Effects of Consecutively Monocultured Rehmannia glutinosa L.on Diversity of Fungal Community in Rhizospheric Soil

Continuous monoculture problems, or replanting diseases, are one of the key factors affecting productivity and quality of Chinese medicinal plants. The underlying mechanism is still being explored. Most of the studies on continuous monoculture ofRehmannia glutinosa L. are focused on plant nutritional physiology, root exudate, and its autotoxieity. However, the changes in the diversity of microflora in the rhizosphere mediated by the continuous monoculture pattern have been remained unknown. In this study, terminal restriction fragment length polymorphism （T-RFLP） technique was used for fingerprinting fungal diversity in the rhizosphere soil sampled from the fields ofR. glutinosa monocultured for 1 and 2 yr. The results showed that the structure of fungal community in consecutively moncultured rhizosphere soil was different from that in control soil （no cropping soil）, and varied with the consecutive monoeulture years （1 and 2 yr）. The comprehensive evaluation index （D） of fungal community estimated by principal component analysis of fragment number, peak area, Shannon-Weiner index, and Margalef index was higher in 1 yr monoculture soil than that in 2 yr monoculture soil, suggesting that consecutive monoculture of R. glutinosa could be a causative agent to decrease the diversity of fungal community in the rhizosphere soil.

Impact of Continuous Chinese Fir Monoculture on Soil

Soil properties were investigated in sites where three succeeding generationsof Chinese fir (Gunning-hamia lanceolata, (Lambert) Hooker) in Nanping, Fujian, China, werecultivated in order to show the impact of a repeated monoculture on site productivity. Compared withthe first generation (FG) stand the soil structure deteriorated in the second generation (SG) andthe third generation (TG) stands. For instance, the destruction rate of the peds increased by 55%-115% in the SG and the TG stands compared to the FG stand. Soil nutrient storage and nutrientavailability also decreased in the SG and the TG stands. For surface soils of 0-20 cm, the organicmatter content, total N and P, and available N and P decreased by 3%-20% relative to those in the FGstand. For many soil parameters, the differences between the FG stand and the SG and the TG standswere statistically significant (LSD test, P < 0.05). Furthermore, with each succeeding generation ofChinese fir, the total number of soil microbes declined, the soil enzyme activity weakened, and thesoil biological activity decreased. In order to maintain sustainable site productivity, newsilvicultural practices need to be developed for management of Chinese fir plantations.

Carbon Return and Dynamics of Litterfall in Natural Forest and Monoculture Plantation of Castanopsis kawakamii in Subtropical China

The amount of carbon returned through litterfall and its seasonal pattern were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata) (CF) in Sanming, Fujian Province, China. Mean annual carbon return through total litterfall over 3 years (from 1999 to 2001) was 5.097 t穐m2 in the NF, 4.337 t穐m2 in the CK and 2.502 t穐m2 in the CF respectively. Of the total carbon return in the three forests, leaf contribution accounted for 58.96%, 68.53% and 56.12% and twig 24.41%, 22.34% and 26.18%, respectively. The seasonal patterns of carbon return from total litterfall and leaf-litter were quite similar among the three forests. A peak of carbon input from litterfall in the NF and the CK occurred in spring except for the highest annual C return through branch litter of the NF in summer, while the CF showed the maximum C return in summer. The results of this study demonstrate that the natural forest has a greater C return through litterfall than monoculture plantations, which is beneficial to the increase of soil organic matter storage and the maintenance of soil fertility.

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce

Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa （PBT） and P. maximowiczii x balsamifera （PMB）, one improved family of Norway spruce （Picea glauca （PA）） and one improved family of white spruce （Picea abies （PG）） growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor （1 × 1 m, 3 × 3 m and 5 × 5 m） and mixture treatments as subplot factor （pure： PBT, PMB, PA and PG, and 1：1 mixture PBT：PA, PBT：PG, PMB：PA and PMB：PG）. Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.

Soil quality index as a tool for Scots pine(Pinus sylvestris) monoculture conversion planning on afforested,reclaimed mine land

In Central Europe, a large portion of post-mining sites were afforested with Scots pine, which is characterized by good adaptability and a tolerance for poor habitat at the beginning of forest ecosystem development. Conversion of monoculture on mine sites into more biodi- verse mixed hardwood forests, especially on more fertile deposits, can be an emerging need in this part of Europe in next decades. The ability to classify the forests at these post-mining sites will facilitate proper species selection as well as the management and formation of the developed ecosystem＇s stability. This work describes the guidelines that can be followed to assess reclaimed mine soil （RMS） quality, using the mine soil quality index （MSQI） and a classification of developed forest sites as a basis of tree-stand species selection and conversion of pine monocul- tures. The research was conducted on four post-mining facilities （lignite, hard coal, sulphur, and sand pit mining areas） on different RMS sub- strates dominant in Central Europe. Soil quality assessment takes into account the following features of the soil： texture soil nutrients （Ca, Mg, K, Na, P）; acidity （pH KC1）; and Corg-to-Nt ratio in the initial organic horizon. An analysis was conducted of classification systems using the MSQI validation correlation （at p =0.05） with vegetation features af- fected by succession： aboveground biomass of forest floor and ecological indicators of vascular plants （calculated on the basis of EUenberg＇s （2009） system）. Eventually, in the analysed data set, the MSQI ranged from 0.270 for soils on quaternary sands to 0.720 for a mix of quaternary loamy sands with neogene clays. Potential forest habitat types and the role of the pine in the next generation of tree stands on different RMS parent rock substrate were proposed.

The effects of teak monoculture on forest soils: a case study in Bangladesh

Teak plantations date back to 1871 in Bangladesh. This study was designed to assess how teak monoculture has impacted the soil properties in Bangladesh. Multiple linear regression and correlation matrices were estimated to evaluate these impacts. The means of soil physicochemical properties were compared across various attributes of the plantations. Older plantations accumulated more organic carbon in the soils than the younger plantations. Excessive removal of litter from the forest floor resulted in reduced levels of N, P, K, and other nutrients in the soils. Since bulk density was continuously decreasing deeper into the soil, the penetration of mineral nutrients into the soil was low. Furthermore, moisture content in the topsoil was significantly lower than that in the bottom layers due to the exposed and dry condition of the forest floor under teak plantations. For improving depleted teak plantation soils, teak could be planted with other tree species rather than just in monocultures. In addition, the forest floor could be enriched with leguminous herbs and shrubs to improve soil health in these plantations.

What is the value of eucalyptus monocultures for the biodiversity of the Atlantic forest? A multitaxa study in southern Bahia, Brazil

Eucalyptus plantations are increasing in Brazil, frequently replacing pastures, but there is still scarce information about its capacity to maintain the fauna of neighbor forest remnants. In this study, we compared descriptors of the communities of leaf litter organisms （lizards, anurans, myriapods, arachnids, orthopterans, coleopterans, and ants） between a large remnant of primary Atlantic Forest and an adjacent eucalyptus monoculture （phase 1）. Then, we compared the same descriptors for leaf litter lizards and anurans, Euglossini bees, and frugivorous butterflies among the largest remnant, small remnants at intermediate regeneration stage, and eucalyptus monocultures that were not adjacent to the largest remnant （phase 2）. Monocultures were sampled immediately before logging. In phase 1, we detected significant differences in structure between the forest and the monoculture in six out of seven communities sampled. Ca. 81% of the species of the landscape were recorded in the forest, but only 54% of these were found also in the monoculture. In phase 2, the structure of two out of four forest communities was significantly different from the structure of small remnants and monocultures. On average, 76% of the species found in the whole landscape were sampled in the forest. Out of this subset, on average 74% of the species were also sampled in small remnants and 68% in monocultures. Findings of the present study point out a moderate capacity of eucalyptus monocultures to harbor species of the forest fauna even when fully grown but highlights the opportunity that they might offer for increasing connectivity in anthropogenic forest landscapes depending on their management.

Histone deacetylase inhibitor promotes differentiation of embryonic stem cells into neural cells in adherent monoculture

Background Embryonic stem （ES） cells poss unlimited self-renewal capacity and the ability to differentiate into cell of all three germ layers in vitro. Induced differentiation of ES cells to neural lineage cells has great potential in basic study of neurogenesis and regeneration therapy of neurodegenerative diseases. Histone deacetylase （HDAC） inhibitors enhance histone acetylation so that globularly activate gene expression and may initiate multilineage differentiation. In this study,we aimed to develop a method to induce the differentiation of ES cells to neural cells combining HDAC inhibition and neural cellselection.Methods In this study, we used HDAC inhibitor sodium butyrate （NAB） to induce the differentiation of mouse embryonic stem cells to neural cells through monolayer culture. After differentiation initiation by histone deacetylase inhibitor sodium butyrate, neural cells were induced and selected with a serum free culture system. Results Homogeneous neurons without glial cells demonstrated by molecular marker expression were differentiated with the method. The resultant neurons were excitable. Conclusion The method combined differentiation induction effect of HDAC inhibitors and selective culture system to derive neural cells from ES cells, and implied the involvement of epigenetic regulation in neural differentiation.

Comparison of soil chemical and microbial properties in monoculture larch and mixed plantations in a temperate forest ecosystem in Northeast China

Background:The introduction of broadleaved tree species in monoculture larch plantations to establish mixed plantations is a feasible way to improve soil properties.However,our understanding of how mixed plantations of larch and broadleaved tree species affect soil properties,particularly microbial community structures and functions,remains limited.We compared three paired monoculture larch(Larix gmelinii)and mixed[L.gmelinii–Fraxinus mandshurica(a dominant broadleaved species)]plantations to investigate the effect of a larch–broadleaved tree species combination on the carbon(C)and nitrogen(N)content,abundance and composition of microbial communities,and enzyme activities associated with litter and soil.Results:The bacterial abundance in the litter,soil N availability,pH and electronic conductivity were significantly higher in the mixed-species plantation in comparison with those of the monoculture plantation.However,in the litter of mixed-species plantation,the relative levels of Agaricomycetes fungi were lower than those of the monoculture plantation,indicating that soil fungal communities were affected more than bacterial communities.In contrast,soil in the mixed-species plantation showed increased exoglucanase and N-acetyl-β-glucosaminidase activities.However,the C and N levels,δ^(13)C andδ^(15)N values,and fungal abundance in litter and soil were not significantly different between the monoculture and mixed-species plantations.Conclusions:Our findings suggest that fungal community compositions and enzyme activities are sensitive to the introduction of broadleaved tree species into larch plantations.Thus,these parameters can be used as important indicators to evaluate the effects of tree species selection on soil restoration.

Effects of monoculture-conditioned soils on common tallgrass prairie species productivity

Aims Within biodiversity-ecosystem function experiments,it is widely understood that yields of some species rapidly decline when planted in monoculture.This effect may arise due to decreased access to soil nutrients or an increase in detrimental soil patho-gens within monoculture plantings.To determine whether or not soil conditioning affects tall grass prairie species biomass produc-tion,we conducted a field experiment to assess species growth in conspecifically and heterospecifically conditioned soils and a greenhouse experiment to elucidate how conspecific soil biota affected species growth.Methods To test for species-specific soil effects,seedlings of the legume Astragulus canadensis,the cool-season grass Elymus canaden-sis,the forb Helianthus maximiliani and the warm-season grass Panicum virgatum were grown in field plots that had either been conspecifically or heterospecifically conditioned over 2 years.Plant growth was recorded over a single growing season,and soils were assessed for differences in their nematode(mesofauna)communities.Seedlings of these species were additionally grown over a 6-week period in conspecifically conditioned soil that was either untreated,heated to 60°C,sterilized(autoclaved at 120°C)or heated to 60°C and reinoculated with conspecific soil biota.The two heating treatments were used to compare growth responses between a low-and high-temperature soil treatment.The reinoculation treatment was used to assess the effect of soil biota in light of any nutrient changes that may have occurred with soil heating.Important Findings Elymus canadensis,H.maximiliani and P.virgatum growth was improved in field plots conditioned by the legume A.canadensis com-pared with their growth in conspecifically conditioned(home)soils.Despite variation(grass versus nongrass)in their soil nematode com-munities,there was no evidence to suggest that these three species were inhibited by conspecific or functionally conspecific soil condi-tioning in the field.Astragulus canadensis was the only species whose growth was reduced in conspecifically conditioned field soil.In the greenhouse,E.canadensis growth increased in all of the heat-treated soils,likely a response to a fertilization effect associated with soil heat-ing.Panicum virgatum growth also increased among the heated soils.However,its growth decreased in heated soils where conspecific soil mesofauna were reintroduced,indicating that this grass may be inhib-ited by soil mesofauna.Finally,A.canadensis growth decreased in soils treated to fully remove soil biota and was not affected by rein-troduction of soil mesofauna,suggesting that this species negatively responds to soil changes that occur with extreme heating.At least for the suite of tallgrass prairie species evaluated within this experiment,it appears that changes in soil chemistry and generalist soil biota,as opposed to increasing species-specific soil pathogens,more strongly contribute to temporal disparities in their performance.

Population-level performance of Arabidopsis thaliana (L.) Heynh in dense monocultures

Aims Very little is known about the performance of non-agricultural plant species in monocultures,even though nearly all agricultural species have experienced the transition from multi-species environments to dense monospecific stands during the breeding process.In the light of recent work that highlighted the possibility that the weedy species Arabidopsis thaliana can offer novel insight into crop breeding,we aimed to test the effect of sowing density on group and individual performance in different photoperiod environments in A.thaliana.Methods We studied the performance of A.thaliana Cvi-0 ecotype.The choice of Cvi-0 was based on a preliminary experiment in which plants of Cvi-0 ecotype exhibited high competitive performance.Sowing densities used were 17.6,8.8,4.4,2.2 and 1.1 cm^(2) per plant and photoperiod environments 12 or 16 h of day light.Important Findings In this experiment,populations attained constant total seed yield for all densities.Some interaction effect occurred,as at high sowing density and at longer day length plants produced heavier seeds,whereas at shorter day length seed weight was negatively related to plant density.These results shed light on different strategies that annual plants can adopt when they face intense intraspecific competition,and could help to offer new perspectives for breeding crops with enhanced group performance.

Effect of light and nutrients on interspecific interactions between submerged macrophytes:implications for restoration of multispecies aquatic vegetation in eutrophic lakes

Constructing multispecies submerged vegetation systems and maintaining stable seasonal succession is crucial for restoring shallow eutrophic lakes.However,little is known about the interactions between successional and existing species of different growth forms,particularly under the low light and high nutrient conditions of eutrophic lakes.We measured the functional traits of mature Vallisneria natans(Lour.)Hara plants and Potamogeton crispus L.shoots in monoculture and mosaic patterns under different light and nutrient conditions.The effect of light on functional traits of the submerged macrophyte species was more significant than that of nutrients,but the reverse was true for P.crispus biomass allocation.Moreover,interspecific interactions affected only the submerged macrophytes under the low light condition and varied with species.Specifically,the interaction of P.crispus to V.natans was biased towards competition,while the interaction of V.natans to P.crispus was converted from facilitation to competition by eutrophication,particularly in the homogenous mosaic growth pattern.This study demonstrates that sufficient light is a prerequisite and patch planting is an effective means to form a multispecies submerged vegetation system.In addition,we emphasize that the coexistence of eutrophication and low light will likely result in a competition between submerged macrophytes thus simplifying the vegetation,even if their growth forms and growing seasons are different.These findings help explain the collapse of multispecies submerged vegetation and guide the restoration of aquatic plants in eutrophic lakes.

Transformation and assessment of Chinese pine pure plantations for soil and water conservation in western Liaoning Province,P. R. China

Western Liaoning Province is characterized by huge areas of lowly-efficient Chinese pine (Pinus tabulaeformis Carr.) pure plantations. How to transform these plantations has become an increasingly significant management problem. In this study, the authors summarized the approaches, which are based on close-to-nature silvicultural system, to transform the pure pine plantations. Native broadleaved trees were planted in three methods: 1) after strip clearcutting, 2) after patch clearcutting; 3) on the open forestland and the forest edge. The transformation targets and the selection of tree species were expatiated in this paper. The key techniques and their application conditions for each method were analyzed and discussed. Through investigation and contrastive analysis, the assessment was made to the stands transformed by strip method. Results showed that the mixed stands at 16 years after transformation had an obvious layered structure and the species richness of understorey vegetation increased by 23.5%–52.9%. Soil enzyme activities of urease, phosphatase and sucrase increased by 6%–142%, 46%–99% and 31%–200%, respetively. Moreover, the transformed stands could effectively control the occurrence of pine caterpillars in plantations. Consequently the transformations enhanced the function of soil and water conservation. Keywords Pinus tabulaeformis - Monoculture - Transformation - Principles and methods - Assessment CLC number S791.254 - S727.22 Document code A Foundation item: This research was supported by grants from the Chinese Academy of Sciences (KZCX3-SW-418), National Natural Science Foundation of China (30100144), and National Key Technologies R & D Program of China (96-007-01-06).Biography: ZENG De-hui (1965-), male, Ph.D. professor in the Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. ChinaResponsible editor: Zhu Hong

Effects of Different Cropping Systems on Soil Quality

[Objective] The aim was to explore the soil properties change in the process of field crops into greenhouse vegetables and their possible adverse effects on the environment.[Method] Fertilization,irrigation,crop growth conditions and soil quality changes in the major cropping systems（greenhouse monoculture,greenhouse rotation and open field rotation）in Chongming Island,Shanghai were investigated from 2007 to 2009.[Result] Different cropping systems significantly affected soil quality.Soil organic carbon,mineral nitrogen,available phosphorus and exchangeable potassium content increased in greenhouse cultivation compared to open field rotation due to excessive application of irrigation and fertilizers.Soil pH values decreased by 0.6 and 0.4 in the greenhouse monoculture and greenhouse rotation,respectively,while did not significantly change in open field rotation.Meanwhile,greenhouse cultivation significantly increased soil EC,and NO-3 and Cl-contents,which showed an increasing trend with the planting years increase.However,the salt content changes were not significant in open field rotation.[Conclusion] High cropping index,excessive fertilizer input and inappropriate fertilization and irrigation resulted in greenhouse soil quality degradation due to weak farmer＇s skill and local extension services.

Soil Biological Changes for a Natural Forest and Two Plantations in Subtropical China

Conversion of natural forests into pure plantation forests is a common management practice in subtropical China.To evaluate the effects of forest conversion on soil fertility, microbe numbers and enzyme activities in topsoils (0-10 cm)were quantified in two 33-year-old monoculture plantations of Castanopsis kawakamii Hayata (CK) and Cunninghamia lanceolata Lamb. (Chinese fir) (CF), and compared to a neighboring relict natural C. kawakamii forest (NF), in Sanming,Fujian. Five soil samples were collected once each in January, April, July, September and November in 2000 in each forest for laboratory analysis. Over the sampling year, there were significant differences for bacteria, fungi and actinomycetes between forests and between seasons (P ＜ 0.05). The largest bacteria and fungi populations were in NF, while CF contained the greatest number of actinomycetes. There were also significant differences (P ＜ 0.05) with microbial respiration for forests and seasons. Additionally, compared with NF, urease and acid phosphatase were significantly lower (P ＜ 0.05)in CK and CF. Also, the correlations of soil hydrolysable N and available P to soil microbial and enzymatic activities were highly significant (P ＜ 0.01). Thus, to alter the traditional Chinese fir monoculture so as to mimic the natural forest conditions, managing mixed stands of Chinese fir and broadleaf trees or conducting crop rotation of conifers and broadleaf trees as well as minimizing forest disturbances like clear-cutting, slash burning and soil preparing, could be utilized.

Phosphorus Transfer and Distribution in a Soybean-Citrus Intercropping System

A mini-plot field experiment was conducted on a loamy clay Oxisol to compare and evaluate P absorption and transfer in plant organs and P movement in soil profile at three P application depths under the soybean-citrus intercropping versus the monoculture using a ^32p tracer technique. Total P absorption （Pt） by soybean and P accumulation （Pa） in soybean organs decreased significantly （P 〈 0.05） under the intercropping in contrast to the monoculture. With intercropping, when ^32p was applied in topsoil （15 cm soil layer）, total ^32p absorption （^32pt） in soybeans was significantly lower （P 〈 0.05）, but when ^32p was applied to deeper soil layers （35 or 55 cm soil layer）, ^32pt in soybeans was significantly greater （P 〈 0.05）. The percentage of P in leaves to total P （Pa/Pt） and 32p in leaves to total ^32p （^32pa/^32pt） for soybean were ≥ 25% and those of root ≥ 12%. When P was applied ia topsoil and 55 cm soil layer, no significant differences were found between intercropping and monoculture for Pt of citrus. The P absorbed by citrus was transferred rapidly to the growing organs of aboveground during the experiment, and the speed of transferring to the growing organs slowed when P was applied to the deeper soil layers. In intercropping, P mobility was heightened in the soil profile, and P in deeper soil layers moved up to topsoil more rapidly.

Plant Phosphorus Uptake in a Soybean-Citrus Intercropping System in the Red Soil Hilly Region of South China

A field microplot experiment was conducted in the red soil hilly region of South China to evaluate plant phosphorus (P)uptake under soybean and citrus monoculture and the soybean-citrus intercropping system using the 32P tracer technique.P fertilizer was applied at three depths(15,35,and 55 cm).The experimental results showed that the planting pattern and 32P application depth significantly affected the characteristics of P uptake by soybean and citrus.Under the soybean-citrus intercropping system,considerable competition was observed when the 32P fertilizer was applied to the topsoil(15 cm);therefore,the 32P recovery rate declined by 41.5%and 14.7%for soybean and citrus,and 32P supplying amount of topsoil to soybean and citrus decreased by 346.8 and 148.1 mg plot-1,respectively,compared to those under the monoculture.However,32P recovery of soybean was promoted when 32P fertilizer was applied to the deeper soil layers (35 and 55 cm)under soybean-citrus intercropping.Under the soybean monoculture,32P fertilizer could hardly be used by soybean when 32P fertilizer was applied at the 55 cm depth or below,with the recovery rate being less than 0.1%;it was up to 0.253%by soybean under intercropping.The higher P recovery of soybean under soybean-citrus intercropping when P was applied in the deeper soil layers was because part of the P nutrient that the citrus absorbed from the deeper soil layers could be released into the topsoil and then it could be used by the soybean.

Conservation of Traditional Rice Varieties in a Globally Important Agricultural Heritage System (GIAHS):Rice-Fish Co-Culture

The traditional rice-fish farming system is selected as a ＂globally important agricultural heritage system＂ （GIAHS） by the Food and Agriculture Organization （FAO）,United Nations Development Programme （UNDP）,and Global Environment Facility （GEF）,etc.In Zhejiang Province of China,where the pilot site for this GIAHS farming system is located,we compared the use of traditional rice varieties in rice-fish co-culture and rice monoculture.Further,we determined how traditional rice varieties were performed in this rice-fish system.Only 19% of the farmers who practiced rice monoculture planted traditional varieties while 52% of farmers who practiced rice-fish co-culture planted traditional varieties.Traditional varieties represented 13% of the total land cultivated under rice in the rice-fish system but only 2% in the rice monoculture system.In the rice-fish system,yield was lower for traditional rice varieties than hybrid varieties but application of fertilizers and pesticides was also lower.In a field experiment in the rice-fish system without pesticides,rice planthopper numbers and sheath blight incidence were lower from three traditional varieties than one hybrid variety;yields were 8 to 32% lower from the traditional varieties than the hybrid.Our results showed that traditional rice varieties can be preserved through conserving GIAHS rice-fish co-culture.Our study also indicated that traditional rice varieties can survive in the rice-fish system because these varieties are helpful to the whole system and beneficial to the farmers.

Effect of Different Rice-Crab Coculture Modes on Soil Carbohydrates

Traditional agricultural systems have contributed to food and livelihood security. Rice-crab coculture （RC） is an important eco-agricultural process in rice production in northern China. Recognizing the soil fertility in RC may help develop novel sustainable agriculture. Soil carbohydrates are important factors in determining soil fertility in different culture modes. In this study, soil carbohydrates were analyzed under three different culture modes including rice monoculture （RM）, conventional rice-crab coculture （CRC） and organic rice-crab coculture （ORC）. Results showed that the contents of soil organic carbon and carbohydrates were significantly higher in the ORC than those in RM. The increasing effect was greater with increased organic manure. Similar tendency was found in CRC, but the overall effect was less pronounced compared with ORC. Carbohydrates were more Sensitive to RC mode and manure amendment than soil organic carbon. Compare to RM, the （Gal＋Man）/（Ara＋Xyl） ratio decreased in all the RC modes, indicating a relative enrichment in plant-derived carbohydrates due to the input of crab feed and manure. While the increasing （Gal＋Man）/（Ara＋Xyl） ratio in ORC modes with increased organic manure suggested that crab activity and metabolism induced microbially derived carbohydrates accumulation. The lower GluN/MurA ratio in ORC indicated an enhancement of bacteria contribution to SOM turnover in a short term. The findings reveal that the ORC mode could improve the quantity and composition of soil carbohydrates, effectively, to ensure a sustainable use of paddy soil.

Effect of nitrogen fertilization on yield, N content, and nitrogen fixation of alfalfa and smooth bromegrass grown alone or in mixture in greenhouse pots

Planting grass and legume mixtures on improved grasslands has the potential advantage of realizing both higher yields and lower environmental pollution by optimizing the balance between applied N fertilizer and the natural process of legume biological nitrogen fixation. However, the optimal level of N fertilization for grass-legume mixtures, to obtain the highest yield, quality, and contribution of N2 fixation, varies with species. A greenhouse pot experiment was conducted to study the temporal dynamics of N2 fixation of alfalfa （Medicago sativa L.） grown alone and in mixture with smooth bromegrass （Bromus inermis Leyss.） in response to the addition of fertilizer N. Three levels of N （0, 75, and 150 kg ha-1） were examined using 15N-labeled urea to evaluate N2 fixation via the 15N isotope dilution method. Treatments were designated NO （0.001 g per pot）, N75 （1.07 g per pot） and N150 （2.14 g per pot）. Alfalfa grown alone did not benefit from the addition of fertilizer N; dry matter was not significantly increased. In contrast, dry weight and N content of smooth bromegrass grown alone was increased significantly by N application. When grown as a mixture, smooth bromegrass biomass was increased significantly by N application, resulted in a decrease in alfalfa biomass. In addition, individual alfalfa plant dry weight （shoots＋roots） was significantly lower in the mixture than when grown alone at all N levels. Smooth bromegrass shoot and root dry weight were significantly higher when grown with alfalfa than when grown alone, regardless of N application level. When grown alone, alfalfa＇s N2 fixation was reduced with N fertilization （R2=0.9376,P=0.0057）. When grown in a mixture with smooth bromegrass, with 75 kg ha-1 of N fertilizer, the percentage of atmospheric N2 fixation contribution to total N in alfalfa （%Ndfa） had a maximum of 84.07 and 83.05% in the 2nd and 3rd harvests, respectively. Total 3-harvest %Ndfa was higher when alfalfa was grown in a mixture than when grown alone （shoots： ｜t｜=3.39, P=0.0096; root： ｜t｜=3.57, P=0.0073）. We believe this was due to smooth bromegrass being better able to absorb available soil N （due to its fibrous root system）, resulting inlower soil N availability and allowing alfalfa to develop an effective N2 fixing symbiosis prior to the 1st harvest. Once soil N levels were depleted, alfalfa was able to fix N2, resulting in the majority of its tissue N being derived from biological nitrogen fixation （BNF） in the 2nd and 3rd harvests. When grown in a mixture, with added N, alfalfa established an effective symbiosis earlier than when grown alone; in monoculture BNF did not contribute a significant portion of plant N in the N75 and N150 treatments, whereas in the mixture, BNF contributed 17.90 and 16.28% for these treatments respectively. Alfalfa has a higher BNF efficiency when grown in a mixture, initiating BNF earlier, and having higher N2 fixation due to less inhibition by soil-available N. For the greatest N-use-efficiency and sustainable production, grass-legume mixtures are recommended for imDrovino orasslands, usino a moderate amount of N fertilizer （75 kq N ha-l） to provide optimum benefits.