Yirong Su

GIS based land suitability assessment for tobacco production using AHP and fuzzy set in Shandong province of China

Fuzzy set, AHP, GIS were used to assess land suitability for tobacco production.Fuzzy set is ideal to transform numerical data into grades of membership.AHP is superior to determine the weights of multiple factors.29.8% of the total areas was highly suitable for crop, 17.7% was unsuitable.The finding facilities the land resource allocation and management for tobacco production. Flue-cured tobacco (Nicotiana tabacum L.) production is important since there are still more than 300millions of smokers in China. It is essential to allocate tobacco to the most suitable land areas precisely for the best production since arable land area has been decreasing. Therefore, we herein assess land suitability for tobacco production in tobacco zone of Shandong province, China. The assessment used 20 factors as suitability parameters, including climatic condition, soil type and nutrient characters, and topography data. The fuzzy set model, analytic hierarchy process (AHP) method, and GIS technique were integrated to create land suitability map. The results showed that 29.82% of the total area was highly suitable for tobacco production and 17.74% was unsuitable. Land in western part of the region had higher suitability, while the eastern region close to the Yellow Sea, had lower suitability. The most limiting factors included the number of continuous days with daily temperature ?20?C and high soil exchangeable Mg. This study demonstrates that Fuzzy set is an excellent mechanism to transform numerical data with various magnitudes into grades of membership functions, and representing land suitability. AHP is an effective and superior method to determine the weights of multiple factors in a systematic and logical way. The modeling results produced are based on individual land mapping unit, which facilities the land resource allocation and management. This result is significant in that it provides effective approaches to increase land use efficiency and better management for tobacco production.

Land reclamation and short-term cultivation change soil microbial communities and bacterial metabolic profiles

BACKGROUND Soil microbes play an important role in many critical ecosystem processes, but little is known about the effects of land reclamation and short-term cultivation on microbial communities in red soil. In this study, soil microbial communities under five land use patterns-artificial pine forest (Fp), tussock and shrub (TS), shrubbery (Sh), sugarcane (Su) and maize and cassava rotation (Ma)-were characterised by DNA fingerprinting and metabolic profiling to reveal how land reclamation and cultivation affect the underlying diversity and function of soil microbial communities in southwestern China. RESULTS Eight years of reclamation and cultivation significantly affected population size, composition and structure, bacterial metabolic profiles and diversity values (Shannon-Wiener index) of soil microbial communities. Soil organic carbon and pH were the most important factors shaping the underlying microbial communities; however, with significant correlations between soil carbon/nitrogen ratio and bacterial taxonomic and metabolic diversities, soil total nitrogen was a potentially important factor for soil microbial composition and function, as well as soil moisture, cation exchange capacity and physical structure to a lesser extent. In addition, the lowest pH, lower nutrient availability and the most compact soil in pine forest resulted in the lowest microbial taxonomic and metabolic diversities among the five land use patterns studied. CONCLUSION Soil organic carbon, nitrogen and pH appeared to be the most important factors influencing microbial biomass, composition and function in red soil of southwestern China. The study suggests that measures to lessen the impact of changes in this edaphic environment should be taken to avoid an imbalance of microbial function and improve ecological sustainability in southwestern China.

Restricted mineralization of fresh organic materials incorporated into a subtropical paddy soil

BACKGROUND Microbial activities involved in the dynamics of organic matter determine the potential for organic carbon (C) accumulation in soil. To understand this for paddy soil, an incubation experiment (25 °C, 45% water-holding capacity) was established using (14)C-labelled glucose and rice straw (500 µg C g(-1) soil) as substrates; an adjacent upland soil was used for comparison. RESULTS The amount of microbial biomass in the paddy soil was approximately 6 times larger and its turnover rate was 1.5-3 times faster than in the upland soil. These proportions of (14)C-labelled glucose and rice straw mineralized in the paddy soil were about 3% smaller (P < 0.01) than those in the upland soil. Also, there was no significant priming effect of fresh substrate additions on the mineralization of native organic C in the paddy soil, while the priming effect was significant in the upland soil. CONCLUSION Although the paddy soil contains a large amount of microbial biomass, which is also very active, the mineralization of fresh substrates is significantly restricted in this soil, along with a small priming effect. This favours the accumulation of organic C in paddy soils.

Community structure analysis of soil ammonia oxidizers during vegetation restoration in southwest China.

Soil ammonia oxidizers play a critical role in nitrogen cycling and ecological restoration. The composition and structure of soil ammonia oxidizers and their impacting factors were studied in four typical ecosystem soils, tussock (T), shrub (S), secondary forest (SF), and primary forest (PF), during vegetation restoration in the Karst region of Southwest China. The composition and structure of the ammonia‐oxidizing bacteria (AOB) and ammonia‐oxidizing archaea (AOA) communities were characterized by sequencing the amoA and arch‐amoA genes, respectively. The diversity of soil ammonia oxidizers (except in S) and plant Shannon diversity index gradually increased with vegetation restoration, and the ammonia oxidizer communities differed significantly (p < 0.001). Amplicons of AOA from the Nitrososphaera cluster dominated all four ecosystem soils. AOB Nitrosospira cluster 3b only appeared in PF and SF soils, while Nitrosospira cluster 3a species were found in all soils. Changes in AOB paralleled the changes in soil ammonium content that occurred with vegetation restoration. Redundancy analysis showed that the distribution of dominant AOB species was linked to pH, soil urease activity, and soil C/N ratio, whereas the distribution of dominant AOA species was mainly influenced by litter nitrogen content and C/N ratio. These results suggested that the composition and structure of the AOB community were more sensitive to changes in vegetation and soil ammonium content, and may be an important indicator of nitrogen availability in Karst ecosystem soils.

Response of soil organic carbon mineralization in typical Karst soils following the addition of 14C-labeled rice straw and CaCO3.

BACKGROUND Organic substrates and calcium are important factors controlling organic matter turnover in Karst soils. To understand their effects on soil organic carbon (SOC) mineralization, an incubation experiment was conducted involving a control treatment (CK), the addition of a (14)C-labeled rice straw (T1), CaCO(3) (T2), and both (14)C-labeled rice straw and CaCO(3) (T3) to two types of Karst soils (terra fusca and rendzina) and a red soil from southwestern China. RESULTS Cumulative mineralization of the rice straw over 100 days in rendzina (22.96 mg kg(-1)) and terra fusca (23.19 mg kg(-1)) was higher than in the red soil (15.48 mg kg(-1); P < 0.05). Cumulative mineralization of native SOC decreased following addition of (14)C-labeled rice straw in the rendzina and terra fusca but increased in the red soil (negative and positive priming effects on native SOC). The turnover times of (14)C-labeled microbial biomass C (MBC) in the red soil, terra fusca and rendzina were 71 ± 2, 243 ± 20 and 254 ± 45 days, respectively. By adding CaCO(3), the accumulation of SOC was greater in the Karst soils than in the red soil. CONCLUSION Although the interactions between rice straw decomposition and priming effects on native SOC are not yet understood, there was considerable variation between Karst and red soils. Soil calcium was a positive factor in maintaining SOC stability. MBC from rice straws was stable in terra fusca and rendzina, whereas it was active in the red soil. The Karst soils (terra fusca and rendzina) used in this study benefited SOC accumulation.

Fate of 14C-labeled dissolved organic matter in paddy and upland soils in responding to moisture

Soil organic matter (SOM) content in paddy soils is higher than that in upland soils in tropical and subtropical China. The dissolved organic matter (DOM) concentration, however, is lower in paddy soils. We hypothesize that soil moisture strongly controls the fate of DOM, and thereby leads to differences between the two agricultural soils under contrasting management regimens. A 100-day incubation experiment was conducted to trace the fate and biodegradability of DOM in paddy and upland soils under three moisture levels: 45%, 75%, and 105% of the water holding capacity (WHC). (14)C labeled DOM, extracted from the (14)C labeled rice plant material, was incubated in paddy and upland soils, and the mineralization to (14)CO2 and incorporation into microbial biomass were analyzed. Labile and refractory components of the initial (14)C labeled DOM and their respective half-lives were calculated by a double exponential model. During incubation, the mineralization of the initial (14)C labeled DOM in the paddy soils was more affected by moisture than in the upland soils. The amount of (14)C incorporated into the microbial biomass (2.4-11.0% of the initial DOM-(14)C activity) was less affected by moisture in the paddy soils than in the upland soils. At any of the moisture levels, 1) the mineralization of DOM to (14)CO2 within 100 days was 1.2-2.1-fold higher in the paddy soils (41.9-60.0% of the initial DOM-(14)C activity) than in the upland soils (28.7-35.7%), 2) (14)C activity remaining in solution was significantly lower in the paddy soils than in the upland soils, and 3) (14)C activity remaining in the same agricultural soil solution was not significantly different among the three moisture levels after 20 days. Therefore, moisture strongly controls DOM fate, but moisture was not the key factor in determining the lower DOM in the paddy soils than in the upland soils. The UV absorbance of DOM at 280 nm indicates less aromaticity of DOM from the paddy soils than from the upland soils. At any of the moisture levels, much more labile DOM was found in paddy soils (34.3-49.2% of the initial (14)C labeled DOM) compared with that in upland soils (19.4-23.9%). This demonstrates that the lower DOM content in the paddy soil compared with that in the upland soil is probably determined by the less complex components and structure of the DOM.

Effects of land cover on soil organic carbon stock in a karst landscape with discontinuous soil distribution

Land cover type is critical for soil organic carbon (SOC) stocks in territorial ecosystems. However, impacts of land cover on SOC stocks in a karst landscape are not fully understood due to discontinuous soil distribution. In this study, considering soil distribution, SOC content and density were investigated along positive successional stages (cropland, plantation, grassland, scrubland, secondary forest, and primary forest) to determine the effects of land cover type on SOC stocks in a subtropical karst area. The proportion of continuous soil on the ground surface under different land cover types ranged between 0.0% and 79.8%. As land cover types changed across the positive successional stages, SOC content in both the 0–20 cm and 20–50 cm soil layers increased significantly. SOC density (SOCD) within 0–100 cm soil depth ranged from 1.45 to 8.72 kg m−2, and increased from secondary forest to primary forest, plantation, grassland, scrubland, and cropland, due to discontinuous soil distribution. Discontinuous soil distribution had a negative effect on SOC stocks, highlighting the necessity for accurate determination of soil distribution in karst areas. Generally, ecological restoration had positive impacts on SOC accumulation in karst areas, but this is a slow process. In the short term, the conversion of cropland to grassland was found to be the most efficient way for SOC sequestration.

Variations in the patterns of soil organic carbon mineralization and microbial communities in response to exogenous application of rice straw and calcium carbonate.

The addition of exogenous inorganic carbon (CaCO3) and organic carbon has an important influence on soil organic carbon (SOC) mineralization in karst soil, but the microbial mechanisms underlying the SOC priming effect are poorly understood. We conducted a 100-day incubation experiment involving four treatments of the calcareous soil in southwestern Chinas karst region: control, (14)C-labeled rice straw addition, (14)C-labeled CaCO3 addition, and a combination of (14)C-labeled rice straw and CaCO3. Changes in soil microbial communities were characterized using denaturing gradient gel electrophoresis with polymerase chain reaction (PCR-DGGE) and real-time quantitative PCR (q-PCR). Both (14)C-rice straw and Ca(14)CO3 addition stimulated SOC mineralization, suggesting that organic and inorganic C affected SOC stability. Addition of straw alone had no significant effect on bacterial diversity; however, when the straw was added in combination with calcium carbonate, it had an inhibitory effect on bacterial and fungal diversity. At the beginning of the experimental period, exogenous additives increased bacterial abundance, although at the end of the 100-day incubation bacterial community abundance had gradually declined. Incubation time, exogenous input, and their interaction significantly affected SOC mineralization (in terms of priming and the cumulative amount of mineralization), microbial biomass carbon (MBC), and microbial community abundance and diversity. Moreover, the key factors influencing SOC mineralization were MBC, bacterial diversity, and soil pH. Overall, these findings support the view that inorganic C is involved in soil C turnover with the participation of soil microbial communities, promoting soil C cycling in the karst region.

Fate of rice shoot and root residues, rhizodeposits, and microbial assimilated carbon in paddy soil - part 2: turnover and microbial utilization

Background and aimsThe turnover of plant- and microbial- derived carbon (C) plays a significant role in the soil organic C (SOC) cycle. However, there is limited information about the turnover of the recently photosynthesized plant- and soil microbe-derived C in paddy soil.MethodsWe conducted an incubation study with four different 13C–labeled substrates: rice shoots (Shoot-C), rice roots (Root-C), rice rhizodeposits (Rhizo-C), and microbe-assimilated C (Micro-C).ResultsShoot- and Root-C were initially rapidly transformed into the dissolved organic C (DOC) pool, while their recovery in microbial biomass C (MBC) and SOC increased with incubation time. There were 0.05%, 9.8% and 10.0% of shoot-C, and 0.06%, 15.9% and 16.5% of root-C recovered in DOC, MBC and SOC pools, respectively at the end of incubation. The percentages of Rhizo- and Micro-C recovered in DOC, MBC, and SOC pools slowly decreased over time. Less than 0.1% of the Rhizo- and Micro-C recovered in DOC pools at the end of experiment; while 45.2% and 33.8% of Rhizo- and Micro-C recovered in SOC pools. Shoot- and Root-C greatly increased the amount of 13C–PLFA in the initial 50 d incubation, which concerned PLFA being indicative for fungi and actinomycetes while those assigning gram-positive bacteria decreased. The dynamic of soil microbes utilizing Rhizo- and Micro-C showed an inverse pattern than those using Shoot- and Root-C. Principal component analysis of 13C–PLFA showed that microbial community composition shifted obviously in the Shoot-C and Root-C treatments over time, but that composition changed little in the Rhizo-C and Micro-C treatments.ConclusionsThe input C substrates drive soil microbial community structure and function with respect to carbon stabilization. Rhizodeposited and microbial assimilated C have lower input rates, however, they are better stabilized than shoot- and root-derived C, and thus are preferentially involved in the formation of stable SOC in paddy soils.

Comparative analysis of basidiomycetous laccase genes in forest soils reveals differences at the cDNA and DNA levels

AimsThis study was undertaken to investigate laccase-containing basidiomycete communities at the cDNA and DNA levels and to assess the influences of vegetation and soil types on the basidiomycete communities in forest soils.Materials and methodsSoil samples were collected from the upper soil layers of two typical subtropical forests (a broad-leaved forest developed in Karst limestone soil and an artificial coniferous forest with Pinus massoniana in red soil) in China. The basidiomycete communities were characterized by cloning and sequencing of the laccase genes at both the cDNA and DNA levels. Compositions of lignin monomers were determined by gas chromatography–mass spectrometry.ResultsMost of the laccase genes obtained in this study were new, highlighting the research gap of this functional group. The trends of the basidiomycetous laccase gene diversity among the upper soil layers of the two forests were consistent between the cDNA and DNA levels. The Agaricales had high activity because they dominated all the tested soils. However, the total basidiomycete communities reflected at the cDNA and DNA levels were significantly different due to the presence of some quiescent basidiomycetous groups. Almost all of the lignin components were decomposed from the O to the A layers in the two forests, and laccases produced by Agaricales were likely responsible for the decomposition of guaiacyl monomers. Both vegetation and soil types had great influences on the active laccase-containing basidiomycete communities, primarily via the pH, C/N, and the contents of lignin monomers.ConclusionsThe cDNA- and DNA-level approaches presented good consistency of diversities but different compositions of laccase-containing basidiomycete communities, thus emphasizing the importance of focusing on laccase genes at the cDNA level in future studies. It is the quality but not the quantity of SOM to determine the diversity and composition of the active laccase-containing basidiomycete communities.