Search

The delayed and irregular germination of Quercus seeds can negatively influence seedling quality and growth.The might be explained by several factores,including mechanical strength of the pericarp,secondary metabolites(e.g.tannins and polyphenols),plant hormones especially abscisic acid(ABA) and indoleacetic acid(IAA),and germination inhibitors.These chemicals produced in plants can prevent the seed germination of themselves or other species.The inhibitory substances in aqueous extracts of pericarp tissue which increased with acorn development have been found by Blanche.Moreover,the presence of inhibitory substances has also been confirmed in the pericarp of mature Quercus nigra acorns.However,the study on whether the germination inhibitors contained in different parts of oak acorns is still lacking.Acorns were divided into three parts: pericarp,cotyledon(cutting off 2/3 of the distal end of acorns) and embryo(here including embryo and 1/3 cotyledon around it).Then they were oven-dried(30°C),crushed and passed through 1-mm sieve.Subsequently,they were extracted in 80% methanol extracts and vacuum concentrated to 1 g/mL,some of which were diluted to 0.5 g/mL.In order to verify if the inhibitory substance in different parts of acorns can lead to delayed and uneven germination,germination percentage and root and shoot length of Beassica pekinensis seeds were investigated which cultivated in a Sanyo growth cabinet and watered by distilled water,80% methanol extracts and the extraction phase of methanol,of petroleum ether,of aether,of ethyl acetate,and of water from the acorn embryo,cotyledon and pericarp with concentrations of 1.0g and 0.5g dry acorn weight per ml methanol(g/mL).The results showed that(1) the germination percentage,shoot and root length of B.pekinensis seeds watered by 1.0 g/mL methanol extracts from embryo,cotyledon and pericarp of Q.variabilis,Q.aliena var.acuteserrata,Q.mongolica,Q.palustris and Q.acutissima seeds were significantly lower than those from control,and the inhibitory effect of germination rates gradually decreased,and 0.5 g/mL methanol extracts from embryo,cotyledon of Q.variabilis acorns reduced the germination percentage of B.pekinensis seeds,while no significant difference was detected in germination percentage of B.pekinensis seeds between those from pericarp of all tree species acorns and the control;(2) methanol extracts from embryo,cotyledon and pericarp of Q.robur and Q.×fangshanensis remarkably reduced shoot and root length of B.pekinensis seeds,but little response in germination percentage;(3) the inhibitory effect of Methanol extracts from embryo,cotyledon and pericarp declined in turn,with higher concentration of methanol extract having stronger inhibitory intension for each section of seeds;(4) the inhibitory strengthen of extraction phase of methanol among 5 extraction phases,was larger than that of extraction phase of ethyl acetate,resulting in the lowest germination rate,shoot or root length of B.pekinensis seeds,meanwhile,negative effects was observed in other extraction phases.The fact of extracted substances having stronger inhibitiory effect on the length of root and shoot than on the germination percentage of B.pekinensis,indicating that the inhibitors of oak seeds mainly restrict germination of root and shoot themselves,which could be the cause of the irregular germination.

A rigorous theoretical derivation on the influence of frequency drift of the carrier has been made in this paper.By analyzing the demodulation formula,the influence formula of frequency drift of the carrier was given.The formula shows that when there is a tiny difference between the frequency of modulation and demodulation signals,the demodulation result will be modulated by a low-frequency signal and the demodulation result will be distorted.Experimental and simulation were carried out on this basis,and the results are completely consistent with the theoretical analysis.

Decomposition has been studied for decades due to its significance in understanding nutrient cycling and carbon sequestration processes.The current study identified the three interacting factors that control decomposion: the physicochemical environment,litter quality,and decomposer organisms.Exsiting biogeochemical models that that are derived by local cliamte and little quality parameters can explain about 70% of the variation in litter decomposition.However,the role of soil organisms has been largely ignored in these models that assume the functions of soil organisms are mainly controlled by temperature,moisture and litter quality.Recent studies suggest that leaf litters tend to decompose more rapidly in the habitat from which it was derived(i.e.home) than in other habitats(i.e.new home away from its origion),this phenomena has been termed as the home-field advantage(HFA) in litter decomposition. In contrast to plant growth,leaf litter-soil feedbacks are expected to consistently cause positive feedback at a home habitat resulting in faster litter decay.This is because 1) leaf litter from different plant species often varies considerably in structure and chemical composition;and 2) leaf litter inputs are a major source of nutrients and energy for soil biota that access decomposed litter.Thus,competition among soil biota for accessing nutrients may create a selective pressure for organisms that are efficient at breaking down litter derived locally resulting in HFA..Unique soil biota developed in the litter derived from the orgional ecosystem has been regarded as the reason for this phenomenon.quantifying HFA is more complex than a simply comparison between the decomposition rates for a litter type at its home site and an away site,because differences in environmental contitions between the sites could also influence decomposition.The method originally developed for evaluating home-site effects in sports allows the HFA to be calculated for each of the litters separately in fully reciprocal transplants experiment of three or more litter species. Existing literature suggests there is a large amount of variation in HFA among reciprocal transplants between different tree species.Differences in litter traits could explain some of these variations,but it is apparent that other factors influence the relationship given the initially large HFA observed in field and laboratory experiments,as well as periods of home-field disadvantage.Thus we need a better understanding of the drivers of HFA and how soil biota are involved in order to address this potential problem in how we model decomposition.Based on the review about the rules of soil organisms on litter decompositon,three mechanisms are considered to reveal the soil biological drive of HFA: soil microorganism adjustability has a weakening effect on the HFA,soil animals′ late entry can lead to different HFA intensity,including a disadvantage of home decomposition,environmental climatic conditions have indirect effects on HFA,especially under soil water stress.Integrating these using an ecosystem approach helps to elucidate the effects of soil organism on the HFA of litter decomposition,and interpret the causes of different intensity,especially negative effect of HFA.In order to clearly understand the effects of soil organisms on HFA,long term reciprocal litter transplant experiments,including in-situ and laboratory,should be established across a large geographic and climatic gradient.Based on the effects of soil organisms on HFA,mathematical models of litter decomposition should incorporate with biological factors.This is especially important for global ecosystems that are used for understaing climate change effects on carbon and nutrient cycles.