ALBERT

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Ruyi LUO, Jiafa LUO, Jianling FAN, Deyan LIU, Jin-Sheng HE, Nazia PERVEEN, Weixin DING〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Alpine grasslands with a high soil organic carbon (SOC) storage on the Tibetan Plateau are experiencing rapid climate warming and anthropogenic nitrogen (N) deposition; this is expected to substantially increase the soil N availability, which may impact carbon (C) cycling. However, little is known regarding how N enrichment influences soil microbial communities and functions relative to C cycling in this region. We conducted a 4-year field experiment on an alpine grassland to evaluate the effects of four different rates of N addition (0, 25, 50, and 100 kg N ha〈sup〉−1〈/sup〉 year〈sup〉−1〈/sup〉) on the abundance and community structure (phospholipid fatty acids, PLFAs) of microbes, enzyme activities, and community level physiological profiles (CLPP) in soil. We found that N addition increased the microbial biomass C (MBC) and N (MBN), along with an increased abundance of bacterial PLFAs, especially Gram-negative bacterial PLFAs, with a decreasing ratio of Gram-positive to Gram-negative bacteria. The N addition also stimulated the growth of fungi, especially arbuscular mycorrhizal fungi, reducing the ratio of fungi to bacteria. Microbial functional diversity and activity of enzymes involved in C cycling (β-1,4-glucosidase and phenol oxidase) and N cycling (β-1,4-〈em〉N〈/em〉-acetyl-glucosaminidase and leucine aminopeptidase) increased after N addition, resulting in a loss of SOC. A meta-analysis showed that the soil C/N ratio was a key factor in the response of oxidase activity to N amendment, suggesting that the responses of soil microbial functions, which are linked to C turnover relative to N input, primarily depended upon the soil C/N ratio. Overall, our findings highlight that N addition has a positive influence on microbial communities and their associated functions, which may reduce soil C storage in alpine grasslands under global change scenarios.〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Jéssica Aparecida Silva MORETTO, João Pedro Rueda FURLAN, Vânia Santos BRAZ, Tamires Aparecida BITENCOURT, Eliana Guedes STEHLING〈/p〉

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Guo CHEN, Shibin LIU, Yangzhou XIANG, Xiaolu TANG, Haitao LIU, Bin YAO, Xuqiang LUO〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The use of living mulch in orchards is a widely accepted management strategy for improving soil quality and enhancing tree productivity. Although the effects of living mulch on soil organic carbon (C) and nutrients have been previously investigated, changes in the stoichiometric ratios of C, soil total nitrogen (N), and soil total phosphorous (P) under different climatic, edaphic, and biotic conditions are currently unknown. These factors are important indicators of elemental balance associated with ecological interactions. In order to examine the effects of living mulch in orchards on soil C:N:P stoichiometry under different conditions, a meta-analysis was undertaken. The results showed that in general, living mulch significantly (〈em〉P 〈〈/em〉 0.05) increased C:P and N:P ratio, while the impact on C:N ratio was not significant, a result that was related to the coupled increase of C and N. Phosphorous limitation occurred shortly after the addition of living mulch; after four years this effect receded. In contrast, an increase in C occurred simultaneously with N increase at all stages. Specifically, the treatment effect was context-dependent. The living mulch did not change soil stoichiometry in orchards with old trees (〉 10 years), an occurrence which may be related to changes in the amount of fungi. Grass life history also had a significant influence on the treatment effect on soil stoichiometry, while N-fixing characteristics did not. The treatment effect was significant in areas with moderate mean annual temperature and mean annual precipitation, which might be related to the litter ratio of grass and trees. Effects on stoichiometric ratios were significant in the top soil layer (0–20 cm), in contrast to the deep soil layers. Therefore, grass species and management practices, such as fertilization, should be selected according to the specific soil and climatic conditions of the management area.〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Shiyu QIN, Hongen LIU, Zhaojun NIE, Zed RENGEL, Wei GAO, Chang LI, Peng ZHAO〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Cadmium (Cd) is a toxic heavy metal occurring in the environment naturally and is also generated through various anthropogenic sources and acts as a pollutant. Human health is affected by Cd pollution in farmland soils because food is the main source of Cd intake in the non-smoking population. For crops, Cd toxicity may result from a disturbance in uptake and translocation of mineral nutrients and disturbance in plant metabolism, inhibiting plant growth and development. However, plants have Cd tolerance mechanisms, including restricted Cd uptake, decreased Cd root-to-shoot translocation, enhanced antioxidant enzyme activities, and increased production of phytochelatins. Furthermore, optimal supply of mineral nutrients is one of the strategies to alleviate the damaging effects of Cd on plants and to avoid its entry into the food chain. The emerging molecular knowledge contributes to understanding Cd uptake, translocation, and remobilization in plants. In this review, Cd toxicity and tolerance mechanisms, agricultural practices to minimize Cd accumulation, Cd competition with essential elements (calcium, copper, iron, zinc, and manganese), and genes associated with Cd uptake are discussed in detail, especially regarding how these mineral nutrients and genes play a role in decreasing Cd uptake and accumulation in crop plants.〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Stella GYPSER, Dirk FREESE〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Based on recent mining rates and the exhaustion of global phosphorus (P) reserves, there is a need to mobilize P already stored in soils, and its recovery from secondary resources such as Ca- and Fe-phosphates is important. The Ca-phosphate hydroxyapatite forms a good fertilizer source, while vivianite is formed in waterlogged soils and sediments. During sludge treatment, the formation of vivianite has been identified, being mainly Fe-phosphate. Long-term P release from both hydroxyapatite and vivianite was studied using different inorganic (CaCl〈sub〉2〈/sub〉 and CaSO〈sub〉4〈/sub〉) and organic (citric and humic acid) reagents during batch experiments. Reagents CaCl〈sub〉2〈/sub〉 and CaSO〈sub〉4〈/sub〉 represent the soil solution, while citric and humic acids as organic constituents affect P availability in the rhizosphere and during the process of humification. Additionally, the flow-through reactor (FTR) technique with an infinite sink was used to study the long-term P release kinetics. The cumulative P release was higher by organic acids than by inorganic compounds. The cumulative P release rates were higher in the FTR with CaCl〈sub〉2〈/sub〉 as compared to the batch technique. The infinite sink application caused a continuously high concentration gradient between the solid and liquid phases, leading to higher desorption rates as compared to the batch technique. The predominant amount of the total P released over time was available for a short term. While inorganic anion exchange occurred at easily available binding sites, organic acids affected the more heavily available binding sites, which could be embedded within the mineral structure. The results showed that organic compounds, especially citric acid, play a superior role as compared to the inorganic constituents of the soil solution during the recovery of already stored P from the tertiary phosphates vivianite and hydroxyapatite.〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: April 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Pedosphere, Volume 30, Issue 2〈/p〉 〈p〉Author(s): Sen DOU, Jun SHAN, Xiangyun SONG, Rui CAO, Meng WU, Chenglin LI, Song GUAN〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Humic substances (HS), which are defined as a series of highly acidic, relatively high-molecular-weight, and yellow to black colored substances formed during the decay and transformation of plant and microbial remains, ubiquitously occur in nature. Humic substances represent the largest stable organic carbon pool in terrestrial environments and are the central characteristic of the soil. However, the validity of the HS concept and the justification of their extraction procedure have been recently debated. Here, we argue that the traditional humic paradigm is still relevant. Humic substances are distinctive and complex because the extracted HS formed during the humification are chemically distinct from their precursors and are heterogeneous among soils. By reviewing the concept, formation pathways, and stabilization of HS, we propose that the key question facing soil scientists is whether HS are soil microbial residues or unique synthesized compounds. Without revealing the distinctiveness of HS, it is impossible to address this question, as the structure, composition, and reactivity of HS are still poorly known owing to the heterogeneity and geographical variability of HS and the limits of the currently available analytical techniques. In our view, the distinctiveness of HS is fundamental to the soil, and thus further studies should be focused on revealing the distinctiveness of HS and explaining why HS hold this distinctiveness.〈/p〉〈/div〉