Shaoqiang Wang

Pattern and change of soil organic carbon storage in China: 1960s–1980s

Soils, an important component of the global carbon cycle, can be either net sources or net sinks of atmospheric carbon dioxide (CO2). In this study, we use the first and second national soil surveys of China to investigate patterns and changes in soil organic carbon storage (SOC) during the period from the 1960s to the 1980s. Our results show that there is a large amount of variability in SOC density among different soil types and land uses in the 1980s. The SOC density in the wetlands of Southwest China was the highest (45 kg m−2), followed by meadow soils in the South (26 kg m−2), forest and woodlands in the Northwest (19 kg m−2), steppe and grassland in the Northwest (15 kg m−2), shrubs in the Northwest (12 kg m−2), paddy lands in the Northwest (13 kg m−2), and drylands in the Northwest (11 kg m−1). The desert soils of the Western region ranked the lowest (1 kg m−2). The density of SOC was generally higher in the west than other regions. Eastern China had the lowest SOC density, which was associated with a long history of extensive land use in the region. The estimation of SOC storage for the entire nation was 93 Pg C in the 1960s and 92 Pg C in the 1980s. SOC storage decreased about 1 Pg C during the 1960s–1980s. This amount of decrease in SOC for the entire nation is small and statistically insignificant. To adequately characterize spatial variations in SOC, larger sampling sizes of soil profiles will be required in the future analyses.

Relationships between net primary productivity and stand age for several forest types and their influence on China’s carbon balance

Affected by natural and anthropogenic disturbances such as forest fires, insect-induced mortality and harvesting, forest stand age plays an important role in determining the distribution of carbon pools and fluxes in a variety of forest ecosystems. An improved understanding of the relationship between net primary productivity (NPP) and stand age (i.e., age-related increase and decline in forest productivity) is essential for the simulation and prediction of the global carbon cycle at annual, decadal, centurial, or even longer temporal scales. In this paper, we developed functions describing the relationship between national mean NPP and stand age using stand age information derived from forest inventory data and NPP simulated by the BEPS (Boreal Ecosystem Productivity Simulator) model in 2001. Due to differences in ecobiophysical characteristics of different forest types, NPP-age equations were developed for five typical forest ecosystems in China (deciduous needleleaf forest (DNF), evergreen needleleaf forest in tropic and subtropical zones (ENF-S), deciduous broadleaf forest (DBF), evergreen broadleaf forest (EBF), and mixed broadleaf forest (MBF)). For DNF, ENF-S, EBF, and MBF, changes in NPP with age were well fitted with a common non-linear function, with R(2) values equal to 0.90, 0.75, 0.66, and 0.67, respectively. In contrast, a second order polynomial was best suitable for simulating the change of NPP for DBF, with an R(2) value of 0.79. The timing and magnitude of the maximum NPP varied with forest types. DNF, EBF, and MBF reached the peak NPP at the age of 54, 40, and 32 years, respectively, while the NPP of ENF-S maximizes at the age of 13 years. The highest NPP of DBF appeared at 122 years. NPP was generally lower in older stands with the exception of DBF, and this particular finding runs counter to the paradigm of age-related decline in forest growth. Evaluation based on measurements of NPP and stand age at the plot-level demonstrates the reliability and applicability of the fitted NPP-age relationships. These relationships were used to replace the normalized NPP-age relationship used in the original InTEC (Integrated Terrestrial Ecosystem Carbon) model, to improve the accuracy of estimated carbon balance for Chinas forest ecosystems. With the revised NPP-age relationship, the InTEC model simulated a larger carbon source from 1950-1980 and a larger carbon sink from 1985-2001 for Chinas forests than the original InTEC model did because of the modification to the age-related carbon dynamics in forests. This finding confirms the importance of considering the dynamics of NPP related to forest age in estimating regional and global terrestrial carbon budgets.

Pools and distributions of soil phosphorus in China

about 8.3 � 10 2 g/m 3 and 5.4 g/m 3 , respectively. The total national soil P pool in the surface half meter is 3.5 Pg (10 15 g). The available P density ranges from 0.7 g/m 3 in the Lithosols to 16.7 g/m 3 in the Irrigated Silting Soils. The total P density ranges from 1.2 � 10 2 g/m 3 in the Lithosols to 19 � 10 2 g/m 3 in the Frigid Desert Soils. The ratio of available P to total P density ranges from 0.6 � 10 � 3 in Aeolian Soils to 21.6 � 10 � 3 in Coastal Solonchaks. The available P content and its vertical distribution show a complex pattern among soil orders of different development stages, possibly indicating the important role of biota’s control over soil available P content. There are large variations of P content in different climatic regions. The tropical and subtropical region has the lowest available P density (4.8 g/m 3 ) and the second lowest total P density (8.2 � 10 2 g/m 3 ) among all climatic regions. The large variation in the soil P content suggests that further study is needed to investigate climatic and land-use controls over the soil P content.

Carbon storage in northeast China as estimated from vegetation and soil inventories

We have estimated the stocks of carbon in vegetation and soil in northeast China based on data for 122 plots from the fourth national forest inventory, and for 388 soil profiles from the second national soil survey. The techniques of Geographic Information System (GIS) have been used to extrapolate site-specific estimates of vegetation and soil organic carbon to the entire area of northeast China. Our estimate indicates that the amount of carbon in vegetation and soil for the region are 2.81 PgC (10(15) g C) and 26.43 PgC, respectively, and that the area weighted average density of vegetation and soil organic carbon are 22.7 MgC/ha and 212.7 MgC/ha, respectively. The eastern and northern parts of the region show much higher carbon storage than the rest of the region. Substantial spatial variations in vegetation and soil organic carbon across northeast China suggest that regional estimates on carbon stocks and fluxes should take into account these spatial variations. We suggest that the methodology developed can be used for the entire nation of China as well as other regions of the world.

Patterns of soil nitrogen storage in China

8.29 � 10 15 g, representing 5.9–8.7% of the total global N storage. The total N storage in China is on average or slightly above the average of its share in the global N storage, even though low nitrogen content soils cover a large area in China. N density varies substantially with soil types and regions. Peat soils in the southeast of Tibet, southwest China, show the highest averaged N density with a value of 7314.9 g/m 3 among all soil types. This is more than 30 times of the lowest N density of brown desert soils in the western desert and arid region. The highest N storages among all the soil types are the felty soil in southeast of Tibet, dark-brown earths in northeast China, and red earths in southeast China with values of 921.1, 611.4, and 569.6 Tg, respectively. N density also varies with land cover types in China. Wetlands in southwest China exhibit the highest N density at 6775.9 g/m 3 and deserts in northwest China have the least at 447.5 g/m 3 . Our analysis also indicates that land cover types are poor predictors of N content. Further research is needed to examine how transformation from organic agriculture to increased use of fertilizers and pesticides has influenced N storage in China.

Estimating and analyzing the spatial distribution of soil organic carbon in China

Abstract Research on the terrestrial carbon cycle is an important component in the study of global change. Soil organic carbon, as the main part of the terrestrial carbon reservoir, plays an important role in the Earths carbon cycle. To accurately estimate soil organic carbon storage, its composition and dynamic change must be determined. This presents a challenge to research on the soil carbon cycle, especially in China where the nationwide soil organic carbon reservoir largely remains unknown. This paper reports a research project that attempts to estimate the nationwide soil organic carbon reservoir. Data from 2473 soil profiles from the second national soil survey were collected and GIS technology was employed to quantify the national soil carbon reservoir. The analytical results show that the total amount of soil organic carbon is about 92.4 Pg (Pg = 1015 g) and that the average carbon density is about 10.53 kg C m−2. The spatial distribution of soil organic carbon was also analyzed and mapped. This study presents basic data and an analysis method for carbon-cycle studies and also provides scientific support for policy-making efforts to control CO2 emissions in China.

Water use efficiency of China’s terrestrial ecosystems and responses to drought

Water use efficiency (WUE) measures the trade-off between carbon gain and water loss of terrestrial ecosystems, and better understanding its dynamics and controlling factors is essential for predicting ecosystem responses to climate change. We assessed the magnitude, spatial patterns, and trends of WUE of China’s terrestrial ecosystems and its responses to drought using a process-based ecosystem model. During the period from 2000 to 2011, the national average annual WUE (net primary productivity (NPP)/evapotranspiration (ET)) of China was 0.79u2009g C kg−1 H2O. Annual WUE decreased in the southern regions because of the decrease in NPP and the increase in ET and increased in most northern regions mainly because of the increase in NPP. Droughts usually increased annual WUE in Northeast China and central Inner Mongolia but decreased annual WUE in central China. “Turning-points” were observed for southern China where moderate and extreme droughts reduced annual WUE and severe drought slightly increased annual WUE. The cumulative lagged effect of drought on monthly WUE varied by region. Our findings have implications for ecosystem management and climate policy making. WUE is expected to continue to change under future climate change particularly as drought is projected to increase in both frequency and severity.

Effects of land use change on the storage of soil organic carbon: A case study of the Qianyanzhou Forest Experimental Station in China

Forests play an important role in sequestrating carbon from the atmosphere. Since the 1980s, reforestation activities have been implemented in the area surrounding the Qianyanzhou Forest Experimental Station in Jiangxi Province, China. Farmland and heavily eroded waste land were replanted with fruit, orchards and forest plantations. The area surrounding the Qianyanzhou Forest Experimental Station was selected as research site to analyze the potential of reforestation in carbon sequestration. This study evaluates the variation of soil organic carbon storage under the different land use types. Soil organic carbon storage varied greatly with land use types. From 1984 to 2002, soil organic carbon storage increased 2.45 × 106 kg across eight land use types. This study demonstrates the potential for carbon sequestration in soils from reforestation. However, a complete understanding of soil carbon fluxes at the landscape scale will depend on the potential and retention period of soil organic carbon.

How recent climate change influences water use efficiency in East Asia

Water use efficiency (WUE), defined as the ratio of gross primary productivity to evapotranspiration, is an important indicator of the trade-off between water loss and carbon gain. We used a biophysical process-based model to examine the relative importance of climate-induced changes in meteorological factors and leaf area index (LAI) on the changes in WUE in East Asia. Validation showed that our simulation could capture the magnitudes and variations of WUE at 18 flux sites in Asia. Regional results indicated that the highest WUE occurred in boreal forests at high latitudes and the lowest WUE in desert areas of China. Changes in meteorological factors negatively affected WUE in the northwestern, northern, and eastern study regions. Changes in LAI had determinant impacts on changes in WUE in most areas except for those with sparse or low-density vegetation (e.g., western interior China, southeast island countries) where meteorological factors dominated. We conclude that, aside from the impact of meteorological factors on WUE, climate-induced changes in LAI may play a prominent role in regulating WUE changes.

Global parameterization and validation of a two-leaf light use efficiency model for predicting gross primary production across FLUXNET sites

Light use efficiency (LUE) models are widely used to simulate gross primary production (GPP). However, the treatment of the plant canopy as a big leaf by these models can introduce large uncertainties in simulated GPP. Recently, a two-leaf light use efficiency (TL-LUE) model was developed to simulate GPP separately for sunlit and shaded leaves and has been shown to outperform the big-leaf MOD17 model at six FLUX sites in China. In this study we investigated the performance of the TL-LUE model for a wider range of biomes. For this we optimized the parameters and tested the TL-LUE model using data from 98 FLUXNET sites which are distributed across the globe. The results showed that the TL-LUE model performed in general better than the MOD17 model in simulating 8 day GPP. Optimized maximum light use efficiency of shaded leaves (epsilon(msh)) was 2.63 to 4.59 times that of sunlit leaves (epsilon(msu)). Generally, the relationships of epsilon(msh) and epsilon(msu) with epsilon(max) were well described by linear equations, indicating the existence of general patterns across biomes. GPP simulated by the TL-LUE model was much less sensitive to biases in the photosynthetically active radiation (PAR) input than the MOD17 model. The results of this study suggest that the proposed TL-LUE model has the potential for simulating regional and global GPP of terrestrial ecosystems, and it is more robust with regard to usual biases in input data than existing approaches which neglect the bimodal within-canopy distribution of PAR.