Greater humification of belowground than aboveground biomass carbon into particulate soil organic matter in no-till corn and soybean crops

Quantifying the amount of carbon (C) incorporated from decomposing residues into soil organic carbon (C_S) requires knowing the rate of C stabilization (humification rate) into different soil organic matter pools. However, the differential humification rates of C derived from belowground and aboveground biomass into C_S pools has been poorly quantified. We estimated the contribution of aboveground and belowground biomass to the formation of C_S in four agricultural treatments by measuring changes in δ¹³C natural abundance in particulate organic matter (C_POM) associated with manipulations of C₃ and C₄ biomass. The treatments were (1) continuous corn cropping (C₄ plant), (2) continuous soybean cropping (C₃), and two stubble exchange treatments (3 and 4) where the aboveground biomass left after the grain harvest was exchanged between corn and soybean plots, allowing the separation of aboveground and belowground C inputs to C_S based on the different δ¹³C signatures. After two growing seasons, C_POM was primarily derived from belowground C inputs, even though they represented only ∼10% of the total plant C inputs as residues. Belowground biomass contributed from 60% to almost 80% of the total new C present in the C_POM in the top 10 cm of soil. The humification rate of belowground C inputs into C_POM was 24% and 10%, while that of aboveground C inputs was only 0.5% and 1.0% for soybean and corn, respectively. Our results indicate that roots can play a disproportionately important role in the C_POM budget in soils. Keywords Particulate organic matter; root carbon inputs; carbon isotopes; humification rate; corn; soybean.     

Inversely estimating temperature sensitivity of soil carbon decomposition by assimilating a turnover model and long-term field data

Change in temperature sensitivity of soil organic carbon (SOC) decomposition with change in soil qualities (i.e. decomposability or lability) is one of the most important issues to be evaluated for projection of future CO₂ emissions from soils. We inversely estimated the temperature sensitivity of SOC decomposition rate by applying a hybrid of the Metropolis-Hasting algorithm and the particle filter method to the extended Rothamsted carbon model (RothC), together with long-term (9 years) experimental data on SOC obtained at five sites in Japanese upland soils. Contrary to the prediction of the Arrhenius kinetics theory, we found no significant differences in temperature sensitivity among soils with different qualities (represented as soil compartments in the RothC model). We also confirmed that there was a positive correlation between the relative temperature sensitivity of the humus compartment and future total CO₂ emissions. The RothC model with default parameterization tended to overestimate future total CO₂ emissions relative to the calibrated model, and the degree of overestimation was larger than that of underestimation.     

Methyl jasmonate treatment promotes flower opening of cut Eustoma by inducing cell wall loosening proteins in petals

Establishing the technique for controlling the rate of cut flower opening is important to maintain appropriate cut flower supplies to meet consumer demand. Cut flowers of Eustoma grandiflorum (Raf.) Shinn. were held in a vase solution containing (±)-abscisic acid (ABA), 6-benzylaminopurine (BA), gibberellic acid-3 (GA), methyl jasmonate (MeJA) or 1-naphthaleneacetic acid (NAA) at 100 μM. MeJA accelerated flower opening. Only the timing of flowering was earlier, and there was no change in maximum flower diameter at the fully open stage. Expansin and xyloglucan endotransglycosylase/hydrolase (XTH), regarded as cell wall loosing proteins, participate in petal growth from bud stage to the fully open stage in Eustoma. MeJA also accelerated the expression of EgEXPA2, EgEXPA3 and EgXTH1 mRNA and the accumulation of expansin and XTH protein in petals. Meanwhile, the acceleration of both flower opening and expression of these genes was not observed by ABA, BA or GA treatment. It was proposed that early flower opening by JA treatment resulted from petal cell wall loosening by accelerated expression of expansin and XTH.     

A Comparison of Satellite-Derived Vegetation Indices for Approximating Gross Primary Productivity of Grasslands

Gross primary productivity (GPP) is a key component of ecosystem carbon fluxes and the carbon balance between the biosphere and the atmosphere. Accurate estimation of GPP is essential for quantifying plant production and carbon balance for grasslands. Satellite-derived vegetation indices (VIs) are often used to approximate GPP. The widely used VIs include atmospherically resistant vegetation index, enhanced vegetation index (EVI), normalized difference greenness index, normalized difference vegetation index, reduced simple ratio, ratio vegetation index, and soil-adjusted vegetation index (SAVI). The evaluation of the performance of these VIs for approximating GPP, however, has been limited to one or two VIs and/or using GPP observations from one or two sites. In this study, we examined the relationships between the nine VIs derived from the moderate resolution imaging spectroradiometer (MODIS) and tower-based GPP at five eddy covariance flux sites over the grasslands of northern China. Our results showed that the nine VIs were generally good predictors of GPP for grasslands of northern China. Overall, EVI was the best predictor. The correlation between EVI and GPP also declined from the south to the north, indicating that EVI and GPP exhibited closer relationships in more southerly sites with higher vegetation cover. We also examined the seasonal influence on the correlation between VIs and GPP. SAVI exhibited the best correlation with GPP in spring when the grassland canopy was sparse, while EVI exhibited the best correlation with GPP in summer when the grassland cover was dense. Our results also showed that VIs could capture variations in observed GPP better in drought period than in nondrought period for an alpine meadow site because of the suppression of vegetation growth by drought.     

Development ofNew InDel Marker to Detect Genotypes of Conferring Fertility Restoration of BT-Type Cytoplasmic Male Sterility inRice简

Restorer line breeding is an important approach to enhance the heterosis and improve the yields of japonica hybrid rice. To improve the selection efficiency of restorer lines for BT-type cytoplasmic male sterility (CMS) in japonica rice, a functional marker InDel-Rf-1a based on the difference of nucleotide sequence in Rf-1a locus between BT-type CMS lines and restorer lines was developed to detect the genotypes of different rice materials. Conventional indica rice varieties, restorer and maintainer lines without 574 bp deletion could restore the fertility for BT-type CMS in japonica rice. By contrast, most conventional japonica rice varieties except Aichi 106 and Yijing 12, with genotype of rf-1arf-1a showed the 574 bp deletion maintained sterility for BT-type CMS lines. To further verify the effect of genotyping detection in Rf-1a locus, this marker was also used to amplify the genomic DNA in different japonica rice restorer lines, CMS lines, hybrids and F₂ segregation population, and three genotypes in Rf-1a locus could be distinguished distinctly. Therefore, the marker InDel-Rf-1a could be widely used for genetic identification and marker-assisted selection (MAS) in breeding japonica restorer lines.     

Soybean (Glycine max (L.) Merr.) growth and development response to CO2 enrichment under different temperature regimes

The carbon dioxide (CO₂) concentration of the global atmosphere has increased during the last decades. This increase is expected to impact the diurnal variation in temperature as well as the occurrence of extreme temperatures. This potentially could affect crop production through changes in growth and development that will ultimately impact yield. The objective of this study was to evaluate the effect of CO₂ and its interaction with temperature on growth and development of soybean (Glycine max (L.) Merr., cv. Stonewall). The experiment was conducted in controlled environment chambers at the Georgia Envirotron under three different temperatures and two CO₂ regimes. The day/night air temperatures were maintained at 20/15, 25/20 and 30/25 °C, while the CO₂ levels were maintained at 400 and 700 ppm, resulting in six different treatments. Plants were grown under a constant irradiance of 850 μmoles m⁻² s⁻¹ and a day length of 12 h; a non-limiting supply of water and mineral nutrients were provided. Five growth analyses were conducted at the critical development stages V4, R3, R5, R6 and R8. No differences in start of flowering were observed as a function of the CO₂ level, except for the temperature regime 25/20 °C, where flowering for the elevated CO₂ level occurred 2 days earlier than for the ambient CO₂ level. For aboveground biomass, an increase in the CO₂ level caused a more vigorous growth at lower temperatures. An increase in temperature also decreased seed weight, mainly due to a reduction in seed size. For all temperature combinations, final seed weight was higher for the elevated CO₂ level. This study showed that controlled environment chambers can be excellent facilities for conducting a detailed growth analysis to study the impact on the interactive effect of changes in temperature and CO₂ on soybean growth and final yield.     

Long-term effect of chemical fertilizer,straw, and manure on labile organic matter fractions in a paddy soil

To assess the effect of long-term fertilization on labile organic matter fractions, we analyzed the C and N mineralization and C and N content in soil, particulate organic matter (POM), light fraction organic matter (LFOM), and microbial biomass. Results showed that fertilizer N decreased or did not affect the C and N amounts in soil fractions, except N mineralization and soil total N. The C and N amounts in soil and its fractions increased with the application of fertilizer PK and rice straw. Generally, there was no significant difference between fertilizer PK and rice straw. Furthermore, application of manure was most effective in maintaining soil organic matter and labile organic matter fractions. Soils treated with manure alone had the highest microbial biomass C and C and N mineralization. A significant correlation was observed between the C content and N content in soil, POM, LFOM, microbial biomass, or the readily mineralized organic matter. The amounts of POM–N, LFOM–N, POM–C, and LFOM–C closely correlated with soil organic C or total N content. Microbial biomass N was closely related to the amounts of POM–N, LFOM–N, POM–C, and LFOM–C, while microbial biomass C was closely related to the amounts of POM–N, POM–C, and soil total N. These results suggested that microbial biomass C and N closely correlated with POM rather than SOM. Carbon mineralization was closely related to the amounts of POM–N, POM–C, microbial biomass C, and soil organic C, but no significant correlation was detected between N mineralization with C or N amounts in soil and its fractions.     

设施菜地土壤次生盐渍化分类与分级标准

近三十年来,我国设施蔬菜栽培发展迅速,已成为我国农业中最有活力的新兴产业之一。但在长期的设施蔬菜生产过程中,普遍存在着不合理施肥、养分比例失调、肥效下降和资源浪费严重等问题,致使土壤养分富集,盐分积累现象日趋严重。本文对我国设施菜地土壤次生盐渍化的现状、发生原因及其对作物的危害进行综述和分析,在此基础上制定设施菜地土壤次生盐渍化分类与分级的标准的建议及初步构架,旨在为防治设施菜地土壤次生盐渍化,实现设施菜地土壤的质量调控与可持续利用提供理论指导和科学依据。     

Allelopathy variation in dryland winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) accessions grown on the Loess Plateau of China for about fifty years

In this study, we investigated the genetic variation of allelopathic potential, its grey correlation with important agronomic characters, and rank analysis on allelopathic stability of fifteen wheat accessions commonly grown in arid regions of the Loess Plateau in China. The genetic variation of allelopathic property in dryland winter wheat showed significant differences between accessions. Allelopathic effects exhibited high heritability (55–95%) throughout the life cycle of wheat. Heritability was highest in the tillering stage and weakest in the seed filling stage. Allelopathic potential varied and was discontinuous throughout the wheat life cycle. Grey correlation analysis indicated a close relationship between allelopathic potential dependant on growth phase and agronomic characters. Allelopathic expression during some growth periods induced a partial correlation effect on some important agronomic characters that affected wheat yield. Allelopathic heritability and its degree of influence on yield were more evident in the vegetative growth stage compared to the reproductive stage. A multiple linear regression was built between allelopathic potential during different growth periods and agronomic characters pursued in wheat breeding. Allelopathic potential had a linear effect on production traits cultivated in wheat breeding. When allelopathic intensity varied from 0 to 1 in the reproductive stage, plant height ranged from 44 to 108 cm, spike length from 6.4 to 9.2 cm, number of spikelets with seeds from 13.4 to 21.0, mean seed number per spike from 41.5 to 50.3 and thousand seed weight from 36.2 to 38.3 g. Based on rank analysis, we concluded that there was a synergistic relationship between allelopathic potential in wheat and genetic, chemical and ecological factors. Triticum aestivum L. ‘No 6 Lankao’ and T. aestivum L. ‘No 22 Xiaoyan’ were identified as stable and relatively strong allelopathic accessions, whereas T. aestivum L. ‘Lankao 95–25’ was a stable but relatively weak allelopathic cultivar. Other varieties showed unstable allelopathic potential.     

Distinguishing between human-induced and climate-driven vegetation changes: a critical application of RESTREND in inner Mongolia

Changes in the spatiotemporal pattern of vegetation alter the structure and function of landscapes, consequently affecting biodiversity and ecological processes. Distinguishing human-induced vegetation changes from those driven by environmental variations is critically important for ecological understanding and management of landscapes. The main objectives of this study were to detect human-induced vegetation changes and evaluate the impacts of land use policies in the Xilingol grassland region of Inner Mongolia, using the NDVI-based residual trend (RESTREND) method. Our results show that human activity (livestock grazing) was the primary driver for the observed vegetation changes during the period of 1981?C2006. Specifically, vegetation became increasingly degraded from the early 1980s when the land use policy??the Household Production Responsibility System??led to soaring stocking rates for about two decades. Since 2000, new institutional arrangements for grassland restoration and conservation helped curb and even reverse the increasing trend in stocking rates, resulting in large-scale vegetation improvements in the region. These results suggest that most of the degraded grasslands in the Xilingol region can recover through ecologically sound land use policies or institutional arrangements that keep stocking rates under control. Our study has also demonstrated that the RESTREND method is a useful tool to help identify human-induced vegetation changes in arid and semiarid landscapes where plant cover and production are highly coupled with precipitation. To effectively use the method, however, one needs to carefully deal with the problems of heterogeneity and scale in space and time, both of which may lead to erroneous results and misleading interpretations.