Climate and species stress resistance modulate the higher survival of large seedlings in forest restorations worldwide.

Seedling planting plays a key role in active forest restoration and regeneration of managed stands. Plant attributes at outplanting can determine tree seedling survival and consequently early success of forest plantations. Although many studies show that large seedlings of the same age within a species have higher survival than small ones, others report the opposite. This may be due to differences in environmental conditions at the planting site and in the inherent functional characteristics of species. Here, we conducted a global-scale meta-analysis to evaluate the effect of seedling size on early outplanting survival. Our meta-analysis covered 86 tree species and 142 planting locations distributed worldwide. We also assessed whether planting site aridity and key plant functional traits related to abiotic and biotic stress resistance and growth capacity, namely specific leaf area and wood density, modulate this effect. Planting large seedlings within a species consistently increases survival in forest plantations worldwide. Species' functional traits modulate the magnitude of the positive seedling size-outplanting survival relationship, showing contrasting effects due to aridity and between angiosperms and gymnosperms. For angiosperms planted in arid/semiarid sites and gymnosperms in subhumid/humid sites the magnitude of the positive effect of seedling size on survival was maximized in species with low specific leaf area and high wood density, characteristics linked to high stress resistance and slow growth. By contrast, high specific leaf area and low wood density maximized the positive effect of seedling size on survival for angiosperms planted in subhumid/humid sites. Results have key implications for implementing forest plantations globally, especially for adjusting nursery cultivation to species' functional characteristics and planting site aridity. Nursery cultivation should promote large seedlings, especially for stress sensitive angiosperms planted in humid sites and for stress-resistant species planted in dry sites.

Evaluation of phytotoxic effects of cationic polyacrylamide polymers: implication for the use of sludges as organic soil amendments in assisted phytostabilization.

Sludges, as biosolids, are organic soil amendments commonly used in assisted phytostabilitation. Extensive studies on their environmental impacts exists, particularly for improper land application and contents of trace elements, organic compounds and pathogens, but not for their content of cationic polyacrylamide polymers (C-PAMs). Direct toxicity of C-PAMs on aquatic organisms has been demonstrated but scarce information about plant toxicity is available. In this study, the effect of C-PAMs on early plant growth was evaluated by means of standard toxicity assays. Firstly, increasing doses of C-PAMs were applied as solutions to seeds of Avena sativa, Lactuca sativa and Solanum lycopersycum to evaluate germination and root elongation. Secondly, the effect of increasing doses of C-PAMs spiked in pig manure and mixed with sand (75 t ha-1 dry base) was evaluated on the emergence, radicle elongation and biomass of A. sativa. Results showed high phytotoxicity of C-PAMs in solutions above 1,000 mg L-1, but no effect was detected when spiked into experimental substrate; a significant effect was only observed above 5,000 mg L-1 for radicle elongation, aerial biomass, and radicle biomass. Results demonstrate direct phytotoxic effects of C-PAMs, which can be mitigated when spiked into an organic (pig manure) and mineral (sand) matrix.

Integrated Management of Pig Residues and Copper Mine Tailings for Aided Phytostabilization.

There is high demand for identifying socio-environmentally sound ways to dispose of large quantities of offensive odor-generating organic residues produced by intensive livestock farming. The use of these residues as amendments at large-scale mine tailings storage facilities for in situ plant-based reclamation may be a useful alternative. We performed a greenhouse assay to evaluate effectiveness of pig slurries and the solid organic fraction of aerobic-aerated pig slurries, both treated and not treated for odor emission, as amendments for copper tailings. Different doses of slurries or the solid organic fraction of the slurries, untreated and treated with either ozone or a commercial product used to manage strong odors (Just a Drop), were incorporated into tailings and stabilized (15 d) under greenhouse conditions. L. (ryegrass) was used as bioindicator for Cu and Zn toxicity. Plant performance (shoot and root dry biomass, Cu and Zn content in leaves) and general physicochemical characteristics of substrates were evaluated. Our results showed that odor management of pig residues was possible with commercial products, and their incorporation into tailings rapidly and effectively reduced odor emission. The solid organic fraction of the slurries neutralized acidic tailings, and both pig residues increased organic matter and nutrient content in tailings while reducing extractable Cu. As a result, ryegrass productivity was significantly improved by incorporation of either slurries or their solid organic fraction into tailings in a dose-dependent form. Foliar Cu content in ryegrass was not affected but foliar Zn content increased; however, Zn remained within acceptable ranges. Both the pig slurries and their soil organic fractions proved to be valuable residues for tailings reclamation.