In order to understand the dynamic change of soil chemical characteristics along with the succession stages for supporting forest restoration,the soil chemical characteristics in different succession stages were compared and analyzed.The results indicated that with the progress of succession,pH value,available P,and total K showed a decreasing trend while organic matters,total P,total N,alkaline hydrolytic N,and available K showed a trend of increase.The correlation analysis indicated that there was an significant correlation between soil chemical characteristics such as total N,alkaline hydrolytic N,available P and organic matters of different horizon in different succession stages.The correlation analysis somehow signified the main source of soil N and P was organic matters.During the forest restoration process,forest litters should be protected so as to increase soil organic matter and improve soil fertilization.
The transpiration experiment was done under greenhouse conditions with a C3 plant sweet pepper(Capsicum annuum Linn.) and two C4 plants,sorghum(Sorghum bicolor L.Moench) and maize(Zea mays Linn.).Three species were irrigated with three different water treatment levels of 100%,66% and 33% which gave a comparison of tolerance and adaptation to irrigation and two different levels of water stress.The measurements of transpiration rate and stomatal conductance were done between 8.00 a.m.and 16.00 p.m.with measurements about each 1.5 h with an infrared gas analyzer.The results showed that Z.mays probably due to a higher leaf area had very low values and was signifi cantly different(LSD pairwise comparison) from C.annuum and S.bicolor.The hypotheses that C4 plants and C3 plants have different transpiration rates and stomatal conductance could not be shown with the results.However,the hypotheses that for the same species,the highest values in transpiration rate and stomatal conductance were with the 100% irrigation treatment and the lowest values were with the 33% irrigation treatment could be accepted due to the results of this trial.
Soil samples were collected from primary forest,natural secondary forest,Pinus caribaea and Acacia mangium stands in Baisha County,Hainan Province,for the determination of soil chemical properties including soil pH,organic matter,total and available N,P and K.The effects of soil layers and forest stands on soil chemical properties were compared.Results showed that forest soils in the studied area were strong acidic,with slight or moderate deficiency of available P,and moderate deficiency of available K(except the primary forest).The highest contents of soil total and available nutrients except for available P and total K were found in the primary forest,followed by natural secondary forest and Acacia mangium stands,and the lowest in Pinus caribaea stands.In soil layer A,except for total N and available P,significant differences were found for organic matter content and very significant differences for soil pH,hydrolyzable N,total P,and total and available K among the four types of forest stand.Similar trend was true for soil layer B.Correlation analysis indicated that soil organic matter content affected the total and available N,P and K in different manner.Soil organic matter had very significant or significant correlation with total N,and significant correlation with hydrolyzable N(only in soil layer B) in primary and natural secondary forests.Significant correlations beween organic matter and total N and P were found in Pinus caribaea stands,but no significant correlations between organic matter and soil nutrients existed in Acacia mangium stands.Some suggestions on forest management were also proposed to improve forest soil quality.
