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Litter decomposition and ecological stoichiometry of nutrient release is an important part of material cycling and energy flow in forest ecosystems. In a study of the ecological stoichiometry and nutrient release during litter decomposition in a pine-oak forest ecosystem of the Grain to Green Program (GTGP) area of northern China, a typical pine and oak species (PDS: Pinus densiflora Sieb., QAC: Quercus acutissima Carr.) were selected in the Taiyi Mountain study area. The ecological stoichiometry characteristics of carbon (C), nitrogen (N) and phosphorus (P) and litter decomposition dynamics were studied by field sampling and quantitative analyses. The results showed the following. (1) The decomposition dynamics of both litters was slow-fast-slow. The most important climatic factor affecting the litter decomposition rate from May to October was precipitation and temperature from November to April of the following year. (2) Throughout the 300-day study, in both litters, C of the two litters was released, N first accumulated and was then released, and P exhibited a release-accumulate-release pattern. (3) C:P was significantly higher than C:N and N:P (p \ 0.05); the C:N of PSD litter was higher than that of QAC (p \ 0.05), but the N:P of QAC litter was higher than that of PSD litter (p \ 0.05). The C:N of both litters was very high in the study area, indicating that the nutrient release ability during litter decomposition in the two typical pine-oak forest ecosystems was relatively weak; therefore, more attention should be paid to nitrogen-fixing species and mixed forests in the GTGP area of northern China.

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Abstract. Efficient use of rainwater is one of the focuses of water resources research around the world, especially in arid and semi-arid regions. Following the rainfall-runoff balance principle of cropland and the theory of rainwater reiterative use, an experiment was designed to investigate the technology and effects of supplemental irrigation with catchment rainwater on maize in the hilly-arid area of northern China. The results showed the following: (1) a water cellar with 60 m3 of storage volume provided enough water for 1.33 ha of maize seedlings with no mulching film and for 5.33 ha with mulching film; (2) compared with the non-irrigated control (CK), when maize received 15 to 45 mm of supplemental irrigation at different growth stages, there was a 0.17 m increase in average plant height, a 0.52 to 0.55 cm increase in average stem diameter, and a 2.61 to 2.84 cm increase in average panicle length; and (3) the booting stage of maize was the best stage for increasing production and rainwater use efficiency (RWUE) with supplemental irrigation, which increased maize production by 22.1% on average for the two years of the study and improved RWUE by 5.2% compared with CK on average for the two years. The sufficient amount of supplemental irrigation was 30 mm, and spare rainwater could be used to irrigate a larger area. The results indicate that the best periods for supplemental irrigation of maize in the hilly-arid area of northern China was during sowing in the spring drought and during the growth stage. Keywords: Catchment rainwater, Hilly-arid area, Rainwater use efficiency, Supplemental irrigation, Water cellar.