Search

Ammonia (NH3) emissions, the most important nitrogen (N) loss, always induce a series of environmental problems such as increased the frequency of regional haze pollution, accelerated N deposition, and N eutrophication. Arbuscular mycorrhizal (AM) fungi play key roles in N cycling. However, whether AM fungi can alleviate N losses by reducing NH3emissions is still unclear. The potential and mechanism by which AM fungi reduce NH3emissions in five land-use types (grazed grassland, mowed grassland, fenced grassland, artificial alfalfa grassland, and cropland) were explored in this study. The results showed that AM fungal inoculation significantly reduced NH3emissions and the mycorrhizal responses of NH3emissions were determined by land-use type. Structural equation modeling (SEM) showed that AM fungi and land-use type directly affected NH3emissions. In addition, the reduction in NH3emissions was largely driven by the decline in soil NH4+-N and pH and the increase the abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB), urease activity and plant N content induced by AM fungal inoculation and land-use type. The present results highlight that reducing the negative influence of agricultural intensification caused by land-use type changes on AM fungi should be considered to reduce N losses in agriculture and grassland ecosystems.

Phosphorus (P) is an essential element for living organisms and a major limiting factor in many ecosystems. In recent years, global warming and nitrogen (N) deposition have become increasingly serious, with significant effects on the P cycle in terrestrial ecosystems. A series of studies were carried out on the soil P cycle, but how climate change affects this remains unclear. Field experiments with warming and N addition were implemented since April 2007. Infrared radiators manipulated temperature, and aqueous ammonium nitrate (10 g m-2 year-1) was added to simulate N deposition. Compared with the control, N addition reduced soil total P; warming and N addition decreased soil available P; warming, N addition and warming plus N addition decreased microbial biomass P, but increased litter P; and warming and N addition increased phosphatase activity significantly. Correlation analysis showed that soil total P, available P, microbial biomass P and phosphatase activity were positively correlated with soil temperature and water content. Soil total P was positively correlated with microbial biomass P and phosphatase activity; and available P was positively correlated with microbial biomass P but negatively correlated with litter P. The results showed that warming and N deposition accelerated the soil P cycle by changing soil physical and chemical properties and soil biological activities (microbial and phosphatase activities). However, N addition reduced the capacity of microbes to fix P and reduced microbial biomass P, resulting in losses to the soil P pool, further aggravating P limitation in the Songnen Grassland ecosystem.

Chenopodiaceae is one of the most important families in arid and saline environments. Several studies have observed the mycorrhizal structure in Chenopodiaceae plants (i.e., chenopods), but the mycorrhizal colonization status of chenopods in saline habitats and the influencing factors are still not well understood. The mycorrhizal colonization of twenty chenopod species in three different saline habitats (a saline alkaline meadow in the Songnen Plain of northeastern China, a saline desert in the Junggar Basin of northwestern China, and a saline alpine meadow in the Tibetan Plateau of western China) and the chenopod-associated environmental factors (including soil moisture, soil available phosphorous (P) concentration, pH, and salt content) were analyzed. Our results showed that approximately 60% of the studied chenopods were colonized by arbuscular mycorrhizal (AM) fungi with a colonization percentage ranging from 5% to 33%. Structural analysis of mycorrhizal association indicated that vesicles were quite common, while arbuscules and hyphal coils were relatively rare. In addition, a positive correlation between mycorrhizal colonization rate and soil electrical conductivity (r=0.920, P<0.01) and two negative correlations of mycorrhizal colonization rates with soil moisture (r=–0.818, P<0.01) and the soil available P concentration (r=–0.876, P<0.01) confirmed that mycorrhizal colonization rate in the roots of chenopods was environment-dependent.

Deposited in plant cells and their intercellular space, phytoliths, a special form of silica, could be used to determine information on plant structure and physiology especially their size and content. With the hypothesis that phytolith in plant would change under variable climate and environment, the dominant plant species in Songnen grassland, guinea grass (Leymus chinensis), was treated by an open-top chamber (OTC) to elevate CO2concentration, infrared heaters, and artificial nitrogen (N) addition for three years from 2006–2008. Phytoliths were extracted by wet-ashing method and analyzed by variance analysis and so on. We found that the responses to elevated CO2are complicated, and warming is positive while N addition is negative to the deposition of phytoliths in L. chinensisleaves. Especially, warming could reduce the negative impact of N addition on phytolith in L. chinensis. The short cell’s taxonomic in graminea is significant because of no disappearance with simulated environmental changes. The phytolith originated in the long cell and plant intercellular space are more sensitive to elevated CO2concentration, warming, and N addition, and could become some new indicators for environmental changes. In conclusion, different phytolith types have various responses to simulated warming, N addition and elevated CO2concentration.

Soil enzymes play vital roles in the decomposition of soil organic matter and soil nutrient mineralisation. The activity of soil enzymes may be influenced by climate change. In the present study we measured soil enzyme activity, soil microclimate and soil nutrients to investigate the response of soil enzyme activity to N addition and experimental warming. Warming enhanced phosphatase activity (35.8%), but inhibited the cellulase activity (30%). N addition significantly enhanced the activities of urease (34.5%) and phosphatase (33.5%), but had no effect on cellulase activity. Significant interactive effects of warming and N addition on soil enzyme activity were observed. In addition, warming reduced soil C (7.2%) and available P (20.5%), whereas N addition increased soil total N (17.3%) and available N (19.8%) but reduced soil C (7.3%), total P (14.9%) and available P (23.5%). Cellulase and phosphatase activity was highly correlated with soil temperature and water content, whereas urease activity was determined primarily by soil N availability. The results show that climate change not only significantly affects soil enzyme activity, but also affects the mineralisation of soil nutrients. These findings suggest that global change may alter grassland ecosystem C, N and P cycling by influencing soil enzyme activity.

•Experiment focusing on the young and old leaves provides a new perspective to study abiotic stress.•Ionomics confirmed that Mg2+and K+were transported from old to young leaves.•Physiological characteristics confirmed that barren tolerant wild soybean leaves could maintain stable photosynthetic assimilation capacity and carbon and nitrogen metabolism levels under nitrogen deficiency.•The comparative study of two genotypes wild soybean provides a theoretical basis for the protection and utilization of wild soybean resources.

Understanding how the seed yield and seed quality respond to global warming is crucial for understanding how new grassland establishment responds to global change. This study evaluated Leymus chinensis, a dominant perennial grass widely distributed in the eastern regions of the Eurasian grassland zone, as a model to investigate the effect of increasing ambient temperature on seed production, seed mass, germinability, and subsequent seedling growth. As the temperature rose, there were significant reductions in the number of flowering plants and in seed number per square metre but significant increase in the number of florets and the number of seeds per plant. Increasing temperature decreased the proportion of light weight seeds, increased the proportion of heavy weight seeds and led to a significant increase in the mean dry weight. Germination success, germination rate and the root:shoot ratio of light weight seeds were reduced, while heavy weight seed did not appear to be affected by elevated temperatures. Finally, germinating seeds per unit area was reduced by increased temperature. The reduction in the number of germinating seeds with increasing temperature implies that continued global warming will further constrain new grassland establishment of L. chinensis in the eastern regions of Eurasia.

Global climate change projections suggest an increasing frequency of droughts and extreme rain events in the steppes of the Eurasian region. Using the eddy covariance method, we measured carbon and water balances of a meadow steppe ecosystem in Northeast China during 2 years which had contrasting precipitation patterns in spring seasons in 2007 and 2008. The meadow steppe sequestrated only 64·2 gC m−2year−1in 2007 compared to 160·5 gC m−2year−1in 2008, due to a severe spring drought in 2007. The 2007 spring drought resulted in a dramatic reduction of leaf area index (LAI) and aboveground net primary productivity (ANPP). However, the meadow steppe still acted as a carbon sink in 2007. The strength of the sink was much greater than that in the typical steppes in Central Mongolia and Inner Mongolia. Spring drought also caused a reduction of plant transpiration (Tr) and total ecosystem evapotranspiration (ET). However, the suppression of ET in 2007 was relatively small in comparison to gross ecosystem productivity (GEP) reduction. Thus, ecosystem water use efficiency (WEU) (GEP/ET) in 2007 was reduced to 5·0 gCO2kg−1H2O or 75% of that of 2008. We concluded that spring drought detrimentally impacted meadow steppe ecosystem by reducing leaf areas, biomass, GEP, WUE and associated increases in soil evaporation (Es) that might aggravate soil salinization of the Songnen Plain. Copyright © 2011 John Wiley & Sons, Ltd.