Soil Effects on Stem Growth and Wood Anatomy of Tamboril Are Mediated by Tree Age

Soil influences the growth of trees and the characteristics of the wood; but could this influence change during the ontogeny of trees? To answer this question, we analyzed the wood anatomy of 9-year-old trees and 2-year-old saplings of Enterolobium contortisiliquum, known as “tamboril”, growing in eutrophic and oligotrophic soil in the Brazilian Cerrado, and assessed the effect of age on plant–soil relationship. Sapwood samples were collected from the main stem, anatomical sections were prepared in the lab, and 12 anatomical wood traits were measured. Individuals in eutrophic soil had greater stem diameter and height than those in oligotrophic soil. Trees in eutrophic soil had vessel-associated parenchyma cells with abundant storage compounds. Fibers walls were 47% thicker and intervessel pits diameter were 14% larger in trees of eutrophic soil. A greater proportion of solitary vessels (74%) was observed in trees rather than in saplings (50%). The secondary xylem of trees was mainly formed by fibers (63%) whereas in saplings it was mainly formed by storage tissue (64%). Our study provides evidence that the influence of soil conditions on tree growth reflects variations in wood anatomical features. No significant response to soil type was observed in saplings, thus demonstrating that the relationship between soil type and wood growth is mediated by tree age. These findings help to develop reliable reforestation strategies in tropical ecosystems characterized by different levels of soil fertility.

Short-Term Canopy and Long-Term Effects Soil of a Native Shrub Under Arid Bioclimate: A Case Study From Tunisia

Interactions between plants (competition and facilitation) in terrestrial ecosystems include: (1) short-term effects primarily quantified with experimental removals; and (2) long-term effects primarily quantified with observational methods. This study, conducted in the National Park of Bou Hedma, examined (1) the relative contributions of short-term canopy and long-term soil effects of a shrub species in explaining differences in biomass, species diversity (richness) and species density of understory plants (i) between shrubs and open areas, (ii) between shrubs and removed shrubs; and (2) the role of grazing in driving changes in direction of short-term and long-term effects in shrub/understory species interactions.Differences in species richness, density and biomass of understorey communities between shrub removed and open areas were mostly due to long-term soil effects, whereas differences beneath shrubs and shrub removed were due to short-term canopy effects, in particular on soil water content.Our study provides the positive effect of savannas shrubs on the understorey vegetation biomass, species density and diversity in arid ecosystems. Additionally, grazing by large herbivores negatively influenced the dynamics of vegetation under an arid bioclimate.

Application of Dairy Manure Amended with Mineral Fertilizer on Stubble-Covered Soil: Effects on Ammonia Emissions

The reduction in the manure application rates through enrichment with mineral fertilizer has the potential to reduce costs, decrease environmental pollution, and extend the manure benefits to greater acreage. A pot experiment was carried out to assess ammonia emissions from dairy manure amended with mineral fertilizers applied on wheat stubble. The treatments were: control (no fertilization), urea (U), calcium ammonium nitrate (AN), dairy manure (MAN), urea + dairy manure (UMAN), and calcium ammonium nitrate + dairy manure (ANMAN). A dynamic chamber system was used to measure NH3 emissions during seven days after soil application. UMAN and ANMAN treatments led to higher NH3 emissions than each isolated component. This might be motivated by the manure pH. Thus, the enrichment of dairy manure with U or AN for application on stubble-covered soil should not be recommended. Nevertheless, some manure pre-treatments, such as acidification, or the use of other mineral fertilizers might improve such solution.