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Halophytes play a crucial role in the ecological restoration of saline and alkaline land and hold promising benefits to food security in China. Although a variety of aspects of halophytes have been extensively addressed, there is still a lack of overall understanding of the leaf nitrogen (N) and phosphorus (P) stoichiometric characteristics, especially at a national scale. We compiled a national dataset of 311 observations from 113 sampling sites across China to explore the changing trends and influencing factors on leaf N and P concentrations, and N:P ratio of halophytes. The results showed that leaf N concentration decreased significantly with increasing latitude (LAT), which was mainly driven by the mean annual temperature (MAT) and mean annual precipitation (MAP). The leaf P concentration increased remarkably with increasing longitude (LON), which was induced by the variation in soil total P (TP) content. The leaf N:P ratio increased as LAT increased and LON decreased, which was potentially regulated by the MAT, MAP, and soil TP content. The scaling exponents of the N-P relationship differed significantly among halophyte types and were 0.40, 0.87, and 1.39 for euhalophyte, pseudohalophyte, and recretohalophyte, respectively. The leaf N concentration exhibited significant differences among ecosystem types and halophyte types, whereas the leaf P concentration and N:P ratio remained relatively stable. In summary, the leaf N concentration and N-P scaling exponent might be the classification criteria for halophyte types from the perspective of plant nutrient resource allocation. Moreover, this study characterized the spatial distribution and allocation strategy of leaf N and P stoichiometry in halophytes by data integration analysis, providing the basic information for nutrient management in the processes of the future domestication and introduction of halophytes. [ABSTRACT FROM AUTHOR]

Forest gaps play an important role in species regeneration and forest succession. Gap size has a primary influence on tree species coexistence and community assembly along an elevation gradient. In this study, we evaluated the regeneration and coexistence of Abies faxoniana, Betula utilis, and Acer maximowiczii at different life history stages in varied gap sizes along an elevation gradient (between 3000 and 3500 m a.s.l). We found that gap size can positively enlarge the effects of elevation on the regeneration density of the three species. In the process of regeneration from seedling to sapling, Abies had stronger regeneration capability, with regeneration niche breadths of more than 0.6 in different gap sizes. A factor analysis of mixed data indicated that regeneration density, soil nutrient contents, and air humidity were mainly related to gap size, but habitat temperature was largely determined by elevation. The connection between the species regeneration density and habitat conditions was due to differences in their regeneration niches, reflecting the selective preemption of environmental resources of different species in different life stages. Microhabitat heterogeneity, controlled by the characteristics of forest gaps along an elevation, affected the regeneration niche differences of the tree species, which contributed to the species coexistence and community assembly processes. [ABSTRACT FROM AUTHOR]

In the southeastern United States, many forest managers are interested in restoring longleaf pine (Pinus palustris Mill.) to upland sites that currently support loblolly pine (Pinus taeda L.). We quantified the effects of four canopy treatments (uncut Control; MedBA, harvest to 9 [m.sup.2] x [ha.sup.-1]; LowBA, harvest to 5 [m.sup.2] x [ha.sup.-1]; and Clearcut) and three cultural treatments (NT, no treatment; H, herbicide release of longleaf pine seedlings; and H+F, herbicide release plus fertilization) on resource availability and growing conditions in relation to longleaf pine seedling response for 3 years. Harvesting treatments reduced competition from canopy trees but resulted in greater abundance of understory vegetation. Harvesting shifted the interception of light from the canopy to the subcanopy vegetation layer; however, total light availability at the forest floor increased with the intensity of canopy removal. Soil moisture was not affected by harvesting or by the cultural treatments. Foliar nutrient concentrations (N, P, and K) of longleaf pine seedlings generally increased with the intensity of the harvest treatment. Of the plant resources measured, we found that light was most strongly correlated with longleaf pine seedling growth and that incorporating the interception of light by subcanopy vegetation improved the relationship over that of canopy light transmittance alone. Key words: foliar nutrients, gap light index, longleaf pine restoration, resource availability, underplanting. Dans le sud-est des Etats-Unis, plusieurs amenagistes forestiers sont interesses a restaurer le pin des marais (Pinus palustris Mill.) sur des stations bien drainees presentement occupees par le pin a encens (Pinus taeda L.). Nous avons quantifie les effets de quatre traitements d'eclaircie du couvert dominant (temoin non traite; surface terriere residuelle de 9 [m.sup.2] x [ha.sup.- 1], MedBA; surface terriere residuelle de 5 [m.sup.2] x [ha.sup.-1], LowBA; et coupe a blanc) et de trois traitements culturaux (temoin non traite, TEM; application d'un herbicide autour des semis de pin des marais, H; et application d'un herbicide et d'une fertilisation, H+F) sur la disponibilite des ressources et sur les conditions de croissance en relation avec la reaction des semis de pin des marais pendant trois ans. Les traitements de coupe ont reduit la competition des arbres du couvert dominant, mais ont entrame une plus grande abondance de la vegetation sous couvert. La coupe a fait passer l'interception de la lumiere du couvert dominant a la strate de vegetation sous le couvert, mais la disponibilite totale de la lumiere au sol a augmente avec l'intensite de l'eclaircie du couvert dominant. L'humidite du sol n'a pas ete influencee par la coupe ou par les traitements culturaux. La concentration foliaire en nutriments (N, P et K) des semis de pin des marais a generalement augmente avec l'intensite des traitements de coupe. Parmi les ressources necessaires a la croissance des plantes que nous avons mesurees, la lumiere etait la plus etroitement correlee a la croissance des semis de pin des marais et cette relation etait amelioree en tenant compte de l'interception de la lumiere par la strate de vegetation sous le couvert dominant en plus de la transmission de la lumiere par le couvert dominant. [Traduit par la Redaction] Mots-cles: nutriments foliaires, coefficient de trouees lumineuses, restauration du pin des marais, disponibilite des ressources, plantation sous couvert., Introduction In forested ecosystems, the combination of abiotic conditions and biotic interactions at the growing site largely controls the establishment success (i.e., growth and survival rates) of individual tree seedlings [...]