Decomposition of Bt transgenic rice residues and response of soil microbial community in rapeseed–rice cropping system

In this study, Bt transgenic rice (KMD rice) residue decomposition and the associated microbial community in a rapeseed–rice cropping system were assessed in comparison with its parental non-Bt rice variety (XiuShui 11). Decomposition was measured as mass loss by straw and root decay in litterbags over two consecutive years. Bacterial and fungal community compositions associated with residue decomposition were detected by terminal restriction fragment length polymorphism (T-RFLP) and the additive main effects multiplicative interaction (AMMI) analysis model. Decomposition dynamics and bacterial and fungal communities associated with decomposition were strongly affected by surface and incorporated placements, and by temporal factors. However, no significant differences were observed between Bt and non-Bt rice variety in either decomposition dynamics or in the soil microbial communities associated with residue decay. Our field study indicated that the insertion of the cry1Ab gene into Xiushui 11 rice genome had no significant effect on the residual decay and decomposition-associated microbial community compositions in the rapeseed-rice cropping system.     

Distribution and pollution evaluation of fluoride in a soil–water–plant system in Shihezi,Xinjiang, China

Fluoride (F) pollution is a serious environmental problem in some areas of China, but it has yet to be reported in a soil–water–plant system in Shihezi, Xinjiang. This study was undertaken to investigate the distribution and migration rule of F in soil, water, and plants, and to evaluate F pollution of soil. Results showed that the average concentration of total F (T-F) in the topsoil in the northwest, north, and southeast of Shihezi was higher than the national average T-F (478 mg/kg), while it was lower in southwest. The highest T-F contents of the soil profile were detected in the depth of 20 cm. The F content in groundwater in the northwest region was higher than the GB/T 14848–93 (1.0 mg/L), whereas the F contents in other water samples were within the standard. The F contents (1.75?2.81 mg/kg) in plant leaves were higher than the food limits (1.0 mg/kg). The obtained comprehensive pollution index of the soil was 1.86, which means a mild concentration of F in Shihezi. This research has reference value for the study of F pollution and comprehensive control in the northwest oasis with the typical arid and saline conditions.     

Long-term manuring and fertilization effects on soil organic carbon pools under a wheat–maize cropping system in North China Plain

The effects of organic manure and chemical fertilizer on total soil organic carbon (C _T), water-soluble organic C (C _WS), microbial biomass C (C _MB), labile C (C _L), C mineralization, C storage and sequestration, and the role of carbon management index (CMI) in soil quality evaluation were studied under a wheat–maize cropping system in a long-term experiment, which was established in 1989 in the North China Plain. The experiment included seven treatments: (1) OM: application of organic manure; (2) 1/2OMN: application of half organic manure plus chemical fertilizer NPK; (3) NPK: balanced application of chemical fertilizer NPK; (4) NP: application of chemical fertilizer NP; (5) PK: application of chemical fertilizer PK; (6) NK: application of chemical fertilizer NK; and (7) CK: unfertilized control. Application of organic manure (OM and 1/2OMN) was more effective for increasing C _T, C _WS, C _MB, C _L, C mineralization, and CMI, as compared with application of chemical fertilizer alone. For the chemical fertilizer treatments, balanced application of NPK (treatment 3) showed higher C _T, C _WS, C _MB, C _L, C mineralization, and CMI than the unbalanced use of fertilizers (treatments 4, 5, and 6). The C storage in the OM and 1/2OMN treatments were increased by 58.0% and 26.6%, respectively, over the NPK treatment, which had 5.9–25.4% more C storage than unbalanced use of fertilizers. The contents of C _WS, C _MB, and C _L in organic manure treatments (treatments 1 and 2) were increased by 139.7–260.5%, 136.7–225.7%, and 150.0–240.5%, respectively, as compared to the CK treatment. The CMI was found to be a useful index to assess the changes of soil quality induced by soil management practices due to its significant correlation with soil bulk density and C fractions. The OM and 1/2OMN treatments were not a feasible option for farmers, but a feasible option for sequestering soil carbon, especially for the OM treatment. The NPK treatment was important for increasing crop yields, organic material inputs, and soil C fractions, so it could increase the sustainability of cropping system in the North China Plain.     

An appraisal of the utility of biochar in a rotation involving tobacco–rice in southern China

The employment of biochar in crop production can not only improve soil quality, but also helps the field ecosystem to fix carbon and reduce emissions. Although the benefits of their application in crop production have been more and more confirmed, it is not clear when it comes to the acidic soil of tobacco and rice rotation. A tobacco–rice rotation experiment was conducted in southern China to probe the application value of biochar under these conditions. Three biochar application rates were employed in this experiment. BC0 (without biochar), BC25 (25 t ha⁻¹), and BC50 (50 t ha⁻¹). The findings show that biochar significantly boosted soil fertility and crop yields. Meanwhile, the soil organic carbon of tobacco rice rotation field with biochar increased by 31.76%. After a whole growth period of tobacco and rice, the cumulative emission reduction of CO₂ and N₂O from the soil by biochar were 15,944 kg ha⁻¹ and 1810 g ha⁻¹, respectively. The use of biochar not only significantly improved the bacterial diversity of tobacco and rice rotation soil, but also altered the original microbial community structure. The profusion of Proteobacteria and Acidobacteria was reduced and the abundance of Actinobacteria and Bacteroidetes was enhanced in the treatments with biochar. Among them, Sphingomonadales, Planctomycotes, and Ktedonobacteria, which are beneficial to plant growth and soil health, have become key phylotypes. The carbon balance analysis data show that the net carbon sequestration of the two treatments with biochar is positive, while that of the treatment without biochar is negative. In terms of economic benefit, the application of biochar increased the average of 2.055 CNY kg⁻¹ consumed energy (CE) in the whole tobacco–rice rotation system. The ecological benefit was 0.51 kg C kg⁻¹ CE. In conclusion, biochar can be effectively used in the practice of tobacco–rice rotation and acidic soil improvement in southern China.     

On a predator–prey system of Gause type

In this paper a Gause type model of interactions between predator and prey population is considered. We deal with the sufficient condition due to Kuang and Freedman in the generalized form including a kind of weight function. In a previous paper we proved that the existence of such weight function implies the uniqueness of limit cycle. In the present paper we give a new condition equivalent to the existence of a weight function (Theorem 4.4). As a consequence of our result, it is shown that some simple qualitative properties of the trophic function and the prey isocline ensure the uniqueness of limit cycle.     

Plant–soil feedback effects on the performance and functional traits of Dodonaea viscosa in a dry-hot valley,China

Plant–soil feedback has been widely studied and may be particularly important in resource-poor areas. However, the roles of direct and indirect biotic effect in affecting plant growth and functional traits in this process still remained unclear. The aim of this study was to explore the roles of soil biota in affecting plant performance and traits by conducting a two-phase feedback experiment in a dry-hot valley, with a conditioning phase during which there were Dodonaea viscosa or no D. viscosa growing in the soil and a feedback phase in which the effect of the conditioned soil biota on D. viscosa performance was measured. Soil N was reduced by the presence of D. viscosa during the conditioning phase. However, D. viscosa showed a positive plant–soil feedback. In the feedback phase, the D. viscosa-conditioned soil increased the stem diameter, total biomass, and leaf dry mass content of D. viscosa, while the specific leaf area was significantly lower in D. viscosa-conditioned soil than that in bare soil. In contrast, soil sterilization had a negative effect on the growth of D. viscosa, with a significant reduction in biomass, especially in D. viscosa-conditioned soil, and soil sterilization significantly increased the root:shoot biomass ratio and litter mass. Furthermore, we showed that although the biota-driven changes in enzyme activities correlated with leaf N and especially P amount, the enzyme activity was not the main reason to promote D. viscosa growth in conditioned soil. These results suggest that the positive biotic feedback effect was superior to the negative nutrient-depleted effect on D. viscosa growth, and the direct biotic feedback effect would drive the positive effect of soil biota to a greater extent than the indirect effect. The positive biotic plant–soil feedback in dry-hot valley plays an important role in ecosystem restoration and helps in understanding plant adaptation to the local environment in this area.

     

Cascading effects of soil organic and inorganic fertilizers on tri-trophic interactions: Plant–aphid–parasitoid wasp as a study system

Understanding the mechanisms underlying tri-trophic interactions between insect herbivores, their host plants and natural enemies is an important aim in ecology. In the present study, the effect of urea fertilizer and vermicompost on a tri-trophic level cascade, comprising safflower, Carthamus tinctorius, safflower aphid, Uroleucon carthami and its primary parasitoid wasp, Praon yomenae, was investigated. Vermicompost increased the number of leaves, leaf area, fresh weight, dry weight, the total number of aphids and reduced the number of winged aphids and aphid load (Aphid load = number of aphids / plant fresh weight). Only two variables, plant phenol content and relative water content, were not significantly affected by vermicompost. Urea fertilizer had no impact on all variables except a significant effect on plant height. In another experiment, the effect of urea fertilizer and vermicompost on the wasp parasitoid was studied. The number of parasitoid mummies, mummification time, developmental time, the number of emerged adults, sex ratio, percentage of parasitism and hind tibia length was measured. Vermicompost had no significant effect on any of the measured parameters, but urea fertilizer increased the hind tibia length of the parasitoid. Vermicompost increased plant growth parameters and had an indirect and inhibiting effect on the safflower aphid itself. There was evidence of a bottom-up cascade to the third trophic level by adding fertilizers in this system: Urea fertilizer enhanced plant height but seemingly had no impact on the attacking herbivore. It is interesting that the effect of urea can be transferred to the third trophic level, that is parasitoid. This suggests that vermicompost could be used simultaneously with urea fertilizer, because urea fertilizer had a positive impact on the parasitoid and vermicompost had a positive impact on plant growth as well as the ability to reduce aphid load.     

Some progress in the study of plant–soil interactions in China

Plants and soil are the base for sustainably surviving human beings on the globe as the role of materials, energy, resources and environment (Shao & Chu 2008; Shao et al. 2008, 2009, 2010, 2012a,b; Liu & Shao, 2010; Ruan et al. 2010; Xu et al. 2010, 2012; Shao 2012; Huang et al. 2013). This topic has been extensively investigated for 100 years with more achievements in many sectors and practical significance in conducting high-efficient agriculture and eco-environmental construction. The plant–soil interaction is the core issue of this topic, which has been given much attention for the past 30 years (Wu et al. 2007, 2010; Zhang et al. 2011, 2013; Xu et al. 2012, 2013).     

Human health risk assessment of heavy metals in the soil–Panax notoginseng system in Yunnan province,China

In this study, a total of 69 topsoil samples and 10 Panax notoginseng samples from Yunnan Province were collected and the concentrations of As, Cd, Cu, Hg, Ni, Pb and Zn in all the samples were determined. The hazard index (HI), total carcinogenic risk (TCR) and estimated daily intake (EDI) of heavy metals were calculated to assess the health risk of P. notoginseng growers and consumers. The average concentrations of As, Cd, Cu, Hg, Ni, Pb and Zn in P. notoginseng planting soils are 43.6, 0.55, 50.8, 0.30, 73.4, 58.2, and 161 mg/kg, respectively. The average Nemerow integrated pollution index of heavy metals in soils is 1.8, indicating that the P. notoginseng planting soils are slightly polluted by those heavy metals. The average HI value is 1.29 and the TCR value of As is above the threshold value, suggesting that As pollution in soil has adverse impact on local growers' health. P. notoginseng is polluted by Cd, As and Pb. 39.1% of estimated daily intakes of As for P. notoginseng consumers through leaf consumption exceeding its permitted daily exposure dosages, suggesting that there is a potential health risk for P. notoginseng consumers to consume P. notoginseng leaves.     

The role of plant–soil feedbacks and land-use legacies in restoration of a temperate steppe in northern China

Plant–soil feedbacks affect plant performance and plant community dynamics; however, little is known about their role in ecological restoration. Here, we studied plant–soil feedbacks in restoration of steppe vegetation after agricultural disturbance in northern China. First, we analyzed abiotic and biotic soil properties under mono-dominant plant patches in an old-field restoration site and in a ‘target’ steppe site. Second, we tested plant–soil feedbacks by growing plant species from these two sites on soils from con- and heterospecific origin. Soil properties generally did not differ between the old-field site and steppe site, but there were significant differences among mono-dominant plant patches within the sites. While soil species origin (i.e., the plant species beneath which the soil was collected) affected biomass of individual plant species in the feedback experiment, species-level plant–soil feedbacks were ‘neutral’. Soil site origin (old-field, steppe) significantly affected biomass of old-field and steppe species. For example, old-field species had higher biomass in old-field soils than in steppe soils, indicating a positive land-use legacy. However, soil site origin effects depended on the plant species beneath which the soils were collected. The predictive value of abiotic and biotic soil properties in explaining plant biomass differed between and within groups of old-field and steppe species. We conclude that the occurrence of positive land-use legacies for old-field species may retard successional replacement of old-field species by steppe species. However, high levels of idiosyncrasy in responses of old-field and steppe plant species to con- and heterospecific soils indicate interspecific variation in the extent to which soil legacies and plant–soil feedbacks control successional species replacements in Chinese steppe ecosystems.     

The effects of river-level oscillations on the macroinvertebrate community in a river–floodplain system

Limnology - Extreme climatic events, such as flooding and drought, can abruptly modify the amplitude of the river level of a river, promoting new environmental conditions and impacting aquatic...     

Local effects of a global problem: modelling the risk of parasite-induced mortality in an intertidal trematode–amphipod system

The interactive effects of climate change and parasitism are of concern because of potentially important consequences for host populations, communities and entire ecosystems. In marine environments, the absence of historic baseline data on parasitism and disease limits our ability to make realistic predictions about these consequences. Here, we adapt a simulation model developed for a Northern Hemisphere intertidal host–parasite system to a comparable system in the Southern Hemisphere. The entire life cycle of the intertidal trematode parasite Maritrema novaezealandensis was modelled in order to investigate the interactive effects of parasitic infections and increasing temperatures on the population dynamics of the amphipod host Paracalliope novizealandiae. Despite uncertainties associated with the model and its parameterisation, most temperature increases that were predicted to cause the collapse of the modelled amphipod population in the long term lay within the range of predicted warming for the study area. The high vulnerability of the amphipods in the modelled system illustrates a potentially important ecological mechanism by which consequences of a global problem might manifest on the local scale.     

Coevolution of dispersal in a parasitoid–host system

Interspecific interactions and the evolution of dispersal are both of interest when considering the potential impact of habitat fragmentation on community ecology, but the interaction between these processes is not well studied. We address this by considering the coevolution of dispersal strategies in a host–parasitoid system. An individual-based host–parasitoid metapopulation model was constructed for a patchy environment, allowing for evolution in dispersal rates of both species. Highly rarefied environments with few suitable patches selected against dispersal in both species, as did relatively static environments. Provided that parasitoids persist, all the variables studied led to stable equilibria in dispersal rates for both species. There was a tendency toward higher dispersal rates in parasitoids because of the asymmetric relationships of the two species to the patches: vacant patches are most valuable for hosts, but unsuitable for parasitoids, which require an established host population to reproduce. High host dispersal rate was favoured by high host population growth rate, and in the parasitoid by high growth rates in both species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cholodny–Went revisited: a role for jasmonate in gravitropism of rice coleoptiles

Gravitropism is explained by the Cholodny–Went hypothesis: the basipetal flow of auxin is diverted laterally. The resulting lateral auxin gradient triggers asymmetric growth. However, the Cholodny–Went hypothesis has been questioned repeatedly because the internal auxin gradient is too small to account for the observed growth asymmetry. Therefore, an additional gradient in indolyl-3-acetic acid (IAA) sensitivity has been suggested (Brauner and Hager in Planta 51:115–147, 1958). We challenged the Cholodny–Went hypothesis for gravitropism of rice coleoptiles (Oryza sativa L.) and found it to be essentially true. However, we observed, additionally, that the two halves of gravitropically stimulated coleoptiles responded differentially to the same amount of exogenous auxin: the auxin response is reduced in the upper flank but normal in the lower flank. This indicates that the auxin-gradient is amplified by a gradient of auxin responsiveness. Hormone contents were measured across the coleoptile by a GC-MS/MS technique and a gradient of jasmonate was detected opposing the auxin gradient. Furthermore, the total content of jasmonate increased during the gravitropic response. Jasmonate gradient and increase persist even when the lateral IAA gradient is inhibited by 1-N-naphtylphtalamic acid. Flooding with jasmonate delays the onset of gravitropic bending. Moreover, a jasmonate-deficient rice mutant bends more slowly and later than the wild type. We discuss a role of jasmonate as modulator of auxin responsiveness in gravitropism.     

The response of soil respiration to different N compounds addition in a saline–alkaline grassland of northern China

不同形态氮化合物添加对中国北方盐渍化草地土壤呼吸的影响 持续增加的氮沉降在提高陆地生态系统生产力的同时也会对土壤微生物产生显著影响;土壤呼吸由植物根系呼吸和土壤微生物呼吸组成,因此影响植物生产力和微生物的因子都会影响到土壤呼吸。以往氮富集对土壤呼吸的研究主要在土壤中性的草地生态系统开展,而对于盐渍化草地土壤呼吸是如何响应氮沉降的研究尚不多见,这限制了全球变化陆地生态系统土壤呼吸模型预测的准确性和完整性。本研究以中国北方农牧交错带盐渍化草地为研究对象,通过3年(2017–2019年)野外监测土壤呼吸及相关生物和非生物因子的变化,探讨了不同形态氮化合物添加(NH₄NO₃、(NH₄)₂SO₄和NH₄HCO₃)对盐渍化草地土壤呼吸的影响及其调控机制。结果表明：(i)土壤呼吸受大气温度、土壤温度及降水的调控,呈现双峰的季节动态变化趋势和显著的年际差异。(ii)与对照相比,经过3年的处理,土壤呼吸在NH₄NO₃、(NH₄)₂SO₄和NH₄HCO₃添加处理下分别提高了19.9%、13.0%和16.6%。(iii)NH₄NO₃添加对土壤呼吸较高的促进作用与较高的地上生物量、地下生物量以及土壤NO₃⁻含量有关。(iv)在NH₄HCO₃ 添加处理下,土壤碳排放(土壤呼吸)显著增加而碳输入(净生产力)无显著改变,表明NH₄HCO₃添加会降低土壤碳的固持。(v)净地下生产力(BNPP)是盐渍化草地土壤呼吸的最主要调控因子,并且土壤阳离子浓度和pH值通过影响土壤微生物间接影响土壤呼吸。上述研究结果表明,草地添加NH₄NO₃的研究高估了氮沉降对土壤呼吸的影响,并且在碳循环预测模型中应充分考虑盐渍化草地土壤碳动态。     

Differential effects of flower feeding in an insect host–parasitoid system

In many insect host–parasitoid systems, both the host and its parasitoids forage on shared floral resources. As a result of insect behaviour, morphology and physiology, flower species may act selectively at different levels of such systems, e.g., between the trophic levels of hosts and parasitoids, between species within a guild, between sexes or individuals within a species or between life history traits within an individual. We asked if effects of selectivity are consistent across levels in the horse chestnut leafminer, Cameraria ohridella, and its parasitoid complex. Insects were exposed singly in no-choice feeding trials to twelve common flower species and their survival and reproduction were recorded. Only one of twelve flower species (Ranunculus acris) tended to selectively favour the longevity of leafminers, but not of parasitoids. No flower species were found to favour parasitoids only. Both trophic levels profited from feeding on Anthriscus sylvestris, however, parasitoids benefited up to eight times more than their hosts. No differences were found among the species of the parasitoid guild, but females lived significantly longer than males, and single individuals within species were able to exploit generally unfavourable flower species. Out of the seven flower species that increased the longevity of leafminer females, only Chaerophyllum hirsutum significantly enhanced the number of eggs laid. Fecundity was generally positively correlated with longevity of leafminer females, but two flower species (C. hirsutum, Taraxacum officinale) had an additional positive effect on fecundity. In conclusion, we demonstrated that flowers act differently on life history traits in a host–parasitoid system at a multitude of biological levels and that these effects are not always consistent across levels. Selective plant-derived resources can therefore modify herbivore–natural enemy interactions in ways that are more complex than currently appreciated.     

Effect of manganese spatial distribution in the soil profile on wheat growth in rice–wheat rotation

Manganese (Mn) deficiency in wheat under rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotation is an important problem in most rice-growing areas in China. A field survey, field trials and a soil column experiment were conducted to determine the relationship between Mn leaching and distribution in soil profiles and paddy rice cultivation and the effects of Mn distribution in soil profiles on wheat growth and its response to Mn fertilization. At five field sites surveyed, total Mn and active Mn concentrations in the topsoil layers under rice–wheat rotations were only 42% and 11%, respectively, of those under systems without paddy rice. Both total and available Mn increased with soil depth in soils with rice–wheat rotations, showing significant spatial variability of Mn in the soil profile. Manganese leaching was the main pathway for Mn loss in coarse-textured soil with high pH, while excessive Mn uptake was the main pathway for Mn loss in clay-textured and acid soil. When Mn was deficient in the topsoil, sufficient Mn in the subsoil contributed to better growth and Mn nutrition of wheat but insufficient Mn in the subsoil resulted in Mn deficiency in wheat.     

Nitrogen fertilization alters the distribution and fates of photosynthesized carbon in rice–soil systems: a 13C-CO2 pulse labeling study

Plant and Soil - Traits of the plant root system architecture (RSA) play a key role in crop performance. Therefore, architectural root traits are becoming increasingly important in plant...     

The root–soil system of Norway spruce subjected to turning moment: resistance as a function of rotation

The reactions of trees to wind, rockfall, and snow and debris flow depend largely on how strong and deformable their anchorage in the soil is. Here, the resistive turning moment M of the root–soil system as a function of the rotation ϕ at the stem base plays the major role. M(ϕ) describes the behavior of the root–soil system when subject to rotational moment, with the maximum M(ϕ) indicating the anchorage strength M _a of the tree. We assessed M(ϕ) of 66 Norway spruce (Picea abies L. Karst) by pulling them over with a winch. These 45- to 170-year-old trees grew at sites of low and high elevation, with a diameter at breast height DBH = 14–69 cm and a height H = 9–42 m. M(ϕ) displayed a strong nonlinear behavior. M _a was reached at a lower ϕ for large trees than for small trees. Thus overhanging tree weight contributed less to M _a for the large trees. Overturning also occurred at a lower ϕ for the large trees. These observations show that the rotational ductility of the root–soil system is higher for small trees. M _a could be described by four monovariate linear regression equations of tree weight, stem weight, stem volume and DBH ² ·H (0.80 < R ² < 0.95), and ϕ at M _a, ϕ _a, by a power law of DBH²·H (R ² = 0.85). We found significantly higher M _a for the low-elevation spruces than for the high-elevation spruces, which were more shallowly anchored, but no significant difference in ϕ _a. The 66 curves of M(ϕ), normalized (_n) by M _a in M-direction and by ϕ _a in ϕ-direction, yielded one characteristic average curve: . Using and the predictions of M _a and ϕ _a, it is shown that M(ϕ) and the curves associated with M(ϕ) can be predicted with a relative standard error ≤25%. The parameterization of M(ϕ) by tree size and weight is novel and provides useful information for predicting with finite-element computer models how trees will react to natural hazards.