Changes of vegetation carbon sequestration in the tableland of Loess Plateau and its influencing factors.

The variations of vegetation carbon sequestration have become a gauge for evaluating the ecological effect of vegetation restoration. In this study, the spatiotemporal patterns of the net ecosystem production (NEP) were simulated using an improved CASA model and GSMSR model. It showed that the NEP markedly increased in the tableland of Loess Plateau during 2003-2012, with an annual average growth of 3.65 g C·m-2 a-1. The mixed broadleaf-conifer forest ranked first (127.23 g C·m-2 a-1) while the bare land and sparse vegetation presented the lowest carbon sequestration (14.64 g C·m-2 a-1). The NEP manifested a significantly uneven overall spatial distribution: high in the southwest and low in the northeast. The spatial variations of NEP resulted from the combined effects of geographic position, terrain, meteorology, and soil and vegetation, respectively. Quantitative isolation revealed that the most dominant factor of vegetation carbon sequestration was soil and vegetation, while terrain exerted insignificant impacts on the NEP.

Effects of lily/maize intercropping on rhizosphere microbial community and yield of Lilium davidii var. unicolor.

Continuous cropping of lily (Lilium davidii var. unicolor) or any other crop seriously affects yield and quality. In this study, we compared continuous cropping with lily/maize intercropping. We also examined the lily rhizosphere microbes community in both sole lily cropping and lily/maize intercropping systems, by the llumina Miseq platform. Here we refer to data of recent years field experimentation of a lily/maize intercrop system in different planting configurations in the Gaolan Ecological and Agricultural Research Station. Treatments included sole crops of lily and maize, an intercrop consisting of strips of four lily rows alternating with one maize rows. The land equivalent ratio (LER) of intercrops was 1.294. The results showed that compared to sole cropping, the yield of lily in the first year of planting increased when lily was intercropped with maize. The species annotation of the high-throughput sequencing experiment showed that there was no difference in the diversity of the lily rhizosphere soil microbes on phylum taxonomic level, but the relative abundance of some genus changed obviously. The relative abundance of harmful fungus Fusarium spp. and, Funneliformis spp., decreased, and the relative abundance of beneficial bacteria Sphingomonas spp. and, Nitrospira spp., increased. In addition, we found that Lecanicillium spp., appeared only in the intercropping lily rhizosphere soil and sole cropping maize rhizosphere soil. In conclusion, the findings indicated that lily/maize intercropping could change soil microenvironment, and affect the diversity and structure of microorganism community in lily rhizosphere, with further beneficial effect on the yield of lily.

Impact of management strategies on the global warming potential at the cropping system level.

Estimating the greenhouse gas (GHG) emissions from agricultural systems is important in order to assess the impact of agriculture on climate change. In this study experimental data supplemented with results from a biophysical model (DNDC) were combined with life cycle assessment (LCA) to investigate the impact of management strategies on global warming potential of long-term cropping systems at two locations (Breton and Ellerslie) in Alberta, Canada. The aim was to estimate the difference in global warming potential (GWP) of cropping systems due to N fertilizer reduction and residue removal. Reducing the nitrogen fertilizer rate from 75 to 50 kg N ha(-1) decreased on average the emissions of N2O by 39%, NO by 59% and ammonia volatilisation by 57%. No clear trend for soil CO2 emissions was determined among cropping systems. When evaluated on a per hectare basis, cropping systems with residue removal required 6% more energy and had a little change in GWP. Conversely, when evaluated on the basis of gigajoules of harvestable biomass, residue removal resulted in 28% less energy requirement and 33% lower GWP. Reducing nitrogen fertilizer rate resulted in 18% less GWP on average for both functional units at Breton and 39% less GWP at Ellerslie. Nitrous oxide emissions contributed on average 67% to the overall GWP per ha. This study demonstrated that small changes in N fertilizer have a minimal impact on the productivity of the cropping systems but can still have a substantial environmental impact.

Arbuscular mycorrhizal fungi assemblages in Chernozem great groups revealed by massively parallel pyrosequencing.

The arbuscular mycorrhizal (AM) fungal resources present in wheat fields of the Canadian Prairie were explored using 454 pyrosequencing. Of the 33 dominant AM fungal operational taxonomic units (OTUs) found in the 76 wheat fields surveyed at anthesis in 2009, 14 clustered as Funneliformis - Rhizophagus, 16 as Claroideoglomus, and 3 as Diversisporales. An OTU of Funneliformis mosseae and one OTU of Diversisporales each accounted for approximately 16% of all AM fungal OTUs. The former was ubiquitous, and the latter was mainly restricted to the Black and Dark Brown Chernozems. AM fungal OTU community composition was better explained by the Chernozem great groups (P = 0.044) than by measured soil properties. Fifty-two percent of the AM fungal OTUs were unrelated to measured soil properties. Black Chernozems hosted the largest AM fungal OTU diversity and almost twice the number of AM fungal sequences seen in Dark Brown Chernozems, the great group ranking second for AM fungal sequence abundance. Brown Chernozems hosted the lowest AM fungal abundance and an AM fungal diversity as low as that seen in Gray soils. We concluded that Black Chernozems are most conducive to AM fungal proliferation. AM fungi are generally distributed according to Chernozem great groups in the Canadian Prairie, although some taxa are evenly distributed in all soil groups.

Role of mineral nutrition in minimizing cadmium accumulation by plants.

Cadmium (Cd) is a highly toxic heavy metal for both plants and animals. The presence of Cd in agricultural soils is of great concern regarding its entry into the food chain. Cadmium enters into the soil-plant environment mainly through anthropogenic activities. Compounds of Cd are more soluble than other heavy metals, so it is more available and readily taken up by plants and accumulates in different edible plant parts through which it enters the food chain. A number of approaches are being used to minimize the entry of Cd into the food chain. Proper plant nutrition is one of the good strategies to alleviate the damaging effects of Cd on plants and to avoid its entry into the food chain. Plant nutrients play a very important role in developing plant tolerance to Cd toxicity and thus, low Cd accumulation in different plant parts. In this report, the role of some macronutrients (nitrogen, phosphorus, sulfur and calcium), micronutrients (zinc, iron and manganese), and silicon (a beneficial nutrient) has been discussed in detail as to how these nutrients play their role in decreasing Cd uptake and accumulation in crop plants.