Figure 1.
Axenic laboratory systems used in the study.
Microcosm with Pinus sylvestris needles in litter bags inoculated with Gymnopus androsaceus (lower, ‘old litter’) and Mycena epipterygia (top, ‘new litter).
Figure 2.
Illustration of the experimental design showing the time line and a description of the sequential treatments. At start, litter bags filled with Pinus sylvestris needles inoculated with either Gymnopus androsaceus or Mycena epipterygia were placed directly on sand receiving 15NH4Cl (+N) or NaCl (-N). After 5 months the old litter (white) was moved to new vessels with sand receiving NaCl and a second layer of new litter (grey), uninoculated (connected litter), inoculated with the same species (single-species interaction), inoculated with the other species, G. androsaceus or M. epipterygia, (two-species basidiomycete) or a Helotiales sp. (two-species ascomycete), was placed on top of the old litter. In some systems, the old litter was incubated without addition of a second litter layer (isolated systems). After an additional 5 months, the experiment was terminated. Control systems with litter bags were incubated in isolation for 5 month only, were also prepared. Number of replicates for each treatment is indicated in brackets.
Figure 3.
15N taken up and translocated by the fungi.
15N excess (μg in each litter bag) in litter bags containing needles colonized by litter degrading fungi. Open bars represent old litter incubated for a total of 10 months and grey bars represent new litter which was placed on top of the old litter after 5 months. The old litter was inoculated with (A) Gymnopus androsaceus or (B) Mycena epipterygia. The new litter was uninoculated or subjected to single-species or two-species interaction, i.e. the new litter was pre-inoculated with the same species, the other basidiomycete or a Helotiales sp. Data are mean ± SEM (for numbers of replicates, see Fig. 2).
Figure 4.
N-reallocation, mycelial growth and litter decomposition.
Total N in needles and mycelium, total fungal biomass C produced and decomposed needle C (mass loss + mycelial C) of old litter (open bars) and new litter (grey bars) colonized by the litter degrading fungi Gymnopus androsaceus (A) or Mycena epipterygia (B). All data is given per g needles at the start of the experiment. ‘Isolated litter layers’ represents old litter and new litter incubated separately. In ‘connected litter layers’ the new litter was placed on top of the old litter after 5 months and then incubated together for an additional 5 months. Data are means ± SEM (for numbers of replicates, see Fig. 2) of systems receiving N during the first incubation period (data for systems without N addition is given in Table S1). In diagrams showing total N in needles and mycelium, the horizontal dashed line represents initial needle N content. In diagrams showing fungal biomass, the horizontal dashed line represents fungal biomass produced during the first 5 months of incubation.
Table 1.
Single-species and two-species interactions.
Figure 5.
Dissolved organic C and N produced.
Dissolved organic C (A) and dissolved organic nitrogen (B) in the sand solution of systems containing needles colonized by litter degrading fungi, related to the amounts of needle C degraded (mass loss + fungal C) during the last 5 months of a total 10 month incubation period. The systems were inoculated with either Gymnopus androsaceus or Mycena epipterygia. ‘Isolated systems’ represents systems with single litter bags incubated for 2×5 months (without and with N addition) and ‘connected litter’ represents systems with old litter receiving new litter during the second incubation period (without and with N addition during the first 5 month). Data are means ± SEM (for numbers of replicates, see Fig. 2).
Figure 6.
N mineralized from the pine needles.
N-mineralization as amounts of NH4-N, produced during the last 5 months of a total 10 month incubation period, in the sand solution of systems containing needles colonized by litter degrading fungi Gymnopus androsaceus (A) and Mycena epipterygia (B). ‘Isolated systems’ represents systems with single litter bags incubated for 2×5 months (without and with N addition) and ‘connected litter’ represents systems with old litter receiving new litter during the second incubation period. ‘two-species asco’ represents systems where the new litter was pre-inoculated with Helotiales, ‘single-species’ represents systems where the new litter was pre-inoculated with the same species as the old litter and ‘two-species basid’ represents systems were the new litter was pre-inoculated with the other basidiomycete. Note the different scales on the y-axis in the two graphs. Data are mean ± SEM (for numbers of replicates, see Fig. 2). Bars sharing the same letters are not significantly different (P>0.05).
Figure 7.
C-use efficiency calculated as mycelial C divided by the decomposed needle C (mass loss + mycelial C) at harvest for systems inoculated with Gymnopus androsaceus and Mycena epipterygia. ‘Isolated old litter’ represents needles incubated for 2×5 months, ‘isolated new litter’ represents needles incubated for 5 months and ‘connected litter’ represents double litter systems were old and new litter where incubated together and interconnected by a common mycelium. Data are mean ± SEM (for numbers of replicates, see Fig. 2). Bars sharing the same letters are not significantly different (P>0.05).
Figure 8.
Relationship between (A) C content and chitin content and (B) N content and chitin content of glass fibre bundles retrieved from needle litter bags colonized by mycelium of Gymnopus androsaceus (open circles) and Mycena epipterygia (filled circles). Each data point represents pooled samples from five to eight system samples.