Effect of prescribed fire on soil properties and N transformation in two vegetation types in South China

Faster recovery of soil biodiversity in native species mixture than in Eucalyptus monoculture after 60 years afforestation in tropical degraded coastal terraces

Afforestation is an effective method to restore degraded land. Afforestation methods vary in their effects on ecosystem multifunctionality, but their effects on soil biodiversity have been largely overlooked. Here, we mapped the biodiversity and functioning of multiple soil organism groups resulting from diverse afforestation methods in tropical coastal terraces. Sixty years after afforestation from bare land (BL), plant species richness and the abundance of plant litter (398 ± 85 g m^-2 ) and plant biomass (179 ± 3.7 t ha^-1 ) in native tree species mixtures (MF) were restored to the level of native forests (NF; 287 ± 21 g m^-2 and 243.0 ± 33 t ha^-1 , respectively), while Eucalyptus monoculture (EP) only successfully restored the litter mass (388 ± 43 g m^-2 ) to the level of NF. Soil fertility in EP and MF was increased but remained lower than in NF. For example, soil nitrogen and phosphorus concentrations in MF (1.2 ± 0.2 g kg^-1 and 408 ± 49 mg kg^-1 , respectively; p < 0.05) were lower than in NF (1.8 ± 0.2 g kg^-1 and 523 ± 24 mg kg^-1 , respectively; p < 0.05). Soil biodiversity, abundance (except for nematodes), and community composition in MF were similar or greater than those in NF. In contrast, restoration with EP only enhanced the diversity of microbes and mites to the level of NF, but not for other soil biota. Together, afforestation with native species mixtures can end up restoring vegetation and most aspects of the taxonomic and functional biodiversity in soil whereas monoculture using fast-growing non-native species cannot. Native species mixtures show a greater potential to reach completely similar levels of soil biodiversity in local natural forests if they are received some more decades of afforestation. Multifunctionality of soil biotic community should be considered to accelerate such processes in future restoration practices.

Effects of prescribed burning for pasture reclamation on soil chemical properties in subalpine shrublands of the Central Pyrenees (NE-Spain)

The abandonment of the traditional pastoral activities in the subalpine grasslands of the Central Pyrenees (NE-Spain) has resulted in shrub encroachment processes that are dominated by species such as the Echinospartum horridum. Therefore, prescribed burning has been recently readopted in this region as a management tool to stop the spread of shrubs and recover grasslands. We aimed to assess the effect that this practice may have on soil chemical properties such as SOC, N, pH, EC, water-extractable and exchangeable cations (Ca²⁺, Mg²⁺ and K⁺), cation exchange capacity, inorganic N forms (N-NH₄⁺ and N-NO₃^-) and available P. We studied two prescribed burnings conducted at the subalpine level of the Central Pyrenees in the municipalities of Tella-Sin (April 2015) and Buisán (November 2015). At each site, the topsoil was sampled in triplicate at soil depths of 0-1, 1-2 and 2-3 cm immediately before (U), immediately after (B0) and one year after (B12) burning, and litter and/or ashes were removed prior to sampling. The results indicate that in the B0 samples, burning significantly reduced the SOC and N contents as well as the exchangeable Ca²⁺ and Mg²⁺ at 0-1 cm, whereas the rest of the studied properties remained virtually unchanged. However, in the B12 samples we detected a decrease of nutrient content that was probably related to leaching and/or erosion processes.

The impact of agricultural soil usage on activity and abundance of ammonifying bacteria in selected soils from Poland

The aim of the study was to demonstrate the impact of soil agricultural usage on the abundance of ammonifying bacteria (AB) and their activity, expressed as arginine ammonification (AA). Five agriculturally exploited types of soils (FAO): Haplic Luvisol, Brunic Arenosol, Mollic Gleysol, Eutric Fluvisol, and Rendzina Leptosol were studied. The controls were non-agricultural soils of the same type located in close proximity to agricultural sites. The tested soils varied in terms of pH (4.18–7.08), total carbon (8.39–34.90 g kg⁻¹), easily degradable carbon content (0.46–1.11 g kg⁻¹), moisture (5.20–13.50 %), and nitrogen forms (mg kg⁻¹): 1.68–27.17, 0.036–0.862, 0.012–3.389 for nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen, respectively. The AB abundance in agricultural soils ranged from 1.1 to 6.4 × 10⁴ cfu g⁻¹, while in the controls it was significantly higher—from 2.0 to 110 × 10⁴ cfu g⁻¹ of soil. Also, AA in the controls was three-times higher than in the agricultural soils. Strong associations between AA and the abundance of AB in the control (r = 0.954***) and agricultural soils (r = 0.833***) were proved. In the agricultural soils, the AB abundance and AA were influenced by pH (r = 0.746*** and r = 0.520***) and carbon content (r = 0.488*** and r = 0.391***). The AB abundance was also affected by easily degradable carbon (r = 0.517**) and nitrite nitrogen (r = 0.376*), whilst ammonium nitrogen influenced AA (r = 0.451*). Our results indicate that the abundance of AB and AA may be good indicators of soil biological conditions.

Should Exotic Eucalyptus be Planted in Subtropical China: Insights from Understory Plant Diversity in Two Contrasting Eucalyptus Chronosequences

Although Eucalyptus is widely planted in South China, whose effects on native biodiversity are unclear. The objective of this study was to quantify the richness and composition of understory plants in two contrasting Eucalyptus chronosequences in South China. One was in Zhangzhou City with plantation age of 2, 4, and 6 years after clear-cutting Chinese fir forests, while the other was in Heshan City with plantation age of 2, 3, and 24 years that reforested on barren lands. Results showed that the richness of understory plants and functional groups was not significantly altered in the Zhangzhou chronosequence, while increased in the 24-year-old plantations, with a significantly larger proportion of woody plants than the younger plantations for the Heshan chronosequence. Moreover, a higher richness of woody plants accompanied by a lower richness of herbaceous species was detected in the Zhangzhou chronosequence compared with the Heshan one. To balance the need for pulp production and plant diversity conservation, we suggest that intercropping approaches between exotic Eucalyptus plantations and native forests should be considered in the fast rotation Eucalyptus plantations. However, Eucalyptus plantations may be used as pioneer species to sustain ecosystem functioning for the degraded lands.