Root Biomass Distribution and Soil Physical Properties of Short-Rotation Coppice American Sycamore (Platanus occidentalis L.) Grown at Different Planting Densities

How does forest fine root litter affect the agricultural soil NH3 and N2O losses?

In farmland shelterbelt systems, the decomposition and/or apoptosis of forest fine root litter could affect farmland soil properties at the tree-crop interface, particularly the soil nitrogen (N) cycling. However, how fine root litter affect the ammonia (NH3) and nitrous oxide (N2O) losses from farmland soil and the crop production is little known. A soil column experiment covering a whole rice season was conducted to evaluate the dynamics aforesaid in response to fine root litter of Populus (RP) and Metasequoia glyptostroboides (RM) with 0 and 240 kg ha-1 N fertilizer input. Both RP and RM had minimal impact on NH3 and N2O emissions from soils without N input. At 240 kg N ha-1 input, RP significantly (p < 0.05) increased total NH3 volatilization (including yield-scaled NH3 volatilization and emission factor) by 37.1%, while RM significantly (p < 0.05) decreased it by 18.1%. Both fine root litter significantly (p < 0.05) reduced the N2O emissions from paddy soil receiving 240 kg N ha-1 by 22.7-27.1%. The reduction of N2O emission in N240 + RM was primarily attributed to higher topsoil ammonium-N but lower nitrate-N contents that indicating a reduced nitrification rate during the mid-season drainage stage. In addition, the decreases in soil AOA amoA (-39.4%) and nirS (-23.7%) gene copies explained the mitigating effect of RP on N2O emission. Regardless of N fertilizer application or not, there was no statistically significant difference in rice grain yield between treatments with and without fine root litter, although RM reduced grain yield by 11.2-14.9% compared to treatments without fine root litter. In conclusion, the impact of fine root litter on N emissions via NH3 and N2O depends on both N input rates and fine root types. RM simultaneously reduce reactive farmland soil N losses via NH3 and N2O in the tree-crop interface soils with N input.

Abandoned Fishpond Reversal to Mangrove Forest: Will the Carbon Storage Potential Match the Natural Stand 30 Years after Reforestation?

Mangroves are essential carbon reserves, and their role in carbon sequestration is remarkable. However, anthropogenic pressures such as aquaculture development threatened this highly susceptible ecosystem. Thus, the need to rehabilitate abandoned aquaculture ponds is a must to offset the ecological losses over the economic gains derived from these mangrove land-use changes. Thus, we chose a reforestation site of a once heavily utilized fishpond devastated by a tsunami in the late 1970s in Zamboanga del Sur, Philippines. We then established a similar study plot in a nearby natural mangrove forest as a point of reference. We determined the heterogeneity in vegetation and estimated the aboveground and soil carbon storage capacities. We also examined the distinct changes in species composition and zonation from the seaward towards the landward zones. About 30 years after the abandoned fishpond rehabilitation, we found the tree density of the Rhizopora mucronata Lamk. and Avicenia marina (Forsk.) Vierh-dominated reforestation site was higher (271 trees ha−1) compared to that of the Rhizophora apiculata Blume-dominated natural stand (211 trees ha−1) (p < 0.05). The total aboveground biomass at the natural mangrove forest was 202.02 Mg ha−1, which was close to that of the reforestation site (195.19 Mg ha−1) (p > 0.05). The total aboveground C in the natural mangrove forest was 90.52 Mg C ha−1, while that of the reforestation site was 87.84 Mg C ha−1 (p > 0.05). Surprisingly, the overall soil C content at the natural forest of 249.85 Mg C ha−1 was not significantly different from that of the reforestation site with 299.75 Mg C ha−1 (p > 0.05). There was an increasing soil C content trend as the soil got deeper from 0–100 cm (p < 0.05). The zonation patterns established across the landward to seaward zones did not affect the aboveground and soil carbon estimates (p > 0.05). Our study highlights the effectiveness of abandoned fishpond rehabilitation and calls for continuous restoration of the remaining abandoned aquaculture ponds in the country because of their ability to sequester and store carbon. Lastly, their potential to store huge amounts of carbon that will counterbalance anthropogenic CO2 emissions is likewise highlighted.