Senhao Wang

The invasion of Spartina alterniflora poses a significant threat to coastal wetlands in China. The large biomass and organic substrates introduced by this species are likely to alter soil microbial communities and drive methane (CH4) and other greenhouse gas emissions; however, the underlying mechanisms remain poorly understood. To address this, we conducted a one-year in situ monitoring of CH4 emission rates, soil properties, dissolved organic matter (DOM) fractions, and CH4-cycling microbial communities in invaded wetlands and adjacent native mangroves. Our results showed that S. alterniflora invasion increased soil CH4 emissions by 8.7-fold relative to mangrove soils. Redundancy analysis and structural equation modeling revealed that this increase was closely linked to invasion-induced shifts in soil conditions, including elevated water content and pH, enrichment of labile DOM fractions (lipids and protein/aliphatic compounds), and decreases in sulfate, soil organic carbon, and total nitrogen. These changes reduced DOM molecular stability and collectively facilitated CH4 production. Moreover, quantitative PCR showed an increase in the absolute abundance of methanogens and a decrease in both the abundance and diversity of methanotrophs in invaded soils. Amplicon sequencing further indicated a higher relative abundance of Methanococcoides and a reduction in type II methanotrophs, weakening methane oxidation capacity. Overall, S. alterniflora invasion enhances wetland CH4 emissions by altering soil physicochemical properties, providing more labile substrates, and restructuring CH4-related microbial communities, thereby weakening the carbon-sink function of coastal wetlands. Integrated management approaches are needed to mitigate invasion-driven methane production while sustaining wetland ecosystem resilience.

Leguminous species have an advantage in acquiring phosphorus (P) compared with non-leguminous species. Nonetheless, it remains unclear whether this advantage would diminish under long-term nitrogen (N) deposition. In the seventh year of a simulated long-term N deposition experiment, we sampled surface soil to measure acid phosphatase activity (ACP) in stands dominated by leguminous and non-leguminous species, respectively. To assess the response of ACP to prolonged N addition, we also collected data on ACP in the second, eighth, twelfth, and thirteenth years of the experiment. We found that the difference in soil ACP between the two plantation types disappeared after long-term N input, and this process was accelerated under high N addition. This occurred due to an exacerbated P-limitation, which primarily prompts ACP production only in non-leguminous species. Additionally, there was a relatively decreased N contribution efficiency to ACP in the stand with leguminous species, indicating that soil N content no longer primarily governs ACP. This study demonstrates that prolonged high N deposition accelerates the loss of the “P-acquiring advantage” in leguminous plantations. To elucidate the differences in P usage strategies between leguminous and non-leguminous species under global change, more systematic research is warranted in the future.

Restoration plantations in subtropical regions, often established with fast-growing tree species such as Acacia auriculiformis A. Cunn. ex Benth and Eucalyptus urophylla S. T. Blake, are frequently developed on highly weathered soils characterized by phosphorus deficiency. To investigate strategies for mitigating nutrient imbalances in such ecosystems, a long-term (≥13 years) fertilization experiment was designed. The experiment involved three fertilization regimes: nitrogen fertilizer alone (N), phosphorus fertilizer alone (P), and a combination of nitrogen and phosphorus (NP) fertilizers. The objective of this study was to investigate the effects of long-term fertilization practices on soil quality in subtropical plantations using a soil quality index (SQI). Consequently, all conventional soil physical, chemical, and biological indicators associated with the SQI responses to long-term fertilization treatments were systematically evaluated, and a principal component analysis (PCA) was conducted, along with a literature review, to develop a minimum dataset (MDS) for calculating the SQI. Three physical indicators (silt, clay, and soil water content), three chemical indicators (soil organic carbon, inorganic nitrogen, and total phosphorus), and two biological indicators (microbial biomass carbon and phosphodiesterase enzyme activity) were finally chosen for the MDS from a total dataset (TDS) of eighteen soil indicators. This study shows that the MDS provided a strong representation of the TDS data (R² = 0.81), and the SQI was positively correlated with litter mass (R² = 0.37). An analysis of individual soil indicators in the MDS revealed that phosphorus addition through fertilization (P and NP treatments) significantly enhanced the soil phosphorus pool (64–101%) in the subtropical plantation ecosystem. Long-term fertilization did not significantly change the soil quality, as measured using the SQI, in either the Acacia auriculiformis (p = 0.25) or Eucalyptus urophylla (p = 0.45) plantation, and no significant differences were observed between the two plantation types. These findings suggest that the MDS can serve as a quantitative and effective tool for long-term soil quality monitoring during the process of forest sustainable management.

Restoration plantations in subtropical regions, often established with fast-growing tree species like Acacia auriculiformis and Eucalyptus urophylla, are frequently developed on highly weathered soils characterized by natural phosphorus (P) deficiencies. To investigate strategies for mitigating nutrient imbalances in such ecosystems, a long-term (≥ 13 years) fertilization experiment was designed. The experiment involved three fertilization regimes: nitrogen (N) fertilizer alone, P fertilizer alone and a combination of N and P (NP) fertilizer. The objective of this study was to investigate the effects of long-term fertilization practices on soil quality in subtropical plantations through a soil quality index (SQI). Principal component analysis (PCA) was used along with a literature review to select a minimum dataset (MDS) to calculate SQI. Three physical indicators (silt, clay, soil water content), three chemical indicators (soil organic carbon, inorganic nitrogen, total phosphorus), and two biological indicators (microbial biomass carbon, phosphodiesterase enzyme activity) were chosen as MDS from a total dataset (TDS) of eighteen soil indicators. Our study showed that long-term fertilization did not significantly change the soil quality as measured by SQI in both Acacia auriculiformis (p=0.25) and Eucalyptus urophylla (p=0.45) plantations. However, investigations of individual soil indicators in the MDS suggested that P addition through fertilization (P and NP regimes) strongly increases the P pool in the subtropical plantation soil. The MDS provided a strong representation of the TDS data (R2=0.81), and the SQI was positively correlated with littermass (R2=0.37). These findings suggest that the MDS can serve as a quantitative and effective tool for long-term soil quality monitoring.

For many years, there has been a prevailing belief that the activity of soil microorganisms in tropical forests is limited by the availability of phosphorus (P). This belief has traditionally found support in experimental research, consistently demonstrating that the addition of P leads to an increase in heterotrophic soil respiration. However, we have introduced an alternative hypothesis that challenges this conventional perspective. Our proposition suggests that the evidence traditionally utilized to substantiate this belief is, in fact, an outcome of increased carbon (C) availability resulting from abiotic processes initiated by the release of organic matter from soil mineral surfaces, which occurs as a consequence of P addition. Indeed, our previous study has empirically established two significant findings: (i) the acceleration of soil respiration through P fertilization, accompanied by the absence of concurrent stimulation in litter decomposition, and (ii) the immediate increase in extracted DOC resulting from the laboratory introduction of P prior to extraction. In the present study, we have expanded upon the existing body of evidence by providing field-based support that soils subjected to P fertilization display a reduced ability to adsorb newly introduced DOC. The prolonged period of 9 years of continuous fertilization tended to diminish the adsorption capacity of experimentally added DOC, which probably facilitated the acquisition of C by soil microorganisms and thus contributed to the stimulation of soil respiration in our study site. Building upon our previous findings, we propose that the traditionally used evidence to substantiate microbial P limitation is, in fact, a consequence of abiotically increased C availability resulting from P addition.