羌塘高原降水梯度植物叶片、根系性状变异和生态适应对策

叶片和根系是植物获取资源的最重要的器官,其性状随环境梯度的变化反映了植物光合碳获取和水分与养分的吸收能力及其对环境变化适应的生态对策。羌塘高原降水梯度带高寒草地群落叶片和根系成对性状关系研究不仅能揭示环境梯度对植物性状的塑造作用,也可为理解寒、旱和贫瘠等极端环境下植物的适应策略提供依据。为此,选择3组具有代表性的叶片和根系成对性状:比叶面积(SLA)和比根长(SRL);单位质量叶氮含量(LN_(mass))和单位质量根氮含量(RN_(mass));单位面积叶氮含量(LN_(area))和单位长度根氮含量(RN_(length)),分析不同优势植物地上、地下成对性状变异特征及其与环境因子的关系,探讨植物性状对高寒生态系统水分和养分限制因素的适应策略。研究表明,区域气候和土壤环境导致的叶片性状变异大于根系性状的变异,干旱端的植物既具有高的SRL,又具有高的叶片和根系的养分含量(LN_(mass),LN_(area)和RN_(mass))。SLA-SRL、LN_(mass)-RN_(mass)、LN_(area)-RN_(length)均表现为权衡关系,在干旱端(年降雨量MAP 400 mm)的高寒草原、荒漠草原和极湿润端(MAP 600 mm)的高寒草甸这种权衡关系更为明显,而中间区域(400 MAP 600 mm)的高寒草甸养分和水分限制不是很强烈,叶片和根系性状更多地表现出协同关系。从植物功能类群来看,苔草和禾草类植物叶片和根系成对性状之间具有更强烈的权衡关系。干旱端植物通过增加SRL和叶片、根系养分含量来提高水分和养分的吸收能力,同时通过叶片高的氮含量提高光合碳获取能力,保障了根系生长的物质来源,表现出地上和地下同时投入的策略。干旱端植物保持较高的养分含量是抵御和适应严酷的寒、旱和贫瘠的环境胁迫的重要策略。而在湿润端植物则采取增加SLA,维持地上光合生产力的生态策略。

Variation of leaf and root traits and ecological adaptive strategies along a precipitation gradient on Changtang Plateau

Leaves and roots are the most important organs for plants to acquire resources. Trait variations across environmental gradients reflect photosynthetic carbon acquisition, the water and nutrient absorption capacity of plants, and their ecological strategies for adapting to environmental changes. Studying leaf and root pairwise traits of alpine grassland communities along a precipitation gradient on Changtang Plateau can not only reveal the shaping effect of environmental gradients on plant traits but also provide a basis for understanding the adaptation strategies of plants in extreme environments such as cold, drought, and barren land. Therefore, we selected three representative pairwise leaf and root traits:specific leaf area (SLA) and specific root length (SRL), unit mass leaf nitrogen content (LN_mass) and unit mass root nitrogen content (RN_mass), leaf nitrogen content per unit leaf area (LN_area) and root nitrogen content per unit root length (RN_length), to analyse the variation in characteristics of above-ground and below-ground pairwise traits of different dominant plants and their relationship with environmental factors. We also explored the adaptation strategies of plant traits to water and nutrient limitations in alpine ecosystems. The results showed that variations in leaf traits caused by regional climate and soil environments were greater than those in root traits. The plants at the dry end had both high SRL and high nutrient contents in the leaves and roots (LN_mass, LN_area, and RN_mass). The SLA-SRL, LN_mass-RN_mass, and LN_area-RN_length all showed a trade-off relationship, especially in the alpine steppe and desert steppe at the dry end (annual rainfall MAP < 400 mm), and alpine meadow under extremely humid conditions (MAP > 600 mm). However, in the middle region (400 < MAP < 600 mm), nutrient and water limitations in the alpine meadow were not very strong, and the leaf and root traits showed a more coordinated relationship. From the perspective of plant functional groups, there was a stronger trade-off between the pairwise traits of the leaves and roots of sedges and grasses. The drought-end plants increase the absorption capacity of water and nutrients by increasing the SRL and leaf and root nutrient contents, meanwhile increasing the photosynthetic carbon acquisition capacity through the high nitrogen content of the leaves. This ensures the source of root growth, showing strategies for simultaneous investment in both above-ground and below-ground. It is an important strategy for drought-end plants to maintain high nutrient content to resist and adapt to severe cold, drought, and barren environmental stress, while for plants at the humid end, the ecological strategy is to increase SLA and maintain above-ground photosynthetic productivity.