Fungal response from oat (Avena sativa) plants and surface residue in relation to soil aggregation and organic carbon

Figures & data

Table 1. Two-way model ANOVA (oats×residue) p values of main effects of the oat plant and residue on soil variables along with interaction term. Post-hoc comparison among residue treatment means by LSD test; No residue (NR), oat straw (ST) with low C:N, corn stalks (CS) with high C:N.

	Two-way ANOVA			LSD comparison of means
	Plant	Residue	Interaction	ST-NR	CS-NR	ST-CS
July
Macroaggregates (%)	0.022*	0.173	0.365	0.069	0.518	0.218
Organic carbon (g kg^−1)	0.974	0.062	0.853	0.040*	0.040*	1.000
Fungal hyphal length (cm g^−1)	0.248	0.139	0.035*	0.250	0.051	0.376
August
Macroaggregates (%)	0.187	0.042*	0.714	0.031*	0.025*	0.920
Organic carbon (g kg^−1)	0.014*	0.045*	0.858	0.110	0.330	0.015*
Fungal hyphal length (cm g^−1)	0.007**	0.454	0.040*	0.371	0.232	0.753
May to August
Change in OC (g kg^−1)	0.343	0.020*	0.450	0.013*	0.950	0.015*
*and **denote ANOVA p values are marked significant at 0.05 and 0.01, respectively.

Figure 1.  Fungal hyphal length (cm g⁻¹ soil) measured over time in plots with treatments of no plant (NP) or oat plants (OT) and with no residue (NR), straw residue (ST) of low C:N, or corn residue (CS) of high C:N from initial planting (May) to harvest (August) 2004. May figures were averaged across all treatments. Error bars represent SEM (n=4).

Figure 2.  Percentage of soil macroaggregates measured over time in plot treatments with no plants (NP) or oats (OT) and with no residue (NR), straw residue (ST) with low C:N, or corn residue (CS) with high C:N from initial planting (May) to harvest (August) 2004. May figures were averaged across all treatments. Plots marked A are significantly greater (p=0.05) than other treatments at August sampling, and B are significantly less (p=0.05) than other treatments at July sampling (n=4) by two-way ANOVA.

Figure 3.  Soil OC (g kg⁻¹dry soil) comparison over time in plots with no plants (NP) or oats (OT) and with treatments of no residue (NR), straw residue (ST) with low C:N or corn residue (CS) with high C:N from initial planting (May) to harvest (August) 2004. May figures were averaged across all treatments. Error bars represent SEM (n=4).

Table 2. Means and SEM in g m⁻² of plant and root biomass, and estimated contributions to changes in soil OC from May to August 2004 in each treatment with oat plants with residue treatments; no residue (NR), straw (ST) of low C:N or corn stalk (CS) with high C:N.

		Oat plant plots
	NR	ST	CS
Soil OC mass balance	g m^−2	g m^−2	g m^−2
Mean harvest plant biomass (fresh wt)	1959	1519	1707
SEM	(206)	(47)	(317)
C fixation per hr (7.6 mg g^−1 shoot h^−1)*	15	12	13
C fixation 12 h day^−1	179	139	156
C fixation 30 days	5360	4156	4669
Mean harvest root biomass (S:R 2.5)	784	608	683
Root biomass C (19% of fixed C)	1018	790	887
Amount decomposed (50%)	509	395	444
Root exudates (0.5% of fixed C)	27	21	23
Mycorrhiza (1% of fixed C)	54	42	47
Total OC from plant to soil	590	457	514
OC loss from residue		122	141
OC assimilated from residue (50%)		61	70
Total OC to soil	590	518	584
Total change in soil OC (May to August)	1625	611	944
SEM	(184)	(305)	(205)
Changes in soil OC in addition to changes in soil alone
Oat plants (OT)	467	−414	293
No oat plants (NP)	0	−322	145
*Carbon fixation and allocation rates by Paul and Kucey (1981); Fixation rate: 7.6 mg of OC per gram shoot per hour; Root allocation: 19% biomass, 28% respiration, 0.5% exudates.

Table 3. Comparison of means±SEM of residue decomposition by loss of mass, OC and Nitrogen in % and mass (g m⁻²), with no plants (NP) or oat plants (OT) between straw (ST) with low C:N and corn (CS) with high C:N. Two-way model ANOVA p values give a comparison of variables between straw and corn residue (n=16).

		NP-ST		NP-CS		OT-ST		OT-CS		ANOVA
Plant/residue		Means	SEM	Means	SEM	Means	SEM	Means	SEM	p
Mass residue loss	g m^−2	213.50	10.22	214.08	19.28	236.47	5.78	224.61	23.42	0.73
OC loss	g m^−2	115.22	8.50	116.25	6.31	122.00	5.86	140.61	18.83	0.40
Nitrogen loss	g m^−2	4.00	0.19	0.78	0.08	3.92	0.28	0.92	0.14	<0.001***
Percentage
Residue loss	%	49.47	2.12	33.98	3.09	53.92	0.95	35.41	3.59	<0.001***
OC loss	%	58.40	4.03	38.23	2.07	60.89	2.85	45.89	5.84	<0.001***
Nitrogen loss	%	64.63	2.90	19.56	2.41	62.10	3.83	22.08	3.82	<0.001***
Residue CN		37.39	2.08	56.95	2.67	33.24	2.31	51.95	6.37	<0.001***
***p significant at 0.001.

Figure 4.  Linear regression of heavy fraction organic matter, expressed as a % of total dry soil mass on hyphal length (g m⁻²) (?) y = 6.0583x - 128.42, r ²=0.7851, p=0.89 and soil organic carbon (g kg⁻¹) (?) y = 0.0648x + 5.9518, r ²=0.6301, p=0.79 in all plots with corn stalk residue (with and without oat plants) at harvest (n=8).