Reducing carbon: phosphorus ratio can enhance microbial phytin mineralization and lessen competition with maize for phosphorus

Figures & data

Table 1. Three-way ANOVA of measured variables.

Factor	Plant P content	MBP	Phosphatase activity
PA	0.046^*	<0.001^c	0.011^*
KH2PO4	<0.001^***	0.517	<0.001^***
Phytin	<0.001^***	0.120	<0.001^***
PA × KH2PO4	0.001^***	0.242	0.094
PA × Phytin	0.670	0.117	<0.001^***
KH2PO4 × Phytin	0.510	0.002^**	0.017^*
PA × KH2PO4 × Phytin	0.001^***	0.455	0.296

PA, different PA (P. alcaligenes) inoculation forms; P, phosphorus; MBP, microbial biomass phosphorus.

Bold values represents: *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.

Figure 1. Plant P content of maize (Z. mays L.) under three bacterial inoculation treatments with (+) and without (−) phytin or KH₂PO₄ addition. –PA, no inoculation with PA; I+PA, inoculation with PA at seedling initiation; 2w+PA, inoculation with PA two weeks after seedling emergence. Different lowercase letters indicate a significant difference (Tukey's HSD, P < 0.05) in P content among the three inoculation forms. Bars represent means + SEs (n = 4).

Table 2. Increase in plant P content and phytin P use efficiency in plants grown in phytin amended soil with additional KH₂PO₄ or not.

	Increase in plant P content after phytin addition (mg)		Plant phytin P use efficiency (%)
Bacterial inoculation	−KH2PO4	+KH2PO4	−KH2PO4	+KH2PO4
–PA	11.4 ± 1.6a*	4.5 ± 1.5c	5.7 ± 0.8a*	2.2 ± 0.7c
I+PA	6.1 ± 0.3b*	8.6 ± 0.4b	3.0 ± 0.1b*	4.3 ± 0.2b
2w+PA	5.3 ± 0.5b*	12.7 ± 0.4a	2.6 ± 0.3b*	6.3 ± 0.2a

Note: Plant phytin P use efficiency = increase in plant P content after the addition of phytin/amount of phytin P added in the soil × 100%. –PA, no inoculation with PA; I+PA, inoculation with PA at seedling initiation; 2w+PA, inoculation with PA two weeks after seeding emergence. Significant differences are indicated by different letters between bacterial inoculation types for the same KH₂PO₄ and phytin application (Tukey's HSD, P < 0.05) or an asterisk between KH₂PO₄ treatments for the same phytin application and bacterial inoculation (t-test, P < 0.05).

Figure 2. MBP in the rhizosphere soil under three bacterial inoculation treatments with (+) and without (−) phytin or KH₂PO₄ addition. –PA, no inoculation with PA; I+PA, inoculation with PA at seedling initiation; 2w+PA, inoculation with PA two weeks after seedling emergence. Different lowercase letters indicate significant difference (Tukey's HSD, P < 0.05) in MBP among the three inoculation forms. Bars represent means + SEs (n = 4).

Figure 3. Phosphatase activity in the rhizosphere soil under three bacterial inoculation treatments with (+) and without (−) phytin or KH₂PO₄ addition. –PA, no inoculation with PA; I+PA, inoculation with PA at seedling initiation; 2w+PA, inoculation with PA two weeks after seedling emergence. Different lowercase letters indicate a significant difference (Tukey's HSD, P < 0.05) in phosphatase activity among the three inoculation forms. Bars represent means + SEs (n = 4).

Figure 4. Correlation between phosphatase activity and plant P content. Each dot inside the figure represents each pot in the experiment. The data were fitted by significant regressions (plant P content = −5.3+11.4 phosphatase activity).