U.S. Department of Agriculture, Agricultural Research Service, Jornada Experimental Range Unit, Las Cruces, New Mexico, 88003, USA.
Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA.
Ecology. 2020 Sep;101(9):e03069. doi: 10.1002/ecy.3069. Epub 2020 Jul 10.
Alternative states maintained by feedbacks are notoriously difficult, if not impossible, to reverse. Although positive interactions that modify soil conditions may have the greatest potential to alter self-reinforcing feedbacks, the conditions leading to these state change reversals have not been resolved. In a 9-yr study, we modified horizontal connectivity of resources by wind or water on different geomorphic surfaces in an attempt to alter plant-soil feedbacks and shift woody-plant-dominated states back toward perennial grass dominance. Modifying connectivity resulted in an increase in litter cover regardless of the vector of transport (wind, water) followed by an increase in perennial grass cover 2 yr later. Modifying connectivity was most effective on sandy soils where wind is the dominant vector, and least effective on gravelly soils on stable surfaces with low sediment movement by water. We found that grass cover was related to precipitation in the first 5 yr of our study, and plant-soil feedbacks developed following 6 yr of modified connectivity to overwhelm effects of precipitation on sandy, wind-blown soils. These feedbacks persisted through time under variable annual rainfall. On alluvial soils, either plant-soil feedbacks developed after 7 yr that were not persistent (active soils) or did not develop (stable soils). This novel approach has application to drylands globally where desertified lands have suffered losses in ecosystem services, and to other ecosystems where connectivity-mediated feedbacks modified at fine scales can be expected to impact plant recovery and state change reversals at larger scales, in particular for wind-impacted sites.
反馈维持的替代状态是出了名的难以逆转，如果不是不可能的话。尽管改变土壤条件的正相互作用可能具有最大的潜力来改变自我强化的反馈，但导致这些状态变化逆转的条件尚未解决。在一项为期 9 年的研究中，我们通过风或水在不同地貌表面上改变资源的水平连通性，试图改变植物-土壤反馈，并将以木本植物为主的状态转回多年生草本植物为主的状态。无论运输载体（风、水）如何，改变连通性都会导致枯枝落叶覆盖度增加，随后 2 年后多年生草本植物覆盖度增加。改变连通性在以风为主导的沙质土壤上最为有效，而在水流作用下稳定性较高、泥沙移动较少的砾质土壤上效果最差。我们发现，在研究的前 5 年，草地覆盖率与降水有关，而在改变连通性 6 年后，植物-土壤反馈发展起来，超过了降水对沙质、风吹土壤的影响。在可变的年降雨量下，这些反馈会随着时间的推移而持续存在。在冲积土壤上，要么在 7 年后形成了不持久的（活跃土壤）植物-土壤反馈，要么没有形成（稳定土壤）。这种新方法适用于全球干旱地区，那里的荒漠化土地已经失去了生态系统服务功能，也适用于其他生态系统，在这些生态系统中，精细尺度上的连通性介导的反馈预计会在较大尺度上影响植物恢复和状态变化的逆转，特别是对受风影响的地点。
