高寒植物叶片性状对模拟降水变化的响应

Abstract

降水变化对高寒草甸生态系统产生了显著影响，植物叶片性状特别是叶脉特征对降水变化非常敏感，然而高寒植物叶片性状特征如何响应降水变化还知之较少。采用集雨棚模拟增减50%降水的条件，以高寒草甸8种主要植物叶片为研究对象，研究了降水变化对叶片的叶脉率、叶脉密度、叶片大小、比叶质量、叶片总有机碳含量、叶片全氮含量、叶片碳同位素相对含量和碳氮比等叶片性状的影响。发现增水显著增加了植物的叶片大小、稳定碳同位素千分值、总有机碳含量、全氮含量，但显著降低了叶脉密度；而减水显著降低了叶片大小、稳定碳同位素千分值。植物叶片性状各指标对降水变化的响应存在协同变化和相互制约。不同水分生态类型的植物对降水变化的响应存在差异，中生植物通过增加叶片大小和减少叶脉密度积极应对降水的增加，矮生嵩草的叶片大小分别增加了200.3%，叶脉密度减小了17.5%，而旱中生植物通过减少叶片大小和增加叶脉密度应对降水的减少，垂穗披碱草和异针茅的叶片大小分别减少54.9%和30.7%，其叶脉密度分别增加25%和22.4%。羽状叶脉植物增加叶脉密度和稳定碳同位素千分值以适应增水条件，花苜蓿、异叶米口袋的叶脉密度的增加了7.8%和4.0%，稳定碳同位素千分值增加2.5%和3.3%，但增水条件下平行叶脉植物的叶脉密度不变或降低和稳定碳同位素千分值保持不变；减水增加了平行叶脉植物叶脉密度并减低了稳定碳同位素千分值，异针茅的叶脉密度增加了22.4%，稳定碳同位素千分值减小2.9%，而对羽状叶脉植物的叶脉密度和稳定碳同位素千分值减少或不变。植物叶片性状对增水的敏感性显著大于对减水的敏感性，增水的效应约为减水的2倍；叶片大小的敏感性显著大于其它叶片性状，约为其它叶片性状的10倍。因此，植物在应对短期降水变化时，植物形态可塑性的作用凸显，放大或缩小叶片大小是植物应对降水变化的最有效的途径，但是不同水分生态类型和叶脉类型植物可塑性的方向存在显著差异。;Variations in precipitation had a significant impact on the alpine meadow ecosystem. Among plant leaf traits, leaf vein properties are very sensitive to the changed precipitation. However, how the leaf traits of alpine plants respond to precipitation variations was still little known. The precipitation in the study area was artificially regulated increase and decrease of rain using rainwater shed, and the responses of leaf properties from 8 main plants in the alpine meadow were systematically analyzed under 50%, 100%, and 150% rainfall treatments. This study investigated the effects of altered precipitation on the vein mass per leaf mass (VMM), vein length per area (VLA), leaf size (LS), leaf mass per area (LMA), total organic carbon concentration (TOC), total nitrogen concentration (TN), carbon isotope discrimination (δ¹³C) and the ratio of carbon to nitrogen (C/N). The results indicated that water increasing significantly enhanced LS, δ¹³C, TOC, and TN, but significantly reduced for VLA. While water decreasing significantly reduced the LS and δ¹³C. There were synergistic changes and mutual constraints in the response of plant leaf traits to precipitation alteration. Plants belonging to different water ecological groups had different responses to precipitation alteration. Mesophytes actively responded to the increase in precipitation by increasing LS and reducing VLA. The LS of Kobresia humilis was increased by 200.3%, and the VLA was reduced by 17.5%. While dry mesophytes responded to the decrease in precipitation by reducing LS and increasing VLA. The LS of Elymus nutans and Stipa purpure decreased by 54.9% and 30.7%, and their VLA increased by 25% and 22.4%, respectively. Pinnate vein plants could enhance VLA and δ¹³C in order to adapt to water increasing condition. The VLA of Medicago ruthenica and Gueldenstaedtia diversifolia increased by 7.8% and 4.0%, and the δ¹³C increased by 2.5% and 3.3%. While for parallel vein plants, they remained unchang or decrease. Water reducing enhanced VLA of parallel veins plant and reduced δ¹³C, while had no impact on pinnate vein plants. The VLA of S. purpure increased by 22.4% and the δ¹³C decreased by 2.9%. The plant leaf traits were much more significantly sensible to water increasing than water reducing, and the effect of water increasing was about 2 times than that of water reduction. LS was the most significantly sensitive among all leaf traits, about 10 times that of other leaf traits. Therefore, plant morphology plasticity played a prominent role when responding to short-term precipitation variation. Enlarging or reducing leaf size was the most effective way to respond to precipitation alteration. However, plant plasticity was significantly different among the water ecological types and leaf vein types.