[Characteristics of rain season atmospheric PM2.5 concentration and its water-soluble ions contents in forest parks along an urban-rural gradient in Guangzhou City of South China].

During the rainy season (April-September) of 2012, the atmospheric particulate matter with a diameter less than 2.5 mm (PM2.5) were sampled from the forest parks in the urban area, suburban area, and rural area of Guangzhou City. The mass concentration of PM2.5 and its water-soluble ions (SO4(2-), NO3-, NO2-, Cl-, F-, Na+, NH4+, Ca2+, K+, and Mg2+) contents were also measured. In the forest parks in the urban area, suburban area, and rural area, the diurnal variation of PM2.5 mass concentration was 21.8-161.7, 19.4-156.3, and 17.2-66.5 microg x m(-3), with an arithmetic average being 55.9, 49.8, and 44.4 microg x m(-3), respectively. SO4(2-), Na+, and NH4+ were the main components of water-soluble ions in the PM2.5, and the SO4(2-) had the highest content and decreased gradually from urban to rural forest parks. The contribution of the SO2 and NOx in the PM2.5 from coal combustion to the forest parks was larger than that from vehicle exhaust, but presented a decreasing trend from urban to rural forest parks, indicating that vehicle exhaust had a greater contribution to the atmospheric SO2 and NOx in the urban forest park. In the sampling period, the contribution of sea salt to the water soluble fractions (especially K+) of the PM2.5 was greater for the suburban forest park than for the other two parks. The equivalent concentration of the NH4+ in the PM2.5 was far less than those of the SO4(2-) and NO3-, with a neutralization ratio being much lower than 1.0, which suggested that the PM2.5 had a higher acidity. The PM2.5 acidity had an increasing trend from rural to urban forest parks.

[Wind-attenuation effect of Sonneratia apetala and Kandelia obovata plantations].

A field monitoring was conducted to examine the wind-attenuation effect of mangrove plantations at the Sanjiang Bay of Dongzhai Harbor, Hainan Province of South China. The wind speed and wind direction were measured at a site 50 m away from the offshore forest fringes of Sonneratia apetala and Kandelia obovata plantations and 2 m above the ground. Both the S. apetala and the K. obovata plantations had obvious effect in attenuating the speed of the wind from northerly to the shore, with the mean wind speed decreased by > 85% and the better effect of K. obovata plantation. With the increase of the wind speed, the wind-attenuation effect of the plantations presented a trend of decreasing first and remained stable then. At 50 m away from the offshore forest fringe of S. apetala plantation, the wind-attenuation rate was higher than 89.8% when the mean wind speed was lower than 5 m x s(-1), tended to be stable when the mean wind speed was 10 m x s(-1), and turned to be 58.9%-63.6% when the mean wind speed was higher than 15 m x s(-1). The S. apetala plantation had better wind attenuation effect in warmer season than in colder season. Under the extremely adverse weather like typhoon, the mean wind speed and extreme wind speed at 50 m away from the offshore forest fringe of S. apetala plantation were decreased by 59.4% and 53.2%, respectively.

[Castanopsis jianfengensis sap flow and its relationships with environmental factors in tropical montane rainforest].

By the method of thermal dissipation and using ICT-2000TE apparatus made in Australia, the Castanopsis jianfengensis sap flow and the variations of environmental factors in a mixed tropical montane rainforest at Jianfengling Nature Forest Reserve (18 degrees 36'N, 108 degrees 52'E, 860 m altitude) were measured synchronously during the dry and rainy seasons, 2002. The results showed that the sap flow density of C. jianfengensis exhibited mono-peak pattern in clear days and multi-peak pattern in cloudy or rainy days. Sap flow density had significant positive correlations with solar radiation, air temperature, vapor pressure deficit and wind speed, but negative correlation with air relative humidity. In dry season, sap flow density was positively correlated with soil temperature but less correlated with soil moisture, while it was in adverse in rainy season, indicating that rainfall had a greater influence on the sap flow. The linear regression patterns between sap flow and environmental factors were built, which all met the significance at 0.01 level with F test. The mean transpiration rate of C. jianfengesis was 103.5 kg x d(-1) and 41.3 kg x d(-1) for whole tree, and 1.94 mm x d(-1) and 0.77 mm x d(-1) for the stand in dry and rainy season, respectively.