B6nassy, C., 1955. R6marques sur deux Aphelinid6s: Aphelinus mytilaspidis Le Baron et Aphytis proclia Walker. Annls l~piphyt. 6: 11-17. Lord, F. T. & MacPhee, A. W., 1953. The influence of spray programs on the fauna of apple orchards in Nova Scotia II. Oyster shell scale. Can. Ent. 79: 196-209. Pickett, A. D., 1946. A progress report on long term spray programs. Rep. Nova Scotia Fruit Grow. Ass. 83 : 27-31. Pickett, A. D., 1967. The influence of spray programs on the fauna of apple orchards in Nova Scotia XIV. Can. Ent. 97: 816-821. Tothill, J. D., 1918. The predacious mite Hemisarcoptes malus Shimer and its relation to the natural control of the oyster shell scale Lepidosaphes ulmi L. Agric. Gaz. Can. 5 : 234-239.

http://link.springer.com/content/pdf/10.1007/BF01976688.pdf

Soil enzymes: Kuprevich, V. F. & Shcherbakova, T. A.: Translated from the Russian edition (1966), published by the Indian National Scientific Documentation Centre, New Delhi 1971. 392 pp., offset printing from type script, paper cover. Obtainable from U.S. Department of Commerce, National Technical Information Service, Springfield, Va. 22151

Microbial diversity in European alpine permafrost and active layers

Abstract The aim of this review is to describe and discuss the concepts that have been employed to interpret N mineralization–immobilization in soil, and how N turnover is related to the characteristics of organic N and the biota conducting the transformations. A brief survey of the period before the arrival of electronic searches became available provides access to the classical literature that can help interpret today's challenges. Classical (acid hydrolysis) and modern spectrometry and spectroscopy techniques indicate that protein N is the prevalent component of organic N in soil. The presence of heterocyclic N can indicate its abiotic, partial synthesis as in fire-affected soils. Clays and pedogenic oxides can protect organic N against microbial degradation. The evidence for such protection is mostly based on in vitro studies involving pure clays, and proteins and their relevance to field conditions requires further work. The proteomic approach, with extraction and characterization of proteins stabilised by soil colloids (structural proteomics) might give further insights into this area. Functional proteomics can improve our understanding of the degradation of organic pollutants and organic debris as well as identifying the molecular colloquia between microorganisms and between soil biota and plant roots. Subdivision of organic N into sub-pools has helped to interpret mechanistic studies and modelling of N dynamics. Uncomplexed organic matter, obtained by physical fractionation procedures, is considered a labile pool. The interpretation of N mineralization measurements is affected by immobilization during microbial attack especially in high-C environments. Transfer of materials among particle size fractions and changes in microbiological properties of aggregates also can occur during fractionation procedures. Classical mineralization–immobilization turnover (MIT) does not always occur since microorganisms (and plants) can take up amino acid N with intracellular deamination. Protozoa, due to their grazing activities, can influence not only N mineralization but also the composition of rhizosphere–plant growth stimulating communities. Differences between N-poor and N-rich microsites, occurring in the same soil, can markedly affect the competition for N between plants and microorganisms especially the nitrifiers. The use of molecular techniques has allowed the identification of unculturable microorganisms and functional genes in the N cycle. Archeae are probably capable of oxidising NH4+ to NO3− and anerobic ammonia oxidation (Ammonox) bacteria have been identified in biofilms and probably also occur in soils. The use of nitrate as an electron acceptor is encoded by specific gene clusters but nitrate reduction also occurs in dissimilatory nitrate reduction.

Erratum to The chemical and functional characterization of soil N and its biotic components

Higher precipitation strengthens the microbial interactions in semi-arid grassland soils

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta-analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N2 O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N2 O emission demonstrated significant positive relationships with rates of CO2 emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia-oxidizing archaea amoA gene, ammonia-oxidizing bacteria amoA and nirK genes. This study provides the first global-scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.

/pdf/elevated-temperature-shifts-soil-n-cycling-from-microbial-2atqx5dx2o.pdf

Elevated temperature shifts soil N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification across global terrestrial ecosystems

The Walker and Syers model of phosphorus (P) transformations during long-term soil development has been verified along many chronosequences but has rarely been examined along climosequences, particularly in arid regions. We hypothesized that decreasing aridity would have similar effects on soil P transformations as time by increasing the rate of pedogenesis. To assess this, we examined P fractions in arid and semiarid grassland soils (0-10 cm) along a 3700 km aridity gradient in northern China (aridity between 0.43 and 0.97, calculated as 1 − [mean annual precipitation/potential evapotranspiration]). Primary mineral P declined as aridity decreased, although it still accounted for about 30% of the total P in the wettest sites. In contrast, the proportions of organic and occluded P increased as aridity decreased. These changes in soil P composition occurred in parallel with marked shifts in soil nutrient stoichiometry, with organic carbon:organic P and nitrogen:organic P ratios increasing with decreasing aridity. These results indicate increasing abundance of P relative to carbon or nitrogen along the climosequence. Overall, our results indicate a broad shift from abiotic to biotic control on P cycling at an aridity value of approximately 0.7 (corresponding to about 250 mm mean annual rainfall). We conclude that the Walker and Syers model can be extended to climosequences in arid and semiarid ecosystems and that the apparent decoupling of nutrient cycles in arid soils is a consequence of their pedogenic immaturity.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015GB005331

Phosphorus transformations along a large‐scale climosequence in arid and semiarid grasslands of northern China

Soil organic nitrogen (N) turnover is significantly influenced by elevated N deposition, precipitation and human-caused disturbances, but the underlying mechanism remains unclear. Identifying the relationships among the soil organic N fractions and N-mineralizing enzymes activities may advance our knowledge of the dynamics of soil organic N. A field experiment was conducted in a semi-arid steppe and an abandoned cropland in northern China to investigate the effects of elevated N deposition and precipitation on soil organic N fractions and their relationships with N-mineralizing enzymes, i.e., protease, amidase, urease and N-acetyl-β-D-glucosaminidase (NAG) activities. The concentrations of N in various fractions were consistently lower in the abandoned cropland compared with the steppe. Nitrogen addition consistently decreased amino acid N content and activities of urease, protease and amidase in both sites but increased amino sugar N content and NAG activity in the steppe. Water addition decreased hydrolysable ammonium N content but increased amino sugar N content and activities of protease and NAG in both sites. Furthermore, urease and NAG activities were significantly positively correlated with the proportions of amino acid N and amino sugar N and, explained significant proportions of the variations in soil organic N fractions in the steppe. However, soil organic carbon (C), rather than N-mineralizing enzymes, explained greatest proportion of the variations in soil organic N fractions in the abandoned cropland. The concurrent increase of N deposition and precipitation could promote the recovery of soil N (and C) losses in the abandoned cropland resulting from previous agriculture. Furthermore, in the steppe where NH4
 + was available at relative high concentrations, enzymatic mineralization was the dominant route involved in potential soil organic N turnover. However, the direct route may be favored over the enzymatic mineralization route with decreasing availability of C relative to N in the abandoned cropland, which is driven by the need for C. These findings confirmed that the forms of N available, and the relative availability of C and N determine N uptake pathways both through enzymatic mineralization route and direct uptake route in the semi-arid grasslands.

Effects of elevated nitrogen and precipitation on soil organic nitrogen fractions and nitrogen-mineralizing enzymes in semi-arid steppe and abandoned cropland

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GB006112

Coupling and Decoupling of Soil Carbon and Nutrient Cycles Across an Aridity Gradient in the Drylands of Northern China: Evidence From Ecoenzymatic Stoichiometry

How climatic factors influence the balance of sulfur (S) with carbon (C) and nitrogen (N) in soils is not well understood. Here we report the results of S, C and N concentrations in 550 soil samples along a 3500-km aridity gradient across arid and semi-arid grasslands in northern China. Our results showed that soil available S (AS) concentrations decreased with increasing aridity index (AI, calculated as '1—the ratio of mean annual precipitation to potential evapotranspiration') when AI\0.91 (90-450 mm rainfall year -1 ), but increased when AI(0.91 (30-90 mm rainfall year -1 ), having a threshold at AI = 0.91 (90 mm rainfall year -1 ). Soil AS concen- trations were positively related to soil organic C (OC), soil total N (TN), microbial biomass C and N con- centrations, and arylsulphatase activities when AI\0.91, but were not positively related to these variableswhenAI(0.91.TopsoilAS:OCandAS:TN ratios mainly depended on OC and TN concentrations when AI\0.91, but mainly depended on AS con- centrations when AI(0.91. The decreased (AI\0.91) and increased total S concentrations (AI(0.91) with increasing AI along the gradient provided further evidence for the existence of this fundamental threshold. High concentrations of sulfate in drier soils were associated with long-term atmo- sphere inputs and groundwater-derived salts with minimal leaching rates. Overall, our findings imply that aridity asymmetrically controls the relationships of soil AS with OC and TN on the two sides of the threshold, i.e. biological processes exerted stronger controls in wetter sites, while geochemical processes played more significant roles in drier sites. These results should be incorporated into predictive models of global biogeochemical cycling under various global climate change scenarios.

A threshold reveals decoupled relationship of sulfur with carbon and nitrogen in soils across arid and semi-arid grasslands in northern China

Variations in plant nitrogen (N) and phosphorus (P) concentrations and ratios have great implications for primary productivity and nutrient cycling. Here, we reported their changes at functional group and community levels along an aridity gradient. We carried out a field investigation and set up 26 sampling sites along a transect in the drylands of northern China to examine the responses of plant nutrient status to increasing aridity and the relationships between plant and soil nutrients. The responses of N and P concentrations to increasing aridity differed between woody (sub-) shrubs and herbaceous species (including annual/biennial forbs and grasses, perennial forbs and perennial grasses). Nitrogen and P concentrations of shrubs decreased while those of herbs generally increased with increasing aridity. Plant N:P ratios increased significantly with increasing aridity for the plant functional groups and at the community level. At both organizational levels, nutrient concentrations in plants were negatively related to those in soils. Our results indicated that the responses of plant nutrition to aridity were dependent on plant functional group. Plant growth appeared increasingly limited by P, and plant and soil nutrients become increasingly decoupled at large spatial scale with increasing aridity.

Jiao Feng

Papers

Phosphorus transformations along a large‐scale climosequence in arid and semiarid grasslands of northern China

Effects of elevated nitrogen and precipitation on soil organic nitrogen fractions and nitrogen-mineralizing enzymes in semi-arid steppe and abandoned cropland

Coupling and Decoupling of Soil Carbon and Nutrient Cycles Across an Aridity Gradient in the Drylands of Northern China: Evidence From Ecoenzymatic Stoichiometry

A threshold reveals decoupled relationship of sulfur with carbon and nitrogen in soils across arid and semi-arid grasslands in northern China

Changes of plant N:P stoichiometry across a 3000-km aridity transect in grasslands of northern China