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Soil samples, which were collected from three typical forests, i.e., Betula ermanii forest, coniferous mixed broad-leaved forest, and Pinus koraiensis forest, at different altitudes along the southern slope of Laotuding Mountain of Changbai Mountain range in Liaoning Province of China, were incubated over a temperature gradient in laboratory. Soil organic carbon mineralization rates (Cmin), soil β-1,4-glucosidase (βG) kinetics and their temperature sensitivity (Q₁₀) were measured. The results showed that both altitude and temperature had significant effects on Cmin · Cmin increased with temperature and was highest in the B. ermanii forest. The temperature sensitivity of Cmin [Q₁₀(Cmin)] ranked in order of B. ermanii forest > P. koraiensis forest > coniferous mixed broad-leaved forest, but did not differ significantly among the three forests. Both the maximum activity (Vmax) and the Michaelis constant (Km) of the βG responded positively to temperature for all the forests. The temperature sensitivity of Vmax [Q₁₀(Vmax)] ranged from 1.78 to 1.90, and the temperature sensitivity of Km [Q₁₀(Km)] ranged from 1.79 to 2.00. The Q₁₀(Vmax)/Q10(Km) ratios were significantly greater in the B. ermanii soil than in the other two forest soils, suggesting that the βG kinetics-dependent impacts of the global warming or temperature increase on the decomposition of soil organic carbon were temperature sensitive for the forests at the higher altitudes.

Enhanced fertilization could decrease nitrogen utilization rate and increase carbon and nitrogen leaching, leading to water pollution in agricultural ecosystem. A long-term field experiment had been established on a reddish paddy soil of Qianyanzhou Ecological Experimental Station (114 degrees 53'E, 26 degrees 48'N) in Jiangxi Province in 1998. Soil solution samples were collected by clay tube and vacuum pump. Four fertilizer species treatments were selected: control with no fertilizer (CK), straw return (ST), nitrogen, phosphorus and potassium mineral fertilizers (NPK) and pig manure (OM), aiming to evaluate the effects of different species of fertilizer on carbon and nitrogen leaching in a double rice cropping system. The results showed that: (1) ammonium nitrogen (NH4(+) -N) was the major type of N in soil leachate in reddish paddy soil. The application of NPK could significantly increase the ammonium nitrogen concentration (1.2 mg x L(-1) +/- 0.1 mg x L(-1)) compared with the CK, ST and OM treatments, and the application of OM could significantly increase the dissolved organic carbon (DOC) concentration (27.3 mg x L(-1) +/- 1.6 mg x L(-1)) in soil leachate. The carbon and nitrogen leaching were more notable in the vegetative growth stage than the reproductive growth stage of rice (P < 0.05); (2) the long-term application of NPK and OM increased the NH4(+) -N, DOC, soil organic carbon (SOC) and total nitrogen (TN) contents. The NPK was best beneficial to improve TN contents and OM to improve SOC contents. (3) The DOC contents in soil leachate and SOC in paddy soil had a positive correlation (P < 0.01), while NH4(+) -N contents in soil leachate and TN contents in paddy soil had a positive correlation (P < 0.01).

Based on the long-term fixed position experimental data from Qianyanzhou Ecological Experiment Station, Chinese Academy of Sciences in 1998, this paper analyzed the effects of applying different kind fertilizers (straw, ST; pig manure, OM; and chemical fertilizer, NPK) on the nutrients (C, N, and P) status and the activities of related enzymes ( beta-1,4-glucosidase, betaG; beta-1,4-N-acetylglucosaminidase, NAG; L-leucine aminopeptidase, LAP; and acid phosphatase, AP) in reddish paddy soil. With the application of OM, the activities of soil betaG, NAG, and LAP increased significantly, as compared with other treatments, and were 1.4, 2. 6, and 1.9 times higher than the control (CK) , respectively. Applying OM also improved the ratio of soil organic carbon to total nitrogen (C/N), but decreased the soil betaG/(NAG+LAP) ratio, suggesting that pig manure could benefit the degradation of soil cellulose and the accumulation of soil organic carbon. Applying NPK increased the activities of soil betaG, NAG, and LAP, but decreased the AP activity, with a decrement of 34% as compared with CK. Under the application of NPK, the soilbetaG/AP and (NAG+ LAP)/AP ratios increased, but the ratios of soil organic carbon to total phosphorus (C/P) and of soil total nitrogen to total phosphorus (N/P) decreased, indicating that chemical fertilizers could induce the accumulation of soil inorganic phosphorus, and inhibit the microbial functions of degrading polysaccharides and phosphate phospholipids.

Understanding the dynamics and underlying mechanism of carbon exchange between terrestrial ecosystems and the atmosphere is one of the key issues in global change research. In this study, we quantified the carbon fluxes in different terrestrial ecosystems in China, and analyzed their spatial variation and environmental drivers based on the long-term observation data of ChinaFLUX sites and the published data from other flux sites in China. The results indicate that gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of terrestrial ecosystems in China showed a significantly latitudinal pattern, declining linearly with the increase of latitude. However, GEP, ER, and NEP did not present a clear longitudinal pattern. The carbon sink functional areas of terrestrial ecosystems in China were mainly located in the subtropical and temperate forests, coastal wetlands in eastern China, the temperate meadow steppe in the northeast China, and the alpine meadow in eastern edge of Qinghai-Tibetan Plateau. The forest ecosystems had stronger carbon sink than grassland ecosystems. The spatial patterns of GEP and ER in China were mainly determined by mean annual precipitation (MAP) and mean annual temperature (MAT), whereas the spatial variation in NEP was largely explained by MAT. The combined effects of MAT and MAP explained 79%, 62%, and 66% of the spatial variations in GEP, ER, and NEP, respectively. The GEP, ER, and NEP in different ecosystems in China exhibited 'positive coupling correlation' in their spatial patterns. Both ER and NEP were significantly correlated with GEP, with 68% of the per-unit GEP contributed to ER and 29% to NEP. MAT and MAP affected the spatial patterns of ER and NEP mainly by their direct effects on the spatial pattern of GEP., (© 2012 Blackwell Publishing Ltd.)

One hundred and twelve sampling sites in the forest ecosystems along the North-South Transect of Eastern China (NSTEC) were selected to study the stoichiometric characteristics and variability of leaf carbon (C), nitrogen (N), and phosphorous (P) of 102 dominant species. The contents of leaf C (Cmass), leaf N (Nmass), and leaf P (Pmass) ranged in 374.1-646.5 mg x g(-1), 8.4-30.5 mg x g(-1), and 0.6-6.2 mg x g(-1), with the arithmetic mean (AM) being 480.1, 18.3 and 2.0 mg x g(-1), and the variation coefficient (CV) being 11.1%, 27.5%, and 56.4%, respectively. The leaf C/N, C/P and N/P ranged from 14.1 to 64.1, from 70.9 to 838.6, and from 1.5 to 21.2, with the AM being 29.1, 313.9 and 11.5, and the CV being 32.8%, 48.3% and 44.1%, respectively. The mass ratio of C:N:P was 313.9:11.5:1, and the atom ratio was 810.9:25.4:1. As compared with those at global scale, the tree leaf Cmass and C/N in the study area were significantly higher, Nmass and N/P were significantly lower, while Pmass and C/P had less differences.

The litters, bulk soils, and soil particle-size fractions were sampled from three typical natural forests, i.e., broadleaf Korean pine (Pinus koraiensis) mixed forest (PB, altitude 740 m), spruce-fir (Picea asperata-Abies nephrolepis) forest (SF, altitude 1350 m), and Erman's birch (Betula ermanii) forest (EB, altitude 1996 m), on the northern slope of Changbai Mountains to analyze their organic matter delta13C values, and the intact soil cores (20 cm depth) from EB (high altitude) were relocated to PB and SF (low altitudes) for a year to study the responses of the delta13C values to simulated warming. It was shown that the litters had a significantly lower delta13C value than the soils, and the delta13C values of the litters and soils increased downward through the litter- and soil layers in all the three typical forest types. Soil particle-size fractions had an increased delta13C value with decreasing particle size fractions. The delta13C value of the litters was in the order of SF (-28.3 per thousand) >PB (-29.0 per thousand) >EB (-29.6 per thousand), while that of the soils was in the order of EB (-25.5 per thousand) >PB (-25.8 per thousand) >SF (-26.2 per thousand). Over one-year soil warming (an increment of 0.7 degrees C - 2.9 degrees C) , the delta13C values of the bulk soils and soil particle-size fractions all presented a decreasing trend, and the decrement of the delta13C value was larger in <2 microm (0.48 per thousand) and 2-63 microm fractions (0.47 per thousand) than in >63 microm fraction (0.33 per thousand). The results suggested that climate warming could have great effects on the older organic carbon associated with fine soil particle-size fractions.

Carbon dioxide (CO2) storage flux in the air space below measurement height of eddy covariance is very important to correctly evaluate net ecosystem exchange of CO2 (NEE) between forest ecosystem and atmosphere. This study analyzed the dynamic variation of CO2 storage flux and its effects on the carbon budget of a temperate broad-leaved Korean pine mixed forest at Changbai Mountains, based on the eddy covariance flux data and the vertical profile of CO2 concentration data. The CO2 storage flux in this forest ecosystem had typical diurnal variation, with the maximum variation appeared during the transition from stable atmospheric layer to unstable atmospheric layer. The CO2 storage flux calculated by the change in CO2 concentration throughout a vertical profile was not significantly different from that calculated by the change in CO2 concentration at the measurement height of eddy covariance. The NEE of this forest ecosystem was underestimated by 25% and 19% at night and at daytime, respectively, without calculating the CO2 storage flux at half-hour scale, and was underestimated by 10% and 25% at daily scale and annual scale, respectively. Without calculating the CO2 storage flux in this forest ecosystem, the parameters of Michaelis-Menten equation and Lloyd-Taylor equation were underestimated, and the ecosystem apparent quantum yield (alpha) and the ecosystem respiration rate (Rref) at the reference temperature were mostly affected. The gross primary productivity (GPP) and ecosystem respiration (Re) of this forest ecosystem were underestimated about 20% without calculating the CO2 storage flux at half-hour, daily scale, and annual scale.

Net ecosystem productivity (NEP) was continuously measured using the eddy covariance (EC) technique from 2003 to 2005 at three forest sites of ChinaFLUX. The forests include Changbaishan temperate mixed forest (CBS), Qianyanzhou subtropical coniferous plantation (QYZ), and Dinghushan subtropical evergreen broad-leaved forest (DHS). They span wide ranges of temperature and precipitation and are influenced by the eastern Asian monsoon climate to varying extent. In this study, we estimated ecosystem respiration (RE) and gross ecosystem productivity (GEP). Comparison of ecosystem carbon exchange among the three forests shows that RE was mainly determined by temperature, with the forest at CBS exhibiting the highest temperature sensitivity among the three ecosystems. The RE was highly dependent on GEP across the three forests, and the ratio of RE to GEP decreased along the North–South Transect of Eastern China (NSTEC) (i.e. from the CBS to the DHS), with an average of 0.77 ± 0.06. Daily GEP was mainly influenced by temperature at CBS, whereas photosynthetic photon flux density was the dominant factor affecting the daily GEP at both QYZ and DHS. Temperature mainly determined the pattern of the interannual variations of ecosystem carbon exchange at CBS. However, water availability primarily controlled the interannual variations of ecosystem carbon exchange at QYZ. At DHS, NEP attained the highest values at the beginning of the dry seasons (autumn) rather than the rainy seasons (summer), probably because insufficient radiation and frequent fog during the rainy seasons hindered canopy photosynthesis. All the three forest ecosystems acted as a carbon sink from 2003 to 2005. The annual average values of NEP at CBS, QYZ, and DHS were 259 ± 19, 354 ± 34, and 434 ± 66 g C m−2 yr−1, respectively. The slope of NEP that decreased with increasing latitude along the NSTEC was markedly different from that observed on the forest transect in the European continent. Long-term flux measurements over more forest ecosystems along the NSTEC will further help verify such a difference between the European forest transect and the NSTEC and provide insights into the responses of ecosystem carbon exchange to climate change in China. [ABSTRACT FROM AUTHOR]

Abstract: Uptake and release of carbon in grassland ecosystems is very critical to the global carbon balance and carbon storage. In this study, the dynamics of net ecosystem CO2 exchange (F NEE) of two grassland ecosystems were observed continuously using the eddy covariance technique during the growing season of 2003. One is the alpine shrub on the Tibet Plateau, and the other is the semi-arid Leymus chinensis steppe in Inner Mongolia of China. It was found that the F NEE of both ecosystems was significantly depressed under high solar radiation. Comprehensive analysis indicates that the depression of F NEE in the L. chinensis steppe was the results of decreased plant photosynthesis and increased ecosystem respiration (R eco) under high temperature. Soil water stress in addition to the high atmospheric demand under the strong radiation was the primary factor limiting the stomatal conductance. In contrast, the depression of F NEE in the alpine shrub was closely related to the effects of temperature on both photosynthesis and ecosystem respiration, coupled with the reduction of plant photosynthesis due to partial stomatal closure under high temperature at mid-day. The R eco of the alpine shrub was sensitive to soil temperature during high turbulence (u * >0.2ms−1) but its F NEE decreased markedly when the temperature was higher than the optimal value of about 12°C. Such low optimal temperature contrasted the optimal value (about 20°C) for the steppe, and was likely due to the acclimation of most alpine plants to the long-term low temperature on the Tibet Plateau. We inferred that water stress was the primary factor causing depression of the F NEE in the semi-arid steppe ecosystem, while relative high temperature under strong solar radiation was the main reason for the decrease of F NEE in the alpine shrub. This study implies that different grassland ecosystems may respond differently to climate change in the future. [Copyright &y& Elsevier]