Mixed afforestation of young subtropical trees promotes nitrogen acquisition and retention

Abstract

Summary1. Afforestation is globally increasing to produce timber and pulp wood, but also to enhance ecosystem services such as carbon sequestration, nutrient retention or groundwater recharge. In China, large areas have been and will be afforested in order to compensate for the negative impacts of former clear-cuttings and to make use of the ecosystem services associated with afforestation. In order to further optimize these services with regard to balanced nutrient (particularly nitrogen) cycles, it is important to know whether the use of mixtures of native tree species in afforestation projects promotes the acquisition and retention of nitrogen compared with the currently established large-scale monocultures. 2. To test the effect of species richness on system N retention and tree sapling N uptake, we conducted a 15 N tracer experiment in a young tree plantation. To this end, saplings of four abundant early successional tree species were planted in monocultures, in two-and four-species mixtures and as single trees.3. Nitrogen retention increased with higher species richness due to enhanced N pools in sapling biomass. These species richness effects strengthened over time. 4. Species-specific differences in 15 N recoveries over time revealed below-ground niche differentiation with regard to N uptake, which is likely to result in complementary resource use among coexisting species. 5. Synthesis and applications. This study provides evidence that mixed afforestation promotes N retention from the sapling stage. To further improve ecosystem services associated with afforestation, we strongly suggest the use of mixtures of native tree species instead of monocultures. Mixtures of four species may reduce system N losses and thus may lessen groundwater contamination due to N leaching. We encourage further investigations to find optimal species combinations that promote a wide range of ecosystem services related to more closed nutrient cycles and minimized soil erosion. In our study, the plantations' capability to retain N could be optimized by means of both increasing tree species richness and by choosing the optimal species combinations.

Positive Effects of Plant Genotypic and Species Diversity on Anti-Herbivore Defenses in a Tropical Tree Species

“…Alternatively, as suggested by other studies, it is possible that plant species diversity improves nutrient acquisition (e.g. nitrogen) and use by plants which in turn increased nutrient concentrations in tissues [28], [55], [58] as well as the concentration of nitrogen-based defenses [28]. Finally, there is evidence that plants are able to recognize conspecific vs. hetero-specific individuals, as well as more closely vs. more distantly related individuals of their species and modulate the release of volatiles associated with defense [59].…”

A Review of Processes Behind Diversity—Productivity Relationships in Forests

“…[ 16,[80][81][82][83][84][85] Nutrient mineralization P F Changes in nitrogen mineralization and nitrification rates can influence nitrogen availability. Lack of mycorrhizal colonization of tree roots in non-native species may be overcome through admixture of native species and increase uptake.…”

Influence of Forest Harvest on Nitrate Concentration in Temperate Streams—A Meta-Analysis

“…Mixed forests do not show an increase in stream nitrate concentration after clearcut and patchcut harvest. Higher species diversity-favoured by microhabitat diversity-may buffer effects of nitrate leaching and lead to a more stable ecosystem [62][63][64]. Nitrate levels in mixed forests dropped even below the pre-harvest level in patchcut and high-intensity selective-harvest forests.…”