Fine root decomposition in forest ecosystems: an ecological perspective

Patterns and controlling factors of soil microbial necromass carbon in global ecosystems

Microbial necromass is a critical source of soil organic carbon (SOC) in terrestrial ecosystems, and the quantity and quality of microbial necromass carbon (MNC) can influence long-term soil carbon sequestration. However, few studies have explored the distribution of soil MNC and its contribution to SOC along the soil profiles across different ecosystems globally. Here, we collected a global dataset (2, 411 samples from 216 papers) of soil MNC at a depth of 0-100 cm depth from wetlands, farmlands, grasslands, and forests. Our findings indicated that the average MNC at 0-30 cm was 2.7 g kg-1 in wetlands, 7.1 g kg-1 in farmlands, 17.2 g kg-1 in grasslands, and 14.6 g kg-1 in forests. The MNC content in deep soils (30-100 cm) was 70 % lower (p < 0.05) than in topsoil (0-30 cm), whereas the contribution of the MNC to the SOC in deep soils (50 %) was higher than in topsoil in forests (32 %). On average, the fungal necromass carbon(FNC) content (7.5 g kg-1) was almost three times higher than the bacterial necromass carbon (BNC) content (2.8 g kg-1) in the topsoill. The mean annual temperature played an important role in affecting the MNC by altering soil total nitrogen, soil texture and microbial biomass. These findings are important for understanding SOC formation mechanisms and the crucial role of microbial necromass in global ecosystems.

Forest Structure, Diversity, and Regeneration in a Community-Managed Forest of Nepal: A Model for Carbon Sequestration and Sustainable Management

Community forestry, a participatory forest management system, encourages forest conservation, enhances carbon sequestration, and advances the Sustainable Development Goals (SDGs) by increasing community ownership of resource management. Community forestry, in terms of policies and practices, directly supports SDG-1, SDG-13, and SDG-15 by promoting community ownership and empowerment as well as ecosystem health. It provides immediate benefits to local livelihoods by enhancing access to ecosystem services such as fuelwood, fodder, and non-timber forest products. Here, we assess the forest regeneration and conservation value of a community forest in Nepal by recording seedlings, saplings, and mature trees in randomly sampled plots. The plots were structurally complex with rich tree diversity; most plots showed high diameter at breast height (DBH) differentiation and diversity. Most tree species followed an abundance distribution of seedlings > saplings > adults, suggesting "good" regeneration. Tree carbon stock was 137.6 tons per hectare and was positively associated with tree density and diversity and negatively with altitude. An increase of one standard deviation in the diversity index ~0.39 was associated with an 11.7% higher tree carbon stock per hectare. Plot-level tree height was positively related to diversity at lower tree heights. Overall, community forestry successfully transformed a degraded forest into one of quality regeneration and conservation value within two decades, outperforming the regional average forest carbon stock and diversity. Thus, community forests can act as an effective model for sustainable forest management and are essential tools for policymakers to promote regeneration, structural diversity, carbon storage, tree growth, and sustainable resource utilization.

Spatiotemporal evolution of vegetation phenology and its response to environmental factors in the upper and middle reaches of the Yellow River Basin

As climate change accelerates, understanding the mechanisms of ecosystem phenology in vulnerable regions is crucial for terrestrial environments. This research systematically used remote sensing data to study the dynamic changes in vegetation phenology in the upper and middle Yellow River Basin (UMYRB), examined the effects of environmental shifts on vegetation phenology, and quantified the contributions of different driving factors. The key findings are as follows: (1) As elevation and latitude increase, the start of the growing season (SOGS) is generally delayed, particularly in the northwest and northeast, where it typically occurs between days 140 and 180. The end of the growing season (EOGS) shifts later from west to east, with 86.66 % of the area experiencing EOGS between days 260 and 300. From 1981 to 2016, approximately 61.35 % of the area exhibited a trend of advancing SOGS (-0.09 days/year), while 60.10 % of the area showed a delay in EOGS (0.08 days/year). (2) Both SOGS and EOGS exhibit significant spatial variability influenced by climatic factors, with the primary pre-season impact period ranging from 1 to 4 months. SOGS is typically negatively correlated with precipitation and temperature, whereas EOGS often shows a positive correlation with precipitation and temperature. Temperature and solar radiation are the primary climatic drivers influencing vegetation phenology in the study region. Temperature accounts for 53.57 % of SOGS and 50.73 % of EOGS, advancing them by 0.18 and 0.22 days, respectively. Solar radiation also significantly influences SOGS and EOGS, advancing them by 0.14 and 0.13 days, respectively. While the impact of diurnal temperature range (DTR) and precipitation is less pronounced, DTR is notably important in high-altitude regions. (3) Vegetation phenology varies significantly across various vegetation types. Forests usually experience an earlier SOGS and a later EOGS, while shrubs in high-altitude areas tend to have a delayed SOGS due to a greater diurnal temperature range. The growing season of grasslands and wetlands is more significantly affected by precipitation and temperature, particularly in the eastern and northern regions. Solar radiation significantly impacts the entire growing season in croplands and grasslands in the central and southern regions. Uncertainty in vegetation phenology was assessed through Bootstrap analysis, and the spatial adaptability of climate driving factors was optimized using the ridge regression model. The results indicate that despite certain sources of uncertainty, the analysis demonstrates high accuracy and stability, providing a reliable scientific basis for ecological management and restoration.

Effects of polyethylene and poly (butyleneadipate-co-terephthalate) contamination on soil respiration and carbon sequestration

To address plastic pollution in agricultural soils due to polyethylene plastic film mulch used, biodegradable film is being studied as a promising alternative material for sustainable agriculture. However, the impact of biodegradable and polyethylene microplastics on soil carbon remains unclear. The field experiment was conducted with Poly (butyleneadipate-co-terephthalate) debris (PBAT-D, 0.5-2 cm), low-density polyethylene debris (LDPE-D, 0.5-2 cm) and microplastic (LDPE-Mi, 500-1000 μm) contaminated soil (0% (control), 0.05%, 0.1%, 0.2%, 0.5%, 1% and 2% w:w) planted with soybean, to explore potential impacts on soil respiration (Rs), soil organic carbon (SOC) and carbon fractions (microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC)), and C-enzymes (β-glucosidase, β-xylosidase, cellobiohydrolase). Results showed that PBAT-D, LDPE-D and LDPE-Mi significantly inhibited Rs compared with the control during the flowering and harvesting stages (p < 0.05). SOC significantly increased in the PBAT-D treatments at both stages, and in the LDPE-Mi treatments at the harvesting stage, but decreased in the LDPE-D treatments at the flowering stage. In the PBAT-D treatments, POC increased but DOC and MAOC decreased at both stages. In the LDPE-D treatments, MBC, DOC and EOC significantly decreased but POC increased at both stages. In the LDPE-Mi treatments, MBC and DOC significantly decreased at the harvesting stage, while EOC and MAOC decreased but POC increased at the flowering stage. For C-enzymes, no significant inhibition was observed at the flowering stage, but they were significantly inhibited in all treatments at the harvesting stage. It is concluded that PBAT-D facilitates soil carbon sequestration, which may potentially alter the soil carbon pool and carbon emissions. The key significance of this study is to explore the overall effects of different forms of plastic pollution on soil carbon dynamics, and to inform future efforts to control plastic pollution in farmlands.

Species mixtures enhance fine root biomass but inhibit root decay under throughfall manipulation in young natural boreal forests

Fine roots play crucial roles in terrestrial biogeochemical cycles. Although biodiversity loss and changes in precipitation are two major drivers of global change, our understanding of their effects on fine root biomass (FRB), root functional traits, and fine root decay (FRD) remains incomplete. We manipulated precipitation in young boreal forests dominated by Populus tremuloides, Pinus banksiana, and their relatively even mixtures using 25 % addition, ambient, and 25 % reduction in throughfall during the growing season. We collected root samples using soil core and trunk-traced methods to quantify FRB and root traits, and we simulated fine root decay using an in-situ experiment over 531 days. We found that compared to the average of single-species-dominated stands, species mixtures increased FRB by 41 % under ambient throughfall, by 89 % under throughfall reduction and by 71 % under throughfall addition. Root surface area, fine root volume, and root length density responded to species mixtures similarly to FRB. Meanwhile, species mixtures reduced FRD across all water treatments. There was a positive relationship between the effect of species mixtures on the FRD of absorptive roots and those on the FRB. Our results highlight that species mixtures could modify carbon cycling by enhancing fine root biomass accumulation and reducing its decomposition of young boreal forests under changing precipitation.