Research ArticleECOLOGICAL PROCESSES

Decoupling of microbial carbon, nitrogen, and phosphorus cycling in response to extreme temperature events

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Science Advances  03 May 2017:
Vol. 3, no. 5, e1602781
DOI: 10.1126/sciadv.1602781
  • Fig. 1 Schematic representation of the microbial processes studied.

    Microbial respiration and gross rates of glucan depolymerization, glucose consumption, protein depolymerization, and amino acid consumption were determined, as well as gross rates of inorganic N and P fluxes, namely, N mineralization, ammonium consumption, nitrification, nitrate consumption, P mineralization, and phosphate consumption. As further proxies of responses of microbial functions involved in the breakdown of high–molecular weight organic compounds, potential activities of four extracellular hydrolytic enzymes (cellobiosidase, chitinase, phosphatase, and peptidase) and two oxidative enzymes (peroxidase and phenol oxidase) were determined.

  • Fig. 2 Mean response ratios of gross microbial process rates, potential enzyme activities, PLFAs, dissolved nutrient pools on a dry mass basis, and N/P stoichiometry.

    Values are for 3 days (resistance) and 3 months (resilience) after disturbance by freeze-thaw or heat. Response ratios were calculated as the treatment replicate over the mean of the respective control. Shown are only response ratios where the disturbed samples were significantly different from the undisturbed control (t test on raw data, P < 0.05). DOC, dissolved organic carbon; DON, dissolved organic nitrogen; DIN, dissolved inorganic nitrogen; DOP, dissolved organic phosphorus; DIP, dissolved inorganic phosphorus. Litter type: S, Schottenwald; K, Klausenleopoldsdorf: O, Ossiach.

  • Fig. 3 Mean response ratios of gross microbial process rates and potential enzyme activities normalized to microbial biomass (that is, total PLFA concentration).

    Values are for 3 days (resistance) and 3 months (resilience) after disturbance by freeze-thaw or heat. Response ratios were calculated as the mean of the treatment replicate over the mean of the respective control. Given are only response ratios where the disturbed samples were significantly different from the undisturbed control (t test on raw data, P < 0.05).

  • Fig. 4 Microbial community composition based on PLFA profiles of three beech litter types (S, K, and O) 3 days and 3 months after disturbance.

    (A and C) The ordination of PCO for 3 days and 3 months after disturbance, respectively. The variance explained by each PCO axis is given in parentheses. (B) The results of CAP for 3 days after disturbance. CAP is a constrained ordination that maximizes the differences among a priori defined groups. The canonical correlation (δ2) of each CAP axis, indicating the association strength between the multivariate data cloud and the hypothesis of differences between disturbances, is given in parentheses. The CAP classification rates (in percent) for each disturbance (C, control; FT, freeze-thaw; H, heat) are given in parentheses next to each cluster. The traceQ_m’HQ_m statistic (sum of canonical eigenvalues) tests the null hypothesis of no significant differences in multivariate location among disturbances.

  • Fig. 5 Similarity of the functional response of microbial communities perturbed by heat and freeze-thaw treatments.

    Given are reduced major axis (RMA) regressions (solid line) between response ratios of the heat and freeze-thaw treatment of the three litter types (S, K, and O) (A) 3 days after disturbance and (B) 3 months after disturbance. The closer the slope of the regression line is to the 1:1 line (dashed line), the higher is the similarity in the functional response of the differently perturbed microbial communities. Response ratios of protein depolymerization of litter type K were excluded from linear regression analysis because the high response ratio of 3.59 in the heat disturbance greatly influenced the regression equation (slope of 1.11 when included in the linear regression). Microbial processes were grouped as follows: C processes: respiration, glucan depolymerization, and glucose consumption rates; N processes: protein depolymerization, amino acid consumption, N mineralization, ammonium consumption, nitrification, and nitrate consumption rates; P processes: P mineralization and phosphate consumption rates; hydrolytic enzymes: potential cellobiosidase, chitinase, phosphatase, and peptidase activities; and oxidative enzymes: potential peroxidase and phenol oxidase activities.

  • Table 1 Effects of temperature disturbance and litter type on gross microbial process rates, potential extracellular enzyme activities, and microbial community composition (PLFA profile) 3 days after disturbance.

    Analyses were performed on process rates and PLFA expressed per gram litter dry weight. Shown are the results of mixed-effect analysis of variance (ANOVA) using litter type as random effect and post hoc pairwise comparisons of the treatments (C, control; FT, freeze-thaw; H, heat). P < 0.1, *P < 0.05, **P < 0.01, ***P < 0.001.

    Three days after disturbance
    LitterDisturbanceLitter × disturbancePairwise comparison
    dfFPdfFPdfFPC-FTC-HFT-H
    Microbial process rates
      Respiration2,338.512,3321.174,330.39***
      Glucan depolymerization2,2930.802,2911.794,291.01**
      Glucose consumption2,2926.672,2925.594,290.80***
      Protein depolymerization2,360.832,362.664,365.17*
      Amino acid consumption2,3621.622,368.594,360.63*
      N mineralization2,3315.692,330.464,331.22
      NH4+ consumption2,3319.292,330.394,331.14
      Nitrification2,3514.202,358.674,350.96*
      NO3 consumption2,3516.982,3529.444,350.55****
      P mineralization2,3373.582,33246.2***4,330.87*****
      PO43− consumption2,335.392,3344.5**4,331.33****
    Potential enzyme activities
      Cellobiosidase2,368.692,3613.654,3656.67*****
      Chitinase2,3612.352,3635.474,3633.48*******
      Phosphatase2,365.692,36248.3***4,363.53*****
      Peptidase2,365.822,363.654,364.31*
      Peroxidase2,363.042,365.264,363.01
      Phenol oxidase2,3520.62,3515.94,351.73**
    PLFA (phospholipid fatty acid)
      Total2,369.962,3615.434,364.62****
      Gram-positive bacteria2,3610.22,3615.554,361.22**
      Gram-negative bacteria2,3672.68***2,3611.734,362.32**
      Fungi2,360.472,368.264,3616.3****
    Dissolved nutrient pools
      DOC2,36132.5***2,3610.214,361.65*
      DON2,36109.1***2,3612.814,361.36**
      DIN2,36164.7***2,365.734,360.66
      DOP2,36241.3***2,3616.454,360.76**
      DIP2,36711.1***2,363.524,360.63
    N/P stoichiometry
      N/P mineralization2,3421.56**2,34120.8***4,340.75****
      Microbial biomass N/P2,3610.682,367.224,363.28**
      DON/DOP2,3641.43**2,365.74,362.22
      DIN/DIP2,36226.4***2,363.044,361.06
  • Table 2 Effect of temperature disturbances on microbial community composition (PLFA profile).

    Shown are the results of PERMANOVA with litter C/N as covariate and pairwise comparison for the treatments (C, control; FT, freeze-thaw; H, heat).

    Three days after disturbanceThree months after disturbance
    dfPseudo-FP (perm)Pseudo-FP (perm)
    Covariate1,4125.950.000139.680.0001
    Disturbance2,424.830.00041.170.2885
    Pairwise comparisontP (perm)
      C-FT2.560.0002
      C-H3.240.0001
      FT-H0.750.5841
  • Table 3 Effects of temperature disturbance and litter type on gross microbial process rates, potential extracellular enzyme activities, and microbial community composition (PLFA profile) 3 months after disturbance.

    Analyses were performed on process rates and PLFA expressed per gram litter dry weight. Given are results of mixed-effect ANOVA using litter type as random effect and post hoc pairwise comparison of the treatments (C, control; FT, freeze-thaw; H, heat). P < 0.1, *P < 0.05, **P < 0.01, ***P < 0.001.

    Three months after disturbance
    LitterDisturbanceLitter × disturbancePairwise comparison
    dfFPdfFPdfFPC-FTC-HFT-H
    Microbial process rates
      Respiration2,341.342,340.384,3413.43***
      Glucan depolymerization2,351.312,353.234,351.54
      Glucose consumption2,358.122,353.594,351.36
      Protein depolymerization2,364.162,362.624,362.27
      Amino acid consumption2,3610.35*2,360.614,362.11
      N mineralization2,3312.3*2,332.614,339.11***
      NH4+ consumption2,3312.9*2,331.224,337.12**
      Nitrification2,3359.22**2,337.144,330.81
      NO3 consumption2,33148.6**2,3339.83**4,330.19****
      P mineralization2,3145.09**2,31153.5***4,311.19****
      PO43− consumption2,312.892,315.484,314.58*
    Potential enzyme activities
      Cellobiosidase2,3647.6**2,3614.9*4,364.17***
      Chitinase2,3597.73**2,3563.74**4,350.50****
      Phosphatase2,366.792,36226.5***4,361.23****
      Peptidase2,361.642,36250.3***4,360.19*****
      Peroxidase2,3532.99**2,350.474,352.03
      Phenol oxidase2,3537.78**2,353.494,351.78
    PLFA
      Total2,3612.34*2,361.564,360.55
      Gram-positive bacteria2,366.252,360.234,360.48
      Gram-negative bacteria2,3628.75**2,361.924,360.85
      Fungi2,362.622,361.414,360.68
    Dissolved nutrient pools
      DOC2,367.74*2,360.134,3633.71***
      DON2,369.86*2,360.684,3618.08***
      DIN2,36110.4***2,364.464,361.7
      DOP2,363.012,360.964,3639.29***
      DIP2,36938.8***2,361.564,360.67
    N/P stoichiometry
      N/P mineralization2,2816.5*2,2827.28**4,283.32*****
      Microbial biomass N/P2,3611.3*2,361.644,360.66
      DON/DOP2,361.162,360.744,3689.6***
      DIN/DIP2,36188.2***2,361.854,362.25

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602781/DC1

    Supplementary Materials and Methods

    table S1. Description of sites of beech litter collection and nutrient content of collected litter types.

    table S2. Effects of temperature disturbance and litter type on gross microbial process rates and potential extracellular enzyme activities normalized to microbial biomass (total PLFA concentration).

    References (7484)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • table S1. Description of sites of beech litter collection and nutrient content of collected litter types.
    • table S2. Effects of temperature disturbance and litter type on gross microbial process rates and potential extracellular enzyme activities normalized to microbial biomass (total PLFA concentration).
    • References (74–84)

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