Effects of long-term partial substitution of inorganic fertilizer with pig manure and/or straw on nitrogen fractions and microbiological properties in greenhouse vegetable soils

Partial substitution of inorganic fertilizers with organic amendments is an important agricultural management practice.An 11-year field experiment(22 cropping periods)was carried out to analyze the impacts of different partial substitution treatments on crop yields and the transformation of nitrogen fractions in greenhouse vegetable soil.Four treatments with equal N,P_(2)O_(5),and K_(2)O inputs were selected,including complete inorganic fertilizer N(CN),50%inorganic fertilizer N plus 50%pig manure N(CPN),50%inorganic fertilizer N plus 25%pig manure N and 25%corn straw N(CPSN),and 50%inorganic fertilizer N plus 50%corn straw N(CSN).Organic substitution treatments tended to increase crop yields since the 6th cropping period compared to the CN treatment.From the 8th to the 22nd cropping periods,the highest yields were observed in the CPSN treatment where yields were 7.5-11.1%greater than in CN treatment.After 11-year fertilization,compared to CN,organic substitution treatments significantly increased the concentrations of NO_(3)^(-)-N,NH_(4)^(+)-N,acid hydrolysis ammonium-N(AHAN),amino acid-N(AAN),amino sugar-N(ASN),and acid hydrolysis unknown-N(AHUN)in soil by 45.0-69.4,32.8-58.1,49.3-66.6,62.0-69.5,34.5-100.3,and 109.2-172.9%,respectively.Redundancy analysis indicated that soil C/N and OC concentration significantly affected the distribution of N fractions.The highest concentrations of NO_(3)^(-)-N,AHAN,AAN,AHUN were found in the CPSN treatment.Organic substitution treatments increased the activities ofβ-glucosidase,β-cellobiosidase,N-acetyl-glucosamidase,L-aminopeptidase,and phosphatase in the soil.Organic substitution treatments reduced vector length and increased vector angle,indicating alleviation of constraints of C and N on soil microorganisms.Organic substitution treatments increased the total concentrations of phospholipid fatty acids(PLFAs)in the soil by 109.9-205.3%,and increased the relative abundance of G^(+)bacteria and fungi taxa,but decreased the relative abundance of G-bacteria,total bacteria,and actinomycetes.Overall,long-term organic substitution management increased soil OC concentration,C/N,and the microbial population,the latter in turn positively influenced soil enzyme activity.Enhanced microorganism numbers and enzyme activity enhanced soil N sequestration by transforming inorganic N to acid hydrolysis-N(AHN),and enhanced soil N supply capacity by activating non-acid hydrolysis-N(NAHN)to AHN,thus improving vegetable yield.Application of inorganic fertilizer,manure,and straw was a more effective fertilization model for achieving sustainable greenhouse vegetable production than application of inorganic fertilizer alone.

Integrated management of crop residue and nutrient enhances new carbon formation by regulating microbial taxa and enzymes

Although returning crop residue to fields is a recommended measure for improving soil carbon(C)stocks in agroecosystems,the response of newly formed soil C(NFC)to the integrated supply of residue and nutrients and the microbial mechanisms involved in NFC are not fully understood.Therefore,an 84-day incubation experiment was conducted to ascertain the microbial mechanisms that underpin the NFC response to inputs of residue and nitrogen(N),phosphorus(P),and sulfur(S)in two black(Phaeozem)soils from experimental plots at Gongzhuling,Jilin Province and Hailun,Heilongjiang Province,China.The results showed that adding residue alone accelerated microbial nutrient mining,which was supported by decreases of 8^(-1)6%in the ratios of C:N and C:P enzyme activities,relative to soils with nutrient inputs.The NFC amounts increased from 1156 to 1722 mg kg^(−1) in Gongzhuling soil and from 725 to 1067 mg kg^(−1) in Hailun soil as the levels of nutrient supplementation increased.Boosted regression tree analysis suggested thatβ-glucosidase(BG),acid phosphatase(AP),microbial biomass C(MBC),and Acidobacteria accounted for 27.8,18.5,14.7,and 8.1%,respectively,of the NFC in Gongzhuling soil and for 25.9,29.5,10.1,and 13.9%,respectively,of the NFC in Hailun soil.Path analysis determined that Acidobacteria positively influenced NFC both directly and indirectly by regulating BG,AP,and MBC,in which MBC acquisition was regulated more by AP.The amount of NFC was lower in Hailun soil than in Gongzhuling soil and was directly affected by AP,indicating the importance of soil properties such as SOC and pH in determining NFC.Overall,our results reveal the response of NFC to supplementation by N,P,and S,which depends on Acidobacteria and Proteobacteria,and their investment in BG and AP in residue-amended soil.

Seasonal changes in soil properties,microbial biomass and enzyme activities across the soil profile in two alpine ecosystems

Microbial biomass and extracellular enzyme activities control the rate of soil organic carbon decomposition,thereby affecting soil carbon pool.However,seasonal dynamics of soil microbial properties at different depths of the soil profile remain unclear.In this study,we sampled soils in the early,middle and late growing season at different soil depths(0–100 cm)in two alpine ecosystems(meadow and shrubland)on the Tibetan Plateau.We measured plant belowground biomass,soil properties,microbial biomass and extracellular enzyme activities.We found that soil properties changed significantly with sampling time and soil depth.Specifically,most of soil properties consistently decreased with increasing soil depth,but inconsistently varied with sampling time.Moreover,root biomass and microbial biomass decreased with increasing soil depth and increased with sampling time during the growing season.However,microbial extracellular enzyme activities and their vector properties all changed with depth,but did not vary significantly with time.Taken together,these results show that soil properties,microbial biomass and extracellular enzyme activities mostly decline with increasing depth of the soil profile,and soil properties and microbial biomass are generally more variable during the growing season than extracellular enzyme activities across the soil profile in these alpine ecosystems.Further studies are needed to investigate the changes in soil microbial community composition and function at different soil depths over the growing season,which can enhance our mechanistic understanding of whole-profile soil carbon dynamics of alpine ecosystems under climate change.

Soil microbial attributes along a chronosequence of Scots pine(Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.

Adaptation of microbial communities to multiple stressors associated with litter decomposition of Pterocarya stenoptera

To understand the further impacts of multiple stressors in freshwater, we investigated the effects of heavy metal （HM, Cu and Zn） and nutrient enrichments （nitrogen and phosphorus, NP） on microbial decomposition of Pterocarya stenoptera litter and the associated extracellular enzyme activities and microbial biomass with microcosms. Results showed that the decomposition rates were slower in the polluted stream waters than those in the unpolluted ones, which corresponded to lower microbial biomass and integrated enzyme activities of cellulose and ^-glucosidase. The decomposition rates were accelerated at low HM level, which was associated with the stimulated enzyme activities of hydrolytic enzymes or was stimulated by both NP levels in polluted stream waters. In particular, the hydrolase enzyme activities of microbial communities in polluted stream waters were stimulated by low HM level, suggesting that low HM level-stimulated litter decomposition may be due to the increased enzymatic activities. When microbial communities were exposed to HM and NP simultaneously, the inhibitory effect （in unpolluted stream waters） or the stimulated effect （in polluted stream waters） of low HM concentration was enhanced and attenuated, respectively, which suggests that the NP antagonistic effect against HM toxicity on litter decomposition may contribute to the litter- associated extracellular enzyme activities. These results suggest that the may have antagonistic effects on stream ecosystem functioning. of HM and NP