日前，中国科学院青藏高原研究所高寒生态学与生物多样性重点实验室罗天祥研究员课题组与中国林业科学研究院荒漠化研究所吴波研究员课题组合作，以我国北方干旱区沙地上广泛分布的油蒿种群为研究对象，跨越不同植被类型和降水梯度，系统分析测定了几个关键叶性状指标和相关冠层特征沿降水的变异规律，发现植物叶性状可指示干旱区植被的地带性分布。研究成果近日发表在《植物学纪事》上。 

　　叶性状是植物适应环境所表现出来的叶片水平上的特征，与生态系统功能关系密切，植物叶性状及其相关关系沿着环境梯度的变化在决定植物分布格局上具有重要作用。因此，一些关键叶性状很可能是一个较客观反映植被本身特征的、可测量和比较的植被区划综合指标。但是，关于植物叶性状与干旱区植被区划关系的研究仍很缺乏。 

　　该研究发现，沿着降水梯度，油蒿叶性状及其相关关系在干旱阈值0.29（年降水量/年潜在蒸散量）下发生显著变化，且干旱阈值0.29与我国北方典型草原和荒漠草原的边界具有很好的吻合性。青海高寒干旱区沙地油蒿数据进一步验证了这一研究发现。这一新认识揭示了植物叶性状对干旱区植被区划的指示意义，对于预测未来气候变化下干旱区植被的动态变化具有重要意义。（来源：中国科学报 陆琦 彭科峰） 

　　Optimal balance of water use efficiency and leaf construction cost with a link to the drought threshold of the desert steppe ecotone in northern China 

　　Background and Aims In arid environments, a high nitrogen content per leaf area (Narea) induced by drought can enhance water use efficiency (WUE) of photosynthesis, but may also lead to high leaf construction cost (CC). Our aim was to investigate how maximizing Narea could balance WUE and CC in an arid-adapted, widespread species along a rainfall gradient, and how such a process may be related to the drought threshold of the desert–steppe ecotone in northern China. 

　　Methods Along rainfall gradients with a moisture index (MI) of 0_17–0_41 in northern China and the northern Tibetan Plateau, we measured leaf traits and stand variables including specific leaf area (SLA), nitrogen content relative to leaf mass and area (Nmass, Narea) and construction cost (CCmass, CCarea), d13C (indicator of WUE), leaf area index (LAI) and foliage N-pool across populations of Artemisia ordosica. 

　　Key Results In samples from northern China, a continuous increase of Narea with decreasing MI was achieved by a higher Nmass and constant SLA (reduced LAI and constant N-pool) in high-rainfall areas (MI>0_29), but by a lower SLA and Nmass (reduced LAI and N-pool) in low-rainfall areas (MI_0_29). While d13C, CCmass and Ccarea continuously increased with decreasing MI, the low-rainfall group had higher Narea and d13C at a given CCarea, compared with the high-rainfall group. Similar patterns were also found in additional data for the same species in the northern Tibetan Plateau. The observed drought threshold where MI¼0_29 corresponded well to the zonal boundary between typical and desert steppes in northern China. 

　　Conclusions Our data indicated that below a climatic drought threshold, drought-resistant plants tend to maximize their intrinsic WUE through increased Narea at a given CCarea, which suggests a linkage between leaf functional traits and arid vegetation zonation. 

　　原文链接：http://aob.oxfordjournals.org/content/118/3/541.full.pdf