Effect Of Increased Canopy Temperature On Cotton Dry Matter Distribution And Yield Relations In Flowing Bolls Period

With the aggravation of the greenhouse effect, the influence of high temperature on plant growth has become a hot research area in recent years. High temperature occur frequently during the cotton boll stage in the cotton-belt of the middle and lower reaches of the Yangtze River in China, which will inevitably become a major obstacle in cotton production in this region. We took the cotton(Gossypium hirsutum L.) cultivars Simian3and Siza3as research material, and tried to simulate the global greenhouse effects by increasing the canopy temperature with (2-3℃) during the boll period under the in2010and2011at the Experimental Station of Nanjing Agricultural University (118°50’E,32°02’N). The experiment were carried out to study the effect of the inceased canopy temperature on the cotton plant source-sink relationship during the boll period and its physiological mechanisms, and to quantitatively evaluate the impact of the greenhouse effect on the quality and yield of cotton. The results would provide reference for cotton breeding in the aggregating global warming background, and provide theoretical basis and technical support for sustainable high cotton yield. The main findings are as follows:1. Effect of increased canopy temperature on yield and quality of cotton.Under the warming conditions during the boll period(with an average daily temperature of32.1℃to35.2℃) in2010and2011, the number of fruit sections and bolls, lint percentage, total boll rate, boll weight and fiber length decreased, but the abscission rate, micronaire value, and the breaking strength significantly increased. Different varieties showed the same changing trend. And we speculated that the influence of warming on the cotton fiber length, micronaire value and the breaking strength is greater than that on the uniformity index and elongation. These results indicate that the plants are in the heat stress state during most time of the boll period under the warming conditions (with an average daily temperature of32.1℃to35.2℃). High temperature would affect the cotton sink activity, resulting in the decline of the cotton dry matter accumulation and yield. At the same time it will affect the material distribution and cotton fiber quality.2. Effect of increased canopy temperature on cotton plant photosynthetic capability.Under warming (2to3℃) conditions, the stomatal conductance (Gs), intercellular CO2concentration (Ci) and chlorophyll a/b value of the stem function leaf rise, while the total chlorophyll and carotenoid content drop. And the net photosynthetic rate (Pn), transpiration rate (Tr) and SPAD value of the stem function leaf vary from year to year under the same conditions. In2010, the net photosynthetic rate (Pn) and SPAD value of the stem function leaf showed a continuous decline, while the transpiration rate (Tr) continued to rise; In2011, however, the net photosynthetic rate (Pn) and SPAD value of the stem function leaf first decreased and then increased, while the transpiration rate (Tr) first increased and then decreased. Different varieties basically get the same trends. These results prove that the plants are in the heat stress state during the boll period under the warming conditions (with an average daily temperature of32.1℃to35.2℃), and that the photosynthetic capacity of cotton plants (or the cotton source ability) is significantly affected.3. Effect of increased canopy temperature on cotton plant source-sink balance.During2011, under the conditions of temperature rise of2to3℃during the boll period (with an average daily temperature of32.1℃to35.2℃), the total plant biomass declined by about10-20%, and the stem partition coefficient and economic coefficient were significantly lower than that of control; And the reproductive organ biomass (ROMC) as well as the ratio of reproductive organ biomass to vegetative organ biomass (RO/VO) reduced, while the vegetative organ biomass (VOMC) grew. Under the same conditions, the ABA content of the stem function leaf first dropped and then rose, and it reached the peak in the late period. And the source ABA content was greater than the sink ABA content. These results show that the plants are in the heat stress state during most time of the boll period under the warming conditions (with an average daily temperature of32.1℃to35.2℃).. The warming inhibits the source ability (cotton photosynthetic ability which can change the output capability of photosynthetic products), resulting in the decline of cotton sink capacity (total dry matter accumulation decreases by about10%-20%). The material distribution coefficient and hormone content are two aspects that can indicate the balance between cotton source and sink.