Xinzhang Song

Chinese Grain for Green Program led to highly increased soil organic carbon levels: a meta-analysis.

The Grain for Green Program (GGP), initiated in 1999, is the largest ecological restoration project in central and western China. Here, for the first time, we performed a meta-analysis and found that the GGP largely increased the soil organic carbon (SOC). The SOC was increased by 48.1%, 25.4%, and 25.5% at soil depths of 0–20 cm, 20–40 cm, and 40–60 cm, respectively. Moreover, this carbon accumulation has significantly increased over time since GGP implementation. The carbon accumulation showed a significantly more active response to the GGP in the top 20 cm of soil than in the deeper soil layers. Conversion of cropland to forest could lead to significantly greater SOC accumulation than would the conversion of cropland to grassland. Conversion from cropland to woodland could lead to greater SOC accumulation than would the conversion to either shrubland or orchard. Our results suggest that the GGP implementation caused SOC to accumulate and that there remains a large potential for further accumulation of carbon in the soil, which will help to mitigate climate change in the near future.

Soil CO2 flux dynamics in the two main plantation forest types in subtropical China

Chinese Fir and Moso bamboo are the two most important forest plantation species in subtropical China. However, information on greenhouse gas emissions from these forests is still scarce. A field study was carried out to compare soil CO(2) flux dynamics in Chinese Fir and Moso bamboo forests over a 12-month period using the LI-8100 Soil CO(2) Flux System. The soil CO(2) flux in both forest types showed similar daily and seasonal dynamic patterns with the highest soil CO(2) efflux at 14:00-16:00 in summer and the lowest in winter. Moso bamboo forest showed significant higher (P<0.01) annual mean soil CO(2) fluxes (52.9 t CO(2)ha(-1)yr(-1)) than Chinese fir forest (27.9 t CO(2)ha(-1)yr(-1)). The large difference in soil CO(2) fluxes may potentially influence the carbon cycle of the two forest types at the ecosystem scale. The CO(2) flux from the soil showed a significant positive correlation (P<0.0001) with soil temperature at 5 cm depth, a significant negative correlation (P<0.01) with air relative humidity, and no significant correlation with soil moisture in either forest types. The Q(10) value of soil respiration was higher in Chinese fir than Moso bamboo forest, indicating that soil respiration under Chinese fir forest will be more sensitive to temperature change. This study contributes to better understanding of the role Moso bamboo and Chinese fir forests may play in carbon cycle and global warming mitigation.

Direct and Indirect Effects of UV-B Exposure on Litter Decomposition: A Meta-Analysis

Ultraviolet-B (UV-B) exposure in the course of litter decomposition may have a direct effect on decomposition rates via changing states of photodegradation or decomposer constitution in litter while UV-B exposure during growth periods may alter chemical compositions and physical properties of plants. Consequently, these changes will indirectly affect subsequent litter decomposition processes in soil. Although studies are available on both the positive and negative effects (including no observable effects) of UV-B exposure on litter decomposition, a comprehensive analysis leading to an adequate understanding remains unresolved. Using data from 93 studies across six biomes, this introductory meta-analysis found that elevated UV-B directly increased litter decomposition rates by 7% and indirectly by 12% while attenuated UV-B directly decreased litter decomposition rates by 23% and indirectly increased litter decomposition rates by 7%. However, neither positive nor negative effects were statistically significant. Woody plant litter decomposition seemed more sensitive to UV-B than herbaceous plant litter except under conditions of indirect effects of elevated UV-B. Furthermore, levels of UV-B intensity significantly affected litter decomposition response to UV-B (P<0.05). UV-B effects on litter decomposition were to a large degree compounded by climatic factors (e.g., MAP and MAT) (P<0.05) and litter chemistry (e.g., lignin content) (P<0.01). Results suggest these factors likely have a bearing on masking the important role of UV-B on litter decomposition. No significant differences in UV-B effects on litter decomposition were found between study types (field experiment vs. laboratory incubation), litter forms (leaf vs. needle), and decay duration. Indirect effects of elevated UV-B on litter decomposition significantly increased with decay duration (P<0.001). Additionally, relatively small changes in UV-B exposure intensity (30%) had significant direct effects on litter decomposition (P<0.05). The intent of this meta-analysis was to improve our understanding of the overall effects of UV-B on litter decomposition.

Dynamic allocation and transfer of non-structural carbohydrates, a possible mechanism for the explosive growth of Moso bamboo (Phyllostachys heterocycla).

Moso bamboo can rapidly complete its growth in both height and diameter within only 35–40 days after shoot emergence. However, the underlying mechanism for this “explosive growth” remains poorly understood. We investigated the dynamics of non-structural carbohydrates (NSCs) in shoots and attached mature bamboos over a 20-month period. The results showed that Moso bamboos rapidly completed their height and diameter growth within 38 days. At the same time, attached mature bamboos transferred almost all the NSCs of their leaves, branches, and especially trunks and rhizomes to the “explosively growing” shoots via underground rhizomes for the structural growth and metabolism of shoots. Approximately 4 months after shoot emergence, this transfer stopped when the leaves of the young bamboos could independently provide enough photoassimilates to meet the carbon demands of the young bamboos. During this period, the NSC content of the leaves, branches, trunks and rhizomes of mature bamboos declined by 1.5, 23, 28 and 5 fold, respectively. The trunk contributed the most NSCs to the shoots. Our findings provide new insight and a possible rational mechanism explaining the “explosive growth” of Moso bamboo and shed new light on understanding the role of NSCs in the rapid growth of Moso bamboo.

Management practices regulate the response of Moso bamboo foliar stoichiometry to nitrogen deposition

Moso bamboo, well known for its high growth rate, is being subjected to increasing amounts of nitrogen deposition. However, how anthropogenic management practices regulate the effects of N deposition on Moso bamboo stoichiometry remains poorly understood. We observed the effects of two years of simulated N deposition (30, 60 and 90 kg N ha−1yr−1) on the foliar stoichiometry of Moso bamboo plantations under conventional management (CM) and intensive management (IM). Young bamboo had significantly greater foliar N and P concentrations and N:P ratios than mature plants (P < 0.05). IM significantly increased the foliar N concentrations of young bamboo and P concentrations of mature bamboo but decreased mature bamboo foliar N:P ratios (P < 0.05). Nitrogen increased foliar N and P concentrations in IM bamboo plantations, but the positive effects were diminished when the addition rate exceeded 60 kg N ha−1yr−1. Nitrogen increased foliar N concentrations but aggravated P deficiency in CM bamboo plantations. The positive effects of N deposition on foliar stoichiometry were influenced by management practices and bamboo growth stage. The effects of N deposition on foliar stoichiometry combined with anthropogenic management practices can influence ecosystem production, decomposition, and subsequent N and P cycles in Moso bamboo plantations.

Effects of biochar application on fluxes of three biogenic greenhouse gases: a meta-analysis

Abstract Biochar application to cropland has been recommended as a strategy to reduce increasing atmospheric 2 concentrations and mitigate climate change. However, the direction and magnitude of responses of greenhouse gas (GHG) fluxes to biochar application to cropland remain unclear. Our meta‐analysis of 296 observations across 61 studies for the first time quantitatively estimated the effects of biochar amendment on fluxes of three s2, N2O, and 4. The results showed that biochar application led to a significant change in soil s emissions: in general, 19% for 2, −16% for N2O (P < 0.05), but no pronounced change in 4 emissions; in paddy, −5% for 2, −20% for N2O, but +19% for 4 (P < 0.05); in upland, −18% for N2O, +12% for 2, and high uncertainty for 4. The responses of soil fluxes to biochar application were regulated mainly by experiment length, biochar application rate, biochar properties, providing a new perspective for more comprehensive understanding on biochar. The biochar derived from husk was recommended to apply to cropland with an application rate of 20–30 t·ha−1.

Nitrogen deposition and management practices increase soil microbial biomass carbon but decrease diversity in Moso bamboo plantations

Because microbial communities play a key role in carbon (C) and nitrogen (N) cycling, changes in the soil microbial community may directly affect ecosystem functioning. However, the effects of N deposition and management practices on soil microbes are still poorly understood. We studied the effects of these two factors on soil microbial biomass carbon (MBC) and community composition in Moso bamboo plantations using high-throughput sequencing of the 16S rRNA gene. Plantations under conventional (CM) or intensive management (IM) were subjected to one of four N treatments for 30 months. IM and N addition, both separately and in combination, significantly increased soil MBC while decreasing bacterial diversity. However, increases in soil MBC were inhibited when N addition exceeded 60 kg N∙ha−1∙yr−1. IM increased the relative abundances of Actinobacteria and Crenarchaeota but decreased that of Acidobacteria. N addition increased the relative abundances of Acidobacteria, Crenarchaeota, and Actinobacteria but decreased that of Proteobacteria. Soil bacterial diversity was significantly related to soil pH, C/N ratio, and nitrogen and available phosphorus content. Management practices exerted a greater influence over regulation of the soil MBC and microbial diversity compared to that of N deposition in Moso bamboo plantations.

Model prediction of biome‐specific global soil respiration from 1960 to 2012

Biome-specific soil respiration (Rs) has important yet different roles in both the carbon cycle and climate change from regional to global scales. To date, no comparable studies related to global biome-specific Rs have been conducted applying comprehensive global Rs databases. The goal of this study was to develop artificial neural network (ANN) models capable of spatially estimating global Rs and to evaluate the effects of interannual climate variations on 10 major biomes. We used 1,976 annual Rs field records extracted from global Rs literature to train and test the ANN models. We determined that the best ANN model for predicting biome-specific global annual Rs was the one that applied mean annual temperature (MAT), mean annual precipitation (MAP) and biome type as inputs (r2 = 0.60). The ANN models reported an average global Rs of 93.3 ± 6.1 Pg C year−1 from 1960 to 2012 and an increasing trend in average global annual Rs of 0.04 Pg C year−1. Estimated annual Rs increased with increases in MAT and MAP in cropland, boreal forest, grassland, shrubland and wetland biomes. Additionally, estimated annual Rs decreased with increases in MAT and increased with increases in MAP in desert and tundra biomes, and only significantly decreased with increases in MAT (r2 = 0.87) in the savannah biome. The developed biome-specific global Rs database for global land and soil carbon models will aid in understanding the mechanisms underlying variations in soil carbon dynamics and in quantifying uncertainty in the global soil carbon cycle.

Towards a paradigm for open and free sharing of scientific data on global change science in China

Abstract Despite great progress in data sharing that has been made in China in recent decades, cultural, policy, and technological challenges have prevented Chinese researchers from maximizing the availability of their data to the global change science community. To achieve full and open exchange and sharing of scientific data, Chinese research funding agencies need to recognize that preservation of, and access to, digital data are central to their mission, and must support these tasks accordingly. The Chinese government also needs to develop better mechanisms, incentives, and rewards, while scientists need to change their behavior and culture to recognize the need to maximize the usefulness of their data to society as well as to other researchers. The Chinese research community and individual researchers should think globally and act personally to promote a paradigm of open, free, and timely data sharing, and to increase the effectiveness of knowledge development.

Analysis of vegetation dynamics and climatic variability impacts on greenness across Canada using remotely sensed data from 2000 to 2009

Abstract. Using time series of moderate-resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) data from 2000 to 2009, we assessed decadal vegetation dynamics across Canada and examined the relationship between NDVI and climatic variables (precipitation and temperature). The Palmer drought severity index and vapor pressure difference (VPD) were used to relate the vegetation changes to the climate, especially in cases of drought. Results indicated that MODIS NDVI measurements provided a dynamic picture of interannual variation in Canadian vegetation patterns. Greenness declined in 2000, 2002, and 2009 and increased in 2005, 2006, and 2008. Vegetation dynamics varied across regions during the period. Most forest land shows little change, while vegetation in the ecozone of Pacific Maritime, Prairies, and Taiga Shield shows more dynamics than in the others. Significant correlations were found between NDVI and the climatic variables. The variation of NDVI resulting from climatic variability was more highly correlated to temperature than to precipitation in most ecozones. Vegetation grows better with higher precipitation and temperature in almost all ecozones. However, vegetation grows worse under higher temperature in the Prairies ecozone. The annual changes in NDVI corresponded well with the change in VPD in most ecozones.