川金丝猴食源地衣长松萝生长、存活与生理学特征对模拟氮沉降的响应

Growth, Survival and Physiological Response of Food Lichens Usnea longissima of Rhinopithecus roxellana to Simulated Nitrogen Deposition

【目的】探讨氮沉降对长松萝生长、存活的影响及其生理响应特征,为理解氮沉降增加背景下神农架地区树生地衣群落的演替趋势、科学管理川金丝猴的地衣食物供应提供理论支撑。【方法】在野外对长松萝个体和繁殖体模拟施加不同强度的氮沉降,测定其个体生长速率和繁殖体存活率;同时开展室内试验,测定地衣体对铵态氮和硝酸盐氮吸收速率、地衣体的氮磷含量及其比值以及氮磷代谢关键酶(谷氨酰胺合成酶、硝酸还原酶和酸性磷酸酶)活性等指标,综合分析氮沉降影响长松萝生长、存活的规律及其生理学指标响应机制。【结果】低强度氮沉降(<20.94 kgN ·hm -2 a -1 )能促进长松萝个体生长,高强度氮沉降(>32.99 kgN ·hm -2 a -1 )则对长松萝生长与繁殖体存活均有显著不利影响( P ≤0.05);与硝态氮相比,长松萝偏向于吸收铵态氮,且吸收量随氮沉降强度增加而增加;长松萝地衣体氮磷比、酸性磷酸酶活性与氮沉降强度显著正相关( P ≤0.05);随氮沉降强度增加,长松萝谷氨酰胺合成酶和硝酸还原酶活性呈先增加后降低趋势。【结论】低强度氮沉降(<20.94 kgN ·hm -2 a -1 )促进长松萝生长和存活,而高强度氮沉降(>32.99 kgN ·hm -2 a -1 )抑制长松萝生长和存活。过量氮沉降损伤长松萝地衣健康是多种生理机制综合作用的结果,包括选择性吸收铵态氮导致的长松萝体内铵态氮的积累、铵态氮积累引起谷氨酰胺合成酶和硝酸还原酶的活性下降以及铵态氮积累导致地衣磷限制等方面。

【Objective】 We aimed to investigate the response of growth and survival, and potential physiological mechanisms of Usnea longissima of Shennongjia Mountain to simulated nitrogen deposition. Our result were of value in winter food management of Rhinopithecus roxellana, as well in understanding the succession of lichen flora under condition of increasing nitrogen deposition of that region.【Method】 In this study, four in-situ or indoor experiments were performed, in which simulated nitrogen deposition were imposed on thalli and propagules of U. longissima. Thereafter, thalli growth rate and propagule survival rate, adsorption of ammonium and nitrate, thalli N ∶P ratio and activity of phosphomonoesterase (PME), glutamine synthetase (GS), and nitrate reductase (NR) were determined. Then we analyzed the growth, survival response of U. longissima and its potential mechanisms to simulated nitrogen deposition.【Result】 The result showed that thalli growth and propagule survival were significantly impacted when high nitrogen deposition(>32.99 kgN ·hm -2 a -1 ) were performed;In contrast, low nitrogen deposition (<20.94 kgN ·hm -2 a -1 ) promoted growth of this lichen. We also found that little nitrate was absorbed, while ammonium was absorbed efficiently. Total nitrogen, N ∶P ratio, activity of PME increased with increased N deposition, indicating that phosphorous limitation occurred when U. longissima treated with higher nitrogen deposition. Activity of GS and NR both responded nitrogen stress in a first up-regulated, and then down-regulated way.【Conclusion】 Low N deposition showed a fertilization effect on the growth of U. longissima, high nitrogen deposition could decrease thalli growth and survival of its propagules. The possible mechanisms underlying it was: U. longissima preferred to uptake and accumulate ammonium, meanwhile high nitrogen stress reduced activity of GS and NR significantly. In addition, high nitrogen stress would induce a phosphorus limitation.