Spectrally monitoring the response of the biocrust moss Syntrichia caninervis to altered precipitation regimes

Kristina E Young,Sasha C Reed

doi:10.1038/srep41793

Abstract

Climate change is expected to impact drylands worldwide by increasing temperatures and changing precipitation patterns. These effects have known feedbacks to the functional roles of dryland biological soil crust communities (biocrusts), which are expected to undergo significant climate-induced changes in community structure and function. Nevertheless, our ability to monitor the status and physiology of biocrusts with remote sensing is limited due to the heterogeneous nature of dryland landscapes and the desiccation tolerance of biocrusts, which leaves them frequently photosynthetically inactive and difficult to assess. To address this critical limitation, we subjected a dominant biocrust species Syntrichia caninervis to climate-induced stress in the form of small, frequent watering events, and spectrally monitored the dry mosses’ progression towards mortality. We found points of spectral sensitivity responding to experimentally-induced stress in desiccated mosses, indicating that spectral imaging is an effective tool to monitor photosynthetically inactive biocrusts. Comparing the Normalized Difference Vegetation Index (NDVI), the Simple Ratio (SR), and the Normalized Pigment Chlorophyll Index (NPCI), we found NDVI minimally effective at capturing stress in precipitation-stressed dry mosses, while the SR and NPCI were highly effective. Our results suggest the strong potential for utilizing spectroscopy and chlorophyll-derived indices to monitor biocrust ecophysiological status, even when biocrusts are dry, with important implications for improving our understanding of dryland functioning.

Highlights

Much of the difficulty in successfully monitoring biocrusts with commonly used biophysical and vegetation indices is centered around biocrust organisms’ limited periods of photosynthetic activity, which occur only when the organisms are wet
The decreasing chlorophyll levels in the Watered mosses as chlorophyll is lost over time is likely due to disruptions in the thylakoid membranes and, a breakdown of chlorophyll a during the repeated movements into and out of desiccation during watering events[39,40]
Because we would have expected to see changes in these pigments in concert with declines in chlorophyll[30], we recognize the utility of coupling the analysis of multiple pigments with spectral assessment to determine the effects of climate change or other perturbation on leaf pigment content and evaluation by remote sensing techniques

Summary

Introduction

Much of the difficulty in successfully monitoring biocrusts with commonly used biophysical and vegetation indices is centered around biocrust organisms’ limited periods of photosynthetic activity, which occur only when the organisms are wet. The ability to spectrally monitor biocrust functional response to climatic change is increasingly important[26], as a growing body of literature suggests these organisms will experience significant shifts in both function and composition, resulting in large scale changes to soil stability, soil fertility, and biogeochemical cycling under future climate[5,15,26,27,28,29] To address this critical gap in our understanding, here we assessed absorbance features and spectral indices for a dominant biocrust moss while subjecting some of the moss samples to experimental, climate-induced changes in physiological and ecological functioning, and leaving other moss samples as controls. Through these lines of investigation, we aimed to assess the relevance of spectroscopy to monitoring biocrusts’ response to global change

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Conclusion