Peikun Jiang

Dissolved soil organic carbon and nitrogen were affected by conversion of native forests to plantations in subtropical China

To better understand the impact of converting native forests to intensively managed plantations on soil carbon (C) and nitrogen (N) dynamics in subtropical China, we examined the seasonal patterns of water-soluble organic C (WSOC) and N (WSON) concentrations in soils in Chinese chestnut (Castanea mollissima Blume) (CF) and bamboo (Phyllostachys praecox C.D. Chu & C.S. Chou) plantation forests (BF) and adjacent native evergreen broadleaf forests (NF) in Ling-long Mountain, Zhejiang Province, China. The plantations were disturbed through surface soil removal and were fertilized and/or mulched, from which economic products (such as nuts and bamboo shoots) were annually harvested. We found that WSOC and WSON had large seasonal variations and were lower in the warmer than in the colder season. Average WSOC concentrations followed the order of BF (58.6) > NF (35.1) > CF (18.1 mg C kg-1), a pattern mainly caused by mulching in BF in winter and the removal of surface soil in CF. Soil total C and N followed the or...

Long-term intensive management increased carbon occluded in phytolith (PhytOC) in bamboo forest soils

Carbon (C) occluded in phytolith (PhytOC) is highly stable at millennium scale and its accumulation in soils can help increase long-term C sequestration. Here, we report that soil PhytOC storage significantly increased with increasing duration under intensive management (mulching and fertilization) in Lei bamboo (Phyllostachys praecox) plantations. The PhytOC storage in 0–40 cm soil layer in bamboo plantations increased by 217 Mg C ha−1, 20 years after being converted from paddy fields. The PhytOC accumulated at 79 kg C ha−1 yr−1, a rate far exceeding the global mean long-term soil C accumulation rate of 24 kg C ha−1 yr−1 reported in the literature. Approximately 86% of the increased PhytOC came from the large amount of mulch applied. Our data clearly demonstrate the decadal scale management effect on PhytOC accumulation, suggesting that heavy mulching is a potential method for increasing long-term organic C storage in soils for mitigating global climate change.

Similar quality and quantity of dissolved organic carbon under different land use systems in two Canadian and Chinese soils

PurposeThe quality and quantity of dissolved organic carbon (DOC) in the soil can be used as indicators of the effects of perturbations on soil C. We studied the effects of land use systems (native forest, grassland, and arable land) in both Alberta, in western Canada, and Heilongjiang, in northeast China, on the quality and quantity of soil DOC.Materials and methodsWe studied the UV absorption, humification index (HIX), and biodegradability of water-extractable organic C, which is operationally defined as DOC. The relationship between biodegradability and the structural chemistry of soil organic matter studied with 13C-nuclear magnetic resonance (NMR) spectroscopy was also investigated.Results and discussionThe UV absorption and HIX, biodegradability of DOC, and the proportion of organic matter functional groups were not different among the land use types in both Canada and China. When the samples from both countries were considered together, the extractability of DOC was negatively correlated with soil organic carbon content and carbonyl C, and positively correlated with O-alkyl C; the biodegradability of DOC was positively correlated with soil C/N ratio, and negatively correlated with the specific UV absorbance and HIX.ConclusionsThe main effect of land use type on soil organic matter was on its content but not the labile C characteristics or organic matter functional group composition, indicating the dominant control of the climate on the quality of DOC of the organic matter under different land use types we studied in the two cold temperate regions.

Lithological control on phytolith carbon sequestration in moso bamboo forests

Phytolith-occluded carbon (PhytOC) is a stable carbon (C) fraction that has effects on long-term global C balance. Here, we report the phytolith and PhytOC accumulation in moso bamboo leaves developed on four types of parent materials. The results show that PhytOC content of moso bamboo varies with parent material in the order of granodiorite (2.0 g kg−1) > granite (1.6 g kg−1) > basalt (1.3 g kg−1) > shale (0.7 g kg−1). PhytOC production flux of moso bamboo on four types of parent materials varies significantly from 1.0 to 64.8 kg CO2 ha−1 yr−1, thus a net 4.7 × 106 –310.8 × 106 kg CO2 yr−1 would be sequestered by moso bamboo phytoliths in China. The phytolith C sequestration rate in moso bamboo of China will continue to increase in the following decades due to nationwide bamboo afforestation/reforestation, demonstrating the potential of bamboo in regulating terrestrial C balance. Management practices such as afforestation of bamboo in granodiorite area and granodiorite powder amendment may further enhance phytolith C sequestration through bamboo plants.

Field-scale variability of soil test phosphorus and other nutrients in grasslands under long-term agricultural managements

Field-scale variation of soil nutrients in grassland is becoming important because of the use of soil-nutrient information as a basis for policies such as the recently introduced EU Nitrates Directive. This study investigates the field-scale variability of soil-test phosphorus (STP) and other nutrients in two grasslands with a long-term history of poultry litter application. Two fields (field 1 for silage and field 2 for grazing pasture) were selected, and soil samples were collected based on 12 m by 12 m (field 1) and 15 m by 15 m (field 2) grids. Data were analysed using conventional statistics, geostatistics, and a geographic information system (GIS). In field 1, STP values ranged from 12.4 to 90 mg L–1 (average 38.5 mg L–1). In field 2, STP values ranged from 4.3 to 130.0 mg L–1 (average 21.4 mg L–1). Attention should be paid to long-term poultry application, as the average STP values in both fields were much greater than the recommended agronomic optimum STP status in Ireland of 8 mg L–1. Coefficient of variation values of soil nutrients in field 2 were much higher than those in field 1. Log-transformation and Box–Cox transformation were applied to achieve normality. Statistically significant (P < 0.01), positive correlations between P and other nutrients were found in both fields. Exponential and spherical models were fitted to the experimental variograms of STP in fields 1 and 2, respectively. Compared with the counterparts in field 1, soil nutrients in field 2 had larger ‘nugget-to-sill’ values, revealing that sheep grazing could weaken the spatial auto-correlation of soil nutrients. A grid of 60 m by 60 m was recommended for soil sampling in grassland, based on this study. High STP concentrations in field 1 were in the north-eastern side, which was related to uneven poultry litter application. Strong spatial similarity of low STP, magnesium, and pH values in their spatial distribution were found in field 2, confirming their strong statistical correlation.

A Study of Phytolith-occluded Carbon Stock in Monopodial Bamboo in China.

Bamboo plants have been proven to be rich in phytolith-occluded carbon (PhytOC) and play an important role in reducing atmospheric concentrations of CO2. The object of this paper was to obtain more accurate methods for estimation of PhytOC stock in monopodial bamboo because previous studies may have underestimated it. Eight monopodial bamboo species, widely distributed across China, were selected and sampled for this study in their own typical distribution areas. There were differences (P < 0.05) both in phytolith content (Phytolith/dry biomass) across leaves, branches and culm, and in PhytOC content (PhytOC/dry biomass) across leaves and branches between species, with a trend of leaf > branch > culm. The average PhytOC stored in aboveground biomass and PhytOC production flux contributed by aboveground biomass varied substantially, and they were 3.28 and 1.57 times corresponding dates in leaves, with the highest in Phyllostachys glauca McClure and lowest in Indocalamus tessellatus (Munro) Keng f. It can be concluded that it could be more accurate to estimate PhytOC stock or PhytOC production flux by basing on whole aboveground biomass rather than on leaf or leaf litter only. The whole biomass should be collected for more estimation of bamboo PhytOC sequestration capacity in the future.

WATER-SOLUBLE ORGANIC MATTER IN SOIL UNDER CHINESE FIR AND MASSON PINE FOREST

In order to understand the behavior of water soluble organic matter (WSOM) in soil under different types of forest, soil samples from twenty sites were sampled and analyzed for each forest in the area of Huzhou, China. Each sample was extracted with both cool water (25°C) and hot water (100°C). Without exception, hot water soluble organic carbon (HWSOC) was more than cool water soluble organic carbon (CWSOC). Chinese fir forest soil contained 1.49 times more CWSOC and 1.34 times more HWSOC than did the masson pine forest soil. The CWSOC and HWSOC in soil under Chinese fir forest account for 1.11% and 1.60% of total soil organic carbon (TSOC), and 0.70% and 1.19% under masson pine forest soil, respectively. CWSOC under Chinese fir forest was closely related to SOM and microbial biomass carbon (MBC) (correlation coefficients were 0.474* and 0.482* respectively), HWSOC, however, has little to do with SOM, MBC and soil enzymatic activities. HWSOC under masson pine forest was generally associated with SOM, MBC and sucrase, urease and protease (correlation coefficients were 0.511*, 0.510*, 0.541*, 0.418*, 0.356, respectively), but CWSOC was only closely related to sucrase (0.560*) and protease (0.581* *). It is concluded that higher amount of WSOC under Chinese fir forest is not good for soil chemical and biological properties.

Effects of Inorganic and Organic Fertilizers on Soil CO2 Efflux and Labile Organic Carbon Pools in an Intensively Managed Moso Bamboo (Phyllostachys pubescens) Plantation in Subtropical China

ABSTRACT Impact of combined application of inorganic and organic fertilizers on soil carbon dioxide (CO2) emission is poorly understood. We investigated the effects of inorganic fertilizer (IF), organic fertilizer (OF), and a mixture of organic and inorganic fertilizers (OIF) applications on the dynamics of soil CO2 efflux in intensively managed Moso bamboo plantations. Soil CO2 efflux and concentrations of water soluble organic C (WSOC) and microbial biomass C (MBC) in the IF treatment were higher than those in the control but lower than those in the OF and OIF treatments. Both OF and OIF treatments increased the SOC stock. Strong exponential relationships (p < 0.01) between soil temperature and CO2 efflux were observed in all treatments. Soil CO2 efflux in all four treatments was correlated with WSOC (p < 0.05) but not with MBC. We concluded the combined approach can possibly contribute to increasing the level of SOC stock in intensively managed plantations.

Production of carbon occluded in phytolith is season-dependent in a bamboo forest in subtropical China.

Carbon (C) occluded in phytolith (PhytOC) is a stable form of C; when PhytOC is returned to the soil through litterfall it is stored in the soil which can be an effective way for long-term C sequestration. However, few estimates on the rate of PhytOC input to the soil are available. To better understand the seasonal dynamics of PhytOC production and the annual rate of stable C sequestration through PhytOC input, we quantified the monthly litterfall, phytolith and PhytOC return to the soil over a year in a typical Lei bamboo (Phyllostachys praecox) forest in subtropical China. The monthly litterfall ranged between 14.81 and 131.18 g m−2, and the phytolith concentration in the monthly litterfall samples ranged between 47.21 and 101.68 g kg−1 of litter mass, with the PhytOC concentration in the phytolith ranged between 29.4 and 44.9 g kg−1 of phytolith, equivalent to 1.8–3.6 g kg−1 of PhytOC in the litterfall (based on litterfall dry mass). The amount of phytolith input to the soil system was 292.21±69.12 (mean±SD) kg ha−1 yr−1, sequestering 41.45±9.32 kg CO2−e ha−1 yr−1 of C in the studied Lei bamboo forest. This rate of C sequestration through the formation of PhytOC found in this study falls within the range of rates for other grass-type species reported in the literature. We conclude that return of C occluded in phytolith to the soil can be a substantial source of stable soil C and finding means to increase PhytOC storage in the soil should be able to play a significant role in mitigating the rapidly increasing atmospheric CO2 concentration.

Phytolith-occluded organic carbon as a mechanism for long-term carbon sequestration in a typical steppe: The predominant role of belowground productivity

Phytolith-occluded organic carbon (phytOC) has recently been demonstrated to be an important terrestrial carbon (C) fraction resistant to decomposition and thus has potential for long-term C sequestration. Existing studies show that plant leaves and sheath normally have high phytOC concentration, thus most of phytOC studies are limited to the aboveground plant parts. Grassland communities comprise herbaceous species, especially grasses and sedges which have relatively high concentrations of phytoliths, but the phytOC production from grassland, especially from its belowground part, is unknown. Here we determined the phytOC concentration in different parts of major plant species in a typical steppe grassland on the Mongolian Plateau, and estimated the phytolith C sequestration potential. We found that the phytOC concentration of major steppe species was significantly (p<0.05) higher in belowground (0.67gkg-1) than aboveground biomass (0.20gkg-1) and that the belowground net primary productivity (BNPP) was 8-15 times the aboveground net primary productivity (ANPP). Consequently, the phytOC stock in belowground biomass (12.50kgha-1) was about 40 times of that in aboveground biomass (0.31kgha-1), and phytOC production flux from BNPP (8.1-15.8kgha-1yr-1) was 25-51 times of that from ANPP. Our results indicate that BNPP plays a dominant role in the biogeochemical silica cycle and associated phytOC production in grassland ecosystems, and suggests that potential phytolith C sequestration of grasslands may be at least one order of magnitude greater than the previous estimation based on ANPP only. Our results emphasize the need for more research on phytolith and phytOC distribution and flux in both above and below ground plant parts for quantifying the phytolith C sequestration.