The impacts of alternating dry and wet conditions on water production and carbon uptake at different scales remain unclear, which limits the integrated management of water and carbon. We quantified the response of runoff efficiency (RE) and plant water-use efficiency (PWUE) to a typical shift from dry to wet episode of 2003-2014 in Australia's Murray-Darling basin using good and specific data products for local application, including Australian Water Availabil-ity Project, Penman-Monteith-Leuning Evapotranspiration V2 product, MODIS MCD12Q1 V6 Land Cover Type and MODIS MOD17A3 V055 GPP product. The results show that there are significant power function relationships be-tween RE and precipitation for basin and all ecosystems, while the PWUE had a negative quadratic correlation with precipitation and satisfied the significance levels of 0.05 for basin and the ecosystems except the grassland and crop-land. The shrubs can achieve the best water production and carbon uptake under dry conditions, while the evergreen broadleaf trees and evergreen needleleaf trees can obtain the best water production and carbon uptake in wet condi-tions, respectively. These findings help integrated basin management for balancing water resource production and climate change mitigation.

Warming in the Arctic accelerates top-soil decomposition and deep-soil permafrost thaw. This may lead to an increase in plant-available nutrients throughout the active layer soil and near the permafrost thaw front. For nitrogen (N) limited high arctic plants, increased N availability may enhance growth and alter community composition, importantly affecting the ecosystem carbon balance. However, the extent to which plants can take advantage of this newly available N may be constrained by the following three factors: vertical distribution of N within the soil profile, timing of N-release, and competition with other plants and microorganisms. Therefore, we investigated species- and depth-specific plant N uptake in a high arctic tundra, northeastern Greenland. Using stable isotopic labelling (N-15-NH4+), we simulated autumn N-release at three depths within the active layer: top (10 cm), mid (45 cm) and deep-soil near the permafrost thaw front (90 cm). We measured plant species-specific N uptake immediately after N-release (autumn) and after 1 year, and assessed depth-specific microbial N uptake and resource partitioning between above- and below-ground plant parts, microorganisms and soil. We found that high arctic plants actively foraged for N past the peak growing season, notably the graminoidKobresia myosuroides. While most plant species (Carex rupestris,Dryas octopetala,K. myosuroides) preferred top-soil N, the shrubSalix arcticaalso effectively acquired N from deeper soil layers. All plants were able to obtain N from the permafrost thaw front, both in autumn and during the following growing season, demonstrating the importance of permafrost-released N as a new N source for arctic plants. Finally, microbial N uptake markedly declined with depth, hence, plant access to deep-soil N pools is a competitive strength. In conclusion, plant species-specific competitive advantages with respect to both time- and depth-specific N-release may dictate short- and long-term plant community changes in the Arctic and consequently, larger-scale climate feedbacks.

Soil moisture plays a vital role in regulating the direction and magnitude of methane (CH4) fluxes. However, it remains unclear whether the responses of CH4 fluxes to climate warming exhibit difference between dry and moist ecosystems. Based on standardized manipulative experiments (i.e., consistent experimental design and measurement protocols), here we explored warming effects on growing season CH4 fluxes in two alpine grasslands with contrasting water status on the Tibetan Plateau. We observed that experimental warming enhanced CH4 uptake in the relatively arid alpine steppe, but had no significant effects on CH4 emission in the moist swamp meadow. The distinct responses of CH4 fluxes were associated with the different warming effects on biotic and abiotic factors related to CH4 oxidation and production processes. Warming decreased soil water-filled pore space (WFPS) and increased the pmoA gene abundance and CH4 oxidation potential in the alpine steppe, which together led to a significant increase in CH4 uptake at this alpine steppe site. However, warming-induced enhancement in CH4 oxidation potential might be counteracted by the simultaneously increased CH4 production potential in the swamp meadow, which could then result in insignificant warming effects on CH4 emission at this swamp meadow site. Based on a meta-analysis of warming effects on CH4 fluxes across the entire Tibetan Plateau, we found that the entire alpine grasslands could absorb an extra 0.042 Tg CH4 (1 Tg = 10(12) g) per growing season if soil temperature increased by 1 degrees C. These findings demonstrate that warming effects on CH4 fluxes differ between two alpine grasslands with contrasting moisture conditions and the entire alpine grasslands may not trigger a positive CH4 feedback to climate system with moderate warming.

In the boreal and subarctic zone, the moss and peat interactions with rainwater and snowmelt water in shallow surface ponds control the delivery of dissolved organic matter (DOM) and metal to the rivers and further to the Arctic Ocean. The transformation of peat and moss leachate by common aquatic microorganisms and the effect of temperature on DOM mineralization by heterotrophs remain poorly known that does not allow predicting the response of boreal aquatic system to ongoing climate change. We used experimental approach to quantify the impact of boreal aquatic bacteria P. reactans, and two culturable bacteria extracted from a thaw lake of the permafrost zone (Bolshezemelskaya tundra, NE Europe): Iodobacter sp. and cyanobacterial associate dominated by order Chroococcales (Synechococcus sp). The interaction of these bacterial cultures with nutrient-free peat and moss leachate was performed in order to (1) quantify the impact of temperature (4, 25 and 45 A degrees C) on peat leachate processing by heterotrophs; (2) compare the effect of heterotrophic bacteria and cyanobacterial associate on moss and peat leachate chemical composition, and (3) quantify the DOC and metal concentration change during cyanobacterial growth on leachate from frozen and thawed peat horizon and moss biomass. The efficiency of peat DOM processing by two heterotrophs was not modified by temperature rise from 4 to 45 A degrees C. The DOC concentration decreased by a factor of 1.6 during 3 days of moss leachate reaction with Iodobacters sp. or cyanobacterial associate at 25 A degrees C. The SUVA(245) increased twofold suggesting an uptake of non-aromatic DOM by both microorganisms. The growth of cyanobacteria was absent on peat leachate but highly pronounced on moss leachate. This growth produced tenfold decrease in P concentration, a factor of 1.5-2.0 decrease in DOC, a factor of 4 and 100 decrease in Fe and Mn concentration, respectively. Adsorption of organic and organo-mineral colloids on bacterial cell surface was more important factor of element removal from organic leachates compared to intracellular assimilation and/or Fe oxyhydroxide precipitation. Overall, we demonstrate highly conservative behavior of peat leachate compared to moss leachate in the presence of culturable aquatic bacteria, a lack of any impact of heterotrophs on peat leachate and their weak impact on moss leachate. A very weak temperature impact on DOM processing by heterotrophs and lack of difference in the biodegradability of DOM from thawed and frozen peat horizons contradict the current paradigm that the warming of frozen OM and its leaching to inland waters will greatly affect microbial production and C cycle. Strong decrease in concentration of P, Fe and Mn in the moss leachate in the presence of cyanobacterial associate has straightforward application for understanding the development of thermokarst lakes and suggests that, in addition to P, Fe and Mn may become limiting micronutrients for phytoplankton bloom in thermokarst lakes.

Arctic ecosystems are characterized by a wide range of soil moisture conditions and thermal regimes and contribute differently to the net methane (CH4) budget. Yet, it is unclear how climate change will affect the capacity of those systems to act as a net source or sink of CH4. Here, we present results of insitu CH4 flux measurements made during the growing season 2014 on Disko Island (west Greenland) and quantify the contribution of contrasting soil and landscape types to the net CH4 budget and responses to summer warming. We compared gas flux measurements from a bare soil and a dry heath, at ambient conditions and increased air temperature, using open-top chambers (OTCs). Throughout the growing season, bare soil consumed 0.22 +/- 0.03g CH4-Cm-2 (8.1 +/- 1.2g CO2-eqm(-2)) at ambient conditions, while the dry heath consumed 0.10 +/- 0.02g CH4-Cm-2 (3.9 +/- 0.6g CO2-eqm(-2)). These uptake rates were subsequently scaled to the entire study area of 0.15km(2), a landscape also consisting of wetlands with a seasonally integrated methane release of 0.10 +/- 0.01g CH4-Cm-2 (3.7 +/- 1.2g CO2-eqm(-2)). The result was a net landscape sink of 12.71kg CH4-C (0.48 tonne CO2-eq) during the growing season. A nonsignificant trend was noticed in seasonal CH4 uptake rates with experimental warming, corresponding to a 2% reduction at the bare soil, and 33% increase at the dry heath. This was due to the indirect effect of OTCs on soil moisture, which exerted the main control on CH4 fluxes. Overall, the net landscape sink of CH4 tended to increase by 20% with OTCs. Bare and dry tundra ecosystems should be considered in the net CH4 budget of the Arctic due to their potential role in counterbalancing CH4 emissions from wetlands - not the least when taking the future climatic scenarios of the Arctic into account.

Winter biogeochemical processes have received considerable attention. Biological processes (e.g., microbial respiration and plant photosynthesis) do not cease, even at sub-zero temperatures. However, our knowledge of plant nitrogen (N) uptake at sub-zero soil temperatures is particularly limited for deciduous plant species, which do not have leaves during winter. We investigated plant N uptake by evergreen and deciduous species and soil N processes during sub-zero soil temperatures in cool temperate forest soil. Isotopically labelled nitrate (NO3-N-15) was injected into soil as a tracer of plant uptake and soil N dynamics at sub-zero temperature soil at a cool temperate field site. Over a period of 41 days, 6-48 mg/kg DW-1 of N-15 accumulated in evergreen species and deciduous tree species. Furthermore, the N-15 content in ammonium increased, suggesting ammonium production at sub-zero soil temperatures. The increase in (NH4)-N-15 was positively correlated with soil moisture, indicating an important role for soil water in N dynamics at sub-zero soil temperatures. Our findings demonstrate that N uptake by plants and soil N transformation did not cease at sub-zero soil temperatures. Further studies are needed to understand the importance of N dynamics at sub-zero soil temperatures.

Stable Zn isotopes fractionation was studied in main biogeochemical compartments of a pristine larch forest of Central Siberia developed over continuous permafrost basalt rocks. Two north-and south-oriented watershed slopes having distinctly different vegetation biomass and active layer depth were used as natural proxy for predicting possible future climate changes occurring in this region. In addition, peat bog zone exhibiting totally different vegetation, hydrology and soil temperature regime has been studied. The isotopic composition of soil profile from Central Siberia is rather constant with a delta Zn-66 value around 0.2 parts per thousand close to the value of various basalts. Zn isotopic composition in mosses (Sphagnum fuscum and Pleurozium schreberi) exhibits differences between surface layers presenting values from 0.14 to 0.2 parts per thousand and bottom layers presenting significantly higher values (0.5 - 0.7 parts per thousand) than the underlain mineral surface. The humification of both dead moss and larch needles leads to retain the fraction where Zn bound most strongly thus releasing the lighter isotopes in solution and preserving the heavy isotopes in the humification products, in general accord with previous experimental and modeling works [GCA 75:7632-7643, 2011]. The larch (Larix gmelinii) from North and South-facing slopes is enriched in heavy isotopes compared to soil reservoir while larch from Sphagnum peatbog is enriched in light isotopes. This difference may result from stronger complexation of Zn by organic ligands and humification products in the peat bog compared to mineral surfaces in North- and South-facing slope. During the course of the growing period, Zn followed the behavior of macronutrients with a decrease of concentration from June to September. During this period, an enrichment of larch needles by heavier Zn isotopes is observed in the various habitats. We suggest that the increase of the depth of rooting zone, and the decrease of DOC and Zn concentration in soil solution from the root uptake zone with progressively thawing soil could provoke heavy isotopes to become more available for the larch roots at the end of the vegetative season compared to the beginning of the season, because the decrease of DOC will facilitate the uptake of heavy isotope as it will be less retained in strong organic complexes.

Changes in snow cover depth and duration predicted by climate change scenarios are expected to strongly affect high-altitude ecosystem processes. This study investigates the effect of an exceptionally short snow season on the phenology and carbon dioxide source/sink strength of a subalpine grassland. An earlier snowmelt of more than one month caused a considerable advancement (40 days) of the beginning of the carbon uptake period (CUP) and, together with a delayed establishment of the snow season in autumn, contributed to a two-month longer CUP. The combined effect of the shorter snow season and the extended CUP led to an increase of about 100% in annual carbon net uptake. Nevertheless, the unusual environmental conditions imposed by the early snowmelt led to changes in canopy structure and functioning, with a reduction of the carbon sequestration rate during the snow-free period.

Aerated forest soils are a significant sink for atmospheric methane (CH4). Soil properties, local climate and tree species can affect the soil CH4 sink. A two-year field study was conducted in a deciduous mixed forest in the Hainich National Park in Germany to quantify the sink strength of this forest for atmospheric CH4 and to determine the key factors that control the seasonal, annual and spatial variability of CH4 uptake by soils in this forest. Net exchange of CH4 was measured using closed chambers on 18 plots in three stands exhibiting different beech (Fagus sylvatica L) abundance and which differed in soil acidity, soil texture, and organic layer thickness. The annual CH4 uptake ranged from 2.0 to 3.4 kg CH4-C ha(-1). The variation of CH4 uptake over time could be explained to a large extent (R-2 = 0.71, P < 0.001) by changes in soil moisture in the upper 5 cm of the mineral soil. Differences of the annual CH4 uptake between sites were primarily caused by the spatial variability of the soil clay content at a depth of 0-5 cm (R-2 = 0.5, P < 0.01). The CH4 uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate. Low CH4 uptake activity during winter was further reduced by periods with soil frost and snow cover. There was no evidence of a significant effect of soil acidity, soil nutrient availability, thickness of the humus layer or abundance of beech on net-CH4 uptake in soils in this deciduous forest. The results show that detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary for a reliable larger scale estimate of the CH4 sink strength in this mixed deciduous forest. The results suggest that climate change will result in increasing CH4 uptake rates in this region because of the trend to drier summers and warmer winters. (C) 2009 Elsevier Ltd. All rights reserved.