Comparison Of Water Use Characteristics Among Co-existing Species Of Old-field Communities In Loess Plateau

The responses of co-existing species to variation of soil moisture,and the comparison of their drought resistance ability,are important for understanding fitness and abundance of co-existing species to precipitation fluctuations,and the subsequent community level effect from the perspective of eco-physiological mechanism of vegetation succession in arid and semi-arid regions.In this paper,invariant and changed water soil bin experiment were used to test the responses of fitiness index(plant height,biomass and survival rate),physiological index(superoxide dismutase(SOD),glutathione(GSH)and carotenoid)and photosynthetic parameters(Chlorophyll a and Chlorophyll b,photosynthetic rate,transpiration rate and water use efficiency)of the ten co-existing species.Invariant water soil bin experiment was carried out under three water deficit levels(severe,moderate and mild water deficits,corresponding to 45%,60% and 75% of field water capacity,respectively)in three growing months.And changed water soil bin experiment was carried out before and after rehydration(corresponding to 40%,75% and 60% of field water capacity,respectively)in three planting density.There was used to test the ten species routinely coexist in middle secondary successional stages in Loess Hilly Region.They are Heteropappus hispidus,Artemisia scoparia,Cleistogenes chinessis,Oxytropis glabra,Agropyron cristatum,Cleistogenes songorica,Artemisia sacrorum,Lespedeza dahurica,Artemisia giraldii and Bothriochloa ischaemum.The results showed that:1)Fitness indicators of the ten co-existing species(plant height,biomass and survival rate)Fitness coexist of the ten co-existing species at the vegetative stage among mild,moderate and severe water levels(rank correlation coefficients were 0.612 and 0.6)had no significant difference.However,fitness of Agropyron cristatum increased along water deficit(mild,moderate and severe levels),but fitness of Artemisia scoparia had declined.Under mild water condition,fitness of Artemisia scoparia was relatively high,but Oxytropis glabra was relatively low at the vegetative stage.Under moderate water deficit,Bothriochloa ischaemum was relatively high,and Cleistogenes chinessis was relatively low.Under severe deficit,Bothriochloa ischaemum was relatively high,Artemisia sacrorum was relatively low.2)Physiological index of the ten co-existing species(SOD,GSH and carotenoid)in drought tolerantIn invariant water soil bin experiment,there were significant differences in GSH and carotenoid among three water deficit levels.The contents of GSH and carotenoid responded positively,their values under severe level were higher in comparison with the ones under mild level,and no such significantly positive responses were observed for the activity of SOD.This meant that GSH and carotenoid contents took more active and positive role for water stress tolerance.However,there were significant differences in SOD,GSH and carotenoid between growing season and species.SOD activity of Cleistogenes chinessis,carotenoid content of Lespedeza davurica,GSH and carotenoid contents of Cleistogenes songorica were relatively high.The relative high GSH and carotenoid contents in Cleistogenes songorica showed that it could tolerate water deficit well.In changed water soil bin experiment,there were significant differences in SOD activity and GSH content between water deficit level and species.The SOD activity,their values under severe level were rapidly higher in comparison with the GSH content.SOD activity of Artemisia giraldii,GSH content of Cleistogenes chinessis was relatively high.The relative high SOD activity in Artemisia giraldii showed that it could rapidly be response to water deficit.3)Water use efficiency of the ten co-existing species(Chlorophyll a and Chlorophyll b contents,photosynthetic parameters)There were significant differences in Chlorophyll a and Chlorophyll b contents,water use efficiency between water deficit level and species.Chlorophyll a and b contents,water use efficiency increased significantly under water deficit,but Chlorophyll a and b contents showed a downward trend under severe level.There were significant differences in Chlorophyll a and b contents,photosynthetic rate,transpiration rate,water use efficiency among species.Photosynthetic rate of Oxytropis glabra,Chlorophyll a content,photosynthetic and transpiration rate of Cleistogenes songorica,Chlorophyll a and b contents,photosynthetic rate of Lespedeza dahurica were relatively higher.Chlorophyll a and b contents,transpiration rate of Oxytropis glabra,Artemisia scoparia,Artemisia sacrorum and Heteropappus hispidus,transpiration rate of Cleistogenes chinessis,Agropyron cristatum,Lespedeza dahurica,Artemisia giraldii and Bothriochloa ischaemum was relatively lower.According to the ratio of photosynthetic rate and transpiration rate of the ten co-existing species,showed that water use efficiency of Oxytropis glabra was relatively higher(4.02?mol·mmol-1),and Bothriochloa ischaemum was relatively lower(1.49?mol·mmol-1).