Effect of rain enrichment on soil respiration of Nitraria sphaerocarpa community in a hyperarid area

In order to analyze the effect of rain enrichment on soil respiration rate of a Nitraria sphaerocarpa community, we measured soil respiration rate in bare and vegetated areas in a hyperarid area （Dunhuang） during the growing season. Results show that rain enrichment can increase bare and vegetated soil respiration rates. The more rainfall enrichment, the greater the increment and the longer duration time effect for soil respiration rate. 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase bare soil respiration rates by 90% and 106% （P〈0.01）, respectively. By contrast, areas with 100% （8 mm）, 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase shrub area respiration rates by 68%, 157% and 205% （P〈0.01）, respectively. The response time of bare and vegetated soil respiration to rainfall enrichment is asynchronous. Response variable of soil respiration in vegetated soil is higher （118%） than in bare soil. There was significant positive correlation between soil respiration rate and soil water content during the growing season （P〈0.01）. For every 1 mm increment of precipitation, soil respiration rate increased by 0.01 and 0.04 pmol/（m2.s）, respectively in vegetated and bare soils.

Coastal blue carbon in China as a nature-based solution toward carbon neutrality

To achieve the Paris Agreement,China pledged to become“Carbon Neutral”by the 2060s.In addition to massive decarbonization,this would require significant changes in ecosystems toward negative CO_(2)emissions.The ability of coastal blue carbon ecosystems(BCEs),including mangrove,salt marsh,and seagrass meadows,to sequester large amounts of CO_(2)makes their conservation and restoration an important“nature-based solution(NbS)”for climate adaptation and mitigation.In this review,we examine how BCEs in China can contribute to climate mitigation.On the national scale,the BCEs in China store up to 118 Tg C across a total area of 1,440,377 ha,including over 75%as unvegetated tidal flats.The annual sedimental C burial of these BCEs reaches up to 2.06 Tg C year^(−1),of which most occurs in salt marshes and tidal flats.The lateral C flux of mangroves and salt marshes contributes to 1.17 Tg C year^(−1)along the Chinese coastline.Conservation and restoration of BCEs benefit climate change mitigation and provide other ecological services with a value of$32,000 ha^(−1)year^(−1).The potential practices and technologies that can be implemented in China to improve BCE C sequestration,including their constraints and feasibility,are also outlined.Future directions are suggested to improve blue carbon estimates on aerial extent,carbon stocks,sequestration,and mitigation potential.Restoring and preserving BCEs would be a cost-effective step to achieve Carbon Neutral by 2060 in China despite various barriers that should be removed.

Recent progresses in mangrove conservation,restoration and research in China

Aims In this paper,we highlighted some key progresses in mangrove conservation,restoration and research in China during last two decades.Methods Based on intensive literature review,we compared the distribution and areas of existing mangroves among selected provinces of China,discussed the issues associated with mangrove conservation and restoration and highlighted major progresses on mangrove research conducted by key institutions or universities in China's Mainland,Hong Kong,Taiwan and Macao.Important findings The population boom and rapid economic developments have greatly reduced mangrove areas in China since 1980s,leaving only 22700 ha mangroves in China's Mainland in 2001.Chinese government has launched a series of programs to protect mangroves since 1980s and has established mangrove ecosystems as high-priority areas for improving environmental and living resource management.During last three decades,a total of 34 natural mangrove conservation areas have been established,which accounts for 80%of the total existing mangroves areas in China.Mangrove restoration areas in China' Mainland accounted for<7%of the total mangroves areas in 2002.A great deal of research papers on Chinese mangroves has been published in international journals.However,more systematic protection strategies and active restoration measurements are still urgently needed in order to preserve these valuable resources in China.

Methylmercury and sulfate-reducing bacteria in mangrove sediments from Jiulong River Estuary,China

Estuaries are important sites for mercury （Hg） methylation, with sulfate-reducing bacteria （SRB） thought to be the main Hg methylators. Distributions of total mercury （THg） and methylmercury （MeHg） in mangrove sediment and sediment core from Jiulong River Estuary Provincial Mangrove Reserve, China were determined and the possible mechanisms of Hg methylation and their controlling factors in mangrove sediments were investigated. Microbiological and geochemical parameters were also determined. Results showed that SRB constitute a small fraction of total bacteria （TB） in both surface sediments and the profile of sediments. The content of THg, MeHg, TB, and SRB were （350 ± 150） ng/g, （0.47 ± 0.11） ng/g, （1.4× 10^011 ± 4.1 × 10^9） cfu/g dry weight （dw）, and （5.0× 10^6 d： 2.7 × 10^6） cfu/g dw in surficial sediments, respectively, and （240 ± 24） ng/g, （0.30 ± 0.15） ng/g, （1.9 × 10^11 ± 4.2 × 10^9） cfu/g dw, and （1.3 × 10^6 ± 2.0 × 10^6） cfu/g dw in sediment core, respectively. Results showed that THg, MeHg, TB, MeHg/THg, salinity and total sulfur （TS） increased with depth, but total organic matter （TOM）, SRB, and pH decreased with depth. Concentrations of MeHg in sediments showed significant positive correlation with THg, salinity, TS, and MeHg/THg, and significant negative correlation with SRB, TOM, and pH. It was concluded that other microbes, rather than SRB, may also act as main Hg methylators in mangrove sediments.

Carbon pools and fluxes in the China Seas and adjacent oceans

The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km^2 from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semiclosed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea,Yellow Sea, East China Sea, and South China Sea, including different interfaces(land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems(mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO_2 sources, releasing about0.22 and 13.86–33.60 Tg C yr^(-1) into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92–23.30 Tg C yr^(-1) of atmospheric CO_2, respectively. Overall, if only the CO_2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO_2, with a net release of 6.01–9.33 Tg C yr^(-1), mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon (DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr^(-1),respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr^(-1), significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr^(-1), respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr^(-1), respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36–1.75 Tg C yr^(-1), with a dissolved organic carbon(DOC) output from seagrass beds of up to 0.59 Tg C yr^(-1). Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr^(-1) and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr^(-1), respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72–104.56 Tg C yr^(-1). The DOC efflux from the East China Sea to the adjacent oceans is 15.00–35.00 Tg C yr^(-1). The DOC efflux from the South China Sea is 31.39 Tg C yr^(-1). Although the marginal China Seas seem to be a source of atmospheric CO_2 based on the CO_2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export,and microbial carbon pump(DOC conversion and output) indicate that the China Seas represent an important carbon storage area.

Responses of soil respiration to simulated precipitation pulses in semiarid steppe under different grazing regimes

Aims Precipitation pulses and different land use practices(such as grazing)play important roles in regulating soil respiration and carbon balance of semiarid steppe ecosystems in Inner Mongolia.However,the interactive effects of grazing and rain event magnitude on soil respiration of steppe ecosystems are still unknown.We conducted a manipulative experiment with simulated precipitation pulses in Inner Mongolia steppe to study the possible responses of soil respiration to different precipitation pulse sizes and to examine how grazing may affect the responses of soil respiration to precipitation pulses.Methods Six water treatments with different precipitation pulse sizes(0,5,10,25,50 and 100 mm)were conducted in the ungrazed and grazed sites,respectively.Variation patterns of soil respiration of each treatment were determined continuously after the water addition treatments.Important Findings Rapid and substantial increases in soil respiration occurred 1 day after the water treatments in both sites,and the magnitude and duration of the increase in soil respiration depended on pulse size.Significantly positive relationships between the soil respiration and soil moisture in both sites suggested that soil moisture was the most important factor responsible for soil respiration rate during rain pulse events.The ungrazed site maintained significantly higher soil moisture for a longer time,which was the reason that the soil respiration in the ungrazed site was maintained relatively higher rate and longer period than that in the grazed site after a rain event.The significant exponential relationship between soil temperature and soil respiration was found only in the plots with the high water addition treatments(50 and 100 mm).Lower capacity of soil water holding and lower temperature sensitivity of soil respiration in the grazed site indicated that degraded steppe due to grazing might release less CO_(2) to the atmosphere through soil respiration under future precipitation and temperature scenarios.

Biophysical regulations of NEE light response in a steppe and a cropland in Inner Mongolia

Aims Ecosystem carbon models often require accurate net ecosystem exchange of CO_(2)(NEE)light-response parameters,which can be derived from the Michaelis–Menten equation.These parameters include maximum net ecosystem exchange(NEE_(max)),apparent quantum use efficiency(a)and daytime ecosystem respiration rate(R_(e)).However,little is known about the effects of land conversion between steppe and cropland on these parameters,especially in semi-arid regions.To understand how these parameters vary in responses to biotic and abiotic factors under land conversions,seasonal variation of light-response parameters were evaluated for a steppe and a cropland of Inner Mongolia,China,during three consecutive years(2006–08)with different precipitation amounts.Methods NEE was measured over a steppe and a cropland in Duolun,Inner Mongolia,China,using the eddy covariance technique,and NEE light-response parameters(NEE_(max),α and R_(e))were derived using the Michaelis–Menten model.Biophysical regulations of these parameters were evaluated using a stepwise regression analysis.Important Findings The maximum absolute values of NEE_(max) occurred in the meteorological regimes of 15℃<T_(a)<25℃,vapor pressure deficit(VPD)<1 KPa and 0.21 m^(3) m^(-3)<volumetric soil water content at 10 cm(SWC)<0.28 m^(3) m^(-3) for both the steppe and the cropland ecosystems.The variations of α and R_(e) showed no regular variation pattern in different T_(air),VPD and SWC regimes.Under the same regime of T_(air),VPDand SWC,the cropland had higher absolute values of NEE_(max) than the steppe.Canopy conductance and leaf area index(LAI)were dominant drivers for variations in NEE light-response parameters of the steppe and the cropland.The seasonal variation of NEE light-response parameters followed the variation of LAI for two ecosystems.The peak values of all light-response parameters for the steppe and the cropland occurred fromJuly to August.The values of NEE light-response parameters(NEE_(max),α and R_(e))were lower in the driest year(2007).Seasonally averaged NEE light-response parameters for the cropland surpassed those for the steppe.Land conversion from steppe to cropland enhanced NEE light-response parameters during the plant growing period.These results will have significant implications for improving the models on regional NEE variation under climate change and land-use change scenarios.

Editorial

Launched by the Oxford University Press on behalf of the Botanical Society of China and the Institute of Botany of Chinese Academy of Sciences,the new Journal of Plant Ecology(JPE)publishes original research articles,reviews and forum pieces covering the entire field of plant ecology.We feel there is a great need for this journal in a time when many other journals are only able to publish a small amount of suitable manuscripts,often those for which they expect the highest impact in terms of citations.To achieve this,these journals focus on concepts and novelty.However,science,in particular the science of ecology,does not simply advance by accumulating concepts and novelty.In the long run,it is the sound results obtained in well-designed studies with sufficient replication and careful measurement and analysis which increase the base of knowledge on which interpretation,understanding and eventually the advancement of science depend.A key criterion by which sound scientific results can be judged is repeatability(a contrast to novelty!).One of the greatest threats to scientific advancement is nonpublication and exclusion of results from subsequent synthesis.By publishing sound scientific results,JPE aims to contribute to the advancement of plant ecology beyond concepts and novelty.