Nitrogen addition does not alter symmetric responses of soil respiration to changing precipitation in a semi-arid grassland.

Concurrent changing precipitation regimes and atmospheric nitrogen (N) deposition can have profound influences on soil carbon (C) cycling. However, how N enrichment regulates the responses of soil C fluxes to increasing variability of precipitation remains elusive. As part of a field precipitation gradient experiment with nine levels of precipitation amounts (-60 %, -45 %, -30 %, -15 %, ambient precipitation, +15 %, +30 %, +45 %, and +60 %) and two levels of N addition (0 and 10 g N m-2 yr-1) in a semi-arid temperate steppe on the Mongolian Plateau, this work was conducted to investigate the responses of soil respiration to decreased and increased precipitation (DP and IP), N addition, and their possible interactions. Averaged over the three years from 2019 to 2021, DP suppressed soil respiration by 16.1 %, whereas IP stimulated it by 27.4 %. Nitrogen addition decreased soil respiration by 7.1 % primarily via reducing microbial biomass C. Soil respiration showed symmetric responses to DP and IP within all the four precipitation variabilities (i.e., 15 %, 30 %, 45 %, and 60 %) under ambient N. Nevertheless, N addition did not alter the symmetric responses of soil respiration to changing precipitation due to the comparable sensitivities of microbial biomass and root growth to DP and IP under the N addition treatment. These findings indicate that intensified precipitation variability does not change but N addition could alleviate soil C releases. The unchanged symmetric responses of soil respiration to precipitation variability under N addition imply that N deposition may not change the response pattern of soil C releases to predicted increases in precipitation variability in grasslands, facilitating the robust projections of ecosystem C cycling under future global change scenarios.

Stronger mutualistic interactions with arbuscular mycorrhizal fungi help Asteraceae invaders outcompete the phylogenetically related natives.

Mutualistic interactions with arbuscular mycorrhizal fungi (AMF) greatly affect the outcome of plant-plant competition, especially for invasive plants competing against native plants. We examined the effects of AMF on the competition between invasive Asteraceae plants and the phylogenetically related native plants. We compared the performance of seven invasive Asteraceae plants from different genera with that of their phylogenetically related native counterparts in response to AMF in monocultures and mixed cultures. We investigated how interactions with AMF impact the competition between Asteraceae relatives. Total biomass increased with AMF colonization in both invasive and native plants. Arbuscular mycorrhizal fungi improved the competitiveness of invasive plants, but decreased that of native plants. Competition increased the shoot nitrogen, phosphorus and root myristic acid concentrations and relative expression of fatty acid transporter genes (RiFAT1 and RiFAT2) in AMF-colonized invasive plants, but decreased those in AMF-colonized native plants. Structural equation models indicated that the presence of AMF increased the uptake of phosphorus, but not nitrogen, by invasive plants, which probably provided more myristic acids to symbiotic AMF in return. These results suggest that invasive Asteraceae plants have greater mutualistic interactions with AMF than their phylogenetically related native counterparts, potentially contributing to invasion success.

[Safety evaluation of allelochemical derivative pyrone on different millet varieties]. / åŒ–æ„Ÿç‰©è´¨è¡ç”Ÿç‰©å¡å–ƒé ®å¯¹ä¸åŒè°·å­å“ç§çš„å®‰å ¨æ€§è¯„ä»·.

The development of new herbicides based on allelochemicals is a potential strategy of weed control in arable field. Pyrone, a novel derivative of tricin, has significant inhibitory effects on weeds. Its safety for crops, especially for millet that are sensitive to commercial herbicides, is still poorly understood. In this study, germination test and pot experiments were conducted to evaluate the safety of pyrone on 20 millet varieties, compared with 2,4-D. The results showed that, except that Jinfen109 was sensitive to high concentration 2,4-D, both pyrone and 2,4-D had no effect on the germination rates of other varieties. Results of the pot experiment showed that pyrone treatment significantly increased the chlorophyll content of millet by 9.0%-67.9%, which was the greatest for Jigu 42. Pyrone treatment did not affect maximal photochemical efficiency, potential photochemical activity, actual photochemical efficiency, and non-photochemical quenching coefficient. On the contrary, 2,4-D significantly inhibited the fluorescence parameters of millet varieties. Pyrone treatment increased the activities of superoxide dismutase, peroxidase and catalase in leaves of Dunza16, Jigu 39, Jigu 41 and Jingu 28, with the magnitude of enhancement being higher than 2,4-D. The results indicated that the allelochemical derivative pyrone is highly safe to the growth of millet seedlings and has the potential to be a new herbicide to millet field.

Polyamines modulate aluminum-induced oxidative stress differently by inducing or reducing H2O2 production in wheat.

Polyamines are important bioactive molecules involved in regulating H2O2 homeostasis, which is recognized as a major stimulus of oxidative stress under aluminum (Al) exposure. In this study, we investigated the involvement of spermidine oxidation in Al-induced oxidative stress, and its modulation by exogenous putrescine (Put) in two wheat genotypes differing in Al tolerance. Aluminum caused more severe oxidative damage at the root apexes in the Al-sensitive genotype Yangmai-5 than in the tolerant Xi Aimai-1, but these effects were significantly reversed by exogenous Put and polyamine oxidase (PAO) inhibitors. Aluminum caused a more significant increase in cell wall-bound PAO (CW-PAO) activity in Yangmai-5 than in Xi Aimai-1. Inhibiting of CW-PAO reduced H2O2 accumulation, restored Spd decline in both genotypes, indicating its potential role in Al-induced H2O2 production through catalyzing Spd oxidation. Additionally, Al significantly increased the activity of plasma membrane-NADPH oxidase, another H2O2 generator, in wheat roots. Put application significantly inhibited the activity of CW-PAO and plasma membrane-NADPH oxidase, and reduced H2O2 accumulation in Al-stressed wheat roots. Antioxidant enzymes were significantly stimulated by Al, but not Put. Overall, Put may protect wheat roots against Al-induced oxidative stress through regulating H2O2 production by inhibiting CW-PAO and plasma membrane-NADPH oxidase.

Effects of organic amendment on soil aggregation and microbial community composition during drying-rewetting alternation.

The alternation of drying and rewetting events could dramatically affect the biological and structural properties of soil and consequently influence nutrient transformation. To examine whether organic amendments could improve the resistance and resilience of microbial function (extracellular enzyme activities), community composition (phospholipid fatty acids), and soil structure to drying-rewetting alternation, cropland soils with or without wheat-straw amendment were allowed to desiccate in a microcosm for two months, followed by moist incubation for five weeks, and continuously moist treatments were maintained at 50% water holding capacity during the entire period, as a control treatment. Straw amendment increased microbial biomass, extracellular enzyme activities, the relative abundance of fungal groups, dissolved organic carbon, and proportion of large macroaggregates (>2000µm), but decreased mineral nitrogen and available phosphorus. The drying-rewetting treatment increased microbial biomass carbon and ß-glucosidase activities by 10% and 13% in straw-amended soils, respectively, but not in unamended soils, and decreased the urease and alkaline phosphomonoesterase activities by >15% in unamended soils, but not in amended soils. The contents of fungi, actinomycetes, Pseudomonas spp., and Bacillus spp. decreased with drying, and more so with the subsequent rewetting, but recovered by the end of the experiment. The drying-rewetting treatment caused a decrease in the nitrate content in both soils (>10%) and an increase in the macroaggregates of straw-amended soils (~8%). These results indicated that improved soil aggregation, as a result of straw amendment, protected microbial communities from drought stress and that nutrient acquisition promoted the post-rewetting colonization of heterotrophic communities characterized by hydrolase production, which consequently facilitated aggregate re-formation. Thus, straw amendment positively contributed to aggregate turnover and to both microbial and enzymatic responses to drying-rewetting events, which suggests that straw amendment is favorable to maintain soil function under conditions of increasing rainfall variability.

Comparative effects of 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD) on ammonia-oxidizing bacteria and archaea in a vegetable soil.

Nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD) have been used extensively to improve nitrogen fertilizer utilization in farmland. However, their comparative effects on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in agricultural soils are still unclear. Here, we compared the impacts of these two inhibitors on soil nitrification, AOA and AOB abundance as well as their community structure in a vegetable soil by using real-time PCR and terminal restriction fragment length polymorphism (T-RFLP). Our results showed that urea application significantly increased the net nitrification rates, but were significantly inhibited by both NIs, and the inhibitory effect of DMPP was significantly greater than that of DCD. AOB growth was more greatly inhibited by DMPP than by DCD, and the net nitrification rate was significantly related to AOB abundance, but not to AOA abundance. Application of urea and NIs to soil did not change the diversity of the AOA community, with the T-RFs remaining in proportions that were similar to control soils, while the community structure of AOB exhibited obvious shifts within all different treatments compared to the control. Phylogenetic analysis showed that all AOA sequences fell within group 1.1a and group 1.1b, and the AOB community consisted of Nitrosospira cluster 3, cluster 0, and unidentified species. These results suggest that DMPP exhibited a stronger inhibitory effect on nitrification than DCD by inhibiting AOB rather than AOA.