Background Stable carbon isotope composition (delta C-13(p)) can be used to estimate the changes in intrinsic water use efficiency (iWUE) in plants, which helps us to better understand plants' response strategies to climate change. This study focused on the variations in delta C-13(p) and iWUE for the different life-form plants (i.e., herbs, shrubs, and trees) along an altitudinal gradient (3300, 3600, 3900, 4100, 4300, and 4500 m) on the eastern slope of Yulong Snow Mountain, southeastern margin of the Qinghai-Tibet Plateau. The response mechanisms of delta C-13(p) and iWUE for different life-form plants to altitude were thoroughly analyzed in this mountain ecosystem. Results The delta C-13(p) values of plants on the eastern slopes of Yulong Snow Mountain ranged from - 30.4 parts per thousand to - 26.55 parts per thousand, with a mean of - 28.02 parts per thousand, indicating a dominance of C-3 plants. The delta C-13(p) and iWUE values varied among different life-form plants in the order of herbs > shrubs > trees, particularly in 3600, 3900, and 4300 m. The delta C-13(p) and iWUE values for herbs and shrubs increased with altitude and were mainly controlled by air temperature. The two parameters for trees exhibited a trend of initial decrease followed by an increase with altitude. Below 3900 m, the delta C-13(p) and iWUE values decreased with altitude, influenced by soil moisture. However, above 3900 m, the two parameters increased with altitude, mainly regulated by air temperature. In addition, iWUE was positively correlated with leaf P content but negatively correlated with leaf N:P ratio, especially for herbs and trees, suggesting that P plays a key role in modulating iWUE in this region. Conclusions The differentiated responses of water availability for different life-form plants to a higher altitudinal gradient are regulated by air temperature, soil moisture, and leaf P content in the Yulong Snow Mountain. These results provide valuable insights into understanding the water-carbon relationships in high-altitude ecosystems.

The Indo-Gangetic Plain (IGP) is a major regional and global emitter of atmospheric pollutants, which adversely affect surrounding areas such as the Himalayas. We present a comprehensive dataset on carbonaceous aerosol (CA) composition, radiocarbon (D14C) -based source apportionment, and light absorption of total suspended particle (TSP) samples collected over a 3--year period from high-altitude Jomsom in the central Himalayas. The 3-year mean TSP, organic carbon (OC), and elemental carbon (EC) concentrations were 92.0 +/- 28.6, 9.74 +/- 6.31, and 2.02 +/- 1.35 lg m-3, respectively, with the highest concentrations observed during the pre-monsoon season, followed by the post-monsoon, winter, and monsoon seasons. The D14C analysis revealed that the contribution of fossil fuel combustion (ffossil) to EC was 47.9% +/- 11.5%, which is consistent with observations in urban and remote regions in South Asia and attests that EC likely arrives in Jomsom from upwind IGP sources via long-range transport. In addition, the lowest ffossil (38.7% +/- 13.3%) was observed in winter, indicating large contributions in this season from local biomass burning. The mass absorption cross- of EC (MACEC: 8.27 +/- 1.76 m2/g) and watersoluble organic carbon (MACWSOC: 0.98 +/- 0.45 m2/g) were slightly higher and lower than those reported in urban regions, respectively, indicating that CA undergo an aging process. Organic aerosol coating during transport and variation of biomass burning probably led to the seasonal variation in MAC of two components. Overall, WSOC contributed considerably to the light absorption (11.1% +/- 4.23%) of EC. The findings suggest that to protect glaciers of the Himalayas from pollution-related melting, it is essential to mitigate emissions from the IGP.(c) 2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Recent climatic changes significantly affected forest ecosystems in northern Eurasia. Trees growing in Siberia are very sensitive to climate change due to strong temperature limitation of their growth. Our study covers high-latitude (northeastern Yakutia, eastern Taimyr, central Evenkia) and high-altitude (Russian Altai) zones in Eurasia, where tree-ring parameters (tree-ring width, cell-wall thickness, and maximum latewood density) mainly record summer air temperature variations. To reveal the impact of moisture changes (e.g., amount of precipitation, vapor pressure deficit, relative humidity and potential evapotranspiration) on tree growth in Siberian forest ecosystems, we evaluated delta C-13 in tree-ring cellulose over the past century. We found that at all the study sites mainly June-July precipitation and June-July evapotranspiration affect larch radial growth, while the strongest influence of vapor pressure deficit on the delta C-13 was observed in northeastern Yakutia. Further increase of vapor pressure deficit and rise of air temperature in the coming decades in Siberian regions will probably lead to drought and related forest mortality even under additional source of water due to permafrost thaw.

Carbon-climate feedback is sensitive in the Qinghai-Tibet Plateau. A series of temporal measurements from Jinsha River and Yalong River, in conjunction with flow information, were used to study the carbon dynamics and predict future carbon fluxes under ongoing climate change. DIC and DOC concentrations showed considerable temporal variations, with low DIC and high DOC concentrations in the high-flow season, and vice versa. DIC and DOC concentrations had negative and positive relationships with runoff changes, respectively, showing the hydro-biogeochemical controls on carbon dynamics. With the increase of runoff, the accelerated chemical weathering and the high carbonate buffering capacity should be responsible for the chemostatic behaviors of DIC. Meanwhile, warm weather would enhance organic carbon degradation, and also thicken the active layer of permafrost in the source area, both of which would produce DOC. In addition, organic carbon degradation in the high-flow season would produce DIC with C-13-depleted values. delta C-13(DIC) also had significant temporal variations, synchronous with runoff changes (i.e., light values under high runoff conditions), supporting that biological carbon plays an important role in carbon dynamics during the warm season. Based on the clear positive correlations between carbon fluxes and runoff, we predicted that the sensitivities of DOC fluxes to temperature changes are 12.2%/degrees C and 8.3%/degrees C for the Jinsha River and Yalong River, respectively. The sensitivities of DIC fluxes to temperature changes are much lower, which are 5.5%/degrees C and 6.1%/degrees C for the Jinsha River and Yalong River, respectively. This study sheds lights on the alpine riverine carbon cycling based on runoff-shifting concentration-isotope (q-C-I) relationships in the Qinghai-Tibet Plateau, which has implications on the understanding of climate forcing on carbon fluxes in alpine areas.

Almost half of the global terrestrial soil carbon (C) is stored in the northern circumpolar permafrost region, where air temperatures are increasing two times faster than the global average. As climate warms, permafrost thaws and soil organic matter becomes vulnerable to greater microbial decomposition. Long-term soil warming of ice-rich permafrost can result in thermokarst formation that creates variability in environmental conditions. Consequently, plant and microbial proportional contributions to ecosystem respiration may change in response to long-term soil warming. Natural abundance delta C-13 and Delta C-14 of aboveground and belowground plant material, and of young and old soil respiration were used to inform a mixing model to partition the contribution of each source to ecosystem respiration fluxes. We employed a hierarchical Bayesian approach that incorporated gross primary productivity and environmental drivers to constrain source contributions. We found that long-term experimental permafrost warming introduced a soil hydrology component that interacted with temperature to affect old soil C respiration. Old soil C loss was suppressed in plots with warmer deep soil temperatures because they tended to be wetter. When soil volumetric water content significantly decreased in 2018 relative to 2016 and 2017, the dominant respiration sources shifted from plant aboveground and young soil respiration to old soil respiration. The proportion of ecosystem respiration from old soil C accounted for up to 39% of ecosystem respiration and represented a 30-fold increase compared to the wet-year average. Our findings show that thermokarst formation may act to moderate microbial decomposition of old soil C when soil is highly saturated. However, when soil moisture decreases, a higher proportion of old soil C is vulnerable to decomposition and can become a large flux to the atmosphere. As permafrost systems continue to change with climate, we must understand the thresholds that may propel these systems from a C sink to a source.

Climate warming is expected to destabilize permafrost carbon (PF-C) by thaw-erosion and deepening of the seasonally thawed active layer and thereby promote PF-C mineralization to CO2 and CH4. A similar PF-C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Delta C-14, delta C-13, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS-L2-4-PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerod warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual-carbon-isotope-based source apportionment demonstrates that Ice Complex Deposit-ice- and carbon-rich permafrost from the late Pleistocene (also referred to as Yedoma)-was the dominant source of organic carbon (66 +/- 8%; mean +/- standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 +/- 4.6 g.m(-2).year(-1)) as in the late Holocene (3.1 +/- 1.0 g.m(-2).year(-1)). These results are consistent with late deglacial PF-C remobilization observed in a Laptev Sea record, yet in contrast with PF-C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF-C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.

The Arctic has experienced rapid warming and, although there are uncertainties, increases in precipitation are projected to accompany future warming. Climate changes are expected to affect magnitudes of gross ecosystem photosynthesis (GEP), ecosystem respiration (ER) and the net ecosystem exchange of CO2 (NEE). Furthermore, ecosystem responses to climate change are likely to be characterized by nonlinearities, thresholds and interactions among system components and the driving variables. These complex interactions increase the difficulty of predicting responses to climate change and necessitate the use of manipulative experiments. In 2003, we established a long-term, multi-level and multi-factor climate change experiment in a polar semidesert in northwest Greenland. Two levels of heating (30 and 60Wm2) were applied and the higher level was combined with supplemental summer rain. We made plot-level measurements of CO2 exchange, plant community composition, foliar nitrogen concentrations, leaf 13C and NDVI to examine responses to our treatments at ecosystem- and leaf-levels. We confronted simple models of GEP and ER with our data to test hypotheses regarding key drivers of CO2 exchange and to estimate growing season CO2-C budgets. Low-level warming increased the magnitude of the ecosystem C sink. Meanwhile, high-level warming made the ecosystem a source of C to the atmosphere. When high-level warming was combined with increased summer rain, the ecosystem became a C sink of magnitude similar to that observed under low-level warming. Competition among our ER models revealed the importance of soil moisture as a driving variable, likely through its effects on microbial activity and nutrient cycling. Measurements of community composition and proxies for leaf-level physiology suggest GEP responses largely reflect changes in leaf area of Salix arctica, rather than changes in leaf-level physiology. Our findings indicate that the sign and magnitude of the future High Arctic C budget may depend upon changes in summer rain.

We studied the relationships between earlywood/latewood width, stable carbon isotope ratio (delta(13)C) of cellulose, and soil moisture at a dry and a wet site in Yakutsk, eastern Siberia, which differed considerably in soil water conditions. Recharge of soil water by snowmelt in spring and subsequent drought in summer provided a marked seasonal contrast in soil water conditions between the earlywood and latewood formation period. Ring index was calculated by dividing each earlywood/latewood width by the 5-year averaged width for each individual. In order to determine whether drought influenced the ring index-delta(13)C relation, the ring index time series were compared with delta(13)C time series. We collected wood samples from eight Larix gmelinii (Rupr.) Rupr. and four Pinus sylvestris L. trees from the two sites and measured the earlywood and latewood widths and delta(13)C of earlywood and latewood formed during the years 1996-2000. At the dry site, seasonal soil water content variation corresponded to seasonal delta(13)C variation of tree rings. We found negative ring index-delta(13)C correlations in latewood for both species at the dry site mainly dominated by Pinus but not in latewood of Larix at the wet site dominated by Larix. Decrease and/or early cessation of latewood growth and increase in delta(13)C under drought conditions possibly explain this negative correlation. This suggests the growth limitation of trees in this region by drought and the prospects of reconstructing past drought with latewood delta(13)C of the dry site.