Coupling strength of human-natural systems mediates the response of ecosystem services to land use change.

Addressing the dynamics of human-natural systems (HNS) driven by land use change (LC) is a key challenge for the sustainable development of ecosystem services (ES). However, how changes to the HNS coupling relationships affect ES is rarely reported. We used network analysis methods to construct an HNS correlation network in the Loess Plateau based on the correlation between the main components of HNS, such as ES, human factors, landscape pattern, vegetation cover, climate change and geomorphic characteristics, and quantitatively described the HNS coupling relationships through key network attributes. We analyzed the variation in HNS network attributes and their relationships with ES along an LC intensity gradient. The results show that carbon storage and soil conservation in the Loess Plateau increased by 0.56% and 0.26%, respectively, during the study period, while the habitat quality and water yield decreased by 0.11% and 0.18%, respectively. An increase in LC intensity reduces connectivity and density in the HNS network, which results in looser connections among HNS components. Importantly, we found that HNS network attributes explained 85% of ES variation across different LC intensity gradients and that connectivity and density had the strongest explanatory power. This means that LC mainly affects ES dynamics by changing the coupling strength of HNS. Our research offers a new perspective for linking LC-HNS-ES, which will help guide practitioners toward establishing and maintaining the sustainability of human well-being amidst changing HNS.

Dynamic characteristics of soil aggregate stability and related carbon and nitrogen pools at different developmental stages of plantations in northern China.

The carbon and nitrogen reserves of forest soil play a key role in combating global climate change. Afforestation is considered an effective measure for increasing carbon and nitrogen reserves in terrestrial forest ecosystems. However, the mechanisms governing how different developmental stages of plantations affect soil carbon and nitrogen stability and storage remain unclear. In this study, we selected three developmental stages of the Larix principis-rupprechtii plantations: medium mature forest (30 yr), near mature forest (40 yr) and mature forest (50 yr). We studied the distribution and stability of soil aggregates at distinct developmental stages, the distribution of carbon and nitrogen pools related to aggregates, and their relationship to environmental factors. We found that with increasing forest age, the soil sand particles became finer. In each developmental stage, the proportion of aggregates >0.25 mm reached more than 85%. The concentrations of carbon and nitrogen in the soil aggregates were lower in the near mature forest (40 a) than in the medium mature forest (30 a), but reached a maximum in the mature forest (50 a). There were significant positive correlations between soil carbon and nitrogen concentrations and soil relative water content (RWC), forest age, and stand density. Soil texture strongly affected the distribution of aggregates. TOC/TN was mainly influenced by aggregate distribution, which was most vulnerable to environmental factors. Environmental factors have a significant negative impact on soil texture, and the path coefficient was -0.812. Environmental factors indirectly affected the concentrations of soil carbon and nitrogen by influencing the distribution and stability of soil aggregates. Therefore, different developmental stages of plantations strongly affected forest carbon and nitrogen pools by changing the soil structure and environmental factors. This study provides a basis for understanding the mechanisms of forest soil carbon and nitrogen storage.

Archaeal and bacterial community structures of rural household biogas digesters with different raw materials in Qinghai Plateau.

The present study aims to investigate microbial community structures household biogas digesters with different raw materials in Qinghai Plateau rural. High-throughput 16S rRNA gene sequencing analysis revealed that Firmicutes, Bacteroidetes, and Proteobacteria are the most abundant bacterial phyla (64.08%). Prevotella group 7 was the most abundant genus in digester YL9 and YL10 (69.72% and 26.96%, respectively) using vegetable waste raw materials. Trichococcus exhibited the highest abundance (14.55%) in YL1 digester using sheep and pig manure. Clostridium sensu stricto 1 (13.89%) and Synergistaceae_uncultured (15.52%) comprised the highest abundances in digester YL5 with mixed raw materials (i.e., dairy manure, sheep manure, and human feces). In addition, Proteiniphilum and Pseudomonas exhibited the highest abundances among bacterial genera in YL4 digester using pig manure. Methanomicrobiales was the most dominant archaeal communities, ranging from 13.35% to 81.34% in abundance. Methanocorpusculum exhibited dominant abundances in all digesters using various raw materials. Methanogenium was the most abundant archaeal genera in YL4 and YL6 digesters, which consume pig manure as primary raw material. In addition, Methanosarcina and Methanosaeta exhibited the highest abundances in digester YL1 (55.03%) and YL9 (51.40%), respectively. Moreover, fermentation temperatures and pH both contributed to the archaeal and bacterial community structures in all the investigated digesters. Specially, fermentation temperature showed positive correlation with the abundances of Synergistaceae_uncultured, Methanogenium, and Methanosaeta, and pH was positively correlated with the abundances of Prevotella group 7 and Methanosarcina abundances.

Dramatic shift in the drivers of ecosystem service trade-offs across an aridity gradient: Evidence from China's Loess Plateau.

Increased aridity creates challenges for sustainable ecosystem management due to the potential for trade-offs among ecosystem services. However, our understanding of how ecosystem service trade-offs (EST) respond to aridification remains limited. Here, generalized additive models and structural equation modeling were used to explore EST dynamics within an aridity gradient on the Loess Plateau, China. Trade-offs between water yield and both carbon storage and habitat quality showed nonlinear relationships with aridity, first increasing and then decreasing. Interestingly, climatic and human factors mostly indirectly influenced EST via effects on landscape characteristics. In regions with an Aridity Index (AI) value of <0.5, climatic and human factors strongly drove EST; in regions with AI > 0.5, landscape characteristics were most important. Therefore, landscape characteristics acted as the key regulators of EST. Importantly, AI values of ∼0.5 represented a transition point, after which dramatic shifts in EST-driver relationships were observed. As >22 % of the Earth's terrestrial surface is projected to reach this level of aridity by 2100, further research on this boundary (between sub-humid and semi-arid areas) is urgently needed to protect ecosystems from the effects of increasing aridity. This study may serve as a valuable reference for mitigating the potential negative effects of increased aridity on human well-being.

Network analysis reveals the regulatory effect of mixed stands on ecosystem structure and functions in the Loess Plateau, China.

Afforestation, an important measure for ecological restoration, has been implemented all over the world, but fragile ecosystem structures and climate change endanger its ecological functions. One major obstacle to optimizing ecological function has been quantifying and characterizing a complex ecosystem structure. Here, the structure and functions of six types of land-use restoration were investigated in the hilly-gully region of the Loess Plateau, China. In total, 44 ecological factors from canopy, understory and soil were determined. We constructed the related network of reforestation ecosystems, quantified the structure of ecosystem through network topology, and explored the relationships between structure and functions. The results showed that changes in plantation type altered the network hubs, but some nodes, such as species height, breast-height diameter and understory biomass, were often keystone hubs. Mixed plantations enhanced the connectivity among different modules. In addition, we found that closeness of network connectivity was an important factor influencing ecological functions, while soil erodibility was the main limiting factor for reforestation ecosystem structure in this region. Moreover, mixed plantations tended to have more balanced topological metrics and ecological functions. Overall, this study suggests that mixed plantations or monoculture plantations should be designed according to the characteristics and ecological demands of the regional ecological environment. Although monoculture plantations may support local ecosystems, mixed plantations offer more resilience to a landscape because they were help to achieve a balance among the ecological functions.

Analyzing Land-Use Change Scenarios for Ecosystem Services and their Trade-Offs in the Ecological Conservation Area in Beijing, China.

It is generally believed that land-use changes can affect a variety of ecosystem services (ES), but the relationships involved remain unclear due to a lack of systematic knowledge and gaps in data. In order to make rational decisions for land-use planning that is grounded in a systematic understanding of trade-offs between different land-use strategies, it is very important to understand the response mechanisms of various ecosystem services to changes in land-use. Therefore, the objective of our study is to assess the effects of land-use change on six ecosystem services and their trade-offs among the ecosystem services in the ecological conservation area (ECA) in Beijing, China. To do this, we projected future land-use in 2030 under three different scenarios: Business as Usual (BAU), Ecological Protection (ELP), and Rapid Urban Development (RUD), using GeoSOS-FLUS model. Then, we quantified six ecosystem services (carbon storage, soil conservation, water purification, habitat quality, flood regulation, and food production) in response to land-use changes from 2015 to 2030, using a spatially explicit InVEST model. Finally, we illustrated the trade-offs and/or synergistic relationships between each ecosystem service quantified under each of the different scenarios in 2030. Results showed that built-up land is projected to increase by 281.18 km2 at the cost of water bodies and cultivated land from 2015 to 2030 under the RUD scenario, while forest land is projected to increase by 152.38 km2 under the ELP scenario. The carbon storage, soil conservation, habitat quality, and the sum of ecosystem services (SES) would enrich the highest level under the ELP scenario. Land-use strategies that follow the ELP scenario can better maintain the ecosystem services and sustainable development of natural and social economic systems.

Soil temperatures and active carbon components as key drivers of C stock dynamics between two different stand ages of Larix principis-rupprechtii plantation.

Forest soils sequester a large amount of carbon (C) and have a significant effect on the global C balance. Forests are commonly managed to maintain certain age structures but the effects of this management on soil C pools (kg C m-2) is still uncertain. We compared 40-year-old (1GF) and 24-year-old (2GF) plantations of Larix principis-rupprechtii in North China. Specifically, we measured environmental factors (e.g., soil temperature, moisture, and pH), the active C and nitrogen (N) pools (e.g., soil organic C, soil total N, dissolved organic C and N, microbial biomass C and N), and soil processes (e.g., C mineralization and microbial activity in different seasons) in five soil layers (0-50 cm, 10 cm for each soil layer) across the growing seasons in three 25 m × 25 m plots in each age class (1GF and 2GF). Findings indicated that the soil organic C pool in the older 1GF forest (12.43 kg C m-2) was significantly higher than 2GF forests (9.56 kg C m-2), and that soil temperature in 1GF forests was 9.8 °C, on average, 2.9% warmer than temperature in 2GF forests. The C lost as carbon dioxide (CO2) as a result of mineralization in the 2GF plots may partly explain the lower soil organic C pool in these younger forests; microorganisms likely drive this process.

Microbial regulation of soil carbon properties under nitrogen addition and plant inputs removal.

BACKGROUND: Soil microbial communities and their associated enzyme activities play key roles in carbon cycling in terrestrial ecosystems. Soil microbial communities are sensitive to resource availability, but the mechanisms of microbial regulation have not been thoroughly investigated. Here, we tested the mechanistic relationships between microbial responses and multiple interacting resources. METHODS: We examined soil carbon properties, soil microbial community structure and carbon-related functions under nitrogen addition and plant inputs removal (litter removal (NL), root trench and litter removal (NRL)) in a pure Larix principis-rupprechtii plantation in northern China. RESULTS: We found that nitrogen addition affected the soil microbial community structure, and that microbial biomass increased significantly once 100 kg ha-1 a-1 of nitrogen was added. The interactions between nitrogen addition and plant inputs removal significantly affected soil bacteria and their enzymatic activities (oxidases). The NL treatment enhanced soil microbial biomass under nitrogen addition. We also found that the biomass of gram-negative bacteria and saprotrophic fungi directly affected the soil microbial functions related to carbon turnover. The biomass of gram-negative bacteria and peroxidase activity were key factors controlling soil carbon dynamics. The interactions between nitrogen addition and plant inputs removal strengthened the correlation between the hydrolases and soil carbon. CONCLUSIONS: This study showed that nitrogen addition and plant inputs removal could alter soil enzyme activities and further affect soil carbon turnover via microbial regulation. The increase in soil microbial biomass and the microbial regulation of soil carbon both need to be considered when developing effective sustainable forest management practices for northern China. Moreover, further studies are also needed to exactly understand how the complex interaction between the plant and below-ground processes affects the soil microbial community structure.

[Effects of thinning on soil active organic carbon contents and enzyme activities in Larix principis-rupprechtii plantation]. / é—´ä¼å¯¹åŽåŒ—è½å¶æ¾äººå·¥æž—åœŸå£¤æ´»æ€§æœ‰æœºç¢³å«é‡åŠé ¶æ´»æ€§çš„å½±å“.

The effects of thinning on soil active organic carbon and related soil enzyme activities were investigated in a Larix principis-rupprechtii plantation in Taiyue Mountain. With the increases of soil depth, the content of soil labile organic carbon, soil nitrogen content and enzyme activities all reduced. For each soil layer, moderate thinning increased soil carbon and nitrogen contents dramati-cally. The activities of sucrase (SC) and peroxidase (PEO) and the activities of polyphenol oxidase (PHO) and urease (UE) in the layer of 0-10 cm could be significantly improved by low thinning and moderate thinning, respectively. For the 10-50 cm layer, the activities of SC and UE were reduced by low thinning, while moderate thinning markedly reduced the activities of cellulase. Results from redundancy analysis showed that dissolved organic carbon (DOC) was the main factor affecting soil enzyme activity in both 0-10 cm and 20-30 cm soil layers and that soil organic carbon (SOC) contents affected the activities of PHO and SC in 10-20 cm soil layer. The microbial biomass nitrogen (MBN) mainly affected the activities of PHO, PEO and UE in 30-40 cm soil layer. The contents of total P (TP) and readily oxidized carbon (ROC) played an important role in affecting soil enzyme activities in 40-50 cm soil layer. The results indicated that thinning could dramati-cally affect soil active organic carbon content and soil enzyme activity in L. principis-rupprechtii plantation. Moderate thinning treatment could obtain the highest soil nutrients and achieve better soil chemical properties such as soil pH, water content and organic matter content than other treatments, which could improve vegetation structure, litter and nutrient cycling process. Therefore, we recommended moderate density adjustment (1404-1422 trees·hm-2) to L. principis-rupprechtii plantation to promote soil carbon and nitrogen retention.

Dynamics of nitrogen and active nitrogen components across seasons under varying stand densities in a Larix principis-rupprechtii (Pinaceae) plantation.

Changes in the concentration of soil nitrogen (N) or its components may directly affect ecosystem functioning in forestry. Thinning of forest stands, a widely used forestry management practice, may transform soil nutrients directly by altering the soil environment, or indirectly by changing above- or belowground plant biomass. The study objectives were to determine how tree stem density affects the soil N pool and what mechanisms drive any potential changes. In this study, N and its active components were measured in the soil of a Larix principis-rupprechtii plantation across two full growing seasons, in 12 (25 × 25 m) plots: (low thinning, removal of 15% of the trees, three plot repetitions), moderate thinning (MT) (35% removal) and heavy thinning (HT) (50% removal) and no thinning control. Environmental indices, like the light condition, soil respiration, soil temperatures, and prescription, were measured in the plots also. Results indicated that soil total nitrogen (STN) was affected by tree stem density adjustments in the short-term; STN generally increased with decreasing tree stem density, reaching its highest concentration in the MT treatment before decreasing in HT. This pattern was echoed by the DON/STN ratio dissolved organic nitrogen (DON) under MT. A lower DON/STN was measured across the seasons. Microbial biomass nitrogen (MBN) and the SOC/STN (soil organic carbon (SOC)) ratio and density treatments influenced MBN concentration and inhibited SOC/STN. MT tended to accumulate more STN, produce lower DON/STN and had a generally higher microbial activity, which may be partly ascribed to the higher MBN value, MBN/STN ratio and lower DON/STN. The water conditions (soil moisture), light and soil temperatures could partly be responsible for the N pool dynamic in the different density treatments.

Response of soil organic carbon and nitrogen to nitrogen deposition in a Larix principis-rupprechtii plantation.

Plant growth and ecosystem production are limited by nitrogen (N), however, the mechanisms of N limitation in terrestrial carbon (C) sequestration in soil remains unclear. To examine these mechanisms N was deposited at rates of 0, 50, 100, and 150 kg N ha-1 yr-1 for two years in a subalpine Larix principis-rupprechtii plantation. Soil C and N components were measured three times encompassing the entire growing season (spring, summer, and autumn) in the second year of the experiment. Results showed that N-deposition affected soil organic carbon (SOC) in the upper soil layer (0-10 cm) especially in the summer season. Dissolved organic carbon (DOC) played the key role in C loss under the high-N treatment (p < 0.01) with higher N-deposition significantly increasing both DOC and DOC/SOC in summer (p < 0.01). In the summer season when there was sufficient precipitation and higher temperatures, the average DOC across all treatments was higher than spring and autumn. The active C components contributed to SOC sequestration in low and medium N- treatment and DOC, DON dynamics in summer were responsible for the C and N pool loss under the high N-treatment.

[Responses of soil microbial carbolic metabolism characteristics to home-field advantage of leaf litter decomposition in Liaoheyuan Nature Reserve of northern Hebei Province, China].

Using litter bag method, we studied the responses of soil microbial biomass carbon (MBC), microbial respiration (MR) and microbial metabolic quotient (qCO2) in 0-5 cm, 5-10 cm and 10-20 cm soil layers to home-field advantage of Betula platyphlla and Quercus mongolica leaf litter decomposition in Liaoheyuan Nature Reserve, northern Hebei Province. The results showed that the contents of MBC in Betula platyphila and Quercus mongolica leaf litter treatments in home environment (Bh and Qh treatments) were significant higher than that in B. platyphlla and Q. mongolica leaf litter treatments in non-home environment (Ba and Qa treatments). There was no significant difference in MR between home and non-home environments. Response degree of MBC and MR to home-field advantage of different litter decomposition was inconsistent. The MBC of the different soil layers in Qa treatment fell by 39.6%, 34.9% and 33.5% compared to Qh treatment, respectively, and that in B. platyphlla treatment was decreased by 31.6%, 27.1% and 17.0%, respectively. MR of the different soil layers in Qa treatment accounted for 96.3%, 92.4% and 83.7% of Qh treatment, respectively, while MR in B. platyphila treatment was 99. 4%, 97. 3% and 101.3%, respectively. In contrast to MBC, qCO2 in soil showed a reverse pattern. Our study suggested that rich nutrients in soil enhanced microbial activity and weakened the conflict of nutrient uptake between plants and microorganisms, which led to the result that MBC and qCO2 had an obvious response to home-field advantage of litter decomposition, when litter decomposed in its home environment. There was a weak response between MR and home-field advantage of litter decomposition, because of influence of soil temperature, water content and their interaction. Furthermore, MBC, MR and qCO2 had a higher response degree to home-field advantage of Q. mongolica litter than B. platyphila litter, since lower quality litter exhibited higher home-field advantage of litter decomposition.

[Responses of soil microbial carbon metabolism to the leaf litter composition in Liaohe River Nature Reserve of northern Hebei Province, China].

Using litter bag method, we studied the effects of single and mixed litters from Betula platyphlla, Populus davidiana and Quercus mongolica on soil microbial biomass carbon (MBC), microbial respiration (MR) and microbial metabolic quotient (qCO2) in 0-5, 5-10 and 10-20 cm soil layers. The results showed that the average contents of MBC in 0-20 cm soil layer were 124.84, 325.29, 349.79 and 319.02 mg . kg-1 in the leaf litter removal treatment, Betula platyphlla treatment, Populus davidiana treatment and Quercus mongolica treatment, and the corresponding average rates of MR were 0.66, 1.12, 1.16 and 1.10 µg . g-1 . h-1, respectively. Meanwhile, in 0-20 cm soil layer, the average contents of MBC in the treatments with single leaf litter, mixed litter of two plant species and mixed litter of three plant species were 331. 37, 418. 52 and 529. 34 mg . kg-1, and the corresponding average rates of MR were 1.13, 1.30 and 1.46 µg . g-1 . h-1, respectively. In contrast to the MBC and MR, qCO2 in soil showed a reverse pattern. Our study suggested that characteristics of microbial carbolic metabolism were influenced by litter quality. Namely, the treatment with high litter quality had higher MBC, MR and utilization efficiency of soil carbon, compared with the treatment with low litter quality. Moreover, mixture of different species of leaf litter improved soil microbial activities, increased utilization efficiency on soil carbon and promoted diversity of microbial metabolic pathways, which could then contribute to maintaining and enhancing soil quality of forestland.

Patterns of biomass and carbon distribution across a chronosequence of Chinese pine (Pinus tabulaeformis) forests.

Patterns of biomass and carbon (C) storage distribution across Chinese pine (Pinus tabulaeformis) natural secondary forests are poorly documented. The objectives of this study were to examine the biomass and C pools of the major ecosystem components in a replicated age sequence of P. tabulaeformis secondary forest stands in Northern China. Within each stand, biomass of above- and belowground tree, understory (shrub and herb), and forest floor were determined from plot-level investigation and destructive sampling. Allometric equations using the diameter at breast height (DBH) were developed to quantify plant biomass. C stocks in the tree and understory biomass, forest floor, and mineral soil (0-100 cm) were estimated by analyzing the C concentration of each component. The results showed that the tree biomass of P. tabulaeformis stands was ranged from 123.8 Mg·ha-1 for the young stand to 344.8 Mg·ha-1 for the mature stand. The understory biomass ranged from 1.8 Mg·ha-1 in the middle-aged stand to 3.5 Mg·ha-1 in the young stand. Forest floor biomass increased steady with stand age, ranging from 14.9 to 23.0 Mg·ha-1. The highest mean C concentration across the chronosequence was found in tree branch while the lowest mean C concentration was found in forest floor. The observed C stock of the aboveground tree, shrub, forest floor, and mineral soil increased with increasing stand age, whereas the herb C stock showed a decreasing trend with a sigmoid pattern. The C stock of forest ecosystem in young, middle-aged, immature, and mature stands were 178.1, 236.3, 297.7, and 359.8 Mg C ha-1, respectively, greater than those under similar aged P. tabulaeformis forests in China. These results are likely to be integrated into further forest management plans and generalized in other contexts to evaluate C stocks at the regional scale.