Non-additive effects of water availability and litter quality on decomposition of litter mixtures

Figures & data

Table 1. Initial quality of the three types of plant litter used in the study.

	Litter type
Parameter	Carex brevicuspis leaves	Miscanthus sacchariflorus leaves	Miscanthus sacchariflorus stems
N (mg g^−1)	7.68 ± 0.18a	4.15 ± 0.85b	1.40 ± 0.25c
P (mg g^−1)	0.89 ± 0.10a	0.48 ± 0.13b	0.14 ± 0.02c
Organic C (%)	38.37 ± 1.77c	43.13 ± 0.85b	49.12 ± 1.70a
Cellulose (%)	14.61 ± 0.31a	18.56 ± 2.53b	18.48 ± 0.14c
Lignin (%)	30.75 ± 1.41a	32.42 ± 0.91b	34.47 ± 2.64c
C:N (g g^−1)	50.02 ± 3.26a	107.73 ± 27.30b	359.86 ± 83.73c
C:P (g g^−1)	433.9 ± 27.85a	943.5 ± 230.7b	3534. ± 605.0c
N:P (g g^−1)	8.72 ± 1.09b	8.87 ± 1.94a	9.97 ± 1.67c
Lignin:N (g g^−1)	40.07 ± 2.09a	80.99 ± 20.76b	253.04 ± 63.35c

All values are means of three replicates, expressed on a dry-mass basis. Different lowercase letters (a, b, c) within rows indicate significant difference in initial litter quality among the three litter types (LSD test, p < 0.05).

Figure 1. Percentage (mean ± SE) of mass, nitrogen, phosphorus, and lignin remaining in three single litters in three water availability treatments. LW, IW, and HW indicate low, intermediate, and high water availability, respectively.

Table 2. Regression statistics (r²) for exponential rates of decomposition (k).

	C. brevicuspis leaves		M. sacchariflorus leaves		M. sacchariflorus stems
Treatments	k	r^.2	k	r^.2	k	r^.2
LW	0.0046	0.83	0.0070	0.70	0.0018	0.80
IW	0.0066	0.66	0.0072	0.76	0.0018	0.65
HW	0.0077	0.71	0.0108	0.83	0.0022	0.94

k is a decomposition constant (d⁻¹) based on an exponential model. LW, IW, and HW indicate low, intermediate, and high water availability, respectively.

Figure 2. Expected (Exp) and observed (Obs) mass, nutrients, and lignin remaining in the three litter mixtures in the three water availability treatments (mean ± SE). LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters a, b, and c indicate C. brevicuspis leaves + M. sacchariflorus leaves, C. brevicuspis leaves + M. sacchariflorus stems, and M. sacchariflorus leaves + M. sacchariflorus stems mixture, respectively.

Figure 3. N remaining in litter according to mixture types (mean ± SE). LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters A, B, C, D, E, and F indicate C. brevicuspis leaves mixed with M. sacchariflorus leaves and M. sacchariflorus stems, M. sacchariflorus leaves mixed with C. brevicuspis leaves and M. sacchariflorus stems, and M. sacchariflorus stems mixed with C. brevicuspis leaves and M. sacchariflorus leaves, respectively.

Figure 4. P remaining in litter according to mixture types (mean ± SE). LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters A, B, C, D, E, and F indicate C. brevicuspis leaves mixed with M. sacchariflorus leaves and M. sacchariflorus stems, M. sacchariflorus leaves mixed with C. brevicuspis leaves and M. sacchariflorus stems, and M. sacchariflorus stems mixed with C. brevicuspis leaves and M. sacchariflorus leaves, respectively.

Figure 5. Lignin remaining in litter according to mixture types (mean ± SE). LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters A, B, C, D, E, and F indicate C. brevicuspis leaves mixed with M. sacchariflorus leaves and M. sacchariflorus stems, M. sacchariflorus leaves mixed with C. brevicuspis leaves and M. sacchariflorus stems, and M. sacchariflorus stems mixed with C. brevicuspis leaves and M. sacchariflorus leaves, respectively.

Figure 6. Observed (Obs) lignin:N, lignin:P, and N:P ratios (mean ± SE) in litter mixtures according to water availability. LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters a, b, and c indicate mixtures of C. brevicuspis leaves + M. sacchariflorus leaves, C. brevicuspis leaves + M. sacchariflorus stems, and M. sacchariflorus leaves + M. sacchariflorus stems, respectively. *p < 0.05; ***p < 0.001.

Figure 7. Mass remaining in litter according to mixture types (mean ± SE). LW, IW, and HW indicate low, intermediate, and high water availability, respectively. The letters A, B, C, D, E, and F indicate C. brevicuspis leaves mixed with M. sacchariflorus leaves and M. sacchariflorus stems, M. sacchariflorus leaves mixed with C. brevicuspis leaves and M. sacchariflorus stems, M. sacchariflorus stems mixed with C. brevicuspis leaves and M. sacchariflorus leaves, respectively.

Table 5. Results of t-tests between expected values and observed values of mass remaining in mixed-litter treatments after incubation (df = 14).

	LW		IW		HW
Mixed litters	t-Value	p-Value	t-Value	p-Value	t-Value	p-Value
Carex brevicuspis leaves + Miscanthus sacchariflorus leaves	17.32	<0.001	11.58	<0.001	10.24	<0.001
C. brevicuspis leaves + M. sacchariflorus stems	5.639	<0.001	4.767	<0.001	4.086	<0.01
M. sacchariflorus leaves + M. sacchariflorus stems	−12.37	<0.001	−3.202	<0.01	0.675	0.511

LW, IW, and HW indicate low, intermediate, and high water availability, respectively.

Table 3. One-way ANOVA results of mass, N, P, and lignin remaining in single litters in single-and mixed- litter bags as well as ratio of lignin:N, lignin:P, and N:P in mixed- litter bags in three water availability treatments (df = 2).

	F-value
	A	B	C	D	E	F
Mass	19.94**	3.95*	3.35*	9.70**	8.19**	9.93**
N	10.03**	4.41*	1.26	20.83**	2.72	3.91*
P	10.49**	5.51**	2.63	11.77**	4.43*	7.19**
Lignin	13.67**	2.32	2.97	13.17**	6.39**	12.80**
Lignin:N				3.18*	1.52	3.35*
Lignin:P				3.26*	1.38	0.31
N:P				0.37	0.12	0.56

* p < 0.05; ** p < 0.01. The letters A, B, C, D, E, and F indicate Carex brevicuspis leaves, Miscanthus sacchariflorus leaves, and Miscanthus sacchariflorus stems, and litter mixtures of Carex brevicuspis leaves + Miscanthus sacchariflorus leaves, Carex brevicuspis leaves + Miscanthus sacchariflorus stems, and Miscanthus sacchariflorus leaves + Miscanthus sacchariflorus stems.

Table 4. Results of t-tests between values at decay alone and values at decay mixed of litter mass, nutrients, and lignin remaining for three litter types after incubation (df = 44).

	Mass		N		P		Lignin
Litter type in mixture	t	p	t	p	t	p	t	p
	Mixed with Carex brevicuspis leaves
M. sacchariflorus leaves	9.176	<0.01	−15.047	<0.01	−12.884	<0.01	4.535	<0.05
M. sacchariflorus stems	11.464	<0.01	−3.545	<0.01	−0.679	0.501	33.901	<0.01
	Mixed with Miscanthus sacchariflorus leaves
C. brevicuspis leaves	0.674	0.475	0.291	0.792	0.136	0.899	0.753	0.474
M. sacchariflorus stems	0.328	0.766	1.122	0.219	0.354	0.748	0.9530	0.336
	Mixed with Miscanthus sacchariflorus stems
C. brevicuspis leaves	0.854	0.405	0.253	0.818	0.167	0.877	−0.821	0.427
M. sacchariflorus leaves	−13.883	<0.01	−4.602	<0.05	−11.385	<0.01	−19.338	<0.01

Table 6. ANCOVA of magnitude of non-additive effects.

	Time		Treatment
Mixed litters	F-value	p-Value	F-value	p-Value
Carex brevicuspis leaves + Miscanthus sacchariflorus leaves	6.496	<0.001	13.100	<0.001
C. brevicuspis leaves + M. sacchariflorus stems	4.426	<0.01	3.696	<0.05
M. sacchariflorus leaves + M. sacchariflorus stems	2.616	0.056	45.594	<0.001