极端干旱和降水对沙垄不同坡向坡位短命植物地上生产力的影响

Effects of extreme drought and extreme precipitation on aboveground productivity of ephemeral plants across different slope positions along sand dunes

近年来,干旱半干旱区极端干旱和极端降水事件出现的频次呈现增加的趋势,深刻影响着生产力和碳循环过程。荒漠生态系统植被对降水变化响应敏感,但短命植物层片地上生产力对极端干旱和极端降水的敏感性差异以及沙垄坡向坡位在其中的调节作用有待研究。该研究选择古尔班通古特沙漠南缘沙垄4个不同坡向坡位(西坡底部、西坡中部、东坡中部、东坡底部),设置连续2年减少和增加65%生长季降水量的野外原位控制实验来模拟极端干旱和极端降水事件,解析了短命植物层片地上生产力对极端干旱和极端降水的敏感性,探讨了坡向坡位因素的协同效应以及降水变化驱动短命植物层片地上生产力的机制。结果表明:(1)整体而言,短命植物层片地上生产力和生长季降水量的关系是非对称的,且地上生产力对极端干旱的敏感性强于极端降水。(2)具体而言,沙垄西坡底部、西坡中部和东坡底部短命植物层片地上生产力和生长季降水量表现为非线性饱和关系,地上生产力增加的幅度随着降水量的增加而降低;沙垄东坡中部共优种的存在改变了短命植物层片地上生产力与生长季降水量的关系,使两者表现为正线性关系。(3)短命植物层片密度(所有物种的种群密度之和)对地上生产力的影响最大,表明极端干旱突破了短命植物生理死亡的阈值,通过降低层片密度减少地上生产力;极端降水则通过增加层片密度以克服分生组织的约束,提高地上生产力。该研究可为极端气候事件频发背景下准确评估荒漠生态系统碳循环动态提供科学依据。

Aims In recent years,the frequency of extreme drought and extreme precipitation events in arid and semi-arid regions is increasing,which has a profound impact on ecosystem productivity and carbon cycling.In desert ecosystems,vegetation is sensitive to precipitation changes,but the differences in sensitivity of aboveground productivity of ephemeral plants to extreme drought and extreme precipitation,and the moderating effect of slope positions on them need to be further studied.Methods In this study,we experimentally reduced and increased precipitation amounts by 65%during two consecutive growing seasons in situ across four different slope positions(the bottom of the sand dune facing west(BW),the middle of the sand dune facing west(MW),the middle of the sand dune facing east(ME),and the bottom of the sand dune facing east(BE))along sand dunes in the southern edge of the Gurbantünggüt Desert.We analyzed the sensitivity of aboveground productivity of ephemeral plants to extreme drought and extreme precipitation,and discussed the synergistic effect of slope position factors and the driving mechanism of aboveground productivity of ephemeral plants.Important findings The results showed that:(1)Overall,the relationship between aboveground net primary productivity(ANPP)of ephemeral plants and precipitation in growing season was asymmetric,and the ANPP was more sensitive to extreme drought than to extreme precipitation.(2)Specifically,the relationship between precipitation and ANPP of ephemeral plants at BW,MW,and BE were non-linear,i.e.,the rate of increase in ANPP decreases with the increased precipitation;The existence of two dominant species in the middle of the sand dune facing east changed the relationship between aboveground productivity and precipitation in the growing season,and the relationship between them showed a positive linear relationship.(3)In addition,the density of ephemeral plants(the sum of all species density)had the greatest direct impact on aboveground productivity of ephemeral plants,suggesting that extreme drought resulted in physiological death of ephemeral plants and reduced aboveground productivity by reducing plant density,while extreme precipitation increased population density to overcome meristem constraints and improve aboveground productivity.This study provides a scientific basis for accurately assessing the dynamics of carbon cycle in desert ecosystems under the background of frequent extreme climate events.