Most root-derived carbon inputs do not contribute to long-term global soil carbon storage

Plant root-derived carbon(C)inputs(I_(root))are the primary source of C in mineral bulk soil.However,a fraction of I_(root)may lose quickly(I_(loss),e.g.,via rhizosphere microbial respiration,leaching and fauna feeding)without contributing to long-term bulk soil C storage,yet this loss has never been quantified,particularly on a global scale.In this study we integrated three observational global data sets including soil radiocarbon content,allocation of photo synthetically assimilated C,and root biomass distribution in 2,034 soil profiles to quantify I_(root)and its contribution to the bulk soil C pool.We show that global average I_(root)in the 0-200 cm soil profile is 3.5 Mg ha^(-1)yr^(-1),~80%of which(i.e.,I_(loss))is lost rather than co ntributing to long-term bulk soil C storage.I_(root)decreases exponentially with soil depth,and the top 20 cm soil contains>60%of total I_(root).Actual C input contributing to long-term bulk soil storage(i.e.,I_(root)-I_(loss))shows a similar depth distribution to I_(root).We also map I_(loss)and its depth distribution across the globe.Our results demonstrate the global significance of direct C losses which limit the contribution of I_(root)to bulk soil C storage;and provide spatially explicit data to facilitate reliable soil C predictions via separating direct C losses from total root-derived C inputs.

A comparison of species composition and stand structure between planted and natural mangrove forests in Shenzhen Bay,South China

Aims For assisting faster restoration of damaged or severely disturbed coastal ecosystems,selected mangrove species have been planted on previously mangrove-inhabited sites of the tropical and subtropical coasts of southern China.The objective of this study was to understand the stand dynamics of the planted mangroves and their functional traits in comparison with natural mangrove forests under similar site conditions.Methods Species composition,stand density,tree size distribution,and aboveground production were investigated along three transects in a 50-year-old planted mangrove stand and three transects in an adjacent natural mangrove stand in Shenzhen Bay,South China.Measurements were made on tree distribution by species,stand structure,and aboveground biomass(AGB)distribution.Analyses were performed on the spatial patterns of tree size distribution and species association.Important Findings We found that the planted and natural mangrove stands did not differ in stand density,average diameter at breast height(DBH),species composition,and AGB.Spatial distribution of AGB and frequency at species level were also similar between the planted and natural stands.However,the traits in stand structure were more variable in the planted stand than in the natural stand,indicating higher spatiotemporal heterogeneity in the development and succession of planted mangroves.Geostatistical analyses show that both DBH and AGB were spatially auto-correlated within a specific range in the direction perpendicular to coastline.More than 60%of the variance in these attributes was due to spatial autocorrelation.The Ripley’s K-function analysis shows that the two dominant species,Kandelia obovata and Avicennia marina,clumped in broader scales in the natural stand than in the planted stand and displayed significant interspecific competition across the whole transect.It is suggested that interspecific competition interacts with spatial autocorrelation as the underlying mechanism shaping the mangrove structure.This study demonstrates that at age 50,mangrove plantations can perform similarly in stand structure,spatial arrangement of selected stand characteristics and species associations to the natural mangrove forests.

Environmental deterioration of farmlands caused by the irrational use of agricultural technologies

Without considering the ecosystem-depen- dence of agricultural production, irrational use of agricultural technologies could bring only short-term economic benefits but leave long-term environmental deterioration. If some agricultural lands have to be abandoned because of these technologies such as chemical films or groundwater depletion, it will aggravate the burden of remaining lands for maintaining or enhancing production. Thus, agricultural production should be a part of public services, requiring the consideration of interests of different stakeholders and sustainability.