[Compensation effect of cotton growth and development after soil salt content reduction at bud stage].

To elucidate the dynamic characteristics of cotton growth and development after soil salt content reduction (SD) at bud stage and its effect on yield formation, a pot experiment was conducted in which soil salt content was declined from 5 per thousand level to 2 per thousand level at cotton bud stage. The results showed that the plant height, biomass, total fruit branch and fruit node number, boll number, boll mass of cotton plants increased after soil salt content reduction at bud stage. The distribution proportions of biomass in root and boll decreased after soil salt content reduction, however, the distribution proportions of biomass in leaf, main stem and fruit branch were on the rise. The growth rate of cotton plant increased after soil salt content reduction. Plant dry matter accumulation rate of SD cotton exceeded CK cotton at 22 days after soil salt content reduction. The response of different organs of cotton plant were different to soil salt content reduction, the plant height was the earliest, followed by the fruit branch and fruit node formation, and the bud and boll were the latest, which indicated that the compensation effect of cotton growth and development after soil salt content reduction at bud stage firstly appeared on the formation and growth of new leaf, fruit branch and fruit node, and on this basis, gradually brought out yield compensation.

[Effects of nitrogen application rate on cotton leaf antioxidant enzyme activities and endogenous hormone contents under short-term waterlogging at flowering and boll-forming stage].

A pot experiment was conducted to study the effects of applying 0, 240, and 480 kg N x hm(-2) on the cotton leaf antioxidant enzyme activities and endogenous hormone contents under eight days waterlogging at flowering and boll-forming stage. Under this short-term waterlogging, the leaf soluble protein content and SOD and CAT activities decreased while the MDA content and POD activity increased, and in the meantime, the leaf ABA content increased while the ZR, GA, and IAA contents as well as the ZR/ABA, IAA/ABA, and GA/ABA ratios decreased, compared with those under normal watering. Treatment 240 kg N x hm(-2) had the lowest contents of leaf MDA and ABA, but the highest contents of leaf ZR, GA, and IAA, highest ratios of ZR/ABA, GA/ABA, and IAA/ABA, and highest net photosynthetic rate. At the 15th day after terminating waterlogging, no significant differences in the leaf antioxidant enzyme activities, MDA content, and endogenous hormone contents were observed between the short-term waterlogged and well-watered cotton. N application promoted the cotton leaf antioxidant enzyme activities, decreased the MDA and ABA contents, and increased the ZR, GA, and IAA contents as well as the ZR/ABA, IAA/ABA, and GA/ ABA ratios, with the highest cotton biomass and yield in treatment 240 kg N x hm(-2).

[Physiological responses of cotton plant to fertlizer nitrogen at flowering and boll-forming stages under soil drought].

With pot culture, the physiological responses of cotton plant to fertilizer nitrogen at flowering and boll-forming stages were studied under soil drought and after re-watering. The results showed that under soil drought, the net photosynthetic rate (Pn) and transpiration rate (Tr) declined rapidly with decreasing soil relative water content (SRWC). At the early stage of soil drought, owing to the declining degree of Tr was greater than that of Pn, the WUE had an increasing trend; but after then, the WUE decreased with declining SRWC and Pn. Soil drought altered the diurnal patters of Pn and Tr, i.e., decreased continuously from 8:00 to 16:00, while in CK, their peak values appeared at 10:00-11:00 and 12:00, respectively. The diurnal patterns of WUE in drought treatment and CK were the same, i.e., decreased first and increased then, with the bottom appeared at 12:00. Under soil drought, the Pn and Tr decreased with increasing fertilizer nitrogen level, while WUE was in adverse. After re-watering, the diurnal patterns of Pn, Tr and WUE were similar to CK, but their values were smaller than CK, especially under nitrogen application. It was suggested that under soil drought, nitrogen fertilization could be helpful to the increase of water use efficiency, but decreased the photosynthesis of cotton plant at its flowering and boll-forming stages.