Soil biocrusts (communities of cyanobacteria, algae, mosses, lichens, and heterotrophs living at the soil surface) are fundamental components of dryland ecosystems worldwide. There is increasing concern over the potential for increasing nitrogen (N) inputs to affect biocrusts. This is of special concern in Mediterranean Basin drylands that face the threat of increased N inputs however, the effect on biocrusts remains poorly studied. We evaluated the potential effects of increased N inputs on biocrust structure and functioning in surrounding Mediterranean shrublands in the seventh year of a N-manipulation field experiment. We tracked the N-driven changes in biotope (changes in bare soil and in the non-legume and the legume occupation areas, and the percentage of radiation intercepted by plant canopies), evaluated biocrust functional traits (based on pigments) and measured biocrust functioning in terms of C and N cycling, soil fertility (macro and micronutrients) and biodiversity, and integrated these multiple soil functions simultaneously (i.e. soil multifunctionality)

Biocrust pigment concentration was significantly influenced by both plant legacy and N input. Biocrust pigments revealed a clear functional shift from: i) biocrusts dominated by photosynthetically inactive cyanobacteria that fix N₂ and are mostly committed to photoprotection at the expense of N-containing pigments under low N inputs; into ii) biocrusts more evenly composed of prokaryotes and eukaryotes, which are more photosynthetically active, but less committed to photoprotection and N₂ fixation under exposure to increased N inputs. The N-driven functional and structural changes in biocrusts resulted in trade-offs in biocrust functioning and processes (only N₂ fixation was affected) and an overall improvement in biocrust multifunctionality. By itself, biocrust pigment evenness accounted for ~50% of the observed variation in biocrust multifunctionality. The biocrust pigment functional approach we adopted to study the effects of increased N inputs from patchy developed anthropogenic landscapes provides novel and critical knowledge of biocrusts community and functioning, which may be used as a tool in biodiversity conservation strategies, ecosystem functions and ecological modelling.

土壤生物结皮（生活在土壤表面的蓝细菌，藻类，苔藓，地衣和异养生物的群落）是全世界旱地生态系统的基本组成部分。人们越来越担心增加氮（N）输入量影响生物结壳的潜力。在面临增加氮输入威胁的地中海盆地干旱地区，这一点特别令人关注，但是，对生物结壳的影响研究仍很少。我们在进行N作业实地试验的第七年中，评估了氮输入增加对周围地中海灌木丛生物结壳结构和功能的潜在影响。我们跟踪了N驱动的生物群落变化（裸露的土壤以及非豆类和豆类占领区的变化，以及植物冠层截获的辐射的百分比），

生物结皮色素的浓度受植物传统和氮输入的影响很大。生物外壳颜料显示出明显的功能转变：i）以光合作用无活性的蓝细菌为主的生物外壳，其固定N ₂并主要致力于光保护，但在低氮输入下以含氮颜料为代价；ii）由原核生物和真核生物组成的生物外壳更均匀，它们具有更强的光合活性，但在暴露于增加的N投入下，对光保护和N ₂固定的投入较小。N驱动的生物结皮的功能和结构变化导致了生物结皮功能和过程的权衡（仅N ₂固定受到影响），生物外壳多功能性得到整体改善。就其本身而言，生物外壳颜料均匀度占生物外壳多功能性中所观察到变化的〜50％。我们采用的生物结壳色素功能性方法研究了片状发达的人为景观增加的氮输入量的影响，为生物结皮的群落和功能提供了新颖而关键的知识，可以用作生物多样性保护战略，生态系统功能和生态建模的工具。