Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14850, USA.
Ecology. 2012 Jul;93(7):1626-36. doi: 10.1890/11-2247.1.
Precipitation patterns including the magnitude, timing, and seasonality of rainfall are predicted to undergo substantial alterations in arid regions in the future, and desert organisms may be more responsive to such changes than to shifts in only mean annual rainfall. Soil biocrust communities (consisting of cyanobacteria, lichen, and mosses) are ubiquitous to desert ecosystems, play an array of ecological roles, and display a strong sensitivity to environmental changes. Crust mosses are particularly responsive to changes in precipitation and exhibit rapid declines in biomass and mortality following the addition of small rainfall events. Further, loss of the moss component in biocrusts leads to declines in crust structure and function. In this study, we sought to understand the physiological responses of the widespread and often dominant biocrust moss Syntrichia caninervis to alterations in rainfall. Moss samples were collected during all four seasons and exposed to two rainfall event sizes and three desiccation period (DP) lengths. A carbon balance approach based on single precipitation events was used to define the carbon gain or loss during a particular hydration period. Rainfall event size was the strongest predictor of carbon balance, and the largest carbon gains were associated with the largest precipitation events. In contrast, small precipitation events resulted in carbon deficits for S. caninervis. Increasing the length of the DP prior to an event resulted in reductions in carbon balance, probably because of the increased energetic cost of hydration following more intense bouts of desiccation. The season of collection (i.e., physiological status of the moss) modulated these responses, and the effects of DP and rainfall on carbon balance were different in magnitude (and often in sign) for different seasons. In particular, S. caninervis displayed higher carbon balances in the winter than in the summer, even for events of identical size. Overall, our results suggest that annual carbon balance and survivorship in biocrust mosses are largely driven by precipitation, and because of the role mosses play in biocrusts, changes in intra-annual precipitation patterns can have implications for hydrology, soil stability, and nutrient cycling in dryland systems.
降水模式包括降雨量的大小、时间和季节性，预计在未来干旱地区会发生重大变化，而沙漠生物对这种变化的反应可能比对年平均降雨量变化的反应更为敏感。土壤生物结皮群落（由蓝藻、地衣和苔藓组成）普遍存在于沙漠生态系统中，发挥着多种生态作用，并对环境变化表现出强烈的敏感性。结皮苔藓对降水变化特别敏感，在小降雨事件后，生物量和死亡率迅速下降。此外，生物结皮中苔藓成分的丧失会导致结皮结构和功能的下降。在这项研究中，我们试图了解广泛存在且通常占主导地位的生物结皮苔藓 Syntrichia caninervis 对降水变化的生理反应。在四个季节都采集了苔藓样本，并暴露于两种降雨事件大小和三种干燥期（DP）长度下。基于单次降水事件的碳平衡方法用于定义特定水合期内的碳增益或损失。降水事件大小是碳平衡的最强预测因子，最大的碳增益与最大的降水事件相关。相比之下，小的降水事件导致 S. caninervis 出现碳亏空。在事件之前增加 DP 的长度会导致碳平衡减少，这可能是由于在更强烈的干燥期之后，水合的能量成本增加所致。采集季节（即苔藓的生理状态）调节了这些反应，DP 和降雨对碳平衡的影响在不同季节的幅度（通常在符号上）不同。特别是，即使事件大小相同，S. caninervis 在冬季的碳平衡也高于夏季。总的来说，我们的研究结果表明，生物结皮苔藓的年碳平衡和存活率主要由降水驱动，由于苔藓在生物结皮中的作用，年内降水模式的变化可能对干旱地区系统的水文、土壤稳定性和养分循环产生影响。
