Forest Soil Carbon Dynamics Research Articles

Thinning enhances forest soil C storage by shifting the soil toward an oligotrophic condition

Forests are significant carbon reservoirs, with approximately one-third of this carbon stored in the soil. Forest thinning, a prevalent management technique, is designed to enhance timber production, preserve biodiversity, and maintain ecosystem functions. Through its influence on biotic and abiotic factors, thinning can profoundly alter soil carbon storage. Yet, the full implications of thinning on forest soil carbon reservoirs and the mechanisms underpinning these changes remain elusive. In this study, we undertook a two-year monitoring initiative, tracking changes in soil extracellular enzyme activities (EEAs), microbial communities, and other abiotic parameters across four thinning intensities within a temperate pine forest. Our results show a marked increase in soil carbon stock following thinning. However, thinning also led to decreased dissolved organic carbon (DOC) content and a reduced DOC to soil organic carbon (SOC) ratio, pointing toward a decline in soil carbon lability. Additionally, fourier transform infrared spectroscopy (FTIR) analysis revealed an augmented relative abundance of aromatic compounds after thinning. There was also a pronounced increase in absolute EEAs (per gram of dry soil) post-thinning, implying nutrient limitations for soil microbes. Concurrently, the composition of bacterial and fungal communities shifted toward oligotrophic dominance post thinning. Specific EEAs (per gram of soil organic matter) exhibit a significant reduction following thinning, indicating a deceleration in organic matter decomposition rates. In essence, our findings reveal that thinning transitions soil toward an oligotrophic state, dampening organic matter decomposition, and thus bolstering the soil carbon storage potential of forest. This study provides enhanced insights into the nuanced relationship between thinning practices and forest soil carbon dynamics, serving as a robust foundation for enlightened forest management strategies.

Changing precipitation effect on forest soil carbon dynamics is driven by different attributes between dry and wet areas

Changes in precipitation patterns have the potential to significantly affect the global carbon (C) cycle by altering soil organic carbon (SOC) dynamics. Comparing the patterns and drivers of soil C responses to precipitation changes in wet and dry forests can improve our understanding of soil carbon-water coupling. In this study, we conducted a meta-analysis to assess the effects of precipitation changes on soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), SOC concentrations, and carbon dioxide (CO2) flux across a broad range of forest sites in dry and wet regions. The results showed that both the soil DOC and MBC concentrations decreased significantly (by averages of 7.8 and 7.9%, respectively) at the wet sites, but increased (by 1.2 and 10.2%, respectively) at the dry sites under increased precipitation conditions. The soil MBC concentrations decreased by 17.5% at the wet sites but by 4.1% at the dry sites under reduced precipitation conditions. The soil CO2 flux decreased by 18.9% and 14.3% at the wet and dry sites, respectively, under reduced precipitation. The responses of the soil MBC concentrations were influenced by precipitation intensity, whereas soil DOC and SOC concentration, and CO2 flux were regulated by the soil texture and climate. Clearly, soil MBC was more sensitive to increased precipitation at the dry sites than at the wet sites. Under reduced precipitation, changes in soil MBC concentration and CO2 flux were stronger at the wet sites than at the dry sites. To enhance forecasting of soil C cycles and functional alterations in a changing climate, the differing response mechanisms in dry and wet areas should be considered using process-based climate models.

森林土壌の炭素動態における土壌中水溶性有機態炭素の役割 : 微生物による二酸化炭素生産との関係( 森林生態系における物質循環研究の新しい展開)

森林土壌の炭素動態における土壌中水溶性有機態炭素の役割 : 微生物による二酸化炭素生産との関係( 森林生態系における物質循環研究の新しい展開)

Effects of manipulated above- and belowground organic matter input on soil respiration in a Chinese pine plantation.

Alteration in the amount of soil organic matter input can have profound effect on carbon dynamics in forest soils. The objective of our research was to determine the response in soil respiration to above- and belowground organic matter manipulation in a Chinese pine (Pinus tabulaeformis) plantation. Five organic matter treatments were applied during a 2-year experiment: both litter removal and root trenching (LRRT), only litter removal (LR), control (CK), only root trenching (RT) and litter addition (LA). We found that either aboveground litter removal or root trenching decreased soil respiration. On average, soil respiration rate was significantly decreased in the LRRT treatment, by about 38.93% ± 2.01% compared to the control. Soil respiration rate in the LR treatment was 30.65% ± 1.87% and in the RT treatment 17.65% ± 1.95% lower than in the control. Litter addition significantly increased soil respiration rate by about 25.82% ± 2.44% compared to the control. Soil temperature and soil moisture were the main factors affecting seasonal variation in soil respiration. Up to the 59.7% to 82.9% seasonal variation in soil respiration is explained by integrating soil temperature and soil moisture within each of the various organic matter treatments. The temperature sensitivity parameter, Q 10, was higher in the RT (2.72) and LA (3.19) treatments relative to the control (2.51), but lower in the LRRT (1.52) and LR treatments (1.36). Our data suggest that manipulation of soil organic matter input can not only alter soil CO2 efflux, but also have profound effect on the temperature sensitivity of organic carbon decomposition in a temperate pine forest.

PH and substrate regulation of nitrogen and carbon dynamics in forest soils in a karst region of the upper Yangtze River basin, China

Nitrogen (N) is the most limiting nutrient for forest development. In this study, using a natural pH gradient, N and carbon (C) mineralization was investigated and the effects of soil pH as well as the total C and N contents and the soil C/N ratio were evaluated in forest soils after mountain closure in a karst region. The N availability was poor based on the low N mineralization potential (N0) and the low active fraction of soil total N (N0/total N), while high microbial decomposition activity was indicated by a high mineralization rate constant (kN). N0 was positively correlated with soil pH as well as the total C and N contents. Additionally, multiple regression analysis revealed that total CN (the product of the soil total C and total N contents) and the C/N ratio had more significant effects on N0 than soil pH. In contrast, the mineralization rate constants kN and kC were positively affected by soil pH. The results indicated that N availability was regulated by soil organic matter (SOM), while microbial activity was restricted by soil pH. Also, the lack of nitrification and the high C0/N0 ratio observed at soil pH <5.5 may be a strong indicator of alterations to the microbial composition prompted by severe soil acidification. Further research is required to determine the changes in soil microbial composition with the drop in soil pH and their effects on SOM decomposition and nutrient availabilities.

Simulating the soil carbon dynamics of Pinus densiflora forests in central Korea

We developed a simple forest soil carbon model (Korean Forest Soil Carbon model, KFSC) requiring a small number of parameters to evaluate the forest soil carbon stocks and dynamics. The KFSC was composed of live biomass (BIO), primary dead organic matter (DOM) (AWD: aboveground woody debris; BWD: belowground woody debris; ALT: aboveground litter; and BLT: belowground litter), and secondary DOM (HUM: humus and SOC: soil organic carbon). The KFSC was validated against six Pinus densiflora forests at Gyeonggi province in central Korea and validation results showed that the model predicted the AWD, ALT, and SOC stocks with high precision (r 2=0.90–0.98, slope = 0.95–0.98). We simulated 160 years of carbon dynamics of the P. densiflora forests in Gyeonggi province (11,607 ha) under alternative clear-cut intervals that had been taking place in the past (30, 50, and 80 years). Simulated total SOC stock ranged from 298.7 to 520.5 Gg C depending on the scenario and increased with time in all scenarios. The estimated total SOC stock was higher in the scenario of less frequent clear-cut, while its annual increment was higher in the scenario of more frequent clear-cut in the past. The KFSC will be useful, especially for simulating soil carbon dynamics in forests with scarce information, and has the potential to estimate soil carbon dynamics at a national scale by incorporating with geographical information system.

Rainfall pulse primarily drives litterfall respiration and its contribution to soil respiration in a young exotic pine plantation in subtropical China

Although litterfall respiration (RL) is a key process of soil carbon dynamics in forests, factors that drive RL and its contribution to soil respiration (RS) have not been sufficiently studied. Using a litter removal method, we researched RL and the ratio of RL:RS in a 20-year-old exotic slash pine ( Pinus elliottii Englem.) plantation in subtropical China. Soil temperature explained 67%, 78%, and 25% of variation in RS, mineral soil respiration (RS-L), and RL, respectively, but had little impact on RL:RS. To study influences besides temperature, measured RS and RS-L were normalized using the Arrhenius equation. Even though this subtropical plantation was characterized by a humid climate with abundant precipitation, a rainfall pulse induced increase in soil moisture primarily drove RL and its contribution to RS but depressed RS-L. The response of RL to rainfall and soil moisture was significantly more sensitive than that of RS-L. Furthermore, the effects of rainfall and soil moisture on RS, RL, and RL:RS were higher during the dry season (July–December) than during the wet season (January–June). In the context of climate change, RL and its contribution to RS are expected to decrease because of the predicted decrease in rainfall amount and frequency in subtropical regions.

Forest management and soil respiration: Implications for carbon sequestration

It is recognized that human activities, such as fossil fuel burning, land-use change, and forest harvesting at a large scale, have resulted in the increase of greenhouse gases in the atmosphere since the onset of the industrial revolution. The increasing amounts of greenhouse gases, particularly CO2in the atmosphere, is believed to have induced climate change and global warming. With the ability to remove CO2from the atmosphere through photosynthesis, forests play a critical role in the carbon cycle and carbon sequestration at both global and local scales. It is necessary to understand the relationship between forest soil carbon dynamics and carbon sequestration capacity, and the impact of forest management practices on soil CO2efflux for sustainable carbon management in forest ecosystems. This paper reviews a number of current issues related to (1) carbon allocation, (2) soil respiration, and (3) carbon sequestration in the forest ecosystems through forest management strategies. The contribution made by forests and forest management in sequestrating carbon to reduce the CO2concentration level in the atmosphere is now well recognized. The overall carbon cycle, carbon allocation of the above- and belowground compartments of the forests, soil carbon storage and soil respiration in forest ecosystems and impacts of forest management practices on soil respiration are described. The potential influences of forest soils on the buildup of atmospheric carbon are reviewed.