Long-term cover cropping seasonally affects soil microbial carbon metabolism in an apple orchard

Figures & data

Table 1. Soil moisture (means and standard deviations) seasonal dynamics under indicated cover crops.

Treatment	Soil moisture %
	May	July	October
AW	10.37 ± 0.68 Bc	6.67 ± 0.80 Cc	16.28 ± 0.15 Aa
AC	10.63 ± 0.47 Bc	6.14 ± 0.52 Cd	16.49 ± 0.15 Aa
AS	12.01 ± 0.71 Bb	7.62 ± 0.63 Cb	16.47 ± 0.99 Aa
AH	10.90 ± 0.94 Bbc	7.08 ± 0.06 Cbc	16.25 ± 0.12 Aa
CT	15.86 ± 0.11 Aa	13.93 ± 0.09 Ba	15.92 ± 0.42 Aa

Note: Means with different lowercase letters are significantly different between the five treatments at p ≤ 0.05 and means with uppercase letters are significantly different between the three times at p ≤ 0.05.

(1) AW – intercropping of apple and white clover (Trifolium repens); (2) AC – intercropping of apple and crown vetch (Coronilla varia L.); (3) AS – intercropping of apple and the grass (Dactylis glomerata L.); and (4) AH – intercropping of apple and bird’s foot trefoil (Lotus corniculatus L.).

Figure 1. Soil organic carbon contents (mean ± standard deviation) under indicated cover crops.

Table 2. Average well color development (means and standard deviations) of samples of soil under indicated cover crops after 120 h incubation.

		AW	AC	AS	AH	CT
Indices	Season	Trifolium repens L.	Coronil la varia L.	Lotuscorn iculatus L.	Dactylis glomerata L.	Clean cultivation
AWCD	Spring	0.87 ± 0.06 Aa	0.89 ± 0.06 Aa	0.90 ± 0.04 Aa	0.59 ± 0.01 Bb	0.58 ± 0.04 Ab
	Summer	0.71 ± 0.06 Ba	0.58 ± 0.07 Bbc	0.50 ± 0.04 Ccd	0.47 ± 0.02 Cd	0.65 ± 0.03 Aab
	Fall	0.94 ± 0.05 Aa	0.93 ± 0.05 Aa	0.66 ± 0.02 Bb	0.64 ± 0.02 Ab	0.54 ± 0.08 Ac

Note: Means with different lowercase letters are significantly different between the five treatments at p≤ 0.05 and means with different capitals are significantly different between the three times at p ≤ 0.05.

(1) AW – intercropping of apple and white clover (Trifolium repens); (2) AC – intercropping of apple and crown vetch (Coronilla varia L.); (3) AS – intercropping of apple and the grass (Dactylis glomerata L.); and (4) AH – intercropping of apple and bird’s foot trefoil (Lotus corniculatus L.).

Figure 2. Biolog absorbance readings showing the efficiency of utilization of indicated carbon sources by samples for the soil under indicated covering crops in May, July and October.

Table 3. Diversity indices (means and standard deviations) of soil microbial communities under indicated cover crops.

		AW	AC	AS	AH	CT
Indices	Season	Trifolium repens L.	Coronil la varia L.	Lotuscorn iculatus L.	Dactylis glomerata L.	Clean cultivation
Shannon H	Spring	3.04 ± 0.02 Aa	2.63 ± 0.05 Bc	3.10 ± 0.04 Aa	2.75 ± 0.03 Ab	2.57 ± 0.11 Bc
	Summer	2.91 ± 0.05 Ba	2.64 ± 0.12 Bb	2.44 ± 0.06 Cc	2.55 ± 0.15 Bbc	2.94 ± 0.03 Aa
	Fall	3.09 ± 0.02 Aa	3.06 ± 0.03 Aab	2.91 ± 0.04 Bbc	2.93 ± 0.04 Ac	2.77 ± 0.16 ABd
Richness S	Spring	21.33 ± 0.52 Bb	16.50 ± 0.66 Bc	23.33 ± 1.38 Aa	15.83 ± 0.80 Bc	16.00 ± 0.66 Bc
	Summer	19.83 ± 1.28 Ba	13.75 ± 1.75 Cb	13.17 ± 1.01 Cb	13.25 ± 0.75 Cb	19.00 ± 0.50 Aa
	Fall	23.50 ± 0.66 Aa	23.17 ± 0.52 Aa	18.58 ± 0.52 Bb	19.25 ± 0.25 Ab	15.42 ± 2.10 Bc
Evenness E	Spring	1.01 ± 0.02 Aab	0.98 ± 0.00 Bb	0.99 ± 0.01 Bab	1.01 ± 0.01 Aab	1.02 ± 0.04 Ba
	Summer	0.98 ± 0.01 Bb	1.09 ± 0.08 Aa	1.09 ± 0.07 Aa	1.09 ± 0.07 Aa	1.01 ± 0.01 Bab
	Fall	0.98 ± 0.00 Bb	0.98 ± 0.00 Bb	1.02 ± 0.00 Bb	1.06 ± 0.06 Ab	1.19 ± 0.12 Aa

Note: Means with different lowercase letters are significantly different between the five treatments at p ≤ 0.05 and means with different capitals are significantly different between the three times at p ≤ 0.05. Bold type means that there is a significant difference between this treatment and control (CT treatment).

(1) AW – intercropping of apple and white clover (Trifolium repens); (2) AC – intercropping of apple and crown vetch (Coronilla varia L.); (3) AS – intercropping of apple and the grass (Dactylis glomerata L.); and (4) AH – intercropping of apple and bird’s foot trefoil (Lotus corniculatus L.).

Table 4. Summary results of the analysis of variance of effects of practices, time and soil depths on indices of microbial functional diversity and utilization of indicated carbon sources.

Variable	Source	D.f	Sum of squares	Mean square	F ratio	Sig.
Treatments	Shannon	0.584	4	0.146	2.331	0.085
	Richness	212.678	4	53.169	7.522	0.000
	Evenness	31.422	4	7.856	9.494	0.000
	AWCD	0.726	4	0.181	10.453	0.000
	Carbohydrates*	1.824	4	0.456	7.468	0.000
	Amino acid*	0.552	4	0.138	3.380	0.025
	Carboxylic acids*	0.493	4	0.123	4.068	0.012
	Polymers*	0.661	4	0.165	3.444	0.023
	Phenols*	0.229	4	0.057	4.124	0.011
	Amines*	0.301	4	0.075	2.391	0.079
Time	Shannon	0.645	2	0.322	5.152	0.014
	Richness	181.693	2	90.846	12.851	0.000
	Evenness	11.640	2	5.820	7.034	0.004
	AWCD	0.393	2	0.197	11.329	0.000
	Carbohydrates*	0.667	2	0.334	5.466	0.011
	Amino acid*	0.959	2	0.479	11.750	0.000
	Carboxylic acids*	0.078	2	0.039	1.281	0.296
	Polymers*	0.424	2	0.212	4.412	0.023
	Phenols*	0.150	2	0.075	5.415	0.011
	Amines*	0.451	2	0.226	7.166	0.004
Treatments × Time	Shannon	1.364	8	0.171	2.724	0.027
	Richness	342.122	8	42.765	6.050	0.000
	Evenness	10.212	8	1.276	1.543	0.195
	AWCD	0.403	8	0.050	2.903	0.021
	Carbohydrates*	0.995	8	0.124	2.037	0.085
	Amino acid*	0.683	8	0.085	2.093	0.077
	Carboxylic acids*	0.634	8	0.079	2.618	0.032
	Polymers*	0.745	8	0.093	1.941	0.100
	Phenols*	0.478	8	0.060	4.304	0.003
	Amines*	0.786	8	0.098	3.121	0.015

* indicates the efficiency of specified carbon sources’ utilization by soil microorganisms.

Figure 3. Correlation analysis results in three seasons (solid line means there was a significant correlation between two factors and p-value<0.01; dotted line means there was a significant correlation between two factors and p-value<0.05).

Figure 4. Soil microbial biomass carbon and nitrogen contents (mean ± standard deviation) under indicated cover crops.