Influence of short-term experimental warming on heat-waterprocesses of the active layer in a swamp meadow ecosystemof the Qinghai-Tibet Plateau

Climate change is now evident in the Qinghai-Tibet Plateau(QTP), with impacts on the alpine ecosystem, particularly on water and heat balance between the active layer and the atmosphere. Thus, we document the basic characteristics of changes in the water and heat dynamics in response to experimental warming in a typical alpine swamp meadow ecosystem. Data sets under open top chambers(OTC) and the control manipulations were collected over a complete year. The results show that annual(2008) air temperatures of OTC-1 and OTC-2 were 6.7 °C and 3.5 °C warmer than the control. Rising temperature promotes plant growth and development. The freeze-thaw and isothermal days of OTCs appeared more frequently than the control, owing to comparably higher water and better vegetation conditions. OTCs soil moisture decreased with the decrease of soil depth; however, there was an obviously middle dry aquifer of the control, which is familiar in QTP. Moreover, experimental warming led to an increase in topsoil water content due to poorly drained swamp meadow ecosystem with higher organic matter content and thicker root horizons. The results of this study will have some contributions to alpine cold ecosystem water-heat process and water cycle under climate change.

Effect of open-field experimental warming on the leaf phenology of oriental oak (Quercus variabilis) seedlings

Aims An open-field warming experiment enables us to test the effects of projected temperature increase on change in plant phenology with fewer confounding factors and to study phenological response to temperature ranges beyond natural variability.This study aims to(i)examine the effect of temperature increase on leaf unfold-ing and senescence of oriental oak(Quercus variabilis Blume)under experimental warming and(ii)measure temperature-related parameters used in estimating phenological response to tempera-ture elevation.Methods Using an open-field warming system with infrared heaters,we increased the air temperature by~3℃ in the warmed plots compared with that of the control plots consistently for 2 years.Leaf unfolding and senescence dates of Q.variabilis seedlings were recorded and temperature-related phenological parameters were analysed.Important Findings The timing of leaf unfolding was advanced by 3-8 days(1.1-3.0 days/℃)and the date of leaf senescence was delayed by 14-19 days(5.0-7.3 days/℃)under elevated air temperatures.However,the cumulative degree days(CDD)of leaf unfolding were not significantly changed by experimental warming,which suggest the applicability of a constant CDD value to estimate the change in spring leaf phe-nology under 3℃ warming.Consistent ranges of advancement and temperature sensitivity in spring phenology and delayed autumn phe-nology and proposed temperature parameters from this study might be applied to predict future phenological change.

“Warming yang and invigorating qi” acupuncture alters acetylcholine receptor expression in the neuromuscular junction of rats with experimental autoimmune myasthenia gravis

Myasthenia gravis is an autoimmune disorder in which antibodies have been shown to form against the nicotinic acetylcholine nicotinic postsynaptic receptors located at the neuromuscular junction.＂Warming yang and invigorating qi＂ acupuncture treatment has been shown to reduce serum inflammatory cytokine expression and increase transforming growth factor beta expression in rats with experimental autoimmune myasthenia gravis.However,few studies have addressed the effects of this type of acupuncture on the acetylcholine receptors at the neuromuscular junction.Here,we used confocal laser scanning microscopy to examine the area and density of immunoreactivity for an antibody to the nicotinic acetylcholine receptor at the neuromuscular junction in the phrenic nerve of rats with experimental autoimmune myasthenia gravis following ＂warming yang and invigorating qi＂ acupuncture therapy.Needles were inserted at acupressure points Shousanli（LI10）,Zusanli（ST36）,Pishu（BL20）,and Shenshu（BL23） once daily for 7 consecutive days.The treatment was repeated after 1 day of rest.We found that area and the integrated optical density of the immunoreactivity for the acetylcholine receptor at the neuromuscular junction of the phrenic nerve was significantly increased following acupuncture treatment.This outcome of the acupuncture therapy was similar to that of the cholinesterase inhibitor pyridostigmine bromide.These findings suggest that ＂warming yang and invigorating qi＂ acupuncture treatment increases acetylcholine receptor expression at the neuromuscular junction in a rat model of autoimmune myasthenia gravis.

Positive adaptation of Salix eriostachya to warming in the treeline ecotone,East Tibetan Plateau

Understanding of treeline ecotone ecophysiological adaptation to climate warming is still very limited. Furthermore, it is difficult to predict which plant species could dominate in the future. For this reason, a study was conducted in the treeline ecotone, East Tibetan Plateau to detect the adaptation of the dwarf willow(Salix eriostachya) to experimental warming. Compared to ambient conditions, the experimental warming advanced the bud break by 12 days, delayed the leaf abscission by20 days, and prolonged the growing period by 28 days.It also increased photosynthesis(47%), number of leaves(333%), leaf area(310%), and carbon sequestration of the dwarf willow. Experimental warming did not affect carbon use efficiency, but decreased water use efficiency significantly.Experimental warming enhanced the clonal ramets of Salix eriostachya(+ 3.7 shrubs m-2). The frequent air temperature fluctuations had minor effect on Salix eriostachya. Based on these findings, we highlighted that Salix eriostachya could dominate in the community treeline ecotone of east Tibetan Plateau in the future climate warming scenario.

Warming Changed Soil Respiration Dynamics of Alpine Meadow Ecosystem on the Tibetan Plateau

Alpine meadow system underlain by permafrost on the Tibetan Plateau contains vast soil organic carbon and is sensitive to global warming.However,the dynamics of annual soil respiration(Rs)under long-term warming and the determined factors are still not very clear.Using opentop chambers(OTC),we assessed the effects of two-year experimental warming on the soil CO2 emission and the Q10 value(temperature sensitivity coefficient)under different warming magnitudes.Our study showed that the soil CO2 efflux rate in the warmed plots were 1.22 and 2.32 times higher compared to that of controlled plots.However,the Q10 value decreased by 45.06%and 50.34%respectively as the warming magnitude increased.These results suggested that soil moisture decreasing under global warming would enhance soil CO2 emission and lower the temperature sensitivity of soil respiration rate of the alpine meadow ecosystem in the permafrost region on the Tibetan Plateau.Thus,it is necessary to take into account the combined effect of ground surface warming and soil moisture decrease on the Rs in order to comprehensively evaluate the carbon emissions of the alpine meadow ecosystem,especially in short and medium terms.

Leaf photosynthesis and simulated carbon budget of Gentiana straminea from a decade-long warming experiment

Aims Alpine ecosystems may experience larger temperature increases due to global warming as compared with lowland ecosystems.Information on physiological adjustment of alpine plants to temperature changes can provide insights into our understanding how these plants are responding to current and future warming.We tested the hypothesis that alpine plants would exhibit acclimation in photosynthesis and respiration under long-term elevated temperature,and the acclimation may relatively increase leaf carbon gain under warming conditions.Methods Open-top chambers(OTCs)were set up for a period of 11 years to artificially increase the temperature in an alpine meadow ecosystem.We measured leaf photosynthesis and dark respiration under different light,temperature and ambient CO_(2)concentrations for Gentiana straminea,a species widely distributed on the Tibetan Plateau.Maximum rates of the photosynthetic electron transport(J_(max)),RuBP carboxylation(V_(cmax))and temperature sensitivity of respiration Q10 were obtained from the measurements.We further estimated the leaf carbon budget of G.straminea using the physiological parameters and environmental variables obtained in the study.Important findings 1)The OTCs consistently elevated the daily mean air temperature by;1.6℃and soil temperature by;0.5℃during the growing season.2)Despite the small difference in the temperature environment,there was strong tendency in the temperature acclimation of photosynthesis.The estimated temperature optimum of light-saturated photosynthetic CO_(2)uptake(A_(max))shifted;1℃higher from the plants under the ambient regime to those under the OTCs warming regime,and the Amax was significantly lower in the warming-acclimated leaves than the leaves outside the OTCs.3)Temperature acclimation of respiration was large and significant:the dark respiration rates of leaves developed in the warming regime were significantly lower than leaves from the ambient environments.4)The simulated net leaf carbon gain was significantly lower in the in situ leaves under the OTCs warming regime than under the ambient open regime.However,in comparison with the assumed non-acclimation leaves,the in situ warmingacclimated leaves exhibited significantly higher net leaf carbon gain.5)The results suggest that there was a strong and significant temperature acclimation in physiology of G.straminea in response to long-term warming,and the physiological acclimation can reduce the decrease of leaf carbon gain,i.e.increase relatively leaf carbon gain under the warming condition in the alpine species.

The effects of climate warming on microbe-mediated mechanisms of sediment carbon emission

Due to significant differences in biotic and abiotic properties of soils compared to those of sediments,the predicted underlying microbe-mediated mechanisms of soil carbon emissions in response to warming may not be applicable for estimating similar emissions from inlandwater sediments.We addressed this issue by incubating different types of sediments,(including lake,small river,and pond sediments)collected from 36 sites across the Yangtze River basin,under short-term experimentalwarming to explore the effects of climatewarming on sediment carbon emission and the underlying microbe-mediated mechanisms.Our results indicated that under climate warming Cc emissions were affected more than CH_(4) emissions,and that pond sediments may yield a greater relative contribution of CO_(2) to total carbon emissions than lake and river sediments.Warming-induced CO_(2) and CH_(4) increases involve different microbe-mediated mechanisms;Warming-induced sediment CO_(2) emissions were predicted to be directly positively driven by microbial community network modularity,which was significantly negatively affected by the quality and quantity of organic carbon and warming-induced variations in dissolved oxygen,Conversely,warminginduced sediment CH_(4) emissionswere predicted to be directly positively driven bymicrobial community network complexity,which was significantly negatively affected by warminginduced variations in pH.Our findings suggest that biotic and abiotic drivers for sediment CO_(2) and CH_(4) emissions in response to climate warming should be considered separately when predicting sediment organic carbon decomposition dynamics resulting from climate change.

Temperature Responses to Infrared-Loading and Water Table Manipulations in Peatland Mesocosms

We initiated a multi-factor global change experiment to explore the effects of infrared heat loading （HT） and water table level （WL） treatment on soil temperature （T） in bog and fen peatland mesocosms. We found that the temperature varied highly by year, month, peatland type, soil depth, HT and WL manipulations. The highest effect of HT on the temperature at 25 cm depth was found in June for the bog mesocosms （3.34-4.27 ℃） but in May for the fen mesocosms （2.32-4.33 ℃） over the 2-year study period. The effects of WL in the bog mesocosms were only found between August and January, with the wet mesocosms warmer than the dry mesocosms by 0.48-2.03 ℃ over the 2-year study period. In contrast, wetter fen mesocosms were generally cooler by 0.16-3.87℃. Seasonal changes of temperatures elevated by the HT also varied by depth and ecosystem type, with temperature differences at 5 cm and 10 cm depth showing smaller seasonal fluctuations than those at 25 cm and 40 cm in the bog mesocosms. However, increased HT did not always lead to warmer soil, especially in the fen mesocosms. Both HT and WL manipulations have also changed the length of the non-frozen season.