Abstract: Paddy soil samples were collected in layers (0〖KG-*2〗-〖KG-*7〗5, 5〖KG-*2〗- 〖KG-*7〗12, and 12〖KG-*2〗-〖KG-*7〗20 cm) during rice growth period to invest igate the characteristics of the N forms and N-transforming bacteria in the soi l profile under different tillage patterns (no-tillage with straw returning, NT S; conventional tillage with straw returning, CTS; no-tillage, NT; and conventi onal tillage, CT). In the whole rice growth period, ammonifying bacteria in 0〖K G-*2〗-〖KG-*7〗5 cm soil layer had the highest number under NTS, and nitrosobac teria in 0〖KG-*2〗-〖KG-*7〗5 cm and 5〖KG-*2〗-〖KG-*7〗12 cm soil layers were more abundant but in 12〖KG-*2〗-〖KG-*7〗20 cm soil layer were lesser under CT than under NT. Nitrosobacteria and denitrobacteria in 0〖KG-*2〗-〖KG-*7〗20 cm soil layer were lesser under NTS than under CTS. At elongating and ripening sta ges, anaerobic N-fixing bacteria in 0〖KG-*2〗-〖KG-*7〗5 cm soil layer were mo re abundant under NT than under CT. In the whole rice growth period, the alkali -hydrolyzable N and total N contents in 0〖KG-*2〗-〖KG-*7〗5 cm soil layer wer e significantly higher but in 5〖KG-*2〗-〖KG-*7〗12 cm and 12〖KG-*2〗-〖KG-*7 〗20 cm soil layers were lower under NT than under CT, and the NH4+-N and N O3--N contents in 0〖KG-*2〗-〖KG-*7〗20 cm soil layer were higher under NT S but in 12〖KG-*2〗-〖KG-*7〗20 cm soil layer had no significant differences be tween NT and CT. Correlation analysis and multiple polynomial regression analysi s further revealed that there were significant relationships between soil NH4 +-N and soil ammonifying bacteria, nitrosobacteria and denitrobacteria, and b etween soil alkali-hydrolyzable N and soil anaerobic N-fixing bacteria. Among the test tillage patterns, NTS could be the more desirable one for the N supply and fertility maintenance of paddy soil.

Key words: tomato, photosynthetic induction, stomatal regulation, water stress.