Silong Wang

Addition of external organic carbon and native soil organic carbon decomposition: a meta-analysis.

Background Extensive studies have been conducted to evaluate the effect of external organic Carbon on native soil organic carbon (SOC) decomposition. However, the direction and extent of this effect reported by different authors is inconsistent. Objective The objective was to provide a synthesis of existing data that comprehensively and quantitatively evaluates how the soil chemical properties and incubation conditions interact with additional external organic C to affect the native SOC decomposition. Data Source A meta-analysis was conducted on previously published empirical studies that examined the effect of the addition of external organic carbon on the native SOC decomposition through isotopic techniques. Results and Conclusions The addition of external organic C, when averaged across all studies, enhanced the native SOC decomposition by 26.5%. The soil with higher SOC content and fine texture showed significantly higher priming effects, whereas the soil with higher total nitrogen content showed an opposite trend. The soils with higher C:N ratios had significantly stronger priming effects than those with low C:N ratios. The decomposition of native SOC was significantly enhanced more at early stage of incubation (<15d) than at the later stages (>15d). In addition, the incubation temperature and the addition rate of organic matter significantly influenced the native SOC decomposition in response to the addition of external organic C.

Relating net primary productivity to soil organic matter decomposition rates in pure and mixed Chinese fir plantations

In a 5-year field trial, we examined plant productivity and soil organic matter decomposition on plots with a mixture of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and broadleaved trees. We compared pure fir (PF) plots to two mixed plots (2:1 ratio of fir to broadleaved trees): MP1 (C. lanceolata and Liquidambar formosana Hance) and MP2 (C. lanceolata and Alnus cremastogyne Burk). The mixed plots differed in that the MP2 plots incorporated a nitrogen-fixing tree (A. cremastogyne). We hypothesized that the mixed plots would have higher soil organic matter decomposition rates than the PF plots as a result of increased primary productivity. The increased productivity would increase carbon input into soils, thus resulting in greater microbial biomass and soil basal respiration. We measured tree biomass, soil organic matter decomposition rates, microbial biomass carbon, total organic carbon, metabolic quotient and microbial quotient for each plot. The results showed that the productivity, microbial biomass carbon, and total carbon in the MP2 plots were significantly higher than in the PF and MP1 plots. Path analyses suggested that soil respiration varied with the amount of tree biomass produced. However contrary to our hypothesis, soil basal respiration was higher in the PF plots than in the MP2 plots.

Carbon Mineralization of Soils from Native Evergreen Broadleaf Forest and Three Plantations in Mid-subtropic China

Mineralization of soil organic carbon (C) plays a key role in supplying nutrient elements essential to plant growth. Changes of C mineralization of mixed stands of Chinese fir and Michelia macclurei (a broadleaf tree), pure M. macclurei stands, and pure Chinese fir (Cunninghamia lanceolata) stands established in 1983 after clear‐felling of a first‐generation Chinese fir forest were analyzed in Huitong, Hunan Province, China, and compared with those of a stand of native secondary evergreen broadleaf forest (NBF). The results showed that NBF soil had the greatest C mineralization. Mixture of Chinese fir and M. macclurei had no effect on total soil organic C in comparison with pure Chinese fir plantation, but significantly increased C mineralization from soils was detected in this study. This positive influence on C mineralization could be explained by the increase of soil labile C pools and soil microbial biomass and activity. From the analysis of C mineralization, soil microbial properties, and labile organic C, mixtures of broadleaf and Chinese fir can be considered to be an effective sustainable management model for a Chinese fir plantation. Given strong correlations with microbiological and biochemical characteristics of soils and an easier process of determination, hot water extraction, hot water–extractable C (HWC) could be used as an integrated measure of forest soil quality in mid‐subtropics.

Autoinhibition and soil allelochemical (cyclic dipeptide) levels in replanted Chinese fir (Cunninghamia lanceolata) plantations

Aims and backgroundDespite increasing knowledge of the role of allelochemicals in the productivity decline of replanted Chinese fir plantations, relatively little is known about the levels and sources of allelochemicals in relation to autoinhibition.MethodsAllelopathic potential of litter, root exudates, and soils in successive rotations of Chinese fir plantations were detected. An allelochemical cyclic dipeptide (6-hydroxy-1,3-dimethyl-8-nonadecyl-[1,4]-diazocane-2,5-dione) from litter, root exudates, and soils in successive rotations was quantified.ResultsExtracts of leaf litter, fine root, and root exudates significantly inhibited the growth of Chinese fir germinants, and inhibition increased with successive rotations. Similar results were observed in the rhizosphere soil, basal soil, and bulk soil. The largest observed inhibition occurred in the rhizosphere soil. Furthermore, cyclic dipeptide was found in litter, root exudates, and soils, and the concentrations increased with successive rotations. The rhizosphere soil had the highest cyclic dipeptide level, followed by basal soil, while bulk soil contained the lowest concentration. There was a significant positive relationship between the inhibition of radicle growth of Chinese fir germinants and the concentration of cyclic dipeptide. Annual release of cyclic dipeptide through root exudation was 2.08–9.78 mol ha−1 annum, but the annual release of cyclic dipeptide through leaf litter decomposition was lowered to 0.32–1.41 mol ha−1 annum.ConclusionsCyclic dipeptide which caused autoinhibition of Chinese fir may be released into the soil through litter decomposition and root exudation. Root exudates provided more contributions to soil cyclic dipeptide levels than litter in Chinese fir plantations.

Effect of monospecific and mixed Cunninghamia lanceolata plantations on microbial community and two functional genes involved in nitrogen cycling

Conversion of native broadleaf forest (NF) and introduction of broadleaf species into monospecific Cunninghamia lanceolata plantations are silvicultural practices driven by the increasing demand for timber production. This study was conducted to evaluate the impacts of successive planting of C. lanceolata and mixed plantations (C. lanceolata-Michelia macclurei, CFM; C. lanceolata-Alnus cremastogyne, CFA; C. lanceolata-Kalopanax septemlobus, CFK) on microbial community diversity. Microbial biomass (MBC) was assessed using chloroform fumigation-extraction. Using denaturing gradient gel electrophoresis (DGGE), we examined the biodiversity within eubacterial (16S rRNA gene) and fungal (28S rRNA gene) species and two genes involved in N cycling: nifH and amoA. Microbial community diversities and microbial biomass decreased as NF was substituted by successive plantings of C. lanceolata plantations, whereas the trend reversed after introducing the broadleaf, M. macclurei, into pure C. lanceolata plantations. A strong positive correlation between MBC changes and total organic C (TOC), total organic N (TON), available N and extractable C (Cext) were seen, which suggests that MBC was tightly coupled with the content of soil organic matter. The Shannon index showed that bacterial diversity and two functional genes (nifH and amoA) diversities associated with monospecific C. lanceolata plantations were lower than that of NF or mixed C. lanceolata plantations, such as CFM and CFA, whereas the opposite was seen for fungal diversity. Bacterial diversity was positively correlated with pH, TOC, TON, Cext and NH4+-N; while fungal diversity was positively correlated with C/N ratio and negatively correlated with pH. Both nitrogen fixing and ammonia oxidizing bacterial diversities were positively correlated with pH. Thus, soil pH was not only significantly positively correlated with bacterial diversity (r = 0.502, P < 0.05), nifH gene diversity (r = 0.564, P < 0.01) and amoA gene diversity (r = 0.659, P < 0.001), but also negatively correlated with fungal diversity (r = − 0.505, P < 0.05), which seemed to be responsible for the discrimination of the soil microbial communities among these plantations. These findings suggest that different silvicultural practices have significant impacts on the soil microbial community through influences on soil chemical properties.

Carbon storage in evergreen broad-leaf forests in mid-subtropical region of China at four succession stages

To better understand the effect of forest succession on carbon sequestration, we investigated carbon stock and allocation of evergreen broadleaf forest, a major zonal forest in subtropical China. We sought to quantify the carbon sequestration potential. We sampled four forest types, shrub (SR), pine (Pinus massoniana) forest (PF), pine and broadleaf mixed forest (MF) and evergreen broadleaf forest (BF). A regression equation was constructed using tree height and diameter at breast height (DBH) and elements of total tree biomass. The equation was subsequently utilized to estimate tree carbon storage. The carbon storage of understory, litter, and soil was also estimated. Carbon storage in biomass increased significantly from the early succession stage SR (6.21 t·ha−1) to the late stage BF (134.87 t·ha−1). The biomass carbon stock of forest layers generally increased with succession except for the understory. The soil organic carbon storage for the total profile increased with forest succession, from 51.16 to 90.49 t·ha−1, but the contribution of SOC to the carbon stock of the forest ecosystem declined from 89.18% to 40.15%. The carbon stock at ecosystem scale increased significantly with succession from SR (57.37 t·ha−1), to PF (154.20 t·ha−1), to MF (170.96 t·ha−1) and to BF (225.36 t·ha−1), with carbon stock of BF 3.93 times that of SR. The forests in our study have great potential for increasing carbon sequestration, and large areas of secondary or degraded evergreen broadleaf forests in the subtropical zone of China could be a great carbon sink in future.

Soil microbial properties and nutrients in pure and mixed Chinese fir plantations

An investigation on soil organic carbon, total N and P, NO3−-N, available P, microbial biomass C, N and P, basal respiration and metabolic quotients (qCO2) was conducted to compare differences in soil microbial properties and nutrients between 15-year-old pure Chinese fir (Cunninghamia lanceolata) and two mixed Chinese fir plantations (mixed plantations with Alnus cremastogyne, mixed plantations with Kalopanax septemlobus) at Huitong Experimental Station of Forest Ecology (26°45′N latitude and 109°30′E longitude), Chinese Academy of Sciences in May, 2005. Results showed that the concentrations of soil organic carbon, total N, NO3−-N, total P and available P in mixed plantations were higher than that in pure plantation. Soil microbial biomass N in two mixed plantations was averagely higher 69% and 61% than that in pure plantation at the 0–10 cm and 10–20 cm soil depth, respectively. Soil microbial biomass C, P and basal respiration in mixed plantations were higher 11%, 14% and 4% at the 0–10 cm soil depth and 6%, 3% and 3% at the 10–20 cm soil depth compared with pure plantation. However, soil microbial C: N ratio and qCO2 were averagely lower 34% and 4% in mixed plantations than pure plantation. Additionally, there was a closer relation between soil microbial biomass and soil nutrients than between basal respiration, microbial C: N ratio and qCO2 and soil nutrients. In conclusion, introduction of broad-leaved tree species into pure coniferous plantation improved soil microbial properties and soil fertility, and can be helpful to restore degraded forest soil.

Microbial Biomass in Subtropical Forest Soils: Effect of Conversion of Natural Secondary broad-leaved Forest to Cunninghamia lanceolata Plantation

Conversion of natural secondary broad-leaved forest to Cunninghamia lanceolata plantation is a common management practice in subtropical China. In this study, we compared soil physico-chemical properties, microbial biomass in one natural secondary broad-leaved forest and two C. lanceolata plantation sites to estimate the effects of forest conversion on soil microbial biomass at the Huitong Experimental Station of Forestry Ecology, Chinese Academy of Sciences. Concentrations of soil organic carbon, total nitrogen, NH4+-N and microbial biomass carbon and nitrogen were much lower under C. lanceolata plantations as compared to natural secondary broad-leaved forest. Soil microbial biomass C in the first and second rotation of C. lanceolata plantations was only 53%, 46% of that in natural secondary broad-leaved forest, and microbial biomass N was 97% and 79%, respectively. The contribution of microbial biomass C to soil organic C was also lower in the plantation sites. However, the contribution of microbial N to total nitrogen and NH4+-N was greater in the C. lanceolata plantation sites. Therefore, conversion of natural secondary broad-leaved forest to C. lanceolata plantation and continuous planting of C. lanceolata led to the decline in soil microbial biomass and the degradation of forest soil in subtropical China.

Thinning effect on photosynthesis depends on needle ages in a Chinese fir (Cunninghamia lanceolata) plantation

Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ13C) and oxygen (δ18O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ13C and declined δ18O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ13C and a constant needle δ18O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ13C, δ18O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future.

Nine new diterpenes from the leaves of plantation-grown Cunninghamia lanceolata

Nine new diterpenes named lanceolatanol hydroperoxide (1), epilanceolatanol hydroperoxide (2), lanceolatanoic acid hydroperoxide (3), epilanceolatanoic acid hydroperoxide (4), lanceolatanol (5), lanceolatanoic acid (6), 11-acetoxylanceolatanoic acid (7), 11-acetoxylanceolatanoic acid methyl ester (8) and epoxyhinokiol (13) were characterized from the leaves of plantation-grown Cunninghamia lanceolata along with twelve known compounds. The compounds were evaluated for their growth inhibitory activities against the human prostate cell line (PC-3).