Data from: Functional correlations between specific leaf area and specific root length along a regional environmental gradient in Inner Mongolia grasslands

Among above- and belowground traits, specific leaf area (SLA, cm2 g−1) and specific root length (SRL, m g−1) are the two key traits reflecting species resource acquisition strategies. However, patterns of variation in SLA and SRL have rarely been examined simultaneously across evolutionary history and environmental gradients, and the SLA-SRL relationship is still controversial on several grounds. We examined the inter- and intraspecific variations in SLA and SRL of different root branching orders and the SLA-SRL relationship across 55 species and 21 plant communities of four vegetation types along a 2,000-km transect in the Inner Mongolia grassland. With increasing root branching order, the interspecific variation in SRL increased but the intraspecific variation in SRL decreased considerably, and the form of SLA-SRL relationship shifted from positive to negative. This indicates that acquisition of soil resources (e.g. water and nutrients) is a fundamental strategy for plant investment to root length. When inter- and intraspecific variations in SLA and SRLs were partitioned into alpha (within-community) and beta (among-community) components, the alpha component exhibited substantially greater inter- and intraspecific variations than the beta component. Across the transect, the evolutionarily late diverged species in phylogenetic tree evolved toward low SLA and SRL-1 (SRL for first-order roots) and tended to distribute in resource-poor conditions along the environmental gradient. The early diverged species, in contrast, had high SLA and SRL-1 and mostly distributed in resource-rich conditions. Our findings suggest that patterns of inter- and intraspecific variations in SLA and SRL of different root branching orders and the form of SLA-SRL relationship could be well explained by within- and among-community filtering processes and species divergence time. Coordination and trade-offs between leaves and roots do not mutually exclude but operate simultaneously at different scales and among different root branching orders in arid and semiarid grasslands.

在地上与地下性状中，比叶面积（specific leaf area, SLA, cm² g⁻¹）与比根长（specific root length, SRL, m g⁻¹）是反映物种资源获取策略的两类关键性状。然而，SLA与SRL的变异格局极少同时在演化历史与环境梯度下被探究，且SLA-SRL的关联在多个维度仍存在争议。本研究针对内蒙古草原沿2000公里样带分布的4种植被类型、55个物种与21个植物群落，分析了不同根分枝等级下SLA与SRL的种间、种内变异，以及SLA-SRL的关联格局。随着根分枝等级提升，SRL的种间变异逐渐增大，但种内变异显著降低，且SLA-SRL的关联形式由正相关转为负相关。这表明获取土壤资源（如水与养分）是植物对根长投资的核心策略。当将SLA与SRL的种间、种内变异划分为α（群落内）与β（群落间）组分时，α组分的种间与种内变异均显著高于β组分。沿样带梯度，系统发育树中演化分化较晚的物种倾向于具备较低的SLA与SRL₋₁（一级根的比根长），且多分布于资源匮乏的生境；与之相反，演化分化较早的物种拥有较高的SLA与SRL₋₁，且主要分布于资源丰富的生境。本研究结果表明，不同根分枝等级下SLA与SRL的种间、种内变异格局，以及SLA-SRL的关联形式，可通过群落内与群落间的过滤过程以及物种分化时间得到较好解释。在干旱半干旱草原中，叶与根的协同与权衡并非相互排斥，而是可在不同尺度与不同根分枝等级下同时发挥作用。