Competition between roots and soil micro-organisms for nutrients from nitrogen-rich patches of varying complexity

TY - JOUR

T1 - Competition between roots and soil micro-organisms for nutrients from nitrogen-rich patches of varying complexity

AU - Hodge, A

AU - Stewart, J

AU - Robinson, D

AU - Griffiths, B S

AU - Fitter, A H

PY - 2000/2

Y1 - 2000/2

N2 - 1 We used Lolium perenne plants grown in microcosms to investigate the responses of root demography, plant N capture, soil fauna populations and microbial community profiles to five organic patches containing the same amount of N but differing in their chemical and physical complexity and C : N ratio. All patches were dual labelled with N-15/C-13. Control patches contained the background sand : soil mix only.2 There was rapid decomposition in, and plant N capture from, the patches of lowest C : N ratio. Early in the experiment C-13 was detected in the soil atmosphere and N-15 in the shoots. No C-13 enrichment was detected in the plant material.3 The rate of root production was slowest in the most complex patch (L. perenne shoot material) but accelerated when patches were simpler and had lower C : N ratios. There was no difference in root mortality between treatments.4 Nitrogen concentrations of shoots and roots and shoot biomass were greater in the N-containing patches than controls, except for the most complex patch, while root biomass did not differ with treatments.5 Total plant N capture was 45-54% of that initially added in patches that had a C : N ratio < 4. However, in the most complex patch (C : N ratio c. 21 : 1) plants captured only 11% of the N added.6 Biomass of microbial-feeding protozoa was related to soil NO3--N concentration in the patch but not to numbers of microbial-feeding nematodes. Patches of greater complexity increased the metabolic diversity of the microbial community (i.e. the number of substrates used in a Biolog GN plate) and altered the pattern of substrate utilization.7 At harvest, the amount of patch-derived N estimated to be in the microbial biomass was much smaller (i.e. 7-13%) than in the plant tissues. Thus, plants were highly effective competitors with micro-organisms when capturing N supplied in patches with a low C : N ratio.

AB - 1 We used Lolium perenne plants grown in microcosms to investigate the responses of root demography, plant N capture, soil fauna populations and microbial community profiles to five organic patches containing the same amount of N but differing in their chemical and physical complexity and C : N ratio. All patches were dual labelled with N-15/C-13. Control patches contained the background sand : soil mix only.2 There was rapid decomposition in, and plant N capture from, the patches of lowest C : N ratio. Early in the experiment C-13 was detected in the soil atmosphere and N-15 in the shoots. No C-13 enrichment was detected in the plant material.3 The rate of root production was slowest in the most complex patch (L. perenne shoot material) but accelerated when patches were simpler and had lower C : N ratios. There was no difference in root mortality between treatments.4 Nitrogen concentrations of shoots and roots and shoot biomass were greater in the N-containing patches than controls, except for the most complex patch, while root biomass did not differ with treatments.5 Total plant N capture was 45-54% of that initially added in patches that had a C : N ratio < 4. However, in the most complex patch (C : N ratio c. 21 : 1) plants captured only 11% of the N added.6 Biomass of microbial-feeding protozoa was related to soil NO3--N concentration in the patch but not to numbers of microbial-feeding nematodes. Patches of greater complexity increased the metabolic diversity of the microbial community (i.e. the number of substrates used in a Biolog GN plate) and altered the pattern of substrate utilization.7 At harvest, the amount of patch-derived N estimated to be in the microbial biomass was much smaller (i.e. 7-13%) than in the plant tissues. Thus, plants were highly effective competitors with micro-organisms when capturing N supplied in patches with a low C : N ratio.

KW - C : N ratios

KW - decomposition

KW - Lolium perenne

KW - organic patches

KW - microbial activity

KW - ANNUAL GRASSLAND

KW - FIELD CONDITIONS

KW - LEGUME RESIDUES

KW - AMINO-ACIDS

KW - PLANT-ROOTS

KW - FINE ROOTS

KW - WHEAT

KW - AVAILABILITY

KW - RHIZOSPHERE

KW - PROTOZOA

M3 - Article

SN - 0022-0477

VL - 88

SP - 150

EP - 164

JO - Journal of Ecology

JF - Journal of Ecology

IS - 1

ER -