| Under the background of increased global nitrogen?N?deposition,Shennongjia Nature Reserve?China?,the esten habitat of Rhinopithecus roxellana,also are threatened by N deposition.Considered that the lichens,an important food resource for Rhinopithecus roxellana in Shengnongjia,are plants sensitive to N deposition,the N deposition might have impotant but neglected impacts on the physiological health and nutritional properties of epiphytic lichens.Five epiphytic lichens foraged by Rhinopithecus roxellana,including Usnea longissima,Usnea luridorufa,Ramalina calicaris var.japonica,Usnea dasopoga and Usnea betulina,were selected as materials,and then field and laboratory N addition experiments on these lichens were performed.Subsequently,there response in N uptake,content of chlorophyll,ergosterol,the content of N and phosphorus?P?,phosphomonoesterase?PME?activity in addition with the nutrient chemistry,including the soluble protein,crude protein,soluble sugar,crude ash and crude fiber were measured.Thereafter,the characteristic of N uptake,the mechanism of N deposition harming the health of lichens,and the effects of N addition on the food quality of lichens were discussed.The main results were presented as following:1)Ammonium uptake was significantly greater than nitrate uptake of the studied lichens.Lichens also assimilated more ammonium and nitrate when the N availability increased,and the N content of lichens was also increased.We concluded that high uptake rates of both ammonium and nitrate of U.dasopoga and U.betulina were one cause that damage them to death under high N addition levels.2)N addition led to changes in the symbiotic balance of the lichens.The low concentration of N addition promoted the growth of alage,reseluting in increased chlorophyll content and chlorophyll-to-ergosterol ratio.But the chlorophyll content decreases when N addition exceeds 0.1 mmol·L-1,and the changes in ergosterol content was not significant under different treatments.In addition,the chlorophyll-to-ergosterol ratio of U.longissima was not significant changed among the N treatments,indicating that it had strong N tolerance through maintaining a stable symbiotic balance.3)With an increased N deposition from 0.6 to 50 kg N ha-11 a-1,the thallus N content of the five lichen species increased significantly,suggesting that those lichens had strong ability to take up and accumulate N resource.Meanwhile,the P content of five lichens increased slower than N content among N treatments,indicating the supply of P was deteriorated when the supply of N increased.The N addition also led to the increase of N:P ratios of five lichens,and it reached a maximum at 50 kg N ha-11 a-1.The PME activity was also upregulated by the N addition.The above results indicated that the balance between N and P was deteriorated in these lichens,and N enrichment would change these five lichen species from being N limited to being P limited.4)The nutrient chemistry of the lichens was affected by N addition,and N addition led to an increase in the content of crude protein,crude ash and crude fiber,and a decrease in the soluble sugar content.In total,these variations in lichen nutrient chemistry led to a decrease in the food quality of lichens.The protein/fiber?PFR?of the lichens had a significant change among N treatments.The N addition led to an increase in PFR of the U.longissima,which was beneficial to feeding by Rhinopithecus roxellana.We concluede that long time over N accumulation could damage the physical health of the lichens,and some epiphytic lichens would have been threatened by present N deposition.Furthermore,N deposition decreased thalli growth,propagule survival rate and food quality of the lichens,which made Rhinopithecus roxellana more difficult to forage them. |
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