Effect of petroleum on decomposition of shrub–grass litters in soil in Northern Shaanxi of China

The impacts of petroleum contamination on the litter decomposition of shrub-grass land would directly influence nutrient cycling, and the stability and function of ecosystem. Ten common shrub and grass species from Yujiaping oil deposits were studied. Litters from these species were placed into litterbags and buried in petroleum-contaminated soil with 3levels of contamination（slight, moderate and serious pollution with petroleum concentrations of 15, 30 and 45 g/kg, respectively）. A decomposition experiment was then conducted in the lab to investigate the impacts of petroleum contamination on litter decomposition rates. Slight pollution did not inhibit the decomposition of any litters and significantly promoted the litter decomposition of Hippophae rhamnoides, Caragana korshinskii, Amorpha fruticosa, Ziziphus jujuba var. spinosa, Periploca sepium, Medicago sativa and Bothriochloa ischaemum. Moderate pollution significantly inhibited litter decomposition of M. sativa,Coronilla varia, Artemisia vestita and Trrifolium repens and significantly promoted the litter decomposition of C. korshinskii, Z. jujuba var. spinosa and P. sepium. Serious pollution significantly inhibited the litter decomposition of H. rhamnoides, A. fruticosa, B. ischaemum and A. vestita and significantly promoted the litter decomposition of Z. jujuba var. spinosa, P.sepium and M. sativa. In addition, the impacts of petroleum contamination did not exhibit a uniform increase or decrease as petroleum concentration increased. Inhibitory effects of petroleum on litter decomposition may hinder the substance cycling and result in the degradation of plant communities in contaminated areas.

Relationship between Arthropods in Forest Litter and Forest Health

As an important part in forest ecosystems, the arthropod communities in the forest litter are closely related to forest health.Based on the ecological function,community structure and biology of the arthropods,we discuss the theoretical basis for the selection of particular groups of arthropods as bio-indicators in this paper,and suggest that the evenness and richness of Collembola(Collembolan), Coleoptera(Beetle) and Hymenoptera(Ant) can serve as forest health indicators.In terms of the relationship between forest litter arthropods and forest health,we summarize the main groups of forest litter arthropods suitable as bio-indicators and their ecological functions in forest ecosystems,and subsequently introduce a simple and accurate new method for selecting forest health indicator species by comparing the frequencies of the various species in different habitats.This method was tested with a real case using forest litter arthropods as a bio- indicator to evaluate rain forest health.Finally,the problems in using forest litter arthropods to evaluate and monitor forest habitat health are discussed and the use of multiple bio-indicator species in order to establish a balanced index system is recommended.