Characteristics of Thermal Climate Resources Changes of Agricultural Production during Frost Period in Jianchang County

[Objective] The characteristics of thermal climate resources changes of agricultural production during frost period in Jianchang County were studied. [Method] By dint of Jianchang climate resources and routine numerical statistics method, the sunlight and temperature changes trend from 1960 to 2009 in Jianchang County were analyzed. [Result] The sunshine hours and sunshine percentages during frost period in Janchang County from 1960 to 2009 tended to decrease. The climate tendency rates were -55.556 h/10 a and -2.39%/10 a respectively, 287 h and 12% of deduction in recent 50 years. There were climate transition in 1981 and 1982. And there were a shortage of 161 h and 7% of sunshine hours and sunshine percentages before and after the transition. The temperature during the frost period generally was increasing. The average temperature, average maximum and lowest temperature tendency rate were 0.386, 0.392 and 0.567 ℃/10 a. There was a growth of 1.93, 1.96 and 2.84 ℃ in recent 50 years. There were temperature transition in 1987 and 1988. The average temperature, average maximum and lowest temperature increased 1.3, 1.2 and 1.7 ℃. In recent 50 years, the sunshine resources during frost period in Jianchang were decreasing, while the thermal resources were strengthening, forming complementary of light and heat. [Conclusion] The study provided climate accordance to the development of local facility agriculture during frost period.

Response of community composition and biomass of submerged macrophytes to variation in underwater light, wind and trophic status in a large eutrophic shallow lake

Light climate is of key importance for the growth, community composition of submerged macrophytes in lakes and, they, in turn, are affected by lake depth and the degree of eutrophication. To test the relationships between submerged macrophyte presence and the ratio of Secchi disk depth(SDD) to water depth, i.e. SDD/depth, nutrients and wind, we conducted an extensive sampling campaign in a macrophyte-dominated area of the eastern region( n = 36) in 2016 in Lake Taihu, China, and combined the data gathered with results from extensive physico-chemical monitoring data from the entire lake. We confirmed that SDD/Depth is the primary factor controlling the community composition of macrophytes and showed that plant abundance increased with increasing SDD/Depth ratio( p < 0.01), but that only SDD/Depth > 0.4 ensured growth of submerged macrophytes. Total phosphorus and total nitrogen also influenced the growth and community composition of macrophytes( p < 0.01), while Chl a was an indirectly affecting factor by reducing underwater light penetration. Wave height significantly influenced plant abundance( p < 0.01), whereas it had little effect on the biomass( p > 0.05). The key to restore the macrophyte beds in the lake is to reduce the nutrient loading. A decrease of the water level may contribute as well in the shallow bays but will not bring plants back in the main part of the lake. As the tolerance of shade and nutrients varied among the species studied, this should be taken into account in the restoration of lakes by addition of plants.