【Objective】 To establish a theoretical basis to improve coastal saline soil and its carbon sink function, this study investigated the effects of organic fertilizer on the dissolved organic carbon (DOC) content and component sources in coastal saline soil, alongside the stability of the soil carbon pool. 【Method】 Two types of saline soil with differing salinities (i.e., high and low salt content) in the Jiangsu coastal area, China, were selected to explore changes in soil DOC content and its ultraviolet-visible (UV-Vis) spectrum and three-dimensional (3D) fluorescence spectrum by UV-Vis spectroscopy and 3D fluorescence spectroscopy. This was carried out alongside parallel factor analysis following the addition of organic cow manure fertilizer.【Result】 The results showed that the DOC content and degree of DOC humification for soils treated with organic cow manure fertilizer increased significantly(P<0.05), compared with the control treated with no organic cow manure fertilizer. The extent of DOC humification in the soil samples collected on days 15 and 60 following the addition of cow manure from the high-salt soil was obvious higher than its low-salt counterpart. The DOC in soil was mainly sourced from the addition of organic cow manure fertilizer; following this, the 3D fluorescence spectrum showed that the DOC fulvic acid peak was clearer. The parallel factor analysis identified four fluorescence components in the soil DOC: (1) C1 was the exogenous short-wave humic-like component (including UV region fulvic-like acid and marine fulvic-like acid); (2) C2 was the exogenous humic-like component (including UV region fulvic-like acid and visible region fulvic-like acid); (3) C3 was the endogenous protein-like component (including tryosine-like acid and tryptophan-like acid); (4) C4 was the endogenous protein-like component (only tryptophan-like acid). The proportion of each component in the soil DOC varied with time. 【Conclusion】 This study demonstrated that the addition of organic cow manure fertilizer to coastal saline soil increased the degree of DOC humification and the proportion of humic-like components in soil, while it significantly reduced the proportion of ammonia-like components (P<0.05). This indicates that the organic cow manure fertilizer is conducive to the stability of the active carbon pool in saline soil. However, as many factors affect soil DOC, the effects of organic cow manure fertilizer on soil DOC may different in other areas.
Plant root inputs are an essential source of forest soil carbon pools. Climate change may cause variations in the carbon flux below ground, affecting forest soil carbon pools and carbon cycles. In this article, we have reviewed the effects of root input on soil carbon accumulation, soil active carbon pools (including soil microbial biomass carbon and soluble organic carbon), and the stability of soil carbon pools. Furthermore, we have discussed the impacts of forest soil respiration, soil microorganisms, and soil enzyme activities on root inputs. We found that : (1) Decreased root input may reduce the priming effect of the rhizosphere and subsequently increase soil organic carbon in the short term but decrease it in the long term; (2) Root exudates may promote the initial formation of aggregates, but its effect on the stability of the metal-organic complex is unclear; (3) Decreased root input reduces soil respiration; (4) The response of the microbial community structure to root input mainly depends on the adaptation of microorganisms to substrate quality and quantity, which vary among forest ecosystems. In addition, whether enzyme synthesis is upregulated depends mainly on the cost efficiency of allocating resources for microbial growth to enzyme production. Many studies have investigated the carbon cycle of root input, especially soil respiration; however, the composition of root input is complex, and the response mechanisms of microorganisms and enzymes to different root inputs are unclear. These responses also differed among forest ecosystems. In addition, the effect of root input on the stability of the soil carbon pool is often neglected; the influence of the interaction between the root system and microorganisms on the carbon cycle and the stability of the soil carbon pool remains uncertain. We suggest strengthening the research on the links among plant roots, soil, and microorganisms, which would contribute to a deeper understanding of the carbon cycle of forest ecosystems in the context of climate change.
The importance of the decomposition of soil organic carbon (SOC) and its temperature sensitivity (Q10) in terrestrial ecosystem carbon (C) cycling have been widely recognized, especially under climate change. A small change in the Q10 of SOC decomposition may result in a large effect on the global C cycle. Therefore, the identification of critical driving factors of Q10 is needed for accurately predicting soil CO2 efflux and its feedback to climate change under a continuously warming scenario. By reviewing the published literatures, we explored how different incubation approaches, substrate quality, physicochemical protection and microbial properties affect Q10. We found that: (1) Varying temperature incubation largely overcomes the issues of substrate depletion and microbial adaption that occur using constant temperature incubation, and provides a more accurate and rapid estimation of Q10. (2) While the results of some studies have shown that the Q10 value of recalcitrant C is higher than that of labile organic C, others have also found that the Q10 of recalcitrant C is not necessarily higher than that of labile C, which is mainly due to the heterogeneity of SOC pool. (3) The protection of soil aggregates and minerals on organic matter can affect Q10 by changing the substrate availability or concentration at reaction microsites. (4) Physiological characteristics and community composition and structure of microorganisms also influence the Q10. Microbial communities and physiological characteristics in warmed soils possess a varying relative abundance of key functional genes involved in the degradation of SOC. the SOC decomposition and its Q10 are the essential aspects of the global C cycle. A better understanding of Q10 could contribute to the development of the global change models and accurate projection of future climate.
【Objective】Mycorrhizal technology may play a critical role in improving soil nutrient conditions, becoming an important biological approach to restore vegetation and soils in rocky desert areas. Readily oxidized carbon (ROC) is sensitive in its response to altered soil variables. This study aimed to reveal changes in the organic carbon pool and soil nutrient properties driven by the symbiosis between arbuscular mycorrhizal fungi (AM) and host plants in rocky desert habitats. We also attempted to elucidate the response of ROC accumulation to these changes.【Method】We inoculated Alnus nepalensis seedlings with three AM species in rocky desert soils sampled in Xundian, Yunnan Province, China. Four treatments were established to explore the association of altered ROC concentration with changes in the carbon pool, soil nutrients, and plant growth for rocky desert habitats: (1) Funneliformis mosseae (FM); (2) Claroideoglomus etunicatum (CE); (3) Rhizophagus intraradices (RI); (4) without AM and plant (CK). The ROC concentrations in the four treatments were determined by potassium permanganate oxidation.【Result】 The symbiosis and growth of host plants were significantly enhanced in the three AM species. The RI fungi had the highest infection effectiveness; the infection rate and density of RI fungi increased by 155% and 100%, respectively, compared with the control. The RI fungi also significantly enhanced the tree height (by 60%) and base diameter (by 46%) of seedlings. Three AM fungal species increased the soil ROC concentration; this increased rate was ranked in descending order as: RI (122%) > CE (78%) > FM (61%). The ROC concentration accounted for the largest proportion in the total organic carbon (TOC) pool. The greatest proportion of ROC was 52%, which was much higher than the microbial biomass carbon (3%-6%). The improvement rate of soil nutrients by the three AM fungi was ranked in descending order as: RI > CE > FM. The RI fungi strongly increased plant available nitrogen (161%), microbial biomass carbon (127%), TOC (110%), and plant available phosphorus (97%). The infection rate of AM fungi (96%), plant available nitrogen (94%), microbial biomass carbon (85%), TOC (78%), and plant available phosphorus (72%) obviously contributed to ROC changes. 【Conclusion】 The data indicate that the symbiosis of AM fungi with A. nepalensis can induce alterations in the soil carbon pool and nutrient properties alongside improving plant growth; this drives the accumulation of oxidized organic carbon in rocky desert soil. The results also help to elucidate the microbiological mechanisms regulating plant growth, soil restoration, and active organic carbon deposition in rocky desert habitats.
