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Xiao Y.L.,Sichuan Agricultural University | Tu L.H.,Sichuan Agricultural University | Hu T.X.,Sichuan Agricultural University | Zhang J.,Sichuan Provincial Key Laboratory of Forestry Ecological Engineering in Upper Reaches of Yangtze River | And 2 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica

The human activities such as combustion of fossil fuels and intensive agriculture, have changed the nitrogen(N) cycle considerably, and have significantly increased the formation and deposition of the reactive N. The increasing deposition of N has exerted much effect on activities of forest ecosystems, such as the alteration of litter production and nutrient concentration of litterfall. In the forest ecosystem, litterfall as the source of soil nutrient and energy plays an important role not only in conserving soil and water and improving the structure and physical-chemical properties of soil, but also in maintaining soil fertility, which links the nutrient pool of vegetation and the soil nutrient pool. The annual nutrient input from litterfall is the product of annual litter production and the nutrient concentration of litterfall, which is the major source of soil fertility. Therefore, exploring the influence of nitrogen deposition on totally annual nutrient input from litterfall has the vital significance, while the related report is rare. From November 2007 to December 2010, a simulated nitrogen (N) deposition experiment was conducted in a Pleioblastus amarus plantation in Rainy Area of West China, which was aimed to explore the effect of nitrogen deposition on the litterfall and related total nutrient input in P. amarus plantation in order to provide some basic data about the material circulation and energy flow of the bamboo ecosystem. Four treatments was installed, i. e., control (0 g N· m-2· a-1), low · a-1) and high nitrogen (30 g N· m-2· a-1). At the end of each month NO3 NH4 was added to each N-treated plots and each square plot was 3 m × 3 m, and randomly distribute in the plantation, which interval was more than 3 m. Litterfall production was measured every half a month through the whole year of 2010. The annual nutrient input from litterfall was measured and calculated. The results showed that simulated N deposition significantly increased the litter production in P. amarus plantation. The concentrations of N, P, K, Ca, and Mg in litter fractions (leaf litter and twig litter) were also significantly increased. This research results suggested that simulated N deposition increased the annual nutrient input from litterfall significantly, which is beneficial for the maintenance of woodland fertility and the continuous growth of P. amarus plantation. Source

Hu H.,Sichuan Agricultural University | Hu H.,Sichuan Provincial Key Laboratory of Forestry Ecological Engineering in Upper Reaches of Yangtze River | Zhang J.,Sichuan Agricultural University | Zhang J.,Sichuan Provincial Key Laboratory of Forestry Ecological Engineering in Upper Reaches of Yangtze River | And 4 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica

Eucalyptus grandis, a fast-growing timber species with outstanding economic efficiency, has been extensively planted as short-term industrial material in southern China. But what's the difference of features in relation to water consumption between E. grandis and common or native tree species of Sichuan Province, whether or not the amount of water consumption of E. grandis would change the original water balance in its cultivation area remains to be answered. In this paper, the net photosynthetic rate (Pn), the transpiration rate (Tr) and the water use efficiency(WUE) of seedlings of E. grandis and other five tree species under different light intensities, air temperatures and atmosphere humidities were determined with the help of LI-6400 photosynthesis meter, the plant total leaf weight, biomass and the water consumption were measured using weighing method, then the water consumption characteristics of these species were evaluated and compared based on the indicators mentioned above. The results were showed as follows:(1) Of all the tested species, E. grandis possessed the highest Tr and the lowest WUE under the same condition, in addition the maximum water consumption per unit biomass, so the water consumption per plant of which was significantly larger than the others, its largest total leaf area was probably one of the important reasons. Its Pn was lower than that of P. × R270, but its biomass accumulation was the largest. We drew a conclusion that E. grandis was a tree species with strong photosynthesis, high transpiration, and low water use efficiency. (2) The Pn and the Tr of the broad-leaved tree species were obviously higher than those of the coniferous tree species, while the WUE of the former was lower than that of the latter. (3) Environmental factors (the light intensity, the air temperature and the atmosphere humidity) influenced the Pn, the Tr and the WUE of plants to a large extent. Particularly, the Pn was mainly affected by the light intensity, the Tr was most sensitive to the atmosphere humidity, and generally the WUE rose with the increase of the atmosphere humidity. In the range of variation temperature (24-32°C), which was set in the experiment, the photosynthesis of these tree species did not changed to a large extent. The light intensity of 800 μmol·m-2·s-1 and the temperature of 28 °C in this study were observed most conducive to plant photosynthesis. (4) Fast-growing tree species such as E. grandis, grew more rapidly and were more potential to fix considerable carbon because of its comparatively stronger capability of photosynthesis, thus higher economic benefit could be obtained. However, in terms of the higher transpiration and lower water use efficiency, replacing the former vegetation(mainly composed by indigenous tree species) with large-scale plantations of E. grandis was more likely to be adverse to the environment of introduction areas because of more water consumption. Therefore, the area for E. grandis plantation should be in a good water condition, especially where abundant annual rainfall and uniform rainfall distribution were seen. Moreover, adequate attention should be paid to the scientific and rational water management. Source

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