Study on Soil Respiration Characteristics and Carbon Balance of <i>Kobresia pygmaea</i>Meadow in Qinghai-Tibet Plateau, China

Although soil respiration is the largest contributor to C flux from terrestrial ecosystems to the atmosphere, our understanding of its characteristics and carbon budget in alpine meadow is rather limited because of extremely geographic situation. This study was designed to examine soil CO2 efflux characteristics of diurnal and seasonal variation, thus obtaining estimates of carbon balance of Kobresia pygmaea meadow in Qinghai-Tibet plateau. The results showed that the soil respiration of diurnal and seasonal rate changed little in growing season and was mainly affected by temperature, and single peak curve that showed afternoon appeared. Composite model which was set by soil respiration rate, soil moisture content and temperature (atmospheric temperature and soil temperature) could explain better the variations of soil respiration rate. The variation range of Q10 ranged from 1.28 to 2.34, which was sensitive to temperature in green-up period and late growth stage, and decreased in growth peak period. Meanwhile, during the growing seasons the observed amount of annual carbon fixation via primary production for Kobresia pygmaea meadow ecosystem was about 120.21 g C·m-2·a-1. The carbon dioxide output via soil heterotrophic respiration was about 37.54 g C·m-2·a-1. So carbon budget had more input than output. The Kobresia pygmaea meadow ecosystem has stronger potential to absorb carbon dioxide, it was a sink of atmospheric CO2, and the plant community had a net carbon gain of 82.67 g C·m-2·a-1.

The current and future of terrestrial carbon balance over the Tibetan Plateau

The contemporary carbon balance over the Tibetan Plateau is highly uncertain with a ten-fold difference between various estimates.In a warming world,the potential exists for a large carbon release from its permafrost which could compromise China’s 2060 carbon-neutral goal.Here,we used a satellite-and inventory-based approach,ecosystem models,and atmospheric inversions to estimate that the carbon sink was 33.12–37.84 TgC yr^(–1)during 2000–2015.The carbon sink induced by climate change and increasing CO_(2) levels largely overcompensated for a livestock grazing-induced carbon source of 0.38TgC yr^(-1).By 2060,the carbon sink is projected to increase by 38.3–74.5% under moderate to high emissions scenarios,with the enhanced vegetation carbon uptake outweighing the warming-induced permafrost carbon release.The restoration of degraded grassland could sequestrate an additional 9.06 TgC yr^(-1),leading to a total carbon sink of 57.78–70.52 TgC yr^(-1).We conclude that the Tibetan Plateau’s ecosystems absorbed two-and-a-half times the amount of its cumulative fossil CO_(2) emissions during 2000–2015 and that their carbon sinks will almost double in strength in the future,helping to achieve China’s pledge to become carbon neutral by 2060.

Reconciliation of research on forest carbon sequestration and water conservation

Carbon sequestration and water conservation are two of the key ecosystem services that forests provide for societal need to address environmental issues.Optimization of the dual services is the ultimate goal in forest management for mitigating global climate change and safeguarding terrestrial water balance.However,there are some tradeoff s between gain in forest productivity and ecosystem water balance.We conducted literature review based on published articles for learned knowledge on forest carbon fi xation and hydrological regulations.Some knowledge gaps and research needs are identifi ed by examining the inter-connections between forest carbon sequestration and water conservation.Past researches have helped gain basic understanding of the mechanisms and controls of forest carbon fi xation and hydrological regulations as two separate issues.Tools and approaches are well established for quantifying and monitoring forest carbon and hydrological issues,operating at diff erent spatial and temporal scales.There are knowledge gaps on how to design aff orestation schemes facilitating enhanced ecosystem services in forest carbon sequestration and water conservation.For the top-down planning of aff orestation in regions where water availability is anticipated to be problematic,the questions of how much and where to plant for given land availability,known environmental implications,and sustained regional development and livelihood need to be addressed.For local management considerations,the questions of what and how to plant prevail.Eff orts are needed in joint studies of forest carbon sequestration and water conservation functionalities,specifi cally in relation to establishment and management of planted forests aiming for delivering regulatory ecosystem services in carbon sequestration,water conservation and other social values.We propose an integrated framework with dual consideration of carbon sequestration and water conservation in forest management for future research pursue.

Evaluation of reservoir environment by chemical properties of reservoir water‒A case study of Chang 6 reservoir in Ansai oilfield,Ordos Basin,China

The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.

Divergent allocations of nonstructural carbohydrates shape growth response to rainfall reduction in two subtropical plantations

Nonstructural carbohydrates(NSC)are indicators of tree carbon balance and play an important role in regulating plant growth and survival.However,our understanding of the mechanism underlying drought-induced response of NSC reserves remains limited.Here,we conducted a long-term throughfall exclusion(TFE)experiment to investigate the seasonal responses of NSC reserves to manipulative drought in two contrasting tree species(a broadleaved tree Castanopsis hystrix Miq.and a coniferous tree Pinus massoniana Lamb.)of the subtropical China.We found that in the dry season,the two tree species differed in their responses of NSC reserves to TFE at either the whole-tree level or by organs,with significantly depleted total NSC reserves in roots in both species.Under the TFE treatment,there were significant increases in the NSC pools of leaves and branches in C.hystrix,which were accompanied by significant decreases in fine root biomass and radial growth without significant changes in canopy photosynthesis;while P.massoniana exhibited significant increase in fine root biomass without significant changes in radial growth.Our results suggested that under prolonged water limitation,NSC usage for growth in C.hystrix is somewhat impaired,such that the TFE treatment resulted in NSC accumulation in aboveground organs(leaf and branch);whereas P.massoniana is capable of efficiently utilizing NSC reserves to maintain its growth under drought conditions.Our findings revealed divergent NSC allocations under experimental drought between the two contrasting tree species,which are important for better understanding the differential impacts of climate change on varying forest trees and plantation types in subtropical China.

Vegetation phenology and its ecohydrological implications from individual to global scales

The Earth is experiencing unprecedented climate change.Vegetation phenology has already showed strong response to the global warming,which alters mass and energy fluxes on terrestrial ecosystems.With technology and method developments in remote sensing,computer science and citizen science,many recent phenology-related studies have been focused on macrophenology.In this perspective,we 1)reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling,and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn;2)elaborated how vegetation phenology affects ecohydrological processes at different scales,and further listed the key issues for each scale,i.e.,focusing on seasonal effect,local feedbacks and regional vapor transport for individual,watershed and global respectively);3)envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes,in combining with machine learning,deep learning and scale transformation methods.We propose that comprehensive understanding of climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.

Energy and protein requirements for maintenance of Hu sheep during pregnancy

This study aimed to determine the effect of stage and level of feed intake on energy metabolism,carbon-nitrogen(C-N)balance,and methane emission to determine energy and protein requirements for maintenance of maternal body including pregnancy tissues during pregnancy using the method of C-N balance.Twenty-one ewes carrying twin fetuses were randomly divided into three groups of seven ewes each in the digestion and respirometry trial at d 40,100,and 130 of gestation,respectively.Three groups were fed a mixed diet either for ad libitum intake,70 or 50%of the ad libitum intake during pregnancy.The results showed that the apparent digestibility of C and N were increased as feeding levels decreased at each stage of gestation.The daily net energy requirements for maintenance(NE_m)were 295.80,310.09,and 323.59 k J kg^(–1)BW^(0.75)(metabolic body weight)with a partial efficiency of metabolisable energy utilization for maintenance of 0.664,0.644,and 0.620 at d 40,100,and 130 of gestation,respectively.The daily net protein requirements for maintenance were 1.99,2.35,and 2.99 g kg^(–1 )BW^(0.75) at d 40,100,and 130 of gestation,respectively.These results for the nutritional requirements of the net energy and protein may help to formulate more balanced diets for Hu sheep during pregnancy.

China’s Forests and Their Impact on Global Carbon Cycle

Forests have multiple benefits and functions, including mitigation of climate change. The impacts of forests on the global carbon cycle include forests as carbon sinks, wood-based products as carbon sinks, bio-energy, and production and use of non-timber products. In the past decades, forest cover of China has increased from 8.6% to 18.21% by large-scale afforestation and conversion of cropland into forests. Forest biomass carbon (C) stock increased from 4.3 Pg C (1 Pg C = 1 015 g C) in the early 1980s to 5.9 Pg C in the early 2000s. China will continue to invest in forestry sector to strengthen its capacity to respond to global climate change and to increase the capability of carbon sequestration by increasing forest areas and stock, increasing forest bio-energy and non-timber products.

Balancing carbon and water for sustainable revegetation in the Loess Plateau

With the support by the National Natural Science Foundation of China and the Major Programme of High Resolution Earth Observation System,the research team led by Prof.Fu Bojie(傅伯杰)at the State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences of Chinese Academy of Sciences,cooperated with the researchers from Peking University and the Laboratoire