Pinus densiflora and P. thunbergii were inoculated with the strains of T. matsutake and R. roseolus, respectively. Under in vitro conditions mycelial growth rates performed best on pH 5 and were better on Modified-Melin-Norkrans-(MMN) based medium and Potato Dextrose Agar (PDA); addition of micronutrients and vitamins in MMN mycelial growth rates had 6–27% differences. Without ECM, plant survival rates on standard media were 30% to below 30% and by inclusion of elements they were 50% to 80%. On in vivo, soil containing different media with ECM allowed successful mycorrhizal association and increased seedling survival rates approximately 100%. Our findings confirm that MMN and PDA allowed higher mycelial growth but poor plant survival (<30%); however, enriched media supported 100% plant survival with successful ECM associations. The present method is advantageous in terms of giving objectivity for ECM by employing suitable media for strains and host plant, and making it possible for mass production of ECM-infected seedlings.

Influence of initial seed moisture and temperature conditions during germination and emergence on seedling survival and yields of soybean (Glycine max L. Merrill)

Injury to soybean seedlings caused by low temperature (5°C) at the beginning of germination was greatly reduced when instead of chilling (10°C) a higher temperature (20°C) was applied at the end of germination and during emergence. A new interpretation of the physiological mechanism involved in this reversibility of chilling injury was proposed. Hydration in water vapour of soybean seeds with initial moisture content of from 5 to 10% to a level of 30%, dry weight basis, increased seedling survival under controlled conditions of germination and emergence at respectively 5°C and l0°C as well as under natural soil conditions in field experiments both after early and late planting dates. A modified method of seed hydration in water vapour (i.e. conditioning or hardening of seeds against cold) was developed for practical application. In field experiments conditioning of seeds increased seedling survival and thus also yields per unit area of plot but had no significant effect on yield per plant. Seed conditioning may have practical significance in soybean growing and for breeding purposes when equalizing the number of plants per plot is important for comparing new varieties and breeding forms.

Effects of cultural treatments, seedling type and morphological characteristics on survival and growth of wild cherry seedlings in Turkey

Wild cherry (Prunus avium L.) is receiving increasing attention from foresters in Europe and Turkey for its fast growth, highly-valued wood and benefits for wildlife and biodiversity. Little documentation may be found concerning the selection of appropriate cultural treatments and the quality and types of seedlings used for wild cherry plantations. This study reports the effects of various combinations of intensive cultural treatments (including weed control, soil tillage, and fertilization) and seedling types on early growth, survival, and nutrition of one-year-old wild cherry seedlings out-planted on four different sites in the western Black Sea Region of Turkey. After two years, early seedling survival and growth were clearly enhanced for potted seedlings. For bare-root seedlings, initial seedling root-collar diameter and height successfully correlated with survival two years after planting. Seedlings with a root-collar diameter of 6-8 mm and height of 60-70 cm demonstrated the best survival rates in the field. The wild cherry seedlings were shown to be highly sensitive to herbaceous weed competition early in their establishment, warranting effective weed control. When used in addition to weed control, neither intensive fertilization nor soil tillage treatments significantly increased seedling survival and growth two years after planting. Therefore, intensive site preparation, as well as fertilization, are not recommended at this stage for planting sites without severe nutrient deficiencies.

Effects of cultural treatments, seedling type and morphological characteristics on survival and growth of wild cherry seedlings in Turkey

Wild cherry (Prunus avium L.) is receiving increasing attention from foresters in Europe and Turkey for its fast growth, highly-valued wood and benefits for wildlife and biodiversity. Little documentation may be found concerning the selection of appropriate cultural treatments and the quality and types of seedlings used for wild cherry plantations. This study reports the effects of various combinations of intensive cultural treatments (including weed control, soil tillage, and fertilization) and seedling types on early growth, survival, and nutrition of one-year-old wild cherry seedlings out-planted on four different sites in the western Black Sea Region of Turkey. After two years, early seedling survival and growth were clearly enhanced for potted seedlings. For bare-root seedlings, initial seedling root-collar diameter and height successfully correlated with survival two years after planting. Seedlings with a root-collar diameter of 6-8 mm and height of 60-70 cm demonstrated the best survival rates in the field. The wild cherry seedlings were shown to be highly sensitive to herbaceous weed competition early in their establishment, warranting effective weed control. When used in addition to weed control, neither intensive fertilization nor soil tillage treatments significantly increased seedling survival and growth two years after planting. Therefore, intensive site preparation, as well as fertilization, are not recommended at this stage for planting sites without severe nutrient deficiencies.

English

Phaius tankervilleae (Banks) Blume is the most attractive and most horticulturally valuable native Phaiusspecies in Taiwan. Due to overharvesting in the wild, however, the plant is on the verge of extinction. Successful cultivation of P. tankervilleae has been achieved through in vitro seeding or tissue culture propagation, but plantlet survival rates are low upon transplantation. Previous studies demonstrated that inoculation with mycorrhizal fungi markedly improved plantlet survival rates, vegetative and reproductive growth in Orchidaceae plants. Four orchid mycorrhizal fungi (OMF), R01 (Rhizoctonia solani), R02 (Rhizoctonia sp., teleomorph = Ceratobasidium sp. AG-A), R15 (Rhizoctonia sp., teleomorph = Ceratobasidium sp. AG-Fb) and R19 (Rhizoctonia sp., teleomorph = Ceratobasidium sp. AG-G) were isolated from Taiwanese native orchid roots that were cultured for more than seven years in our laboratory. These fungi all proved to be non-pathogenic and were inoculated onto the root of P. tankervilleae. Inoculation with the appropriate OMF increased seedling survival rate 27 to 31% (R02; R15), plant height 6.3 cm (R15), leaf length 3.5 cm (R15), flower stalk length 10.2 cm (R19) and number of flowers per stalk (3.5) in ex vitro-grown P. tankervilleae. Inoculation with OMF (R19) promoted reproductive growth in P. tankervilleae, while OMF (R02) inoculation significantly increased photosynthetic rate and carbohydrate content. P. tankervilleae seedlings inoculated with the R15 isolate had a higher survival rate than with other treatments. Inoculations with Rhizoctonia spp. isolates R02, R15, or R19 also promoted reproductive growth in P. tankervilleae. Key words: Pelotons, Phaius tankervilleae, reproductive growth, Rhizoctonia species, survival rate, vegetative growth.

Optimising seed broadcasting and greenstock planting for restoration in the Australian arid zone

Vegetation within some parts of Western Australia has been degraded by resource extraction, and ecological restoration is necessary to prevent erosion and reinstate plant biodiversity. Two restoration approaches, seed broadcasting and planting of seedlings, were tested with plant species (Acacia tetragonophylla F. Muell., Atriplex bunburyana F. Muell. and Solanum orbiculatum Poir.) known to have been dominant prior to mining activities in the World Heritage Area at Shark Bay. For broadcast seeding, soil raking and/or ripping increased seedling emergence, but only after sufficient rainfall. Survival of A. bunburyana seedlings (≤92%) was higher than A. tetragonophylla (≤13%) almost two years after planting and soil ripping partly alleviated soil impedance and resulted in increased seedling survival. Shoot pruning, fertiliser and moisture retaining gel had a reduced or detrimental effect on survival. Seedling survival differed between the three experimental sites, with electrical conductivity being the most noted soil difference between the sites. Restoration in the arid environs of the World Heritage Area at Shark Bay in Western Australia is challenging, but this study shows that seedling establishment is technically feasible and provides methodology useful to other arid restoration projects.

Experimental manipulation of seed shadows of an Afrotropical tree determines drivers of recruitment

The loss of animals in tropical forests may alter seed dispersal patterns and reduce seedling recruitment of tree species, but direct experimental evidence is scarce. We manipulated dispersal patterns of Manilkara mabokeensis, a monkey-dispersed tree, to assess the extent to which spatial distributions of seeds drive seedling recruitment. Based on the natural seed shadow, we created seed distributions with seeds deposited under the canopy ("no dispersal"), with declining density from the tree ("natural dispersal"), and at uniform densities ("good dispersal"). These distributions mimicked dispersal patterns that could occur with the extirpation of monkeys, low levels of hunting, and high rates of seed dispersal. We monitored seedling emergence and survival for 18 months and recorded the number of leaves and damage to leaves. "Good dispersal" increased seedling survival by 26%, and "no dispersal" decreased survival by 78%, relative to "natural dispersal." Using a mixed-effects survival model, we decoupled the distance and density components of the seed shadow: seedling survival depended on the seed density, but not on the distance from the tree. Although community seedling diversity tended to decrease with longer dispersal distances, we found no conclusive evidence that patterns of seed dispersal influence the diversity of the seedling community. Local seed dispersal does affect seedling recruitment and survival, with better dispersal resulting in higher seedling recruitment; hence the loss of dispersal services that comes with the reduction or extirpation of seed dispersers will decrease regeneration of some tree species.

Needle-clipping of longleaf pine ( Pinus palustris Mill.) can increase seedling survival while reducing transpiration and root growth potential

Clipping needles of longleaf pine (Pinus palustris Mill.) prior to transplanting has been shown to increase seedling survival but the mechanism for this effect is not well documented. A greenhouse trial was conducted to examine the effect of clipping needles on transpiration, root-growth potential (RGP) and seedling survival. Clipping longleaf pine needles to a length of 5 cm reduced transpiration and reduced RGP but it increased seedling survival by 34% points. Clipping to a length of 15 cm had an intermediate effect on these variables. The results support the common practice of clipping needles in the nursery. Key words: Nursery, container, reforestation, seedling quality.

Endophyte infection of Festuca eskia enhances seedling survival to drought and cutting at the expense of clonal expansion

Symbiotic relationships between fungal endophytes and grass species are known to increase stress resistance in the grass host; however, there is little evidence to suggest that the positive effects occur early in the grass life cycle. In this study, we explored the effects of the endophyte Epichloë festucae on the growth and survival of Festuca eskia seedlings under drought and frequent cutting stress. Festuca eskia seedlings were collected from the western part of the plant repartition area in a non-symbiotic population located in a mesic and heavily grazed site (W-NS) and from the eastern part in a symbiotic population from a xeric and lightly grazed site (E-S). The E-S population was experimentally freed from its endophyte (E-F). Two greenhouse experiments were conducted to compare growth and survival between the three seedling types under drought stress and frequent cutting. In the first experiment, 126 seedlings per seedling type (n = 378) were grown for 6 weeks under non-limiting conditions before the cessation of watering. After 3 weeks without irrigation, full irrigation was restored for 10 days to measure the survival rate. Leaf length, leaf elongation rate and survival rate were assessed per population. In the second experiment, 156 seedlings per seedling type (n = 468) were grown under non-limiting conditions. All seedlings were cut to 3 cm high, twice a week, during the first month of growth. Leaf elongation and tillering were monitored on 52 seedlings per seedling type. For each type, seedling survival rate was determined by the number of plants alive after 10 days of regrowth, without cutting. The drought experiment revealed a phenotypic differentiation to drought in 30 F. eskia populations, suggesting adaptive differentiation: the eastern seedlings showed the highest survival rate. A trade-off between growth and survival was highlighted: the highest drought survival rate was associated with the lowest leaf elongation rate under non-limiting water conditions. Endophyte presence in the eastern population increased seedling drought survival. In contrast, cutting survival rate was similar between W-NS and E-S because the presence of the endophyte increased seedling survival to frequent cutting. However, this positive effect came with a cost: the endophyte reduced seedling tillering rate.

Using hydrogel and clay to improve the water status of seedlings for dryland restoration

In dryland ecosystems, post-transplant water stress produces high seedling mortality after the first summer following outplanting. Our aim was to assess the effects of clay and hydrogel, both on the water holding capacity of the growing media and on various morphological and physiological characteristics of Quercus suber seedlings in the nursery and, subsequently, during the first 2 years in the field. Quercus suber L. seedlings were grown in four types of growing media: CS (Control growing media, standard mixture of limed peat and coconut peat, 1:1 v/v ratio), SC-10 (CS mixed with sepiolite clay at 10% v/v) and HS (CS mixed with hydrogel Stockosorb® K-400 at two doses, 0.7 and 1.5% w/w). HS-1.5 showed the best results, increasing the water holding capacity of the root plug, improving seedling water status and increasing seedling survival in the field. SC-10 showed an intermediate effect on seedling response in the field. Mixing hydrogel with a peat-based growing medium to form root plugs is a suitable technique for cultivating species to be planted in areas with a strong water deficit. This technique reduces post-transplant water stress in seedlings during their first months in the field and contributes to improve forest-restoration methods in dryland ecosystems.

Can environmental variation affect seedling survival of plants in northeastern Mexico?

The effects of global warming increase the frequency and intensity of many climate events such as rainfall. We evaluated the effects of environmental conditions on early stage seedling survival of the native thorn scrub species Caesalpinia mexicana A. Gray, Celtis pallida Torr., Cordia boissieri A. DC., and Ebenopsis ebano (Berland.) Barneby and J.W. Grimes, during the summer of 2009 and 2010. The experimental design had two factors, two levels of rainfall and three microhabitats of thorn scrub: (i) open interspace, (ii) thorn scrub edge and (iii) under the canopy of dense thorn scrub. In dense thorn scrub, seedling survival was higher for Caesalpinia mexicana and Celtis pallida, and for Cordia boissieri and Ebenopsis ebano seedling survival was higher in dense thorn scrub and thorn scrub edge. The effect of rainfall on seedling survival depended on the year. Rainfall in 2010 and dense thorn scrub increased seedling survival of native species. For survival, the limiting factors of microhabitats appear to change across the years. Besides rainfall events, biological aspects like competition and mycorrhiza effects would need to be considered in models of plant establishment.

Post-fire restoration of Mediterranean forests: Testing assembly rules mediated by facilitation

Abstract In view of the importance of facilitative interactions between plants, nurse-based planting has been proposed as a restoration technique for Mediterranean vegetation. However, facilitation efficiency is known to depend on the environmental context and the particular pair of interacting species. Understanding these context- and pair-specific dependences is fundamental to understanding Mediterranean vegetation dynamics and to improving the use of nurse-based plantation for restoration. We assessed the effectiveness of nurse-based plantation and the significance for post-fire restoration of some assembly rules mediated by facilitation. In two nearby areas of different burning ages, we compared seedling establishment of 13 tall shrubs and trees planted in open ground and under nurses. Nurses and planted seedlings were selected from different life-forms. Tests of the assembly rules were provided by the partitioning of the statistical interaction effect between nurse and planted seedling life-forms in a two-factor design. Nurse-based plantation increased seedling survival 2–9 times compared to plantation in open ground, depending on the year. The higher efficiency of nurse-based plantation was consistent for the two burned areas and occurred in many species even in years with contrasting rainfall. We detected pair-specific differences in the efficiency of facilitation. This pair-specificity was partly explained by the dependence between life-forms of nurse and guest species, suggesting the existence of assembly rules. Our results confirm that nurse-based plantation would be an appropriate post-fire restoration technique in Mediterranean mountains under dry-subhumid climate, but suggest that attention to the life-form assemblage rules is needed for an efficient implementation of such technique.

Long-term response of weed control intensity on Scots pine survival, growth and nutrition on former arable land

The effects of post-planting weed control intensity on the cover and composition of ground vegetation, and on growth, survival and foliar nutrient concentrations of 4-year old bare-rooted Scots pine (Pinus sylvestris L.) seedlings were studied over a 15-year period with experimentation on former arable land. Weed control treatments with terbuthylazine and glyphosate were carried out 1–3 times during successive years, either as overall or as spot applications. The vegetation cover and the shading effect of vegetation decreased with increasing weed control intensity. The more intensive the weed control was, the better was the afforestation result in terms of tree seedling growth and survival. Overall application repeated three times increased seedling survival by 79 percentage points, and their final height, breast height, diameter, and stand volume after 15 years were increased by 183, 19, 15, and 822%, respectively. Weed control did not affect the foliage nutrient concentrations, except for magnesium. However, increase in weed control intensity was reflected in larger needle size 5 years after planting.

The shrubRhodomyrtus tomentosaacts as a nurse plant for seedlings differing in shade tolerance in degraded land of South China

Questions: What are the nurse effects of Rhodomyrtus tomentosa in degraded land of South China? Are canopy or soil factors responsible for the main nurse effect? Do facilitative effects increase with the shade tolerance of the target species? Location: Degraded shrubland in South China. Methods: Seedlings of three native climax woody species (Schima superba, Michelia macclurei, Castanopsis fissa) that differ in shade tolerance were subjected to four treatments by transplantation: (1) under the canopy of R. tomentosa shrubs; (2) in open interspaces without vegetation cover (control); (3) under the canopy of R. tomentosa from which canopies had been removed; and (4) in open interspaces without vegetation but covered by branches and leaves of R. tomentosa. Results: At low soil nutrient levels, increased canopy shade, soil porosity and soil moisture under the canopy of R. tomentosa increased seedling survival of the climax tree species S. superba, C. fissa and M. macclurei, and shoot height of S. superba. The nurse effect (a form of facilitation) of R. tomentosa depended more on canopy shade than on soil amelioration. The magnitude of facilitation or nurse effect was positively correlated with shade tolerance of the target species. Conclusions: Use of nurse plants in restoration differs from traditional reforestation (clearing and/or burning to reduce interspecific competition between target tree species and non-target species) because it focuses on positive interactions between nurse plants and target plants that increase establishment of target species and reduce time required for restoration. Because nurse effects of R. tomentosa shrubs tended to be larger on target species with greater shade tolerance, shade-tolerant plants are suggested as target species to accelerate restoration.