Variability in soil enzyme activity may have important implications for the knowledge of underground ecosystem functions driven by soil extracellular enzymes. To illustrate the temporal variation in soil enzyme activity after afforestation, we collected soil samples during different vegetative growth periods in three Caragana korshinskii Kom. stands of different ages (20, 30, and 40 years) and in a slope cropland in the Loess Plateau. These samples were used to analyze the catalase, sucrase, urease and alkaline phosphatase activities, the soil water content and the available soil nutrients (i.e., dissolved organic carbon, dissolved organic nitrogen, and available phosphorus). The results illustrated that the soil enzyme activities significantly increased following afforestation and varied with temporal variation. Overall, soil enzyme activities were higher in June and August, particularly, and both alkaline phosphatase and sucrase were more sensitive to temporal variation than the other two enzymes. In addition, redundancy analysis showed that soil enzyme activities were greatly correlated with soil nutrients, especially for dissolved organic carbon and dissolved organic nitrogen. Therefore, the results highlighted the importance of soil enzyme activities to soil nutrients under temporal variation following afforestation in the Loess Plateau, which may have practical significance for forest managers’ fertilization management of plantation in different seasons and different stand ages.

Abstract-This paper discussed a method of PLC controlling motor. Including the start and stop, forward and inversion of motor, Positive &negative switching in the process of Running. And realizing low speed, high speed, medium speed and switch operation, accurate control of step motor number. it was elaborated the programming block diagram and ladder diagram of the implementation status in detail.

Forest restoration and soil structure stabilization are the focus of forestry and ecology. However, the combined mechanisms of soil microorganisms and organic and inorganic aggregate binding agents on soil aggregation is unclear. In order to explore the effects of subtropical forest restoration types on soil aggregates and the underlying mechanisms, we collected soil samples from subtropical natural forests and coniferous and broad-leaved plantations that are commonly used for forest restoration. The mean weight diameter (MWD) of the soil aggregate was used to indicate the aggregates’ stability. The soil microbial diversity and structure, the organic and inorganic aggregate binding agents including the mycorrhizal density, the glomalin-related soil protein and the Fe and Al oxides were investigated. Results showed that the Shannon and Simpson indices of soil microbial communities in the coniferous plantations were both significantly higher than those in the natural forests. At the annual level, compared with the natural forests, the plantations decreased the proportion of 0.25–1 mm aggregates while the MWD significantly increased. The forest type also significantly affected the mycorrhizal density, the easily extractable glomalin-related soil proteins (EEG) and the Fe oxide. A variance decomposition analysis showed that soil microbial communities, organic and inorganic binding agents, and their interactions together contributed to the aggregates’ composition and stability by 75.07%. The MWD was positively correlated with the microbial diversity, mycorrhizal density and Fe oxide. We therefore suggest that the combined effects of the soil microbial communities and the organic (mycorrhizal density) and inorganic binding agents (Fe oxide) can be the main mechanisms of soil aggregation in the study area, resulting in a higher soil aggregate stability in the subtropical coniferous plantation than in the natural forest.

In a silvi-medicinal system, the plant secondary metabolites (PSMs) released from medicinal herbs could affect tree litter decomposition and nutrient release. However, the specific effects of PSMs on arboreous litter decomposition are still not well understood. In this study, the extracts of nine types of medicinal herbs were used to treat Pinus armandii Franch. and Larix gmelinii (Rupr.) Kuzen. litter during a simulated half-year decomposition. The effects of the extracts on the decomposition and the N and P release of the conifer litter were investigated. The results indicated that most of the medicinal herb extracts significantly inhibited the late decomposition of P. armandii litter, whereas only two of them accelerated the entire decomposition process. Only a few significantly affected the decomposition of the L. gmelinii litter. Four of the nine types of extract significantly inhibited the N and P release of the P. armandii litter, while 3/9 and 6/9 inhibited the N and P release of the L. gmelinii litter, respectively. The accelerating effects of the extracts on the cellulase activity and the inhibitory effects on the polyphenol oxidase activity might be responsible for the early acceleration and late inhibition of litter decomposition, while the effects of the extracts on the activities of protease and phosphatase might not be the main reason for the inhibitory or accelerating effects on the N and P release. In general, the inhibitory effects of medicinal herbs on the nutrient cycling of ecosystems should be taken into consideration when building silvi-medicinal systems, especially in P. armandii forests.

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