Coupled patterns of natural and anthropogenic resources in typical ecosystems in coastal areas of China.

The coastal area of Yancheng, China, is one of the hotspots for ecological research. Under the coupling of human and natural ecosystems, the region has gradually evolved into a coexistence of aquatic, agricultural and mudflat ecosystems. What are the patterns of natural and artificial resource inputs and patterns of change in ecosystems? How can ecological flows be analyzed at a uniform scale? Here, we selected six typical local ecosystems, namely, rice‒wheat for enterprises (RWE), rice‒wheat for smallholder households (RWS), chrysanthemum‒wheat (CW), fish polyculture (FP), juvenile crab farming (JF) and clam polyculture (CP), and analyzed their energy flow flux and sustainability based on emergy theory. The results showed that anthropogenic resource inputs were higher than natural resource inputs in all ecosystems, and the inputs of aquatic ecosystems were greater than those of agroecosystems. The greatest total input was 2.0 E+17 seJ/ha/yr for FP, and the lowest was 1.9 E+16 seJ/ha/yr for RWE. The proportions of renewable and artificial inputs for RWE, RWS, CW, FP, JF and CP were 32.8% vs. 96.1%, 40.3% vs. 96.5%, 34.7% vs. 97.0%, 32.6% vs. 99.4%, 55.1% vs. 98.5%, and 62.5% vs. 98.6%, respectively. The highest input to agroecosystems was nitrogen fertilizer, while in JF and CP, it was water, and feed (63.3%) accounted for the highest percentage of input in FP. JF and CP had lower environmental loads and higher sustainability than other ecosystems, but this still represents a high input compared to agroecosystems. Human-led resource coupling profoundly affects ecosystem sustainability, and various thresholds of energy use and ecological sustainability need to be studied in depth. Continuous exploration of methods and mechanisms for the maintenance and evolution of ecosystems with low total inputs and low inputs of non-renewable resources can contribute to high-quality sustainable development of an area or region.

Shifts of active microbial community structure and functions in constructed wetlands responded to continuous decreasing temperature in winter.

Important functions of constructed wetland related to biogeochemical processes are mediated by soil microbes and low-temperature damage is the main limiting factor for microbes in winter. However, the response thresholds for active microbial community and enzyme activities to continuous decreases in temperature remain unclear. In this study, total 90 soil samples were collected every week over a 6-week period to track the dynamics of four enzymes involved in cycles of C, N, P and active bacterial community as field soil temperature decreased continuously from 6.62 °C to 0.55 °C. Enzyme activity changed suddenly when the temperature decreased to 4.83 °C, the nitrite reductase activity reduced by 36.2%, while alkaline phosphatase activity is increased by 396%. The cellulase and urease were only marginally influenced by cold stress. Decreased nitrite reductase activities corresponded with loss of nir-type denitrifiers important for nitrite reduction. For cold stress, N-related bacteria were sensitive species. Whereas increased alkaline phosphatase activity may be due to the fact that P-related bacteria were opportunistic species. Key functional taxa connected with degradation of cellulose promoted species coexistence and microbial network stability. The lower and upper temperature thresholds for community change were 4.85 °C and 6.30 °C, respectively. Collectively, these results revealed that microbial taxa involved in C, N and P cycling respond differently to continuous decreases in temperature and higher than 4.85 °C is an ideal environment to prevent loss of microbial diversity and functions in winter, providing a scientific reference for the targeted isolation and cultivation of key microbial taxa in rhizosphere soil and adjusting temperature range to improve the purification capacity of wetlands during low temperature periods.

Fungi drive soil multifunctionality in the coastal salt marsh ecosystem.

Salt marshes are highly productive intertidal wetlands located in temperate climatic zones, in which marine-to-terrestrial transition significantly influences microbial life. Numerous studies revealed the important coupling relationship between microbial diversity and ecosystem functions in terrestrial ecosystems, however, the importance of microbial diversity in maintaining soil functions in coastal ecosystems remains poorly understood. Here, we studied the shifts of microbial communities and soil multifunctionality (SMF; nine functions related with C, N and P cycling) along a vegetation gradient in a salt marsh ecosystem and investigated the microbial diversity - ecosystem function relationship. The aboveground vegetation shifted from mud flat (MF) to Scirpus triqueter (SM) and then Phragmites australis (PA) with increasing distance away from the sea. Average approach showed that the SMF was much higher in halophytes covered zones including SM and PA than in MF. Structural equation model (SEM) analysis confirmed that vegetation was an important predictor on SMF besides moisture and organic carbon. Linear regression and multiple threshold methods showed that in MF and SM zones, fungal rather than bacterial richness was significantly and positively correlated with SMF, while in the PA zone microbial diversity did not relate with SMF. Random forest analysis identified several Ascomycota taxa with preference over marine environment as strong predictors of SMF. Taken together, our study lays the basis for a better understanding on the relationships between belowground microbial diversity and soil functions in coastal ecosystems.

Study on life histroy traits of Stellera chamaejasme provide insights into its control on degraded typical steppe.

The increase of unpalatable Stellera chamaejasme plants has become commonplace in degraded grasslands of China, which can hinder the establishment and growth of palatable plants and have an impact on sustainable development of livestock production. Controlling S. chamaejasme is thus a necessary, yet usually problematic step towards the degraded grassland. Various measures have been implemented to control S. chamaejasme but relatively little is known about the growth and development of S. chamaejasme in degraded grassland. Therefore, focusing on the life history traits of S. chamaejasme can provide theoretical support underpinning its management. In this study, different age classes of S. chamaejasme plants were surveyed and studied from a degraded typical steppe in China, and the variation of the phenotypic traits, biomass increasement, biomass allocation, reserves and nutrient content were described. These analyses could be of great importance in identifying the management practices of S. chamaejasme that are most consistent with the development of S. chamaejasme in degraded grasslands. We found that most of the phenotypic traits and biomass of all organs increased by different patterns with age class. Like many other species, there has been three developmental phases in S. chamaejasme, however, previous researches only focus on the S. chamaejasme in the adult reproductive phase, therefore leading to a delay between the time of S. chamaejasme's seedling and the time when it begins to establish. Our findings demonstrate that S. chamaejasme mainly distributes the biomass to belowground part (RMF and SMF), which is conducive to the survival of S. chamaejasme on degraded grasslands, making mowing fail to eradicate S. chamaejasme in practice. Partial least squares path modeling suggested that nutrient content (N) played a key role in flowering of S. chamaejasme, but the indirect effect was greater than direct effect. The results from this study highlight that control efforts and the management of S. chamaejasme should not only focus on the S. chamaejasme individual in unreproductive phase, but also on the belowground part of plant in reproductive phase.

Spartina alterniflora Leaf and Soil Eco-Stoichiometry in the Yancheng Coastal Wetland.

Carbon, nitrogen, and phosphorus-nutrient and restrictive elements for plant growth and important components of the plant body-are mainly transferred and exchanged between plants and the soil environment. Changes in the carbon, nitrogen, and phosphorus eco-stoichiometry greatly impact the growth and expansion of Spartina alterniflora, and understanding these changes can reveal the nutrient coordination mechanism among ecosystem components. To explore the relationship between leaf and soil eco-stoichiometry and determine the key soil factors that affect leaf eco-stoichiometry, we collected leaf and soil samples of S. alterniflora at different tidal levels (i.e., 1, 3, and 5 km away from the coastline) in a coastal wetland in the Yancheng Elk Nature Reserve, Jiangsu province. We measured the leaf and soil carbon, nitrogen, and phosphorus contents and ratios, as well as the soil salinity and soil organic carbon. The results revealed the following. (1) The leaf stoichiometric characteristics and soil properties of S. alterniflora differed significantly between tidal levels; for example, total carbon, nitrogen, soil organic carbon were detected at their highest levels at 3 km and lowest levels at 5 km. (2) Significant correlations were detected between the leaf stoichiometric characteristics and soil characteristics. Additionally, nitrogen limitation was evident in the study area, as indicated by the nitrogen-phosphorus ratio being less than 14 and the soil nitrogen-phosphorus ratio being less than 1. (3) Soil salinity and the soil carbon-nitrogen ratio were shown to be the key factors that affect the eco-stoichiometric characteristics of S. alterniflora. These findings furthered our understanding of the nutrient distribution mechanisms and invasion strategy of S. alterniflora and can thus be used to guide S. alterniflora control policies formulated by government management departments in China.

The creation of "Ecosystem Core" hypothesis to explain ecosystem evolution.

BACKGROUND: Humans have dramatically changed natural ecosystems around the world as their capacity to manage their environment for multiple uses has evolved in step with agricultural, industrial and green revolutions. Numerous natural ecosystems have been replaced by various artificial or semi-artificial ecosystems, the ecosystem has changed. To a certain extent, this is ecosystem evolution. So far, there is no definite ecological theory about the mechanism for evolution of an ecosystem. Even though the discipline of community ecology has a relatively comprehensive and well-described theory of succession, at the different ecological research levels, is it the same mechanism for the community succession and ecosystem evolution? What is the factor that drives ecosystem evolution? RESULTS: This paper puts forward the "Ecosystem Core" hypothesis to scientifically address the above problems. We define abiotic component of ecosystem as "Ecosystem Core" or "Resource Core", which provides the foundation (matter and energy) for the existence and progress of organisms and should be the nucleus of an ecosystem. In this paper, we explain the basic meaning of this hypothesis, review its theoretical foundation, and provide a demonstration (based on emergy theory, which is an accounting tool that considers both the environmental and economic inputs that are directly or indirectly required by a process to generate a product and it measures real wealth, independent of financial considerations) of the hypothesis, and discuss the mechanism of ecosystem evolution. The "Ecosystem Core" hypothesis reveals the quantitative relationship between the energy input and ecosystem evolution. CONCLUSIONS: The input of artificial auxiliary energy is the direct cause of ecosystem evolution. Different combinations of natural and purchased emergy are coupled to maintain the same ecosystem under the different environmental conditions. When artificial energy enters the ecosystem, its role is similar to that of the microscopic particles that collide with the nucleus in the nuclear reaction, and after mutual reaction, the atom will form a new atomic structure, and for the ecosystem, a new form of resource composition and energy action will appear, and the corresponding species of life will change, then ecosystem complete its evolution.

Spatiotemporal Variation Characteristics of Ecosystem Service Losses in the Agro-Pastoral Ecotone of Northern China.

Being subject to climate change and human intervention, the land-use pattern in the agro-pastoral ecotone of Northern China has undergone complex changes over the past few decades, which may jeopardize the provision of ecosystem services. Thus, for sustainable land management, ecosystem services should be evaluated and monitored. In this study, based on Landsat TM/ETM data, we quantitatively evaluated the losses of ecosystem service values (ESV) in three sections of the agro-pastoral ecotone from 1980-2015. The results were as follows: (1) the main characteristic of the land conversions was that a large area of grassland was converted into cultivated land in the agro-pastoral ecotone; (2) on the spatial scale, the ESV losses of the agro-pastoral ecotone can be called an "inclined surface" in the direction of the northeast to southwest, and the northeastern section of the agro-pastoral ecotone lost more ESV than the middle and northwest sections (p < 0.05), on the temporal scale, the order of losses was 1990-2000 > 1980-1990 > 2000-2015; (3) the agro-pastoral ecotone lost more ESV, which was mainly due to four kinds of land conversion, which were grassland that was transformed into cultivated land, grassland transformed into unused land, grassland transformed into built-up areas, and cultivated land transformed into built-up areas; (4) although these land conversions were curbed after the implementation of protection policies at the end of the 1990s, due to reduced precipitation and increasing temperatures, the agro-pastoral ecotone will face a more severe situation in the future; and, (5) during the period of 1990-2015, the overall dynamic processes of increasing population gradually expanded to the sparsely populated pastoral area. Therefore, we believe that human interventions are the main cause of ecological deterioration in the agro-pastoral ecotone. This study provides references for fully understanding the regional differences in the ecological and environmental effects of land use change and it helps to objectively evaluate ecological civilization construction in the agro-pastoral ecotone of Northern China.

Grazing effects on the nutritive value of dominant species in steppe grasslands of northern China.

BACKGROUND: Forage nutritive value plays an important role in livestock nutrition and maintaining sustainable grassland ecosystems, and grazing management can affect the quality of forage. In this study, we investigated the effects of different grazing intensities on the nutritive values of Leymus chinensis (Trin.) Tzvelev, Artemisia spp. and Carex duriuscula C. A. Mey in the steppes of China during the growing seasons from 2011 to 2013. Five grazing management treatments were implemented: (1) rest grazing in spring, heavy grazing in summer and moderate grazing in autumn (RHM), (2) rest grazing in spring, moderate grazing in summer and heavy grazing in autumn (RMH), (3) heavy grazing though all seasons (HHH), (4) heavy grazing in spring and summer and moderate grazing in autumn (HHM) and (5) continuous moderate grazing in all seasons (MMM). RESULTS: There were significant effects of year, season, treatment, and year × season and year × treatment interactions only on the crude protein of L. chinensis (P < 0.05). The crude protein concentrations of L. chinensis in the plots of constant high grazing pressure (HHH) and reduced grazing pressure in the last grazing stage (HHM) were higher than with deferred grazing (RMH and RHM, P < 0.05) in spring from 2011 to 2012. For Artemisia spp. and C. duriuscula, the crude protein concentration in HHH was higher than that in RMH (P < 0.05) in the summer of 2011. There were no significant differences (P > 0.05) for ether extract, neutral detergent fiber, acid detergent fiber and Ca concentration for any of the grasses in spring and summer from 2011 to 2013 under the different grazing management treatments. CONCLUSIONS: The nutritive value of L. chinensis was more responsive to grazing disturbance than Artemisia spp. and C. duriuscula, and heavy grazing maintained a relatively high crude protein content in all species. Seasonal and interannual seasonal differences in grazing management combinations were two of the most important factors in determining the variability of forage nutritive value, including crude protein, ether extract, neutral detergent fiber, acid detergent fiber and calcium, for L. chinensis, Artemisia spp. and C. duriuscula. We suggest that moderate grazing should be adopted to ensure the quality and yield of forage and promote the sustainable development of animal husbandry.

Effect of grazing on methane uptake from Eurasian steppe of China.

BACKGROUND: The effects of grazing on soil methane (CH4) uptake in steppe ecosystems are important for understanding carbon sequestration and cycling because the role of grassland soil for CH4 uptake can have major impacts at the global level. Here, a meta-analysis of 27 individual studies was carried out to assess the response patterns of soil CH4 uptake to grazing in steppe ecosystems of China. The weighted log response ratio was used to assess the effect size. RESULTS: We found that heavy grazing significantly depressed soil CH4 uptake by 36.47%, but light and moderate grazing had no significant effects in grassland ecosystem. The response of grassland soil CH4 uptake to grazing also was found to depend upon grazing intensity, grazing duration and climatic types. The increase in soil temperature and reduced aboveground biomass and soil moisture induced by heavy grazing may be the major regulators of the soil CH4 uptake. CONCLUSIONS: These findings imply that grazing effects on soil CH4 uptake are highly context-specific and that grazing in different grasslands might be managed differently to help mitigate greenhouse gas emissions.

Stable carbon isotope as a signal index for monitoring grassland degradation.

Grassland degradation due to overgrazing is common in many areas of the world. This study analyzed the potential of the stable carbon isotope (δ(13)C) value as a structural microcosmic index to monitor processes of grassland degradation. The δ(13)C values of plant leaves, roots and soils in non-grazed (NG) and over-grazed (OG) grassland were measured from samples collected from the seven types of grassland in China. We found that the leaf δ(13)C values of palatable species (δ(13)Cleaf) and root δ(13)C values (δ(13)Croot) in OG grasslands were reduced compared with those from NG grasslands. Furthermore, the δ(13)Cleaf and δ(13)Csoil were positive correlation with elevation and latitude, δ(13)Croot was negative correlation with them at high altitude (3000~5000m), and δ(13)Croot and δ(13)Csoil were negative correlation with them at low altitude (0~2000m), respectively. Consequently, tracing of the δ(13)C variations in grassland ecosystem can provide a powerful tool to evaluate the degree of grassland degradation.

Sound management may sequester methane in grazed rangeland ecosystems.

Considering their contribution to global warming, the sources and sinks of methane (CH4) should be accounted when undertaking a greenhouse gas inventory for grazed rangeland ecosystems. The aim of this study was to evaluate the mitigation potential of current ecological management programs implemented in the main rangeland regions of China. The influences of rangeland improvement, utilization and livestock production on CH4 flux/emission were assessed to estimate CH4 reduction potential. Results indicate that the grazed rangeland ecosystem is currently a net source of atmospheric CH4. However, there is potential to convert the ecosystem to a net sink by improving management practices. Previous assessments of capacity for CH4 uptake in grazed rangeland ecosystems have not considered improved livestock management practices and thus underestimated potential for CH4 uptake. Optimal fertilization, rest and light grazing, and intensification of livestock management contribute mitigation potential significantly.